W A T L O W
thermocouple (T/C) A temperaturesensing device made by joining twodissimilar metals. This junction
produces an electrical voltage in
proportion to the difference in
temperature between the hot junction(sensing junction) and the lead wire
connection to the instrument (coldjunction). thermistor
thermocouple aging or aging range A positive shift in electromotive force(EMF) in nickel-based
thermocouple
alloys that is caused by a temperaturegradient along the thermocoupleelements. Factors that cause EMF shift
are the measured temperature, theprevious thermal history of theelement, the amount of time spent atthe aging temperature and the amount
of the element subjected to the agingtemperature. Different thermocoupletypes age differently under differentapplication conditions. A temperature sensingdevice made of a semiconductormaterial that exhibits a large change in
resistance for a small change in
temperature. Thermistors usually have
negative temperature coefficients,
although they are also available with
positive temperature coefficients.
Application Guide catalog - 7347 Glossary
temperature, ambient Thetemperature of the air or other mediumthat surrounds the components of a
thermal system. switching sensitivity In on-offcontrol, the temperature changenecessary to change the output fromfull on to full off. See “hysteresis.” tera (T) A prefix meaning 10
thermocouple break protection Theability of a control to detect a break inthe
thermocouple circuit and take apredetermined action. Systems Internationale (SI) Thesystem of standard metric units.
12 (onetrillion in the US).
thermocouple extension wire A pairof wires connecting a thermocouplesensor to its reference junction or
instrumentation. The electromotiveforce (EMF) characteristics of theextension wire must be similar to the
EMF characteristics of thethermocouple. TFE A common short handabbreviation for PTFE ,polytetrafluoroethylene, or Teflon
T
® . TCP Transmission Control Protocol.One of two primary protocols thatdistinct Internet hosts use to establish
a connection and exchange data whileensuring that data packets arereceived in the same order as they
were sent. TCP is a session-based
transport layer protocol defined by the
IETF. See “IP” and “TCP/IP.” thermal conductivity The quantity ofheat transmitted by conductionthrough a body per unit area, per unit
time, per unit thickness for atemperature difference of 1 Kelvin.This value changes with temperature inmost materials and must be evaluatedfor conditions given. Expressed inBtu/hr-ft-°F or Watts/meter-°C. TCP/IP Transmission ControlProtocol/Internet Protocol. The twoprimary protocols used to connect
hosts and exchange data on the
Internet. TD Timed derivative. The derivativefunction. Teflon thermal EMF The ability of athermocouple to produce a voltagethat increases or decreases inproportion to its change in
temperature. thermal expansion An increase in thesize of a material that is caused by anincrease in temperature. Expressed asthe number of inches/inch/°F orcm/cm/°C per reference length. thermal gradient The distribution ofdifferential temperatures through abody or across a surface.
Glossary ® A registered trademark of E.I.duPont de Nemours & Company,covering a family of fluorocarbonmaterials that includes FEP, PFA and
PTFE. thermal lag The delay in thedistribution of heat energy throughouta system. Thermal lag can causeprocess temperature instability. Tefzel
® (ETFE) Fluoropolymer material,ethylene tetrafluoroethylene, withexcellent mechanical properties,
particularly important in wire and cable
applications. Tefzel thermal shunt A condition in whichthe mass of the sensor absorbs aportion of the heat being measured,
which results in an erroneous reading.
® is a registeredtrademark of the E.I. duPont deNemours & Company. thermal system A regulatedenvironment that consists of a heatsource, heat transfer medium or load,sensing device and a control
instrument. Telecommunication IndustryAssociation (TIA) A trade group thatsets standards for thetelecommunications industries. temperature calibration point Atemperature at which the output of asensor is compared against a
standard. temperature limit switch FactoryMutual (FM) Standard 3545. See “limitcontrol.” 209
