Ecotech Aurora 1000 User manual

www.ecotech.com
Aurora 1000
Single Wavelength
Integrating
Nephelometer
User Manual
Version: 1.3

www.ecotech.com

Aurora 1000 User manual 1.3 Front Matter
i
Manufacturers statement
Thank you for selecting the Aurora 1000 Integrated Nephelometer. The Aurora 1000
is a single-wavelength Nephelometer with innovative design features, designed
primarily for visibility and particulate sampling. By following the guidelines
contained in this manual and with the implementation of a good quality-assurance
program, the user can obtain accurate and reliable data.
The Aurora 1000 is the next generation of sampler, it uses a single wavelength for
visibility measurements at either of three wavelengths (450nm, 525nm or 635nm).
The Aurora 1000 is a product of exceptional quality capable of producing years of
maintenance free operation.
This User Manual provides a complete product description including operating
instructions, calibration, and maintenance requirements for particulate sampling
techniques.
Reference should also be made to the relevant standards, which should be used in
conjunction with this manual. Some relevant standards are listed in the References
section of this manual.
If, after reading this manual you have any questions or you are still unsure or unclear
on any part of the Aurora 1000 then please do not hesitate to contact Ecotech.
Ecotech also welcomes any improvements that you feel would make this a more
useable and helpful product then please send your suggestions to us here at Ecotech.
Please help the environment and recycle the
pages of this manual when finished using it.
Notice
The information contained in this manual is subject to change without notice. Ecotech
reserves the right to make changes to equipment construction, design, specifications
and /or procedures without notice.
Copyright © 2009. All rights reserved. Reproduction of this manual, in any form, is
prohibited without the written consent of Ecotech Pty Ltd.

Front Matter Aurora 1000 User manual 1.3
ii
Safety requirements
•To reduce the risk of personal injury caused by electrical shock, follow all
safety notices and warnings in this documentation.
•If the equipment is used for purposes not specified by Ecotech, the protection
provided by this equipment may be impaired.
•Replacement of any part should only be carried out by qualified personnel,
only using parts specified by Ecotech. Always disconnect power source before
removing or replacing any components.
Factory service/warranty
This product has been manufactured with care and attention.
The product is subject to a 12-month warranty on parts and labour. The warranty
period commences when the product is shipped from the factory. Consumable items
are not covered by this warranty.
To ensure that we process your factory repairs and returned goods efficiently and
expeditiously, we need your help. Before you ship any equipment to our factory,
please call your local Ecotech service response centre (or distributor) to obtain a
return authorisation number.
When you call please be prepared to provide the following information:
1. your name, telephone number and Facsimile number
2. Your company name
3. The model number or a description of each item
4. The serial number of each item, if applicable
5. A description of the problem or the reason you are returning the equipment
(eg, sales return, warranty return, etc)
If you are required to return the equipment an accompanying document with:
1. Your name, number and Facsimile number
2. Your company name with return shipment
3. The model number or a description of each item
4. The serial number of each item, if applicable
A description of the problem/reason you are returning the equipment

Aurora 1000 User manual 1.3 Front Matter
iii
Claims for Damaged Shipments and
Shipping Discrepancies
Damaged shipments
1. Inspect all instruments thoroughly on receipt. Check materials in the
container(s) against the enclosed packing list. If the contents are damaged
and/or the instrument fails to operate properly, notify the carrier and Ecotech
immediately.
2. The following documents are necessary to support claims:
a. Original freight bill and bill lading
b. Original invoice or photocopy of original invoice
c. Copy of packing list
d. Photographs of damaged equipment and container
You may want to keep a copy of these documents for your records also.
Refer to the instrument name, model number, serial number, sales order
number, and your purchase order number on all claims. Upon receipt of a
claim, we will advice you of the disposition of your equipment for repair or
replacement.
Shipping Discrepancies
Check all containers against the packing list immediately on receipt. If a shortage or
other discrepancy is found, notify the carrier and Ecotech immediately. We will not be
responsible for shortages against the packing list unless they are reported promptly.

