Question

What is the output of a thermocouple?

• A. Voltage
• B. Current
• C. Resistance
• D. Change in capacitance

Hint:

Thermocouples are active transducers, meaning they generate their own electrical signal (voltage) and do not require an external power source to operate.
This distinguishes them from passive sensors like RTDs and thermistors, which change resistance.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the electrical output variable generated by a thermocouple when it measures temperature.

Step 2: Detailed Explanation:

• A thermocouple is an active analog transducer used for temperature measurement.

• It consists of two wires of dissimilar metals joined together at one end to form a measuring (hot) junction, while the other ends are kept at a reference (cold) junction.

• When there is a temperature difference between these two junctions, a thermoelectric electromotive force (EMF) is produced due to the Seebeck Effect.

• This induced EMF is a small voltage (typically in the millivolt range) that is directly proportional to the temperature difference:
\[ V = \alpha \cdot (T_{\text{hot}} - T_{\text{cold}}) \] where $\alpha$ is the Seebeck coefficient.

• Because it generates an electrical potential difference directly, the physical output of a thermocouple is voltage.

Step 3: Final Answer:
The output of a thermocouple is voltage.