[time-nuts] HP10811 Double oven, oven jump?

dan at irtelemetrics.com dan at irtelemetrics.com
Wed Nov 26 22:53:48 EST 2014

     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 

  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... 


> 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 <dan at 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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