**Abstract**

There are three main types of temperature sensors: thermometers, resistance temperature detectors and thermocouples. These sensors measure a physical property that changes as a function of temperature, and temperature sensors are classified into contact and non-contact sensors. Contact sensors detect the degree of hotness or coldness of an object when placed in direct contact with the object. It can be used to sense the degree of hotness or coldness in liquids, solids or gases in a wide range of temperatures. Contact temperature sensors include thermometers, thermocouples and thermistors. A thermometer detects the body temperature of human beings, and a thermocouple is a thermoelectrical thermometer that works on the principle of the Seebeck effect; they are cheap; hence, their model and basic materials are easy to get, and non-contact sensors are not placed in contact with the object that it measures; however, they measure the temperature by utilizing the radiation of the heat source. IR sensors detect the energy of an object remotely and emit a sign to an electronic circuit that senses the object's temperature by a specific calibration diagram. Other types of temperature sensors are available and produced based on the working principle, size, temperature range and their function and application.

**Keywords:** sensors, temperature, thermometer, thermistor, non-contact type sensor, contact type sensor
