Some Questions about Infrared Thermometer
How to choose a suitable thermometer
1 Determine the temperature measurement range
The temperature measurement range is the most important performance index of the thermometer, and each type of thermometer has its own specific temperature measurement range. Generally speaking, the narrower the temperature measurement range, the higher the resolution and accuracy of the output signal for monitoring temperature. If the temperature measurement range is too wide, the temperature measurement accuracy will be reduced. Therefore, the user should select a thermometer with a suitable measurement range according to the specific operating temperature.
2 Determine the emissivity of the object under test
At the same temperature, the ratio of the radiation output of the actual object to the black body can represent a physical characteristic of the object, and this ratio is called the emissivity of the actual object. Emissivity reflects the thermal radiation properties of a material. According to the law of radiation, as long as the emissivity of the material is known, the infrared radiation characteristics of the object can be known.
The emissivity is used to compensate the influence of different objects on the measured temperature due to different emissivity.
3 Determining the response time
The response time indicates the reaction speed of the infrared thermometer to the change of the measured temperature. The choice of the response time of the infrared thermometer should be adapted to the situation of the target to be measured. If the target is dynamic, the response time is generally shorter.
4 Determining the distance factor (optical resolution)
The distance factor is determined by the ratio of D:S, which is the ratio of the distance D between the infrared thermometer probe to the target and the diameter of the measured target. If the infrared thermometer must be installed far away from the target due to environmental conditions, and to measure small targets, a high optical resolution thermometer should be selected. The higher the optical resolution and the larger the D:S ratio, the more expensive the pyrometer will be. For a thermometer with a fixed focal length, the minimum position of the focal spot of the optical system, the focus position near and far from the scene, will increase the existence of two distance coefficients. Therefore, in order to focus on near and far distances and measure temperature accurately, the size of the target to be measured should be larger than the spot size at the focal point.
Some Factors Affecting Calibration
1 working distance
The working distance refers to the distance between the mirror surface of the thermometer and the bottom surface of the black body cavity. Daily experiments show that different working distances will have a significant impact on the calibration indication of the thermometer.
2 ambient temperature
Ambient temperature change is the main factor affecting the short-term stability of the thermometer, and it is also a source of error in the calibration of the thermometer. It is more appropriate for the calibration laboratory to be at (20±3)°C.
3 aiming
Many infrared thermometers do not have a special focusing device, usually a laser red dot to aim at the blackbody cavity, and there is no uniform standard for it. The aiming error mainly comes from two aspects: one is the inhomogeneity of the bottom surface temperature of the blackbody cavity; the other is the problem of the aiming method itself.
