Temperature is the most commonly measured process variable and the precision measurement and control of temperature is crucial in many applications. Heaters and chillers generate or remove heat while thermocouples, RTDs, infrared sensors, and thermal imagers measure temperatures. Controllers allow users to maintain process temperatures through the use of PID, on-off, profile, rate of ramp or limit control action. To maintain optimal accuracy of temperature instruments, black body, dry block, liquid bath and other calibration options are available.