Source for Ring Thermocouples?

[North Coast Cab]

I've purchased them before, but I can't find the online source anywhere. Looking for the 14mm ring thermocouple for use with CHT gauge.

Thanks, John

[randywebb]

Omega has all sorts -- but you need to know what type it is - K is a good bet.

[Grady Clay]

I agree with Randy, you first need to know what type of thermocouple. Omega is a good source of info if not product.

You can buy copper 14 mm ID electrical connections for a few ¢ that will work well. Pay attention to insulating the junction with some heat-shrink and allowing proper clearance for the plug wrench.

There are better ways of measuring head temperature than under the sparkplug but this will do.

Best,
Grady

[North Coast Cab]

Type K or KX
I have the extension wire, but can't remember where I bought the ring terminals from.

[unclebilly]

Actually, if you use copper or other type connectors, you may introduce error to your temperature measurement if you have junctions at different temperatures.

I don't want to bore you with peltier effect nuances but if you run a copper wire from the thermocouple to the gauge and say the temp is 100°C at the thermocouple to copper wire junction and say 20°C at the gauge where you connect from the copper wire to the gauge terminal you could be out by as much as 80°C on your measurement depending on the corrosponding voltage generated by the Chromel - Copper junction and the Alumel - Copper juntion on the other side of the circuit (assuming type K).

Using copper connectors should be OK because you can assume constant temp from where the connector terminated to where it touches the thermocouple wire.

An alternative source for thermocouples (cheaper and better quality than OMEGA) is Thermokinetics.

[randywebb]

Let me put it this way - every junction or connection you make where different metals meet IS a thermocouple. You only want one thermocouple, and that's at the end.

... that's the simple version.

[Joeaksa]

Look for something like this in an aircraft supply store. Look for experimental aircraft that use VW or Subie car engines in an airplane.

www.wicksaircraft.com
www.aircraftspruce.com

http://www.chiefaircraft.com/cgi-bin/air/hazel.cgi/hzpi/u/HzSt0202I5821GovAl/hazel.cgi?action=SEARCH

[unclebilly]

Originally posted by randywebb
Let me put it this way - every junction or connection you make where different metals meet IS a thermocouple. You only want one thermocouple, and that's at the end.

... that's the simple version.

You are right but if you go from Metal A to Metal B you get positive x volts at a certain temp. When you go from Metal B to Metal A, you get negative x volts at that same temp. So if your junction has a constant temp, you don't get any effect in your measured voltage (temp) because the 2 thermocouples you add by introducing a third metal cancel out.

Like I said above, where you can get into trouble is if you use copper wire that has a different temp at each end.

I think we are in viscous agreement here.

[randywebb]

we are - I posted the "simple version" so we could avoid confusing everybody...

...look at the K&N filter thread as one example of how things can quickly get out of hand.


Not everybody knows what they can get away with, so avoiding all 'other' thermocouples will keep them safe & warm at night.

[North Coast Cab]

Does anyone have a direct link to buy 14mm ring thermocouples and extension leads? I need two type K for my dual CHT gauge.