PSN-L Email List Message
Subject: Re: Haunted system misbehaving again
From: chrisatupw@.......
Date: Thu, 21 Jun 2012 20:26:41 -0400 (EDT)
From: Larry Conklin lconklin@............
Sent: Wed, 20 Jun 2012 2:19
Subject: Re: Haunted system misbehaving again
Hi Larry,
****Not a silly question at all, but one I've considered in the past. Have=
=20
arefully checked and cleaned around the pendulum, etc to get rid of any=20
ossible webs or critters, with no noticeable effect.
****Regarding the enclosure, it isn't much bigger than it needs to be to=20
nclose the volume surrounding the sensor. And I have a couple of power=20
esistors on an aluminum plate at the top of the box to try to create a=20
emperature inversion, but I've never been able to convince myself that=20
t makes any real difference. Maybe I need to make it a little hotter.=20
Hi Larry,
The enclosure needs to be well insulated, with the heater inside=20
the top of the enclosure. It can work well with a few watts. Too much=20
power can stir up the air and give noise. Try switching the power off=20
completely when you get noise ? I reckon not more than about 20 watts=20
heating for my large Lehman enclosure. You only get reverse convection=20
noise when the air temperature falls below the ground temperature,=20
typically at night in the early hours of the morning. You can check for=20
this with one of the cheap indoor / outdoor electronic digital=20
thermometers.
=20
***At one time I tried to take up as much of the empty space with baffles=
=20
ade of corrugated cardboard, but that didn't seem to help either and it=20
ade the cover of the enclosure surprisingly heavy. I wound up=20
crapping that cover and making a new one out of celotex panels. It=20
ould probably be a good idea to fill the empty space in this enclosure=20
ith something light and insulating, like styrofoam.
Open cell polyurethane foam is a much better filler than sealed=20
cell polystyrene. Stick it on with lines of adhesive silicone rubber ?=20
****But none of those possibilities really fit the history of the problem v=
ery well.=20
cell polystyrene. Stick it on with lines of adhesive silicone rubber ?=20
****But none of those possibilities really fit the history of the problem v=
ery well.=20
=20
# I could write a small book on all the things I've considered and tried, s=
everal of=20
which have seemed to cure the problem, only to have it come back months lat=
er.=20
=20
While it may be relatively unlikely, you could have several causes ?
=20
****I really don't have any real reason to suspect the electronics, other t=
han I=20
don't have any other ideas. The basement is humid, so at one time I took th=
e board=20
out and baked it under a hundred watt light bulb for a couple of days, clea=
ned it=20
and put it back. No effect.
=20
=20
You can check for power line interferance with a MW / LW AM radio. Tune=
it in between=20
stations and then listen for cracks and pops in the background noise. You c=
ould have a serious=20
problem / intermittent contact somewhere in your house wiring, or in an app=
liance - like a deep=20
freeze chest ? =20
=20
It is fairly easy to test most of the electronics. Put a digital=20
multimeter onto the tilt test point and earth. Very carefully /=20
gently, insert two wood wedges between the sensor plates and the=20
oscillator plate so that the tilt output voltage is still ~0 V.=20
This effectively zeroes the input vibration signal, but all opamps=20
except U6 are still operating, so any noise on the recorder is in the=20
circuit itself. The only opamp not tested is U6, the NE5534 feedback=20
coil driver. They are not expensive. =20
=20
****Since I can see corresponding glitches in the output of both channels,
if there is a problem with the board it either has to be upstream of the po=
int where=20
the two channels separate, or possibly in the power supply. But, with the l=
imited test=20
equipment I have, I don't see anything amis in the power. And at one time, =
I decided=20
it was worth the trouble, and replaced the first stage op amp. No dice.
So.... What other ideas have you got?
=20
Check that the two suspension foils have not been visably damaged,=20
showing folds, wrinkles.... Check for continuity of the feedback wiring and=
=20
coil with a multimeter.=20
Now, the most likely problem, what are the levelling screws resting on=
=20
and what are the screw ends like ? Pointed, rounded, etc ?
