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Photoacoustic
Extinctiometer
(PAX)
Operator Manual
DOC-0301 Revision D-6
2545 Central Avenue
Boulder, CO 80301-5727 USA
COPYRIGHT © 2014 DROPLET MEASUREMENT TECHNOLOGIES,
INC.
Manual, Photoacoustic Extinctiometer (PAX)
Copyright © 2014 Droplet Measurement Technologies, Inc.
2545 CENTRAL AVENUE
BOULDER, COLORADO, USA 80301-5727
TEL: +1 (303) 440-5576
FAX: +1 (303) 440-1965
WWW.DROPLETMEASUREMENT.COM
All rights reserved. No part of this document shall be reproduced, stored in a retrieval system, or
transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without
written permission from Droplet Measurement Technologies, Inc. Although every precaution has
been taken in the preparation of this document, Droplet Measurement Technologies, Inc. assumes
no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from
the use of the information contained herein.
Information in this document is subject to change without prior notice in order to improve accuracy,
design, and function and does not represent a commitment on the part of the manufacturer.
Information furnished in this manual is believed to be accurate and reliable. However, no
responsibility is assumed for its use, or any infringements of patents or other rights of third parties,
which may result from its use.
Trademark Information
All Droplet Measurement Technologies, Inc. product names and the Droplet Measurement
Technologies, Inc. logo are trademarks of Droplet Measurement Technologies, Inc.
All other brands and product names are trademarks or registered trademarks of their respective
owners.
Warranty
The seller warrants that the equipment supplied will be free from defects in material and
workmanship for a period of one year from the confirmed date of purchase of the original buyer.
Service procedures and repairs are warrantied for 90 days. The equipment owner will pay for
shipping to DMT, while DMT covers the return shipping expense.
Consumable components, such as tubing, filters, pump diaphragms, and Nafion humidifiers and
dehumidifiers are not covered by this warranty.
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Manual, Photoacoustic Extinctiometer (PAX)
Software License
DMT licenses PAX software only upon the condition that you accept all of the terms contained in this
license agreement.
This software is provided by DMT “as is” and any express or implied warranties, including, but not
limited to, the implied warranties of merchantability and fitness for a particular purpose are
disclaimed. Under no circumstances and under no legal theory, whether in tort, contract, or
otherwise, shall DMT or its developers be liable for any direct, indirect, incidental, special,
exemplary, or consequential damages (including damages for work stoppage; computer failure or
malfunction; loss of goodwill; loss of use, data or profits; or for any and all other damages and
losses).
Some states do not allow the limitation or exclusion of implied warranties and you may be entitled to
additional rights in those states.
Laser Safety
The PAX is a Class 1 Laser Product.
This label can be found on the rear panel of the instrument:
On the 870 nm PAX, a Class 4 free-space diode laser module is wholly enclosed within the
instrument. Invisible laser radiation may be present when the lid of the internal
enclosure is removed and its interlocks are defeated.
On the 532 nm PAX, a Class 3B fiber-coupled laser module is wholly enclosed within the
instrument. Visible laser radiation may be present when the lid of the internal enclosure
is removed and its interlocks are defeated.
This label is present in two locations upon the internal acoustic enclosure:
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Additional Labels
The following label appears on the back panel of the instrument:
Warning: If not properly grounded, the instrument can cause an electrical shock.
Use a three-conductor cord and a plug appropriate for the location in which the
instrument will be used. Connect the plug to a properly grounded receptacle.
CAUTION: Use of control or adjustments or performance of procedures other than
specified in this manual may result in hazardous radiation exposure.
An identification label is located on the rear panel of PAX.
CAUTION – Use of controls or adjustments or performance of procedures other than those
specified herein may result in hazardous radiation exposure.
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Manual, Photoacoustic Extinctiometer (PAX)
CONTENTS
1.0
Introduction ......................................................................... 10
2.0
Unpacking and Set-up............................................................. 11
2.1
Unpacking................................................................................... 11
2.2
Set-up ....................................................................................... 11
2.2.1 Standard AC Power Setup ............................................................ 11
2.2.2 12 VDC Power Setup .................................................................. 12
2.2.3 Reducing Noise in the PAX System .................................................. 13
2.2.4 Ethernet Connection .................................................................. 13
2.3
Initial Startup .............................................................................. 13
2.4
External Features .......................................................................... 14
2.4.1 Front Panel Features ................................................................. 14
2.4.2 Rear Panel Features .................................................................. 14
2.5
Checking for Acoustic Noise on the Inlet ............................................... 15
3.0
Overview of Operation ........................................................... 15
3.1
Design ....................................................................................... 15
3.2
Components ................................................................................ 16
3.2.1 870 nm PAX ............................................................................. 16
3.2.2 532 nm PAX ............................................................................. 18
3.3
Flows ........................................................................................ 19
4.0
Navigation ........................................................................... 19
4.1
Internet-Access Requirements ........................................................... 20
4.2
PAX Start-up Screen ....................................................................... 21
4.3
Running Header ............................................................................ 21
4.4
Navigation Pane............................................................................ 22
4.4.1 More and Less Buttons ................................................................ 22
4.4.2 Overview of Buttons .................................................................. 23
4.5
General Navigation Tips .................................................................. 23
4.5.1 Menu Buttons on Right Side of Pages............................................... 23
4.5.2 Numeric Controls (Up-and-Down Arrows).......................................... 24
4.5.3 ACCEPT Button......................................................................... 25
4.6
Laser and Pump Buttons .................................................................. 25
4.7
Data Recording............................................................................. 25
4.8
Pages ........................................................................................ 25
4.8.1 Data Page ............................................................................... 25
4.8.2 Alarm Page ............................................................................. 27
4.8.3 Graph Page (Not Currently Functional) ............................................ 27
4.8.4 File Access Page ....................................................................... 28
4.8.5 Zero Now Page ......................................................................... 29
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4.8.6
4.8.7
4.8.8
4.8.9
4.8.10
4.8.11
4.8.12
Setup Page.............................................................................. 30
Time Setup ............................................................................. 31
Network Page .......................................................................... 32
Calibration Page ....................................................................... 33
About Page ........................................................................... 33
Analog In Page ....................................................................... 34
Analog Out Page .................................................................... 35
5.0
Transferring and Removing Data Files from the PAX ...................... 36
6.0
Maintenance ........................................................................ 37
6.1
Schedule for Replacing Consumable Parts ............................................. 37
6.2
Checking Flow .............................................................................. 37
6.3
Cleaning Window Cartridges ............................................................. 38
6.3.1 Frequency of Cleaning ................................................................ 38
6.3.2 Required Materials .................................................................... 38
6.3.3 Instructions............................................................................. 39
6.4
Replacing the PAX Laser Module ........................................................ 43
6.5
Operation in Severe Environments ...................................................... 43
6.6
Recommended Spare Parts ............................................................... 43
7.0
Calibration ........................................................................... 43
7.1
Recommended Frequency ................................................................ 43
7.2
Calibration Overview...................................................................... 43
7.3
Step-by-Step Procedure .................................................................. 44
7.3.1 Scattering Calibration ................................................................ 44
7.3.2 Absorption Calibration for 870 and 405 nm PAX.................................. 48
7.3.3 Absorption Calibration for 532 nm PAX ............................................ 50
7.3.4 Laser Calibration ...................................................................... 51
8.0
Troubleshooting .................................................................... 53
8.1
PAX Start-up Screen Does Not Appear .................................................. 53
8.2
PAX Grows Increasingly Noisy ............................................................ 54
8.3
PAX Stops Recording Data ................................................................ 54
8.4
Negative Data and Background Data Values ........................................... 55
8.4.1 For PAXes of All Wavelengths ....................................................... 55
8.4.2 For 405-nm and 532-nm Wavelength PAXes ....................................... 55
8.5
Low Laser Power Reading ................................................................ 55
8.6
High Scattering Background Reading (Bkgrnd Bscat) ................................. 56
8.7
Spikes in Absorption (Babs) and Background Absorption (Bkgrnd Babs) Values for
405 and 532-nm PAXes ............................................................................ 56
8.8
Difficulty Downloading Data to a USB Flash Drive .................................... 56
Appendix A: Specifications ............................................................... 57
General Specifications ............................................................................ 57
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Physical Specifications ............................................................................ 58
Operating Limits ................................................................................... 58
Appendix B: Phase—What it is and How it’s Used .................................... 58
The Minimum You Need to Know ................................................................ 58
The More Complete Explanation................................................................. 59
Appendix C: Calculations................................................................... 61
Calculation of Phase, Background Phase, and The Absorption Coefficient (B abs)......... 61
Calculating the Raw Absorption Coefficient (Babs, raw) ........................................ 62
Calculating the Scattering Coefficient (Bscat) .................................................. 63
Calculating Black Carbon Mass ................................................................... 63
How DMT Calculates the Default Value of Black Carbon Mass Absorption CrossSection (BC MAC) ................................................................................ 64
Appendix D: Serial Stream Output ....................................................... 64
Appendix E: PAX Data and Configuration Files ........................................ 65
Main PAX Data File................................................................................. 65
File Names ....................................................................................... 65
Output Channels ................................................................................ 65
Channel Definitions ............................................................................. 66
Measurement-Mode-Only Data Files............................................................. 71
PAX Config Files .................................................................................... 71
Appendix F: Wiring and Assembly Instructions for Buccaneer Connector ...... 74
Appendix G: Recommendations for Sampling Ambient Air ........................ 75
Inlets ................................................................................................ 75
Sample line system ................................................................................ 76
Conditioning system ............................................................................... 76
Appendix H: Revisions to the Manual ................................................... 77
Figures
Figure
Figure
Figure
Figure
Figure
Figure
1: PAX with Touch-Screen Display .............................................. 10
2: Attaching AC Power Supply ................................................... 11
3: Attaching DC Power Supply ................................................... 12
4: PAX Front Panel Features ..................................................... 14
5: PAX Rear Panel Features ...................................................... 14
6: The Cell ........................................................................... 15
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Figure 7: 870 nm PAX Interior with Components Labeled ......................... 17
Figure 8: 532nm PAX Interior with Components Labeled .......................... 18
Figure 9: PAX Flow Diagram ............................................................... 19
Figure 10: Accessing the PAX via the Internet ........................................ 20
Figure 11: PAX Data Page with Running Header ...................................... 21
Figure 12: Navigation Pane ................................................................ 22
Figure 13: Menu Buttons ................................................................... 24
Figure 14: Numeric Controls .............................................................. 24
Figure 15: ACCEPT Button ................................................................. 25
Figure 16: Data Page ........................................................................ 26
Figure 17: Alarm Page ...................................................................... 27
Figure 18: File Access Page ............................................................... 28
Figure 19: Zero Now Page ................................................................. 29
Figure 20: Setup Page ...................................................................... 30
Figure 21: Time Setup Page ............................................................... 31
Figure 22: Network Page ................................................................... 32
Figure 23: Calibration Page ............................................................... 33
Figure 24: About Page ...................................................................... 34
Figure 25: Analog In Page .................................................................. 35
Figure 26: Analog Out Page................................................................ 36
Figure 27: Items Involved in Cleaning the PAX Windows ........................... 38
Figure 28: Removing PAX Cover .......................................................... 39
Figure 29: Removing Cover to the Acoustic Enclosure .............................. 39
Figure 30: Thumbscrews (Circled) Securing Window Cartridge Restraint. There
are four thumbscrews on both restraints. ........................................ 40
Figure 31: Unscrewing the Window Cartridge Restraint ............................ 40
Figure 32: Removing Window Cartridge Restraint ................................... 40
Figure 33: Removing the Window Cartridge ........................................... 41
Figure 34: Folding Absorbond Wiper .................................................... 41
Figure 35: Pouring Solvent onto Pad .................................................... 42
Figure 36: Cleaning the Window ......................................................... 42
Figure 37: Extinction Equation ........................................................... 44
Figure 38: Flow Diagram for PAX Calibration ......................................... 45
Figure 39: Laser Power During Calibration Procedure .............................. 46
Figure 40: Regression Plot of Calculated Extinction Measurement against B scat
.............................................................................................. 47
Figure 41: Laser Power during Absorption Calibration Procedure ............... 48
Figure 42: Regression Plot of Calculated [ Extinction-Scattering] Measurement
against Babs. .............................................................................. 49
Figure 43: Penguin Display on PAX Screen............................................. 53
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Figure 44: Unseated SD Card, with Black Portion of the Card Visible ........... 54
Figure 45: Properly Seated SD Card ..................................................... 54
Figure 46: Babs,raw' and its two components: (1) Babs,bg', which reflects acoustic
noise, and (2) Babs', which reflects absorbing particles. The horizontal axis
corresponds with the phase of the laser modulation. .......................... 60
Figure 47: Rotating Babs Components to Yield a Real-Number Babs Value ...... 60
Figure 48: Random phases resulting from Individual Babs Measurements in
Low-Particle Conditions ............................................................... 61
Figure 49: PAX Config File Opened in Excel ........................................... 72
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1.0
Introduction
The Photoacoustic Extinctiometer (PAX), shown in Figure 1, is a sensitive, highresolution, fast-response instrument for measuring aerosol optical properties relevant for
climate change and carbon particle sensing. The instrument directly measures in-situ
light absorption and scattering of aerosol particles, from which it derives extinction,
single scattering albedo and black carbon (soot) mass concentration.
Intuitive menus may be navigated with the integrated graphical touch-screen on the PAX
front panel, affording access to real-time data and instrument status information.
The ability of the instrument to be powered by either a universal range of AC input (90264 V @ 47-63Hz) or 12 VDC makes the PAX a versatile measurement tool ready for
deployment virtually anywhere.
Figure 1: PAX with Touch-Screen Display
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2.0
Unpacking and Set-up
2.1 Unpacking
Unpack the PAX and ensure all the components are present. Shipped with your
PAX instrument are the following items:

This document, the Photoacoustic Extinctiometer (PAX) Operator Manual

North America Type B NEMA-5-15 (115V) power cable

Continental Europe Type E/F Hybrid CEE 7/7 (230V) power cable

A USB flash drive containing the PAX Maintenance Console (PMC) installer, as well
as electronic copies of this manual and the PMC Software Manual (DOC-0319)

Keyboard

Two port connectors

Extra filter (for noise suppression when exhaust is not hooked up)
2.2 Set-up
2.2.1
Standard AC Power Setup
To set up the PAX, remove the Swagelok® caps from the inlet and exhaust connectors on
the instrument’s rear panel (see circled areas in Figure 2). Plug in the power supply cable
to the back-panel power entry receptacle (see arrow). Plug the other end of the cable
into a power source. Voltages from 90V-264V at frequencies from 47-63 Hz are
acceptable for use. See warning below.
Figure 2: Attaching AC Power Supply
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Warning: If not properly grounded, the instrument can cause an electrical
shock. Use a three-conductor cord and a plug appropriate for the location in
which the instrument will be used. Connect the plug to a properly grounded
receptacle.
2.2.2
12 VDC Power Setup
1.) Attach the included Buccaneer connector to the 12 VDC power connection on the
PAX’s rear panel (Figure 3).
Figure 3: Attaching DC Power Supply
2.) Wire the other end of the connector to the power supply. The customer is
responsible for wiring the Buccaneer connector and connecting it to the supply.
Polarity will be indicated on the rear panel silkscreen. For additional guidance,
consult the Wiring and Assembly instructions from the manufacturer (see Appendix
F). Follow the instructions for the “flex mounting in-line” option. The connector is
the PX0736/S model.
Warning: Do not leave instrument connected to the 12V battery when turned off.
Because internal fans remain on when 12VDC is supplied, even when instrument is in
“off” condition, battery performance may be adversely impacted. Note that normal “on”
operation, under either AC or DC power, is not affected by this issue.
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2.2.3
Reducing Noise in the PAX System
The PAX is sensitive to acoustic noise, and background noise can interfere with the
instrument’s results. For this reason, DMT recommends adding approximately 18” of
tubing to reduce audible noise from the exhaust getting back into the instrument. Attach
this tubing to the ¼” Swagelok port connector on the PAX, and then attach the filter to
the other end of the tubing. Ensure the filter is attached in the correct orientation for
proper flow.
In addition, adjustments to the inlet system should be made with extreme care so as not
to create additional noise. To determine if acoustic noise on the inlet is interfering with
your data collection, follow the procedure outlined in section 2.5.
2.2.4
Ethernet Connection
The Ethernet port is used to connect the PAX to a network or a computer. This allows the
user to access the PAX display via the Internet, transfer PAX data files via the PAX
Maintenance Console (PMC), and examine real-time data.
You can use either a standard or crossover cable for the Ethernet connection.
2.2.4.1
Connecting the PAX to a Network
Trained information technology (IT) staff should be consulted when networking the PAX.
The PAX must have a static IP address before users can connect to it via the PMC.
2.2.4.2
Connecting the PAX to Another Computer
To make the Ethernet work, you need to assign compatible static IP addresses to your
laptop and to the PAX. Consult your IT staff for more information.
2.3 Initial Startup
Remove the Swagelok® caps from the inlet and exhaust connections, if they are
present. Press the front panel power switch (see Figure 4) to power up the
instrument. The switch will illuminate when the instrument is on.
If you are using the PAX to sample ambient air, please read Appendix G:
Recommendations for Sampling Ambient Air before you begin.
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2.4 External Features
2.4.1
Front Panel Features
1. Power Switch
2. Touch-screen
3. Two USB ports
1
2
3
Figure 4: PAX Front Panel Features
2.4.2
Rear Panel Features
1. 12V DC power connection
6. Ethernet port
®
2. Exhaust—Swagelok compression
fitting for ¼” tube
7. Fan inlet
8. Analog Inputs (2X BNC)
3. Nine-pin serial (RS-232) port
9. Analog Outputs (4X BNC)
4. Power entry receptacle—AC (IEC C13)
5. Sample inlet—Swagelok® compression
fitting for ¼” tube
2
3
1
6
4
5
8
7
9
Figure 5: PAX Rear Panel Features
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2.5 Checking for Acoustic Noise on the Inlet
Before using the PAX in the field, it is important to ensure acoustic noise on the inlet will
not interfere with data results. Follow the procedure below to determine if such noise is
a problem.
1.) Situate the PAX in relatively low-particle conditions (i.e., ambient air rather than
source sampling).
2.) Turn on the instrument and sample for several minutes.
3.) Look at the output data 1 and examine the results for the Babs (1/Mm) and Babs
noise (1/Mm) signals.
4.) Insert a filter on the PAX inlet and sample for several minutes.
5.) Look at the output data and examine the results for the Babs (1/Mm) and Babs
noise (1/Mm) signals.
6.) Compare the results from Steps 3 and 5. If Babs (1/Mm) fluctuated dramatically in
step three and these fluctuations disappeared in step five, or if the Babs noise
(1/Mm) signal dropped by more than 50%, there is a problem with acoustic noise
on the inlet.
3.0
Overview of Operation
3.1 Design
At the heart of the PAX is the cell, depicted in Figure 6.
Figure 6: The Cell
1
Note that you cannot use the PAX screen to view Babs Noise (1/Mm)—this channel is only
available in output data or via the PAX Maintenance Console (PMC).
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The PAX uses a modulated diode laser to simultaneously measure light scattering and
absorption. The standard infrared, 870-nm wavelength option2 is highly specific to black
carbon particles, since there is relatively little absorption from gases and non-BC aerosol
species at this wavelength.
A nominal 1 L/min aerosol sample flow is drawn into the PAX using an internal vacuum
pump controlled by two critical orifices. The flow is split between the nephelometer and
photoacoustic resonator for simultaneous measurement of light scattering and
absorption.
The absorption measurement uses in-situ photoacoustic technology. A laser beam
directed through the aerosol stream is modulated at the resonant frequency of the
acoustic chamber. Absorbing particles heat up and quickly transfer heat to the
surrounding air. The periodic heating produces pressure waves that can be detected with
a sensitive microphone. Phase-sensitive detection is used for all sensors.
The PAX uses a wide-angle integrating reciprocal nephelometer to measure the light
scattering coefficient. The scattering measurement responds to all particle types
regardless of chemical makeup, mixing state, or morphology.
A host of sensors and transducers support the function of the cell. When the laser beam exits
the cell, the beam power is measured by a photodiode in a laser power monitor. Transducers
on the cell measure internal pressure, relative humidity, and temperature. Active feedback
maintains laser diode temperature at a constant, set temperature.
Signals from the scattering photodiode, microphone, laser power photodiode, cell
transducers, and housekeeping subsystems are processed, and the resulting data is written to
a file. The user specifies the data recording interval on the PAX Setup Screen, in the Data
Average Time (Secs) field. Appendix E lists the data file contents. Select variables are also
displayed in real-time on the front panel display.
3.2 Components
3.2.1
870 nm PAX
Figure 7 shows the 870 nm PAX with its components labeled.
2
The PAX is also offered in 405 nm and 532 nm wavelengths.
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1
Acoustic
Enclosure
7
6
5
4
3
2
8
9
1
18
13
14
15
17
19
15
16
10
11
12
Figure 7: 870 nm PAX Interior with Components Labeled
In Acoustic Enclosure:
1.
2.
3.
4.
5.
Laser interlock switches
Laser and mount
Laser mirrors
Scattering detector board
Microphone board
6.
7.
8.
9.
Laser power monitor
Cell
Nephelometer (scattering) flow
Absorption flow
15.
16.
17.
18.
19.
Air filters
Laser driver
Exhaust line
Inlet line
Pump assembly
In Main Enclosure:
10.
11.
12.
13.
14.
Power distribution board
Power supply
Fan
Touchscreen display
Control board
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3.2.2
532 nm PAX
Figure 7 shows the 532 nm PAX with its components labeled.
7
1
3
4
Acoustic
6
5
Enclosure
8
9
1
2
18
14
13
12
15
15
15
16
17
10
11
12
Figure 8: 532nm PAX Interior with Components Labeled
In Acoustic Enclosure:
1. Laser interlock switches
2. Laser head
3. Laser mirrors
4. Scattering detector board
5. Microphone board
6.
7.
8.
9.
Laser power monitor
Cell
Nephelometer (scattering) flow
Absorption flow
15.
16.
17.
18.
Air filters
Laser power supply
Inlet line
Exhaust line
In Main Enclosure:
10.
11.
12.
13.
14.
Power distribution board
Power supply
Fans
Touchscreen display
Control board
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3.3 Flows
Figure 9 is a diagram of the PAX flows.
Figure 9: PAX Flow Diagram
4.0
Navigation
The PAX features a touch-screen interface. You can access this interface either from the
PAX itself or using a web browser, for example, over the internet. Note that controlling
the PAX is considerably faster over the network than via the touch-screen. If you have
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many adjustments to make in the software, DMT recommends making them over the
network.
4.1 Internet-Access Requirements
The PAX user-interface program is supported for Google Chrome and Firefox. Using other
internet browsers may result in display and performance issues.
To connect to the PAX via a web browser, first ensure the PAX is connected to the
network. See section 2.2.4.1. Next, type the instrument’s internet protocol (IP) address
in the browser URL field, followed by “/www/pax/pax.html” (Figure 10). The PAX
window should appear (for example, "192.168.1.152/www/pax/pax.html" as shown
below).
Figure 10: Accessing the PAX via the Internet
Note that when connecting to the PAX via a web browser, you may need to refresh the
screen to see changes.
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4.2 PAX Start-up Screen
Figure 11 shows the startup screen for the interface, with the Data page active.
Navigation button
Running Header
Figure 11: PAX Data Page with Running Header
The most important feature of the PAX interface is the PAX Navigation button, in the
upper left of the display. This button appears on every page. Clicking it brings up the
Navigation Pane, shown in Figure 12.
4.3 Running Header
The Navigation button is part of a running header that also displays the following
information:


PAX wavelength (underneath PAX logo in upper left)
PAX ID (a user-identified name, for example the name of the field site and/or
instrument number)
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





