On 2012-06-22 1:16, hsvham wrote:
> Hi Larry (Conklin) -
> I'm just now catching up on the PSN email traffic and the "Haunted 
> System" thread.
> FWIW, my SG seems to do the same thing as yours from time to time.  I 
> built the sensor many years ago, and built up the electronics board 
> from Larry Cochrane's schematics.  I am still running it at present, 
> alongside my much newer force-balance vertical instrument.
> Every so often, the SG channel will either (1) go totally dead silent, 
> or (2) get extremely noisy.  In the past when I see this, I'll power 
> down the instrument and run through the various connectors in the 
> system, re-level the sensor, and fire it back up.  And everything is 
> OK in that channel for the next several weeks / months.  I have yet 
> to successfully trace the problem to an offending connector or 
> electronic part.
> So my SG seems "haunted" by the same ghost as yours. ...go figure...
> Steve Jones
> AlabamaQuake
>
> --- On *Thu, 6/21/12, Larry Cochrane //* wrote:
>
>
>     From: Larry Cochrane 
>     Subject: Re: Haunted system misbehaving again
>     To: psnlist@..............
>     Date: Thursday, June 21, 2012, 5:00 PM
>
>     Hi Larry,
>
>     Have you tried locking down the pendulum so it can't move and
>     letting you system run
>     for a while? Looking at the schematic I see two parts I would
>     replace. They are the
>     two back-to-back 100uf (I think) capacitors driving the feedback
>     coil. I would
>     replace them with one 47uf non-polarized cap. DigiKey has these
>     http://www.digikey.com/product-detail/en/ECE-A1VN470U/P1190-ND/227631
>     in-stock.
>
>     Regards,
>     Larry Cochrane
>     Webtronics
>
>     On 6/20/2012 7:11 PM, Larry Conklin wrote:
>     > Hi Roger,
>     >
>     > I think I remember your having posted an account of your "rug
>     affair".
>     > In fact I think that it prompted me to improve the leveling
>     screws on my
>     > system, which at the time were rather flimsy. I replaced them with
>     > larger, stiffer screws and I think that it may have helped, or even
>     > "solved" the problem for a while.  I'm now using fairly substantial
>     > screws and the system is (and already had been) sitting on a
>     couple of
>     > 1/8 inch thick strips of aluminum that are epoxied to the basement
>     > floor.  The assumption being that the plates are a more rigid
>     surface
>     > than the bare concrete would be.
>     >
>     > The only pivot points I can identify are the pendulum hinge itself
>     > (consisting of thin metal shim material, phosphor bronze or some
>     such).
>     > But there is certainly the possibility that the contacts between the
>     > feet and the plates might shuck around a little with temperature
>     changes?
>     >
>     > I also have had a series of cover experiments. Original cover was a
>     > wood box that sat on the frame of the sensor. Very bad idea.
>     Rebuilt it
>     > to fit over the sensor and sit on the floor. Better, but probably
>     > vulnerable to transmitting noise to the instrument.  Added
>     "stuffing" to
>     > fill up the unused volume and suppress air movement. Not much
>     noticeable
>     > change.  Current cover is light weight, built of insulating
>     board and
>     > sitting on the floor.  At times I've duct taped it to the floor,
>     but at
>     > the moment it's just sitting there.  Maybe putting the tape back
>     would
>     > be a good idea.
>     >
>     > But the overall behavior of the problem makes a lot of these
>     > possibilities seem unlikely.  In one subset of episodes of the
>     problem,
>     > the noise starts abruptly and then continues indefinitely for
>     days of
>     > weeks at a time.  The data shown on my web page is typical of this
>     > "class".  (And I noticed that this episode started on March 30,
>     and is
>     > still ongoing, although there were couple of periods of a week or so
>     > duration since them where things were much better.)  Other
>     episodes have
>     > emerged gradually over the course of several hours, continued
>     for days
>     > or even weeks at a time and then subsided.  I'm at a loss to come up
>     > with a theory that is consistent with both kinds of behavior. 
>     And none
>     > of the experiments I've tried have made any clear and lasting
>     impact on
>     > the problem, although I've tried a few things that I've thought
>     fixed
>     > it, only to have it crop up six months later.
>     >
>     > I guess that's what makes this business interesting.
