An iron-constantan thermocouple is to be used to measure temperatures between 0

Question

An iron-constantan thermocouple is to be used to measure temperatures between 0 and 200 degree C. The e.m.f. (electromotive force) at 0 degree C is 0mV, at 100 degree C it is 6.35mV and at 200 degree C it is 11.16mV. What will be the non-linearity error at 100 degree C as a percentage of the full scale reading if a linear relationship is assumed between the e.m.f. and temperature over the full range? (Answer in %, i.e., if the answer is 5%, please fill in 5, do not fill in 0.05. This is very important!)

Explanation / Answer

Given Values:-

T1 = 0oC, T2 = 2000C,

Electromotive Force : - at 0oC = 0 mV, at 100OC = 6.35 mV , at 200OC = 11.16 mV

Solution:-

If there is a linear relationship between the e.m.f and temperature, the e.m.f. at 100OC will be half of the e.m.f at 200OC i.e. 5.58 mV. This is the e.m.f for which the linear thermocouple indicates 100OC.

The actual e.m.f. is 6.35 mV at 100OC so there is an error of 5.58 - 6.35 = -0.77 mV.

As a percentage of full scale reading,

Error = (Error of e.m.f) / (e.m.f at 200oC)

= (-0.77) / ( 11.16 )

= - 0.0689 %

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