Brief Description Of Appliance Function; Serial Interface; Analyzer Part; System Adjustment - Bosch ETT 008.31 Repair Instructions

3.

Brief description of appliance function

The exhaust-gas analyzer is designed for the following measuring
ranges:
Carbon monoxide (CO)
Hydrocarbons (HC)
Carbon dioxide (CO )
2
Oxygen (O )
2
Engine speed
Oil temperature
Excess air factor
(λ, Lambda)
3.1

Serial interface

The exhaust-gas analyzer has a serial interface for connection to
the following items of equipment:
- Operator data terminal for entering the necessary identity data
during exhaust-gas tests, for entering the necessary measuring
parameters or for setting the internal battery-backed clock
(e.g. following a fault in the appliance).
- External printer (if the exhaust-gas analyzer does not feature an
integrated printer).
- Emission system analysis (3.110, 3.140, 3.250).
- Engine tester MOT 240 / 250 / 251 or FSA 560 / 600.
A special connecting line must be used for this purpose (see
operating instructions of different systems).
3.2 Analyzer part (measurement of CO, HC and CO
The channels for measuring CO, HC and CO
ding to the infrared pulsating-light method. In this process, the
properties of the different gases are used to absorb infrared rays
of particular wavelengths. The infrared rays are produced by a
lamp, interrupted in cycles by a chopper wheel and fed one after
another through an analysis system for CO, HC and CO
individual analysis systems are sensitive to infrared light of diffe-
rent wavelengths and can therefore be mechanically arranged
one behind the other.
Each of these systems consists of an analyzing chamber through
which test gas flows, and a receiving chamber filled with a
suitable gas mixture.
The systems are constructed in such a way that when zero gas
(air) flows through the analyzing chamber, a maximum electrical
alternating-voltage signal - the measured-value signal - is genera-
ted in the receiving chambers.
The signal is amplified by the appropriate channel amplifier,
rectified and conveyed on the motherboard to an analog-to-digital
converter (ADC). The digitalized signal is read and stored by the
MPU.
When test gas containing the component to be measured flows
through the analyzing chambers, component-specific wa-
velengths of the infrared ray are attenuated accordingly.
A smaller measured-value signal is generated in the receiving
chambers (see gas-route diagram, Section 12).
6
0...10.00 % vol.
0...9999 ppm
0...18 % vol.
0...21 % Vol. (optional)
0...9990 rpm
0...150 °C
0.500...1.800 (optional)
function accor-
2
3.3

System adjustment

After the warm-up time and during various other processes, the
exhaust-gas analyzer performs a system adjustment in con-
junction with a self-test. Each time that the exhaust-gas analyzer
carries out system adjustment, a solenoid valve switches the
zero-gas inlet (with carbon canister) into the test-gas duct for the
duration of the adjustment. During this process, the actual system
sensitivity of the HC, CO and CO
mined using zero gas (air) and stored as the zero point.
A system adjustment is always started automatically when the
system switches over to analyzing mode and the infrared measu-
red values at this moment differ from zero. If the exhaust-gas
analyzer is still in analyzing mode after 15 minutes, the system
adjustment is repeated. Here, the analyzer automatically checks
whether analysis is currently taking place and, if it is, delays
system adjustment until all measured values have dropped to
zero.
3.4

Self-test

In conjunction with the system adjustment, the exhaust-gas
analyzer performs a self-test during which it checks its most
important functions. Any malfunctions it detects result in an error
message (Section 7).
3.5 Fine-tuning (HC, CO and CO
During fine-tuning with test gas (upper-range value gas), the
measurement effect (difference from zero) is measured. The
analyzer is informed by means of a "setpoint" which test-gas
concentration corresponds to this measurement effect.
Fine-tuning is also carried out with mean-value gas (concentrati-
on in the middle of the measuring range).
Following this process, the exhaust-gas analyzer can then deter-
mine the characteristic curve, and all measured values which
occur within the measuring range can be interpreted and correct-
ly indicated.
)
2
3.6 O measuring channel (optional)
2
The sensitivity of this measuring channel is fine-tuned automati-
cally during each system adjustment. Here, the measured oxygen
content is set against the compensating air = 20.9 % and the
condition of the O
. The
2
The zero of this O
(see Section 4.1.8).
The oxygen measurement function can be deactivated
(Section 4.1.3).
3.7

Correction of pressure influence

Different levels of atmospheric pressure mean that different
concentrations are measured in the analysis system. In order for
the exhaust-gas analyzer to be able to display the correct value,
it is informed of the atmospheric pressure by means of a built-in
pressure sensor or by the entry of the mean altitude. The analyzer
can then calculate the correct display value itself.
In exhaust-gas analyzers without a built-in air-pressure gauge, the
new altitude must be entered if its location is changed
(Section 4.1.7).
measuring channels is deter-
2

measuring channels)

2
measuring sensor is monitored.
2
measuring channel is fine-tuned manually
2