Emerson Rosemount OCX8800A Manual page 122

F Fieldbus
™
OUNDATION
December 2022
Potential cause
When the heater thermocouple alarms are initiated, they diagnose one of three
states:
1. Open
2. Shorted
3. Reversed
The problem could be caused by a mechanical failure in the probe tip or at the
electronics. Cycle power to the transmitter to resume operation. Diagnose at the
transmitter. Refer to
Recommended action
Check the thermocouple wires for loose or broken connections, a short circuit
condition, or a reverse wire condition.
Sensor Heater Malfunction
The T/C Heater Alerts tab displays one of the following alarms:
1. O
2. Comb Heater Failure
3. SB Heater Failure
4. O
5. Comb Heater Ramp Rate Exceeded
6. SB Heater Ramp Rate Exceeded
7. Heater Relay Failed
This alert indicates that no measurable heat energy is being detected at the
oxygen sensor or that the heater temperature is rising too fast.
Potential cause
Mechanical or thermal stress may eventually cause the heater to fail. The
resistance of a properly functioning cell heater measures less than 100 ohms. A
failed heater generally measures an open circuit. Diagnose at the transmitter.
Refer to
The Heater Ramp Rate Exceeded problem is usually caused by the inability of the
transmitter to limit power to the heater. This could be caused by a shorted triac
component in the power supply in the electronics stack. Diagnose at the
transmitter. Refer to
Recommended actions
122
Diagnostic alarms
Heater Failure
2
Heater Ramp Rate Exceeded
2
Diagnostic alarms for details.
Diagnostic alarms
1. Check heater circuit for loose or broken connections.
2. Check thermocouple wiring.
3. Test or replace the heater.
for details.
for details.
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Manual
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