[time-nuts] Regulating a pendulum clock

Don Latham djl at montana.com
Mon Aug 9 05:09:19 UTC 2010


Yep, injection locling works just fine
Don

----- Original Message ----- 
From: "paul swed" <paulswedb at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Sunday, August 08, 2010 7:37 PM
Subject: Re: [time-nuts] Regulating a pendulum clock


> Now I will get myself in a lot of trouble.
> Why wouldn't a constant pulse at a 2 sec interval essentially lock the
> pendulum after a bit.
> If the pulse is always there and occurs just after the mid swing. I 
> suspect
> you do need to adjust current with a pot to get things settled. But
> essentially open loop.
> I have often thought about tinkering exactly like this if I ever ran 
> across
> a nice clock like the one at television network TVA in Montreal that used 
> to
> run network time. Unfortunately they would not part with it.
> Good luck
>
> On Sun, Aug 8, 2010 at 7:22 PM, Bruce Griffiths
> <bruce.griffiths at xtra.co.nz>wrote:
>
>> Mere fast blow fuses aren't usually precise enough to protect transistors
>> against over current unless one uses rather large transistors.
>> Overcurrent protected drivers are available and readily designed/built.
>> Protection against di/dt transients due to external events is also
>> advisable.
>>
>> Minimising the parts count isn't necessarily conducive to improved
>> reliability when external hazards aren't taken into account.
>>
>> Merely resonating the coil without other filtering doesnt necessarily 
>> lead
>> to low EMI when driving it with a voltage waveform having high edge slew
>> rates.
>> Some edge filtering to control the current flowing in the load 
>> capacitance
>> is also advisable.
>>
>> Bruce
>>
>>
>>
>> Don Latham wrote:
>>
>>> fast blow fuse, resonate the coil to the pwm frequency. Parts count 
>>> small,
>>> tinkering in software instead of breathing lead fumes or whatever 
>>> noxious
>>> stuff the Europeans have forced us to use...
>>> Don
>>>
>>> Bruce Griffiths
>>>
>>>
>>>> No protection against external shorts or other undesired events.
>>>> Extensive analog filtering to avoid creating an effective radiator of
>>>> noise may also be necessary.
>>>> Simple analog techniques are probably simpler/cheaper once the 
>>>> necessary
>>>> filtering and protection are included.
>>>>
>>>> Bruce
>>>>
>>>> Don Latham wrote:
>>>>
>>>>
>>>>> Hmmm lemme see. I think I'd use a 12 volt supply and two transistors
>>>>> driven by two outputs on my Arduino,basic stamp,picaxe or other 
>>>>> whizzie.
>>>>> I'd then implement a PID controller essentially using the 1 sec pulse
>>>>> from
>>>>> the pendulum and the 1 sec pulse from my Rb, satellite receiver, 
>>>>> crystal
>>>>> clock, or whatever. The appropriate output pin will be brought to
>>>>> ground,
>>>>> and the other driven as a pdf with the rate given by the pid loop.
>>>>> Temperature and even pressure corrections can be applied within the
>>>>> gizzie
>>>>> software. External parts, minimum. Opportunity to play with tuning,
>>>>> maximum.
>>>>> Don
>>>>>
>>>>> Bruce Griffiths
>>>>>
>>>>>
>>>>>
>>>>>> J. Forster wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> You are picking very unimportant nits.
>>>>>>>
>>>>>>> If there were a small noise spike from the opamp, it'd goose the
>>>>>>> pendulum
>>>>>>> a tiny amount. That would be corrected on the next swing.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> Heuristic analysis of this type is counter productive.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> You are turning a trip to the corner store into an Apollo Moon
>>>>>>> Mission.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> Reliability is paramount in a circuit that may be required to work 
>>>>>> for
>>>>>> decades.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> BTW, since the =drive does not to be bipolar, one of the NPN and PNP
>>>>>>> transistors can be deleted. They never turn on. So you are left with
>>>>>>> two
>>>>>>> opamsa, =each with a simple emitter follower.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> The original request was for a bipolar drive.
>>>>>> The lack of short circuit protection is poor design practice when
>>>>>> driving an external load.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> -John
>>>>>>>
>>>>>>> ==============
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> Bruce
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at 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 at 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 at 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 at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there. 




More information about the time-nuts mailing list