Morris's figure of "taking over a minute to stop oscillating" at 25Hz, implies a Q in the ballpark of 25*60, or Q>1500, which is quite good for a tuning fork in air (usually quoted around 1000).
Tim N3QE On Thu, Mar 16, 2017 at 2:04 PM, Bill Hawkins <bill.i...@pobox.com> wrote: > Hi Morris, > > If there's no active devices (and you'd be sure to see them, not solid > state) where does the power to operate the motor come from? Is it the > same contacts that drive the fork? > > It's amazing that there is high Q when contacts must be operated by the > fork. > > Did it come with instructions for setting the weights at the end of the > fork tines? > > Best regards, > Bill Hawkins > > -----Original Message----- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Morris > Odell > Sent: Thursday, March 16, 2017 4:23 AM > To: time-nuts@febo.com > Subject: [time-nuts] Antique precision timing device without electronics > > Hi all, > > I was recently asked to resurrect this interesting device by a colleague > who collects antique scientific instruments. It's a "Chronoscope" made > by the H. Tinsley company in London in the early 20th century and used > to measure time intervals with the precision of those days. It's large > and heavy in a polished wooden case with a top deck that hinges up to > reveal the innards. > > The timing reference is a large tuning fork about 30 cm (1 foot) long > and running at 25 cps. It's normally in a glass fronted housing (removed > for the video) that includes a pair of hinged mechanical arms for > starting it. It's maintained in oscillation by an electromagnet and > contact arrangement powered from a 12V DC supply. The fork amplitude is > controlled by a rheostat - too much and the tines impact on the magnet. > The video frame rate makes the fork look slower than it actually is. I > was able to extract a signal and measure the frequency with a modern GPS > disciplined counter - it's 0.007% off its specified 25 Hz! The frequency > is too low for my HP 5372A so I was not able to easily get an idea of > stability or do an ADEV measurement. The fork has quite a high Q and > takes over a minute to stop oscillating after the power is turned off. > There's a built in higher voltage AC power supply, probably a mains > transformer, potted in beeswax in a polished wooden box inside that is > intended to > energise a large neon strobe lamp used to adjust the fork. > Unfortunately the lamp was not with the unit and is no doubt > irreplaceable. > > The 25 Hz signal is filtered by an LC network and used to run a > synchronous motor in the Chronoscope unit. Synchronous motors not being > self-starting, you need to tweak a knob to get it going - there's a joke > in there but I can't for the life of me think what it could be ?? The > "Contact" switch and associated socket on the back controls an > electromagnetic clutch that connects the clockwork counter mechanism to > the motor and the contact "on" time is indicated on the dials with 10 mS > resolution. > > There's not a single active device in there and after a clean and lube > it runs very nicely from a modern 12V DC plugpack. My friend is very > pleased with it and it will take pride of place in his collection. > > I'd be interested to know if any time nuts have knowledge or experience > of this lovely instrument. > > A video of it is at https://youtu.be/i5S8WS9iN_E > > Enjoy! > > Morris > > _______________________________________________ > 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.