Thermocouple signal levels: What is the typical output voltage magnitude produced by a standard thermocouple sensor under normal temperature ranges?

Introduction:
Thermocouples generate a small voltage due to the Seebeck effect at the junction of two dissimilar metals. Knowing the order of magnitude of this voltage is essential for designing low-noise amplifiers, cold-junction compensation, and wiring practices.

Given Data / Assumptions:

• Standard industrial thermocouples (Types J, K, T, etc.).
• Measurement spans typical process ranges (e.g., −200 °C to 1200 °C).
• Open-circuit output is measured (before any amplifier).

Concept / Approach:
Thermocouple sensitivities are usually a few tens of microvolts per degree Celsius (e.g., Type K around 41 µV/°C near room temperature). Over hundreds of degrees, total open-circuit voltage is still in the tens of millivolts. Thus, the typical output is well below 100 mV, requiring precision amplification and noise mitigation.

Step-by-Step Solution:

Verification / Alternative check:
Reference thermocouple tables show millivolt outputs across the full range; instrumentation amplifiers with gains in the 50–1000 range are standard practice.

Why Other Options Are Wrong:

• Greater than 1 V: Far larger than typical thermocouple outputs.
• Thermocouples vary resistance: False; RTDs/thermistors vary resistance, thermocouples generate voltage.
• None of the above: Incorrect since a valid option exists.

Common Pitfalls:
Confusing thermocouples with RTDs or thermistors; forgetting cold-junction compensation, which is necessary for accurate absolute temperature measurement.

Final Answer:
less than 100 mV