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A simple rugged device for monitoring temperature. The device is made by fastening two metal strips that have different coefficients of linear thermal expansion
Bimetallic strip thermometer
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A precision resistance-measuring device that is calibrated to give the proper temperature reading.
Bridge circuit
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The change in resistance per degree change in temperature, usually expressed as a percentage per degree of temperature.
Coefficient of resistance
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A sensor (typically thermocouple) used to measure the surface temperature of components through physical contact with the component.
Contact Pyrometer
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An indirect temperature measuring device constructed of pure metals or certain alloys that increase linearly in resistance as temperature increases and, conversely, decrease in resistance as temperature decreases.
Resistance temperature detector (RTD)
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A measure of the average kinetic energy of the molecules of a substance.
Temperature
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A temperature measuring device consisting of a pair of dissimilar metal wires joined at one end.
Thermocouple
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A sensor (typically infrared) used to measure the surface temperature of components without physical contact
Optical Pyrometer
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An electrical device used for measuring electrical resistance. It consists of a conductor joining two branches of a circuit.
Wheatstone bridge
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STATE the three basic functions of temperature detectors
Temperature detectors are used to provide three basic functions: indication, alarm, and control
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DESCRIBE the two alternate methods of determining temperature when the normal temperature sensing devices are inoperable
The dual-element RTD has two sensing elements, of which only one is normally connected. If the element in use becomes faulty, the second element may be connected to provide temperature indication.
If an installed spare is not utilized, a contact pyrometer (portable thermocouple) may be used to obtain temperature readings on equipment or systems that are accessible.
If the malfunction is in the circuitry and the detector is still functional, it may be possible to obtain temperatures by connecting an external bridge circuit to the detector. Resistance readings may then be taken and a corresponding temperature obtained from the detector calibration curves.
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STATE the two environmental concerns that can affect the accuracy and reliability of temperature detection instrumentation
Ambient temperature variations will affect the accuracy and reliability of temperature detection instrumentation. Variations in ambient temperature can affect the resistance of components in a bridge circuit and the resistance of the reference junction for a thermocouple.
Ambient temperature variations can affect the calibration of electric/electronic equipment. The effects of temperature variations are reduced by the design of the circuitry and by maintaining the temperature detection instrumentation in the proper environment.
Humidity will also affect most electrical equipment, especially electronic equipment. High humidity causes moisture to collect on the equipment. This moisture can cause short circuits, grounds, and corrosion, which, in turn, may damage components. Maintaining the equipment in the proper environment controls the effects due to humidity.
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EXPLAIN the basic theory of operation of a bimetallic strip thermometer
- A bimetallic strip thermometer is a simple, rugged device for monitoring temperature. The element is made by
- fastening together two strips of metals with different coefficients of thermal expansion. The general range of
- bimetallic elements is from –200°F to 1,000°F
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DESCRIBE the basic construction of a thermocouple including
- A thermocouple is constructed by joining two dissimilar metal wires at one end. The other end of each wire is
- connected to a measuring instrument
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