thermocouple soldering to D-type connector

[asimpson]

Is it possible to solder K-type thermocouples to a D-type connector? Need it for a vacuum chamber feed-through.

How can I do this?


Thanks

 

[BrianG]

K-type is made with chromel/alumel wires, both high in nickel. These may solder with the right flux, but note that you will get a cold junction on each pin. This may possibly cause an error in your application unless you apply compensation.

 

[VEBill]

A common approach is to employ a suitable 'thermocouple terminal block' to transition to normal copper wire.

This assumes that you can find a suitable location (avoiding extreme temperature) for the transition inside the chamber.

 

[Compositepro]

I have seen laboratory instruments that have used DB-9 connectors for thermocouples. You do want to keep the connector at a uniform temperature, which should not be difficult.

 

[waross]

The copper wire extensions may work well in lab applications but in industrial and commercial applications thermo-couple extension wire of similar composition to the thermocouple leads should be used.
Part of the effect of a thermo-couple is a characteristic potential gradient when the ends of a conductor are at different temperatures.
The use of thermo-couple extension wires alows the accurate determination of the temperature difference between the measured point and the cold junction and compensation circuits.
The voltage gradient is not the same for different materials. The use of copper extension wires will tend to ignore any temperature difference between the ends of the copper extension wires.
Copper extension wires may be used only when the transition to copper is at the same temperature as the measuring circuit
OR
An informed decision has been made to ignore the errors introduced by the use of copper extension wires.
Again, the voltage developed by a thermocouple has two components:
First, the junction voltage.
Second the difference between the voltage gradients of the extension wires.
Back to the original question.
Soldering results in two junctions. wire to solder and solder to wire. These junctions will cancel each other and should not effect the accuracy. The challenge is to find a solder/flux combination that will perform well.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[btrueblood]

Can you not use a crimp termination for the D-sub connector pins? All problems with calibration noted above still apply, but at least you can get a reasonably repeatable connection. Soldering of TC wire is tricky under the best of circumstances, you will need a fairly acidic flux to cut the nickel and chromium oxides. Regular electronics-grade rosin flux won't do it.

 

[catserveng]

The engine mounted TC rails on many CAT engines use soldered connections for amphenol type connectors, I've had to field repair many.

http://www.michsci.com/pdf/TC-soldering.pdf

The above link was helpful to me, key is get it clean, clean, clean.

The standard field connection for most of the CAT (and many other manufacturers) these days are Deutsch DT style connectors with gold plated pins.

Hope that helps, Mike L.

 

[ScottyUK]

You will probably find that a solder wire with a fairly active flux is required. Rosin is next to useless on nickel, but the water-washable synthetic fluxes are often good, if selective. You must absolutely must clean it off after making the joint because it is quite aggressive.. Failing that, a plumber's flux such as Fry 'Powerflow' will likely make the joint but again make sure you clean it off.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[asimpson]

Thanks Everybody