I think Bob Pease of National Semiconductor fame mentioned looking for the earliest use of phase locked loops and finding a reference to a European clock maker who had a master pendulum clock with a mechanical coupling that phase locked newly built clocks when left connected overnight.
On Thu, 16 Mar 2017 20:22:42 +1100, you wrote: >Hi all, > >I was recently asked to resurrect this interesting device by a colleague who >collects antique scientific instruments. ItÂ’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 t o > 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.
