temperature sensors

Hi there, I'm looking to sense the temperature of liquids (i.e. boiling water in a kettle). I've looked at the sensors available over at sparkfun. I want the temperature reading to be as accurate as possible.

Are there waterproof sensors available where i could drill a small hole in the bottom of a plastic mug, insert a sensor, and seal the hole? How would you guys go about doing this?

If I were to use a contact sensor attached to the outside, i would need to take into account the insulation of the container. For that I would probably need to consult my old physics books.

I've seen digital meat thermometers with a long cord that goes from a metal stake inserted into a turkey in the oven, and connects to a digital output placed on the stove top. Is there anything similar that I could use to put into a tea kettle and connect to an arduino on the outside?

Thanks for the help, it is much appreciated -Jordan

Well in industrial application for such access, they use a thermowell. It's just a metal tube with a ID dimension needed by the sensor (1/4" is common) that is closed on one end and open on the other. The vessel has a hole drilled to the OD diameter of the thermowell tube and the tube is inserted all the way in with the closed end inside the vessel. The open end of the tube is then either tapped and scewed or welded to the outer surface of the vessel. That way any temperature sensor can be inserted into the tube to measure the temperature of the internal liquid. It also has the advantage of being able to insert or remove the sensor without having to remove the contents of the vessel.

Here is a picture of an industrial model. You could probably get by with a lot simpler DIY model made from copper tubing.



using a thermowell or copper tubing could work very well for what i have in mind, thanks!

follow up question: What type of heat resistant sealant would you use? it is important to note that the sealant would come in contact with water ranging up to 100 C, and the water itself will be used for consumption (i.e. a non-toxic sealant would be preferred).