Principles of Infrared Thermometers and Problems in Application
The basic principle of infrared temperature measurement
The infrared thermometer is based on the infrared radiation characteristics of the object, relying on its internal optical system to gather the infrared radiation energy of the object to the detector (sensor), and convert it into an electrical signal, and then pass through the amplification circuit, compensation circuit and linear processing, in the The display terminal displays the temperature of the measured object. The system consists of optical system, photodetector, signal amplifier, signal processing, display output and other parts. Its core is an infrared detector, which converts incident radiant energy into measurable electrical signals.
How to Improve the Accuracy of Infrared Thermometer
A typical high-temperature furnace for producing graphite fibers has a maximum furnace temperature of 3000°C, and the process requires an oxygen-free atmosphere with a slightly positive pressure inside. Infrared thermometers are successfully applied with unique advantages
It is used to measure the temperature of the furnace and cooperate with the PLC system to realize automatic control. However, in order to ensure the accuracy of temperature measurement, some problems should be paid attention to in the selection and use of infrared thermometers.
Determine the temperature range of the infrared thermometer
The temperature measurement range is the most important performance index of the infrared thermometer. For example, the temperature measurement range of Optris (Opris) products covers 250-3300°C, but this cannot be done by one type of infrared thermometer, each type of infrared thermometer has its own specific temperature measurement range. Therefore, the user must consider the temperature range to be measured accurately and comprehensively, neither too narrow nor too wide. According to the law of black body radiation, in the short wavelength band of the spectrum, the change of radiation energy caused by temperature will exceed that caused by emission.
The change of radiant energy caused by rate error, therefore, it is better to choose short wave when measuring temperature. Generally speaking, the narrower the temperature measurement range, the higher the resolution of the output signal of the monitoring temperature, the higher the accuracy, and the more accurate the temperature measurement. If the temperature measurement range is too wide, the temperature measurement accuracy will be reduced and the error will be large.
Determining the Response Time of an Infrared Thermometer
Response time indicates the reaction speed of the infrared thermometer to the measured temperature change, defined as the time required to reach 95% of the energy of the final reading, and it is related to the time constant of the photodetector, signal processing circuit and display output system. Determining the response time is mainly based on the moving speed of the target and the temperature change speed of the target. If the moving speed or heating speed of the target is very fast, a fast-response infrared thermometer should be selected; for static or target thermal processes with thermal inertia, the response time requirements of the thermometer can be relaxed.