Front Matter Aurora 1000 User manual 1.3
iv
Internationally recognised symbols used
on Ecotech Equipment
Electrical fuse IEC 60417, No. 5016
Earth (ground) terminal IEC 417, No. 5017
Equipotentiality IEC 417, No. 5021
Alternating current IEC 417, No. 5032
Caution, hot surface IEC 417, No. 5041
Caution, refer to
accompanying documents
ISO 3864, No. B.3.1
Caution, risk of electric shock ISO 3864, No. B.3.6

Aurora 1000 User manual 1.3 Front Matter
v
Manual Revision History
Ecotech Manual ID: MAN 0056
Manual PN: M01 0001
Current Revision: 1.3
Date released: May 2009
Description: User Manual for the Aurora 1000
This manual is a newly created document for use of the Aurora 1000.
Edition Date Summary Affected Pages
1.00 November
2007
Initial release all
1.1 October 2008 Updated mounting procedure
Updated initial check
Calibration tolerance updated
19
23
39
1.2 February
2009
Amended analogue outputs 35-36
1.3 May 2009 Updated light source
information
Various

Front Matter Aurora 1000 User manual 1.3
vi
Table of Contents
2H1INTRODUCTION............................................................................................................ 183H1
3H1.1 DESCRIPTION .................................................................................................................. 184H1
4H1.2 SPECIFICATIONS ............................................................................................................. 185H1
5H1.2.1 MEASUREMENT ............................................................................................................. 186H1
6H1.2.2 CALIBRATION ................................................................................................................ 187H1
7H1.2.3 POWER........................................................................................................................... 188H2
8H1.2.4 OPERATING CONDITIONS ............................................................................................... 189H2
9H1.2.5 PHYSICAL DIMENSIONS ................................................................................................. 190H2
10H1.2.6 COMMUNICATION AND DATA ....................................................................................... 191H2
11H1.3 NOMENCLATURE............................................................................................................. 192H3
12H1.4 BACKGROUND/THEORY................................................................................................. 193H4
13H1.4.1 BACKGROUND ............................................................................................................... 194H4
14H1.4.2 MEASUREMENT THEORY............................................................................................... 195H6
15H1.4.3 CALIBRATION THEORY.................................................................................................. 196H8
16H1.5 INSTRUMENT DESCRIPTION.......................................................................................... 197H11
17H1.5.1 CELL ............................................................................................................................ 198H12
18H1.5.2 PMT ............................................................................................................................ 199H12
19H1.5.3 SHUTTER ..................................................................................................................... 200H12
20H1.5.4 LIGHT SOURCE ............................................................................................................ 201H13
21H1.5.5 SAMPLE PUMP ............................................................................................................. 202H13
22H1.5.6 ZERO PUMP.................................................................................................................. 203H14
23H1.5.7 ZERO/SPAN FINE FILTER ............................................................................................. 204H14
24H1.5.8 SPAN &ZERO VALVE.................................................................................................. 205H14
25H1.5.9 TEMPERATURE /RH SENSOR ...................................................................................... 206H15
26H1.5.10 PRESSURE SENSOR .................................................................................................... 207H15
27H1.5.11 SAMPLE HEATER ....................................................................................................... 208H16
28H1.5.12 MICROPROCESSOR..................................................................................................... 209H16
29H1.5.13 KEYPAD &DISPLAY.................................................................................................. 210H17
30H1.5.14 BACKUP BATTERY..................................................................................................... 211H17
31H1.5.15 ELECTRICAL CONNECTIONS ...................................................................................... 212H17
32H1.5.16 PNEUMATIC INLETS ................................................................................................... 213H18
33H2INSTALLATION ........................................................................................................... 214H19
34H2.1 INITIAL CHECK.............................................................................................................. 215H19
35H2.2 ASSEMBLY ..................................................................................................................... 216H20
36H2.2.1 CONNECTING THE CALIBRATION GAS ........................................................................ 217H20
37H2.2.2 CONNECTING THE POWER ........................................................................................... 218H20
38H2.2.3 EXTERNAL CABLE CONNECTIONS............................................................................... 219H21
39H2.3 MOUNTING/SITING ....................................................................................................... 220H23
40H2.4 INSTRUMENT SETUP...................................................................................................... 221H24
41H3OPERATION.................................................................................................................. 222H25
42H3.1 STARTUP ........................................................................................................................ 223H25
43H3.2 GENERAL OPERATIONAL INFORMATION..................................................................... 224H26
44H3.2.1 DISPLAY PANEL AND KEYPAD..................................................................................... 225H26
45H3.2.2 DISPLAY BACKLIGHT .................................................................................................. 226H27

