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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