Combustion Oxygen Monitor
Endura AZ20 Series Probe 3 Troubleshooting – Quick Checks
IM/AZ20M–EN Rev. B 7
3.3 Checking the Heater Resistance
Referring to Fig. 3.3:
1. At the 9-way terminal block A, measure the resistance
across the heater leads B (brown and blue).
2. The measured resistance should be within the ranges
shown in Table 3.1:
3. If the measured resistance is out of range, check the
heater wiring and, if necessary, replace the heater
assembly – refer to Section 5.9, page 24.
If the measured resistance is within range, proceed to
Section 3.4.
3.4 Checking the Thermocouple / Electrode
Assembly Resistance
Referring to Fig. 3.4:
1. Ensure the probe is at ambient temperature (–20 to 70 °C
[–4 to 158 F]).
2. At the 9-way terminal block
A, check the thermocouple /
electrode assembly terminals
B (TC+ green and TC–
white) for open- or short-circuit.
3. Check that the thermocouple / electrode assembly is
isolated from the probe body earth. If it is not isolated,
check for short-circuits to earth in the probe’s internal
wiring.
4. The resistance measured should be within the following
range:
5. If the measured resistance is out of range, replace the
thermocouple / electrode assembly – refer to Section 5.8,
page 20.
If the measured resistance is within range, proceed to
Section 3.5.
Fig. 3.3 Heater Connections
Probe Type Resistance
AZ20 Standard Probes
0.5 to 4.0 m (1.64 to 13.12 ft)
185 to 220
AZ20/ZFG2 Version 25 to 37
Table 3.1 Heater Resistance by Probe Type
Fig. 3.4 Thermocouple / Electrode Assembly
Connections
Probe Length Resistance
0.5 to 2.0 m (1.64 to 6.6 ft) 10 to 17
2.5 to 4.0 m (8.2 to 13.1 ft) 17 to 23
Table 3.2 Thermocouple / Electrode Assembly
Resistance by Probe Length
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