Topics

Effect of open case vs. closed case & other issues


James Meaton
 

Hello there.
I am a relatively new member to the group and have been fascinated by all the practical and theoretical science that is being discussed around the running and accuracy of a Synchronome Master clock.
I served my apprenticeship at the factory in Westbury during the 60s & 70s, and after many years as their toolmaker I spent my last couple in the drawing office before being made redundant.
(I will have to search through my old college reports and other paperwork to be more accurate with dates).
Whilst obviously respecting the considerable knowledge of the group, I can not remember such research being done at the factory on many of these issue.  (I was the senior shop steward for most of my time there so had good access to all departments).
I do have a few spare sculling about in my workshop that I will catalogue when it gets a little warmer should anybody be interested.
I also have a mechanism that was built in to one of the fire alarm charger boxes that compares “50 hertz frequency time” from a synchronous motor against an input from a master clock.  Again I will take a good look at that early next year and make a few photographs available.  Unfortunately the case is quite rusty, but I am sure most of the mechanism is in reasonable condition.
My main hobby now revolves around music, so I do not really have the time or the space to involve an interest in Synchronome product, although I do regret not making a higher bid on eBay for a Master clock from a guy in Salisbury.
Good wishes to all.

James Meaton



On 4 Dec 2019, at 14:35, Tom Van Baak <tvb@...> wrote:

Bepi,

A few years ago I measured a Synchronome; case closed vs. case open. The change is quite immediate, dramatic, and easily measurable.

You mentioned Q. Yes, the state of the glass case door will affect Q. My goal back then was to actually compare how stable the rate was, that is, how good the timekeeping was, in both cases. For example, even though the calculated Q is higher with case open, it is possible that a clock actually keeps better time with a case closed. In other words calculated Q and actual performance are not absolutely linked.

Now, about the effect of the glass door. Rather than find that old data, I just re-ran the experiment for you. The three plots below cover the past 14 hours, about 3 PM to 5 AM.

1)

Clock rate is shown below. On the left is 5 hours of normal running, that is, closed case. On the right is 5 hours of open case. In the middle I opened and closed the door a few times, an hour apart.

<sync2b-dec4-14h-rate.png>

The results are pretty clear. For this experiment, rate increases about 15 ppm when the case is open. That's 1.3 sec/day. I hope this roughly agrees with results others have found. If not, let me know.

Closer inspection of the plot shows that it takes a while (about an hour) for clock rate to fully stabilize when the case is opened. This is not unexpected. An open case is less resistance for the bob, and since the impulse is fixed, the energy (amplitude) will slowly increase, impulse by impulse, until a new equilibrium is reached. It appears to take less time for rate to stabilize when the case is once again closed.

2)

Speaking of amplitude. Whether using Microset of picPET I always monitor amplitude. This is derived from the measured width of the photogate pulse. The larger the amplitude, the more energy in the swing, the faster the bob travels at BDC, the narrower the pulse as the thin flag passes through the photogate sensor. So here is a plot of amplitude for the same 14 hour run.

<sync2b-dec4-14h-ampl.png>

Note: rather the measure amplitude in degrees or radians the y-axis scale is percent where 100% is the normal amplitude with case closed. Comparing the left 5 hours with the right 5 hours we see amplitude increases by 6% when the clock runs with case open.

Also notice that in both cases, going from case closed to case open, or case open to case closed, there is a nice exponential ramp between the lower and the higher amplitude. The time constant conveys how aggressively the clock reaches a new equilibrium.

Quick guess. If the clock were running normally (case closed) at 2.7 degrees semi-arc (+/- 5.0 mm displacement), a 6% change means the new amplitude is 2.86 degrees. Circular error changes from 143 ppm to 161 ppm for a net change of 17 ppm. So some of the rate change is due to differential circular error.

(3)

Finally, for completeness, a temperature plot for these 14 hours. Normally my eye-level wall-mounted Synchronome is fully enclosed with an oversized, 6 foot tall, 12 cu ft, sound isolated and thermally insulated, temperature controlled vertical "coffin". In order to perform this door closed/open experiment I had to remove the coffin and set it aside. This occurred at 8 PM, 5 hours into the run. This exposes the clock to normal room temperature.

<sync2b-dec4-14h-temp.png>

The left part of the plot shows how well the enclosure works. The temperature of the clock is always about 79.2 F and often stays within 0.1 F.

The right side of the plot shows the clock running at room temperature, about 74 F. Also, it shows the effects of HVAC cycling, wiggles that are highly attenuated on the left. The middle hours of the plot show the Synchronome slowly shedding 5 degrees of heat. It takes about 3 or 4 hours.

I hope these three plots help answer your question and stimulate some thought. Let me know if you have any questions.

Thanks,
/tvb

Plots also available at: http://leapsecond.com/pend/synchronome/case.htm




Stephen Hibbs
 

Hello, All,
    I’m an even newer member to the group and am not yet quite certain of its mechanics, but here goes with a reply for Mr. Meaton, who mentioned that he regrets not bidding higher for a master clock from “a guy in Salisbury”.
    His posting got my attention because I won an eBay bid for a master clock from the UK (exact location unknown) more than a year ago. The seller went by the eBay handle of yellowheadgasket. 
    If it’s the same clock, it may intrigue Mr. Meaton to know it has come to a good home in California, near Lake Tahoe. It’s a beauty and the seller was more than helpful. I polished the case, mounted the clock on the wall next to another Synchronome master clock in an earlier-style case, and it has been running happily ever since. I hope it’s comforting, at least, to know it went to another Synchronome enthusiast. Pictures will follow when I can get back to my desktop computer if there’s interest.

