Honeywell 7866 Operation And Maintenance Manual page 82

Troubleshooting
Symptom
6. Output signal is
unstable.
7. Alarm malfunction.
*For hydrogen spans greater than 10 %, current increase should be about 80 uA.
**For higher ranges minimum reading is proportionately higher, e.g., for 0 % to 30 % H
***On flowmeters calibrated for air, note that actual flow may exceed that indicated for H
****Temperature regulator is a high-frequency variable-duty cycle controller and field repair is not recommended.
Replace the entire sensing-unit card and return the faulty unit to the factory for repairs.
72 7866 Triple Range Digital H
Possible Cause
6a. Temperature control is
inoperative.
6b. Temperature control cycles.
6c. Sample flow rate or
composition varies.
7a. Alarm set point calibration is
inaccurate.
7b. Relay contacts worn or
damaged.
7c. Relay fails to energize (alarm
condition always indicated).
7d. Relay fails to de-energize
(alarm condition never
indicated).
and CO Analyzer/Indicator - Operation and Maintenance
2 2
Recommended Checks
6a. Check cell block for approximately 50 °C
(122 °F) temperature (too hot to hold in the
hand for very long). Check heaters for 30
ohms nominal resistance for series pair.
Ambient temperature must not exceed 50 °C
(122 °F).
6b. Check that temperature-sensing thermistor is
screwed tightly into the cell block and that its
tip and threads are coated with silicone
grease. Connect a 0 to 1 amp meter in series
with one of the heater leads. During warm-up,
current should be approximately 800 mA.
When 50 °C (122 °F) is reached current will
decrease, cycling 2 or 3 times before current
stabilizes at a lower value. If cycling
continues, replace the sensing unit circuit-
card assembly.****
6c. Check stability when operating on zero gas. If
stable, check for large sample flow variations,
water vapor variations due to unstable drier or
cooler operation, etc.
7a. Adjust "Alarm 1" or "Alarm 2". (See Section
5.8.)
7b. Replace circuit board if required.
7c. Check alarm limits. (See Section 5.8.)
7d. This is normal while in Range 1 or 2. Check
alarms limits while in Range 3.
, reading should be 30 mV.
2
2
or other gases.
9/06