Perivale/Bentima beat rate question

Phil G4SPZ

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Can anyone tell me the correct beat rate for this Bentima three-train mantle clock with English Perivale movement, please? By successive approximation I’ve arrived at 10,300 BPH but it would be nice to know the correct figure as I don’t have the luxury of a fortnight to spend on regulation!

A source of beat rate data for popular clocks would be ideal, but I haven’t been able to find anything online.

The movement serial number is 249866. Many thanks,

Phil
 

dickstorer

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Phil, over the many years I have been repairing clocks I have no idea of what you are talking of. Pictures always are helpful. And what is successive appproximation?
 

Phil G4SPZ

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Sorry Dick, I completely forgot to upload the pictures!

Successive approximation is my rather flowery language for “trial and error”... simply adjusting the rating nut a bit at a time over a short period until the clock doesn’t gain or lose too much.

As in this case, I frequently find myself having to replace a damaged or missing pendulum or suspension. When the design length isn’t known, it is very helpful to know the correct number of beats per hour. This can be worked out by counting wheel and pinion ratios, or more simply by counting the number of beats it takes for the minute hand to rotate a full revolution. Sadly I don’t have a device that can just count beats; my Clockmaster timing ‘app’ only measures BPM.

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Best regards,

Phil
 

Willie X

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I think, in your case, "beats" and BPM are one in the same?
A beat counter can certainly give you a quick approximation of the clocks rate. This is assuming your numbers are correct, and the machine is reading the clock correctly, and you are reading the machine correctly, etc. :) Fine adjustment usually takes at least several weeks for any clock, regardless of the type and grade.
The approximation you seek can be done against any quartz clock with a second hand or chime. Just check your error at the top of each hour and make the required adjustment, you should have your approximation by the end of a day's run and it only takes a minute or two, actual time spent, no assumptions.
Willie X
 
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Dick Feldman

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Phil,

You can also get a fairly accurate goal BPH by interpolation.
1. Measure the BPH now and jot that down
2. Set the clock hands at the correct time of day.
3. Wait a known period of time, say 12 hours and note the time according to the clock hands. Write that down.
A simple ratio can give you a goal BPH for correct time keeping.
The elapsed time shown by the clock hands divided by the actual elapsed time should equal your initial BPH divided by your goal BPH.
Since the goal BPH would be “X” in an algebraic equation, one needs to solve for “X”

Consider this example:

If your beginning BPH is measured at 1000,
Your hands were set at 12:00 am (The correct time)
You ended your trial time at 12:01 PM (12 hours, one minute)
And if your hands showed 12:12PM at 12:01PM actual time.
{where 721 equals 12 hours and one minute, the actual elapsed time and 732 equals 12 hours and 12 minutes, the elapsed time shown by the clock hands}
732 minutes divided by 721 minutes equals 1000BPM divided by goal BPH or:
732/721=1000/ “X”
Or: 1000 multiplied by 721 divided by 732= “X”
Your goal BPH in this example will be 984.97 BPH, Call it 985.
If you would adjust the rate adjusting mechanism to 985 BPH with your machine, you would be very close to correct time keeping for this example.

The longer the interval between the starting and ending time, the more accurate your results will be. This method takes into account the BPH variation for a short time during any chime/strike warn periods. This is a much more accurate method than published beat rate charts and also calculations using wheel teeth counts.

Dick
 
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shutterbug

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Jeff Hamilton has been recording beats for years. Click here to get his beat book.
If you set your counter to just count beats, it's easy to get an accurate beat for any clock. Disable any chimes or strikes. Then use the minute hand and a point on the dial you'll remember. When the minute hand touches that point, start the counter. Let the minute hand rotate about three times, and stop the counter when it touches the point you selected. Now divide the count by the number of revolutions the hand made. That will be a very accurate BPH for your clock.
 
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Phil G4SPZ

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Thank you all. Dick’s method is the one I’ve used in the past, but thanks for spelling it out with such clarity.

Jeff Hamilton’s book looks ideal, and a good investment as it is likely to help solve the “missing pendulum” problem. Must check if it’s available here in the UK.

Thank you all once again,

Phil
 

Dick Feldman

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Jeff Hamilton has been recording beats for years. Click here to get his beat book.
If you set your counter to just count beats, it's easy to get an accurate beat for any clock. Disable any chimes or strikes. Then use the minute hand and a point on the dial you'll remember. When the minute hand touches that point, start the counter. Let the minute hand rotate about three times, and stop the counter when it touches the point you selected. Now divide the count by the number of revolutions the hand made. That will be a very accurate BPH for your clock.
Measuring BPH with the chime/strike trains taken out of the system will give you an false or inaccurate reading.
Doing that will introduce error over a long period of time, which is how clocks run.
The true rate will vary somewhat with warn periods and an average "normal" rate over a long period is more useful than one with a train operating without normal influences.
Dick
 

Phil G4SPZ

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Re post #7, Jeff Hamilton's Beat Book is effectively priced out of the UK market by virtue of the shipping costs - an eye-watering $57.75, on top of the fairly reasonable $24.95 for the book itself. A downloadable copy doesn't seem to be available.

Phil
 

Phil G4SPZ

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Sadly not. I did try to order it from his website. The book simply does not appear to be readily available from other sources here in the UK, and the excessive shipping charges render a purchase from the USA unjustifiable.

Phil
 

shutterbug

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Call him and talk to him. He has a software equivalent that can be downloaded and run on a PC. It has the same information.
 

Phil G4SPZ

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Jeff has kindly arranged shipping by US Postal Service for $12, which is a lot more reasonable. A copy of the Beat Book is winging its way to me now.

Thanks for all the advice,

Phil
 

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