Selection method and principle of infrared temperature sensor

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Selection method and principle of infrared temperature sensor [Copy link]

I. Selection method

1. Working conditions and use environment

(1) Working conditions of infrared temperature sensors. Ambient temperature, window, display and output, protective accessories, etc. are all issues that need to be considered when purchasing. These are closely related to the maintenance and repair of the instrument.

(2) The infrared temperature measurement range is from dozens of degrees below zero to more than 3000 degrees. Such a wide temperature measurement range cannot be completed by one infrared temperature sensor. Each type of sensor has its own specific temperature measurement range. Generally speaking, the wider the measurement temperature range, the better. The narrower the temperature range, the higher the resolution of the output signal of the monitored temperature, and the easier it is to solve the problem of accuracy and reliability. If the temperature measurement range is too wide, the temperature measurement accuracy will be reduced. Therefore, the measurement range is also one of the selection principles of infrared temperature sensors. When selecting a temperature sensor, it should be based on the actual temperature measurement requirements on site, and the measurement range should not be too wide or too narrow. (3) The environment in which the sensor is used also determines which infrared temperature sensor you choose. 2. Target size and distance coefficient The optical resolution is determined by the ratio of D to S, which is the ratio of the distance D between the sensor and the target to the diameter S of the measuring light spot. If the sensor must be installed far away from the target due to environmental conditions, and a small target needs to be measured, a sensor with high optical resolution should be selected. The higher the optical resolution, that is, the larger the D:S ratio, the higher the cost of the thermometer. If the sensor is far away from the target and the target is small, a sensor with a high distance coefficient should be selected. 3. Response time refers to the speed at which the infrared temperature sensor reacts to changes in the measured temperature. It is defined as the time required to reach 95% of the energy of the final reading. It is related to the time constant of the photoelectric detector, signal processing circuit and display system. The response time of the new infrared temperature sensor can reach 1ms. This is much faster than the contact temperature measurement method. If the target moves very fast or measures a target that heats up quickly, a fast response sensor should be used. Infrared temperature sensors should be used, otherwise sufficient signal response will not be achieved, which will reduce measurement accuracy.

However, not all applications require fast-response infrared temperature sensors. For stationary or target thermal processes with thermal inertia, the response time requirements of the thermometer can be relaxed. Therefore, the choice of infrared temperature sensor response time should be adapted to the conditions of the target being measured.

4.Signal processing function

Measuring discrete processes (such as parts production) is different from continuous processes, requiring infrared temperature sensors to have signal processing functions (such as peak hold, valley hold, average value). For example, when measuring the temperature of glass on a conveyor belt, peak hold must be used, and the output signal of the temperature is transmitted to the controller.

2. Working Principle

1. Infrared ray

Infrared ray is a kind of light that is invisible to human eyes, but in fact, it is an objective substance like any other light. As long as the temperature of any object is higher than thermodynamic zero, infrared ray will radiate to the surrounding. Infrared ray is located at [u rl=https://baike.baidu.com/item/%E5%8F%AF%E8%A7%81%E5%85%89/1241853]The light other than red light in visible light[/url] is called infrared light. Its wavelength range is roughly within the spectrum range of 0.75~100μm.

2. Infrared radiation

The physical nature of infrared radiation is [ Thermal radiation. The higher the temperature of an object, the more infrared rays it radiates, and the stronger the energy of the infrared radiation. Studies have found that various solar spectra can be divided into two categories: The thermal effect of monochromatic light gradually increases from purple light to red light, and the largest thermal effect occurs within the frequency range of infrared radiation, so people also call infrared radiation thermal radiation or heat rays.

3. Sensing principle

Thermal sensors use the radiation thermal effect to cause the temperature to rise after the detection device receives radiation energy, thereby changing the performance of a column in the sensor related to the temperature. By detecting the change of one of the properties, radiation can be detected. In most cases, radiation is detected through the Seebeck effect. When the device receives radiation, it causes a physical change in a non-electrical quantity, which can also be measured after being converted into an electrical quantity through appropriate changes.

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