Tempertaure Measurement.ppt
- 2. Pyrometer • A pyrometer is a device that is used for the temperature measurement of an object. • The device actually tracks and measures the amount of heat that is radiated from an object. • The thermal heat radiates from the object to the optical system present inside the pyrometer. • The optical system makes the thermal radiation into a better focus and passes it to the detector.
- 4. As shown in the figure above, an optical pyrometer has the following components. 1. An eye piece at the left side and an optical lens on the right. 2. A reference lamp, which is powered with the help of a battery. 3. A rheostat to change the current and hence the brightness intensity. 4. So as to increase the temperature range which is to be measured, an absorption screen is fitted between the optical lens and the reference bulb.
- 5. Working 1.The radiation from the source is emitted and the optical objective lens captures it. 2.The lens helps in focusing the thermal radiation on to the reference bulb. 3.The observer watches the process through the eye piece and corrects it in such a manner that the reference lamp filament has a sharp focus and the filament is super-imposed on the temperature source image. 4.The observer starts changing the rheostat values and the current in the reference lamp changes. 5.This in turn, changes its intensity. This change in current can be observed in three different ways.
- 6. The filament is dark. That is, cooler than the temperature source. Filament is bright. That is, hotter than the temperature source. Filament disappears. Thus, there is equal brightness between the filament and temperature source
- 7. • Advantages 1. Provides a very high accuracy with +/-5º Celsius. 2. The biggest advantage of this device is that, there is no direct contact between the pyrometer and the object whose temperature is to be found out. • Disadvantages 1. As the measurement is based on the light intensity, the device can be used only in applications with a minimum temperature of 700º Celsius. 2. The device is not useful for obtaining continuous values of temperatures at small intervals.
- 9. • the radiation pyrometer has an optical system, including a lens, a mirror and an adjustable eye piece. The heat energy emitted from the hot body is passed on to the optical lens, which collects it and is focused on to the detector with the help of the mirror and eye piece arrangement. The detector may either be a thermistor or photomultiplier tubes. Though the latter is known for faster detection of fast moving objects, the former may be used for small scale applications. Thus, the heat energy is converted to its corresponding electrical signal by the detector and is sent to the output temperature display device.