Andros 6900 User manual

Incorporated
Model 6900 Product Manual
Reorder Number 891166-001
Models 6900/6500/6510
Compact
Automotive Gas
Subsystem and Components
Andros Incorporated
870 Harbour Way South vRichmond, CA 94804
Voice [phone] vFAX [phone]

Preface
Table of Contents
Table of Contents ................................................................................................iii
Preface...................................................................................................................7
About This Manual....................................................................................................................................................................... 7
Andros Notation........................................................................................................................................................................... 8
Manual History.............................................................................................................................................................................. 8
Chapter 1 —Introduction ....................................................................................9
Key Features and Configurations............................................................................................................................................... 9
Pneumatics Configurations .......................................................................................................................................................10
Government Programs Supported...........................................................................................................................................12
End-User Maintenance ..............................................................................................................................................................12
Options and Accessories ...........................................................................................................................................................12
Chapter 2 —Specifications...............................................................................13
Environmental Specifications ...................................................................................................................................................13
Mechanical Specifications..........................................................................................................................................................13
Power Specifications ..................................................................................................................................................................13
Gas Measurement Accuracy, Repeatability, Noise, and Resolution...................................................................................14
Propane Equivalency Factor (PEF).........................................................................................................................................15
Cross-Gas Interference..............................................................................................................................................................15
System Transport Time..............................................................................................................................................................16
System Response Time ..............................................................................................................................................................16
Model 6500/6510 Analyzer/Sensor Response Time............................................................................................................16
Host Communications Interface..............................................................................................................................................17
Auxiliary I/O Interfaces ............................................................................................................................................................17
Chapter 3 —Operation ......................................................................................19
Gas Concentration Measurement.............................................................................................................................................19
HC, CO, and CO2Measurement ..............................................................................................................................................19
Simple NDIR Gas Analyzer Model..........................................................................................................................................19
The Infrared Transmission Spectra .............................................................................................................................................20
Air-Fuel Ratio and the Stoichiometric Point ...............................................................................................................................21
Lambda ( l ) and Catalytic Converter Efficiency ..........................................................................................................................22
O2and NOXMeasurement........................................................................................................................................................22
Functional Description ..............................................................................................................................................................23
Pneumatic System.......................................................................................................................................................................23
Infrared Source ...........................................................................................................................................................................24
Optical Block .............................................................................................................................................................................24
System Board Assembly..............................................................................................................................................................24
O2and NOXSensors.................................................................................................................................................................24

Preface
Configuration Modes .................................................................................................................................................................25
Model 6900 / 6500 / 6510 Operating Modes........................................................................................................................25
Start-up Operating Mode............................................................................................................................................................25
Normal Operating Mode ............................................................................................................................................................25
Standby Operating Mode............................................................................................................................................................25
System Fault Operating Mode ....................................................................................................................................................26
6500 Process Flow .....................................................................................................................................................................27
Model 6500 / 6510 Temperature Measurements ..................................................................................................................28
Pressure Measurements..............................................................................................................................................................28
Chapter 4 —Calibration.....................................................................................29
Factory Characterization............................................................................................................................................................29
Field Calibration..........................................................................................................................................................................29
Zero Calibration.........................................................................................................................................................................29
$02 Zero/O2Span Calibration Procedure..................................................................................................................................30
Additional ISO 3930/OIML R 99, and BAR-97 Zero Calibration Requirements.................................................................32
Span Calibration........................................................................................................................................................................32
$03 Span Calibration Procedure.................................................................................................................................................32
Additional ISO 3930/OIML R 99, and BAR-97 Span Calibration Requirements................................................................34
$09 Reset Span..........................................................................................................................................................................34
Chapter 5 —Hardware Interfaces.....................................................................35
Configuration Jumpers...............................................................................................................................................................38
Jumper............................................................................................................................................................................................38
Configuration Function.....................................................................................................................................................................38
Power and Interface ...................................................................................................................................................................39
Model 6500/6510 Circuit Board Connector Locations........................................................................................................39
Outline and Mounting Dimensions Model 6500/6510........................................................................................................40
Outline and Mounting Dimensions Model 6900...................................................................................................................41
Chapter 6 —Sample Delivery............................................................................43
Pneumatics Ports ........................................................................................................................................................................43
Hose and Probe Sample Gas Port.......................................................................................................................................43
Room Air Port........................................................................................................................................................................43
Calibration Gas Port..............................................................................................................................................................43
Zero Gas Port.........................................................................................................................................................................43
Calibration Check Gas Port .................................................................................................................................................43
Exhaust Gas Port......................................................................................................................................................................44
Water Drain Port....................................................................................................................................................................44
Pump.............................................................................................................................................................................................44
Room Air Filtration....................................................................................................................................................................44
Water Trap / Filter Assembly...................................................................................................................................................44
Sample Delivery Configurations...............................................................................................................................................45
OIML 6900 Pneumatics Configuration (standard) ....................................................................................................................45
BAR-97 6900 Pneumatics Configuration (customer option).......................................................................................................46

