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6.3
6.4
6.5
6.6
6.7
INM MTL 130-0175 Rev 4
Checking the Temperature Controller and Heater Circuit
of the Oxygen Sensor
Switch the analyser off and allow the sensor to cool down. Using a multi-meter set to read
resistance check that the resistance across terminals 3 and 5 (the thermocouple) is between 1
and 6 . Next check the heater resistance as follows. Remove the heater power connection
from terminal 1 to disconnect it from the power transformer, and use the multi-meter to
measure the resistance across heater wires 1 and 2. This should be 4
produces abnormal readings then the sensor heater/thermocouple assembly will need to be
replaced -proceed to section 6.4 for instructions on how to remove the module.
Checking the Temperature Controller and Heater Circuit of the Catalytic
Reactor
Switch the analyser off and allow the sensor to cool down. Using a multi-meter set to read
resistance check that the resistance across terminals 14 and 16 (the thermocouple) is between
1 and 6 . Next check the heater resistance as follows. Remove the heater power connection
from terminal 12 to disconnect it from the power transformer, and use the multi-meter to
measure the resistance across heater wires 12 and 13. This should be 4
test produces abnormal readings then the catalytic reactor assembly will need to be replaced
-proceed to section 6.5 for instructions on how to remove the catalytic reactor.
Sensor Removal and Replacement
Remove power from the analyser and allow the reactor/sensor assembly to cool to ambient
temperature before proceeding. Also take great care when working with the fragile ceramic
Remove the sensor signal connector and lead by carefully unclipping it from the ceramic
sensor. Unscrew the sensor and withdraw it from the heater body. Replacement is the
reversal of removal.
ENSURE THAT THE ELECTRICAL LEADS ARE SEPARATED FROM ALL HOT SURFACES BY AT
LEAST 12mm AND NOT PLACED VERTICALLY ABOVE THEM.
Catalytic Reactor/Sensor Heater
The sensor heater and catalytic reactor are supplied as two separate assemblies.
Replacement is by substitution of either assembly.
ENSURE THAT THE ELECTRICAL LEADS ARE SEPARATED FROM ALL HOT SURFACES BY AT
LEAST 12mm AND NOT PLACED VERTICALLY ABOVE THEM.
After replacement the analyser must be recalibrated as described in section 4.3
Spares & Service
Contact your local MTL Gas sales office for all spares and service.
WHENEVER SPARE PARTS ARE ORDERED IT IS IMPORTANT TO PROVIDE THE INSTRUMENT
SERIAL NUMBER.
For electronic cards, specify full input and output requirements if different from original
equipment.
CAUTION
of the sensor.
± 10%. If either test
± 10%. If either
11
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