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Note: Temperatures discussed are inrelation to table #7, page 15, of ANSIMC96.1, August, 1982.When ordering thermocouple wire orelements, be certain that the Type (K, J, E, etc.) corresponds to that of theinstrument with which it will be used. unexposed Hot junctionexposed or unexposed. An thermocouple junction is whether it’s grounded or ungrounded. In thegrounded construction, the thermo-couple junction is electrically connect- ed to the sheath or protecting tubematerial. An ungrounded construction has its junction electrically isolated from its sheath or protecting tube.Each style has advantages and dis-advantages depending on your par- ticular application and electricalconsiderations. exposed junction has its bare thermoelementsin contact with the substance being measured. An unexposed junction has a shielding to protect it from hostile environments. Unexposed junctions are commonly found in thermocouples made from mineralinsulated, metal-sheathed cable.Another aspect of the Thermocouple Selection Thermocouple specifications areselected to meet the conditions of the application. Only general recommen- dations on wire gauge size and type can be given. Some of the consider- ations involved are:•Length of service •Application temperature•Atmosphere•Desired response time •Accuracy The temperature ranges of the com-monly used thermocouple types are given in the (Initial CalibrationTolerancesTable on pages61 - 62.)Smaller wiregauges provide faster response at the expense of service lifeat elevated temperatures. Largergauge sizes providelonger service life at the expense of response. As ageneral rule, it is advisable to protectthermocouple elements with a suitable protection method.

Application Guide catalog - 7347 Application Guide

The Art of TemperatureSensing

Thermocouple Junction All thermocouples have Hot and Cold junctions. Further, the Hot junction maybe physically exposed or unexposed (protected).The

Thermocouples

Cold, Hot or junction reference junction, is the junction subject-ed to the heat being measured. The is anotherjunction in the thermocouple circuit,usually at, or compensated to, 0°C(32°F). Continued Cold junctions are generallyeliminated in the thermocouple circuit by using electrical or hardware compensating methods.A thermocouple’s thermoelectric volt-age is generated between the Hot and Cold Cold junction end. The thermocouple’s physical con-struction may have its junctions, not where the twothermoelements are physically joined. The Seebeck effect takes place in the temperature gradients between theisothermal portion at the Hot junctionend and the isothermal portion at the 40