GasTech D-Guard2, Operator'S Manual

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D-Guard
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12.6. Dynamic Response Time Test Function
The Dynamic Response Time (DRT) test function allow the operator to perform a check on the actual gas measurement
response time for the detector. Unlike a 'static' calibration where the adjustments are made to bring the readings to
an expected steady state calibrated value, DRT dynamically checks the time taken for the gas reading to reach both 50%
and 90% of the applied gas value.
This check should be carried out when the detector is new (e.g. after initial detector installation).
Once an initial test is carried out, the detector calculates the pass/fail limits and stores them for reference for future
tests. User DRT checks use these stored values to compare against.
Reading response time can slow down if waterproof membranes become clogged or sensors become old and
unresponsive.
Dynamic Response Time Test Screen 12.6.1 Running the DRT Checks
The DRT main screen displays entries for T50 and T90
response times. Until gas is applied, these values are blanks
and the detector waits for gas to be applied to trigger the start
of the checks.
The target timing values are shown in the upper status
banner. Once test gas is applied, the test begins automatically. A
message indicating the test is running is displayed.
Note: it is
absolutely essential to use the same span gas concentration
each time this test is carried out.
This gas concentration must
be set in the user calibration gas setup menu (see section
12.1.4). If the same gas concentration is not used for each
test, the results will not reflect a proper comparison against
the stored reference timings.
Test Completed - All Passed Test Completed - Failures
Once the measured gas concentration reaches 90% of the
applied gas, the test will complete and the results displayed.
If both timings for T50 and T90 lie within the reference values,
then the test is considered passed. Results are stored in the
detectors non-volatile memory. It is possible for one of the tests to fail if the sensors response
is no longer close to the typical exponential type curve that
gas sensors exhibit. Old sensors can be very slow to respond
making it possible for the T50 to fail but the T90 to pass. Of
course a very slow, old sensor or badly blocked waterproof
membrane could cause both tests to fail.
Note: - DRT function does not operate for Infra-Red type sensors