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?
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???
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
It is clear you are on the edge of resorting to your normal abuse.
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
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 ..
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.
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
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
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
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.
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.
On 08/06/17 12:52, Gareth's Downstairs Computer wrote:
Hadn't heard of that, so looked it up and found:
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 :-)...
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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