[time-nuts] HP5061 Cesium ion pump question

Wed Dec 2 10:46:58 UTC 2020

I think there's quite a bit of variation in leakage rates between individual
physics packages, and there's also variation in the accuracy of the
metering. I recently started up my spare 5061A after over a year in storage.
The Ion current meter showed zero with the Cs off but about 40 in the Open
Loop position. I tried connecting an external +3500V supply through a
microammeter as described in the manual and that showed less than 10 uA. The
unit kept trying to start and pulsed for about 12 hours at a peak reading of
40 and then settled down nicely to a zero reading and hasn't missed  a beat
since.

I have a spare tube sitting here that hasn't been powered up for several
years. It was removed from a junked 5061A that wouldn't start at all but
after the unit was parted out some failed caps were found in one of the
modules that could have explained the fault. I plan to try it on the bench
with the +3500 V supply and microammeter but I don't know whether I can
trust the reading. If the tube in one of my functioning units fails one day
then I'll give it a try.

Morris

------------------
From: paul swed <paulswedb at gmail.com>
To: Time-nuts <time-nuts at lists.febo.com>
Subject: [time-nuts] HP5061 Cesium ion pump question

During my HP 5061Cesium testing last week I was watching the ion pump
current and am curious.
What is the typical behavior people see on the tube after say 3 months of
being turned off.
With 3 units I see one that pumps doen from 8 to 2 in 40 minutes. Another
maybe at 25 and takes 28 hours to get to 18. Just seems to be all over the
place.
Regards
Paul
WB8TSL

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Message: 10
Date: Tue, 01 Dec 2020 06:19:25 +0000
From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
To: Discussion of precise time and frequency measurement
	<time-nuts at lists.febo.com>, paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] HP5065a cfield issue
Message-ID: <86443.1606803565 at critter.freebsd.dk>
Content-Type: text/plain; charset="us-ascii"

--------
paul swed writes:

> Guessing far less than 3 ma. by adding up resistors.

More like typical 4 mA: there is a factory select resistor in
parallel with the current-setting resistor.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

------------------------------

Message: 11
Date: Tue, 1 Dec 2020 10:40:54 +0000 (UTC)
From: ew <ewkehren at aol.com>
To: time-nuts at lists.febo.com
Subject: Re: [time-nuts] EOL Motorola Oncore Remote Antenna
Message-ID: <1292998389.3097482.1606819254766 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

Jim, I agree. As part of my OSA 8607A GPSDO project I planned to place the
OCXO in an aluminium box to eliminate pressure change. Step one included
buying a separate unit to make sure the rubber gasket did do the job.
Attached first results. Temperature does change pressure more than ambient.
The vertical steps are the result of gentle tightening the lid, did not know
how much lid had to be tightened. Now I know and have a 10 day test running.
With AC running, the AC control at the other end of the house lab
temperature stays within ! C. Today a cold front hit, no AC and temperature
will drop more than 1 C. Taking advantage of the forecast I am extending the
test for a couple more days.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Doe to the low power
dissipation of the 8607 fan cooling is not an option but I will use the box
, seal it and characterize the 8607 for pressure and temperature and use
external pressure and temperature sensors for compensation once combined
with a new generation GPSDO.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ??

I'll bet pressure changes inside the "sealed" radome due to temperature 
changes are bigger than those due to local barometer changes.

But an interesting thing - water vapor will go through cracks, porosity, 
that liquid water will not. The commercial success of GoreTex is an 
example of this, but cracks, o-rings that aren't quite right, etc. are 
also ways it can happen.

Making a truly hermetic box is hard.

> 
> -----Original Message-----
> From: Poul-Henning Kamp <phk at phk.freebsd.dk>
> Sent: Sunday, November 29, 2020 11:19 PM
> To: Discussion of precise time and frequency measurement
<time-nuts at lists.febo.com>; Art Sepin <art at synergy-gps.com>
> Subject: Re: [time-nuts] EOL Motorola Oncore Remote Antenna
> 
> --------
> 
>> It's obvious from the photo that the O-Ring seal failed its purpose
>> over its many years of service. Has the unit totally failed or does the
electronic portion still function?
> 
> No, the electronics is stone dead.
> 
> To me it looks more like water ingress through micro-cracks in the
plastic-dome, and the O-ring did its job and kept that water in.
> 
> The microcracks are uniform and seem to follow the molding flow, and that
is probably to be expected in our climate:? We have a lot of humid
freeze-thaw cycles.
> 
> I wonder if buffing the radomes with car-wax would help ?
> 
>> I said lucky because I found some GSynQ parts here in an engineering
>> storage cabinet that we? can send to you at no charge to revive your
unit.
> 
> Thanks for the offer, but dont bother: I had a spare on hand, and I may
still have third one lying around somewhere.
> 

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