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Temp.

QuestionAnswer
Thermocouple electrical thermometer consisting of 2 dissimilar metal wires joined @ one end, and a volt meter at the other end of the 2 wires
Thermocouple junction the point where the 2 dissimilar wires are joined
hot junction (measuring) end of the thermocouple that is exposed to the process to be measured
Cold junction (reference) end of the thermocouple that is kept at a constant temperature to provide a reference point
Seeback effect a thermoelectric effect where continuous current is generated in a current where the junctions of 2 dissimilar metals are kept @ different temperatures
Peltier effect thermoelectric effect where heating and cooling occurs at the junctions of 2 dissimilar conductive materials when a current flows through the junctions
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.
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
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
Zero thomson effect no heat is generated or absorbed. Lead only
seeback voltage peltier effect voltage @ junctions & Thomson effect voltage along dissimilar wires
law of intermediate temperatures temperature @ the end of wires determines the electrical potential regardless of the intermediate temperatures
laws of intermediate metals other metals may be used in a thermocouple circuit as long as the junctions are at the same temperature
Constantan Copper-Nickel
Chromel Nickel-Chromium
Alumel Nickel-Aluminum; (magnetic)
Type J Thermocouple iron / constantan (most common – can’t be used above 1400oF)
Type K Thermocouple chromel / alumel
Type T thermocouple copper / constantan
type E thermocouple chromel /constantan
Types R, S, B thermocouples contain platinum
thermopile electrical thermometer consisting of several thermocouples connected in series to provide a higher voltage output. Voltages of each thermocouple are added together
Grounded Thermocouples have a faster temperature response time than ungrounded because the heat is conducted through the metal walls
If one of the wires in a thermocouple breaks the voltage @ the cold joint will read zero
When the hot & cold junctions are the same the reading will be zero
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
wheatstone bridge circuit used to measure the resistance change of an RTD
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
Infrared Radiation Thermometer measures IR radiation emitted by an object to determine the object's temperature
IR detector provides an electrical output proportional to the amount of infrared radiation focused on it
Emissivity the ability of a body to reflect thermal energy
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)
Pyrometer used to measure temperatures beyond the range of a mercury thermometer
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
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
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
microbath small tank containing a stirred liquid used to calibrate thermometers. Range: -20°F to 400°F
Many transmitters include an optical isolator to eliminate an electrical path for ground currents & other electrical path for ground currents & other electrical noise
Created by: vahajuddin
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