What is the error of infrared thermometer?
Infrared thermometers are generally around 0.2.
Many of the infrared thermometers currently on the market are modified from industrial thermometers to prevent SARS. They are greatly affected by the ambient temperature at that time, and the measured body temperature may have an error with the actual temperature.
Factors affecting the error of infrared thermometer
1. Radiation rate
Radiation rate is a physical quantity that measures the radiation ability of an object relative to a black body. In addition to being related to the material shape, surface roughness, concavity and convexity of the object, it is also related to the direction of the test. If the object has a smooth surface, its directionality is more sensitive. The emissivity of different materials is different. The amount of radiation energy received by an infrared thermometer from an object is proportional to its emissivity.
(1) The setting of the emissivity is based on Kirchhoff's theorem: the hemispheric monochromatic emissivity (ε) of the object's surface is equal to its hemispheric monochromatic absorptivity (α), ε=α. Under thermal equilibrium conditions, the radiant power of an object is equal to its absorbed power, that is, the sum of absorptivity (α), reflectivity (ρ), and transmittance (γ) is 1, that is, α+ρ+γ=1. For opaque (or with a certain thickness) objects, the transmittance can be seen as γ=0, and there are only radiation and reflection (α+ρ=1). When the emissivity of the object is higher, the reflectivity is smaller, and the influence of background and reflection is The smaller the value, the higher the accuracy of the test; conversely, the higher the background temperature or the higher the reflectivity, the greater the impact on the test. It can be seen from this that during the actual detection process, attention must be paid to the corresponding emissivity of different objects and thermometers, and the emissivity setting should be as accurate as possible to reduce the error of the measured temperature.
(2) Test angle
The emissivity is related to the test direction. The larger the test angle, the greater the test error. This is easily overlooked when using infrared for temperature measurement. Generally speaking, the test angle is preferably within 30°C, and generally should not be greater than 45°C. If the test has to be greater than 45°C, the emissivity can be appropriately lowered for correction. If the temperature measurement data of two identical objects are to be judged and analyzed, the test angles must be the same during the test, so that they are more comparable.
2. Distance coefficient
The distance coefficient (K=S:D) is the ratio of the distance S from the thermometer to the target and the diameter D of the temperature measurement target. It has a great influence on the accuracy of the infrared thermometer. The larger the K value, the higher the resolution. . Therefore, if the thermometer must be installed far away from the target due to environmental conditions, and small targets need to be measured, a thermometer with high optical resolution should be selected to reduce measurement errors. In actual use, many people ignore the optical resolution of the thermometer. Regardless of the diameter D of the measured target point, turn on the laser beam and align it with the measurement target to test. In fact, they ignored the S:D value requirement of the thermometer, so the measured temperature would have a certain error.
3. Target size
The object being measured and the field of view of the thermometer determine the accuracy of the instrument's measurement. When using an infrared thermometer to measure temperature, it can generally only measure the average value of a certain area on the surface of the target being measured. There are generally three situations during testing:
(1) When the measured target is larger than the test field of view, the thermometer will not be affected by the background outside the measurement area and can display the true temperature of the measured object located in a certain area within the optical target. The test effect is best at this time .
(2) When the measured target is equal to the test field of view, the background temperature has been affected, but it is still relatively small, and the test effect is average.
(3) When the measured target is smaller than the test field of view, the background radiation energy will enter the visual and acoustic branches of the thermometer and interfere with the temperature measurement reading, causing errors. The instrument only displays the weighted average of the measured object and background temperatures.
4. Response time
The response time indicates the reaction speed of the infrared thermometer to the change of the measured temperature. It is 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. If the target moves very fast or when measuring a rapidly heated target, a fast-response infrared thermometer should be used. Otherwise, sufficient signal response will not be achieved and the measurement accuracy will be reduced. But not every application requires a fast-responding infrared thermometer. For stationary or thermal inertia of the target thermal process, the response time of the thermometer can be relaxed. Therefore, the choice of the response time of the infrared thermometer must be adapted to the conditions of the target being measured.