The seismometer itself changes in length and width by a tiny amount as it's=
=20
temperature changes - the ground / floor changes at a different rate and mu=
ch=20
more slowly. I glue 1/8" thick SS plates to concrete with pool cement, or=
=20
similar and cap the ends of the adjusting screws with dome headed stainless=
=20
steel nuts. You can also use glass or most hard, really smooth materials fo=
r=20
the mounting surface.=20
=20
On 6/19/2012 6:52 PM, Larry Cochrane wrote:
> Silly question Larry. Are you sure the noise is not being caused by=20
> spiders, also known as spiderquakes, or some other insect getting=20
> inside the enclosure? I guess it could also be air currents inside the=20
> enclosure. Do you have a lot of free air space inside your sensor box?=20
=20
=20
****I think I remember your having posted an account of your "rug affair". =
=20
In fact I think that it prompted me to improve the leveling screws on my=20
system, which at the time were rather flimsy. I replaced them with=20
larger, stiffer screws and I think that it may have helped, or even=20
"solved" the problem for a while. I'm now using fairly substantial=20
screws and the system is (and already had been) sitting on a couple of=20
1/8 inch thick strips of aluminum that are epoxied to the basement=20
floor. The assumption being that the plates are a more rigid surface=20
than the bare concrete would be.
****The only pivot points I can identify are the pendulum hinge itself=20
(consisting of thin metal shim material, phosphor bronze or some such). =20
But there is certainly the possibility that the contacts between the=20
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=20
wood box that sat on the frame of the sensor. Very bad idea. Rebuilt it=20
to fit over the sensor and sit on the floor. Better, but probably=20
vulnerable to transmitting noise to the instrument. Added "stuffing" to=20
fill up the unused volume and suppress air movement. Not much noticeable=20
change. Current cover is light weight, built of insulating board and=20
sitting on the floor. At times I've duct taped it to the floor, but at=20
the moment it's just sitting there. Maybe putting the tape back would=20
be a good idea.=20
=20
NOT in my opinion. You DON'T want to either have the cover so=20
well sealed as it reacts to air pressure changes, or that there are=20
'leak channels' which blow in jets of air - although quite slowly.=20
I am strongly in favout of sticking a continuous 1/2" strip of the=20
very soft open cell foam door / window strip to the base and then=20
putting a weight on top of the enclosure to compress it onto the=20
ground. =20
****But the ovea dry rall behavior of the problem makes a lot of these=20
possibilities seem unlikely. In one subset of episodes of the problem,=20
the noise starts abruptly and then continues indefinitely for days of=20
weeks at a time. The data shown on my web page is typical of this=20
"class". (And I noticed that this episode started on March 30, and is=20
still ongoing, although there were couple of periods of a week or so=20
duration since them where things were much better.) Other episodes have=20
emerged gradually over the course of several hours, continued for days=20
or even weeks at a time and then subsided. I'm at a loss to come up=20
with a theory that is consistent with both kinds of behavior. And none=20
of the experiments I've tried have made any clear and lasting impact on=20
the problem, although I've tried a few things that I've thought fixed=20
it, only to have it crop up six months later.
This is starting to sound more like a failing opamp / component or dry =
solder joint.=20
On 6/20/2012 9:41 AM, RSparks wrote:
> Hi Larry,
>
> My experience parallels yours with loose mounted components. I once=20
> went through a rug to concrete below and failed to make good contact=20
> with one screw on the concrete. I was effectively floating on the rug=20
> with one of the three seismometer legs! Very noisy!
>
> Based on this experience, I am careful to make all mechanical contacts=20
> solid connections in some way. I even drilled holes into the concrete=20
> and mounted my seismometer solidly. I thought there was a small=20
> improvement in the noise level after taking this somewhat extreme=20
> measure.
>
> I also avoid pivot points in favor of bending joints to avoid noise. =20
> Friction is present in our seismometers if there is a moving joint and=20
> mechanical friction is always noise.
>
> Maybe look more carefully at any mechanical connection that might be=20
> loose, maybe not only in the leveling screws. Look also at the=20
> mounting of the surrounding air/insulating box, making sure it is not=20
> rocking from the ever present 0.2 Hz peak noise or more likely, the=20
> thermal air currents in your room.
