Precision Temperature and Humidity Instrumentation
Overall Measurement Accuracy
The error in measuring temperature with thermocouples is related to several factors which affect the overall accuracy of the measurement. These are:
Thermocouple wire error: This is the error resulting from the fact that a given sample of thermocouple wire will not exactly meet the temperature vs millivolt relationship given in the standard tables. In fact the allowed deviation from the standard tables is substantial, as indicated in the above section.
Reference junction error: This is the error in determining the temperature of the reference junction.
Voltage measurement error: This is the error in the measurement of the small voltage produced by the temperature difference between the measuring junction and the reference junction.
Linearization error: The temperature vs. millivolt relationship for thermocouples is inherently non-linear. The accuracy of the conversion from voltage to temperature depends on what method is used to make this conversion. Most commonly there is a fit to standard polynomials or by interpolation within the table values. Both of these methods are subject to some degree of error.
GEC Instruments has been able to achieve very high accuracy in measuring temperatures with thermocouples by using special proprietary techniques to minimize the reference junction error, the voltage measurement error and the linearization error. And the easy-to-use two point calibration functionality within our PinPoint Monitor software enables the user to minimize the effects of thermocouple wire error by calibrating individual thermocouples against a known standard.
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