I am learning electronics and I just got stumped. I was just looking at a flame sensor and it appears to have only has one connector.
I thought sensors in general need two wires to form a complete circuit. How can current travel from the flame to the rod to create a complete circuit? If you wanted to measure the voltage or current of the sensor on an open flame, how can this be done with a multimeter? What do you reference it against? I thought the metal collar was a grounding point, but this is used to bolt the sensor to a furnace. Is the furnace acting as a reference point?