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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