Main features of portable thermometer
1. Collimator
The collimator has this function, and the measuring block or point referred to by the thermometer can be seen. Large areas of the measured object can often be without the collimator. When measuring small objects and distant distances, it is recommended to use a sight in the form of a transparent mirror with a dashboard scale or laser pointing point.
2. Lens
The lens determines the measured point of the thermometer. For large objects, a thermometer with a fixed focal length is generally sufficient. But when the measurement distance is far from the focal point, the image of 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 new thermometer has a replaceable lens with zoom, and the near and far lenses can be replaced without calibration and re inspection.
3. Sensors, i.e. spectral receivers
The temperature is inversely proportional to the wavelength. At low object temperatures, sensors sensitive to the long wavelength spectral region (hot film sensors or thermoelectric sensors) are suitable. At high temperatures, photoelectric sensors composed of germanium, silicon, indium gallium, etc. that are sensitive to short wavelengths will be used.
When selecting spectral sensitivity, consideration should also be given to the absorption spectral bands of hydrogen and carbon dioxide. Within a certain wavelength range, known as the "atmospheric window," H2 and CO2 almost penetrate infrared light. Therefore, the sensitivity of the thermometer to light variation must be within this range to exclude the impact of atmospheric concentration changes. When measuring thin films or glass, it is also necessary to consider the materials that are not easily penetrated within a certain wavelength range. In order to avoid measurement errors caused by background light, appropriate sensors that only receive surface temperature are used. Metals have this physical characteristic, and the emissivity increases with the decrease of wavelength. Based on experience, when measuring metal temperature, the shortest measurement wavelength is generally chosen.
