Honeywell Searchline Excel Cross-Duct Technical Handbook page 40

MAN0889_Issue 3_03/13
The beam path has become
obscured
No signal or very
low signal at
Receiver
No output from Transmitter
Plastic test filters are only an
approximate simulation of gas
Unit does not
respond exactly
as expected to
test filters
Contamination of windows
Drift of unit's zero position
Unit appears to
Misinterpretation of
be reporting a
BEAM-BLOCK
negative gas
currents that are output on the
reading on the
4-20mA
4-20mA
Contamination of windows
Diagnostics
report
Neg Gas
Reading
Negative drift of unit's zero
position
Diagnostics
Contamination of windows
report
Baseline
Drift
Drift of unit's baseline
5. Problem Solving
,
INHIBIT
or
LOW SIGNAL
Searchline Excel Cross-Duct Technical Handbook
Check that the beam path is clear from Transmitter and Receiver
to the Reflector Panel. Remove any obstruction if present.
1) Check that the Transmitter is flashing. When viewed on the
axis, an orange flash can be seen coming from the Transmitter.
Alternatively, listen for a distinct ticking sound when the lamp
flashes.
Note: The infrared beam is invisible and eye safe.
2) If the Transmitter is not flashing, check that the +24V supply is
reaching the Transmitter correctly.
Searchline Excel units are calibrated on real gas. This results in
a variation of the response of different Excel units to plastic test
filters. See section 3.6.6
1) Check that the response to the test filters is within the limits
stated in this handbook compared to the response obtained at
initial installation. See section 4.3.2
2) Check that the correct test filter is being used.
1) Check the Transmitter and Receiver and Heated Reflector
Panel windows for build up of contamination. Clean windows if
required. See Chapter 4.
2) Re-zero unit.
1) Verify that there is no gas in the beam path.
2) Re-zero the unit
Searchline Excel does not report negative gas readings on the
4-20mA.
1) Configure controller/PLC to interpret and present currents
below 4mA correctly, or
2) Familiarise operators with the interpretation of sub 4mA output
currents from Excel as follows:
FAULT 0mA
INHIBIT
2mA
BEAM-BLOCK 2.5mA
LOW SIGNAL
3mA, or
3) Reconfigure the INHIBIT, BEAM-BLOCK and LOW SIGNAL
currents output by the Excel unit.
1) Check the Transmitter and Receiver and Heated Reflector
Panel windows for build up of contamination. Clean windows if
required. See Chapter 4.
2) Re-zero the unit.
Re-zero the unit
1) Check the Transmitter and Receiver and Heated Reflector
Panel windows for build up of contamination. Clean windows if
required. See Chapter 4.
2) Re-zero the unit.
Re-zero the unit
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