Re: making thermocouple temp probes?


JazzMan wrote:
> I've got some 1/8" OD 316 stainless tubing on order from
> McMaster-Carr, already have some thermocouple wire rated
> for 2K°F, and will be buying some fittings for mounting
> the probes in the exhaust manifold of my engine. My thought
> was to TIG one end shut on a 2" length of the tube and use
> a stainless compression fitting to lock the probe in place.
> I have several questions. One is, do I need to pot the
> thermmocouple wire inside the tube? If so, with what? Would
> it matter if the potting agent was conductive? Do I need to
> somehow weld the thermocouple junction to the end of the
> tube being used as the probe body? Or would simple contact
> be suffient?
>
> For reference, the engine's been modified and I've been
> editing the fuel maps in the ECM. Knowing the EGT at
> individual cylinders allows me to address flow balance
> issues in the intake manifold, for instance.
>
> JazzMan
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Like your motto, Jazz.

Exposed thermocouple beads can be grounded at the point they're
measuring (sometimes there's no other way), as long as your instrument
measuring the thermocouple is floating (like a battery-powered
thermocouple meter). As long as you've got a floating meter, a
grounded bead and a SS compression fitting is a great idea. You might
want to put a sliver of mica between the compression fitting and the
T/C bead to ensure you're not shorting out the T/C by grounding it at
more than one point. Other than that, you're in good shape.

Sounds like you've got a good plan.

Good luck
Chris

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