pyrometers and its types

2. Pyrometers
Pyrometry is a technique for measuring temperature
without physical contact. It depends upon the
relationship between the temperature of hot body and
electromagnetic radiation emitted by the body.
It is a technique for determining a body’s temperature
by measuring its electromagnetic radiation .
‘ Pyro’ is the ‘Greek’ word which means fire.
A pyrometer is a non-contacting device.
Pyrometer intercepts and measures thermal radiation.
This device can be used to determine the temperature
of an object's surface without contact to the surface.

3. Pyrometers – Radiation
fundamentals
 The Thermal emission is based on the Black Body
concept.
 Black Body is an object that absorbs all
electromagnetic radiation that falls onto it.
 No radiation passes through it and none is reflected.
 Electromagnetic radiation just depends on the
temperature of black body.
 The total emittance from a black body including all
wavelengths is directly proportional to the Fourth
power of its temperature. This temperature is called
“Brightness Temperature, T”
 It is based on Stepen-Boltzman Law

4. Types of Pyrometers
 OPTICAL PYROMETER
 RADIATION PYROMETER

5. Optical (Partial Radiation
Pyrometers)
 The Optical Pyrometer is a highly-developed and well
accepted noncontact temperature measurement
device.
 It is widely employed for accurate measurement of the
temperature of furnaces, molten and other heated
materials.
 It is primarily used in the range of 1000 to 5000 ⁰F.

6. Types
 Single Color Pyrometers(Monochromatic)
Operate over a narrow range of Wavelengths
Basically used for glass at 5.14μm. Metals can also be
measured as their rate of emissivity is high only in a
narrow band.
Spectral response of a particular device depends on the
type of the detector used.
Works on selected wavelength range with the help of
filters.
Also called “ Disappearing Filament Type
Pyrometer”

7.  Chromatic Pyrometers(two color Pyrometers):
 Measures the radiated energy of an object between two
narrow wavelength bands and then calculates the ratio of
the two energies.
 This ratio is the function of the temperature of the object.
 Even if the object does not fully cover the spot the output
signal will not change.
 Temperature measurement is independent of emissivity, so
the errors caused by the emissivity variation, surface finish,
and energy absorbing materials between the pyrometer
and the target can be minimized or removed.
 Used for measuring high temperature.

8. Principle of working
 Optical Pyrometers work on the basic principle of
using the human eye to match the brightness of the
hot object to the brightness of a calibrated lamp
filament inside the instrument.
 The radiation from the source is emitted and the
optical objective lens captures it. The lens helps in
focusing the thermal radiation on to the reference
bulb.

10. Working
In an optical pyrometer, a brightness comparison
is made to measure the temperature. As a measure of the
reference temperature, a color change with the growth in
temperature is taken. The device compares the brightness
produced by the radiation of the object whose temperature is to
be measured, with that of a reference temperature.
The reference temperature is produced by a lamp
whose brightness can be adjusted till its intensity becomes
equal to the brightness of the source object. For an object, its
light intensity always depends on the temperature of the object,
whatever may be its wavelength.
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

11. This change in current can be observed in three different
ways :

12. Radiation Pyrometers
 The main theory behind a radiation pyrometer is that
the temperature is measured through the naturally emitted
heat radiation by the body. This heat is known to be a
function of its temperature.
 According to the application of the device, the way in
which the heat is measured can be summarized into two:
1. Total Radiation Pyrometer – In this method,
the total heat emitted from the hot source is
measured at all wavelengths.
2. Selective Radiation Pyrometer – In this
method, the heat radiated from the hot source is
measured at a given wavelength.

13.  Some of the Radiation Sensing Elements are:
Thermopile
Single Thermocouple
Germanium Diode

14. Radiation Pyrometer

15. Radiation Pyrometer - Working
 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.

16. Sources of Errors
 Error due to Emissivity of object
 Errors due to Flames, water vapor, smoke etc
 Error due to sighting windows
 Due to ambient temperatures
 Due to temperature gradients in sighting tube

17. ADVANTAGES
i. Simple assembling
ii. Provides a very high
accuracy with +/-5
degree Celsius
iii. no need of any direct
body contact
iv. The device can measure
very high temperatures
v. It can also be used to
see the heat produced
by the object/source
DISADVANTAGES
i.Not useful for obtaining
continuous values of
temperatures
ii.Only useful for
measuring very high
temprature
iii.Higher cost as compared
to conventional
thermocouples
iv.Advanced radiation
thermometers involve
extra complicated design
and optics.

18. Applications
 In the blast furnace & metallurgical furnace
 To measure the steam temperature
 To measure the moving objects
 The application is used in smelter industry, over
the bath pyrometer, steam boiler, hot air
balloons and gas turbine engine.
 for measuring the temperature through the
Tuyere