High Temperature Thermocouple Wire

[bostonman]

I'll do more testing later today.

At first I wanted to confirm the connectors were correct and assumed they'd read fine. The first obstacle was not seeing a polarity indicator (I don't know why the manufacture doesn't make the plus sign a bit more obvious - even the old ones have a tiny plus sign - anyone who doesn't know better wouldn't catch on).

I'll try the suggestions later today and update. As for the terminals being equal temperature, this could have been an issue since I went from outside to the basement. Also, I did want to submerge the ends in water so to provide a "constant" temperature.

What happens if the wire end is submerged and I hold the thermocouple wire at some mid point, does holding it cause it to sense a different voltage due to the heat from my hand or is dependent on the wire ends (I assume the answer is that I'll change the temperature by holding it at some mid point).

[mag_therm]

Type K welding recipe.

Oxy Acetylene Size 00 tip
Acet pressure ~ 4 psi, 50 kPa
Cut back t/c insulation to expose bright clean wires, and twist for about 1 turn.
Clamp so that the twist is exposed, protruding horizontally ready to weld.
Set flame as normal, then reduce oxy for excess actet feather about 10mm (3/8") long.
(That is to get the flame temperature down)
For the weld, don't allow the t/c to get in the feather, use the edge of outer cone (*) about 25mm away.
The 2 wires will melt into 2 blobs, follow them with the flame,
 which will then hopefully fuse them into one as the blobs melt back into the twist.
Then immediately remove the flame as there is no possibility to work the shape further.

Starting with 0.2mm wires, I get an oval blob about 0.7mm by 1mm
(*) The outer flame cone contains mostly CO2 and H2O. The inner flame has C and H which can cause metallurgical problems.

[LaserSteve]

McMaster Carr sells beautiful stainless steel  jacketed probes with MgO or other ceramic insulation.

That Said, Our commercial TC welder at work consists of 24,000 uF of low ESR  capacitor, an internal 1-24v adjustable  cap charger, and a metal can power scr. Triggering is provided by a string of closely spaced gate pulses to .
reduce dud welds.  Wiring to the electrodes is perhaps #8 in a very flexible welding grade flex cable.

One discharge wire (Like Litz inside) is welded to a pair of pliers, the other to some sort of moderately porous graphite composition block that is almost ceramic like in composition.

When I opened it up, my first thought was why didn't I just build this.
However whatever is mixed with the graphite and sintered is worth having. Especially if your making 100 identical TCS a year like I need to do in one batch.

You can get a good weld with a big copper stud as "side B" instead of the composition.  You just have to clean it fairly often.

I usually tightly wrap a few turns of 18 ga chromel tightly around the copper or alumel, snip the inner wire flush to the outermost coil turn, grab both conductors with the pliers. Take the exposed final turn with inner, press it firmly onto the block and hit the fire button.  I'll then hit it with a second pulse. On good welds you do not hear the audible snap on the second , but you will see the EMF shake the welding cable.

If set correctly I end up melting and fusing 1/2 turn to the inner.

Beading my old way.

Hf  start TIG welder set for  short pulse after the Argon comes on will nicely bead type T and Type K. Have not tried it with other pairings. Clamp the twisted pair into a vise..  Make the bench vise one side of the tig circuit. If needed line the vise jaws with copper plates.. Hold the Tig head about 1/16 inch above the new junction. Hit the foot pedal. Flash Bang Click puff of oxide
 done.  Hf in this case means the welder has the little Tesla coil built in to start the arc without contact.

You will never see me use the cheap plated connectors.


Steve

[bostonman]

Interestingly enough, after I stretched the new thermocouple wires, and compared them to my original, all were within about 0.5 degrees F.

Initially I kept the wire twist on the themocouple before should I need to return them due to the connector not fitting or whatever the case. Either (as previously stated) the leads that plug into the meter need to settle to equal room temperature, or, leaving the wires in a twisted state causes a difference in voltage.

Our commercial TC welder at work consists of 24,000 uF of low ESR  capacitor, an internal 1-24v adjustable  cap charger, and a metal can power scr. Triggering is provided by a string of closely spaced gate pulses to .
reduce dud welds.  Wiring to the electrodes is perhaps #8 in a very flexible welding grade flex cable.

I actually have a bench top mini welder on my wish list to tackle small projects. Some time in the future I plan to research a good one (and not too costly) to purchase.

On a side note, my original thermocouple wires were failing and I thought it was a poor connection, however, the connector was glued. Eventually I got frustrated and cracked open one connector. What I discovered was due to 'turning' the thermocouple wire over time, the exposed metal wrapped around each other causing a short at the connector junction.

These are the two types I bought:

https://www.amazon.com/dp/B00OLNZ6XI?psc=1&ref=

https://www.amazon.com/dp/B0967ZS74R?ref=ppx_yo2