The LH0032, LH0033 and LH0063 come to mind again. - Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960
-----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Saturday, August 07, 2010 10:29 PM To: j...@quik.com; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: > Since it's inside a closed loop, the design is uncritical. > > One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You > would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and > sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V > out. I'd use something like a 100 K FB resistor and a 10K from the DAC, > assuming it's a voltage output DAC. A 1 M to the -25 V supply would > provide the 2.5 V offset. > > Another option would be to use two series opamps with the first set up as > above, and the second as a unity gain inverter with input connected to the > output of the first. The coil would connect between the two OA outputs. As > one output swings high, the other mirrors that and goes low (just as in an > H bridge). Stability might be an issue, but this has the advantage of only > needing a +/- 15 supplies. > > FWIW, > > -John > > ============= > > > > > >> Hi all, >> >> I have a Seimens master clock with a Reiffler pendulum. A lovely piece >> of work that used to provide time services in the 40s. >> >> Being a master clock it has contacts that open and close on each >> pendulum swing and so I can monitor it's accuracy quite easily using >> gps and my 5370B. >> >> I've adjusted it as best I can and the best I can get is about 50 ms >> over 24 hours. However that was a one off. Temp and air pressure cause >> variations of up to 300 ms and it changes direction too. Basically >> it's hard to keep accurate. >> >> It also has a coil mounted near the pendulum and a fixed magnet on the >> pendulum bar and this coil connects to a box down below with a meter >> and a knob. They are labelled in sec/day. The electronics in the box >> are not clear (being quite old) but by measuring the current in the >> coil it quite simply increases the current one way to slow the clock >> and the other way to speed it up. (I'll admit the physics of this >> doesn't make sense to me - but it works!) >> >> It's about 25v in the coil and goes up to 60mA max. Even at levels of >> 2mA has an effect. >> >> Using this control it's quite easy to manually bring the clock back to >> the right time if it's say half a second fast. >> >> What I want to do is control the current in the coil with a micro >> controller which I have attached to a rubidium oscillator. Getting the >> pps from the pendulum clock in and comparing to actual time is easy, >> but I need a way to control the current through the coil so it can >> dynamically adjust the clock. >> >> I need the current to go from say -10 to +10 mA (at 25v) and this >> needs to be controlled via a micro controller output (which goes from >> 0 to 5 with 2.5 being the 0mA point). >> >> I can either use the D/A in the controller (or PWM an output I suppose). >> >> I'd appreciate some thoughts on circuits to do this. Software side is >> not a problem. >> >> Jim Palfreyman >> >> _______________________________________________ >> 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. >> >> >> > > > _______________________________________________ > 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. > > _______________________________________________ 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. _______________________________________________ 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.