Preface
Chapter 7 —Host Communications.................................................................49
Communications Protocol ........................................................................................................................................................49
Host Command Format ............................................................................................................................................................50
ACK Response Format..............................................................................................................................................................50
NAK Response Format.............................................................................................................................................................51
NAK Error Codes ......................................................................................................................................................................51
Command Set ..............................................................................................................................................................................52
Command Set Summary.............................................................................................................................................................52
$01 —Data/Status .................................................................................................................................................................53
$02 —Zero/O2Span Calibration...........................................................................................................................................59
$03 —Span Calibration...........................................................................................................................................................60
$04 —System ID.....................................................................................................................................................................62
$05 —Miscellaneous Data .......................................................................................................................................................63
$06 —Extended Data/Status ..................................................................................................................................................64
$07 —Pump On/Off...............................................................................................................................................................65
$08 —Device Control...............................................................................................................................................................66
$09 —Reset Span ....................................................................................................................................................................70
$0A —New NOXSensor........................................................................................................................................................71
$0B —Leak Test.....................................................................................................................................................................72
$F0 —Reset.............................................................................................................................................................................73
$F1 —Configuration Mode Control..........................................................................................................................................74
$11 —1 Point Pressure Span/Reset Span Calibration..............................................................................................................76
$12 —Raw NOx and O2 Data...............................................................................................................................................77
$13 —Channel Switch ON/OFF command.............................................................................................................................78
$14 —Read User Memory .......................................................................................................................................................79
$15 —Write User Memory ......................................................................................................................................................80
$16 —Pressure Data.................................................................................................................................................................81
$17 —Standby Enable / Disable command.............................................................................................................................82
$18 —SW Checksum..............................................................................................................................................................83
Chapter 8 —Service Procedures......................................................................84
Maintenance and Service ...........................................................................................................................................................84
General Maintenance Considerations ..........................................................................................................................................84
Water Trap / Filter Element Replacement.................................................................................................................................85
6900 Subassembly Maintenance Items........................................................................................................................................86
Model 6500/6510 Analyzer Maintenance Items.......................................................................................................................87
Sample Cell Cleaning .................................................................................................................................................................89
Bench Upgrade Download Procedure...........................................................................................................................................90
Troubleshooting Error Status...................................................................................................................................................90
System Fault Error ..............................................................................................................................................................91
CO2, CO, and HC Channel Errors .................................................................................................................................91
Zero Calibration Errors .....................................................................................................................................................91
Span Calibration Errors .....................................................................................................................................................92
Sample Delivery Errors ......................................................................................................................................................92
New NOXor O2Sensor Required ..................................................................................................................................92
IR Signal Lost Error ...........................................................................................................................................................93
Ambient Temperature Error ............................................................................................................................................93

Preface
Chapter 9 —Product Support...........................................................................94
Technical Support and Training...............................................................................................................................................94
How To Return Products For Service ....................................................................................................................................94
To Andros USA Service Depot From The USA.......................................................................................................................95
To Andros USA Service Depot From International Locations...................................................................................................96
To Andros Europe Service Center...............................................................................................................................................97
Appendix A —Supplemental Documentation.................................................98
$01 Data/Status Reference Chart ............................................................................................................................................98
Appendix B —Supplemental Documentation.................................................99

