A mechanical phase locked loop!

Gareth's Downstairs Computer wrote on 8/6/2017 1:37 PM:


I understand perfectly and explained it for you in excruciating detail. The change in phase of the Shortt clock slave pendulum is due to the FIRST ORDER change in the effective gravitational constant in the pendulum equation by engaging the leaf spring. While the reduced amplitude of the swing *will* cause a SECOND ORDER effect in the motion of the pendulum, it will be MUCH SMALLER than the FIRST ORDER effect.
What part of this do you not understand or not agree with?
--

Rick C

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On 06/08/2017 18:52, rickman wrote:

It's not that I do not understand nor disagree with you, it's that you're off on a complete tangent to what I was suggesting, and do not realise it.
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On 06/08/2017 19:15, Gareth's Downstairs Computer wrote:

No he isn't, you are not keeping up.
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On 06/08/2017 19:16, Brian Reay wrote:

If he's not keeping up then he needs Viagra.
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I expect that Mrs Evans has been putting bromide in his tea since shortly after they got married.
--
STC / M0TEY /
http://twitter.com/ukradioamateur
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Gareth's Downstairs Computer wrote on 8/6/2017 2:15 PM:

Sorry, I was talking about how the Shortt clock adjusts the timing of the slave pendulum. What are you talking about?
--

Rick C

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On 06/08/2017 22:15, rickman wrote:

This is one of Evans' usual tactics Rick, he is out of his depth so he is trying to muddy the water. Before long he will be hurling abuse in earnest.
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On 06/08/2017 22:15, rickman wrote:

I ... explained it for you in excruciating detail.
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Gareth's Downstairs Computer wrote on 8/6/2017 6:10 PM:

No, you simply state that the circular error exists for pendulum clocks and that the swing of the Shortt clock slave pendulum is shortened a small amount. You imply the shorter swing of the pendulum invokes the circular error factor to change the speed of the pendulum changing the phase.
None of that is wrong. But the circular arc error a very small effect. As I have clearly explained to you the leaf spring also causes the first order effect of changing the constant in the pendulum equation. This is a *much* larger effect than the small circular error effect.
You say you understand what I am saying, but it directly shows what you are describing is at best, a second order effect. If you don't disagree with that how can it be tangential to what you are saying? Or is that a play on words with the circular error???
--

Rick C

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On 06/08/2017 18:37, Gareth's Downstairs Computer wrote:

Nothing in any of rick's posts he does understand the above, or anything else. Plus, what you have posted is exactly what I explained to you earlier.
It is clear you are on the edge of resorting to your normal abuse.
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On 05/08/17 14:34, Chris wrote:

The amplitude is not, but the frequency is - why do you think the amplitude should be related to the difference in phase?

Ah, yes there is, see below.

Are you referring to the kick given to the master pendulum? That is not part of the PLL system. The kicks given to the master pendulum are specifically designed not to affect the phase of the master pendulum at all.
If not, if you are referring to the kick given to the slave pendulum (these are quite different kicks) that is not how the clock works.
The slave pendulum is kicked from time to time, ad kicked a little more often when the phases get too far apart - the difference in phases is the error signal mentioned above - and these kicks do affect the phase of the slave pendulum.

That is exactly what a PLL is - and it is almost (though not quite) what this clock does. It is certainly what the slave does.

Not necessarily continuous - a bang-bang action is allowable, and does not prevent a system from being a PLL.

A PLL does not necessarily keep the phase offset constant, just within the interval =/- 2pi.

Not necessarily continuously updated, or updated every cycle - as long as the offset is continuously within the range -2pi to 2pi, the phases are locked.

Yes - but that doesn't mean it is not a PLL, as long as the error is less than +/- 2pi.
A phase-locked loop is a system which produces a (slave) vibration the integral of whose phase in comparison to the phase of another (master) vibration is continuously between -2pi and 2pi over long periods.
A last requirement is that the phase-locked loop system should have no effect whatsoever on the master vibration. That's it.
If it does that, the phases are locked - they may not be tightly locked, but the vibrations do not skip or add beats.
More advanced PLLs might keep the difference between phases much smaller, as in this clock - but that is not a requirement of a PLL. There is no such thing as absolutely tightly locked, there is only unlocked or locked.
Neither is continuous updating necessary, though the integral should be continuously in that interval.
In this clock the hit-and-miss synchroniser action undoubtedly does act as a PLL.
However it might be argued that the slave does subsequently have some (very small) input to the master, when it operates the gravity drive (whuzzat? I am not a clockmaker).
That certainly has an effect on the amplitude of the master; although as the idea an intention and practical effect is that it has no effect whatsoever on the phase of the master, thus the slave clock action overall most definitely should be considered a PLL.
-- Peter Fairbrother
ps; the +/- 2pi bit is not really a requirement either, as long as the system can keep count of the missing/extra beats - but as most systems don't do that we shall just gracefully ignore that for now ..
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Peter Fairbrother wrote on 8/5/2017 11:01 AM:

