Temp.
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| Thermocouple | electrical thermometer consisting of 2 dissimilar metal wires joined @ one end, and a volt meter at the other end of the 2 wires
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| Thermocouple junction | the point where the 2 dissimilar wires are joined
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| hot junction | (measuring) end of the thermocouple that is exposed to the process to be measured
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| Cold junction | (reference) end of the thermocouple that is kept at a constant temperature to provide a reference point
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| Seeback effect | a thermoelectric effect where continuous current is generated in a current where the junctions of 2 dissimilar metals are kept @ different temperatures
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| Peltier effect | thermoelectric effect where heating and cooling occurs at the junctions of 2 dissimilar conductive materials when a current flows through the junctions
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| Thomson effect | thermoelectric effect where heat is generated or absorbed when an effective current passes through a conductor in which there is a
temperature gradient. There are 3 types.
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| Positive thomson effect | heat is generated as a current flows through the object from hot to cold; heat is absorbed from cold to hot. Copper & zinc
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| Negative thomson effect | heat is absorbed as current flows through the object from hot to cold; heat is generated as current flows from cold to hot. Iron, nickel, cobalt
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| Zero thomson effect | no heat is generated or absorbed. Lead only
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| seeback voltage | peltier effect voltage @ junctions & Thomson effect voltage along dissimilar wires
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| law of intermediate temperatures | temperature @ the end of wires determines the electrical potential regardless of the intermediate temperatures
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| laws of intermediate metals | other metals may be used in a thermocouple circuit as long as the junctions are at the same temperature
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| Constantan | Copper-Nickel
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| Chromel | Nickel-Chromium
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| Alumel | Nickel-Aluminum; (magnetic)
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| Type J Thermocouple | iron / constantan (most common – can’t be used above 1400oF)
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| Type K Thermocouple | chromel / alumel
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| Type T thermocouple | copper / constantan
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| type E thermocouple | chromel /constantan
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| Types R, S, B thermocouples | contain platinum
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| thermopile | electrical thermometer consisting of several thermocouples connected in series to provide a higher voltage output. Voltages of each thermocouple are added together
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| Grounded Thermocouples have a faster temperature response time than ungrounded | because the heat is conducted through the metal walls
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| If one of the wires in a thermocouple breaks | the voltage @ the cold joint will read zero
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| When the hot & cold junctions are the same | the reading will be zero
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| RTD | consists of a high-precision resistor with resistance that varies with temperature, a voltage or current source, & a measuring circuit. Resistance increases with
an increase in temperature
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| wheatstone bridge | circuit used to measure the resistance change of an RTD
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| thermistor | a temperature-sensitive resistor consisting of solid-state semi-conductors made from sintered metal oxides & lead wires, hermetically sealed in glass. Higher resistance than RTDs
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| Infrared Radiation Thermometer | measures IR radiation emitted by an object to determine the object's temperature
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| IR detector | provides an electrical output proportional to the amount of infrared radiation focused on it
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| Emissivity | the ability of a body to reflect thermal energy
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| Transmisivity | the ability of objects – like glass – to allow IR radiation to pass through. (Ex. Feeling the sun trough a window on a sunny day)
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| Pyrometer | used to measure temperatures beyond the range of a mercury thermometer
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| thermal imager | an infrared device hat uses a two-dimensional array of IR detectors to generate a thermal image, and may be non-radiometric or radiometric
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| infrared radiation thermometers | are calibrated with a blackbody calibrator. Heated or unheated surfaces whose emissivity is nearly 1.0. Often measured with a certified RTD
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| dry well calibrator | temperature-controlled well or box where a thermometer can be inserted & the output compared to the known dry well temperature. Uses a reference thermometer made of a
platinum RTD. Range: -50°F to almost 2200°F
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| microbath | small tank containing a stirred liquid used to calibrate thermometers. Range: -20°F to 400°F
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| Many transmitters include an optical isolator | to eliminate an electrical path for ground currents & other electrical path for ground currents & other electrical noise
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