Research on the wrong method of self-calibration error of infrared thermometer gun
With the development of modern technology, infrared thermometers are widely used in power line inspection, maintenance and substation operation work to detect temperature abnormalities in power equipment, distribution equipment, cables, electrical joints, etc. under operating and live conditions, and find that Defects in electrical equipment. Whether the infrared thermometer in use is in good working condition directly affects the stable operation of the power grid. In order to improve work quality and ensure safety, self-calibration of infrared thermometers must be carried out to ensure that the running infrared thermometers are in good working condition.
1 Principles of blackbody radiation and infrared temperature measurement
All objects with a temperature above zero are constantly emitting infrared radiation energy into the surrounding space. The size of the infrared radiation energy of an object and its distribution by wavelength are closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, the optical system of the thermometer is converted into electrical energy on the detector. The signal and the display part of the infrared thermometer display the surface temperature of the object being measured, and its surface temperature can be accurately measured. This is the objective basis on which infrared radiation temperature measurement is based.
Features of infrared thermometer: non-contact measurement, wide temperature measurement range, fast response speed, and high sensitivity. However, due to the emissivity of the measured object, it is almost impossible to measure the true temperature of the measured object. What is measured is the surface. temperature.
The standardized calibration method for infrared thermometers is to use blackbody furnace calibration. A black body refers to an object whose absorption rate of incident radiation of all wavelengths is equal to 1 under any circumstances. A black body is an idealized object model, so a radiation coefficient, that is, the emissivity, is introduced that changes with the material properties and surface state. , which is defined as the ratio of the radiation performance of an actual object to that of a blackbody at the same temperature. The law of radiation and absorption of infrared radiation by an object satisfies Kirchhoff's law. When a beam of radiation is projected onto the surface of any object, according to the principle of conservation of energy, the sum of the object's absorption rate, reflectivity, and transmittance of the incident radiation Must be equal to 1. Generally, the emissivity is not easy to measure. The emissivity can usually be determined by measuring the absorption rate. Therefore, the blackbody radiation source is used as a radiation standard to test the radiation intensity of various infrared radiation sources.
Infrared thermometer consists of optical system, photoelectric detector, signal amplifier, signal processing, display output and other parts. The radiation from the measured object and the reflection source is demodulated by the modulator and then input to the infrared detector. The difference between the two signals is amplified by the inverse amplifier and controls the temperature of the feedback source so that the spectral radiance of the feedback source is the same as the spectral radiance of the object. The display indicates the brightness temperature of the object being measured. The temperature measured by the infrared thermometer is the radiation temperature of the object rather than the actual temperature of the object. Since the black body does not exist, the total thermal radiation of the actual object is always smaller than the total black body radiation at the same temperature, so infrared measurement The temperature measured by the thermometer should definitely be lower than the actual temperature of the object. When measuring temperature, the emissivity of the infrared thermometer should be set as much as possible (for infrared thermometers with adjustable emissivity) to the same emissivity value as the material being measured, so that the measured value is as consistent as possible. The actual temperature of the object is consistent.
2 Introduction to self-calibration method of infrared thermometer
The most important factors for an infrared thermometer to ensure temperature measurement accuracy are the emissivity, the distance to the light spot, the position of the light spot, and the field of view. Through communication and consultation with infrared temperature measurement experts and technical personnel of equipment manufacturers, and repeated practice with various methods, a set of calibration equipment was made based on the principle of a blackbody furnace, and the method was verified through comparison. Self-calibration comparison Practical and feasible. During self-calibration, the comparison of basic errors, the impact of changes in measurement distance, and the determination of the range of emissivity are completed. Before testing, the infrared thermometer is adjusted to the best state and then used for on-site testing.
