Honeywell 7866 Operation And Maintenance Manual page 81

Symptom
3. Insufficient span with
"span" gas flowing
and SPAN
ADJUSTER turned
fully clockwise.
4. Slow response.
5. Noisy output signal or
electrical interference.
9/06 7866 Triple Range Digital H
Possible Cause
3a. Faulty current regulator for
detector bridge.
3b. Faulty sensing-unit amplifier.
3c. Damaged measuring
detector.
4a. Low flow rate.
4b. Sample lines too long; filter
volumes too large, etc. for
flow rate.
4c. Measuring detector or cell
block is dirty.
5a. Lack of earth ground
5b. Power line not grounded
correctly.
5c. Flow rate too high
5d. Cracked or dirty measuring
detector.
5e. Faulty detector bridge-current
regulator.
and CO Analyzer/Indicator - Operation and Maintenance
2 2
Recommended Checks
3a. Check for 3.75 volts ± 0.4 volts between pin E
and terminal 13. (This is equivalent to
checking bridge current for 55 mA ± 5 mA.)
3b. Disconnect the lead at terminal 12 in the
sensing unit and connect a 0-1 mA current
meter across terminals 12 (+) and 13 (–).
Refer to Table 8-2 and increase the coarse-
zero binary count (on the coarse-zero jumper
pattern described in the Course Zero
Adjustment procedure) by one number.
Current flow should increase about 250 uA.
This verifies that gain is normal.*
3c. Connect a millivolt meter across circuit points
A and D (at center of round card). Make the
zero adjustment in accordance with the Re-
calibration procedure. Pass a span-gas
mixture equivalent to a full-scale
measurement through the sensing unit. The
meter reading for 1% H
mV.** If it is less, the detectors must be
cleaned or replaced.
4a. Increase flow rate to 2000 cc/min. for
maximum speed or response.
4b. Increase flow rate above 2000 cc/min.,
venting excess flow above 2000 cc/min. with
a by-pass valve upstream of the analyzer.
4c. Remove detectors and check for flow
between inlet and cell before remounting the
detectors.
5a. Check that ground wire is connected to
ground terminal and that controller case is
connected to ground terminal.
5b. Check that terminal L2/N is connected to the
neutral or grounded side of power line. If one
side of line is not grounded, install an isolation
transformer and ground terminal L2/N.
5c. Check that flow does not exceed 2000
cc/min.***
5d. Remove measuring detector, inspect for
cracks in glass or loose dirt in cell.
5e. Replace sensing-unit printed circuit card
assembly.****
Troubleshooting
should be at least 10
2
71