TABLE OF CONTENTS Temperature may be measured with the basic thermometer to the more advanced nuclear temperature measurement. In most cases, the temperature element voltage or resistance has to be amplified and converted to a current for process measurement. The actual temperature, the accuracy, the application, and the speed of response will be the determining reason on what type of temperature measurement is used.
Temperature measurement is not always what is expected. Although the sensing element can be accurate to within a tenth of a degree, the measurement of a gas or liquid temperature may be off by many degrees. The mounting and location of a temperature sensor is extremely important. If a temperature reading does not agree with a calculated temperature or simply does not agree with other temperature sensors in a system, the following should be considered: check the calibration of the transmitter. If the transmitter uses a filled temperature bulb, check actual sensor calibration with a field "dry block" calibration device or a liquid bath. If the sensor is an RTD or thermocouple, first check the output of the transmitter by using a temperature simulator/calibrator, and remember to correct for the reference junction compensation if the device is not automatically compensated. If the loop calibration is still incorrect, check the actual sensor with a field "dry block" calibration device.
If the results of this calibration do not provide a correct reading, consider the following suggestions:
Is the sensor compatible with the process? Some thermocouples deteriorate in oxidizing...