Steve Hibbs

On Wed, Dec 4, 2019 at 6:59 AM James Meaton via Groups.Io <soundhutch=blueyonder.co.uk@groups.io> wrote:
Hello there.
I am a relatively new member to the group and have been fascinated by all the practical and theoretical science that is being discussed around the running and accuracy of a Synchronome Master clock.
I served my apprenticeship at the factory in Westbury during the 60s & 70s, and after many years as their toolmaker I spent my last couple in the drawing office before being made redundant.
(I will have to search through my old college reports and other paperwork to be more accurate with dates).
Whilst obviously respecting the considerable knowledge of the group, I can not remember such research being done at the factory on many of these issue.  (I was the senior shop steward for most of my time there so had good access to all departments).
I do have a few spare sculling about in my workshop that I will catalogue when it gets a little warmer should anybody be interested.
I also have a mechanism that was built in to one of the fire alarm charger boxes that compares “50 hertz frequency time” from a synchronous motor against an input from a master clock.  Again I will take a good look at that early next year and make a few photographs available.  Unfortunately the case is quite rusty, but I am sure most of the mechanism is in reasonable condition.
My main hobby now revolves around music, so I do not really have the time or the space to involve an interest in Synchronome product, although I do regret not making a higher bid on eBay for a Master clock from a guy in Salisbury.
Good wishes to all.

James Meaton



On 4 Dec 2019, at 14:35, Tom Van Baak <tvb@...> wrote:

Bepi,

A few years ago I measured a Synchronome; case closed vs. case open. The change is quite immediate, dramatic, and easily measurable.

You mentioned Q. Yes, the state of the glass case door will affect Q. My goal back then was to actually compare how stable the rate was, that is, how good the timekeeping was, in both cases. For example, even though the calculated Q is higher with case open, it is possible that a clock actually keeps better time with a case closed. In other words calculated Q and actual performance are not absolutely linked.

Now, about the effect of the glass door. Rather than find that old data, I just re-ran the experiment for you. The three plots below cover the past 14 hours, about 3 PM to 5 AM.

1)

Clock rate is shown below. On the left is 5 hours of normal running, that is, closed case. On the right is 5 hours of open case. In the middle I opened and closed the door a few times, an hour apart.

<sync2b-dec4-14h-rate.png>

The results are pretty clear. For this experiment, rate increases about 15 ppm when the case is open. That's 1.3 sec/day. I hope this roughly agrees with results others have found. If not, let me know.

Closer inspection of the plot shows that it takes a while (about an hour) for clock rate to fully stabilize when the case is opened. This is not unexpected. An open case is less resistance for the bob, and since the impulse is fixed, the energy (amplitude) will slowly increase, impulse by impulse, until a new equilibrium is reached. It appears to take less time for rate to stabilize when the case is once again closed.

2)

Speaking of amplitude. Whether using Microset of picPET I always monitor amplitude. This is derived from the measured width of the photogate pulse. The larger the amplitude, the more energy in the swing, the faster the bob travels at BDC, the narrower the pulse as the thin flag passes through the photogate sensor. So here is a plot of amplitude for the same 14 hour run.

<sync2b-dec4-14h-ampl.png>

Note: rather the measure amplitude in degrees or radians the y-axis scale is percent where 100% is the normal amplitude with case closed. Comparing the left 5 hours with the right 5 hours we see amplitude increases by 6% when the clock runs with case open.

Also notice that in both cases, going from case closed to case open, or case open to case closed, there is a nice exponential ramp between the lower and the higher amplitude. The time constant conveys how aggressively the clock reaches a new equilibrium.

Quick guess. If the clock were running normally (case closed) at 2.7 degrees semi-arc (+/- 5.0 mm displacement), a 6% change means the new amplitude is 2.86 degrees. Circular error changes from 143 ppm to 161 ppm for a net change of 17 ppm. So some of the rate change is due to differential circular error.

(3)

Finally, for completeness, a temperature plot for these 14 hours. Normally my eye-level wall-mounted Synchronome is fully enclosed with an oversized, 6 foot tall, 12 cu ft, sound isolated and thermally insulated, temperature controlled vertical "coffin". In order to perform this door closed/open experiment I had to remove the coffin and set it aside. This occurred at 8 PM, 5 hours into the run. This exposes the clock to normal room temperature.

<sync2b-dec4-14h-temp.png>

The left part of the plot shows how well the enclosure works. The temperature of the clock is always about 79.2 F and often stays within 0.1 F.

The right side of the plot shows the clock running at room temperature, about 74 F. Also, it shows the effects of HVAC cycling, wiggles that are highly attenuated on the left. The middle hours of the plot show the Synchronome slowly shedding 5 degrees of heat. It takes about 3 or 4 hours.

I hope these three plots help answer your question and stimulate some thought. Let me know if you have any questions.

Thanks,
/tvb

Plots also available at: http://leapsecond.com/pend/synchronome/case.htm




Bepi
 


-- 

James, you have to make an effort and tell us more about what was going on at the factory when you were working there. Equipment, discussions, union activities, oldtimer stories, anything. The main reason why today we can investigate the working of this clock differently is because we can make use of electronic aid unimaginable at that time at present day prices.

Bepi