Nancy Marshall wrote:
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I hope 1 °F precision of temperature is suitable.

`What is your temperature range ? If its a 1000 degrees 1 deg (f or C) is a high accuracy, especially from a thermocouple.

If the sensor fails, It is desirable to see that sensor with a LED indicator as an visual alarm signal. But I don't know,


Easy, the answers become wildly out of range. Experiment by measuring the output of your sensing circuit in the two obvious fault conditions open and short circuit.

but your sound is good, triac will be better as an switching device.

Triacs are good, but you will need to do some zero volt crossing control somehow. What is your sampling interval ? Surely not three hours ?

Steve