1. Temperature Measurements Principles Measuring Devices Applications بِسْـــــمِ اللهِ الرَّحْمَنِ الرَّحيـــــِمِ

2. Definition of Temperature An expression for the kinetic energy of vibrating atoms and molecules of matter. Can be measured by various secondary phenomena, e.g., – change of volume or pressure, –electrical resistance, –electromagnetic force, –electron surface charge, or –emission of electromagnetic radiation. BME 353 - Biomedical Measurements and Instrumentation 212 Oct. 2015

3. Direct and Indirect Many engineering applications require direct measurement of temperature. –Synthetic fuel research, –solar energy conversion and –new engine development are a few of these disciplines. –All industries place new emphasis on energy efficiency. Hence, the fundamental measurement of temperature assumes new importance. Temperature also effects measurement of most physical variables and it must be measured for compensation purposes as well. BME 353 - Biomedical Measurements and Instrumentation 312 Oct. 2015

4. Temperature Scale Celsius, divide the difference between the freezing and boiling points of water into 100° Fahrenheit which divide the difference between the freezing and boiling points of water into 180° °C = (5 /9) (°F - 32), and °F = (9 /5) °C + 32. The thermodynamic scale begins at absolute zero, or 0 Kelvin, the point at which all atoms cease vibrating and no kinetic energy is dissipated. 0 K = –273.15° C = –459.67° F. –The official Kelvin scale does not carry a degree sign. The units are expressed in “kelvins,” not degrees Kelvin. BME 353 - Biomedical Measurements and Instrumentation 412 Oct. 2015

5. Reference Temperatures No temperature divider or adder We must rely upon temperatures established by physical phenomena which are easily observed and consistent in nature. The International Temperature Scale (ITS) establishes seventeen fixed points and corresponding temperatures. Examples: –the triple-point (the temperature and pressure at which solid, liquid, and gas phases of a given substance are all present simultaneously in varying amounts) of water = 0.01  C, –triple-point of hydrogen = -259.3467  C, and –freezing point of silver = 961.78  C. BME 353 - Biomedical Measurements and Instrumentation 512 Oct. 2015

6. Heat Gain and Heat Loss Heat gain: –Environment –Metabolism –Hot food –Shivering Heat loss: –Convection –Conduction –Evaporation –IR radiation BME 353 - Biomedical Measurements and Instrumentation 612 Oct. 2015

7. Temperature measuring devices Temperature can be measured via a diverse array of sensors. All of them infer temperature by sensing some change in a physical characteristic. In the chemical process industries, the most commonly used temperature sensors are thermocouples, resistive devices and infrared devices. thermocouples, resistance temperature devices –RTD’s and –Thermistors infrared radiators, I.C. sensors, bimetallic devices, liquid expansion devices, change-of-state devices. BME 353 - Biomedical Measurements and Instrumentation 712 Oct. 2015

8. Thermocouples Two strips or wires made of different metals and joined at one end. Changes in temperature at that junction induce changes in the emf between the other ends. As temperature goes up, this output emf of the thermocouple rises, though not necessarily linearly. V AB =  T, where , the Seebeck coefficient, is the constant of proportionality. For real world thermocouples,  is not constant but varies with temperature. BME 353 - Biomedical Measurements and Instrumentation 812 Oct. 2015

9. Peltier effect If a voltage is applied, then there will be temperature change at the junction. This is called the Peltier effect and can be used for heating and cooling (refrigeration). BME 353 - Biomedical Measurements and Instrumentation 912 Oct. 2015

10. Equation of a thermocouple The output voltage “V” of a simple thermocouple (with a reference temperature T 0 = 0  C = 32  F) is: where T is the temperature of the measuring junction in  C, A, B, and C are constants that depend upon the thermocouple material. The sensitivity volts, volt/  C BME 353 - Biomedical Measurements and Instrumentation 1012 Oct. 2015

