Midas
®
Gas Detector
17-4
maintenance fault indications on the 4-20 mA loop,
relays or digital outputs. Before starting a test, ensure
that suitable steps have been taken to prevent these
indications from triggering unwanted actions. The
Midas
®
gas detector has a special mode for bump
testing where the alarm outputs are inhibited (see
Section 7.4.1).
See Tech Note 1998-0219
Protocol for Testing Toxic
Gas Detectors
for additional information. The NF
3
pyrolyzer should be tested in the same way as an
extractive system, but using NF
3
as the test gas.
If NF
3
is not available, chlorine can be used at a
concentration of 5 ppm. If using chlorine, the Freon
filter must be removed from the unit before the test
and replaced after the test.
For the PFC High-Temperature pyrolyzer, chlorine can
also be used as a suitable bump test gas.
Note
A test with chlorine operates the
electrochemical cell and the unit’s
electronics, but does not test the pyrolyzer
module itself.
Note
The electrochemical CO
2
cell (MIDAS-S/E-
CO2) is not designed for use in applications
that are oxygen decient (<15% O
2
).
Calibrations should always be carried out in
CO
2
balanced with air.
Finishing
Wait for the gas reading to return to normal levels.
This may take some time, especially if concentrations
above the recommended levels have been used or if
the test gas has been applied for an extended period
of time.
Ensure that any latched faults or alarms that have
been generated by the testing have been cleared.
Make sure that the gas detection system is fully
restored to its normal operating state and that any
control system overrides used during the testing have
been removed.
The alarms generated by the testing will have created
entries in the transmitter’s history log.
Troubleshooting
If the test does not produce a satisfactory result,
check the following points:
1. Check the gas cylinder concentration and type
are correct
2. Check the expiration date of the cylinder.
3. Check that there is sufficient gas left in the
cylinder.
4. Check that there are no leaks on the test
system.
5. Make sure that the tubing length is as short as
possible and that there are no blockages.
6. Make sure that the transmitter is not displaying
a fault before the test is started.
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