B&B Electronics TCDA manual Thermocouple Overview, Thermocouple Non-linearity

Chapter 2: Thermocouple Overview

To understand the operation of the TCDA it is necessary to understand the basic construction of the thermocouple. A thermocouple consists of two solid wires, composed of dissimilar metals, joined at one end. The joining of dissimilar metals generates a small DC voltage based on the temperature of this junction. The TCDA amplifies this small voltage to a usable level for A/D converters.

The output of a thermocouple does not have a linear relationship with temperature. A close approximation for a K-type thermocouple is 40.6∝ V/° C. This approximation is used with the TCDA. Figure 2.1 contains a plot of thermocouple output voltage over a temperature range.

0.0406

Output Voltage ( V)

Figure 2.1: Thermocouple Non-linearity

Note: This plot is not to scale, and the nonlinearity has been exagerated.

Ideal line (40.6uV/C)

Actual thermocouple output

0

0 Temperature 1000

( OC )

Documentation Number TCDA0997 Manual 3

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