[time-nuts] Making a HP 10811 better

[Bob Camp]

Hi

.... and part of the gain is the insulation ... and the 10811 has thin insulation (compared to what people try to put on it ....).
 
--------------

I seem to remember going to a paper that talked about a lot of those nasty little component tempco's by ... ummm..... err...

Yes, I think it was your paper :)...

I also remember a comment about the numbers in the paper being "later proved optimistic". I don't think that part got into the final paper. 

Bob


On Mar 30, 2010, at 8:18 PM, Rick Karlquist wrote:

> The problem you described was more of an issue in the 5061.
> Len Cutler was extremely relieved that the 5071 didn't have to
> have an analog integrator.
> 
> In the 10811, the biggest problem is that the capacitor is
> barely large enough for loop stability purposes.  That prevents
> you from increasing the gain regardless of how many megohms
> you can achieve.  The last time I checked, you still could not
> get a larger capacitor value that would physically fit in the space in
> the 10811.  Everything in the 10811 is max'ed out, per
> discussions with the designers, who recently retired.
> 
> It is also worth noting that you can get a thermal gain of over
> 1000 by optimizing the power sharing between the resistors.
> This experiment is done with the oscillator in B mode so the
> crystal is a thermometer.  Unfortunately, this thermal gain
> maximization does not optimize the 10811 tempco because it
> ignores the tempco of the electronics.  You have to make the
> oven tempco cancel out the electronics tempco.  This cannot happen at
> a turnover of course, which leads to another discussion.  A large
> fraction of 10811 crystals do not have a turnover, only a
> region of very low tempco.  Thus the discussion about getting
> right on the turnover point is moot.
> 
> In the E1938A, we had crystals that definitely had turnovers,
> and set each one at a turnover.  What a nightmare in production.
> The 10811 paradigm looked really good by comparison.
> 
> You can now see how complicated it gets if you fool around with
> a 10811.
> 
> Rick Karlquist N6RK
> 
> 
> 
> Bob Camp wrote:
>> Hi
>> 
>> Here's the gotcha with the "integrator". The poor thing starts out with a
>> closed loop gain of a bit over 4. That's *very* low by oven controller
>> standards. The gain gets up to 40 or so by the time the gizmo labeled 2 uf
>> gets up to 40 meg ohms. It's going to have a hard time going 10X above
>> that. Getting up to 400 Meg on the pc board is going to be a challenge.
>> You have to guess what the cap is made out of, so coming up with an exact
>> mega ohm microfarad product for it is a challenge. It's likely that it's
>> going ot cut in below 1 G ohm. That's when everything is new, clean and
>> dry.
>> 
>> Then if you just happen to have dust / dirt / humidity / spider webs ...
>> there goes your 400 Meg. Humidity in particular is nasty. It goes in
>> easily and it's very hard to drive out.
>> 
>> The DC gain is unlikely to make it past a few hundred under the best of
>> conditions. You are getting maybe a 10X boost over a normal controller
>> when it all works right. When the insulation resistance starts to go down,
>> you pay for it with shifts.
>> 
>> Bob
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>