Preface 7
Preface
About This Manual
Important Note : This manual contains preliminary technical information and all features, specifications, procedures, and
descriptions are subject to change prior to final product release. If you have any questions, please contact your Andros sales or
technical representative.
Chapter 1
Introduction
Key features, applications, and configurations of the Model 6900 compact
automotive emissions gas subsystem are described. Supported government
mandated emissions programs are listed. Options and Accessories for the
6900 are listed.
Chapter 2
Specifications
Model 6900/6500/65106900 / 6500 / 6500 product performance
specifications are defined.
Chapter 3
Operation
The Model 6900 subsystem and Model 6500/6510 analyzer’s gas
concentration measurement techniques are discussed. Functional
descriptions are proved for the primary components and subassemblies. The
start-up, warm-up, normal, standby and boot program operating modes are
defined. The 6900 configuration mode control is reviewed.
Chapter 4
Calibration
Zero and span calibration is covered in detail.
Chapter 5
Hardware Interfaces
Model 6900/6500/6510 power, communications, and auxiliary I/O interfaces
are described in detail.
Chapter 6
Sample Delivery
The 6900 pneumatic components and configurations are discussed. The
6900 leak test procedure is detailed.
Chapter 7
Host Communications
The Model 6900/6500/6510’s communications protocol and command set are
defined.
Chapter 8
Service Procedures
The 6900 maintenance and service guidelines, replacement procedures, and
troubleshooting are covered in detail.
Chapter 9
Product Support
Depot service, technical support, and training programs are identified.
Appendices Additional reference information for the 6900 is provided.

Preface 8
Andros Notation
The Model 6500/6510 always refers to the Andros bench analyzer. The Model 6500 contains all the associated driver
circuitry and connections necessary to support the operation of a 12 VDC pump and solenoids, and is used in the
Model 6900. The Model 6510 does not support the operation of a pump and solenoids. Users of the Model 6510 are
required to supply all pump and solenoid controls separately.
The Model 6900 is the product number for a family of subsystems that are built around the Model 6500/6510
analyzer. When the term“6900”is used without reference to the term “Model”in this manual it may be referring to
the bench analyzer, or one of the analyzer’s functions, within a general subsystem context.
Hexadecimal numbers are preceded by a $ (dollar sign). The $F0 Reset command requires transmission of the
hexadecimal command code $F0, which is equivalent to 240 decimal or 11110000 binary.
Analog-to-digital converters and their output values are abbreviated as both A–D and ADC.
Both NO and NOx are used to refer to nitric oxide (NO) and nitrogen dioxide (NO2) collectively.
Individual bytes or bits in host system commands and ACK/NAK responses are specified in the following format:
Command_Code—Byte_Name—Bit_Number.
Bit numbers are not referred to when the entire byte is defined.
Example #1: $01–STAT1–5 refers to the $01 Data/Status command, STAT1 (System Status) byte, bit 5 (Zero
Request).
Example #2: $03–TVM refers to the $03 Span Calibration command, TVM (Tag Value Mask) byte.
Example #3: $01-STAT2-7,6 = 11 refers to the $01 Data/Status command, STAT2 (Data Status 1) byte, CO2
Data status field (bits 7 and 6). In this example the CO2 Data status is reported as CO2 Zero Fail
(11). Bits are always shown with the most significant bit listed first (on left).
Manual History
Revision Date Description
1 8/11/05 First preliminary release
2 16-MAY-06 Added new commands, updated drawings, added Model 6510 data
3 17-AUG-06 Various, changes reflect validation and B-Test issues, added new commands
4 19-OCT-06 Chapter 7: revised command descriptions; Chapter 5: revised connector locations and pinouts;
Chapter 8: revised service procedures
5 15-MAR-07 Chapter 7: Added $18, SW Checksum command; revised Zero request conditions; Removed Flash
Read/Write commands and support documentation; Chapter 5: Corrected connector tables J8 and J9;
Chapter 3: revised Standby/Warm up specifications