>     >
>     > Larry
>     >
>     >
>     >
>     > On 6/20/2012 9:41 AM, RSparks wrote:
>     >> Hi Larry,
>     >>
>     >> My experience parallels yours with loose mounted components.  I
>     once
>     >> went through a rug to concrete below and failed to make good
>     contact
>     >> with one screw on the concrete.  I was effectively floating on
>     the rug
>     >> with one of the three seismometer legs!   Very noisy!
>     >>
>     >> Based on this experience, I am careful to make all mechanical
>     contacts
>     >> solid connections in some way.  I even drilled holes into the
>     concrete
>     >> and mounted my seismometer solidly.  I thought there was a small
>     >> improvement in the noise level after taking this somewhat extreme
>     >> measure.
>     >>
>     >> I also avoid pivot points in favor of bending joints to avoid
>     noise.
>     >> Friction is present in our seismometers if there is a moving
>     joint and
>     >> mechanical friction is always noise.
>     >>
>     >> Maybe look more carefully at any mechanical connection that
>     might be
>     >> loose, maybe  not only in the leveling screws.  Look also at the
>     >> mounting of the surrounding air/insulating box, making sure it
>     is not
>     >> rocking from the ever present 0.2 Hz peak noise or more likely, the
>     >> thermal air currents in your room.
>     >>
>     >> Good luck,
>     >>
>     >> Roger
>     >> .------ ------ ------ ------ ------ ------ ------ ------ ------
>     >> ------. | Message 3 | '------ ------ ------ ------ ------ ------
>     >> ------ ------ ------ ------' Subject: Haunted system
>     misbehaving again
>     >> From: Larry Conklin      >
>     Date: Tue, 19 Jun 2012
>     >> 14:54:30 -0400 I have an SG sensor that has intermittently had
>     serious
>     >> noise problems, literally for years. Mechanically, it is very
>     similar
>     >> to the design that is shown on Larry's PSN web site, and it uses
>     >> Larry's electronics board, which I believe he is no longer selling.
>     >> When the thing is running properly I've been quite happy with
>     it. But
>     >> occasionally, for reasons I have never been able to pin down, it
>     >> exhibits extreme low frequency noise, to the point where it is
>     >> basically useless. The current episode began with the system
>     running
>     >> very well, but it was in need of leveling, which I've typically
>     need
>     >> to do every couple of weeks or so. Before I adjusted the leveling
>     >> screw, it was quiet. After messing with it it became extremely
>     noisy.
>     >> So, you'd believe that it was some sort of mechanical problem,
>     right?
>     >> And I've had several other episodes that began the same way. This
>     >> time, when I brought it upstairs on the bench, I did in fact
>     discover
>     >> that the lock nut on the leveling screw was loose, and I
>     "fixed" the
>     >> problem by re-tightening it. Ran pretty well for a week or so
>     >> thereafter, but not really as quiet as it should be. Then, it
>     >> spontaneously got quite noisy again, interspersed with periods
>     where
>     >> it ran ok. I have a lot of other history with seemingly mutually
>     >> exclusive symptoms/probable causes, but the bottom line is I don't
>     >> have a clue what is really going on. I'm tempted to believe
>     that there
>     >> is something subtle wrong with the electronics board, but in past
>     >> attempts to trouble shoot it, haven't been able to find
>     anything. If
>     >> there is anyone out there who has one of Larry's SG boards that
>     >> they're willing to part with, I'd be interested in buying it.
>     If for
>     >> no other reason than to rule out the board as the source of the
>     >> problem. For the curious, I have a little web page that I dump drum
>     >> reports up to daily. The report for today (so far) shows a
>     >> particularly noisy day, but does include the quake that happened in
>     >> the Aleutians this afternoon. The page also shows drum reports from
>     >> the day this round of the problem started. The day started just
>     fine,
>     >> until the big transient that resulted when I went down and adjusted
>     >> the leveling, at which point all hell broke loose. You can also see
>     >> the consequences of two subsequent leveling adjustments later
>     in the
>     >> day. After that data was recorded, I didn't mess with the thing for
>     >> maybe a week, until I finally got around to taking a closer look at
>     >> it, at which point I realized that the leveling screw was loose and
>     >> re-tightened it. I'd be very interested in anyone's thoughts on
>     this
>     >> problem. The link to my web page follows:
>     >> http://home.roadrunner.com/~lwconklin/
>      Larry Conklin
>     Liverpool, NY .-
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Cold Solder Joint  someplace ???

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