High temp K-type temperature probe + controller ?

[PekkaNF]

Friend of mine got a pottery oven and wants to convert it metal hardening/tempering oven.

Original temperature control system is shot, specially the sensor itself. K-type should be fine and ebay is flush with them, like this:

http://www.ebay.com/itm/3m-High-Temperature-100-1250-Degree-Thermocouple-K-type-100mm-Probe-Sensors-L-/381019882519?hash=item58b68e0417:g:WE4AAOSwxCxT0zoU

However, how realistic any of those figures are?
Operating Temperature:-100 – 1250℃
Probe Material:Stainless Steel

Cable External Shielding:Stainless Steel Braiding
Cable Internal Insulation:Fiberglass

last time I checked the fibre class has a whole lot lower temperature rating, more something like this:
http://www.awcwire.com/producttoc.aspx?id=fiberglass-thermocouple-wire

Mineral fibre might get you 500-700C.

or any recommendation for 230VAC/16A controller/probe for 900C or above?

Thanks,
Pekka

[AdeV]

The cable should be well outside of the heated area, and thus will (should!) not be affected by the high temperatures within. The hottest I've ever had a thermocouple is around 700C (in an engine exhaust stream), and it coped with that just fine - rated to 1250C, but until I pick up a certain forge, I've got nothing that'll reach those sort of temperatures to test with...

With an oven, I suspect the trick would be to drill a "tight fit" hole so the end of the probe sticks into the oven through any refractory, well away from the elements; the heat loss through the probe should be fairly minimal.

[PekkaNF]

True.....but - yeah but no but little britain...

The thermocouple junction still hast be at that temperature and part of that jacket too. I'm not overly worried outside of the probe, but hope that the insulation inside the jacket is something else. Is it possible or just too much to ask for that price and land?

Original thermocouple had ceramic beads all over it and pretty much open on the oven wall.

Pekka

[awemawson]

If you'd like ceramic beads I have a box of them tucked away somewhere

[PekkaNF]

Thanks. I'll need to check what he actually wants and gets, sizes and all. But that is a good "plan B".

Pekka

[appletree]

Stainless steel sheathed mineral insulated K type thermocouples are good for 1100 deg c.
The termination end is easy to place outside the process area.
Try this link https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiYhq2O_pLKAhXCgQ8KHS7VAsEQFggnMAA&url=http%3A%2F%2Fwww.tc.co.uk%2F&usg=AFQjCNH4LM-gNKW56WNgIHGneTrr1y1_dA&sig2=EYPjmyBEqOPpX6U7anoQrw

[tom osselton]

I saw a video a while back where they used a K type for dipping into the crucible, they used a length of round graphite from a lab supply that was drilled out for the thermalcoupler.

[awemawson]

Type K are available for use up to 1350 deg C.

I used to use a platinum / platinum-rhodium thermocouple when I had my foundry up and running, and it was supposed to be ok up to 1800 deg C, but the tip didn't last long, so it got shorter and shorter as I cut it and re-welded using oxy-acetylene.