How to use Thermocouples for Temperature Measurement – 8500911

Criteria for Temperature Selection of T/C and RTD Sensor Types

This is part two of a comprehensive three-part series that provides information for choosing an industrial temperature sensor from Thermocouple (T/C) and Resistance Temperature Detector (RTD) sensor types.

The Basics of Temperature Measurement Using Thermocouples

You are probably somewhat familiar with the thermocouple, or you wouldn’t be reading this white paper. But there are important points about thermocouples that must be understood and that will help you to make an informed selection between sensor types and avoid potential problems in your application.

First, we need to clear up a common misconception about how thermocouples work. You may have been told something like “a thermocouple produces a small voltage created by the junction of two dissimilar metals.” This simplification of the thermocouple is at best only half true, and very misleading. The reality is that it is the temperature difference between one end of a conductor and the other end that produces the small electromotive force (EMF), or charge imbalance, that leads us to the temperature difference across the conductor.

OK, simple enough, but how do you actually measure this EMF in order to discern its relationship to temperature?

The “EMF” or electromotive force refers to a propensity level, or potential for current flow as a result of the charge separation in the conductor. We refer to this propensity for current flow between two points as its potential difference, and we measure this difference of potential in volts. But in order to actually measure the EMF or voltage difference, we need two points of contact. That is, we must complete the circuit by adding a return electrical path. If we simply choose to use the same metal as a return path, the temperature difference between the ends of your original conductor would simply create an equal and opposite EMF in the return path that would result in a net EMF of zero–not very useful for measuring temperature.

To download the complete whitepaper; How to use RTDs for Temperature Measurement, click the link at the bottom of the page.

Learn More

You can find the other whitepapers in this three part series in the links below:

Part 2: How to use RTDs for Temperature Measurement

Part 3: The Best Temperature Sensor for Process Control: Thermocouple vs RTD