Aurora 1000 User manual 1.3 Front Matter
vii
46H3.2.3 DISPLAY ADJUSTMENT................................................................................................ 227H27
47H3.2.4 NAVIGATING THE MENU SYSTEM: ............................................................................... 228H27
48H3.2.5 EDITING PARAMETERS: ............................................................................................... 229H27
49H3.2.6 OBTAINING READINGS................................................................................................. 230H27
50H3.3 MAIN SCREEN................................................................................................................ 231H28
51H3.4 SAMPLING...................................................................................................................... 232H28
52H3.5 MENUS AND SCREENS ................................................................................................... 233H29
53H3.5.1 READINGS.................................................................................................................... 234H30
54H3.5.2 SYSTEM COUNTS ......................................................................................................... 235H30
55H3.5.3 SYSTEM STATUS.......................................................................................................... 236H31
56H3.5.4 CALIBRATION .............................................................................................................. 237H32
57H3.5.5 CONTROL..................................................................................................................... 238H34
58H3.5.6 REPORT PREFERENCES ................................................................................................ 239H35
59H3.5.7 ANALOGUE OUT .......................................................................................................... 240H35
60H3.5.8 SERIAL IO.................................................................................................................... 241H37
61H3.5.9 ADJUST CLOCK............................................................................................................ 242H37
62H3.5.10 DATA LOGGING ......................................................................................................... 243H37
63H4CALIBRATION ............................................................................................................. 244H39
64H4.1 PRECISION CHECK........................................................................................................ 245H39
65H4.1.1 SPAN CHECK ................................................................................................................ 246H40
66H4.1.2 ZERO CHECK................................................................................................................ 247H40
67H4.2 FULL CALIBRATION...................................................................................................... 248H41
68H4.2.1 SETUP .......................................................................................................................... 249H41
69H4.2.2 PROCEDURE................................................................................................................. 250H41
70H4.2.3 ZERO ADJUST .............................................................................................................. 251H42
71H4.3 AUTO CALIBRATION ..................................................................................................... 252H43
72H4.4 SENSOR CALIBRATION ................................................................................................. 253H43
73H4.4.1 PRESSURE CALIBRATION............................................................................................. 254H43
74H4.4.2 SAMPLE TEMPERATURE AND HUMIDITY CALIBRATION ............................................. 255H43
75H4.5 CALIBRATION VIA EXTERNAL IO/RS232.................................................................... 256H44
76H4.5.1 INITIATING A CALIBRATION VIA THE EXTERNAL IO................................................... 257H44
77H4.5.2 INITIATING A CALIBRATION VIA THE RS232 INTERFACE............................................ 258H45
78H4.6 CALIBRATION GASES/STANDARDS .............................................................................. 259H46
79H4.6.1 ZERO AIR..................................................................................................................... 260H46
80H4.6.2 SPAN GAS .................................................................................................................... 261H46
81H4.6.3 AUSTRALIAN CALIBRATION STANDARD (AS3580.12.1:2.2001)................................. 262H46
82H5DOWNLOADING DATA ............................................................................................. 263H48
83H5.1 RS232 INTERFACE ........................................................................................................ 264H48
84H5.1.1 MULTIDROP PORT ....................................................................................................... 265H48
85H5.1.2 SERVICE PORT ............................................................................................................. 266H49
86H5.1.3 ESTABLISHING COMMUNICATIONS ............................................................................. 267H49
87H5.1.4 UNPOLLED................................................................................................................... 268H49
88H5.1.5 REMOTE CONTROL ...................................................................................................... 269H49
89H5.2 INTERNAL DATA LOGGING .......................................................................................... 270H50
90H5.2.1 CONFIGURATION ......................................................................................................... 271H50
91H5.2.2 DATA DOWNLOADER SOFTWARE................................................................................ 272H51
92H5.2.3 IMPORTING DATA INTO MS. EXCEL............................................................................ 273H52
93H5.3 EXTERNAL DATA LOGGING ......................................................................................... 274H55
94H5.4 EXTERNAL ANALOG DATA LOGGING ......................................................................... 275H56

