there are two types of pyrometers (thermometers):
- Optical devices. To radiation they are sensitive to a certain frequency band;
- Radiation device. They are sensitive to radiation over the entire frequency range.
In this article we will talk about optical thermometers. Thanks to a special filter, such devices are sensitive in a narrow range of waves. Temperature measurement of the controlled object (subject) analyzed by the detector or the source test measurements.
The most common option is the use of the measuring device with a disappearing filament. Working with such devices, the user must be in the visible spectrum and in a narrow range of wavelengths to compare the two radiation intensity: measured and incandescent tungsten filaments (control). As soon as the brightness becomes smooth, the filament will disappear. Optical indicator of temperature of the measured object is the heating power of the filament. The temperature can be determined by the calibration curve or at the device scale is applied.
If the coefficient of spectral radiation of the surface of the measured object (the subject) equals one (all black body), then measured by the optical thermometer (luminance, spectral) temperature equal to true. In practice, however, the measured value is less than the true temperature. Therefore, it is necessary to introduce an amendment. It is derived from the spectral emissivity (indicated in the table) and the measured temperature.
For example, for λ (wavelength) of 0.65 nm, the spectral emissivity of the porcelain (iron) amounts to 0.78 (0,35) at a temperature of 1200°C (800°C).
Pyrometers disappearing filament – a simple and convenient device. But they have drawbacks: limitation on the lower temperature limit and a certain subjectivity of values of the measurements. However, the amendment, which enters into the measurement result (if the emitting objects are not black) is much more accurate than for radiation devices. If you want to buy optical pyrometer, it is possible to purchase devices equipped with a photovoltaic element (objective a receiver).
Measurements with this thermometer are with a two-meter distance and up to infinity. Special optics allow to adjust the distance. The lower temperature limit – 650°C (for the objective of the receiver – 200°C), upper – not more than 2500°C. the Pyrometers will graduate on:
- Bulb equipped with tungsten filament;
- Black emitter.
In most cases, to measure the temperature suitable radiation pyrometers of the series “ThermaLine” BALTECH TL or infrared camera BALTECH TR-0180 Zorro infrared Windows BALTECH TR-95W.