 Process Calibrators are used by technicians to measure and calibrate sensors and transmitters. Using an RTD, or 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°C and 100°C, representing freezing and boiling points 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 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 a transmitter range of 4 to 20 mA, the expected output at the low end of the temperature range of 0°C is 4 mA. At the high end of the temperature range of 100°C, the expected output of the transmitter is 20 mA. Calibration is performed by using the zero and span adjustments to tune the appropriate current value for the simulated temperature.