PYROMETERS

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• PYROMETERS

• Presented by
• 2007-chem-14

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PYROMETERY

• Pyrometery is the art and science of measurement
  of high temperatures. Pyrometery makes use of
  radiation emitted by the surface to determine
  its temperature
• Temperature measuring devices invented are called
  pyrometers

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PYROMETERS

• Pyrometer is a device capable of measuring
  temperatures of objects above incandescence i.e.
  objects bright to the human eye).
• It is a non contact device
• A device that measures thermal radiation in any
  temperature range.

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PRINCIPLE

• A pyrometer has
• optical system
• detector
• It is based upon Stephan Boltzmann law
• Es AT4

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BLACK BODY SPECTRUM
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CLASSIFICATION

• Broadband radiation pyrometers
• Narrow band radiation pyrometers
• Ratio radiation pyrometers
• Optical pyrometers
• Fiber optic radiation pyrometers

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BROADBAND RADIATION PYROMETERS

• Standard ranges include 32 to 1832F (0 to
  1000C), and 932 to 1652F (500 to 900C).
• accuracy is 0.5 to 1
• response from 0.3 microns wavelength to an upper
  limit of 2.5 to 20 microns

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OPERATION

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CONSIDERATIONS

• The optical system must be kept clean, and the
  sighting window protected against any corrosives
  in the environment. 
• The path to the target must be unobstructed

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NARROW BAND PYROMETERS

• It can also be referred to as single color
  pyrometers .
• it can measure temperatures above 1102F
  (600C).
• range 0.5-1.2 microns.

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COMPONENTS

• Filters
• selection of filter depends on the wavelength
  of radiation to be measured
• Photo detector
• its selection depends upon the
  sensitivity to a particular wavelength

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OPERATION

• A photoconductive detector exhibits a change
  in resistance as the incident radiation level
  changes whereas a photovoltaic cell exhibits an
  induced voltage across its terminal which is also
  a function of incident radiation level.

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ADVANTAGE DISADVANTAGES

• ADVANTAGE
• They are less sensitive to emissivity changes.
• DISADVANTAGE
• They are non linear in behavior.

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OPTICAL PYROMETERS

• The color of an object is an indication of its
  temperature, and the brightness of a hot object
  is also a measure of its temperature
• Range 500 0C to 16000 C

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COMPONENTS

• Red filter
• wavelength of radiation 0.65 microns
• Filament lamp
• Absorbing gas filter
• for temp higher than 13500 C

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COMPONENTS
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OPERATION
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OPERATION
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ADVANTAGES

• It is a non contact device.
• Useful for the measurement of high temperatures.
• Useful for monitoring the temperature of moving
  objects.
• Good accuracy.
• Smaller in size and light in weight

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DISADVANTAGES

• Only use for the measurement of clean gases.
• Expensive device.
• It requires manual adjustments in readings.
• Cant be used in alarm system
• Emissivity errors
• It cant be used for temp greater than 1600 0C

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RADIATION PYROMETER

• Radiated energy is converted into an
  electromotive force by the thermopile, this
  potential then be measured by one of the number
  of the ways
• it can respond to very short wavelength as
  well as very short wavelength

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COMPONENTS

• There are two components.
• Lens
• Radiation detector

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OPERATION
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ADVANTAGES DISADVANTAGES

• ADVANTAGES
• It can measure the temperature higher than the
  optical pyrometer.
• Non contact device.
• Fast response
• DISADVANTAGES
• Emissivity errors are introduced
• Errors due to the absorption of radiation by
  carbon dioxide, water or other apparently
  transparent gases.

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INFRARED RADIATION PYROMETERS

• Infra red spectrum range from 0.22µm to 17µm and
  the commonly used portion is 2 to 7µm.

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APPLICATION

• A very practical application of infrared
  pyrometer in the 8 to 14µm range is a hot spot
  detector

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OPERATION
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ADVANTAGES

• They are able to measure high temperature.
• There is no need for contact with target of
  measurement.
• They possess fast response speed.
• They have high output and moderate cost.

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DISADVANTAGES

• There scale is non-linear.
• Errors due to presence of intervening gases or
  vapours that absorb radiating frequencies is
  possible in these pyrometers.
• Emissivity of target material affect measurement

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TWO COLOR RADIATION PYROMETERS

• They are also called Ratio pyrometers
• PRINCIPLE
• These devices measure the radiated energy of an
  object between two narrow wavelength bands, and
  calculates the ratio of the two energies, which
  is a function of the temperature of the object

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PRINCIPLE
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OPERATION
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ADVANTAGES

• The ratio technique may eliminate, or reduce,
  errors in temperature measurement caused by
  changes in emissivity, surface finish, and energy
  absorbing materials, such as water vapor, between
  the thermometer and the target.

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OPTICAL FIBRE PYROMETERS

• They are used when accuracy is critical
• If the target object is undergoing a physical or
  chemical change.
• It can be useful in measuring object temperatures
  to as low as 210F (100C).

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COMPONENTS

• Fiber optic cable,
• Temperature measuring system will include an
  array of components such as probes, sensors or
  receivers, terminals, lenses, couplers,
  connectors, etc. 

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ACCUFIBER TEMPERATURE SENSOR

• One extremely accurate form of extrinsic
  sensor is a device known as the Accufibre
  temperature sensor. This is a form of radiation
  pyrometer which has a black-box cavity at the
  focal point of the lens system. A fiber optic
  cable is used to transmit radiation from the
  black-box cavity to a spectrometric device which
  computes the temperature.

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RANGE

• Typical commercially available ranges are 1652 to
  5432 F (900 to 3000C) and 120 to 6692F (50 to
  3700C). Typical accuracy is 0.5 of reading on
  narrow spans, to 2 of full scale.

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REFERENCES

• McMillan, G.K. and Douglas M. C.,
  Process/Industrial Instruments And Controls
  Handbook, McGraw-Hill, Inc., New York, San
  Francisco, Washington, D.C., Auckland, Bogota
  Caracas, Lisbon, London, Madrid, Mexico City,
  Milan, Montreal, New Delhi, San Juan, Singapore,
  Sydney, Tokyo, Toronto, 5th edition, pages
  4.8-4.47, 1999.
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• Morris A. S., Measurement and Instrumentation,
  Prentice hall of India private Ltd., 2nd edition.
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• Boyes W., Instrumentation Reference Book,
  Butterworth Heinemann, Boston Oxford
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REFERENCES

• Johannesburg Melbourne New Delhi Singapore, 3rd
  edition, Pages 278-292, 2002.
•  
• Dunn W.C., Industrial Instrumentation and
  Process Control, McGraw-Hill Co., New York
  Chicago San Francisco Lisbon London Madrid Mexico
  City New Delhi San Juan Seoul Singapore Sydney
  Toronto, 2005.
•  
• Grundler P., Chemical Sensors An introduction
  for Scientist and Engineers, Springer, Germany,
  2007.
• Bolton D. J., A.M.I.E.E., Electrical Measuring
  Instruments and Supply Meters, Chapman Hall,
  Ltd., London, 1923.