****But the ovea dry rall behavior of the problem makes a lot of these=20
possibilities seem unlikely. In one subset of episodes of the problem,=20
the noise starts abruptly and then continues indefinitely for days of=20
weeks at a time. The data shown on my web page is typical of this=20
"class". (And I noticed that this episode started on March 30, and is=20
still ongoing, although there were couple of periods of a week or so=20
duration since them where things were much better.) Other episodes have=20
emerged gradually over the course of several hours, continued for days=20
or even weeks at a time and then subsided. I'm at a loss to come up=20
with a theory that is consistent with both kinds of behavior. And none=20
of the experiments I've tried have made any clear and lasting impact on=20
the problem, although I've tried a few things that I've thought fixed=20
it, only to have it crop up six months later.
This is starting to sound more like a failing opamp / component or dry =
solder joint.=20
On 6/20/2012 9:41 AM, RSparks wrote:
> Hi Larry,
>
> My experience parallels yours with loose mounted components. I once=20
> went through a rug to concrete below and failed to make good contact=20
> with one screw on the concrete. I was effectively floating on the rug=20
> with one of the three seismometer legs! Very noisy!
>
> Based on this experience, I am careful to make all mechanical contacts=20
> solid connections in some way. I even drilled holes into the concrete=20
> and mounted my seismometer solidly. I thought there was a small=20
> improvement in the noise level after taking this somewhat extreme=20
> measure.
>
> I also avoid pivot points in favor of bending joints to avoid noise. =20
> Friction is present in our seismometers if there is a moving joint and=20
> mechanical friction is always noise.
>
> Maybe look more carefully at any mechanical connection that might be=20
> loose, maybe not only in the leveling screws. Look also at the=20
> mounting of the surrounding air/insulating box, making sure it is not=20
> rocking from the ever present 0.2 Hz peak noise or more likely, the=20
> thermal air currents in your room.
I don't follow Larry Cochrane's point about the two 100muF capacitors. =
There aren't=20
any in his circuit - assuming that you are using his board ?=20
I hope that this helps,=20
Regards,=20
Chris Chapman
=
From: Larry Conklin
lconklin@twcny=
..rr.com
Sent: Wed, 20 Jun 2012 2:19
Subject: Re: Haunted system misbehaving again
Hi Larry,
****Not a silly question at all, but one I've considered in the past. Have=
=20
carefully checked and cleaned around the pendulum, etc to get rid of any=20
possible webs or critters, with no noticeable effect.
****Regarding the enclosure, it isn't much bigger than it needs to be to=20
enclose the volume surrounding the sensor. And I have a couple of power=20
resistors on an aluminum plate at the top of the box to try to create a=20
temperature inversion, but I've never been able to convince myself that=20
it makes any real difference. Maybe I need to make it a little hot=
ter.
The enclosure needs to be w=
ell insulated, with the heater inside
the top of the enclosure. It ca=
n work well with a few watts. Too much
power can stir up the air and g=
ive noise. Try switching the power off
completely when you get noise ?=
I reckon not more than about 20 watts
heating for my large Lehman enc=
losure. You only get reverse convection
noise <=
/TT>when the air temperature falls below =
the ground temperature,
typically at night in the early hours of the morning. You c=
an check for
this with =
one of the cheap indoor / outdoor electronic digital
thermometers.
****At one time I tried to take up as much of the empty space with b=
affles=20
made of corrugated cardboard, but that didn't seem to help either and it=20
made the cover of the enclosure surprisingly heavy. I wound up=20
scrapping that cover and making a new one out of celotex panels. It=20
would probably be a good idea to fill the empty space in this enclosure=20
with something light and insulating, like styrofoam.
Open cell polyurethane foam i=
s a much better filler than sealed
cell polystyrene. Stick it on with lines of adhesive silicone rubber ?
****But none of those possibilities really fit the history of the problem v=
ery well.
=
=
# I could write a small book on all the things I've=
considered and tried, several of
=
which have seemed to cure the problem, only to have it c=
ome back months later.=20
<=
/FONT>
&=
nbsp; While it may be relatively unlikely=
, you could have several causes ?
