Answer / carl_ellis

Analog output trim is done on all process field
transmitters that do not communicate over a digital
protocol like Profibus or Foundation Fieldbus.

Modern electronics use an A/D to digitize a value from a
sensor, a microprocessor to process the value and a D/A to
output the process value as an analog signal.

Adjusting the zero and span of the D/A is commonly
called 'trim'. It trims the D/A output a small amount,
generally about ±1% at the zero and at the span
(separately), generally to match a variation or deviation
of an analog input's resistance value.

Trim is NOT setting the URV and LRV values to correspond to
process inputs, as was once done with analog electronic
transmitters.

Carl Ellis
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