Temperature is a basic physical quantity, and all processes in nature are closely related to temperature. The temperature sensor is the earliest and most widely used type of sensor. The market share of temperature sensors exceeds that of other sensors. From the beginning of the 17th century, people began to use temperature for measurement. With the support of semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors and integrated temperature sensors have been developed in succession. Correspondingly, acoustic temperature sensors, infrared sensors and microwave sensors have been developed in succession according to the laws of interaction between waves and matter.
According to the contact method, it can be divided into 2 categories:
1, contact type temperature sensor
2, non-contact temperature sensor
Contact temperature sensor features: The sensor is directly in contact with the measured object for temperature measurement. Because the heat of the measured object is transmitted to the sensor, the temperature of the measured object is reduced. Especially when the measured object has a small thermal capacity, the measurement accuracy is low. Therefore, the precondition for measuring the true temperature of the object in this way is that the heat capacity of the measured object is large enough.
The non-contact temperature sensor mainly uses the heat radiation of the measured object to emit infrared rays, thereby measuring the temperature of the object and performing remote measurement. Its manufacturing cost is high and measurement accuracy is low. The advantages are: no heat is absorbed from the measured object; it does not interfere with the temperature field of the measured object; continuous measurement does not produce consumption; and the reaction is fast.
In addition, there are microwave temperature sensor, noise temperature sensor, temperature chart temperature sensor, heat flow meter, jet thermometer, nuclear magnetic resonance thermometer, Mosbauer effect thermometer, Josephson effect measurement Thermometer, low temperature superconducting conversion thermometer, optical fiber temperature sensor, etc. Some of these temperature sensors have been applied, and some are still under development.
(A) Contact temperature sensor
1 commonly used thermal resistance
Range: -260 to +850°C; Accuracy: 0.001°C. After the improvement, it can work continuously for 2000h, the failure rate is less than 1%, and the service period is 10 years.
2. Tube cable thermal resistance Temperature measurement range is -20 ~ +500 °C, the maximum upper limit is 1000 °C, accuracy is 0.5.
3. Ceramic thermal resistance The measurement range is –200 to +500°C with an accuracy of 0.3 and 0.15.
4. Ultra-low temperature thermal resistance Two types of carbon resistors can measure temperatures of –268.8 to 253°C to 272.9 to 272.99°C, respectively.
5. Thermistor Suitable for use in high sensitivity and small temperature measurement applications. Economical and cheap.
(B) Non-contact temperature sensing
l. Radiation pyrometer Used to measure temperatures above 1000°C. Four types: optical pyrometers, colorimetric pyrometers, radiant pyrometers, and electro-optical pyrometers.
2. Spectrometer pyrometer The YCI-I automatic temperature measurement universal spectrometer developed by the former Soviet Union has a measuring range of 400-6000°C. It uses an electronic automatic tracking system to ensure that there is sufficient accuracy for automatic measurement.
3. Ultrasonic temperature sensor Features fast response (about 10ms or so), strong directionality. At present, there are products that can measure up to 5000°F in foreign countries.
4. Laser temperature sensor Suitable for temperature measurement in remote and special environments. For example, NBS uses a helium-neon laser as a light reflectometer to measure very high temperatures with an accuracy of 1%. The Massachusetts Institute of Technology is developing a laser thermometer with a maximum temperature of 8000°C that is dedicated to nuclear fusion research. The Browa Borer Research Center in Switzerland uses a laser temperature sensor to measure high temperatures of several thousand K.