How can I turn an ordinary electronic tester into a pyrometer for measuring the temperature of a ceramic kiln?

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legionlabs8 years ago
I've done this with a parts tester with an ohmmeter and a thermistor before (at lower temperatures). Just be sure to calibrate it! You can do this by measuring the resistance of the thermistor at various known temperatures, then either performing a linear regression or just graphing it in openoffice/Excel. If you're lucky enough to have a datasheet for a thermistor, that sort of works too. Alternatively, you could use the thermistor as a frequency determining resistor in an astable 555 oscillator, then use a frequency counter on your electronics tester if it has that option. While this may seem more complicated, it will be easier to interface the system to a microcontroller if you decide to some day. Finally, it's worth mentioning that an infrared photodiode combined with an op-amp could measure the temperature at a distance, but would be a pain to calibrate.
rosquillo (author)  legionlabs8 years ago
Thank you for your reply Legionlabs. I wish to measure temperatures inside a ceramics kiln and i'm afraid that at about 1.000 ºC, thermistor wil burn. Regards.
You're right, it will. A quick search on digikey does not find any thermistors that work in that range.

A peltier effect device (thermocouple) may work, as it generates a small voltage based on the temperature difference between its two sides. That might work at a higher temperature.

However, at 1000 degrees... I'd be tempted to try remote sensing. You could buy a "temperature gun" for 200$ or so, or try to fake it by building an array of infrared photodiodes and measuring the *current* (not voltage) that is produced when they have line of sight to the center of the kiln. This would require careful calibration.

Ah wait, on second thought... you can use a thermistor. The thermistor will need to be placed into a sealed metal container filled with some small amount of insulation (sand?). Rather than measure the absolute value of the temperature using the thermistor, you can measure the rate at which it heats up while insulated. Knowing the initial temperature of the water and the rate of change, you can extrapolate the actual heat of the surroundings using Newton's Law of Cooling.

...honestly though, I'd gladly pay for a temperature gun rather than do calculus.
rosquillo (author)  legionlabs8 years ago
Thank you again, Legionlabs. A clever idea the last one. I think I'll end buying a second hand pyrometer in eBay. I haven't neither much spare time nor the high mathematics and electronics knowledge to finish a project like the one you suggest.
walkthewalk8 years ago
Maybe you could use your ohm meter with a thermistor.