Measurement Error Analysis and Compensation Experiment Research of Infrared Thermometer
The amount of radiant energy received by an infrared thermometer from an object is proportional to its emissivity. The emissivity of an object is not only related to the shape of the object's material, surface roughness, unevenness, etc., but also related to the direction and angle of the measurement. If the object is a smooth surface, its directionality is more sensitive. The larger the measurement angle, the larger the measurement error. This is easily overlooked when calibrating infrared thermometers. Generally speaking, when measuring, the infrared thermometer should be vertically aligned with the mouth of the blackbody furnace cavity, and its optical axis coincides with the axis of the target surface of the radiation source. When measuring, the angle is best controlled within 30°, and should not be greater than 45°. If you have to measure more than 450, you can properly lower the emissivity of the thermometer.
Measured target size
The size of the target to be measured and the field of view of the infrared thermometer determine the accuracy of the instrument's measurement. When using an infrared thermometer to measure temperature, only the temperature value of a certain area on the surface of the measured target can be measured. When determining the measurement distance, it should be ensured that the area of the target to be measured is equal to or greater than the field of view of the measured thermometer. For laser sight type thermometers, the laser point should be above the center of the target, with an offset distance of 12mm. Generally, there are three situations in the measurement:
(1) When the measured target is larger than the test field of view, the thermometer will not be affected by the background radiation energy outside the measurement area, and can display the real temperature of the measured object located in a certain area within the optical target. At this time, the measurement effect is the best . Just like when verifying an infrared thermometer, the diameter of the target surface of the blackbody radiation source should be greater than or equal to the target diameter required by the thermometer.
(2) When the measured target is equal to the test field of view, it has been affected by the background radiation energy, but the impact is relatively small, and the measurement effect is average.
(3) When the measured target is smaller than the test field of view, the background radiation energy will interfere with the temperature measurement readings, resulting in errors. Therefore, in the actual temperature measurement, the size of the measured target should exceed 50% of the field of view of the thermometer.
4 Response time and environmental factors
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. It is related to the time constant of the photodetector, signal processing circuit and display system. The choice of the response time of the infrared thermometer should be adapted to the situation of the measured target. If the moving speed of the measured target is fast or the temperature changes quickly, a fast-response thermometer should be selected, otherwise the signal response will not be sufficient and the measurement accuracy will be reduced.
Accuracy; for static targets or targets with slow temperature changes, the response time of the thermometer can relax the requirements. In addition, a large change in the ambient temperature will affect the measurement accuracy of the infrared thermometer. For the infrared thermometer to be verified, it needs to be placed in the laboratory for more than 30 minutes before it can be verified.