Front Matter Aurora 1000 User manual 1.3
viii
95H5.4.1 ANALOGUE OUTPUT PORTS ......................................................................................... 276H56
96H5.4.2 ANALOGUE OUTPUT CALIBRATION ............................................................................. 277H57
97H5.5 UPGRADING THE AURORA 1000 FIRMWARE............................................................... 278H58
98H6MAINTENANCE ........................................................................................................... 279H60
99H6.1 MAINTENANCE TOOLS.................................................................................................. 280H60
100H6.2 MAINTENANCE SCHEDULE ........................................................................................... 281H60
101H6.3 MAINTENANCE PROCEDURES....................................................................................... 282H61
102H6.3.1 PRECISION CHECK ....................................................................................................... 283H61
103H6.3.2 MEASUREMENT CELL CLEANING ................................................................................ 284H61
104H6.3.3 SAMPLE INLET AND BUG TRAP CLEAN......................................................................... 285H62
105H6.3.4 ZERO PUMP INLET FILTER............................................................................................ 286H62
106H6.3.5 ZERO SPAN FINE FILTER .............................................................................................. 287H62
107H6.3.6 LEAK CHECK................................................................................................................ 288H63
108H6.3.7 BATTERY REPLACEMENT............................................................................................. 289H63
109H6.3.8 PNEUMATICS CLEANING .............................................................................................. 290H64
110H6.3.9 PMT REPLACEMENT ................................................................................................... 291H64
111H6.3.10 MEASUREMENT CHAMBER CLEANING...................................................................... 292H67
112H7TROUBLESHOOTING ................................................................................................ 293H69
113H7.1 LIGHTSOURCE FAIL...................................................................................................... 294H69
114H7.2 SHUTTER FAIL............................................................................................................... 295H70
115H7.3 RH SENSOR &TEMPERATURE SENSOR FAIL .............................................................. 296H71
116H7.4 PMT FAIL...................................................................................................................... 297H72
117H7.5 ENCLOSURE TEMPERATURE SENSOR FAIL ................................................................. 298H72
118HAPPENDIX A AURORA COMMAND SET....................................................................... 299H73

Aurora 1000 User manual 1.3 Front Matter
ix
List of Figure
119HFigure 1 Light path layout .......................................................................................................... 300H6
120HFigure 2 Block diagram.............................................................................................................. 301H8
121HFigure 3 Aurora Calibration Curve............................................................................................. 302H9
122HFigure 4 Aurora 1000 (with cover removed)........................................................................... 303H11
123HFigure 5 Cell ............................................................................................................................ 304H12
124HFigure 6 PMT ........................................................................................................................... 305H12
125HFigure 7 Shutter....................................................................................................................... 306H12
126HFigure 8 Light source............................................................................................................... 307H13
127HFigure 9 Sample pump ............................................................................................................308H13
128HFigure 10 Zero pump ............................................................................................................... 309H14
129HFigure 11 Zero Filter ................................................................................................................ 310H14
130HFigure 12 Span and Zero valve ............................................................................................... 311H14
131HFigure 13 Temperature/RH sensor.......................................................................................... 312H15
132HFigure 14 Pressure sensor ...................................................................................................... 313H15
133HFigure 15 Cell Heater .............................................................................................................. 314H16
134HFigure 16 Microprocessor board.............................................................................................. 315H16
135HFigure 17 Keypad and Display ................................................................................................ 316H17
136HFigure 18 Electrical connections to the Aurora 1000............................................................... 317H17
137HFigure 19 Pneumatic connections to the Aurora 1000 ............................................................ 318H18
138HFigure 20 Span gas plumbing installation ............................................................................... 319H20
139HFigure 21 Aurora Service & Multi-drop Serial Port Cable........................................................ 320H21
140HFigure 22 Correct sample inlet connection.............................................................................. 321H23
141HFigure 23 Display panel and keypad ....................................................................................... 322H26
142HFigure 24 Main screen............................................................................................................. 323H28
143HFigure 25 Menu system tree.................................................................................................... 324H29
144HFigure 26 Temperature/Humidity sensor................................................................................. 325H43
145HFigure 27 External Span & Zero Control ................................................................................. 326H44
146HFigure 28 Aurora Data Downloader......................................................................................... 327H51
147HFigure 29 clear the data store window .................................................................................... 328H52
148HFigure 30 Open Window.......................................................................................................... 329H52
149HFigure 31 Step 1. ..................................................................................................................... 330H53
150HFigure 32 Step 2. ..................................................................................................................... 331H53
151HFigure 33 Step 3. ..................................................................................................................... 332H54
152HFigure 34 Imported Data.......................................................................................................... 333H54
153HFigure 35 Regional Settings. ................................................................................................... 334H55
154HFigure 36 Communications Window........................................................................................ 335H58
155HFigure 37 File Window............................................................................................................. 336H58
156HFigure 38 Operations Window. ................................................................................................ 337H59
157HFigure 39 Data Transfer Window............................................................................................. 338H59
158HFigure 40 Aurora internal components .................................................................................... 339H61
159HFigure 41 Insect trap removal.................................................................................................. 340H62
160HFigure 42 Aurora with Filters highlighted and leak test setup shown ...................................... 341H63
161HFigure 43 Internal pneumatic tubing........................................................................................ 342H64
162HFigure 44 Removal of cell fittings ............................................................................................ 343H65
163HFigure 45 Removing the PMT.................................................................................................. 344H66
164HFigure 46 New PMT inserted................................................................................................... 345H66
165HFigure 47 Removal of cell fittings ............................................................................................ 346H67
166HFigure 48 Measurement chamber right cylinder components ................................................. 347H68
167HFigure 49 Removing Light Trap ............................................................................................... 348H68

