Neville Michie wrote:
> I am not trying to start an argument, but I would like to point out > that PID controllers are only > good at controlling a certain class of system. > The thermal block controllers work well because of the dominant > integrating effect of the block, > the time delay for a heat front to propagate through the block is the > only concern for instability. > When instability is a problem I relocate the thermistor closer to the > heater, giving a marginal degree of under- > control. > Because the block is well insulated it soon becomes very close to > isothermal. > cheers, Neville Michie I would like to point out that the E1938A uses a PID controller and has a *transient* thermal gain of many 1000's not to mention a static gain that has in some cases exceeded 1,000,000 for a single oven. Your last statement is not generally true. The block cannot be well insulated because of the thermal overhead of the oven circuitry (the heat has to escape). I explained in my 1997 FCS paper how to achieve the isothermal condition, which is achieved by symmetry rather than high amounts of insulation. The E1938A oven works quite well if the insulation is omitted or replaced by poor insulation, except that it consumes more power. Rick Karlquist N6RK _______________________________________________ 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.
