Hi Steve,

Since the time interval between the measured values of sensor is 3 hours, as you see it is a long duration, I think, there will not be importance of time accuracy.
I have used thermocouple as a temperature sensor within the Electronic circuit, due to the temperature variation output voltage of the circuit is changing between 0.7 and 4.3 Volts. I want to use this signal as an input and also I'll convert this analog value to digital within the program to store and do some arithmetical operation at the decision subroutine.
I hope 1 °F precision of temperature is suitable.
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, How I' ll write the program to obtain such feature. Please help.
At the begining, I decided to use the ordinary relays, but your sound is good, triac will be better as an switching device.
Thanks for your help. I look forward your opinion about this project.

Nancy