27 Field Instrumentation GEN Rev)
It is used to measure furnace tube temperature. It is installed by welding pad to tube or other surface.
SPECIAL FEATURES OF THERMOCOUPLES THERMOPILE: Thermocouples connected in series to measure net voltage of thermocouples.
THERMOPILE
DIFFERENTIAL TEMPERATURE Two thermocouples can be used for measuring differential temperature between two points. Connections are made in such away that emfs developed oppose each other. If temperature of
both thermocouples is equal , net emf is zero. It can be used to measure differential temperature of top and bottom of steam line.
28 Field Instrumentation GEN Rev)
AVERAGE TEMPERATURE To measure average temperature
across a vessel or duct, thermocouples maybe used in parallel connection. Net voltage produced at instrument is average voltage developed by thermocouples. For accurate measurement, resistance of all thermocouples and extension wires should be same. Due to variation in temperature of thermocouple
and length of extension wire, a swamping resistor is used (1.5 Kilo ohm normally)
Thermocouple Advantages and Disadvantages Advantages • Thermocouples are used on most transformers. The hot junction is inside the transformer oil and the cold junction at the meter mounted on the outside. With this
simple and rugged installation, the meter directly reads the temperature rise of oil above the ambient temperature of the location.
• In general, thermocouples are used exclusively around the turbine hall because of their rugged construction and low cost.
• A thermocouple is capable of measuring a wider
temperature range than an RTD Share with your friends: 