Introduction 9
Chapter 1 —Introduction
Key Features and Configurations
· Standard 6900 subsystems can be ordered as either 4-gas or 5-gas subsystems.
· Standard 6900 subsystems are shipped with a single-solenoid valve. The multi-solenoid valve version can
be configured for BAR-97 gas delivery (e.g., zero calibration uses bottled zero gas). It requires an
additional sample pump and solenoid valves which are to be supplied by customer.
· Custom 6900 subsystems can be designed for the high-volume OEM. Additional sample delivery
options and accessories are available. Custom sheet metal to meet the OEMs system requirements can
be provided.
· All Model 6900s include a Model 6500 Miniature Automotive Gas Analyzer.
· All 6900s exceed BAR-97 and OIML Class 0 gas measurement accuracy.
· All 6900s are ready for integration into OIML Class 0/1 systems.
· Single +12 VDC input power requirement (+9 to +16 VDC). Can be powered by +12 VDC power
supply or automotive battery.
· Small-volume gas analysis subsystem package.
· Lightweight (2.0 to 2.4 kg, depending on configuration).
· Low power consumption: 13.5 watts nominal.
· Rugged design and construction.
· Fast warm-up time (within 35 seconds). Defined as the time from Power On Reset (POR) until Start-Up
Status bit clears.
· Easy-to-use host system command set and RS-232C, USB 1, or TTL (3.3VDC) communications
interface.
· End-user maintainable particulate filtration, O2sensor and NOxsensor. These assemblies are mounted
on the outside of the 6900 for easy end-user access. Optionally, the O2 and NOxsensors can be mounted
behind a panel or cover when mandated by a government program.
· 10,000 hours MTBF (excluding O2 sensor, NOxsensor, pump and end-user replaceable filters).
· End-user or service-depot cleanable or replaceable sample cell and source.

Introduction 10
Pneumatics Configurations
The 6900 subsystems are available in the following pneumatics configurations. Custom pneumatics configurations
can be delivered.
Standard
(Single-Solenoid
Valve)
6900
Pneumatics
Configuration:
Designed to support the lowest cost subsystem requirements, a Basic 6900 subsystem includes the following:
§ High-capacity, fast-response sample delivery design.
§ Wet- and dry-side pneumatic pump.
§ Water trap/filter assembly: User-replaceable particulate filter. Automatic water bowl drain. Float check valve
positively protects the Model 6500/6510 analyzer if the water trap bowl ever fills.
§ Sample gas/room air solenoid valve.
§ Calibration gas port.
§ Designed to support diagnostic/repair applications and Inspection/Maintenance (I/M) programs (e.g., OIML
Class 0 and Class 1).
Gas Measurement Configurations
All 6900 subsystem configurations can be ordered with an Andros NOx sensor included (5-gas) or without (4-gas).
Note: All 4-gas 6900s can be field upgraded to a 5-gas operation by installing a NOxsensor and performing a gas
span calibration.
Caution: Any procedures involving bottled NO and/or NO2should be performed with
adequate active venting to prevent lung damage due to exposure to toxic gases.

Introduction 11
Model 6900 shown with Model 6500
6900 Subassembly (OIML configuration shown)

Introduction 12
Government Programs Supported
The 6900 subsystem exceeds worldwide gas-measurement performance specifications for automotive emissions. The
following governmental programs are supported:
Location Agency
United States (EPA) EPA ASM
United States (California) ASM / BAR-97
Europe ISO 3930/OIML R99, Class 0 and Class 1
Rest of World Other agencies use variants of BAR or OIML
End-User Maintenance
The 6900 is designed to support end-user maintenance for the following components:
Component Typical Life Cycle
Water Trap
Filter Element
Every 80 vehicle tests, or once
per week *
Room Air Filter Once per month, or as required
O2Sensor 12 to 18 months
NOXSensor 12 to18 months
IR Source 36 to 42 months minimum
Sample cell Cleanable or replaceable as an assembly
* Type, age and operating condition of vehicles may necessitate more frequent filter changes.
Options and Accessories
The following Andros accessories are available for integration with the 6900 subsystem:
¨ Hose and probe assembly
¨ Solenoid manifold
¨ 12 VDC sample pump

