Basic concepts of Temperature Measurement
- 1. Dr. Vishal Patil Post Doc. IIT Bombay, Associate Professor, Department of Mechanical Engineering 1 Sharad Institute of Technology, College of Engineering, Yadrav- Ichalkarnji Department of Mechanical Engineering Lecture 02: Fundamental Concepts Temperature and it’s Measurement
- 2. 2 Content 1. General aspects of Instruments 2. Classification of Instruments 3. Commonly used Instruments 4. Temperature 5. Absolute Temperature 6. Temperature Measuring Instruments 7. Thermometer (Thermal Expansion Type) 8. Thermocouple 9. Optical thermometers, Pyrometer
- 3. 3 1. General Aspects of Instruments 1. Operating Guidance 2. Performance Calculations 3. Maintenance and repair guidance 4. Economical supervision 5. Cast Allocation
- 4. 4 2. Classification of instruments The two general classification of instruments are 1. Those employing electro-mechanical methods 2. Those employing purely mechanical method Instruments can be also be classified as follows. 1. Indicating 2. Recording 3. Indicating and recording 4. Indicating and integrating 5. Indicating, recording and integrating
- 5. 5 3. Commonly used instruments Pressure gauge Thermometer Thermocouple Liquid level gauge Flow meter (Steam and Gas) pH measuring instruments Gas analyzer Humidity measuring instruments Impurity measuring instruments Speed measuring instruments Steam and fuel calorimeter Alarms Electrical instruments Ammeter Voltmeter Wattmeter Power factor meter Reactive volt meter Ground detector
- 6. 6 4. Temperature Temperature can be defined as a thermal state which depends upon the internal or molecular energy of the body. 1.Celsius or centigrade scale: This scale is first used in 1742. this scale is mostly used by engineers and scientists. The freezing point of water on this scale is marked as zero, and boiling point of water as 100. The space between these two points has equal 100 divisions, each division represents one degree Celsius (briefly written as °C). 2.Fahrenheit scale: This scale was first used in 1665. In this scale, the freezing point of water is marked as 32 and boiling point of water as 212. The space between these two points has equal 180 equal divisions and each division represents one degree Fahrenheit (Briefly written as °F). The relation between Celsius scale and Fahrenheit scale
- 7. 7 5. Absolute Temperature The zero readings of Celsius and Fahrenheit scale are chosen arbitrarily for the purpose of simplicity. It help us in our calculations, when changes of temperature in process are known. Whenever the value of temperature is used in equations relating to fundamental laws, then the value of temperature, whose reference point is true zero or absolute zero is used. The temperature below which the temperature of any substance can not fall is known as absolute zero temperature. The absolute zero temperature, all sorts of calculations is taken as -273.16 °C in case of Celsius scale and -460 ° F in Fahrenheit scale. The temperature measured from this zero are called absolute temperature. The absolute temperature in Celsius scale is called as degree Kelvin (K) such that, K= °C + 273.16. Similarly The absolute temperature in Fahrenheit scale is called as degree Rankine (°R) such that, °R = °F + 460
- 8. 8 6. Temperature Measuring Instruments 1. Non electrical method a) By using change in volume of liquid when its temperature is changed b) By using change in pressure of a gas when its temperature is changed c) By using change in vapour pressure when its temperature is changed 2. Electrical method a) By thermocouple b) By change in resistance of material with change in temperature c) By comparing colors filaments and object whose temperature is to be found out d) By Ascertaining the energy received by radiation
- 9. 9 6. Temperature Measuring Instruments 3. Thermometers i) Expansion thermometer a) Liquid in glass thermometer b) Bimetallic thermometer ii) Pressure thermometers a) Vapour pressure thermometer b) Liquid filled thermometer c) Gas filled thermometer 4. Thermocouple 5.Resistance thermometer 6.Radiation pyrometer 7.Optical pyrometer
- 10. 10 7. Thermometer The temperature measurement is carried out by measuring the expansion of a liquid under the effect of heat. Mercury thermometer (Hg) Daniel Gabriel Fahrenheit invented in 1724. Mercury is the most efficient liquid because it does not wet the glass, its temperature range is very extensive and good thermal conductivity enable a rapid thermal equilibrium with the material in contact. Mercury is a liquid metal in the range -39 ° C to 360 ° C, it becomes solid below -39 ° C and gas beyond 400 ° C. The measurement accuracy is better than 0.1 ° C.
- 11. 11 Alcohol Thermometer Alcohol has replaced the mercury in the nineteenth century for reasons of public health and cost. it operates on the same principle as that described above but with alcohol colored red or blue for readability because it is naturally transparent fluid. The temperature range of maximum temperature is -80 C to + 75 ° C. this thermometer is one of the most common measure with an accuracy of up to 0.1 ° C Other liquids may be used such as pentane (-200 °C to 30 °C), Xylene (-100 °C to 250 °C), toluene (-90 °C), gallium (1000 °C) or Creosote-ethyl alcohol mixtures, mercury-thallium, gallium-mercury providing suitable temperature ranges in the physical limit of evaporation and solidification points. it is possible to work from - 200 ° C / 1000 ° C depending on the nature of the fluid. Other liquids Ref: https://sites.google.com/site/celciusinstrumentsthermometer/types-de-thermometre/thermometres-a-dilatation-de-liquide 7. Thermometer
- 12. 12 8. Thermocouple Mili voltmeter or temperature recorder Copper Leads Reference Junction Hot Body Measuring Junction Metal 1 Metal 2 Thermocouple
- 13. 13 8. Thermocouple Symbol Alloy Temperature range in ° C J Fe Cu-Ni (Constantan) -210 to 1200 K Ni-Cr (Chromel) Ni-Al (Alumel) -270 to 1372 T Cu Cu-Ni (Constantan) -270 to 400 E Ni-Cr (Chromel) Cu-Ni (Constantan) -270 to 1000 N Ni-Cr-Si (Nicrosil) Ni-Si (Nisil) -270 to 1300 S Pt-10% Ro Pt -50 to 1768 R Pt-13% Ro Pt -50/1768 B Pt-30% Ro Pt 0 to 1820 C You Rhe-5% You Rhe-26% 0 to 2320 https://sites.google.com/site/celciusinstrumentsthermometer/types-de-thermometre/thermometres-thermocouples
- 14. 14 These are thermometers or optical pyrometer based on the relationship between the temperature of a body and the radiation emitted by this body. The remote measurement is carried out by measuring the object's radiation in the field of infrared range. the choice of the sensor depends on the ambient conditions, the measurement accuracy, response time and emissivity of the body. The measurement is simple but is less accurate than a contact thermometer 9. Optical Thermometers, Pyrometer Ref: https://sites.google.com/site/celciusinstrumentsthermometer/types-de-thermometre/thermometres-optiques-ou-pyrometriques
- 15. 15 Reference: Power Engineering, Prof. R. K. Rajput This video is prepared for academic use only.