1. Temperature and Pressure Sensors Seth Price Department of Chemical Engineering New Mexico Tech Rev. 10/27/14

2. Temperature Sensors Thermal expansion –Thermometer –Bimetallic strip Thermoelectrical –Thermocouple –RTD –Thermistor Thermal emission –Optical pyrometry

3. Bimetallic Strip Metallic strip can be used to close a switch Often found in dial thermometers and thermostats

4. Thermocouples Seebeck Effect: –Two different metals in direct contact at one end will generate a voltage –This voltage linearly relates to temperature

5. Cold Junction Compensation Voltage arises from difference in temperature at T 1 and T 2 (relative temperature) T 2 must be known to know T 1. Ways to do this: –Hold T 2 constant –Use another thermocouple to measure T 2 –Handled through software/hardware configuration (NI uses this)

6. Thermopiles Thermocouple voltage is small Signal must be amplified Connect multiple thermocouples in series (thermopile) –VT = V1 + V2 + … + Vn Caveat: Thermocouples should be at the same temperature

7. Resistance Temperature Detectors (RTD) Resistance in metals increase with increasing temperature Resistance also changes with strain –Metal in RTDs should have minimal residual strain Much slower response than other temperature sensors Wire lead resistance is a problem

8. Resistance of Metals

9. Thermistors Semiconductor that changes resistance with temperature –Similar to RTDs Has much higher resistance –Wire lead resistance becomes insignificant Fast response times

10. Optical Pyrometer Uses emissions from the object to determine its temperature

11. Optical Pyrometer Receives radiation and can calculate temperature Typically used for higher temperatures Used to determine if UV shielding is needed

12. Bourdon Tube A coiled tube uncoils with respect to pressure Linked to a needle on a gauge Really common

13. Gas Cylinders Safety –Transport with cap in place (not regulator!) –Chain to wall when regulator is in place Regulators –2 Stage regulator keeps constant pressure –Different gases use different regulators –Open or close all the way (except acetylene)

14. Piezoelectric Transducer Piezoelectric: generate voltage when pressure is applied –Barium Titanate BaTiO3 –Quartz (SiO2)

15. Strain Gauges A diaphragm is deflected by increased pressure, causing a strain Strain measured with a small strain gauge

16. Parallel Plate Capacitor Sensor Pressure moves one plate of the capacitor to change capacitance Depends on dielectric constant Can be used to measure pressure or vacuum C = (Є*Є 0 *A)/dC = (Є*Є 0 *A)/(d+Δ)

17. Thermocouple Pressure Sensing A heater is placed near a thermocouple junction Convective heat transfer is proportional to gas pressure 1 to 0.01 torr

18. Other Uses for Pressure Gauges Level gauge –Pressure gauge at the bottom of a tank –Calibrate voltage output to % full Flow meter –Pressure gauge (measuring differentially) across an orifice plate Proximity sensor –Pressure steps from baseline to positive value

19. Calibration Compare voltage (or current) measured to a standard (ex. thermometer) Change environment, recheck voltage and standard Plot voltage (or current) vs. physical phenomenon

20. Ex: Thermocouple Calibration Volts, V Temperature, F

21. In LabVIEW Create a sub-VI to convert from voltage to temperature Document when you did this calibration –If possible, include serial numbers

22. References http://en.wikipedia.org/wiki/Pressure_measurement http://www.freepatentsonline.com/6604428-0-large.jpg http://en.wikipedia.org/wiki/Pressure_regulator http://www.stanford.edu/class/me220/data/lectures/lect08/lect_4.htmlhttp://www.stanford.edu/class/me220/data/lectures/lect08/lect_4.html http://zone.ni.com/cms/images/devzone/tut/a/d11edcae1720.jpg http://www.pchemlabs.com/files/images/531_gauge_tube.jpg http://www.lesker.com/newweb/Gauges/gauges_technicalnotes _1.cfmhttp://www.lesker.com/newweb/Gauges/gauges_technicalnotes _1.cfm http://www.varianinc.com/image/vimage/docs/products/vacuum/ pumps/ion/vacion150/shared/vacion150-180.gifhttp://www.varianinc.com/image/vimage/docs/products/vacuum/ pumps/ion/vacion150/shared/vacion150-180.gif http://www.plasmainstrument.com/images/duo5pump.jpg http://commons.wikimedia.org/wiki/File:Cut_through_turbomolec ular_pump.jpghttp://commons.wikimedia.org/wiki/File:Cut_through_turbomolec ular_pump.jpg http://www.medivactech.com/images/cryotorr_6.jpg

23. References http://www.thermoworks.com/products/logger/images/logmaster/RFTC4 000A_240x225.jpg http://z.about.com/d/homerepair/1/0/0/5/-/-/mercury_tstat_1.jpg http://img.alibaba.com/photo/11295842/Thermistor_Sensors.jpg http://www.cih-group.co.uk/reheating.htm http://www.yearone.com/enthusiast/restoarchives/spring98/sp98motow nmuscle/momuscle2.htm http://www.lumasenseinc.com/files/Image/technology/temperature.jpg