I am trying to build an oven (smoker) temperature control, and need to build a temperature sensor that works in the 80-400F range.

I have been looking at thermocouples. They are expensive, and they seem to measure temperature differences, not absolute temperature... and they will need signal conditioning. (Op-amp with noise filtering). On the positive side, there are many thermocouple probes available at fairly reasonable prices, all ready to go to work in an oven. I may end up back with a thermocouple.

Common thermistors are available for the -50 to 300C range. That is up to about 580F, which is fine for my use. However, I have the problem that I need to find a way to connect leads, and I need to find high-temperature tolerant insulated wire. I also may need to wrap/protect the sensor itself. How can I do this?

• Will a crimped tube keep a solid connection in the rough environment? Or will I need to braise the connection (perhaps with jewelry silver solder, mostly silver)?
• Is there a non-conductive material that I can coat or wrap the sensor in that will survive a dirty and hot environment?
• Heat tolerant insulated wire is quite expensive. Is there a common appliance that may have some that I can scrounge?
• Thermocouple wire is easier to find than heat tolerant wire. Is thermocouple extension wire a reliable, consistent conductor that I can use to hook up leads? The thermocouple voltages are very small, so I think I can work around any minor voltage bias at thermocouple junctions... assuming thermocouple extension wire is actually thermocouple wire. I just don't know. It might be cheaper, thermocouple-friendly alloy.
• I have seen spec sheets on thermistor probes (pre-wired with covered sensor area). I'm still trying to find them in DigiKey or similar. They are frequently even more expensive than thermocouple probe assemblies.

Check out:

http://www.sparkfun.com/products/251

That seems to be similar. Great tutorial. Typically the AD conversion needs a calibration to be more accurate. If you have access to a Fluke 80TK or Thermometer that would be helpful in getting it set correctly. I've seen the 80Tks on ebay for 30 bucks, great deal.

you sure those are thermocuple? perhaps tonight i can hook a ohm meter to the nearly identical one i have with my YATC2 kit and see if the ohmage changes with temp. i suspect since those kits only have the probe to detect with they are either digital temperature sensors or thermisters.