I am almost finished with a major overhaul of the PID I use for roasting.

I was connecting the thermocouple wires when I came upon an issue with the color codes.

I just bought some Type K from Omega, and it came with a cert which said that red is -.

I have some type K wire I bought from ebay, stuff that comes from China, and for those, I think red is +.

Based on the information here
http://www.omega.com/techref/thermcolorcodes.html

the difference seems plausable. It seems that the US standard for K is red is -, but if you look at Japan and Europe, red is +. I am guessing that the Chinese are using the Japanese standards.

So, is this another Metric versus Imperial thing, just to confuse me?

I am going to try playing with the wires some more tonight, to make sure, but right now I think that my Chinese ebay thermocouples are red +, and the omega wire is red -.

Randy

In the US and Canada, red is always the negative lead on a thermocouple. The color of the positive lead varies (K = yellow, T = blue, J = black, E = violet).

The use of red on all negative leads must have made sense to somebody, but never did to me

If presented with a pair of t/c wires that are red/yellow, then I would assume type K with red negative, regardless of origin.

Jim

I'll hook up an chinese ebay thermocouple directly to my PID tonight, and give it my polarity test.

My test is to turn it on, check temp, and put the tip between my fingers. If temp rises, polarity is right, temp falls, polarity is reversed.

Randy

I tested my thermocouples last night.

First one was tested by connecting directly to a fuji PID. After I figured out the polarity of that wire, I used that wire to make a female connector for the PID, and the others were connected to the PID via this connection.

Three ebay chinese bead tc's, red = positive
one ebay probe tc red = positive
one ebay chinese bead can't tell the color
omega wire red = neg

So, I am convinced for the tc's from China, which is where the cheap ebay ones come from, red = +

Randy

Interesting. On the red-positive samples, what color is the other lead?

Jim

I think they are white, at least most of them were.
I'll take a look when I get a chance, I'm not getting home until late tonight, so may be Friday evening before I can check.

Randy