Precommissioning calibration for transmitter

What is the need for pre-commissioning calibration?

Transmitters are factory calibrated by the manufactures, even though the sensor should be trimmed before installation, because it may drift during shipment.

The same sensor is used in a device’s 4-20 mA /HART, FOUNDATION fieldbus, Wireless HART, and PROFIBUS version. They, therefore, have the same fundamental precision and stability. The present loop of 4-20 mA contributes some inaccuracy and drift, but less than the detector. Sensor trimming or not before installation doesn’t rely on the protocol, it’s how rough the sensor is.

Pre-commissioning calibration:

To correct the mounting position effect, the pressure transmitters need zero trim. This issue usually only arises for transmitters of pressure and temperature-probably because there are mobile calibrators for temperature and pressure.

There is no discussion of site calibration for gas or liquid flowmeters, and not for many other transmitters-probably because it would be much harder to do.

Loop Check:

The major commissioning distinction between 4-20 mA / HART and Fieldbus is that 4-20 mA / HART needs a five-point loop test at 4 mA, 8 mA, 12 mA, 16 mA and 20 mA to identify discrepancies in the range between the scheme and the transmitter, to guarantee that the present signal is not restricted (inadequate loop resistance voltage) or otherwise distorted owing to installation problems (floor loop) and to guarantee that the range is selected.

The range of the 4-20 mA transmitter is typically also checked. Fieldbus, PROFIBUS, or WirelessHART do not have an analog current or range so that five point loop tests do not have to be performed. This will save a lot of time. A straightforward check of plausibility is enough.


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