11. Characteristics of thermocouples Constantan is a metal alloy with %60 copper and %40 nickel BME 353 - Biomedical Measurements and Instrumentation 1112 Oct. 2015

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13. Resistance Temperature Devices RTD’s R = R 0 [1 +  (T – T 0 )] platinum, nickel, or ni alloys –fine platinum wire wrapped around a mandrel and covered with a protective coating (also abbreviated PRTD). – most stable temp trans. Film RTD –a platinum or metal-glass slurry film is deposited or screened onto a small flat ceramic substrate, etched with a laser- trimming system, and sealed –device size itself is small, which means it can respond quickly to step changes in temperature. Film RTD’s are less stable Thermistors –NTC –PTC most sensitive temperature transducer BME 353 - Biomedical Measurements and Instrumentation 1312 Oct. 2015

14. Equation of a thermistor Steinhart-Hart equation: a simpler equation: BME 353 - Biomedical Measurements and Instrumentation 1412 Oct. 2015

15. The Self-Heating Problem BME 353 - Biomedical Measurements and Instrumentation 1512 Oct. 2015

16. Integrated Circuit (I.C.) Sensors BME 353 - Biomedical Measurements and Instrumentation 1612 Oct. 2015

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18. Bimetallic Devices BME 353 - Biomedical Measurements and Instrumentation 1812 Oct. 2015

19. Fluid-Expansion Devices Types: –the mercury type: an environmental hazard, so there are regulations governing the shipment of devices that contain it. –the organic-liquid type. –gas instead of liquid type No electric power, do not pose explosion hazards, and are stable even after repeated cycling. On the other hand, –they do not generate data that are easily recorded or transmitted, and –they cannot make spot or point measurements. BME 353 - Biomedical Measurements and Instrumentation 1912 Oct. 2015

20. Chemical (Change-of-State) Sensors Change-of-state temperature sensors –labels, pellets, crayons,lacquers or liquid crystals whose appearance changes when a certain temperature is reached. –They are used, for instance, with steam traps – when a trap exceeds a certain temperature, a white dot on a sensor label attached to the trap will turn black. –Response time typically takes minutes, so these devices often do not respond to transient temperature changes, and accuracy is lower than other types of sensors. –the change in state is irreversible, except in the case of liquid-crystal displays. –Even so, change-of-state sensors can be handy when one needs confirmation that the temperature of a piece of equipment or a material has not exceeded a certain level, for instance for technical or legal reasons, during product shipment BME 353 - Biomedical Measurements and Instrumentation 2012 Oct. 2015

21. Radiation Detectors (IR Sensors) BME 353 - Biomedical Measurements and Instrumentation 2112 Oct. 2015

22. Spectral radiant emittance versus wavelength for a blackbody at 300 K on the left vertical axis; percentage of total energy on the right vertical axis. 5 0.001 0.002 0.003 0.00312 101520 T = 300 K m = 9.66  m 25 20 40 60 80 100% % Total power Spectral radient emittance, W-cm -2 ·mm -1 BME 353 - Biomedical Measurements and Instrumentation 2212 Oct. 2015

23. 1 0 10 50 100 10 Fused silica Sapphire Arsenic trisulfide Thallium bromide iodine Wavelength,  m 100 Spectral transmission for a number of optical materials. BME 353 - Biomedical Measurements and Instrumentation 2312 Oct. 2015

24. 123 Wavelength,  m Indium antimonide (InSb) (photovoltaic) Lead sulfide (PbS) All thermal detectors 0 20 60 100 45678 Spectral sensitivity of photon and thermal detectors. BME 353 - Biomedical Measurements and Instrumentation 2412 Oct. 2015

25. The infrared thermometer opens a shutter to expose the sensor to radiation from the tympanic membrane. BME 353 - Biomedical Measurements and Instrumentation 2512 Oct. 2015

26. Details of the fiber/sensor arrangement for the GaAs semiconductor temperature probe. BME 353 - Biomedical Measurements and Instrumentation 2612 Oct. 2015