Pat wrote, on Tue, 23 Dec 2014 11:01:12 -0500:

I don't think you fully understood his battery analogy. It really
generates voltage. Google thermocouple. If you put it in a bunsen
burner, use your Fluke on its DC voltage range and measure the voltage
to see if it is good.

I will fully agree with you!
I do *not* know how the flame sensor works.

It appears to have two *external* electrical connections.
1. The spade end that has the controller wire connected to it, and,
2. The body (which is bolted down and presumably grounded as a result).

What is not clear are the *internal* connections (if any).

When I tested it cold, there was no connection between the spade end
and the body ground:
https://c4.staticflickr.com/8/7470/1...d3a691fb_b.jpg