What is Pyrometer ?
•All the temperature-measuring methods studied earlier require physical contact of thermometer with the body whose temperature is to be measured.
•But at high temperatures above 1400°C, the thermometer may melt due to direct physical contact.
•To solve these problems a non-contact method of temperature sensing is used. •Also this method is also convenient for moving bodies.
•Pyrometry is a technique for measuring temperature without physical contact.
•Pyrometry is a technique for determining a body’s temperature by measuring its electromagnetic radiation.
•Two types of pyrometers
- Radiation Pyrometer.
- Optical Pyrometers.
- Infrared Pyrometers.
Radiation Pyrometer
It is mostly used in industries for temperature measurement.
Principle of Radiation Pyrometer
Operation of radiation pyrometer is based on the measurement of radiant energy emitted by the hot body.
Construction of Radiation Pyrometer
Radiation Pyrometer Diagram
As shown in Fig.
•It consists of a lens to focus radiated energy from the body, whose temperature is required on to a receiving element.
•This receiving element may have a variety of forms such as resistance thermometer, or a thermocouple.
•A temperature indicator, recorder or controller is attached with the receiving end to indicate the temperature.
Working of Radiation Pyrometer
•When the total energy radiated by a hot body, whose temperature is to be measured, enters the pyrometer it is focused by the lens on to the detector (i.e. receiving element).
•The detector is a thermopile whose measuring junctions are attached to a backened disk.
•The disc absorbs energy when the pyrometer is focused on a hot body, and its temperature increases.
•The reference junction of the thermopile is attached to the pyrometer case.
•The difference in temperature between the measuring junction attached to the disc and the reference junction attached to the case generates a voltage that is directly related to the temperature of the backened disc, which is indicated by the recording instrument.
Advantages of Radiation Pyrometer
Advantages of radiation pyrometers are as follows –
- Ability to measure high temperature.
- No physical contact with target of measurement.
- Fast response speed.
- High output and moderate cost.
Disadvantages of Radiation Pyrometers
Disadvantages of radiation pyrometers are as follows –
- Non-linear scale.
- Possible errors due to pressure to intervening gases or vapours that absorb radiation.
- Emissivity of target material affecting measurement.
Applications of Radiation Pyrometer
Applications of radiation pyrometer are –
- Used for temperature above the physical operating range of thermocouples.
- Used in the environment which limit the life of thermocouples.