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Jan Ysselstein

Thermocouple well

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I am looking to buy some Stainless Steel Thermocouple wells like those used for salt furnaces..does any one have a good source?

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Wherever you buy your thermocouples should be able to supply them. Otherwise search for "thermowell". I'm the wrong side of the pond to recommend suppliers.

Although they are used a lot in industry, they are not often the best solution in "our" applications.

Thermowells tend to slow thermocouple response and tend to be very spendy in anything more exotic than 316 SS. Mineral Insulated thermocouple asssemblies are often a better option. 

I strongly recommend spending a few minutes scrutinising and understanding the process you are dealing with and the temperature you need to measure, before sitting down with a cup of coffee, notebook, pen and calling the technical sales folks at Omega to ask their advice. 

It is worth mentioning that bespoke thermocouples are pretty normal in industry, so the premium for non-standard is usually surprisingly small. It does mean dealing with a specialist temperature control business, rather than a box-shifter, but this gives you access to their technical knowledge and experience. 

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I bought a type S thermocouple for my kiln. They are almost impervious to oxygen but being made out of ceramic, you have to be careful not to hit them. And you must buy a reader that can be set for type S.

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Joel,

Type S thermocouples are made of two dissimilar metals, like all other thermocouples I am familiar with.  In this case a platinum/rhodium alloy and pure platinum (which gives you an idea of why they are so expensive).  Your's may be covered by a high alumina ceramic casing, but the operative parts are the wires.  Please note two things:

  1. The ceramic casings are quite fragile and also can be prone to thermal shock.  Avoid any impact or rapid thermal cycling.  If the casing cracks the wires can be vulnerable to the forge atmosphere (especially if you are using a lot of caustic flux).
  2. For an accurate reading you must use the correct thermocouple wires for the particular type of thermocouple between the actual thermocouple and the controller or gauge you are using for a readout.  Regular copper wires will give a false reading.

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Ouch. What did it cost?

I’ve been fortunate enough to salvage a few type S over the years. Even without having to consider the cost, their fragility is quite limiting. 

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2 hours ago, Dan Hertzson said:

Joel,

Type S thermocouples are made of two dissimilar metals, like all other thermocouples I am familiar with.  In this case a platinum/rhodium alloy and pure platinum (which gives you an idea of why they are so expensive).  Your's may be covered by a high alumina ceramic casing, but the operative parts are the wires.  Please note two things:

  1. The ceramic casings are quite fragile and also can be prone to thermal shock.  Avoid any impact or rapid thermal cycling.  If the casing cracks the wires can be vulnerable to the forge atmosphere (especially if you are using a lot of caustic flux).
  2. For an accurate reading you must use the correct thermocouple wires for the particular type of thermocouple between the actual thermocouple and the controller or gauge you are using for a readout.  Regular copper wires will give a false reading.

Yeah, I compared the temperature with another t/c and it was within 2°f so it should be good. But I fully understand your point, I was given the same advice before :)

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