Currently displayed page (e.g., “Data”)
PAX Mode (“Measure,” “Zero,” “Flush,” “Acstc Cal”)
The number of seconds remaining in the current mode (i.e., before the next mode
transition)
The current local time on the PAX
The current date in yyyy-mm-dd format
An alarm indicator, which indicates the highest level of alarm currently being
generated
4.4 Navigation Pane
The navigation pane is a basic navigation menu. It appears on top of whatever page you
are currently viewing.
Figure 12: Navigation Pane
4.4.1
More and Less Buttons
Clicking the pane’s More button brings up a second panel with additional options.
Clicking Less reverts to the original display shown in Figure 12.
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4.4.2
Overview of Buttons
From the Navigation Pane, you can click on the buttons below. The buttons in the top
portion of the table are visible when you first click on the navigation button. The buttons
on the bottom, shaded in gray in the table, are visible when you click on More.
Button
Data
Alarm
Graph
Files
Zero
Pump On/Off
Laser On/Off
Setup
Time
Ntwrk
Calib.
About
Analog In
Analog Out
Function
Displays PAX data such as Bscat, Babs, Albedo, etc.
Alerts you to potential problems with the instrument
Displays graphs of variables of interest (not currently functional)
Allows you to write PAX data to a USB flash drive
Allows you to start a zero/acoustic calibration
Allows you to turn the PAX pump On or Off
Allows you to turn the PAX laser On and Off
Allows you to configure the PAX’s ID, location, and other parameters
Allows you to change the time and date of the PAX system and to specify
the PAX’s time zone
Displays configurable internet communications information
Allows you to modify calibration coefficients
Displays information about the PAX
Allows you to configure analog input channels
Allows you to configure analog output channels
Table 1: Overview of Navigation Buttons
Click on Less to view the original buttons again.
4.5 General Navigation Tips
4.5.1
Menu Buttons on Right Side of Pages
Many of the PAX user-interface pages display menu buttons on the right. For instance, the
Calibration page features four menu buttons—laser power, scattering, microphone, and
phase correction:
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Menu Buttons
Figure 13: Menu Buttons
The currently active menu is highlighted with a white border. In Figure 13, the Laser
Power is active. This means the controls in the middle of the screen adjust the laser
power calibration coefficient. Clicking on the Scattering menu button will bring up
controls to adjust the Scattering coefficient.
4.5.2
Numeric Controls (Up-and-Down Arrows)
Many pages also feature numeric controls like those shown on the Calibration page. In
such cases, large-scale adjustments can be made using the arrows on the left, while
arrows on the right make smaller-scale adjustments. In Figure 14, for instance, clicking
on arrow #1 changes the current coefficient from 11.95 to 21.95. Clicking on arrow #2
changes the current coefficient to 12.95. Clicking on arrow #3 changes it to 11.96.
1
2
3
Figure 14: Numeric Controls
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4.5.3
ACCEPT Button
Finally, many PAX screens feature an ACCEPT button like that shown below. This button
is used to confirm changes you may have made to a page’s parameters.
Figure 15: ACCEPT Button
If you exit the screen without clicking Accept, the program will discard any changes
made.
4.6 Laser and Pump Buttons
The Laser Button on the navigation pane allows you to turn the laser on and off. The
button also displays the laser’s current status. Similarly, the Pump button allows you to
turn the pump on and off and displays the pump’s current status.
4.7 Data Recording
When the PAX is powered on, it is always recording data. These files are stored on the
PAX computer. To transfer files to a USB flash drive, use the File Access page described
in section 4.8.4. You can also use the PAX Maintenance Console (PMC) software to read
files from the PAX. For details on the PMC, see the PMC Software Manual (DOC-0319).
4.8 Pages
4.8.1
Data Page
Figure 16 displays the PAX Data page.
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Figure 16: Data Page
The Data page displays current values for channels of interest. Definitions and supplemental
information for these variables can be found in Appendix E, under “PAX Data Files.”
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4.8.2
Alarm Page
Figure 17: Alarm Page
The Alarm page shows important PAX indicators. These indicators and their expected
values are defined in Appendix E in the “PAX Data Files” section.
In cases where values are unacceptably outside the expected range, the system displays
an alarm (red icon). When values are approaching the limits of the expected range, the
system displays a warning (yellow icon). When values are within the expected range, the
system displays a green icon, like those depicted above.
4.8.3
Graph Page (Not Currently Functional)
The Graph page is not currently functional.
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4.8.4
File Access Page
To get to the File Access page (Figure 18), click on the Files button on the navigation
pane. The File Access page allows you to write PAX data to a USB flash drive. It also
displays the currently available memory.
Figure 18: File Access Page
To transfer data to the USB device, follow the steps below.
1) Insert the USB Flash Drive into the PAX USB port.
2) The USB status (No Device in Figure 18) should change to Mounting. Wait until it
changes to Device Ready. (You may see a No Device status appear briefly just
after Mounting, but just ignore this reading; the status will soon change to Device
Ready.)
3) On the PAX File Access window, set the dates for the data you want transferred.
4) Press ACCEPT.
5) The USB device status will change to Start Write and then Device Busy. This
indicates data are being written to the device.
6) When the data transfer is finished and the USB status is Safe to Remove, remove
the USB device.
Notes about USB data transfer:
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


4.8.5
Data are always being recorded to the PAX hard drive when the instrument is
powered on. The File Access screen is only used to write data to the USB flash
device.
A maximum of 30 days’ worth of data can be transferred to the USB device during
a single operation. If the user selects more data than this, the PAX will write only
the first 30 days specified. This limitation is imposed because transferring large
amounts of data slows down the CPU.
The PAX computer scans the USB device when the device is first inserted in order
to detect and repair any issues with file system integrity. This scan creates a few
files that are not normally of interest to the user.
Zero Now Page
Clicking on the navigation pane’s Zero button brings up the Zero Now page, shown in
Figure 19.
Figure 19: Zero Now Page
Clicking the blue Zero Now button puts the system into a short flush mode, followed by a zero
mode. The flush mode is designed to clear out particle-laden air before the zeroing begins.
The system then does another flush before reverting to measurement mode. The second flush
mode reintroduces particle-laden air into the PAX.
Clicking on Fix Laser Power turns the fixed laser power on and off. When the fixed laser
power is on, it is “fixed” or set to 700 mW. This feature is useful in checking laser power
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levels and in testing to see if the optical windows are dirty. It is also useful for checking
acoustic and electronic performance of the instrument.
The Acoustic Test button is not currently functional.
The Laser Phase button enables and disables Babs phase (deg), the measured phase of the
Babs measurement. An enabled, non-zero Babs phase (deg) value can be useful in calibrating
Babs measurements. However, it can also result in negative data values.
Set Zero Interval (Secs) brings up controls for you to adjust the current number of seconds
between zero events. This number affects the time between automatic zero events.
Example: When Set Zero Interval (Secs) is set to 600, there are ten minutes between the
start of one zero interval and the start of the next. There are always 70 seconds required for a
zeroing: 20 seconds for a flush, then 30 seconds for the actual zeroing, then another 20
seconds for a second flush. Thus, the measurement period will be 530, or 600 – 70. The
Countdown Timer (sec) in the output file will start at 529 and count down to zero.
Once you have set the Zero Interval, click on ACCEPT to commit these changes. Clicking on
the black Zero Now button in the upper right brings you back to the Zero-Now controls.
4.8.6
Setup Page
The Setup page, shown in Figure 20, allows you to modify several PAX parameters.
Figure 20: Setup Page
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Current ID specifies the name of the PAX station. Location sets the name of the station’s
location. Both of these parameters are user-specified and can be modified using a
keyboard. These parameters should be combinations of alphanumeric characters and
spaces. Do not use commas for names or locations, as this will result in errors in the .csv
files.
BC MAC (m2/g) sets the Black Carbon Mass Absorption Cross-Section. See Appendix C for
more information.
Data Average Time (Secs) specifies the data recording rate. Data are averaged over this
sampling period. For instance, if you set Data Average Time (Secs) to ten, the PAX will
record data to the file every ten seconds. Recorded data will be averaged over this tensecond interval.
Once you have modified these parameters, click on ACCEPT to confirm your changes.
4.8.7
Time Setup
Clicking on the Time button from the navigation pane brings up the Time Setup page
(Figure 21).
Figure 21: Time Setup Page
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On this page you can modify the current local time and date using the numeric controls
(up-and-down arrows). Note: Currently, you must restart the PAX for Time changes to
take effect. This is a known bug that will be fixed in future versions of the program.
Clicking on Time Zone allows you to specify the PAX’s time zone and location. (Different
regions within one time zone can follow different daylight-savings rules, so location is
used to determine time.) If you change the time zone, you will need to reboot the PAX
for the change to take effect.
Once you have modified parameters on the Time Setup page, click on ACCEPT to update
them to the new values.
4.8.8
Network Page
The Network page (Figure 22) allows you to specify the PAX’s internet protocol. The IP
menu item displays information about the IP address, Netmask, and Gateway. You can
modify these parameters using a keyboard.
Note that these parameters are rarely modified and you should not need to access this
page frequently.
Figure 22: Network Page
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In the future, clicking on the NTP button will bring up a dialog box that allows you to
specify whether the PAX should synchronize with the Network Time Protocol (NTP). This
feature is currently disabled.
The UDP feature allows you to send data over a network.
4.8.9
Calibration Page
The Calibration page (Figure 23) allows the user to modify calibration coefficients for
Laser Power, Scattering, the Microphone and Phase Correction.
Figure 23: Calibration Page
Click on the relevant menu button to bring up controls for the calibration coefficient you
want to modify. Click on the up and down arrows to increase or decrease the coefficient.
Once you are finished, click on ACCEPT to confirm your changes.
For details on how to obtain calibration coefficients, see section 7.0.
4.8.10 About Page
The About page provides a description of the PAX instrument, including measured and
derived parameters.
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Figure 24: About Page
4.8.11 Analog In Page
Figure 25 shows the Analog In page.
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Figure 25: Analog In Page
The Analog In page allows you to configure inputs from two analog devices. You can set
the low and high ranges for these inputs. You can also name them (e.g., “Anemometer”)
by clicking on Input Name and using a keyboard to enter a name.
Once you are finished making changes, click on Accept to update the parameters.
4.8.12 Analog Out Page
The Analog Out page allows you to configure up to four 0-10V analog output channels.
For each channel, select a low range, a high range, and the channel number.
The low and high range values are used to scale analog outputs from voltages into
appropriate units. For instance, if your analog output reflects a temperature that ranges
from -50 to 50 °C, -50 would be the low range and 50 would be the high range.
When you specify a channel number for an analog output, the PAX will show the
corresponding channel name in the menu buttons to the right of the screen.
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Figure 26: Analog Out Page
The analog outputs of the PAX are driven by buffer amplifiers and have an output
impedance of 50 ohms. The current is short-circuit protected at 15mA.
5.0
Transferring and Removing Data Files from
the PAX
To transfer or delete PAX data files, use the PAX Maintenance Console (PMC) software. This
software is included on the USB flash drive sent with the PAX, and it is described in the PMC
Software Manual (DOC-0319). For the PMC to work, the PAX must be connected via the
Ethernet port to another computer or to a network. See section 2.2.4.
If the PAX is allowed to accumulate files until the disk is almost full, the instrument will begin
deleting the oldest files to accommodate newer ones. However, this will not happen until the
PAX has accumulated many files. It is best to transfer and delete files relatively frequently so
that the data files are easily identifiable and do not clutter up the disk.
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6.0
Maintenance
DANGER
The laser used in the PAX is a CLASS 4 Laser
The standard laser operates at 870 nm and is rated at 2 Watts.
Caution
The use of controls, adjustments, or procedures other than those
specified in this document may result in hazardous radiation exposure.
In particular, reflections caused by placing an object in the laser beam
path can cause skin burns and/or blindness.
6.1 Schedule for Replacing Consumable Parts
Consumable parts must be periodically replaced. DMT recommends the following
schedule for replacing consumable parts
Once a Year
Change three filters (#16 in Figure 7,
DMT part number FLTR-0022)
Change tubing in zero valves




