It's 10:40 AM, Thursday April 7, 2011. I started the test at 10:00 PM on Tuesday, April 5, 2011. So I am 36 hours into the test. I plan on going to noon tomorrow, for a total of around 60 hours, or 2.5 days.
So far, the temperature controller has worked flawlessly. However, the 'dawn-to-dusk' (DTD), as mentioned in the previous post, appears to have been designed so as to have a deliberate delay. This delay is causing the temperature to swing a little wider (known as deadband) than I would like - it's settled out at +/- 7 dF. Because of this, at a setpoint of 140, the temperature was getting up to around 146, which is too high. So yesterday I lowered the setpoint to 137. With this setpoint, the highest reading to date is 143.95, which is rare to have happen.....most of the time it gets up around 141, while the low temperature has been 130.65, and most of the time gets no lower than 133.
I forgot to mention it, but the temperature controller is taking a temperature once per second, and thus making decisions on whether to heat (250 watt bulb in oven turned on), or coast (bulb in oven turned off).
Also, in the past, for my BBQ air inlet damper controller I developed (1999), I used Atmel AVR microcontrollers. I'm still using those, but now in the form of an Arduino. The Arduino, which has an Atmel AVR on it, really only gives me a hardware platform, with a thermocouple 'shield'. My previous development used an AVR 12-bit ADC and relays, so I had to do more development to convert microVolts to temperature, and it used some relays to control the damper motor rather than the DTD commercial product I'm using for this test. Not sure yet which direction I'll go for future product of low temperature oven. This is the Arduino UNO, which uses an ATMEGA328 microcontroller.
So things appear to be on-track for a successful test.
Test results will be eaten at noon tomorrow!