Process Calibrators are used by technicians to measure and calibrate sensors and transmitters.
Using an RTD (Resistance Temperature Detector) as an example the initial step of calibration is verifying the accuracy of the temperature sensing device.To perform the measurement the process calibrator is programmed to the specific RTD type.The accuracy is determined by measuring the temperature of water at 0 deg C and 100 deg C representing freezing and boiling point of water.Connecting the RTD output to the calibrator the measured temperature is displayed using the measure function.
After the sensor accuracy is confirmed the next step is to verifying the accuracy of the transmitter using the process calibrator. The calibrator provides an input signal to the transmitter that simulates the output of the sensor at multiple measurement points.With the transmitter range of 4 to 20 ma the expected output at low end of the temperature range of 0 deg C is 4 ma.At he high end of the temperature range of 100 deg C the expected output of the transmitter output is 20 ma.
Calibration is performed by using the zero and span adjustments to till the appropriate value of the simulated temperature.
HART communicator is an example of Calibration device. How to use HART communicator