ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: ThermocouplesOutlineReference listTo explore further (survival pointers of web references etc)What is a thermocouple?Major applicationsBasic working principleSlide 8Intermediate Metals and Extension WiresSlide 10Slide 11Thermocouple ConstructionNo cold Junctionexample non-cold junctionType T Thermocouple TableMajor specificationsThermocouple TypesLimitationsHow to chooseWhere to buyECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Assignment#01: Literature Survey on Sensors and Actuators Topic: ThermocouplesPrepared by:Jacob BrownDept. of Chemistry and Biochemistry Utah State UniversityE: [email protected] ; T: (435)797-1314W: http://www.chem.usu.edu/faculty_staff/webpages/jacobbrown.php3/7/200801/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-2Outline –Reference list–To probe further –What is a Thermocouple–Major applications–Basic working principle illustrated–Intermediate Metals and Extension Wires–Thermocouple Construction–Major specifications–Limitations–where to buy–how to choose01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-3Reference list1. Beckwith, T. J, Marangoni, R. D. and Lienhard, J. H., Mechanical Measurements, 5th ed. Addison-Wesley, 2003, pp. 676-691.2. Omega, Temperature Measurement Handbook and Encyclopedia, vol. MMX 6th ed., pp xx-xx, 2000.3. Seebeck, T. J. Evidence of Thermal Current of the Combination of Bi-Cu by Its Action on Magnetic Needle. Berlin: Abt. D. Königle, Akad. D. Wiss. 1822-23, p. 265.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-4To explore further (survival pointers of web references etc) •Omega, Thermocouple Selection Guide–http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=SEL_GUIDE_THERMOCOUPLE•A Wikipedia entry for thermocouple–http://en.wikipedia.org/wiki/Thermocouple•Temputures.com–http://www.temperatures.com/tcs.html01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-5What is a thermocouple?•A thermocouple is a temperature measurement sensor that consists of two dissimilar metals joined together at one end (a junction) that produces a small thermoelectric voltage when the junction is heated.[2]•The thermoelectric effect was discovered by T. J. Seebeck in 1821.[1]•The thermoelectric voltage occurs when a wire experiences a temperature gradient.•Two dissimilar wires experiencing the same temperature gradient will produce dissimilar potentials and thus create a very small µV-mV thermoelectric voltage.•The change in thermoelectric voltage is interpreted by the thermocouple thermometers as a change in temperature.[2]•Thermocouples are often abbreviated as TC01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-6Major applications •Measuring temperature of–Surface of a solid or semi-solid–Core of a Liquid or semi-solid–Gas or vacuum–Objects with small mass or small area–Oven Temperatures up to 2000°F/1100°C–Molds, dies and platens01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-7Basic working principle•In 1821, T. J. Seebeck discovered that an electromotive force exists across a junction formed by two dissimilar metals [3]–The coupling of two temperatures via two dissimilar wires A, B is the simplest of thermocouples (see figure 16.9 , [1])01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-8Basic working principle•Note that at minimum two junctions are required.–one is generally the desired sensing spot–and the other is at known preferably stable temperature•Typically referred to as the cold junction or hot junction•The thermoelectric voltage (emf) is generated by to two separate sources[1]–Peltier Effect•Created by the joining of the two metals at the junction–Temperature gradient within the junction of the Thermocouple–Major contributor–Thomson effect•Created by the temperature gradient along the wires.–Usually ignored with proper selection of wires/insulation01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-9Intermediate Metals and Extension Wires•The inclusion of a third metal has no effect on the total emf so long as:–The two ends of the wire are at the same temperature–The wire completes the simple thermocouple circuit•Figure 16.10 from [1]a) Third wire added in lineb) Third wire added at junction, typically done in order to measure the emf with a miliVolt meter01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-10Intermediate Metals and Extension Wires•It may be desirable to add copper extension leads to reduce cost.–Thermocouple wire is relatively more expensive than general copper wire•Figure 16.14(a) [1] is an appropriate use of copper extension–Temperature Tr must be known.•Figure 16.15(b) is an appropriate use of copper to extend a Copper-Constantan thermocouple.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-11Intermediate Metals and Extension Wires•Typically the Reference is a cold ice water bath–Ice water having the nice properties of•Consistent Temp = 0°C•stable until all ice is melted•Other References may be used–Constant voltage supply–Heater element temperature•Hot junction01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-12Thermocouple Construction•Thermocouples may be prepared by twisting the two wires together and brazing, or preferably welding, as shown in Fig. 16.11 [1]•Point j in Fig. 16.11 is the location of the effective junction.–Notice it is on the inside between the two wires at the first point of contact–This point is where the effective temperature is being measured01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-13No cold Junction•If no cold junction is used.–The voltmeter terminal temperature must be known.–Preferably held constant•Allow system to run for an hour before operating–Once temperature of terminals is known it can be added/subtracted from the measurement.01/14/19ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-14example non-cold junction•Example–Temp of non-cold junction = 20°C–Emf read by milivolt meter = 2.887mV–Thermocouple
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