Don wrote:
In that case, what and where is the reference for the heater servo?
It will be a voltage or current, suitably regulated and conditioned. The temperature sensor's signal will be (or will be converted to) a voltage or current that is compared to the reference voltage or current. Zeroing and scaling are done in the servo amplifier and/or the reference conditioning.
In principle, you could do the same thing with frequency -- feed a voltage-controlled oscillator into a frequency-to-voltage converter and servo the FVC output to a reference voltage. But the physical signal we can generate directly most accurately is frequency (using quartz crystals or atomic resonators). Think about it -- most time nuts have one or more frequency standards that are not only stable, but accurate to E-9 or better (sometimes quite a lot better), and can scale that accuracy to a wide range of frequencies. The volt nut, on the other hand, struggles to maintain repeatability -- much less accuracy -- to parts in E-7 at just one voltage.
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
