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MAN0530 Issue 09 October 03
2104M0506
Fault/Problem
Causes
No signal or
Receiver misaligned
very low signal
at Receiver
Transmitter misaligned
The beam path has become
obscured
No output from Transmitter
Unit does not
Plastic test filters are only an Searchline Excel units are calibrated on real gas.
respond exactly approximate simulation of
as expected to
gas
test filters
Receiver misaligned
Contamination of windows
Drift of unit's zero position
Unit appears to
Misinterpretation of INHIBIT, Searchline Excel does not report negative gas readings on
be reporting a
BEAM-BLOCK or LOW
negative gas
SIGNALcurrents that are
reading on the
output on the 4-20mA
4-20mA
6. PROBLEM SOLVING
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. 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.
This results in a variation of the response of different Excel
units to plastic test filters. See section 5.1.2.
1)
Check that the response to the test filters is within the
limits stated in this 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.
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.
80
Searchline Excel
0mA
2mA
2.5mA*
3mA*
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