Millivolt Thermocouple

[HayZee518]

Thermocouples are used to measure the "bath" temperature in a steel plant. They are cheap and almost 100% reliable.

[HayZee518]

I worked at a hydro generating station in Western Mass and we used RTDs embedded in the high voltage windings of the generator to measure winding temperature. The output of the RTDs fed to measurement equipment which in turn was connected to trip relays in the master element of the generator control circuit. High temperatures would alarm an annunciator and would in turn trip the unit if it got too hot.

[HayZee518]

An RTD is a resistance thermal device used to measure temperatures in alarm systems. It can't be used as a thermocouple. Read up on thermocouples and thermopiles. They are two different devices.

[HayZee518]

Attached is a millivolt thermocouple and how it is connected in a "Mr Heater" propane infrared heater. I imagine all millivolt systems are about the same construction for the primary pilot. They all generate a millivolt signal that actuates a very small, sensitive electromagnet within the valve packet.