Honeywell Searchline Excel Technical Handbook page 64

MAN0530 Issue 10 - 11/09
2104M0506
Fault/Problem
No signal or
very low signal
at Receiver
Unit does not
respond exactly
as expected to
Unit appears to
be reporting a
negative gas
reading on the
4-20mA
5. PROBLEM SOLVING
Causes
Receiver misaligned
Transmitter misaligned
The beam path has become
obscured
No output from Transmitter
Plastic test filters are only
an approximate simulation of gas real gas. This results in a variation of the
filters is within the limits stated in this
Receiver misaligned
Contamination of windows
Drift of unit's zero position
Misinterpretation of iNhibit,
beam-bloCK or loW
siGNalcurrents that are
output on the 4-20mA
Remedies
Re-align the Receiver, first using the
telescope and then using the Interrogator.
Re-align the Transmitter using the telescope.
Check that the beam path is clear from
Transmitter to Receiver.
Remove any obstruction if present.
1) Check that the Transmitter is flashing.
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
response test filters of different Excel
units to plastic test filters. See section
5.1.2.
1) Check that the response to the test
handbook. See section 5.1.2.
2) Check that the value being used for
response testing corresponds correctly to the
target gas that the unit has been calibrated for.
1) Use the telescope and Interrogator to
optimise Receiver alignment.
2) Re-zero unit.
1) Check the Transmitter and Receiver
windows for build up of contamination.
Clean windows if required. See Chapter 5.
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
INHIBIT
BEAM-BLOCK
LOW SIGNAL
or,
3) Reconfigure the INHIBIT, BEAM-BLOCK
and LOW SIGNAL currents output by the
Excel unit.
64
Searchline Excel
0mA
2mA
2.5mA*
3mA*