Specifications 13
Chapter 2 —Specifications
Environmental Specifications
The 6900 subsystem will perform to specification when subjected to any combination of the environmental
conditions listed below.
Operating Range Storage Range
Temperature 0 to 70ºC (32 to 158ºF) (reduced
accuracy > 50ºC)
–25 to 70ºC (1) (–4 to 158ºF)
Humidity 5 to 95% (non-condensing) (2)
Altitude –300 to 3,000 m (–1,000 to 9,750 ft) –300 to 3,000 m (–1,000 to 10,000 ft)
Vibration 1.0 g sinusoidal, 5 to 1,000 Hz 0.01 g2/Hz(3)
Shock 7.6 cm (3.0 inch) drop on any corner (in final system enclosure)
EMI/EMC CFR Title 47, Part 15, Subpart J, Class A and B. CFR Title 47, Part 68.
1. Storage temperature range for Andros supplied NOXsensor is –20 to 50ºC; sensors may be stored
outside this range for up to 10 days. The optimal storage temperature for the NOXsensor is 5 to
20ºC.
2. NOXsensor humidity range is 15 to 90% RH.
3. Installed configuration or packaged for shipment.
Mechanical Specifications
Model 6900 Shelf Subsystem (excluding
water trap/filter assembly)
Model 6500/6510
NDIR Bench
Basic OIML ALL
Width 27.0 cm (10.6 in) 27.0 cm (10.6 in) 19.7 cm (7.7 in)
Depth 20.06 cm (7.3 in) 18.5 cm (7.9 in) 7.3 cm (2.87 in)
Height 10.16 cm (4.0 in) 10.0 cm (4.0 in) 5.0 cm (2.0 in)
Weight 2.1 kg (4.63 lb.) 2.1 kg (4.63 lb.) 0.3 Kg (0.8lb)
Power Specifications
The following input power specifications define the worst-case conditions for acceptable operating performance of
the 6900 shelf subsystem:
Input Voltage +12 VDC nominal
(+9 to +16 VDC)
Model
6900
Model
6500/6510
Average Power Consumption (1) 13.5 W 1.8 W
Maximum Power Consumption 18.5 W 2.4 W
(1) 12 VDC input power @ 25°C

Specifications 14
Gas Measurement Accuracy, Repeatability, Noise, and Resolution
Gas Measurement Range Accuracy Repeatability Noise (rms.) Resolution
HC
n-Hexane
0 to 2,000 ppm
2,001 to 7,000 ppm
7,001 to 15,000 ppm
15,001 to 30,000 ppm
±4 ppm abs. or ±3% rel.
±5% rel.
± 15% rel
unspecified.
±3 ppm abs. or ±2% rel.
±3% rel.
±5% rel.
unspecified
2 ppm abs. or 0.8% rel.
1 ppm
HC
Propane
0 to 4,000 ppm
4,001 to 30,000 ppm
30,001 to 60,000 ppm
±8 ppm abs. or ±3% rel.
±15% rel.
unspecified
±6 ppm abs. or ±2% rel.
±5% rel.
unspecified
4 ppm abs. or 0.8% rel.
1 ppm
CO 0.00% to 10.00%
10.01% to 15.00%
±0.02% abs. or ±3% rel.
±5% rel.
±0.02 abs. or ±2% rel.
±3% rel. 0.01% abs. or 0.8% rel. 0.001vol. %
CO20.00 to 16.00%
16.01 to 20.00%
±0.3% abs. or ±3% rel.
±5% rel.
±0.1% abs. or ±2% rel.
±3% rel. 0.1% abs. or 0.8% rel. 0.01vol. %
NOX0 to 4,000 ppm
4,001 to 5,000 ppm
±25 ppm abs. or ±4% rel.
±5% rel.
±20 ppm abs. or ±3% rel.
±4% rel. 10 ppm abs. or 1% rel. 1 ppm
020.00 to 25.00% ±0.1% abs. or ±3% rel. ±0.1% abs. or ±3% rel. 0.1% abs. or 1.5% rel. 0.01 vol. %
Notes:
1) The Models 6900 / 6500 / 6510 can report outside of its specified measurement ranges.
2) The Models 6900 / 6500 / 6510 can report gas concentrations at reduced accuracy when operated outside of specified
conditions defined by ISO3930/OIML R 99 and BAR i.e., temperature > 50°C or < 0°C.
3) Negative gas concentrations can indicate either of the following:
a) Negative measurement drift, or
b) Incorrect HC, CO, CO2zero calibration (e.g., zero calibration when IR absorbing gas or moisture is present in the
sample cell).
4) When both absolute and relative measurement tolerances are specified, the greater measurement tolerance of the two is
used.
5) The accuracy table is based on California BAR-97 requirements between the temperatures between 35 to 110°F (1.7 - 43°C)
6) ISO 3930/OIML R 99, Class 0 allows for ±5% relative error for temperatures between 32 to 122°F (0 - 50°C)
7) Drift is measured with Nitrogen flowing through the sample cell at one to two liters per minute. All zero requests are honored
when indicated. Maximum stability occurs per BAR 97 ASM 30 minutes after POR.
Measurement Range: The range that is applicable to the accuracy and noise measurements.
Accuracy: The 6900 gas concentration measurement tolerance.
Repeatability: An individual 6900s measurement tolerance when repeating the same measurement.
Resolution: The smallest increment reported.
Noise: Measurement transients produced by the analyzer .