Once Every Three Years
Change sample pump
Check if laser needs replacement3
6.2 Checking Flow
Users should check the PAX inlet and exhaust flows before field campaigns, or if a flow
problem is suspected. To check flows, attach a bubble flow meter to the inlet or exhaust.
Flow should nominally be 1.0 L/min ±10% at 21 °C and 1 atm. If either flow differs
significantly from this value, contact DMT for assistance.
3
Laser lifetime depends on the frequency of instrument use. In all cases, lasers should work for
several years before needing replacement.
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6.3 Cleaning Window Cartridges
DMT advises users to keep a supply of clean window cartridges on hand. This way a dirty
one can be quickly replaced and cleaned when convenient. DMT part numbers for window
cartridges are as follows:
PAX Wavelength
DMT Part Number for Window Cartridge
870 nm
532 nm
405 nm
ASSY-0701
ASSY-0916
ASSY-0973
6.3.1
Frequency of Cleaning
PAX windows require no maintenance unless the Laser Power reading drops by more than
10% or the Bkgrnd Bscat (1/Mm) reading increases by a factor of two or more. See the
troubleshooting section for more details.
6.3.2
Required Materials
The following materials are recommended for cleaning the PAX windows:
1. Texwipe TX404 Absorbond wiper, DMT part number OP-0155
2. An optical grade solvent, available from chemical supply vendors. Ethanol or
acetone is preferred
3. Tweezers or forceps
4. Window restraint—this will be removed from the PAX during the procedure
5. Window cartridge—this will be removed from the PAX during the procedure
6. Rubber gloves (not pictured)
2
4
5
1
3
Figure 27: Items Involved in Cleaning the PAX Windows
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To clean the windows, you will need to remove the window restraint (item 4 above) and
then the window cartridge (item 5).
6.3.3
Instructions
1. Disconnect power to the instrument.
2. Remove the instrument cover (Figure 28).
Figure 28: Removing PAX Cover
3. Remove the cover of the acoustic enclosure (Figure 29).
Figure 29: Removing Cover to the Acoustic Enclosure
4. Loosen the four captive thumbscrews of the window cartridge restraint (Figure 30
and Figure 31).
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Figure 30: Thumbscrews (Circled) Securing Window Cartridge Restraint. There are four thumbscrews on both
restraints.
Figure 31: Unscrewing the Window Cartridge Restraint
5. Remove the restraint (Figure 32).
Figure 32: Removing Window Cartridge Restraint
6. Remove the Window cartridge (Figure 33).
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Figure 33: Removing the Window Cartridge
7. Put on gloves, if you haven’t already.
8. Remove one sheet of Absorbond wiper from the bag using tweezers to avoid
contaminating that sheet or the other in the bag.
9. Fold the wiper into a pad about 2.5 to 3 cm, making sure there are about 10 or more
layers (Figure 34). Hold the folded sheet so that the folded edge is facing outward.
Figure 34: Folding Absorbond Wiper
10. Saturate the pad with the optical grade solvent (Figure 35). Shake the pad of excess
solvent.
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Figure 35: Pouring Solvent onto Pad
11. Ensure that the optical surface is free of any dust or particulate that could damage
the surface if it was dragged across on the wiper.
12. Make a single wiping motion across the face of the optic, rotating the wiper as it
moves across the face so that fresh surface is continually exposed. One swipe across
the face should suffice.
Figure 36: Cleaning the Window
After the solvent evaporates, the optic should appear clean and streak-free. If not,
replace the window cartridge. DMT recommends keeping a supply of window cartridges
on hand for easy window maintenance.
Installation of the window cartridge is the opposite of disassembly.
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6.4 Replacing the PAX Laser Module
Customers wishing to replace their laser module should send the PAX back to DMT. While
replacing the laser is straightforward, aligning it is quite complex and should only be
done by trained personnel.
6.5 Operation in Severe Environments
In situations with especially dense BC concentrations, the window cartridges will require
more frequent cleaning or changing. If Laser Power drops by more than 10%, or if the
Bkgrnd Bscat reading doubles, this is a good indication that the window cartridges need
cleaning or replacement.
6.6 Recommended Spare Parts
DMT recommends users keep the following equipment on hand:
 One set of replacement window cartridges (see section 6.3 for part numbers)
 Three replacement filters (supplied, DMT part number FLTR-0022)
 Spare conductive tubing (DMT part number TUB-0079; in the unit, tubing is
pinched where it attaches to the solenoid valve, so it occasionally needs to be
replaced)
7.0
Calibration
7.1 Recommended Frequency
DMT recommends calibrating the PAX before and after field campaigns. At a minimum,
when the instrument is operated continuously, the PAX should be calibrated once every
six months.
7.2 Calibration Overview
The PAX is capable of measuring the scattering coefficient, Bscat, and the absorption
coefficient, Babs. It calculates the extinction coefficient, Bext, by summing the scattering
and absorption coefficients (Bext = Bscat + Babs). However, the instrument is also capable of
independently measuring the extinction coefficient as follows:
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Bext  
1
I
ln .10 6 [ Mm 1 ]
.354 I 0
Figure 37: Extinction Equation
where
0.354 =
The path length of the laser beam through the cavity in meters
10 6
=
A conversion factor to express extinction in Mm 1
I0
=
The average laser power before and/or after calibration
I
=
The laser power during calibration
Since extinction can be calculated using two different methods, the instrument can easily
be calibrated. Specific procedures for this are given in the following sections.
7.3 Step-by-Step Procedure
Procedures for calibrating the scattering and absorption measurements are described
below. Note that the recommended absorption-calibration procedure depends on the
wavelength of your PAX.
DMT recommends repeating calibration procedures to avoid calculation errors. Results
from the second calibration should be within a few percentage points of the first
calibration. If this is the case, the results of either calibration can be entered into the
PAX.
Users should maintain dated records of calibration coefficients. Doing so can help identify
any long-term drift in the coefficient values.
7.3.1
Scattering Calibration
7.3.1.1
Required Materials



PAX
Aerosol generator
Drying column
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
200-260 nm PSL particles
Note: other materials can replace the PSL particles, so long as they are highly scattering
and have negligible absorption, e.g. ammonium sulfate particles.
7.3.1.2
Part 1: Data Collection
1. Allow the instrument to warm up for 1 hour, sampling air with filter on the inlet.
(If the room air is fairly clean, i.e. Bscat < 20 Mm 1 , you don’t need the filter.)
2. Press the ZERO button (in the running header) and collect two minutes of data
with the filter on the inlet of the PAX. This will allow the I 0 measurement. Wait
for the zero and calibration cycle to finish before starting the data collection
period.
3. Prepare a high-concentration solution of approximately 200-260 nm PSL particles
in an aerosol generator with the drying column. See Figure 38. The concentration
should be high enough to give a scattering level of about 20,000 Mm -1. Once the
initial scattering aerosol concentration is high, it is best to avoid rapid
fluctuations during this step. A variation of less than 10% is recommended.
Figure 38: Flow Diagram for PAX Calibration
4. Collect two to four minutes of data with the PSL particles entering the PAX. Laser
power I will be measured in this step (Laser power (W) in the output file).
5. Remove the PSL particle stream from the PAX and put the filter on the inlet.
6. Collect another 2 minutes of background data while measuring particle-free air.
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7.3.1.3
Part 2: Data Analysis
Graph the laser power reading results that were recorded during steps 2 – 6. The graph
should have the approximate shape of Figure 39 below.
I0 – Step 2
I0 – Step 6
Laser power
(mW)
I – Step 4
Time
Figure 39: Laser Power During Calibration Procedure
1. Average approximately one minute of laser-power data collected with the filter on
either before or after the scattering measurement—i.e., in step 2 or 6 above. You
can also calculate the average from both steps. This average value will be the I 0 .
2. Calculate the extinction for both the filtered air periods and the period when the
measurement of the PSL particles is stable. Use the following expression:
Bext  
1
I
ln .10 6 [ Mm 1 ]
.354 I 0
where I is the laser power (W).
3. Plot the calculated extinction from the equation in the previous step against the
measured scattering as shown in Figure 40. Prepare a linear regression with
calculated extinction as the y value and measured scattering as the x value. (Since
absorption is negligible, the slope of a linear regression line represents the
correction factor for the scattering calibration factor.)
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25000.00
y = 1.0454x - 7.8118
R2 = 0.9997
20000.00
Extinction (1/Mm)
15000.00
Bext
Linear (Bext)
10000.00
5000.00
0.00
0.00
5000.00
10000.00
15000.00
20000.00
25000.00
-5000.00
Scattering (1/Mm)
Figure 40: Regression Plot of Calculated Extinction Measurement against Bscat
7.3.1.4
Part 3: Entering the New Calibration Coefficient
1.) Click on the Navigation Button.
2.) Click on More.
3.) Click on the Calib. button.
4.) Click on Scattering.
5.) Multiply the current value of Scattering by the slope of the regression line to
produce the new value.
6.) Update the Scattering value.
7.) Click on ACCEPT.
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7.3.2
7.3.2.1
Absorption Calibration for 870 and 405 nm PAX
Required Materials


PAX
A suitable source of black carbon, for instance one of the following:
o A kerosene lamp operated under fuel-rich conditions and producing large
amounts of black smoke. DMT suggests filling a garbage bag with the smoke
and allowing it to mix in the bag for 5 minutes before sampling.
Glassy carbon spheres (GCS), distributed by Alpha Aesar (stock # 38008). If you use GCS,
they should be nebulized through an aerosol generator and passed through a drying
column before entering the PAX inlet. See Figure 38.
With any source of absorbing aerosol, the absorption should be greater than 5,000 Mm -1,
preferably closer to 10,000 Mm-1.
7.3.2.2
Part 1: Data Collection
Repeat the procedure used for calibrating the scattering measurement (section 7.3.1.2)
except use the black carbon source.
7.3.2.3
Part 2: Data Analysis
The post-processing of output differs slightly from that done for scattering calibration.
The absorption calibration analysis is described below.
The laser power reading graphed across time should have the approximate shape of
Figure 41 below. I0 is derived by averaging laser-power readings taken when the filter is
on.
I0 – filter on
I0 – filter on
Laser Power
(mW)
I – BC
Time
Figure 41: Laser Power during Absorption Calibration Procedure
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1. Average approximately one minute of laser-power data collected with the filter on
either before or after the absorption measurement. You can also calculate the
average from both steps. This average value will be the I 0 .
2. Calculate the extinction for both the filtered air periods and the period when the
measurement of black carbon is stable. Use the following expression:
Bext  
1
I
ln .10 6 [ Mm 1 ]
.354 I 0
where I is the laser power (W).
3. Using the values of Bext obtained in the previous step, plot ( Bext  Bscat ) against
the measured absorption as shown in Figure 42. Scattering is not negligible in this
case, which is why it must be factored into the analysis.
Figure 42: Regression Plot of Calculated [ Extinction-Scattering] Measurement against Babs.
4. Prepare a linear regression with calculated [extinction – scattering] as the y value
and measured absorption the x value.
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The slope of the linear regression line represents the correction factor for the absorption
measurement.
7.3.2.4
Part 3: Entering the New Calibration Coefficient
The absorption measurement is adjusted by changing the Microphone calibration value,
as follows:
1.) Click on the Navigation Button.
2.) Click on More.
3.) Click on the Calib. button.
4.) Click on Microphone.
5.) Divide the current value of Microphone by the slope of the regression line to
produce the new value.
6.) Update the Microphone value.
7.) Click on ACCEPT.
7.3.3
Absorption Calibration for 532 nm PAX
7.3.3.1



