[time-nuts] PLL Math Question

Magnus Danielson magnus at rubidium.dyndns.org
Fri Mar 14 11:42:03 EDT 2014

Hi Bob,

On 12/03/14 19:26, Bob Stewart wrote:
> Hi Magnus,
> Thanks very much for this response!  It will be very easy to add the exponential averager to my code and do a comparison to the moving average.  I have no experience with PI/PID.  I'll have to look over the literature I have on them and relate that to what I'm controlling.
> It should be mentioned that I'm more interested in the adventure than in just copying someone else's code or formulae and pumping this out.  I have an idea of how I want to do this and...

The effect of additional filtering can be a little tricky to analyze 
sometimes, but the exponential averager, the normal 1-pole low-pass 
filter, is however well-understood when the cut-off frequency is well 
above the normal PI-loop bandwith. K*4 seems to pop up in my head.

It's a hint which comes from experience of others as well as myself.
You can also look into the Stanford Research PRS-10 manual, which also 
optionally have such a filter in it's PPS slaving mode.


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