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Thermometer for furnace

OK I have created Shark500's furnace (which was an awesome Instructable). I have made some modifications to it. Now I'm curious can some one help me make a inexpensive thermometer for it? I have made mine a bit bigger and I am using a 16oz propane tank as my crucible with about a 1/2" thick cement coating on it and the top is my lid. I figure I could wire a sensor through the old valve but I don't know where to start to make something like this. could some one please assist me in this it would be greatly appreciated.

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110100101108 years ago
try copper wire stretched by a spring mounted to the furnace the copper wire expands more than whatever the furnace is built of connect a long arrow as lever to the point where the wire and the spring are together so small move there makes large move at the end of the arrow use ice and boiling water to write that temperatures on the place where the arrow points afaik the strech of metals is linear so just divide it to equal parts (and go higher than the water boiling temp if needed)
Jdogg55 (author)  110100101108 years ago
wow this is a clever idea i will give it a try thanks a bunch
most mechanical thermometers and thermostats work this way. its called 'bimetallic effect'
. What you are talking about is just plain ol' thermal expansion. Bimetallic thermometers use two metals with different coefficients of expansion.
LinuxH4x0r8 years ago
Try using an infrared thermometer. You can find them for as low as $20 and they don't have to actually touch the surface to measure the temp (ideal for molten metals)