What are the sources of error that affects smart transmitters?


1.Absolute accuracy…No instrument is perfectly accurate.Typically an error of 0.05% to 1% or worse,depending on on instrument type

2.Error due to change in ambient temperature.This can be significant source of error.Typically an error of 0.005% to 0.1% of span degree C,depending on instrument type.

3.Error due to time.Electronic component age and over time,the transmitter accuracy will change.Some transmitters “self calibrate”,using built in stable signal reference that is typically measured every few seconds.but even these transmitters will eventually drift and become less accurate over time.

4.Cold junction compensation error.This can be significant source of error.

5.Error due to lead wire resistance (3 and 4 wire RTD)

  1. Hysteresis, (dead band) .This error is usually most significant in instruments that use a mechanical transducer.Calibration does not eliminate this error.

7.Analog to digital converter resolution.Usually not a significant source of error but input “step” change become noticeable in some transmitters when measuring an extremely small input span.Calibration does not eliminate this error.

8.Error due to EMI (electromagnetic interface) .High level of electrical noise can affect analog measurement,especially low level signals like thermocouples.Calibration usually wont help,it is best to separate the measurement point from the source of noise.