Simtronics GD10-P00 Operating Manual page 22

the product, as the zero point and calibration will stay inside the given tolerances.
This implies that slight offsets from the zero point of 4.0mA (0%LEL) is to be
expected and values up to 4.5mA at room temperature are within specification.
In some environments with excessive heat and/or vibration we have noticed that a
higher percentage of the detectors develop an offset outside the specified
tolerances. These detectors should normally be returned to the factory for service.
An alternative is to do this re-zeroing on site with a dedicated hand held terminal,
or HART® communicator.
Note that "on site" does not mean "in service". Before concluding that re-
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zero is necessary, proper cleaning of the detector should be done (even
an invisible layer of oil on the lens or mirror can have negative impact on
the zero-point reading). Then, before re-zeroing is conducted, the
detector should be removed from the system and moved to a controlled
environment in a workshop.
6.4.1. Test of zero-point in the workshop
Prior to conducting a re-zero, a controlled checking of the zero level should be done
with a sample flow housing and nitrogen test gas (clean instrument air may be used
if nitrogen is unavailable).
1) Clean the sensor optics again, both mirror and lens.
2) Attach a Sample Flow housing.
3) Connect the power supply and HART® terminal (according to section 0) or a
Hand Held terminal according to its separate operating manual.
4) Switch on power and wait approx. 2 minutes until the output has stabilized.
5) Apply nitrogen gas to the Sample Flow housing.
6) Read current loop output.
7) If output is outside specification, then a re-zero may be applicable.
6.4.2. Re-zeroing with HART® communicator
See section 5.2.4.10.
6.4.3. Re-zeroing with Hand Held Terminal
Refer to the user guide of the Hand Held Terminal (850-816611).
GD10P Page 22 of 32 850-811250-R05