PID- Thermocouple wire color

[el34]

I want to undo a mistake I've posted a few times in posts dealing with building PID controllers and the meaning of the wire color on thermocouples. Recently I have learned from three different projects that the tc's from China don't adhere to US/Canadian industry standards.

What's (sometimes) coming from China-
Red=positive
Blue=negative

This revelation, probably already well known by others, came from info from dikman, 3jimbo3, and bigarm.

That is bassackwards from ANSI standards-
http://www.omega.com/techref/colorcodes.html upper left corner

Fortunately nothing bad happens from connecting it backwards, the controller will show a stupid temp reading but that's all.

For those building a controller and including connectors to allow unplugging the TC from the enclosure, be aware the connectors chosen should be specifically made for type K tc's. The metal used for the contacts needs to be correct. Auberins is a great source.

[Mike W1]

BTW, just ordered another TC from Aubers to use with my Multimeter on my smelting pot. For an extra $1 bill they'll put the connector on it. Remembering how much I "enjoyed" putting them on before it was a buck well spent.

[htuong95]

I read that the red is negative and the blue is positive. I tried that, but it caused the temperature reading to drop when heat is applied. So I made red positive and blue negative, now it works like it should. Yes, my TC came from China.

[Handloader109]

Posted this before, can't trust those foreigners. BTW, probably why they are so cheap, they are defects due to wrong wiring

[dikman]

I was in telecommunications for a lonnnng time, and red has always been + ve, blue is - ve. This applied to all the equipment we bought from Sweden, Germany, Japan etc. Also, before we changed our AC wiring colours, red was always active and black neutral (now brown is active and blue neutral).

Mike, that sounds like a bargain!

[el34]

It is enormously common for red to signify + in a DC system. I was able to remember TC color definitions because they were so wrong!

The Chinese got it right.

From Beagle-

On my TC, red/white is positive and green/white is negative.

Since no damage occurs from having it backwards other than bewilderment, knowing it may be a 50/50 chance it'll need to be reversed is ok.

[HATCH]

If you hook a TC up backwards it will read the opposite.
When the probe temp goes up, the display will go down.

[jsizemore]

I got 3 TC's over a 5 year period and they're all backwards from spec color coding.

[Beagle333]

Today I had a short in my powdercoating oven TC and had to break a new one out of the plastic and wire it up with a K plug and it was a red/yellow wire choice. Today, red was negative! Who knows?

I wired it up the other way and stuck it in the oven and the temp started dropping fast..... so I immediately knew. 'Good thing there's not much commitment when wiring up those things.

[el34]

Today I had a short in my powdercoating oven TC and had to break a new one out of the plastic and wire it up with a K plug and it was a red/yellow wire choice. Today, red was negative! Who knows?

I wired it up the other way and stuck it in the oven and the temp started dropping fast..... so I immediately knew. 'Good thing there's not much commitment when wiring up those things.

Check that link posted above, it shows the US/Canadian standard for thermocouples is red=negative, the other wire color identifies the type. And yellow=type K.

You got a proper one there my friend.

[Yodogsandman]

Uh, Oh, I haven't got all my parts yet but, I checked mine and I have a white wire with a red tracer stripe, red connector and a white wire with a blue tracer stripe and blue connector. I ordered two!

[dikman]

I wouldn't sweat it, my guess would be re = +, blue = -. As el has pointed out, no big deal if it's not. Fortunately with the probes no damage is done if it's wired in the wrong way.

[el34]

I wouldn't sweat it, my guess would be re = +, blue = -.
Agree wit ya.

The IEC (international) standards don't even have a red wire on either end.

[Beagle333]

^^True! Just flip the wires. Nothing bad happened, no smoke, no sparks, nothing except the PID reads colder as something heats up. You'll figure it out real quick if yours is backwards. Just swap em and smile. :drinks:

[el34]

^^True! Just flip the wires. Nothing bad happened, no smoke, no sparks, nothing except the PID reads colder as something heats up. You'll figure it out real quick if yours is backwards. Just swap em and smile. :drinks:

The value of being forewarned is it'll hopefully save that significant emotional moment 'oh no something's horribly wrong and I don't know what to do about it'.
Hate when that happens.

[Beagle333]

'oh no something's horribly wrong and I don't know what to do about it'

And that's exactly what I say when something like that happens too. Exactly. http://thefiringline.com/forums/images/smilies/tongue.gif