Specifications 15
Warm-Up
The bench/subsystem will transition from start-up to normal operating mode within 35 seconds after POR, after
which it will request a zero. After the first zero, the analyzer is useable at reduced accuracy for the next three (3)
minutes, after which it will request a second zero. The unit is at full accuracy after the second zero is performed. Zero
drift as defined by the BAR 97 ASM specifications is measured after the unit has been allowed to stabilize for 30
minutes after POR.
Propane Equivalency Factor (PEF)
The 6900 subsystem Propane Equivalency Factor (PEF) value is nominally in the range of 0.470 to 0.560 for HC
(n-Hexane) concentrations up to 2,000 ppm when the Models 6900 / 6500 / 6500 are operated at an ambient
temperature environment of 25°C ±10°C. This applies to BAR-97 applications. For OIML and diagnostics
applications the calculated variable PEF can be in the range of 0.470 to 0.585.
The 6900 variable PEF value (reported by $05–PEF1, PEF2) is calculated in real-time, and defines the n-hexane
concentration as a fraction of the (optically) equivalent propane concentration that may be reported as the current HC
concentration. The variable PEF range is 0.470 to 0.585.
Cross-Gas Interference
The presence of one gas can cause errors in the measurement of a second gas. Maximum 6900 cross-gas interference
effects conform to ISO 3930/OIML R 99, Class 0/1 and BAR-97 specifications and are listed below:
Primary
Gas
Maximum
Cross-Gas
Interference Maximum Interfering Gas Concentrations
HC ±4 ppm
CO ±0.02%
CO2±0.20%
NOX±20 ppm
1) 16% carbon dioxide in nitrogen.
2) 1,600 ppm hexane in nitrogen.
3) 10% carbon monoxide in nitrogen.
4) 3,000 ppm nitric oxide in nitrogen.
5) 75 ppm hydrogen sulfide in nitrogen.
6) 75 ppm sulfur dioxide in nitrogen.
7) 18% carbon dioxide and 9% carbon monoxide in
nitrogen.
8) h) Water-saturated hot air.

Specifications 16
System Transport Time
System transport times are specified for a 6900 with 8m-hose/probe and particle filter/water trap as follows:
System Transport Time
HC £ 5 seconds.
Propane £ 5 seconds.
CO £ 5 seconds.
CO2£ 5 seconds.
NO £ 7 seconds.
O2£ 7 seconds.
Method: Create a rapid step change in gas concentration at the probe tip. System transport time is the time
required to report the first analyzer gas concentration change.
System Response Time
System response times are specified for a 6900 with 8m-hose/probe and particle filter/water trap as follows:
Rise Time Fall Time
HC T90 £ 8.0 seconds. T10 £ 8.0 seconds.
Propane T90 £ 8.0 seconds. T10 £ 8.0 seconds.
CO T90 £ 8.0 seconds. T10 £ 8.0 seconds.
CO2T90 £ 8.0 seconds. T10 £ 8.0 seconds.
NO T90 £ 12.0 seconds. T10 £ 12.0 seconds.
O2Response time from 20.9% to 0.10% O2£40 seconds, and T90
response time £ 15.0 seconds.
Method: Create a rapid step change in gas concentration at the probe tip. System response times (at a flow rate
into the water trap at 6 liters/minute) are the times required to report the specified analyzer gas concentration
changes.
Model 6500/6510 Analyzer/Sensor Response Time
Analyzer /sensor response time is measured as follows:
Rise Time Fall Time
HC T90 £ 3.0 seconds. T10 £ 3.0 seconds.
Propane T90 £3.0 seconds. T10 £ 3.0 seconds.
CO T90 £ 3.0 seconds. T10 £ 3.0 seconds.
CO2T90 £ 3.0 seconds. T10 £ 3.0 seconds.
NO T90 £ 5.0 seconds. T10 £ 6.0 seconds.
O2Response time from 20.9% to 0.10% O2£ 40 seconds.
Rise time for 1.10% O2to 20.9% O2£ 20 seconds.
Method: With a minimum gas flow of 1 liters/minute, create a rapid step change in gas concentration at the inlet port
of the Model 6500/6510 analyzer. Analyzer/Sensor response times are the times required to report the specified
analyzer gas concentration changes.