Required Materials
PAX
0 -2 W Laser power meter
A source for highly concentrated NO2 gas (see below).
Light at the 532 nm wavelength is strongly absorbed by NO2 gas. Each ppb of NO2 gas will
produce approximately 0.395 Mm-1 absorption at standard temperature and pressure (STP)
of 0˚C and 1013.25 mBar. The recommended concentration of NO 2 gas for this procedure
is 200,000 ppb, which will produce an absorption signal of 79,000 Mm-1 at STP.
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7.3.3.2
Part 2: Data Collection
Follow the same procedure as for the scattering calibration (see section 7.3.1.2), except
use NO2 gas instead of PSL particles.
7.3.3.3
Part 3: Data Analysis
The analysis is similar to that for scattering particles (section 7.3.1.3), except that the
data plot uses
Babs
on the x axis. Prepare a linear regression with calculated extinction
as the y value and measured absorption the x value. The slope of the linear regression
line represents the correction factor for the absorption measurement.
7.3.3.4
Part 4: Entering New Calibration Coefficient
The absorption measurement is adjusted by changing the Microphone calibration value,
as follows:
1.) Click on the Navigation Button.
2.) Click on More.
3.) Click on the Calib. button.
4.) Click on Microphone.
5.) Divide the current value of Microphone by the slope of the regression line to
produce the new value.
6.) Update the Microphone value.
7.) Click on ACCEPT.
Note that you do not need to calibrate the laser before performing this procedure.
7.3.4
Laser Calibration
The laser is calibrated at DMT, and the user should not need to calibrate the laser. In the
event that the laser requires calibration for some reason, however, instructions for this
procedure are presented below.
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1. Turn off Power to the PAX. WARNING: Failure to shut down the PAX may expose
the user to dangerous laser radiation if the laser-interlock switches are defeated
when the covers are removed.
2. Remove the instrument cover and the cover of the acoustic enclosure.
3. Remove the laser power monitor (see Figure 7) and put a 0–2 W laser power meter
in its place. Make sure the laser meter is properly placed to intercept the beam
exiting the cell. Reinstall the acoustic-enclosure cover to engage the interlocks.
4. Turn on the PAX. Make a note of the laser power reading displayed on the laser
power meter.
5. Shut down the PAX once again.
6. Remove the acoustic-enclosure cover, replace the laser power monitor, and
reinstall both covers.
7. Turn on the PAX and record the Laser Power reading displayed on the PAX Status
screen.
8. Calculate the new Laser Power Calibration Coefficient and update the system:
a.) Click on the Navigation Button.
b.) Click on More.
c.) Click on the Calib. button.
d.) Click on Laser Power.
e.) Multiply the current value of Laser Power by the slope of the regression line
to produce the new value.
f.) Update the Laser Power value.
g.) Click on ACCEPT.
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8.0
Troubleshooting
8.1 PAX Start-up Screen Does Not Appear
If the SD card becomes unseated, the PAX will not boot up properly. The screen will
illuminate but will not move past the penguin display (Figure 43).
Figure 43: Penguin Display on PAX Screen
If this happens, one possibility is that the SD card has become unseated (Figure 44). This
can happen if the top panel of the instrument was jostled. To reseat the card, do the
following:
1. Turn off the PAX.
2. Unscrew and remove the instrument’s top panel.
3. Push the SD card downward until you hear a small click and the card position
resembles that shown in Figure 45. The SD card is located right behind the PAX
display screen.
4. Restart the PAX. The PAX screen should boot up and display the Data screen.
5. Replace the instrument’s top panel.
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Figure 44: Unseated SD Card, with Black Portion of the Card Visible
Figure 45: Properly Seated SD Card
8.2 PAX Grows Increasingly Noisy
Make sure the inlet and outlet plug caps have been removed. These plugs should be
removed before turning on the instrument.
8.3 PAX Stops Recording Data
If you delete the current day’s data file from the PAX, the PAX will stop recording data.
To restart data recording, turn off power to the instrument. Wait two minutes, and then
turn power back on. Data recording will resume.
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8.4 Negative Data and Background Data Values
8.4.1
For PAXes of All Wavelengths
Negative but near-zero data values for channels like the Absorption Coefficient (Babs),
the Scattering Coefficient (Bscat), or Black Carbon Mass Concentration (BC Mass) do not
necessarily indicate a problem with the PAX.
The negative values arise because of how the PAX accounts for background noise. During
a zero event, when clean air is entering the PAX, the system averages the Babs and Bscat
readings. Since the air is clean, the resulting averages represent an estimation of the
noise signals. (The Babs noise average is stored in Bkgrnd Babs, while the scattering
average is stored in Bkgrnd Bscat.) After the zero mode completes, these averaged noise
signals are subtracted from Babs and Bscat respectively to get an accurate estimation of
absorption and scattering signals that are not due to noise. However, because the overall
signal bounces around slightly, there may be occasions where a below-average signal
results in a negative Babs or Bscat reading after noise has been accounted for. This
happens only when the sample air has a very low concentration of black carbon.
Note that if phase compensation is enabled, you may see larger negative values for Babs
and Bscat, as well as negative readings for Bkgrnd Babs and Bkgrnd Bscat. The phase
compensation feature is very complex and users who are interested in this feature are
advised to contact DMT for help interpreting their data.
8.4.2
For 405-nm and 532-nm Wavelength PAXes
The 532-nm PAX and especially the 532-nm PAX are sensitive to NO2 gas. If the amount of
NO2 gas remains constant, the background absorption value, Bkgrnd Babs (1/Mm), will
adjust accordingly and the presence of the gas should not affect the measurement.
However, if NO2 amounts are fluctuating and happen to spike during a zero, the Bkgrnd
Babs (1/Mm) value may get set too high. This will cause negative Babs values if NO2
concentrations decrease after zeroing is complete. To solve this problem, place the PAX
in an environment without fluctuating NO2 levels. Alternatively, you can use a denuder or
UV lamp to purge NO2 gas from the sample before it enters the PAX.
8.5 Low Laser Power Reading
If the laser power has dropped by 10% or more, there may be dirt or debris on the PAX
windows. To solve the problem, clean the PAX windows using optics-grade ethanol and
Absorbond® swabs.
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8.6 High Scattering Background Reading (Bkgrnd Bscat)
A high Bkgrnd Bscat reading also can result from dirty windows. Clean the PAX windows
using optics-grade ethanol and Absorbond® swabs.
8.7 Spikes in Absorption (Babs) and Background Absorption
(Bkgrnd Babs) Values for 405 and 532-nm PAXes
This problem can be due to fluctuating NO2 gas levels in the PAX sample. See section
8.4.2 for details.
8.8 Difficulty Downloading Data to a USB Flash Drive
One possible cause of this problem is that the USB flash drive does not contain sufficient
memory. PAX data files are relatively large, so DMT recommends using a USB device with
at least 4 GB of storage when downloading files.
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Appendix A: Specifications
General Specifications
Measured Parameters
Auxiliary Parameters
Derived Parameters
Measurement Range – Absorption and Scattering
Laser (standard option)
Modulation Frequency
Angular Integration for Scattering
Sample Flow
Flow Control
Pump
Response Time
Data Averaging Time
Calibration Particles
Calibration Interval
Zero Check and Acoustic Calibration
Maintenance Schedule
User Interface
Front Panel Features
Rear Panel Connections
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Absorption coefficient, Babs
Scattering coefficient, Bscat
Temperature
Pressure
Relative Humidity
Extinction coefficient, Bext
Single scattering albedo, SSA
Dew Point
< 1 Mm-1 - 100,000 Mm-1 (870 nm, 60 sec. averaging)
870 nm, 2 W
1500 Hz nominal, square wave
6 to 174°
1 L/min
Critical orifice
Diaphragm
< 10 sec; one second resolution
1, 10 or 60 seconds; user selectable
Absorption:
Strongly absorbing particles such as black smoke
from a fuel-rich gas lamp, or glassy black carbon.
Scattering:
Strongly scattering particles such as ammonium
sulfate, or polystyrene latex (PSL) spheres, 200-260
nm diameter.
Recommended every 6 months, or before and after
critical projects.
On demand, or automated at a user-selectable
interval of 5, 15, 20, 30, or 60 minutes.
Zero check with high-efficiency filtered air sample;
acoustic calibration for resonance frequency and
resonator quality factor.
See section 0 for user maintenance schedule.
Touch-screen or standard keyboard and mouse
 Graphical color touch-panel display screen
 Two USB-A ports
 Power switch
 12V DC Inlet port
 Ethernet port
 Serial (RS-232) port
 Sample inlet (compression fitting for ¼” tube)
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Pump exhaust (compression fitting for ¼”
tube)
 Power entry receptacle
 Two analog BNC inputs
 Four analog BNC outputs
Ethernet 100/10 Mbps, RS-232 Serial
90 - 264 V, 47 - 63 Hz (AC Power) or 12 VDC