Front Matter Aurora 1000 User manual 1.3
x
List of Tables
168HTUTable 1 Calibration Data.UT ................................................................................................. 349H8
169HTUTable 2 Properties of Calibration Gases at different wavelengths.UT................................ 350H10
170HTUTable 3 RS232 pins and their functionsUT......................................................................... 351H21
171HTUTable 4 Aurora 1000 External I/O connectorUT ................................................................. 352H22
172HTUTable 5 Calibration check criteria.UT ................................................................................. 353H39
173HTUTable 7 Keypad ControlsUT ............................................................................................... 354H49
174HTUTable 6 Analog Multiplier and OffsetsUT............................................................................ 355H56
175HTUTable 8 Maintenance scheduleUT...................................................................................... 356H60
List of Equations
176HTUEquation 1 Beer-Lambert lawUT .................................................................................................... 357H4
177HTUEquation 2 Koschmieder’s FormulaUT........................................................................................... 358H4
178HTUEquation 3 Light attenuation equationUT ....................................................................................... 359H4
179HTUEquation 4 Scattering CoefficientUT .............................................................................................. 360H5
180HTUEquation 5 Absorption CoefficientUT ............................................................................................. 361H5
181HTUEquation 6 Relationship of ExtinctionUT ........................................................................................ 362H5

Aurora 1000 User manual 1.3 Introduction
1
1
1
1 I
I
In
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t
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n
1.1 Description
TThe Aurora will measure, continuously and in real-time, light scattering in a sample
of ambient air due to the presence of particulate matter. (Specifically, the scattering
coefficient σBspB.) The measured values are adjusted automatically and in real-time by
on-board temperature and pressure sensors.
TCalibrations and zero / span checks are fully automatic, with checks initiated
automatically, at user-selectable intervals. There is provision for several types of
calibration gases.
TA processor-controlled sample heater can eliminate the effects of relative humidity on
scattering behaviour. The heater can be enabled and disabled by the user.
TAll these options are available from an easy-to-use menu system with a large 4-line
backlit LCD display and keypad mounted on the instrument case.
TOver 45 days’ data can be stored in the internal data logger for later downloading
through the RS-232 port. Instantaneous data can also be logged externally via the
RS232 port or by using the four (4) real-time analogue outputs.
TThe Aurora also features low power consumption, very long-lasting and reliable
LED’s as the light source and has an exceptional signal-to-noise ratio.
1.2 Specifications
1.2.1 Measurement
Range:
Measurement: <0.25 to 2000 MmP
-1
P
Light scattering angle: 10°– 170°
Wavelength: 450nm, 525nm or 635nm
Lower detectable limit:
< 0.3 MmP
-1
Pover 60 seconds integration
Sample flow rate:
5 l/minute
1.2.2 Calibration
Calibration gases supported:
COB2BSF6
FM-200 R-12
R 22 R-134
Automatic Calibration intervals:
3, 6, 12, 24 hours, weekly or user designated day

