[time-nuts] E1938A source code/ firmware

[Adrian Godwin]

I would agree that antiwindup is important when you have integrators. They
always seem to cause trouble without it, in applications as diverse as car
throttle control and time-domain filtering of respiratory data.  I would
also recommend, sometimes, the use of feed-forward control to provide an
estimate of power demand without relying on the integrator : although most
useful for speeding the response, it can also reduce the expected
integrator term and hence allow more aggressive antiwindup.


On Sat, Jul 6, 2019 at 9:00 AM Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:

> Hi Rick
>
> Thank you very much for the reply and the suggested leads. I think your
> work on the balanced bridge oscillator was both preeminant and seminal .
>
> I have read all the papers on it, and there are few other things in my
> 30 years of this field professionally that really impress me as much  in
> the new approaches and new thinking on the entire unit. Agreed on the
> PII^2D control system.
>
> I've built a few OCXOs back in the 90s, the best I did on (inner) oven
> control was using dual glass bead thermistors in a bridge configuration
> with lots of gain driving a simple opamp integrator. The opamp was
> chopper stabilized and I ensured the op amp never operated in the
> crossover region of the opamp output driver.  These were on AT cuts  at
> 97 deg C ...
>
> cheers
>
> Glen. AI6UM  / VK1XX
>
>
>
> On 6/07/2019 2:37 PM, Richard (Rick) Karlquist wrote:
> > On 7/5/2019 8:20 PM, Glen English VK1XX wrote:
> >> Has anyone got this , is the PIC read data prohibited ?
> >>
> >> Is it still a closely guarded secret?, there were some very clever
> >> and novel ideas used in that slab, in my opinion.
> >>
> >> Glen
> >>
> >
> > Hi Glen.  I worked on this project, but am an RF/Analog
> > guy.  The product line was sold to Symmetricom 20 years
> > ago and they didn't continue the E1938A.  At that point,
> > there were no closely guarded secrets.  I don't know what
> > happened to the source code.  The last contract manufacturer
> > for the E1938A was Scotts Valley Magnetics.  You could
> > contact them and see if they have the PIC info.  In theory,
> > they would have had to have it to program the PIC's.
> >
> > The most clever thing in the PIC (AFAIK) is the oven
> > controller with the double integrator.  "P, I, I^2, D".
> > Len Cutler was the mastermind behind this.  I believe
> > he leveraged his experience with double integrators used
> > in Cs control loops.  I remember him telling me that the
> > secret was to have an "anti-windup" algorithm.  Whatever
> > he did, the results were phenomenal.  I spent countless
> > days in the lab exercising the loop and it always worked
> > perfectly.
> >
> > Rick Karlquist, N6RK
> >
>
>
>
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