Communications Output
Power Requirements
PAX Maintenance
(included)
Console
Computer Requirements
(computer not included)
for
(PMC)
Software
PMC
Software
Executable program written in LabVIEW; external
software package for instrument maintenance, data
playback and archiving. Computer and software are
not required to operate the instrument.
Windows XP, Vista, or Windows 7
Minimum 1GB RAM
Physical Specifications
Weight:
Dimensions:
18 kg (40 lb)
18 cm H x 48 cm W x 61 cm D (7 x 19 x 24 inches);
rack mountable
Operating Limits
Temperature:
Relative Humidity:
0 – 40°C (32 – 104°F)
0 – 90% RH non-condensing
Appendix B: Phase—What it is and How it’s Used
The Minimum You Need to Know
Phase correction is used to ensure that absorption data are valid even when acoustic
background noise is present. It is not a cause for concern if the reported Babs phase (deg)
value is random—in fact, this value should be random in the absence of absorbing
particles in the sample. When absorbing particles are present and the absorption is more
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than 1000 Mm —1, the Babs phase (deg) value should be less than 10 degrees. If this is not
the case, then the instrument should be re-calibrated.
The More Complete Explanation
The scattering signal is always directly in phase with the laser modulation, because the
speed of light is so large. The acoustic signal that measures absorption, however, travels
at the speed of sound, which is much slower. Therefore there may be a phase shift
between the acoustical signal and the laser modulation. In addition, amplifier inversions
can contribute phase shifts of 180 degrees. These various shifts must be accounted for to
preserve data validity.
The shifts described above apply to the overall acoustic signal ( Babs,raw'). This acoustical
signal is in turn composed of two components: a contribution from absorbing material in
the air (Babs'), which is what we are interested in, and a background signal ( Babs,bg'), which
is the acoustical signal when no absorbing material is present. Both of these contributions
also have phases. Finally, the background-corrected value Babs', which is not yet
corrected for phase, is adjusted based on the PAX’s microphone calibration value. The
result is the reported Babs value, Babs, which has its own phase as well. All of these
different phases are measured to ensure the PAX is working properly.
Complex numbers (denoted by boldface type) are used to describe signals and their
phases. If we use a vector-space representation, phase can be visualized as the angle of
the vector, and the magnitude of the signal can be visualized as the length of the vector.
Figure 1 illustrates the relationships between the various Babs measurements and their
respective phases. The prime (') notation is used to indicate that these vectors represent
measurements before the phase correction has been applied.
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Figure 46: Babs,raw' and its two components: (1) Babs,bg', which reflects acoustic noise, and (2) Babs', which
reflects absorbing particles. The horizontal axis corresponds with the phase of the laser modulation.
We ultimately want to report Babs from absorbing particles as real number rather than a
complex one. Thus, the next step is change the phase reference so that the phase of the
absorbing-particle component, Babs', is zero. This is done by rotating all the vectors above
to the right by  cor .  cor is the microphone calibration phase entered on the PAX
Calibration screen. Thus Babs,bg (a complex number) is subtracted from Babs,raw (another
complex number) to yield the background-corrected Babs (a real number). See the Figure
2.
Figure 47: Rotating Babs Components to Yield a Real-Number Babs Value
After this adjustment, in theory Babs should always have a phase of zero.4 This is indeed
what happens when the PAX is sampling many absorbing particles. Because in this case
the background signal is a small component of the overall Babs,raw reading, and because
the phase of the absorbing material is zero, the corrected Babs phase is also zero or very
close to it.
When no particles are present, however, the Babs phase is usually nonzero and random.
This is because when the Babs,raw signal is small it is subject to other acoustical noise. The
microphone calibration phase is thus not always the same. Figure 3 illustrates this
microphone-calibration-phase correction in vector space for three data points taken
during low-particle conditions. The solid vector represents the background-corrected
value Babs', while the dotted vector represents the microphone calibration value.
4
In theory, the background-subtracted value Babs' should always have the same phase. This
phase would then be perfectly offset by the microphone calibration phase
 cor .  cor
is
measured in the calibration procedure, when there is plenty of absorbing material in the sample.
In cases where there is not much absorbing material, the microphone calibration phase may
vary.
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Figure 48: Random phases resulting from Individual Babs Measurements in Low-Particle Conditions
Because the microphone calibration value is the average correction that will yield a
phase of zero, when it is applied to individual background-corrected Babs signals, the
result is a complex number with a small magnitude and a random phase. In the diagram
on the left, phase is approximately 90 degrees; in the middle diagram, it is -90 degrees;
and in the right diagram, it is around -10 degrees. These random values are not
problematic and in fact indicate the instrument is properly calibrated.
Note: The reported phases in the data file are relative to the phase from the absorbing
material, rather than relative to the laser modulation.
Warning: Finally, there is another phase which the user will normally never need to
consider. This is a precessing phase between two independent clocks in the instrument. It
appears in a column labeled “Laser Power phase,” and also when both “Fixed Laser
Power” on and “Phase” off are selected in the “zero” menu. The column labeled “Laser
Power phase” can be ignored. The user should normally use “Fix Laser Power” off and
“phase” on.
Appendix C: Calculations
Calculation of Phase, Background Phase, and The Absorption
Coefficient (Babs)
Background phase bg is calculated during the auto-zeroing process and represents the
phase of the averaged background signal relative to the phase of the laser power signal
plus the phase correction:
bg =  mic,bg - laser,bg + cor
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The resulting phase of the Babs signal,  , is calculated as follows. The Babs signal can be
viewed as a complex number re i where r = Babs / cos  . ( Babs reported by the PAX is the
real part of re i .) Background signal is expressed as rbg e
Babs,bg reported by the PAX is the real part of rbg e
the Babs, raw
correction:
ibg
ibg
, where rbg = Babs, bg / cos bg . (
.) Let  raw represent the phase of
signal relative to the phase of the laser power signal plus the phase
 raw =  mic,raw - laser,raw + cor
Let Babs,raw represent the real part of the complex representation of the raw signal
rrawe iraw .(For information on how Babs,raw is calculated, see the following section.) Then
the resulting background-subtracted value is calculated as Babs = rei  rrawe
iraw
 rbg e
ibg
.
When no absorption signal is present, e.g., a filter is on the inlet, the phase  will be
random (  180    180 ). On the other hand, during sampling of high concentrations of
absorbing aerosol, the phase  will approach zero.
Calculating the Raw Absorption Coefficient (Babs, raw)
Since the heating from absorbing particles is periodic, with frequency f res , the resultant
sound wave will have frequency fres. The absorption coefficient Babs,raw is calculated as
follows:
Babs,raw 
Pmic  Ares   2  f res
 cos( raw )
PL (  1)  Q
where
Pmic
=
Microphone pressure at fres
Ares
=
Cross-sectional area of the resonator
fres
=
Resonance frequency in Hz (calculated from temperature, pressure,
and RH)
PL
=
Laser power
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
=
Ratio of isobaric and isochoric specific heat
Q
=
Resonator quality factor (calculated from temperature, pressure,
and RH)
 raw
=
The phase of the Babs,raw signal relative to the phase of the laser
power signal plus the phase correction
Calculating the Scattering Coefficient (Bscat)
The scattering coefficient Bscat is calculated as follows. First, the raw signal B scat,raw,
which includes the Bscat background, is calculated according to the formula below:
Bscat,raw 
Pscat
PL
where
Pscat
=
Calibrated readings from the photomultiplier tube (this variable is
calculated internally and not recorded in the data file)
PL
=
Laser Power
Then Bscat is calculated as follows:
Bscat  Bscat,raw  Bscat,bg
where
Bscat,bg is the background for Bscat on filtered air.
Calculating Black Carbon Mass
Black Carbon (BC) Mass in µg/m3 is calculated as follows:
BC Mass (µg/m3) = Babs(1/Mm) / BC MAC (m2/g)
where BC MAC varies depending on the laser wavelength and the BC mixing state.
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For reasons explained below, the default value of BC MAC is set as follows:
Wavelength of PAX
BC MAC Default Value
870 nm
532 nm
405 nm
4.74
7.75
10.19
Users can change this value on the Setup screen.
How DMT Calculates the Default Value of Black Carbon Mass Absorption
Cross-Section (BC MAC)
Bond and Bergstrom5 demonstrate that for fresh soot, the value of BC MAC at 550 nm
wavelength is 7.5 ± 1.2 m2/g. Since BC MAC varies inversely with wavelength, and since
the standard PAX has an 870 nm wavelength, the value of BC MAC for fresh soot is
calculated as follows:
BC MAC
=
7.5 m2/g * (550 nm / 870 nm) = 4.74 m2/g
Note that BC MAC can increase by as much as 50% depending on the mixing state. 6 The
more coated the BC particles, the higher BC MAC will be. Thus for an 870-nm PAX, BC
MAC ranges from 4.74 – 7.11 m2/g. DMT uses a default value of 5 m2/g. Note that if
particles are more coated than the value of BC MAC reflects, then the PAX will
overestimate BC mass.
Appendix D: Serial Stream Output
Serial stream data is RS-232, 115200 baud, 8N1 format. Data are comma-delimited ASCII
characters. They are not fixed-width, and a control-linefeed (CR-LF) appears at the end
of each line. One line is sent for each averaging interval. Note that the serial port is not
bidirectional, i.e., commands cannot be sent to the PAX through the serial port.
5
Bond, Tami C. and Bergstrom, Robert W., (2006) “Light Absorption by Carbonaceous
Particles: An Investigative Review,” Aerosol Science and Technology, 40:1, 27 – 67, DOI:
10.1080/02786820500421521.
6
Bond, T. C., G. Habib, and R. W. Bergstrom (2006), “Limitations in the enhancement of visible
light absorption due to mixing state,” J. Geophys. Res., 111, D20211, doi:
10.1029/2006JD007315.
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The serial stream output channels are exactly the same as the output channels in the PAX
data file. Appendix E lists the order of these channels and provides their definitions.
A standard, straight-through cable rather than a null modem cable should be used to
connect to the RS-232 serial port.
Note that the Pax Maintenance Console (PMC) generally requires an Ethernet rather than
serial port connection. The only thing that the PMC can do with the serial port connection
is to display real-time data in time-series graphs. It cannot transfer files over the serial
port.
Appendix E: PAX Data and Configuration Files
Both data and configuration files are .csv files that can be opened easily with any
spreadsheet program.
Main PAX Data File
The PAX records a new data file each day it is running. In the event that the PAX is
turned off and restarted during the same day, the later data will be appended to the
original data file.
File Names
A date stamp appears in the file name for easy identification. The file name also contains
the instrument serial number, which allows users with multiple instruments to easily
identify which PAX generated the file.
Output Channels
Table 2 provides a list of PAX data files store in order. Definitions for each channel
appear after the list. Note: In some cases, these channels have slightly different names
on the PAX screens than they do in the PAX .csv output file. For instance, the “Cell
Pressure (mbar)” channel displayed on the PAX screen is recorded in the output file as
“HK Cell Pressure (mbar).” In such cases, the definitions below cross-reference each
other.
Data are not recorded until after the first flush completes. Thereafter, data are recorded
for each sampling instance.
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Sec UTC
DOY UTC
Year UTC
Sec Local
DOY Local
Year Local
Bscat (1/Mm)
scat_raw
Babs (1/Mm)
Babs phase (deg)
Babs noise (1/Mm)
Laser power (W)
Laser power phase (deg)
Q factor
Mic press at res freq (dB)
Resonance frequency (Hz)
Bkgrnd Bscat (1/Mm)
mic_raw
Bkgrnd Babs (1/Mm)
Bkgrnd Babs phase (deg)
Bext (1/Mm)
Single Scat Albedo
BC Mass (ug/m3)
Relative Humidity (%)
Temperature (C)
Dewpoint (C)
Analog Input 1
Analog Input 2
HK Spare U13 CH2
HK Spare U13 CH3
HK Spare U13 CH4
HK Spare U13 CH5
HK Spare U13 CH6
HK Spare U13 CH7
HK Spare U85 CH0
HK plus5V
HK 3.3V
HK Spare U85 CH3
HK 5Vdig
HK RTC_BATT
HK Spare U85 CH6
HK Spare U85 CH7
HK Laser PD Current (Amp)
HK Laser Current (Amp)
HK Laser Temp (C)
HK minus5V
HK Cell Pressure (mbar)
HK Inlet Pressure (mbar)
HK Sample Pump Vac (mbar)
HK 12V
Sample Count
Mode
Countdown Timer (secs)
Disk Free Space (Gbytes)
Laser On Time (hours)
Spare 1
USB Status
Alarm
Local Date
Local Time
Table 2: PAX Output Channels
Channel Definitions
Alarm: This channel reflects the current state of the PAX alarms. These alarms start with
Bscat, the seventh channel in the output file, and continue in sequential order.
g=green(no alarm), y=yellow(approaching alarm state) and r=Red (in alarm state).
Analog Input 1 & 2: Analog input channels.
Absorption Coefficient βabs: See Babs (1/Mm).
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Babs (1/Mm): The absorption coefficient in 1/Mm, Babs, measured at the relevant laser
wavelength. For information on how this coefficient is calculated, see Appendix C.
Babs noise (1/Mm): The uncertainty estimate for the measurement of Babs (1/Mm). This is a
useful metric of instrument response. The Babs noise should stay fairly constant.
Babs phase (deg): The phase of the Babs measurement relative to the phase of a signal