What they fail to see is that the amplitude of the kick *is* adjusted. It's just the adjustment is binary, on or off. But that is still *adjustment* and is in response to the measured phase.

Not only that, but if you examine the equations for a PLL you will find it is *impossible* to maintain a constant phase offset with any variations in the reference or noise in the system.

In a typical PLL isn't the requirement to be within +/- pi rather than 2 pi? If you exceed a range of +/- pi from the intended alignment the feedback will start to push the controlled oscillator further out of alignment potentially aligning with another cycle of the master.
--

Rick C

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On 05/08/17 16:19, rickman wrote:

[..

Yup.
Compare with pwm (pulse width modulation) or ppm (pulse position modulation) - I forget what the actual modulation in the clock is called, but it is just another modulation, despite being binary and fixed in amplitude.

Indeed.. in some ultimate sense, perhaps that is the final purpose of a PLL.

Yes, in a typical PLL - however I was considering a more theoretical one where eg the phase offset was known to be positive or negative.
On reflection, is a system where the phases are several full cycles out-of-phase, but where the system over time adjusts the slave to (close to) the actual phase of the master, still a PLL?
On further reflection, I think it must be - so perhaps a better definition might be that the integral of the phase difference remains close to zero over long periods time (while leaving how close and how long as an exercise for the reader) :) .
-- Peter F
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Jeff wrote on 8/5/2017 5:45 AM:

You are making pointless distinctions. A phase locked loop is not defined by its mechanics but by the nature of its control. The Shortt clock maintains the relative *phase* of the two clocks by brief adjustments to the frequency via a spring. This is controlled by measuring the relative *phase* of the two clocks.
It's that simple. You are just making things more complicated by talking about the details of how the adjustment works and the time function of the frequency. NO PLL can keep the two clocks perfectly in sync.
Calling it open loop is just absurd. The loop is closed because it *measures* the phase of the clocks and adjusts the phase according to the measurement. It may be binary, but the adjustment is controlled by the measurement.
--

Rick C

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Wrong! It does NOT measure the relative phase, it makes NO measurement of the phase difference. All it does is detect if there is a phase lag of any degree. It could be a fraction of a degree or 180 degrees, the same correction is then applied regardless.

Wrong again it is open loop, there is no measurement, just the same adjustment regardless of the phase difference.
Jeff
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On 08/06/17 10:38, Jeff wrote:

Might be easier to define a set entitled "Locked Oscillators, of which the phase locked loop, injection locked and hit and miss synchronised are all members.
Are there other candidates ?...
Chris
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On 06/08/2017 12:24, Chris wrote:

From pre-war, the Goyder Lock?
Which raises an interesting point; before the 3-tier coffer-filling fiasco was the spawn of the RSCB, the candidature for the RAE tended to know all about the history of amateur radio before getting their licence, but now they seem to know sweet FA even after getting their licences, such as the difference between sideband and sidetone.
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On 06/08/2017 13:52, Gareth's Downstairs Computer wrote:

House!
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On 08/06/17 12:52, Gareth's Downstairs Computer wrote:

Hadn't heard of that, so looked it up and found:
http://www.dxmaps.com/discuss/oven.html
Which was an interesting read, but not enlightening.
Some of the early scope timebases, puckle, for example sounded interesting, but they were effectively injection lock, of course. I guess a triggered timebase is a variation of the hit and miss model.
Couldn't grok the relevance of the following paragraph above :-)...
Chris
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On 06/08/2017 15:27, Chris wrote:

It relates to the abysmal lack of technical acumen amongst those who are today's would-br radio amateurs, most of whom are really CBers-masquerading-as-radio-hams, identifiable by their M3 and M6 callsigns past and present.
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