Factors that affect accuracy of thermocouple

The error in measuring temperature with thermocouples with any instruments is related several factors that combine together to affect the overall accuracy of the measurement:

1.Thermocople wire error:this is the error resulting from the fact that a given sample of bare thermocouple wire will not exactly meet the temperature versus millivolt relationship given the standard tables. The most accurate designation is for Type T thermocouple wire. The errors allowed for T type over the range -40 to 130℃ are 1.0 for standard wire and 0.5℃ for speical limits of error wire.

2.Reference junction error: this is the error in determing the temperature of the reference junction. Sometimes called “cold junction”.

3.Voltage measurement error: this is error in the measurement of the small voltage produced by the temperature difference between the measuing junction and the reference junction.

4.Linearization error: the temperature vs. millivolt relationship for thermocouples is inherently non-linerar. The accuracy of the conversion from voltage to temperature depends on the method that is used to make this conversation. Most commonly there is a fit to standard polynomials or interpolation within the table values. Both of these methods are subjection to some degree of error.

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