[time-nuts] Antique precision timing device without electronics

iovane at inwind.it iovane at inwind.it
Thu Mar 16 20:34:39 EDT 2017

This is mine, used to calibrate some aircraft related equipment:


and its diagram:



>----Messaggio originale----
>Da: "Mike Seguin" <n1jez at burlingtontelecom.net>
>Data: 16/03/2017 22.33
>A: "Discussion of precise time and frequency measurement"<time-nuts at febo.com>
>Ogg: Re: [time-nuts] Antique precision timing device without electronics
>Very interesting use of a tuning fork.
>I have only seen this once before. I have the tuning fork used with an 
>Ampex Model 300 reel to reel tape machine. The tuning fork was used as a 
>reference in the power supply that drove the capstan motor for accurate 
>It's 60 Hz not 25 Hz. It's marked B E Eisenhour. Patent is here:
>Pic is here:
>On 3/16/2017 2:04 PM, Bill Hawkins 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-bounces at febo.com] On Behalf Of Morris
>> Odell
>> Sent: Thursday, March 16, 2017 4:23 AM
>> To: time-nuts at 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

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