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

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@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.

There is a power amplifier that was available at the time. It's called a
relay.
It would probably take two or three stages to get enough power to drive
the motor.
Were there any relays in the box?

Conservation of power says some must be taken from the fork to operate
the contacts.
This would reduce the Q, but only while the fork was touching the
contacts.
When the battery is switched off, amplitude would decay until the
contacts were no longer touched.
Then you'd get over a minute for it to stop.

At least, that's how it looks to this mechanical engineer.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Bill
Hawkins
Sent: Thursday, March 16, 2017 1:05 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Antique precision timing device without
electronics

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@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.

On British submarine telegraph cable systems, repeater stations and receiving sites employed tuning forks. Repeater sites were at cable traffic junctions or islands; e.g., Ascension and St Helena Islands in the Atlantic, Cocos Keeling in the Indian Ocean, Norfolk Island (junction) and Fanning (repeater) in the Pacific.

The purpose of the tuning fork was to govern transmitted symbol rates for outgoing traffic. “Cable code” is a bipolar form of international telegraph code (almost exclusively what one hears on the radio today), where both the “dot” and “dash” elements have equal duration.

Equal-duration dots and dashes saved time, meaning more revenue-generating traffic could be sent. This was especially important when cables had no compensation, and the transmission rates were extremely slow due to large cable capacitance.

Dots and dashes in cable code are instead distinguished by their polarity. Alternating dot-dash sequences, when they occurred, created polarity reversals on the cable used to recover the best point for pulse sampling.

When no telegrams were being sent, an idling polarity-reversal sequence was periodically injected into the cable (every 15-20 seconds or so) to maintain pulse detection synchronization with the distant receiver.

The tuning fork rate was governed by a Synchronome master clock (and its backup). An implementation of electro-mechanical frequency control (EMFC?) employed a stepper relay to move the weights on the fork by small amounts to maintain frequency synchronization with the Synchronome. Here’s one surviving system, the master clock and tuning fork for PK http://telegraphmuseum.org/object/synchronome-clocks/ (Porth Curno), the landing point in Cornwall England used for most of the Empire’s submarine telegraph cables networks (and for many optical fiber cables today). The Submarine Telegraph Museum (originally established by Cable & Wireless) on this site is a fascinating visit.

Frequencies around 15 Hz were common on early 20th century cables, depending on the degree of success in compensating for the inherent capacitance on a cable thousands of miles long surrounded by conductive sea water. Cable compensation is an entirely separate subject outside the scope of a time-nuts forum.

Basically, every function we see today in fiber optic or electrical synchronous transmission systems (timing, encoding, transmission, pulse regeneration, reception, decoding, printing) was invented in electro-mechanical form for submarine telegraphy — and realized in beautiful brass & mahogany machinery.