Introduction Aurora 1000 User manual 1.3
2
Automatic Calibration types:
Zero Check
Span Check
Zero and Span Check
Zero Adjust
1.2.3 Power
Operating voltage:
110-250VAC 50 or 60Hz
11-14VDC
Power consumption:
60VA max
1.2.4 Operating conditions
Ambient Temperature Range:
0-40°C
Relative Humidity
10-95%
1.2.5 Physical dimensions
Case dimensions:
LxWxH = 175 x 700 x 235 mm (with feet)
Weight: 11.2kg
1.2.6 Communication and Data
Comm ports:
1 multidrop (RS232)
1 Serial port (RS232)
External I/O
Analog 2 Voltage outputs
2 Current outputs
2 digital inputs
1 digital output
Data properties
Averaging period: 1 or 5 minutes
Stored properties: σBspB, Air Temperature, RH, Pressure, Enclosure Temperature,
Time, Visibility
Capacity: 45 days (5 min)
10 days (1 min)

Aurora 1000 User manual 1.3 Introduction
3
1.3 Nomenclature
Span
When gas of known Rayleigh factor is passed through instrument and
measured as a reference. This measurement is used to correct measure
coefficients.
Zero
When air with no particulate matter is passed through instrument and
measured as a reference. This measurement is used to ascertain the
effect of air (COB2B, CO etc) on scattering coefficient.
Shutter count
The shutter count is the measurement of light shone directly through a
dark glass with known transmittance. This measurement is used as a
reference for light intensity and PMT measurement.
Dark count
Measures background light scattering when light source is off (should
be 0 but readings less than 200 are considered typical). Used to subtract
from measure count to eliminate noise from background interference.
Measure count
Measures the light scattering of particulates in the sample air within the
cell.

Introduction Aurora 1000 User manual 1.3
4
1.4 Background/ Theory
The effects of air pollution on human health and lifestyle are of a major concern
today. There are many parameters contributing to air pollution, airborne particulates
are a major contributor.
The Ecotech Aurora 1000 Integrating Nephelometer measures σBspB, the scattering
coefficient of light due to particles.
σBspBmay be used as a measure of particulate pollution, the higher the value of σBspBthe
higher the concentration of particles. It may also be used as a measure of atmospheric
visibility, the higher the value of σBspBthe lower the visibility.
The dimension of σBspBare inverse length. The Aurora 1000 reports σBspBin units of the
inverse megametre (MmP
-1
P). Conversion factors are:
1 MmP
-1
P= 10P
-3
PkmP
-1
P(inverse kilometres) = 10P
-6
PmP
-1
P(inverse metres).
1.4.1 Background
Extinction Coefficients σBextB
Attenuation of light (that is, reduction in its intensity) is usually expressed using the
Beer-Lambert law:
x
ext
eII
σ −
=0
Equation 1 Beer-Lambert law
where:
IB0B= initial light intensity,
I = intensity after distance x,
x = distance,
σBextB= the attenuation, or extinction coefficient.
(sometimes the symbol b is used instead of σBextB)
The relationship between extinction coefficient and visual range is expressed in
Koschmieder’s Formula.
Lv = 3.912 / σBextB
Equation 2 Koschmieder’s Formula
where:
LBvB= visual range,
σBext B= extinction coefficient.
The larger σBext B, the more rapidly the light is attenuated (ie reducing visibility).
Assumptions
Light may be attenuated either by scattering off objects or absorption by
objects. Thus the extinction coefficient σBextBmay be broken down into a
scattering coefficient σBscatBand an absorption coefficient σBabsB:
σBextB= σBscatB+ σBabsB.
Equation 3 Light attenuation equation

Aurora 1000 User manual 1.3 Introduction
5
For light attenuation in the atmosphere, the objects responsible can be either
gas molecules or airborne particles. The scattering and absorption coefficients
may therefore be further broken down into
σBscatB= σBsgB+ σBspB
Equation 4 Scattering Coefficient
and σBabsB= σBagB+ σBapB,
Equation 5 Absorption Coefficient
where the subscripts denote:
s: scattering
a: absorption
g: due to gas molecules
p: due to particulate matter.
σBspB, for example, is the extinction coefficient due to scattering from particulate
matter. Scattering due to gas molecules (coefficient σBsgB) is also called
‘Rayleigh scattering’.
NOB2Bis the most significant gaseous absorber and soot the most significant
particulate absorber. However, except in extremely high concentrations, the
effects of absorption are negligible compared to the effects of scattering.
Therefore, to a very good approximation,
σBextB≈σBscatB= σBsgB+ σBspB.
Equation 6 Relationship of Extinction
coefficient with scattering Coefficient
It is σBscatBthat the Aurora 1000 measures directly. When the instrument
performs a zero adjust in particle-free air (that is, where only Rayleigh
scattering is present), the σBsgBcomponent of σBscat Bis subtracted leaving σBspBas the
reported parameter.
Higher particulate concentrations mean more scattering, so σBspBis a good
measure of particulate pollution.
In urban situations σBspBwill be much greater than Rayleigh scattering (σBsgB). σBspB
is therefore also a good measure of atmospheric visibility.
Effects of Wavelength
Absorption and scattering are dependent on the wavelength of the incident
light. In the Aurora 1000 either one of three different wavelengths can be
chosen (450nm, 525nm or 635nm). Each wavelength interacts differently with
particulate matter and thus differences in particulate composition can be
inferred.
•450nm (blue) interacts strongly with fine and ultrafine particulates
(wood fires, automobiles)

