Advantages of Measuring Temperature with Infrared Thermometers
Non-contact temperature measurement by receiving infrared rays radiated by the object under test has many advantages. In this way, the temperature of objects that are difficult to reach or are in motion can be measured without any problem, such as materials with poor heat transfer properties or very small heat capacity. The short response time of the infrared thermometer enables effective regulation loops to be quickly implemented. Thermometers have no parts that wear out, so there are no ongoing costs associated with using a thermometer. Especially for very small objects to be measured, such as contact measurement, a large measurement error will occur due to the thermal conductivity of the object. Thermometers can be used without any problems here, and are used with corrosive chemicals or sensitive surfaces, such as paint, paper and plastic rails. Through long-distance remote control measurement, it can be far away from the dangerous area, so that the operator is not in danger.
The principle structure of infrared thermometer
The infrared rays received from the object to be measured are focused on the detector through the lens and the filter. The detector generates a current or voltage signal proportional to the temperature through the integration of the radiation density of the measured object. In the connected electrical components, the temperature signal is linearized, the emissivity area is corrected, and converted into a standard output signal.
In principle, there are two types of portable thermometers and fixed thermometers. Therefore, when choosing a suitable infrared thermometer for different measurement points, the following characteristics will be main:
1. Sight
The sight has this function. The measuring block or measuring point pointed by the thermometer can be seen. The sight can often be used without the sight when measuring a large area. For small objects and long measurement distances, a sight in the form of a light-transmitting lens with a dashboard scale or a laser pointing point is recommended.
2. Lens
The lens determines the measured point of the thermometer. For large-area objects, a thermometer with a fixed focal length is generally sufficient. But when the measurement distance is far away from the focus point, the image at the edge of the measurement point will be unclear. For this reason, it is better to use a zoom lens. Within the given zoom range, the thermometer can adjust the measurement distance. The latest thermometers have replaceable lenses with zoom. The near lens and far lens can be replaced without calibration recheck. .
3. Sensor, namely spectrum receiver
Temperature is inversely proportional to wavelength. At low object temperatures, sensors sensitive to the long-wave spectral region (hot film sensors or pyroelectric sensors) are suitable. At high temperatures, sensors sensitive to short wavelengths composed of germanium, silicon, indium-gallium, etc. will be used. Photoelectric Sensors.
When choosing spectral sensitivity, the absorption spectral bands for hydrogen and carbon dioxide should also be considered. Within a certain wavelength range, the so-called "atmospheric window", H2 and CO2 are almost transparent to infrared rays, so the light change sensitivity of the thermometer must be within this range to eliminate the influence of atmospheric concentration changes. , when measuring film or glass, it should also be considered that these materials are not easy to penetrate within a certain wavelength. In order to avoid measurement errors caused by background light, use a suitable sensor that only receives surface temperature. Metal has this physical property, and the emissivity increases as the wavelength decreases. Speaking from experience, when measuring the temperature of metal, generally choose the shortest measurement wavelength.
