Hi Bob,
Yeah it did. This is running as part of one of Bob Stewart's GPSDO's.
It's been up for about two weeks now. The log indicated there was a
phase jump compared to the GPS PPS input. EFC made a jump to correct
for it. A few hours later, it made a small jump back in the other
direction, with a corresponding phase and EFC correction there also. By
the phase jump, I would have though it was the crystal doing something.
But the fact that it showed up in the oven monitor voltage also has me
a bit worried.
The outer oven controller didn't show anything similar.
I've been wracking my brain about what could be causing this. It's
way to sudden to be anything one would expect from a normal analog
circuit. The room temp cycles are visible, but are nice and smooth
compared to this. It makes me think there is something mechanical going
on.
Who knows, maybe the crystal changing affects power dissipation from
the oven? Still trying to figure out exactly how much of a change in
oven power this is, but I suspect it's very small. With the three
transistors in darlington and 100K resistor feeding the base, a 1mV
change on the inner oven controller differential amp would indeed be a
small change.
I was thinking, I also need to rule out the power supply. But, I need
to setup a voltage divider to get that to within the ADC input range...
Dan
Hi
Did the frequency shift at the same time? If not, the first suspect
would be the data collection system.
Bob
> On Nov 26, 2014, at 11:00 AM, Dan Kemppainen <d...@irtelemetrics.com> wrote:
> > Hi All,
> > I've been playing with some double oven HP10811's. I've been
monitoring the internal oven feedback vs. temperature and noticed
something interesting last night. There was a sudden step change in
internal oven feedback voltage. This is the voltage coming from the
amplifier monitoring the bridge that feeds the heater transistors.
> > The step change was on the order of two or three times as large
as normal swings caused by the furnace cycling in the house. The
voltage was being monitored by a 8Ch ADC card. All of the other
voltages on that card were stable.
> > The jump was very small. I don't recall exactly (Not near that
unit right now), but somewhere around a mV or less. But it was very
sudden and compared to everything else on that line, or other
voltages being monitored.
> > I'm wondering if there is something going on in there that may
require attention. Bad solder, cracked trace, bad component???
> > Any idea what might have caused this?
> > Has anyone seen anything similar?
> > Thanks,
> Dan
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