Hobby Electronics Basics making thermocouple temp probes?

> I've got some 1/8" OD 316 stainless tubing on order from
> McMaster-Carr, already have some thermocouple wire rated
> for 2K=B0F, 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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>
> 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.

> 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.

> I appreciate the advice. The t-couple wire pair is insulated in
> a single woven material, and each individual wire is also
> insulated. I'll have to remove the main insulation to get
> the two wires to fit inside the tube. The potting agent would
> be used to seal the two wires going into the tube to keep
> water and dirt out. The patting agent I looked at in the catalog
> has aluminum in it, so it would presumably be conductive. I
> don't know if the agent would soak through the woven insulation
> around the individual wires.

>
>JazzMan wrote:

>> 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.