Characteristics and development trend of temperature measurement technology?

A temperature sensor refers to a sensor that can sense temperature and convert it into a usable output signal. Temperature is a physical quantity closely related to human living environment, one of the three major parameters of industrial process (flow, pressure and temperature) and one of the seven basic physical quantities in the International System of Units (SI). Temperature measurement is a classic and ancient topic. For a long time, a variety of temperature measuring elements and sensors have been popularized in this field, but until today, in order to meet the extensive needs of various industrial departments, scientific research, medical care, household appliances and so on. New temperature measuring elements and sensors, new temperature measuring methods, new temperature measuring materials and new market applications are still under development. It is not easy to measure the temperature accurately, such as improper selection of temperature measuring elements and measurement methods, which can not get satisfactory results.

According to the statistics of relevant departments, the sales of sensors in China in 2009 was 32.7 billion yuan, of which temperature sensors accounted for 14% of the whole sensor market, and were mainly used in communication electronic products, household appliances, building automation, medical devices, instruments, automotive electronics and other fields.

The bimetallic thermometer TBI with sanitary clip process connection is designed for temperature measurement in sanitary applications.

(Source: Baomeng Company)

Characteristics of temperature sensor

As an ideal temperature sensor, it should have the following requirements: wide measurement range, high precision, good reliability, small time drift, light weight, fast response, low price and mass production. However, there is no temperature sensor that meets the above conditions at the same time, and all kinds of temperature sensors should be used flexibly according to the application situation. This is because different temperature sensors have different characteristics.

The measuring range and characteristics of different temperature sensors are different.

The temperature measuring range and characteristics of several important types of temperature sensors are shown in Table 1.

Table 1, temperature sensor and temperature range classification table

The accuracy of temperature measurement is related to the measurement method.

According to the use method of temperature sensor, it is usually divided into contact measurement and non-contact measurement. The characteristics of the two measurement methods are shown in Table 2.

Table 2 Comparison of temperature contact measurement and non-contact measurement

● Different temperature measuring elements should use different measuring circuits.

There are three commonly used measuring circuits. "Measuring circuit of resistance temperature measuring element" should consider eliminating the influence of nonlinear error and thermal resistance wire on measuring accuracy. The "measuring circuit of potential temperature measuring element" needs to consider linearization and cold end compensation, and the signal processing circuit is more complicated than thermal resistance. Semiconductor integrated temperature sensor is the most typical current-mode temperature measuring element. When the power supply voltage changes and the external conductor changes, the output current of the circuit is basically unaffected, which is very suitable for long-distance temperature measurement.

The latest development of temperature measurement

● Develop temperature measuring elements and sensors suitable for various industrial applications.

The thickness of platinum film temperature sensor is 1μm, which can be placed in a very small measuring space to measure the temperature field distribution. The response time is less than 1ms, the minimum diameter of thermocouple wire is 25μm, the thermocouple volume is less than 1× 10-4mm3, and the mass is less than1μ g. ..

Multicolor colorimetric temperature sensor can obtain the approximate emissivity of the measured object in real time and improve the accuracy of radiation temperature measurement.

The temperature resolution of the resonant tuning fork temperature sensor can reach 0.0009℃, the accuracy can reach 0.02℃, the measuring range can reach -200 ~ 260℃, and the linearity can reach 0. 1 ~ 0.05%.

The new temperature control device composed of Z element has the characteristics of simple circuit structure, high precision, high speed, low power consumption and low cost.

The integrated temperature sensor adopts diffused silicon technology with good consistency and sensitivity of 1 1.3/℃, which is suitable for mass production.

W-Re temperature sensor is a high temperature sensor made of W-Re thermocouple, which can detect the upper limit temperature of 2300℃ and is suitable for high temperature measurement in reducing, inert, vacuum, nuclear radiation and other environments.

Intelligent temperature sensor adopts MEMS technology, which combines typical temperature measuring elements, signal conditioning circuit and microprocessor with digital bus interface into a whole to form an intelligent temperature sensor system.

● Temperature measurement technology has developed from "wired" to "wireless".

Traditional temperature measurement usually adopts wired cable connection, but for some occasions, such as the temperature measurement of rotating or moving objects, places where people can't set foot in harsh environment and environments where wires are not suitable, with the application of intelligent temperature sensors, from the perspective of saving wiring costs, temperature measurement technology began to develop from "wired" to "wireless".

The wireless temperature measurement virtual instrument system using passive surface acoustic wave resonator introduces signal processing method and feedback control, which reduces the system cost and improves the measurement accuracy and distance. Combined with general computer platform and data I/O board, through flexible control of software, the measurement parameters can be automatically adjusted according to different environments and measurement processes to realize adaptive detection. When the transmission power is 100mW, the uncertainty of repeated measurement of resonance frequency is about 0.09kHz, and the uncertainty of temperature measurement sensitivity at 3m is about 0. 1℃.

Temperature and humidity sensor system for air conditioning. The system consists of a host and an extension. The extension regularly transmits the data measured by the built-in temperature and humidity sensor to the host computer in a wireless way. The host converts it into an electrical signal through the output unit and sends it to the control equipment. Because the extension is powered by battery, it can be placed anywhere, and the control signal is transmitted wirelessly, which is very convenient.

For the data measured by sensors installed on the site, the wireless inspection system does not need inspection personnel to go to the site for visual inspection or recording, but carries out wireless inspection of sensors in wireless transmission mode through the wireless data acquisition system. This detection system will be very convenient for the detection of dangerous places and high places.

The method of lengthening thermocouple can be used for deep temperature measurement, but it is inconvenient to use. A special deep temperature measuring device can be used, which consists of a heater, a metal frame, a thermal insulation layer and a temperature measuring element (such as a thermistor). The principle is that on the surface of the heater, the temperature gradient can be eliminated, and the surface temperature can be measured to know the deep temperature.

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