I've lost track of who said what in this thread, but someone cautioned against over-insulating the oven. The quest for the best insulation is not necessary or desired.
If you use aerogel and your oven controller has the least bit of overshoot, it will take a long time for the overshoot to dissipate, during which time your controller has no control over the slowly decreasing temperature. Indeed, the PID algorithm could drive the output to the heater all the way to zero while the temperature comes back to and slightly below the setpoint. This is guaranteed to produce another overshoot as the temperature continues to drop while the controller raises the output from zero. You need to have enough heat leakage to keep the heater running at a reasonable value. If you want to do something different, try using coarse and fine heaters. The coarse heater and control provide fast warmup to a small deadband where the fine heater takes over. Commercial ovens don't add the expense of a coarse heater because they assume that warmups will be infrequent. The user can wait for some warmup time before using the device. OTOH, fast warmup may be bad for the crystal. One other thing to consider when designing an oven: put the temperature sensor as close as possible to the crystal. Distance delays the sensing of crystal temp, called dead time. Dead time will cause the controller to oscillate at lower gain, so the gain has to be reduced. This reduces the ability of the controller to respond to external temperature changes, called load disturbances. Hope this was of some use. Bill Hawkins _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
