There are many types of temperature sensors available, but the most common ones for chemical processes are thermocouples, resistance temperature detectors (RTDs), thermistors, and infrared sensors. Thermocouples are made of two dissimilar metals that generate a voltage proportional to the temperature difference between their junctions. They are inexpensive, rugged, and versatile, but they have low accuracy and stability, and require a reference junction and a cold junction compensation. RTDs are made of a metal wire or film that changes its resistance with temperature. They have high accuracy and stability, but they are more expensive, fragile, and susceptible to self-heating and lead wire effects. Thermistors are made of a ceramic material that changes its resistance with temperature in a nonlinear way. They have high sensitivity and fast response time, but they have low accuracy and stability, and a limited temperature range. Infrared sensors measure the thermal radiation emitted by an object and convert it to a temperature reading. They are non-contact, fast, and immune to electromagnetic interference, but they have low accuracy and stability, and are affected by ambient temperature, emissivity, and distance.