from absorbing material in the air. This reading should always be very close to zero when
there is a lot of signal. When there is no signal, this channel should be random between
negative 180 and positive 180 degrees.
Background, Absorption: see Bkgrnd Babs (1/Mm).
Background, Scattering: see Bkgrnd Bscat (1/Mm).
BC Mass (ug/m3): Black carbon mass concentration in µg/m3. For information on how BC
Mass is calculated, see Appendix C.
Bext (1/Mm): The extinction coefficient in 1/Mm, Bext, measured at the relevant laser
wavelength. The extinction coefficient is the sum of the Scattering coefficient and the
absorption coefficient—i.e., βext = βscat + βabs.
Bkgrnd Babs (1/Mm): The background for the absorption measurement. Background is
determined during instrument zero, when the cell is filled with filtered air. Background
readings change with variables like temperature, but these channels should stay relatively
constant during stable environmental conditions. Dramatic changes can indicate a problem.
Bkgrnd Babs phase (deg): The phase of the Babs background measurement relative to
the phase of a signal from absorbing material in the air.
Bkgrnd Bscat (1/Mm): The background for the scattering measurement. Background is
determined during instrument zero, when the cell is filled with filtered air. Background
readings change with variables like temperature, but these channels should stay
relatively constant during stable environmental conditions. Dramatic changes can
indicate a problem.
Black Carbon Mass Concentration (µg/m3): Black carbon mass concentration in µg/m3.
This channel is stored as BC Mass (ug/m3) in the PAX data file.
Bscat (1/Mm): The scattering coefficient in 1/Mm, Bscat, measured at the relevant laser
wavelength. For information on how this coefficient is calculated, see Appendix C.
Cell Pressure (mb): See HK Cell Pressure (mbar).
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Cell Temperature (°C): The temperature inside the PAX cell.
Countdown Timer (secs): The number of seconds left before the next instrument mode
change begins.
Dewpoint (C): The dew point of the sample air in ºC.
Disk Free Space (Gbytes): The gigabytes of free disk space on the PAX computer.
DOY Local: The day of year in local time. This is a count of days elapsed since January 1.
For instance, DOY Local for data taken July 20, 2011 would be 200, since July 20 is the
200th day of 2011.
DOY UTC: The day of year in UTC time. This is a count of days elapsed since January 1.
For instance, DOY UTC for data taken July 20, 2011 (UTC) would be 200, since July 20 is
the 200th day of 2011.
Extinction Coefficient βext: See Bext.
HK 3.3V: A circuit-board health indicator that should normally read 3.3 ± 5%.
HK 5Vdig: A circuit-board health indicator that should normally read 5.0 ± 5%.
HK 12V: A circuit-board health indicator that should normally read 12.0 ± 5%.
HK Cell Pressure (mbar): The pressure inside the PAX cell. This reading should be slightly
lower than the inlet pressure.
HK Inlet Pressure (mbar): The pressure at the PAX inlet. This pressure should be near
ambient pressure.
HK Laser Current (Amp): The laser current in amps.
HK Laser PD Current (Amp): The output of the laser photodiode within the laser module
(870 nm lasers only). This parameter provides a relative measure of laser health,
especially useful over long periods. This channel in the output file corresponds to the
Photodiode Current reading on the Status screen.
HK Laser Temp (C): The laser temperature in °C. This should be between 20 and 25 °C
and should stay relatively stable.
HK minus5V: A circuit-board health indicator that should normally read around -5.0.
HK plus5V: A circuit-board health indicator that should normally read around 5.7.
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HK RTC_BATT: This channel is currently unused.
HK Sample Pump Vac (mbar): The pump vacuum pressure. The choked flow through the
orifices (to ensure 1 L/min flow through the cell) requires this value to be less than about
½ of the inlet pressure. This channel in the output file corresponds to the “Pump
Vacuum” reading on the Status screen.
HK Spare U13 CH[x]: These channels are unused.
HK Spare U85 CH[x]: These channels are unused.
Inlet Pressure: See HK Inlet Pressure (mbar).
Laser On Time (hours): The number of hours the laser has been on.
Laser power (W): The instantaneous laser power, measured after the beam passes through
the cell.
Laser power phase (deg): The relative phase between the microphone and the laser power
modulation. These readings have a pattern to them, but the pattern will change if the
modulation frequency changes.
Laser Temperature: See HK Laser Temp (C).
Local Date: The local date in MM/DD/YYYY format.
Local Time: The local time in HH:MM:SS format.
Mic press at res freq (dB): The microphone pressure at the resonant frequency.
mic_raw: The measured value of the microphone reading in relative units.
Mode: The current operating mode of the PAX. Modes are defined as follows:
Number
0
1
2
3
Mode
Measure
Zero
Flush
Acstc Cal
Description
Measurement
Zero Event
Flush
Acoustic Calibration
Photodiode Current: See HK Laser PD Current (Amp).
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Q factor: The resonator quality factor, which is calculated from temperature, pressure,
and relative humidity.
Relative Humidity (%): The relative humidity of the sample air measured inside the
instrument.
Resonance frequency (Hz): The resonance frequency of the microphone.
Resonator Q: See Q Factor.
Sample Count: The number of samples used in an average. Normally, if averaging time is
set to 20 seconds, there would be 20 samples. However, since pressing the ZERO button
can change the number of samples used in an interval, it is not always easy to determine
how many samples factored into the average. The Sample Count parameter tracks this
number.
scat_raw: The raw scattering signal from the detector board in relative units.
Scattering Coefficient βscat: See Bscat (1/Mm).
Sec Local: The seconds in local time.
Sec UTC: The seconds in UTC time.
Single Scat Albedo or Single Scattering Albedo: The ratio of scattering coefficient to
total extinction coefficient. A single scattering albedo of one implies that all particle
extinction is due to scattering, while a single scattering albedo of zero implies that all
extinction is due to absorption.
Spare 1: An unused channels reserved for future use.
Temperature (C): See Cell Temperature (C).
USB Status: An indicator that stores information about the state of the USB flash drive.
The status indicators are as follows:
Value
USB Status
0
1
2
3
4
5
No device
Device ready
Device busy
Safe to remove
Mounting
Starting Write
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Manual, Photoacoustic Extinctiometer (PAX)
Note that the PAX config file contains a different channel called USB State.
Year Local: The year in local time.
Year UTC: The year in UTC time.
Measurement-Mode-Only Data Files
The PAX also generates a “measurement-mode-only” file that provides users with the
most important data. The file name consists of the PAX serial number, followed by
“_m0_”, followed by the date. Data are only recorded to this file when the PAX is in
measurement mode, and only the following channels are recorded:
Date
Time
Bscat(1/Mm)
Babs(1/Mm)
Bext(1/Mm)
SSA
BC Mass(ug/m3)
Definitions for these channels can be found in the previous section.
A new measurement-mode-only file is recorded for each day the instrument is running. In
the event that the PAX is turned off and restarted during the same day, the later data
will be appended to the original data file.
PAX Config Files
The PAX records a new config file each month. A year-and-month stamp appears in the
file name for easy identification.
The format for data files is as follows. The top row is a header row containing the names
of the parameters the Config file defines. Subsequent rows provide values for these
parameters. Each time the configuration is altered, the latest values get stored in a new
row beneath the previous values. In this way, the configuration file presents a log of
previous configuration settings as well as the current configuration information. When a
new configuration file is started at the beginning of the month, the last row of the old
month’s file is copied into the second row of the new month’s file.
The right-most two columns do not have a header row. They contain a date stamp and
time stamp indicating when the configuration changes were made.
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Manual, Photoacoustic Extinctiometer (PAX)
Figure 49: PAX Config File Opened in Excel
The header row determines the channel names for many channels in the output file.
Altering the names and values in the configuration file will alter the names and values in
the PAX display.
Note that the PAX Config file is a record of the state of the PAX machine, not just a
standard configuration file. For instance, the PAX Config file will record and update
changes such as events such as the user pressing the ZERO button.
For information about Sec UTC, DOY UTC, and other config file channels that appear in
the data file, see the “PAX Config Files” section. Information about the remaining config
channels appears below.
Laser On: A parameter that determines if the laser is on or off at PAX start-up. 1 = ON, 0
= OFF.
Pump On: A parameter that determines if the pump is on or off at PAX start-up. 1 = ON,
0 = OFF.
test_mode: A two-digit channel that records the status of fix laser and phase use. The
first digit describes the fix laser status, with 0 indicating fix laser is off and 1 indicating it
is on. The second digit describes the phase use status, with 0 indicating off and 1
indicating on. Thus a reading of 10 indicates fix laser is on but phase use is off.
Zero Now: A Boolean indicator that records whether the user pressed the ZERO button.
1 = True, 0 = False.
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Zero Interval (sec): The default setting for the number of seconds between zero event
intervals.
Zero Number: The number of measurements used during a zero calibration.
Zero Enable: An unused parameter reserved for future use.
Acoustic Cal Interval (sec): The default setting for the number of seconds between
acoustic calibration intervals.
Cal BC MAC (m2/g): The default value for the BC MAC coefficient displayed on the Setup
screen.
Cal Laser Power (mV/W): The default value for the Laser Power coefficient displayed
on the Calibration screen.
Cal Scattering (VMm/W): The default value for the Scattering Photodiode coefficient
displayed on the Calibration screen.
Cal Mic (mV/Pa): The default value for the Microphone coefficient displayed on the
Calibration screen.
Cal Phase Cor (deg): The default value for the Phase Correction coefficient displayed
on the Calibration screen.
Data Avg Time:
screen.
The default value for the Data Ave. Time displayed on the Setup
Set Laser Power: A parameter indicating whether laser power is artificially set to a
DMT-determined value. 1 = True, 0 = false. This parameter is used during diagnostics.
DHCP: A Boolean indicator that records whether the system was using a dynamic host
configuration protocol. 1 = True, 0 = False.
Spare [A-D]: Parameters that are unused.
IP Address: The IP address of the PAX, as displayed on the Setup tab under “Internet
Protocol.”
IP Mask: The NetMask of the PAX, as displayed on the Setup tab under “Internet
Protocol.”
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IP Gateway: The GateWay of the PAX, as displayed on the Setup tab under “Internet
Protocol.”
Analog Out [i] Index: The default output channel for Analog Output i, as displayed on
the Setup tab.
Analog Out [i] Min: The default low value for Analog Output i, as displayed on the Setup
tab.
Analog Out [i] Max: The default high value for Analog Output i, as displayed on the
Setup tab.
Analog In [i] Name: The default label for Analog Input i, as displayed on the Setup tab.
Analog In [i] Min: The default low value for Analog Input i, as displayed on the Setup
tab.
Analog In [i] Max: The default high value for Analog Input i, as displayed on the Setup
tab.
USB State: An indicator of when the user has pressed the “Accept” button on the File
Access screen in order to write data to the USB. When the user has pressed this button,
USB State is 1. Otherwise it is zero.
Time Zone: The current time zone for the PAX.
NTP: A Boolean indicator that records whether the system used the Network Time
Protocol. 1 = True, 0 = False. This indicator is currently not functional.
Station ID: The default value for the Station ID, as it appears on the Setup tab.
Location: The default value for the Station ID, as it appears on the Setup tab.
Appendix F: Wiring and Assembly Instructions for
Buccaneer Connector
See the following pages for the manufacturer’s wiring and assembly instructions.
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Standard Buccaneer Waterproof Electrical Cable Connector
Wiring and Assembly Instructions
Buccaneer connectors are available in 2, 3, 4, 6, 7, 9, 12 or 25 pin and
BNC coaxial versions (50/75Ω).
It is important that these instructions are fully complied with to ensure the
product is completely watertight and electrically safe IF IN DOUBT CONSULT A QUALIFIED ELECTRICIAN.
Always wire the socket insert to supply, and the plug insert to appliance.
Plug/socket inserts can be fitted into any style of main body to give
correct plug/socket combination for your application.
FLEX MOUNTING
IMPORTANT SAFETY NOTICE
For your protection all mains (250V)
equipment used out of doors, in damp or
wet conditions should be supplied from a
correctly fused source and protected by
an approved R.C.D. Eg: BS7071, BS7288,
BS4293, BSEN61008 or BSIEC1008.
IF IN DOUBT SEEK ADVICE
Use smooth circular cable only (6-8mm dia). Other cable glands are
available to suit different cable diameters, please enquire.
FLEX MOUNTING IN-LINE
ASSEMBLY/WIRING INSTRUCTIONS
1 To remove plug or socket inserts for wiring, use cap assembly tool to
unscrew locking ring.
2 As appropriate to main body type, thread cable through component
parts as shown in the illustrations.
3 Strip insulation from cable as shown in Flex Mounting diagram.
4 2 to 7 pole inserts:
Insert bare wire ends into terminals on plug/socket insert and fully
tighten screws.
Note: If connector is to be used on mains voltage ensure that wires are
connected as shown below.
LOW PROFILE FLANGE MOUNTING
