Subject: instrument and process control

1. Government Engineering College,
Bharuch.
Sub:-Instrumentation & Process Control
Topic:-Radiation Pyrometer
Sem :5 th
Prepared by

2. Radiation Pyrometer
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.
• In an optical pyrometer, a brightness comparison is made to
measure thetemperature.

3. • The device compares the brightness produced by
the radiation of the object whose temperature is to
be measured,
• For an object, its light intensity always depends on
the temperature of the object.
• After adjusting the temperature, the current passing
through it is measured using a multimeter, as its
value will be proportional to the temperature of the
source when calibrated.
• Pyrometry is a technique for measuring
temperature without physical contact. It depends
upon the relationship between the temperature of
hot body and electronic magnetic radiation
emitted by the body.

4. Types of Pyrometer
The following are some of the most commonly and widely used
pyrometer:
1.Optical pyrometer
2.Radiation pyrometer
3.Digital pyrometer
4.Infrared pyrometer

5. Radiation pyrometer
Working construction:-
 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.

6.  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.

7. Advantages:-
o Easy to operate
o High output .
o Moderate cost .
o It is simple in design and construction.
o Ability to measure high temp.
o It has Fast speed o response.
o It has no physical contact with target of measurement.
Disadvantages:-
o Emissivity errors are introduced
o It is relatively expensive.
o The radiation pyrometer is complex in nature.
o External radiation may affect the measurement.
o Emissivity of target material affecting measurement.
o It has non linear scale.
o Errors due to the absorption of radiation by carbon
dioxide, water or other apparently transparent gases.

8. Application:-
i. They are used for temperatures above the practical operating
range of thermocouples.
ii. They can be used in the environments which contaminate or
limit the life of thermocouple.
iii. Used for moving targets.
iv. They are used for measurement of average temperature of
large surface areas.
v. They are used for the targets which would be damaged by
contact with primary elements like thermocouples and
resistance thermometers.

9. Limitations of Radiation Pyrometer
1) Availability of optical materials limit on the wavelengths
that can be measured.
2) The surface of the hot object should be clean
3) It should not be oxidized.
4) Scale formation does not allow to measure radiation
accurately.
5) Emissivity correction is required.
6) Chane in emissivity with temp need to consideration.