the thremocouple should extend into the firing chnber at lest 1 inch beond the brick, the acrual priobe is in the very tip, but you want it clear of the brick, which will be cooler than the interior of the chamber.
leavew a 1 inch clearance around the probe during loading too.. cooler ware can throw off the reading..
In addition to Moose Hunter's good advice on 1 inch clearance and protrusion, I would add that while some folks use naked probes, I am a fan of putting the probe in a protective ceramic sheath. That should help the life of the thermocouple by keeping it away from the corrosive effects of kiln gasses. Also, thermocouples can be "poisoned" by these gasses such that they give an erroneous reading, so the sheath should reduce that as well.
You will see differences of opinion on what type of thermocouple to use. The usual advice is to go for the platinum R or S types. These tend to be pricey, as you might imagine. I have been quite happy with type K (Chromel-Alumel), except for when I was just starting out and used too-thin a wire gage on home-made thermocouples (welded with a car battery and a carbon rod from a dry cell). Those died in less than 2 dozen firings.
And note that whatever type of thermocouple you use, you probably want to have the readout away from the kiln, in a cooler area. That's especially critical with older-style pure-analog pyrometers, since they typically contained no compensation for the temperature at the meter. This is called "reference junction" or "cold junction" compensation and is ABSOLUTELY CRITICAL because there are always at least TWO thermocouples in every system, like it or not: The one formed by the two dissimilar metals that you put insert into the kiln (the :hot junction") and the one (or usually two) where those same wires connect to the readout device (the "cold" or "reference" junction). The measured voltage is the total of all the junction voltages in the system, with the cold junction voltage opposing the hot junction. So if you have an uncompensated pyrometer that was calibrated for an ambient of (say) 30C and it is really at 40C, your readings could be off by 10C, the equivalent of a cone or more.
Modern electronic readouts are probably compensated (but it wouldn't hurt to check), but you still probably want to keep the electronics away from a hot kiln.
Which brings up the issue of thermocouple type again, since you can only use the same type of wire if you need an extension (or you would have to contend with the junction temperature at the connection). The wire gage is unimportant here, so you can have a short heavy-gage thermocouple in the kiln, connected to a long thin-gage extension. But with platinum, even the extensions can get pricey.
Best regards,
Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis
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Thanks for the info, I think between you and the good folks at Axner, I maybe have a handle on it. I have to say though, I don't get the reference to Moose hunting.:) Thanks again Sa
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