Thermocouple measurement — What is the primary purpose of compensation in a thermocouple measurement system?

Introduction:
Thermocouples generate a voltage proportional to temperature difference between the measurement (hot) junction and the reference (cold) junction. Practical systems require compensation so the indicated temperature corresponds to the desired absolute or referenced value rather than an uncontrolled junction temperature.

Given Data / Assumptions:

• Two junctions exist: measuring junction and reference (cold) junction.
• The thermocouple voltage depends on temperature difference, not absolute temperature alone.
• Electronics can implement reference-junction compensation (RJC).

Concept / Approach:

Compensation senses the reference junction temperature and adds (or subtracts) an equivalent correction so the system reports the true temperature of the measuring junction. In effect, it cancels the unwanted voltage arising from the cold junction being at an ambient temperature different from the standard reference (e.g., 0 °C).

Step-by-Step Solution:

Verification / Alternative check:

Comparing corrected readings with an ice-point reference or a calibrated thermometer validates that compensation removes the cold-junction offset over typical ambient ranges.

Why Other Options Are Wrong:

• decrease temperature sensitivity: Compensation maintains accuracy, not sensitivity scaling.
• increase voltage output: The aim is correctness, not maximizing signal level.
• used for high-temperature circuits: Compensation is universal, not only for high temperatures.
• eliminate reference junctions: Physics still requires a reference; compensation models it digitally/analogically.

Common Pitfalls:

• Neglecting wire type and junction location, leading to unintended junctions and errors.
• Using linear approximations beyond valid ranges; thermocouple curves are nonlinear.

Final Answer:

to cancel unwanted voltage output of a thermocouple