What is a thermostat?
Temperature controllers have a variety of names, such as temperature control switches, temperature protectors and temperature controllers. According to the working principle, it can be divided into jump type thermostat, liquid type thermostat, pressure type thermostat and electronic type thermostat. In modern industrial control equipment, digital thermostat is the most commonly used type. According to the structure, the temperature controller can be divided into integrated temperature controller and modular temperature controller.
What are the thermometers?
The temperature measuring body is a component that converts the temperature signal into an electrical signal, and is usually installed in the detection part of the controlled object to monitor its temperature value. In the field of industrial control, commonly used thermometers include thermocouples, thermal resistors, thermistors and non-contact sensors. Among them, the first three are contact thermometers.
1. Thermocouple
The principle of temperature measurement for thermocouples is based on the Seebeck effect (thermoelectric effect). When two metals of different materials (usually conductors or semiconductors, such as platinum-rhodium, nickel-chromium-nickel-silicon and other materials paired) form a closed loop and apply different temperatures to their two connecting ends, an electromotive force is generated between the two metals. Such a loop is called a "thermocouple," while the two metals are called a "thermal electrode," and the resulting electromotive force is called a "thermoelectric motive force." Thermocouples are characterized by their wide measuring temperature range, fast thermal response, and strong vibration resistance.
2. Thermal resistance
Thermal resistance is a component that converts a temperature signal into an electrical signal, and its working principle is mainly based on the characteristics of metal resistance changes with temperature. Specifically, thermal resistors take advantage of this property of the metal to measure temperature.
In industrial control, the commonly used types of thermal resistance include platinum, copper and nickel. Among them, platinum resistance is the most common one. The thermal resistance has the characteristics of good temperature linearity, stable performance and high precision in the field of normal temperature. Therefore, in the application environment of moderate temperature, no vibration and high precision requirements, the use of platinum resistance is usually preferred.
3. Thermistor
A thermistor is a component that converts a temperature signal into an electrical signal, and its working principle is mainly based on the characteristics of a semiconductor's resistance changing with temperature. Specifically, thermistors take advantage of this property of semiconductors to measure temperature. Compared with the thermal resistance, the resistance of the thermistor changes greatly with the change of temperature, so its temperature measurement range is relatively narrow (-50~350℃).
Thermistors are divided into NTC thermistors and PTC thermistors. NTC thermistors have a negative temperature coefficient, and their resistance value decreases as the temperature increases. PTC thermistor has a positive temperature coefficient, and its resistance value will increase with the increase of temperature. Because of its unique resistance temperature characteristics, thermistor has a wide range of applications in temperature detection, automatic control, electronic devices and other fields.
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