What is the typical no-load output voltage range of a thermocouple?

The typical no-load output voltage range of a thermocouple is generally around 15 to 20 mV, which is the correct answer. Thermocouples work on the principle of thermoelectric effect, where they generate a voltage that is proportional to the temperature difference between the junctions of different metals. In common thermocouple types used in commercial applications, the output voltage will often fall within this range, making it suitable for many temperature sensing applications.

In understanding this output, it's important to note that the specific output voltage can vary based on the type of thermocouple, its design, and the temperature range it's measuring. However, most widely used types, like Type K and Type J thermocouples, typically output voltages closer to the 15 to 20 mV range when at standard operating conditions without any load. This is crucial for technicians to know when diagnosing thermocouple performance and interpreting the readouts during service work.