Thermocouple, Manufacturer of Thermocouple, Thermocouple Type, Thermocouple

Nutech Engineers
143-D Government Industrial Estate, Kandivli West, Mumbai - 400 067

Phone : 91-22-28683549 / 28684580,  Fax : 91-22-28674580
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Temperature Sensing Devices

Technical Information

Differential Temperature(T) Measurement with

Thermocouples are often used for differential temperature (∆T) measurement in industrial processes where the differential is of a span sufficient to generate the required signal for the associated instrumentation.  Thermocouples provide a possible advantage over other sensor types where small size and ease of interchangeability are important.

The output of a given span is not linear for the common thermocouple calibrations.  When the process requires ∆T measurement over only a restricted range of working temperatures, the non-linearity may not be significant.  The combined limits of error in degrees for two thermocouples in ∆T measurement is equal to the square root of the sum of the squares of the individual thermocouple limits of error.  For J and K calibrations, and standard limits of error for thermocouples below 277oC,  Intermediate connections should be minimized in the ∆T thermocouple circuit to lessen the introduction of parastic EMF's and the reduction of accuracy that can result.  One, or both, of the thermocouples should be ungrounded.

When two thermocouples are connected for ∆T measurement either the positive or negative legs of the thermocouples are connected together, with the remaining legs connected to the instrument. There is a reversal in polarity of the differential temperature signal when the thermocouple junctions change relationship regarding the "hot" and "cold" designations.  If a zero-centered span is not available on the associated instrument, then provisions must be made to reverse polarity at the instrument.  Reference junction compensating is not utilized for the individual thermocouples when they are connected for ∆T measurement.

A ∆T measurement is not absolute and, as such, will not give an indication of undesirable over-temperature condition in a process, location of the sensors, and installation details.

REFERENCE: R. B. Crawford "Industrial Applications of Temperature Difference Measurements", Temperature, Its Measurement and Control in Science and Industry (Remhold Publishing Corporation, New York, 1962. Volume 3, Part 2, PP.913-925

Schematic Wiring for ∆T with Thermocouples.

Thermocouple, Manufacturer of Thermocouple, Thermocouple Type, Thermocouple Assemblies, Resistance Temperature Detectors, India


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