Following up on Brian's comment yesterday, I'm investigating sources for very low leakage caps. If I find some, I'll let the group know, and if there's a minimum purchase quantity that's reasonable, I may just buy a bunch and make them available to the group here.
John ---- buehl wrote:
John:
If circuit has an electrolytic, following may influence how/ when you recalibrate.
Electrolytics change value and leakage with no voltage applied for long periods. So if the long TC cap has been switched out for months it will need a long time with "in circuit" to stabilize again. The electrolytic barrier "forms" as a result of the electric field across it.
Tom Buehl
At 07:41 PM 4/5/2005, you wrote:
Thanks, Brian. That's very helpful. I looked at the schematic and the cap they are using for LTC is 8uF that's simply put between the input and the output of the op amp module.
I guess the question is whether the leakage causes any stability problems, or just a constant offset. Time for some experiments...
John ----
[EMAIL PROTECTED] wrote:
John-
I have seen the same effect on my HP-5060A. I had attribute it to leakage in the loop filter capacitor.
Should you find that you need to replace that cap in your standard, you might want to try some of the very low leakage current caps from WIMA in Germany. If you're in a pinch I have a couple 1uF WIMA caps that I could send you.
-Brian, WA1ZMS
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Ackermann N8UR Sent: Tuesday, April 05, 2005 9:53 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] 5061 Cs frequency shift with long time constant?
This is very odd (I seem to be collecting these sorts of problems) and I wonder if anyone else has seen something similar.
I got my 5061A trimmed to the point where a 5 day run against GPS showed an offset of less than 1x10e-13. I then switched the unit into the long time constant mode and now see that the offset (over 36 hours) is -1.7x10e-12. Nothing else in the setup has changed.
It's hard for me to see how simply changing the loop time constant would change the frequency of the standard, especially by this much, but stranger things have happened.
Has anyone else experienced a shift like this when switching the time constant?
Thanks,
John
PS -- I was able to partially, but not completely, reproduce the phase shift that I wrote about a couple of weeks ago by jiggling the 1 PPS cable to the counter. Replacing that cable seems to have resolved that problem.
_______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
_______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
_______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
_______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
_______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
