Adjusting The Channel Amplifier - Bosch ETT 008.31 Repair Instructions

10.5.1 Adjusting the channel amplifier

i The amplification of the channel amplifier in question must only be adjusted if,
following replacement of a receiving chamber, the new receiving chamber does not
comply with the ADC limit values of + 1.5 V to + 3 V.
In new analyzers, the amplification is fine-tuned together with the actual integrated
components - lamp, analyzing chamber and chopper.
The receiving chamber as a replacement part is calibrated together with a standard
analyzer part, which means that amplification may have to be adjusted following its
installation.
This adjustment may be performed once only when a new receiving chamber is
installed.
During amplifier adjustment, take care to ensure that the analyzing chamber is
perfectly clean (Section 10.4) and that zero gas is in perfect condition.
Procedure for amplifier adjustment:
- Unsolder the resistor R 7 on the channel amplifier in question.
- Connect a decade resistor in place of R 7.
- In the Test mode menu, change the display to the A/D voltage values (Section 4.2).
- Introduce a flow of zero gas (ambient air) into the exhaust-gas analyzer via the test-gas
inlet.
- By changing the decade resistor, determine the resistance at which the measured
value of the channel amplifier being tested reaches 2.5 V + 0.5 V.
- Solder on the appropriate trimming resistor R 7 from the range below:
HC measuring channel:
1.2 - 5 kΩ no less than 1.2 kΩ
CO measuring channel:
2.2 - 7 kΩ no less than 2.2kΩ
CO measuring channel.
2
10.0 - 100 kΩ no less than 10.0 kΩ
R 7
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