Mains Wire Connections
Important - connect
wires Brown to terminal
L, Blue to terminal N
and Green/Yellow to
terminal E
9 pole inserts:
Pins and sockets are supplied loose for pre-crimping. Crimping tools
(including hand versions) and a contact extraction device are available.
Please enquire.
FRONT OF PANEL MOUNTING
12 and 25 pole inserts:
Pins and sockets are supplied loose for pre-crimping and pre-soldering.
Crimping tools (including hand version) and a contact extraction device
are available. Please enquire.
5 After connecting wires, draw cable back until plug/socket insert is
correctly seated in D shaped location in the main body. Screw home
locking ring using cap assembly tool.
6 For cable mounted units, slide gland cage and gland down cable and
into main body then screw gland nut fully home. It is essential to
ensure that the gland nut is fully tightened to ensure cable is securely
sealed and clamped. For panel, bulkhead and flange units correctly
seat sealing washer and main body onto mounting surface and screw
down using rear nut or screw/bolts with seals. Ensure seals and glands
are kept clean. Locking cap secures plug to socket.
REAR OF PANEL MOUNTING
Note:
To ensure that the correct sealing properties of the connector are
achieved it is imperative that all ‘O’ rings are correctly located and seated
before assembly. Please refer to the exploded diagrams for the locations
of these seals.
BULKHEAD/SURFACE MOUNTING
Part No: 13158, issue 7
ASSEMBLY INSTRUCTIONS BUCCANEER R.F. INSERT (BNC COMPATIBLE)
For use with cables:
50Ω - URM 76, URM 43, RG58c/u.
75Ω - URM 70.
Crimp Tool - Hex Cavities,
Centre Contact
1.69 A/F (B.S. ‘W’/ERMA XA.)
Braid
6.48 A/F (B.S. ‘E’/ERMA XH.)
FLEX MOUNTING
CO-AXIAL CABLE
CONNECTOR
1 Flex Mount
Fit gland nut, washer, gland & main body loosely over cable, followed by
BNC plug/jack metal body.
Chassis/Bulkhead
Fit main body to chassis/bulkhead, ensuring sealing washer(s) are in
position. Then assemble BNC plug/jack body to cable.
2 Crimp centre contact onto cable centre conductor (butting to cable inner
insulator).
3 Slide knurled ferrule over contact & cable inner insulator & under cable braid.
4 Snap-Fit insulator over centre contact (support insulator with assembly
mandrel, or against hard surface).
5 Push body over assembly, pressing insulator, until ferrule bottoms in body.
(SA3155 assembly mandrel is available to aid assembly if required).
6 Crimp body to secure cable braid.
7 Lock BNC body flange into main body using locking ring. Ensure correct
alignment of flat.
8 At cable entry, seat gland & washer, tighten gland nut to seal (for
flex mount).
FLEX MOUNTING
IN-LINE CO-AXIAL
CABLE CONNECTOR
CABLE TRIM & PIECE PARTS
PANEL CUT-OUTS
BUCCANEER®
Waterproof
Electrical Cable
Connectors
FRONT PANEL MOUNTING
BULKHEAD/SURFACE MOUNTING
SEALING CAP/ASSEMBLY TOOL
REAR PANEL MOUNTING
Wiring and
Assembly
Instructions
Manual, Photoacoustic Extinctiometer (PAX)
Appendix G:
Recommendations for Sampling
Ambient Air
A major challenge when measuring ambient air is to transport the sample from the
outside environment to the instrument without modifying the properties of the sample.
The temperature of the sample air can increase or decrease depending on the difference
between the outside temperature and the instrument temperature. The instrument
temperature depends on both heating caused by the instrument itself (e.g., from internal
pumps) and the temperature of the room or shelter where the instrument is located.
Heating the sample can drive off semi-volatile material and/or water, while cooling it
can lead to additional condensation of semi-volatile material and/or water. The
temperature differences also cause changes in the sample relative humidity since the
absolute amount of water vapor in the air is usually conserved. The amount of water
associated with particles depends on relative humidity, so changes in relative humidity
can affect the measured particle properties. Gases and particles can also be lost to the
sample lines through a variety of mechanisms, leading to biases in measured
concentrations. A final concern is sampling the particles and gases desired at high
efficiency while preventing other, undesired material from reaching the instrument, such
as debris, insects and precipitation.
Successful measurement of ambient air properties without biases related to sampling
artifacts requires careful thought and the design of the inlet/sample system will depend
on the sampling environment and the properties being measured. Here we provide some
brief guidelines. Instrument users seeking additional information are encouraged to
consult reference books (e.g., Aerosol Measurement: Principles, Techniques and
Applications, P. A. Baron and K. Willeke, 2001), the World Meteorological Association
guidelines
for
GAW
stations
(http://www.wmo.int/pages/prog/arep/gaw/gawreports.html), and the NOAA Global Monitoring Division website for a description of their
site
setup
(http://www.esrl.noaa.gov/gmd/aero/instrumentation/instrum.html)
[courtesy John Ogren]. There are also numerous examples of aerosol/gas conditioning
systems in the scientific literature.
Inlets
The inlet system should be designed to prevent the collection of precipitation and/or
large debris and insects into the sample lines where they could potentially reach the
instruments and cause damage. Debris in the inlet and/or sampling lines can also obstruct
the flow leading to losses. The inlet diameter should be selected based on the total
sample flow rate that will be collected through the inlet. Turbulent flow should generally
be avoided as this can lead to particle losses. Baron and Willeke (2001) discuss design
criteria for still-air sampling related to sampling efficiency.
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The inlet should have a mesh bug screen or other method to prevent the collection of
insects and large debris into the sampling system. A rain hat can be used to prevent
precipitation from reaching the instrument, or the inlet can be inverted (like a candy
cane) to prevent moisture from falling into the inlet system. In cold environments where
icing could occur inlets should have a controlled heating system to keep the inlet from
icing over and becoming blocked.
Sample line system
The sample line system connects the inlet to the instrument. It should be constructed of
material that will not remove the gas or particles being sampled. For gases the material
will depend on the exact gas being measured. For particles, C=conductive tubing (e.g.,
stainless steel, copper or carbon-impregnated silicon) should be used to avoid staticrelated losses. Some care should be taken in the use of carbon-impregnated silicon for
some applications as it has been shown to emit vapors that interact with particles (Timko
et al., 2009). Copper should not be used in environments susceptible to corrosion (e.g.,
marine) for long periods of time. The sample line should be kept as short as possible and
avoid sudden bends to prevent losses of large particles. The inner diameter of the sample
line should be sufficient to avoid turbulent flow in the lines for the flow rate of the
system. The sample line may be heated or cooled for extreme environments to prevent
the sample temperature from changing too much and causing changes in semi-volatile
partitioning.
Conditioning system
Optional sample conditioners can be used to heat and/or dry the sample and remove
particles above a desired size range. Cyclones and impactors can remove particles above
a specific aerodynamic diameter. Their design depends on the sample flow rate and the
desired cutpoint. Some DMT instruments are supplied with cyclones designed for the
standard instrument flow rates (e.g., PAX).
Dryers must be used to prevent condensation in instruments that sample humid,
warm air but operate in cool buildings/shelters. Specifically, if the outdoor dew point
temperature is higher than the instrument temperature condensation will build up in the
instrument and possible damage it. Drying the sample also has the benefit of eliminating
uncertainties associated with water taken up by particles, which can affect light
scattering and absorption measurements, and sizing measurements.
There are several methods for drying aerosol samples. The simplest approach is to dilute
the sample stream with dry air at a known dilution rate to reduce the sample dew point.
The NOAA Global Monitoring Division employs this method at several high humidity
locations (http://www.esrl.noaa.gov/gmd/aero/instrumentation/instrum.html). The
measurements must be post-corrected to account for this dilution, so the flow rates must
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Manual, Photoacoustic Extinctiometer (PAX)
be carefully controlled and measured. The main drawback to diluting the sample is in
clean environments the detection limits of instruments may not be sufficient to measure
the diluted sample. Diffusion dryers avoid dilution and have an inner aerosol transport
region that is mechanically separated from a drying material in an outer annular tube.
Diffusion dryers that use desiccant (silica gel, drierite, molecular sieves) must be recharged periodically depending on the amount of moisture in the air sample (available
from DMT). Alternatively dry air can be used as a drying material through commercially
available PermaPure drying systems. The aerosol sample is separated from the dry air by
a semi-permeable membrane. Dryers introduce another loss mechanism, so any system
used should keep this in mind. It is difficult, if not impossible, to both dry particles and
avoid particle losses. The best solution is usually to dry particles to a known relative
humidity and to characterize losses of particles through the system as a function of size
and apply a correction to the measurements. Dryers should be placed upstream of inlet
cyclones or impactors as water associated with particles will affect their aerodynamic
size.
An alternative to drying the sample is to modify the instrument to match the ambient
sampling conditions. In practice this is quite difficult as the humidity and temperature in
the measurement region of the instrument must be carefully controlled to match ambient
conditions. Ambient temperatures and relative humidity can also reach extreme values
that most instruments are not designed to operate in. Users interested in such systems
should consult DMT for more detailed discussions.
A final form of sample conditioning is the removal of undesired gases that can interfere
with measurements. A specific example is the removal of ozone and NO2 upstream of
photoacoustic measurements. DMT photoacoustic instruments have a zeroing procedure
to account for NO2 and ozone contributions to absorption at 405 and 532 nm, but in
rapidly changing environments scrubbers can be used to avoid the need for frequent
zeroing.
Prepared 3 July 2013 by Gavin R. McMeeking
[email protected]
Appendix H: Revisions to the Manual
Rev. Date
Rev. No.
Summary
Inserted updated cell diagram
Revised calibration interval to six months
10/11/11
A-2
Section
3.0
6.1, App. A
Omitted recommendation for annual cleaning and
calibration
App. A
Added 12 VDC Power Option
App. A
Changed “Software” and “Computer Requirements” specs
to clarify they applied to PMC software
App. A
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Manual, Photoacoustic Extinctiometer (PAX)
11/2/11
B
Updated manual to reflect user-interface changes
11/28/11
B-1
Updated Figure 1
12/19/11
B-2
Updated screen shots to reflect new software; explained
why negative, non-zero data values sometimes arise
4.7.5, 7.1
1/3/12
B-3
Updated number of port connectors included; updated
description of 12 VDC connection process; inserted
instructions for transferring data to USB device; expanded
description of Zero page
2.1, 2.2.2,
4.7.5,
Appendix E
1/19/12
B-4
Added caution about inlet noise influencing results
1/23/12
B-5
Added recommendation for users to use network connection
rather than touch-screen when making multiple
adjustments
1/26/12
B-6
Updated manual to reflect removal of rear-panel Ethernet
port
1/31/12
C
4.0, 6.0
1.0
2.2.3
4.0
2.4.2,
Appendix A
Removed Welcome Screen screenshot
4.1
Inserted procedure for distinguishing acoustic inlet noise
from particle-response noise
2.5
Inserted section describing phase calculation
Appendix B
2/9/12
C-1
Corrected definitions for Babs phase (deg), Bkgrnd Babs
phase (deg), and Laser power phase (deg)
Appendix E
2/9/12
C-2
Updated output channel list
Appendix E
2/9/12
C-3
Updated phase calculation
Appendix C
Added example of how Set Zero (sec) Interval affects
Countdown Timer (sec)
3/12/12
C-4
Inserted PAX flow diagram and updated pictures of PAX
interior and rear panel
Inserted explanation of Phase and updated Phase
Calculation section
Inserted warning about rebooting PAX if Time Zone
parameter is changed
3/15/12
C-5
4/9/12
C-6
Inserted section on serial-stream data
Updated warranty information to include service warranty
Appendix B
and C
4.7.7
Appendix D
Front matter
2.2.3
Added information on using Ethernet port
2.2.4
Expanded information on analog output channels
D
2.4.2, 3.2, 3.3
Clarified instructions to add noise-reducing tubing to
exhaust port
Described how to connect to Internet
7/3/12
4.7.5
4.1
4.8.12
Defined Alarm Channel in Output file
Appendix E
Added information about fluctuating levels of NO2 gas
interfering absorption values for 405 and 532-nm PAXes
7.1.2, 7.4
Noted that users connecting to the PAX via a web browser
may need to refresh screen to see changes
Removed information about Lock feature and updated
screenshots
Changed Ethernet port references to reflect the fact this
port is now located on the PAX’s rear panel
4.1
Throughout
2.4, Appendix
A
Updated information on USB status and data transfer
protocol
4.8.4
Added labeled photo of 532 nm PAX’s interior
3.2.2
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Added troubleshooting item on reseating SD card
8.1
Added troubleshooting item on deleting current day’s data
file
8.3
7/27/2012
D-1
9/5/12
D-2
Corrected instructions for updating microphone calibration
value
9/17/12
D-3
Minor edits throughout
8/14/13
D-4
Added recommendations for ambient air sampling
Appendix G
11/14/13
D-5
Inserted warnings about grounding instrument and using
three-conductor cord
Frontmatter,
2.2.1
2/6/14
D-6
Updated PAX 870 nm components picture
3.2.1
Expanded section on cleaning PAX windows
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6.3
7.3.2.4,
7.3.3.4
All
79