Specifications 17
Host Communications Interface
The Models 6900 / 6500 / 6500 commands, status, and data-transfer are provided by the host communications
interface. Refer to the Hardware Interfaces chapter for connector pin assignments.
Interface Type :RS-232C asynchronous or USB 1.1.
Baud Rate :19,200 bps (default) or 9,600 bps (optional via Model 6500/6510 parameter change).
RS-232 Format :1 start bit; 8 data bits; no parity bit; 1 stop bit.
Signals :Transmit data; receive data; signal ground. CTS and RTS handshaking signals are not used by
current Model 6900 / 6500 / 6500 configurations.
Auxiliary I/O Interfaces
Auxiliary interfaces are provided for attachment of external devices to the 6900 subsystem. Refer to the Hardware
Interfaces chapter for additional specifications and connector pin assignments.
TTL Outputs :AUXOUT 6 and AUXOUT 7 are user-defined TTL outputs host system controlled via the
$08 Device Control command.
Tachometer Input : TACHIN is a TTL compatible pulse counter input dedicated to a tachometer function.
Analog Input: Model 6900/6500 Mode: ADC1 and ADC2 are user-defined analog inputs. Input range is 0.01
to 4.0 VDC. A companion reference signal (V Ref) and the Model 6900 / 6500 / 6500 analog
ground is also provided.

Specifications 18
User Notes Page

Operation 19
Chapter 3 —Operation
Gas Concentration Measurement
The Model 6900 /6500 / 6510 measures the following automotive exhaust sample gas concentrations: CO2, CO, HC
(either n-hexane or propane, host system selectable), O2, and NOX.
HC, CO, and CO2Measurement
The NDIR measurement method uses fixed, non-scanning infrared light frequencies to characterize HC, CO, and
CO2gas concentrations. NDIR absorption profiles are the basis for measurement. The concentration of a gas volume
is a function of the quantity of gas molecules in the sample. The absorption of infrared light increases with the
number of gas molecules in the light path. As the concentration of infrared-absorbing gas increases, the transmission
of infrared light decreases. A basic automotive NDIR measurement system includes the following elements:
Sample
Delivery:
The portion of the vehicle’s exhaust gas is transported to the 6900 where liquid water and particulates are removed before
the gas is introduced to the Model 6500/6510-analyzer module.
Infrared
Source:
An infrared light source produces a wide range of light at frequencies covering the infrared band and extending into the
visible spectrum.
Sample
Cell:
The conditioned vehicle exhaust gas to be measured which is transported through a sample cell that allows infrared light
to pass through the sample.
Infrared
Filters:
An optical band pass filter is used to select a specific band of infrared light. The filter wavelength is based on the gas to be
measured. Separate infrared filters are used in the measurement of HC, CO, and CO2gas concentrations.
Infrared
Detector:
Infrared light not absorbed by the sample gas is transmitted to infrared detectors. The detectors produce an output voltage
that is proportional to the measured light.
Simple NDIR Gas Analyzer Model

Operation 20
The Infrared Transmission Spectra
The concentration of a subject gas in the sample is computed as a function of the light intensity measured by the
detector. The figure below characterizes the absorption and band pass filter curves for HC, CO, and CO2 gases.