Introduction Aurora 1000 User manual 1.3
6
•525nm (green) interacts strongly throughout the human range of
visibility (smog, fog, haze)
•635nm (red) interacts strongly with large particulate matter (pollen, sea
salt)
These different wavelengths overlap in measurements and do not directly
measure differences in particulate composition, they merely infer differences.
Effects of Humidity
Above about 60% relative humidity, particles collect water droplets and grow
because of the water vapour condensing on them, hence scattering more light.
The Aurora contains an internal heater which if enabled (section X363H3.5.5X) heats
the incoming sample when the relative humidity of the air sample rises above
a threshold chosen by the user. This decreases the relative humidity and
evaporates the water droplets.
Switching on the heater (dry measurement) would give a more reliable
measure of airborne pollutant concentrations, as this evaporates (much of) the
water droplets. Switching off the heater (wet measurement) would give a more
reliable measure of local atmospheric visibility, because the sample inside the
Nephelometer is then more representative of the particle sizes in the outside
atmosphere.
Please consult your local Standards to determine whether the heater should be
switched on for measurement of σBspBand to determine what relative humidity
limit should be used.
The Australian Standard, for example, requires the use of a heater to maintain
the relative humidity at 60% or less (AS/NZS 3580.12.1:2001).
1.4.2 Measurement Theory
During normal operation three main measurements are undertaken. They are Shutter
count, Dark count and Measure count.
Figure 1 Light path layout
Shutter Count
Periodically (every 30 seconds) the shutter mounted inside the cell (see X364HFigure 1X), is
closed for about 4 seconds. During this time, there is a direct light path from the Light
Source, to the shutter and then to the photomultiplier tube. The shutter glass is a
material with known transmittance that allows the Nephelometer to adjust for
variations in the measuring system. This measurement does not rely on air scattering.

Aurora 1000 User manual 1.3 Introduction
7
The results from the Shutter measure are stored as the Shutter Count and should be in
the order of 0.8M to 1.6M.
Dark Count
The light source periodically flashes on and off in less than 1 second. When the light
source is off, the PMT measures the Dark Count. That is, the background light
incident upon the PMT when the light source is off. Ideally, this should be 0, however
readings from 0 to 1000 are normal, as are fluctuations.
Measure Count
The measure count is taken when the shutter is open and the light source is on. The
measured counts from the PMT are a result of scattering due to gaseous and
particulate matter inside the measurement volume. As the concentration of scattering
components inside the cell increases, so do the measure counts. Typical measure
counts can vary from 5k to 500k.
Measure Ratio
The measure ratio (MR) is the ratio between the Measure count (CBmB) and the shutter
count (CBshB).
MR = CBmB/ CBshB
Eg. If CBmB= 15,000 & CBshB= 1,200,000, then MR = 12.5 x 10P
-3
P.
Because the CBshBis a known source, the MR is directly proportional to σBscatB.
If there are changes in the measurement system (ie. Light intensity or temperature),
then both CBmB& CBshBwill change proportionally. Therefore the MR will remain
constant. However if the σBscatBof the sample changes, then only the CBmBwill vary.
Kalman Filter
The Aurora 1000 has the option of using a fixed 30 second Moving Average Filter or
the advanced digital Kalman filter (selectable from the Report Prefs menu).
The Kalman filter provides the best possible compromise between response time and
noise reduction for the type of signal and noise present in the ambient air.
Ecotech’s implementation of the Kalman filter enhances the Aurora 1000
measurement method by making the time constant variable, depending on the change
rate of the measured value. If the signal rate is changing rapidly, the instrument is
allowed to respond quickly. When the signal is steady, a longer integration time is
used to reduce noise. The system continuously analyses the signal and uses the
appropriate filtering time.