PYROMETERS

1. PYROMETERS • Presented by: • 2007-chem-14

2. 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

3. 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.

4. PRINCIPLE A pyrometer has • optical system • detector It is based upon “Stephan Boltzmann law” E=σ AT4

5. BLACKBODYSPECTRUM

6. CLASSIFICATION • Broadband radiation pyrometers • Narrow band radiation pyrometers • Ratio radiation pyrometers • Optical pyrometers • Fiber optic radiation pyrometers

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

8. OPERATION

9. 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

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

11. 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

12. 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.

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

14. 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

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

16. COMPONENTS

17. OPERATION

18. OPERATION

19. 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

20. 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

21. 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

22. COMPONENTS There are two components. • Lens • Radiation detector

23. OPERATION

24. 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.

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

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

27. OPERATION

28. 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.

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

30. 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

31. PRINCIPLE

32. OPERATION

33. 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.

34. 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 210°F (100°C).

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

36. 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.

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

38. 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, Bogot´a Caracas, Lisbon, London, Madrid, Mexico City, Milan, Montreal, New Delhi, San Juan, Singapore, Sydney, Tokyo, Toronto, 5th edition, pages 4.8-4.47, 1999. • Morris A. S., “Measurement and Instrumentation”, Prentice hall of India private Ltd., 2nd edition. • Boyes W., “Instrumentation Reference Book”, Butterworth Heinemann, Boston Oxford

39. 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.