Faulty Channel Identification; Faulty Temperature Compensation - Bosch ETT 008.31 Repair Instructions

8.5

Faulty channel identification

The "channel amplifier" modules feature a coding plug S 1.
The connection assigned here enables the microprocessor unit
(MPU) to identify the measuring channel in question.
Take care to ensure the correct coding when replacing a receiving chamber!
Check that the jumper plug is correctly situated.
8.6

Faulty temperature compensation

Each channel amplifier is equipped with a temperature sensor (NTC). These sensors are connected in parallel on the motherboard,
in order to enable a mean temperature value to be achieved and further processed.
The measured value acquired here is used for the purpose of temperature compensation during processing of the measured value.
At the same time, the analyzer part is monitored to ensure that it remains within upper and lower temperature limits.
An error message occurs if the temperature is outside the range 0°C to +75°C.
In test mode (see Section 4.2), call up and make a note of the temperature of the analyzer part.
Using a digital multimeter, check the plausibility of the temperature signal at test point X 101 (reference point X 16) on the motherboard.
A temperature of 0°C corresponds to a voltage of + 2.15 V
75°C corresponds to a voltage of + 2.80 V
If the measured value is plausible yet the display still shows an error, replace the motherboard (incorrect processing of measuring
values).
If the measured value at X 101 lies outside the premitted range of + 2.15 V bis + 2.80 V:
There is a temperature error or a sensor is faulty.
Continue to use test point X 101. Remove the signal lines of the channel amplifiers from the motherboard (X 100, X 200 and X 300).
Check: DM = 0V
Re-attach signal lines X 100, X 200 and X 300 one by one.
Check: That measured values at X 101 differ only slightly from one another.
The temperature signal usually differs in voltage from one receiving chamber to another by < 10mV. A large difference
indicates that the temperature sensor or the circuitry on the receiving chamber in question is defective. Replace the receiving
chamber as described in Section 10.3.
i
The upper temperature limit (75°C) of the analyzer part can only be exceeded in the event of excessively high ambient temperature
or a serious fault in the exhaust-gas analyzer. In case of doubt, check the temperature of the analyzer part with a thermometer.
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459558/11Ha