I have made plots of the effects of everything I can find that effects the
freq of a HP10811.
Most things are much slower than minutes, more like an hour time constant,
such as anything effecting the outside case's temperature
OR the effect is much faster than minutes, things such as voltage and load
changes.
The only thing that I've seen that responds to instantaneous changes within
"minutes" is the oven loop.
If one assumed Rick's data is correct, then one likely cause of what was
happing (not why it was happening)
is that the oven set point temperature was changed.
That is the ONLY thing I've seen that can cause that sort of freq change
over that kind of time period.
It does not take much, a degree or so change in the oven's set point could
do it.
If I saw a real plot of freq change with time, I could be more sure of the
cause.
But even if the exact reason is not known, This string does show,
If you want the best from your 10811 then it is NOT a good idea to heat it
up in an oven to near its limits and then dump in water.
I have to wonder if the unit being tested had its high impedance oven
control points lifted off the PCB board and on Teflon standoffs like the
production units?
If not just blowing with your mouth on theses sensitive points could cause
this type of freq change.
ws
**************
"Within minutes the frequency changed more than the spec"
Rick
For humidity to get thru something like that it takes weeks or more IF
it does it at all.
That fast of reaction, Sure sounds like some other effect like blowing a
little air on the case or loading the osc output with water in the
output cable etc, etc.
I think it is safe to say the effect was not due to water inside, unless
there was a hole.
ws
***********************
The effect we saw was like parts in 10^8 of something. Way too big
to be related to output loading or air on the case. In any event,
the air blowing on the case was constant during the test.
We saw that when we didn't even try to seal the 10811 and also
when we tried to seal it.
Richard (Rick) Karlquist
**************
Blowing on the case? Did you consider the increased cooling that higher
humidity provides?
Cheers,
Magnus
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