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I tend to agree with the try your luck with it the way it is .
If you just have to know , refractory brick drill easy the k type pyrometer is probably the cheapest way to moniter temps with a reasonable degree of accuracy.
You just want to try to get a probe that gets you somewhat centered between the heat coils
You want over 700 degrees, so you need a type "K" thermocouple .
6061 Aluminum melts at 1112 F so you want to check the accuracy of the oven.
Set a piece of aluminum in the oven and have it "bridge" between two pieces of copper wire
Feed the copper wire outside the oven without grounding the wire or touching each other and have a simple Ohm-meter measure the resistance
of the wires as it sees with the Aluminum ... Now turn on the oven and set it for 900. at the same time, watch the Ohm-meter
Gradually raise the temp. when the Ohm-meter goes to infinity, the Aluminum has melted and broken the circuit and you should see what your control says ! If the control says it is at 1100 or so, you are good to go
Rich
Perfect, thank you. A cheap home shop method for testing readout/control accuracy close to the range that I need accuracy. If it's not pretty darn close, I'll know I need to invest more time and attention (money) toward gaining accuracy I need.
johnfreese wrote: ↑Tue Jun 22, 2021 5:01 pm
PID temperature controllers with digital readout are quite cheap as are the thermocouples to go with them. Check the bay.
So it's easier if something is inexpensive and can be bought for everyday use.
Many years ago when I was playing with thermocouples to measure the temperature of a Stirling engine hot end, I only had an analog meter that read in Degree Fahrenheit but needed calibration. I did have some type K thermocouples from my research work in engineering school.
Thermocouple output is a pretty linear voltage vs temperature curve, unless you are chasing fractions of a degree. Thus, using a good digital voltmeter that reads millivolts, you are good to go with a look-up table for that thermocouple type.
Unfortunately I had no access to such a voltmeter, and I proceeded to calibrate my setup as follows.
Obtained some pure copper, such as electrical wire, and some pure tin. Placing these into a small sample crucible I heated these up with a propane torch until the sample melted, plus a little more.
Then I stuck the thermocouple bead into the molten pool and watched the temperature drop. The temperature remained constant until all the metal had solidified. This gave me time to adjust the meter's series resistance to show that metal's melting temperature.
I did this twice to get two points on the curve; one for tin, with a melting point of about 450 deg F., and the other for copper, with a melting point of just under 2000 deg F. (note that these temps are from memory!!). For a type K thermocouple these are excellent calibration points.
As I stated above, the voltage/temperature relationship is very linear and was confirmed by my tests.
If I were to do this again I'd settle for a single point confirmation by using pure aluminum such as electrical wire. (I think that's pretty pure, but better check).
But a good digital voltmeter as described above is nowadays sufficient. Unless you want to experiment yourself:-))