Things to consider with infrared thermometers
1. Determine the temperature measurement range
Determine the temperature range: temperature range is a thermometer * an important performance indicator. Such as TI210 products cover the range of -20 ℃ - +1200 ℃, but this can not be completed by a model of infrared thermometer. Each model of pyrometer has its own specific temperature measurement range. Therefore, the user's measured temperature range must be considered accurately and thoroughly, neither too narrow nor too wide. According to the blackbody radiation law, in the short wavelength band of the spectrum by the temperature caused by the change in radiant energy will be more than by the emission rate error caused by the radiant energy of the
Rate error caused by the change in radiant energy, therefore, temperature measurement should try to choose the better short-wave. Generally speaking, the narrower the temperature measurement range, the higher the resolution of the output signal to monitor the temperature, and the accuracy and reliability can be easily solved. Temperature measurement range is too wide, it will reduce the accuracy of temperature measurement. For example, if the measured target temperature is 1000 degrees Celsius, first determine whether the online or portable, if portable. There are many models that meet this temperature, such as TI130, TI120, TI200, etc. If the measurement accuracy is the main thing, * good choice of TI200 model.
2. Determine the target size
Infrared thermometer according to the principle can be divided into monochrome pyrometer and two-colour pyrometer (radiation colorimetric pyrometer). For single-colour pyrometer, temperature measurement, the measured target area should be filled with pyrometer field of view. It is recommended that the target size exceeds 50% of the field of view size. If the target size is smaller than the field of view, the background radiant energy will enter the pyrometer's visual acoustic signature and interfere with the temperature reading, resulting in an error. Conversely, if the target is larger than the pyrometer's field of view, the pyrometer will not be affected by the background outside the measurement area. In the case of a colorimetric pyrometer, the temperature is determined by the ratio of the radiant energy in two separate wavelength bands. Therefore, when the measured target is small and does not fill the field of view, the presence of smoke, dust, obstruction on the measurement path, attenuation of the radiant energy, are not significant impact on the measurement results. For small and in motion or vibration of the target, the colourimetric thermometer is * the best choice. This is due to the small diameter of the light, flexible, can be bent, blocked and folded channel transmission of optical radiation energy.
3. Determination of the distance coefficient (optical resolution)
Distance coefficient is determined by the ratio of D: S, that is, the pyrometer probe to the target between the distance D and the diameter of the target to be measured ratio. If the pyrometer due to environmental conditions must be installed away from the target, but also to measure small targets, you should choose a high optical resolution of the pyrometer. The higher the optical resolution, i.e. increasing the D:S ratio, the higher the cost of the pyrometer. Times infrared thermometers with D:S range from 8:1 (low distance factor) to higher than 80:1 (high distance factor). If the pyrometer is far away from the target and the target is small, a pyrometer with a high distance factor should be selected. For fixed focal length pyrometers, the spot is *smaller* at the focal point of the optical system, and the spot increases both nearer and further away from the focal point. There are two distance coefficients. Therefore, in order to be able to accurately measure temperature at distances near and far from the focal point, the size of the target to be measured should be larger than the spot size at the focal point, and the zoom pyrometer has a *smaller focal point position, which can be adjusted according to the distance to the target. Increase D: S, the received energy is reduced, such as not increasing the receiving calibre, the distance coefficient D: S is difficult to make large, which should increase the cost of the instrument.
4. Determine the wavelength range
Target material emissivity and surface properties determine the spectral corresponding wavelength of the pyrometer For high reflectivity alloy materials, there are low or changing emissivity. In the high-temperature region, the measurement of metal materials, * the best wavelength is near infrared, can be selected 0.8 ~ 1.0 μm. Other temperature zones can be selected 1.6 μm, 2.2 μm and 3.9 μm. Due to some materials at a certain wavelength is transparent, infrared energy will penetrate these materials, the material should be selected for this special wavelength. Such as measuring the internal temperature of the glass selected 1.0μm, 2.2μm and 3.9μm (the measured glass should be very thick, otherwise it will pass through) wavelength; measuring the surface temperature of the glass selection of 5.0μm; measurement of low-temperature zone selection of 8 ~ 14μm is appropriate. Such as the measurement of polyethylene plastic film selection of 3.43μm, polyester class selection of 4.3μm or 7.9μm, the thickness of more than 0.4mm selection of 8-14μm. such as the measurement of CO in the flame with a narrow band of 4.64μm, the measurement of NO2 in the flame with a 4.47μm.
5. Determine the response time
Response time indicates that the infrared thermometer on the measured temperature changes in response speed, defined as the last reading to reach 95% of the energy required by the time, it is with the photoelectric detector, signal processing circuits and display system time constants. Times new infrared thermometer response time of up to 200ms. this is much faster than contact temperature measurement methods. If the target's movement speed is very fast or measure the target of rapid heating, to choose fast response infrared thermometer, otherwise it can not reach enough signal response, will reduce the measurement accuracy. However, not all applications require a fast response infrared thermometer. For stationary or target thermal processes there is thermal inertia, the response time of the pyrometer can relax the requirements.
Therefore, the choice of the response time of the infrared thermometer should be adapted to the situation of the target to be measured. Determine the response time, mainly based on the target's speed of movement and the target's temperature change rate.
For stationary targets or targets involved in thermal inertia, or the speed of existing control equipment is limited, the response time of the pyrometer can relax the requirements.
6. Signal processing capabilities
In view of the discrete process (such as parts production) and continuous process is different, so the requirements of the infrared thermometer has a multi-signal processing capabilities (such as peak hold, valley hold, average) can be selected, such as temperature measurement conveyor belt on the bottle, it is necessary to use the peak hold, and the temperature of the output signal transmitted to the controller. Otherwise the pyrometer reads out the lower temperature value between bottles. If the peak hold, set the thermometer response time is slightly longer than the time interval between bottles, so that at least one bottle is always in the measurement.
