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PowerPoint ® Presentation Chapter 6 Electrical Thermometers Thermocouples Resistance Temperature Detectors (RTDs) Thermistors Semiconductor Thermometers.

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Presentation on theme: "PowerPoint ® Presentation Chapter 6 Electrical Thermometers Thermocouples Resistance Temperature Detectors (RTDs) Thermistors Semiconductor Thermometers."— Presentation transcript:

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2 PowerPoint ® Presentation Chapter 6 Electrical Thermometers Thermocouples Resistance Temperature Detectors (RTDs) Thermistors Semiconductor Thermometers

3 Chapter 6 Electrical Thermometers A thermocouple creates an electrical potential when the junction is at an elevated temperature.

4 Chapter 6 Electrical Thermometers The Seebeck effect causes an electrical potential when two dissimilar wires are joined and the end is heated.

5 Chapter 6 Electrical Thermometers The Peltier effect can be used to build thermo- electric coolers.

6 Chapter 6 Electrical Thermometers The Thomson effect causes heating or cooling when there is current flow through a temperature gradient in a wire.

7 Chapter 6 Electrical Thermometers The law of intermediate temperatures states that the temperature at the end of the wires determines the electrical potential regardless of the inter- mediate temperatures.

8 Chapter 6 Electrical Thermometers The law of inter- mediate metals states that other metals may be used in a thermocouple circuit as long as the junctions are at the same temperature.

9 Chapter 6 Electrical Thermometers A complete thermocouple circuit includes extra junctions from the copper wire in the leads to the voltmeter.

10 Chapter 6 Electrical Thermometers A 32°F ice bath is the reference temperature for thermocouple tables.

11 Chapter 6 Electrical Thermometers An isothermal block can be used to establish a reference temperature for the cold junction.

12 Chapter 6 Electrical Thermometers A modern digital thermo- couple system includes a voltage to temperature conversion, cold junction compensation, and a digital readout of the temperature.

13 Chapter 6 Electrical Thermometers Conventional thermocouple construction uses insulator beads to isolate the two thermocouple wires.

14 Chapter 6 Electrical Thermometers Thermocouple designations require that the wires follow a particular voltage- temperature curve.

15 Chapter 6 Electrical Thermometers Thermocouple color codes have been standardized in many countries.

16 Chapter 6 Electrical Thermometers Sheathed thermo- couples can be wired in several ways for different applications.

17 Chapter 6 Electrical Thermometers Difference thermo- couples are made of two thermocouples wired in series with reversed polarity.

18 Chapter 6 Electrical Thermometers A thermopile consists of several thermocouples wired in series in order to amplify the signal.

19 Chapter 6 Electrical Thermometers A swamping box uses resistors in each thermocouple circuit to eliminate errors when measuring an average reading of a set of thermocouples.

20 Chapter 6 Electrical Thermometers A thermocouple pyrometer uses a variable potentio- meter to balance loop resistance.

21 Chapter 6 Electrical Thermometers A resistance temper- ature detector (RTD) contains a resistor with a resistance that varies with temperature.

22 Chapter 6 Electrical Thermometers RTDs consist of precision wires wrapped around an insulator and encapsulated in a protective sheath.

23 Chapter 6 Electrical Thermometers Thermistors are available in a variety of shapes and sizes.

24 Chapter 6 Electrical Thermometers The changing resistance of a thermistor can be used as a temper- ature switch.

25 Chapter 6 Electrical Thermometers PTC thermistors have a resistance that increases with increases in temperature.


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