[time-nuts] Z380XA The saga of the aging 10811

[Bob Benward]

Robert,
The drift has slowed down to something around 8xE-10, which is a bit over
the spec of <5E-10.  But this is the single oven, I have not reassembled the
double oven yet.

If the oven regulation was off, I would suspect I would see the EFC go back
and forth a bit, maybe a general trend up, but some retracing would be
expected.  The oven control is an integrator, so unless the offset is very
large compare to the output of the thermistor, a continuously changing
offset voltage will not have a large effect on setpoint.  A crystal
resonator will drift about 1-5E-8/degC, so I guess a loose temperature
control would certainly exhibit the drift I am seeing.

Bob



>>> -----Original Message-----
>>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of George
>>> Atkinson
>>> Sent: Monday, September 14, 2015 2:42 PM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Z380XA The saga of the aging 10811
>>> 
>>> Well, if the batch/revision of op-amps had a doping, contamination or
similar
>>> issue, the input offset could be drifting fairly constantly causing a
>>> temperature channge in one direction.
>>> 
>>> Robert G8RPI.
>>> 
>>> On 9 September 2015 at 04:40, Bob Benward <rbenward at verizon.net>
>>> wrote:
>>> 
>>> > Hi Ed,
>>> > OK, a bad oven.  I can buy that.  But then if the oscillator is
>>> > constantly drifting, would that not imply that the oven is constantly
>>> > changing temperature, in one direction?
>>> >
>>> > BTW, the curve is starting to flatten out.  It might be flat before It
>>> > gets to 1000K counts.
>>> >
>>> > Bob
>>> >
>>> > >>> -----Original Message-----
>>> > >>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of
>>> > >>> ed breya
>>> > >>> Sent: Tuesday, September 08, 2015 10:55 AM
>>> > >>> To: time-nuts at febo.com
>>> > >>> Subject: Re: [time-nuts] Z380XA The saga of the aging 10811
>>> > >>>
>>> > >>> It could be that the inner oven temperature regulation is off a
>>> > >>> bit, or
>>> > even
>>> > >>> failed. There was a report at one of the popular time-nuts
>>> > >>> oriented
>>> > websites (I
>>> > >>> forget which one, but it's the one that had extensive coverage of
>>> > >>> the
>>> > Z3801A)
>>> > >>> about inner oven problems a few years ago. I took mine apart and
>>> > >>> found
>>> > that
>>> > >>> it had an IC of a particular date code range that was prone to
failure.
>>> > I can't
>>> > >>> recall whether I replaced it with the same type but different
>>> > >>> date, or
>>> > an
>>> > >>> alternative, but it worked just fine after that, with no tweaking
>>> > >>> of
>>> > coarse EFC
>>> > >>> needed.
>>> > >>>
>>> > >>> The IC was a dual opamp I think, that controlled the oven
>>> > >>> temperature according to the thermistor signal, and drove the
heater
>>> transistor(s).
>>> > >>> It was a fairly high performance type, but not that unusual. I
>>> > >>> think it
>>> > was a
>>> > >>> Linear Technology brand part.
>>> > >>>
>>> > >>> Ed
>>> > >>> _______________________________________________
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