Chris wrote on 8/3/2017 6:33 PM:
On 08/03/17 21:31, rickman wrote:

I don't know what you guys are seeing. The two pendulums of the Shortt
clock are in lock step. The fact that they are only compared every 30
seconds does not change the nature of the design.

The phase comparison signal from a PLL is typically "grainy" in the same
way and has to be filtered to become a control signal. The only reason
you say they are in "lock step" is because the grain is very fine. The
Shortt clock grain is very fine as well typically adjusting only every
other 30 second period.

I guess the difference is the Shortt clock is adjusting the
instantaneous phase and the average frequency while a typical PLL
adjusts the instantaneous frequency to try to keep the phase aligned.
Both will see variations in phase over time.


I would see the Shortt clock as a frequency locked loop, not the same
thing as a pll. Different level of instantaneous precision.

Not sure why you say that. What is measured and adjusted is the phase.
Either the slave is a bit ahead or a bit behind and it is either spurred on
a bit or it is not. The frequency of the pendulum is not impacted other than
at the moment of phase adjustment.

--

Rick C