PSN-L Email List Message
Subject: Re: Seismograph noise problem
From: Larry Conklin lconklin@............
Date: Mon, 11 Feb 2008 20:27:39 -0500
Yeah, I've thought about resoldering the entire **** board too, but it's
not my first choice of things to try. When I tried to bake out the
board under an incandescent lamp that one time, I did seem to get some
improvement, but it certainly wasn't very impressive.
Regarding the apparent non-randomness of the noise. I had the thought
that dampness had gotten into one of the gain pots resulting in a larrge
increase in the gain. But, despite the high noise level, I am still
able to record quakes and they produce records that are just about the
amplitude I would expect. I got a record of the mid-atlantic quake that
was good enough that I was able to set the phase picks. Even when the
thing is running acceptably, I still notice the same 20 second or so
I do monitor the leveling test point continuously. I put a zero center
meter on it so that I better center the leveling. I added a readout of
the voltage at the test point to my data logging program. I have a line
from the test point connected to a spare channel on my A/D converter.
Several of your other suggestions are things I wouldn't have thought of.
Tapping in with headphones would be interesting to try in any event.
I'm in a residential area not far from a busy street, and I have no
doubt that I'm getting a lot of higher frequency noise from traffic and
such. I can see a definite dinural variation, quieter at night,
noiseier during the day. But I see no variation whatsoever for days on
end when the thing is acting up.
Interesting. As I have been typing this, the excess noise has
diminished very substantially over the span of about 15 minutes, and
has stayed pretty low ever since. It would be a sort of Murphy's law in
reverse if just when I have been getting motivated to make an all out
attack on the problem, it went away spontaneously. Wouldn't be the
At any rate, you've given me a lot of food for thought, for which I
> In a message dated 11/02/2008, lconklin@............ writes:
> Regarding corrosion under solder joints, I haven't really checked
> thoroughly for that yet, but the board looks very clean.
> Hi Larry,
> I had a whole Sony TV with crevice corrosion. The joints looked
> perfect, but you could peel them off a black corrosion coat on the
> circuit strips. I had to unsolder, clean and resolder every joint on the
> **** board.
> Re. your and Roger's comments about the cover, It will take me a little
> time to build a new one.
> Putting the cover on the floor isolates the seismometer from
> pneumatic effects. I use 2" Celotex, but it isn't cheap. Bubble wrap can
> also be very useful in reducing temperature changes and drafts ....
> One other thing that I'd be interested in hearing your thoughts on is
> the fact that the "noise" isn't really as random as I'd expect from
> something like bad solder joints and such. If you look at the data I
> posted, especially from the LF channel, there definitely seems to be a
> dominant component with a period of around 20 seconds or so.
> I had noted that. It looked as if you were experiencing greatly
> increased gain, rather than just random noise. This could be resistors,
> solder joints, diodes or the opamp.
> Do measure the DC levels on TP. Does the Red/Green LED ever light up?
> The NE5534 does take about 0.5 micro A to drive it - quite thirsty...
> Try tapping the components?
> Unsoldering C49 would isolate everything downstream of the first two
> Could there be any strong radio signals at 2 / 4 / 8 / 12 MHz? You
> do have two radio receivers on the input... Electricity Utility time
> switches work off radio signals on the power lines.
> Try connecting an audio amplifier to the circuit before the
> integrator and listening with headphones? I have solved some noise
> problems this way. I was getting quite large random pulses which seemed
> to be real, not instrumental. When I listened, I heard a heavy lorry
> approaching a sunken drain grating on the corner of the local main road....
> I've got too many irons in the fire right now to devote full time to
> debugging this, but I plan to revisit all of your suggestions.
> Aside with messing with the cover a little, the other very easy test
> will be
> to disconnect the oscillator to see what happens. I still have an
> old test data file from the last time I tried it, and it doesn't
> look much different from what I saw then with everything hooked up,
> or now.
> I would expect there to be a simple fault which is sensitive to
> humidity - since heating the board reduced the signal. Good Luck!
> Chris Chapman
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