On 2012-06-22 1:21, Larry Conklin wrote:
> 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 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.
>
> But I find your suggestion of replacing that capacitor very 
> intriguing, and I will definitely try it.  I keep a zero center meter 
> connected to the leveling test point as an aid to getting good 
> centering.  And when I've been having problems, I have noticed some 
> jitter of the pointer around the set point.  So I'm very willing to 
> believe that the problem might be in the feedback circuit.  And, it's 
> a pretty easy experiment to try.  I'll let you know what happens.
>
> As fate would have it, the thing has been running pretty well all day 
> today.
>
> Larry
>
>
>
> On 6/21/2012 6:00 PM, Larry Cochrane wrote:
>> 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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>>>
>>>
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>>
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>
>
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Im no expert, but Id not use electrolytics in any circuits but power 
circuits.

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