Temperature limits for thermocouple

[NCARalph]

First, this forum is excellent!

The ETC-CB-K3MPNT thermocouple states it can be used up to 450C. Does that apply only to the tip or the entire probe and wire? For example, if I put it into a charcoal BBQ running around 600F with the tip and a couple of feet of wire exposed to that temperature will it be OK?

Also, are any of the thermocouples fast acting (< 5 sec) similar to the Thermopen?

[Entropy]

Temperature ratings for thermocouples means for the thermocouple and the attached leads and anything else attached to it unless specifically stated as an exception so it is okay for your leads of this thermocouple to be in the hot end of things.

This is a sheathed probe general purpose thermocouple and i would guess of fairly large wire. It is also type K. There are many thermocouples available with faster response times. Type T thermocouples are faster than Type K but can withstand less heat although there are t-type thermocouples that easily would handle the heat you are dealing with. Type t thermocouples are less linear however so a lot of oven applications stick with the common Type K. Only the tip of your thermocouple reads temperature and the real tip of the thermocouple is sealed inside that metal sheath. Thus, there is a lag involved in that the heat has to transfer through the metal sheath and packing to the actual thermocouple. There are exposed tip thermocouples that are used for faster response times although they can't be immersed in fluids but would do okay in your firebox i would think.

Further--the thinner the thermocouple wire, the faster the response time (and the lower the max temperature--but this is a moderate decline and charts with specs are available for type, wire size listing response times--which is a precise technical definition--and max temperature ratings. The thinner the thermocouple, the more fragile also and this would be a factor with barbeque applications i would think.

So to summarize: response time is a matter of 1) thermocouple type, 2) sheathing style and 3) thermocouple wire size.

And i should add that thermocouples are much faster than RTDs (generally three wire) while RTDs are more accurate.

There are sheathed metal transition type thermocouples similar to this down to a diameter of about .020". There are smaller ones some of which are commonly used in high temperature ovens that would not be sheathed. I have .005". .003", and .0005" Type K thermocouples. The latter are extremely fragile and come only bare wire with 8 inch leads--you have to insulate them yourself and likely add on extensions. They are cheap though and generally used in disposable applications that need accuracy.

My general impression is that a general purpose thermocouple should be fine for a barbeque as isn't barbeque a slow cook technique? The small wires are used in technical fields such as soldering where the temperature profile ramps at a rather rapid pace to prevent damage to chips, pcbs, and whatnots.

If you wanted a quicker slightly better quality sheathed type K .020" thermocouple expect to spend say $50 - $75. I could tell you my preferred source but don't feel comfortable with that as these folks here seem to be pretty good folks. It doesn't make sense they offer more than general purpose inexpensive options to me as that is fine for most--why they are general purpose and there isn't much distinction in true quality--it isn't anything other than wire. The better ones are better at the little things such as the nature of the soldered bead that holds the two wires together which is of no consequence except in highly critical applications.

the advantage of a sealed probe of course is that you can immerse it into the meat (they do have immersion probes specifically designed for this) whereas a bare wire, exposed tip would have to read either the temp of the surrounding gases or a piece of metal inside your rig--which my guess might be of some use but of less than your meat temperature.

If that helps.