On 6/24/2012 6:10 PM, chrisatupw@....... wrote:
> From: Larry Conklin 
> To: psnlist 
> Sent: Fri, 22 Jun 2012 2:22
> Subject: Re: Haunted system misbehaving again
>
> Well, I haven't tried locking the pendulum, but in an earlier
> incarnation of this problem (in '03!) it tried a few experiments where I
> disconnected the lead that supplies the power to the oscillator and the
> connection to the feedback coil.  Monitored the output and found that
> with the cables connected from the detectors I had significant noise and
> with the cables disconnected still pretty much the same.  But if I
> terminated the inputs with 2K resistors, the output went to zero, save
> for a little +/- 1 count jitter.  So, at that time I concluded that the
> board probably wasn't the source of the problem.
> Hi Larry,
>      This strongly suggests RF pickup. Can you tune a radio to
> 4 M Hz and find out what signals there are ? You are using two quite
> sharply tuned circuits to detect movement. Do you have any RF
> SCREENING around the seismometer ? It would be well worth trying ?
Have never tried any kind of electromagnetic shielding.  Would be a bit 
of a project, but if I get desperate enough....  I don't have anything 
around that will tune to the frequency of my pendulum oscillator.  One 
thing that I did realize after reading Larry's suggestion that the 
capacitor in the damping circuit might be bad, is that my experiments 
with disabling the oscillator and disconnecting the damping coil tell me 
exactly nothing regarding the state health of the damping circuit.  So, 
that needs another look.
>
> As fate would have it, the thing has been running pretty well all day today.
>
>      Snarl at your electronics occasionally !
I think you would be very impressed with the richness of the vocabulary 
I use when I talk to that thing!

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