Cable Guide - Thermocouple Cable

We hope that you liked our first blog of our monthly series 'Cable Designers Guide'. In case you did not get the chance to go through it kindly click on the link to read it. 

Here we will provide more information about Thermocouple cables. 

When a junction of two dissimilar metals is heated, an emf is generated and it is the proportional to the temperature difference between the hot junction and the point where it is measured. This principle is universally used in the industry to measure and control the temperature in process. The junction is know as Thermocouple. 

The follow types of Thermocouples have been standardised across the world with relevant standards being ANSI, BS, IEC & IS.

Thermocouple Type	+ve conductor	-ve conductor	Working temperature range	Limits of error
K - Extension	Chromel	Alumel	0 to 1100 °c	+/- 2.2 °c
K - compensation	Copper	Constantan	0 to 1100 °c	+/- 2.2 °c
T - Extension	Copper	Constantan	-185 to 300 °c	+/- 1.0 °c
J - Extension	Iron	Constantan	20 to 700 °c	+/- 2.2 °c
E - Extension	Chromel	Constantan	0 to 800 °c	+/- 1.7 °c

R-S Compensation	Copper	Constantan	0 to 1500 °c	+/- 5.0 °c
B - Compensation	Copper	Constantan	0 to 1500 °c	-

Please note: Solid wire constructions are recommended for extension and compensation cable as in case of multi stand conductor if there is a slight variation in the composition of the strands, they form their own internal Thermocouples and may add to error. 

Most commonly used conductor size is 16 AWG (1/1.29 mm)

Based on the temperature range that needs to be measured different material for insulation and sheathing are recommended. Those details will be cover in the next newsletter.

*Next newsletter in the pipeline for Cable Guide Series: Instrumentation Cables (Monthly Series)*Next newsletter in the pipeline for Cable Design Guide Series: Conductor Material Selection (Monthly Series) - Stay tuned
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