<=
/FONT>
*=
***I really don't have any real reason to suspect the electronics, other th=
an I
d=
on't have any other ideas. The basement is humid, so at one time I took the=
board
o=
ut and baked it under a hundred watt light bulb for a couple of days, clean=
ed it
a=
nd put it back. No effect.
<=
/FONT>
You can check for power line interferance w=
ith a MW / LW AM radio. Tune it in between
stations and=
then listen for cracks and pops in the background noise. You could have a =
serious
problem / intermittent contact somewhere in your house wiring,=
or in an appliance - like a deep
freeze chest ?
<=
/FONT>
&=
nbsp; It is fairly easy to test most of t=
he electronics. Put a digital
m=
ultimeter onto the tilt test point and earth=
.. Very carefully /
g=
ently, insert two wood wedges between the sensor plates and the
o=
scillator plate so that the tilt output =
;voltage is still ~0 V.
T=
his effectively zeroes the input vibrat=
ion signal, but all opamps
e=
xcept U6 are still operating, so any noise on the recorder is in the
c=
ircuit itself. The only opamp not tested is U6, the NE5534 feedback
c=
oil driver. They are not expensive.&nbs=
p;
<=
/FONT>
*=
***Since I can see corresponding glitches in the output of both channels,=
FONT>
i=
f there is a problem with the board it either has to be upstream of the poi=
nt where
t=
he two channels separate, or possibly in the power supply. But, with the li=
mited test
e=
quipment I have, I don't see anything amis in the power. And at one time, I=
decided
i=
t was worth the trouble, and replaced the first stage op amp. No dice.
S=
o.... What other ideas have you got?
<=
/FONT>
&=
nbsp; Check that the two suspension foils=
have not been visably damaged,
s=
howing folds, wrinkles.... Check for continuity of the feedback wiring and&=
nbsp;
c=
oil with a multimeter.
&=
nbsp; Now, the most likely problem, what are the levelling scre=
ws resting on
a=
nd what are the screw ends like ? Pointed, rounded, etc ?<=
/div>
T=
he seismometer itself changes in length=
and width by a tiny amount as it's
t=
emperature changes - the ground / floor changes at a different rate an=
d much
m=
ore slowly. I glue 1/8" thick SS plates=
to concrete with pool cement, or
s=
imilar and cap the ends of the adjusting scr=
ews with dome headed stainless
s=
teel nuts. You can also use glass or most ha=
rd, really smooth materials for
t=
he mounting surface.
&=
nbsp;
O=
n 6/19/2012 6:52 PM, Larry Cochrane wrote:
&=
gt; Silly question Larry. Are you sure the noise is not being caused by
&=
gt; spiders, also known as spiderquakes, or some other insect getting
&=
gt; inside the enclosure? I guess it could also be air currents inside the =
&=
gt; enclosure. Do you have a lot of free air space inside your sensor box? =
<=
/FONT>
<=
/FONT>
*=
***I think I remember your having posted an account of your "rug affair".&n=
bsp;
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).&nbs=
p;
But there is certainly the possibility that the contacts between the <=
br>
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 a=
t
the moment it's just sitting there. Maybe putting the tape back would=
be a good idea.
=
FONT>
=
FONT>
NOT in m=
y opinion. You DON'T want to either have the cover so =
TT>
well sealed as it reacts to=
air pressure changes, or that there are <=
/div>
'leak =
TT>channels' which=
blow in jets of air - although quite slowly.
I am strongly in favo=
ut of sticking a continuous 1/2" strip of the
very soft open cell foam d=
oor / window strip to the base and then =
div>
putting a weight on <=
/FONT><=
FONT color=3Dblack size=3D2 face=3Darial>=
top of the enclosure to compress it onto the
ground. <=
/div>
****But the ovea dry rall behavior of the problem makes a lo=
t 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 ha=
ve
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 <=
br>
with a theory that is consistent with both kinds of behavior. And non=
e
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.
This is starting to sound more like a fai=
ling opamp / component or dry solder joint.
On 6/20/2012 9:41 AM, RSparks wrote:
> Hi Larry,
>
> My experience parallels yours with loose mounted components. I o=
nce
> went through a rug to concrete below and failed to make good contact <=
br>
> with one screw on the concrete. I was effectively floating on th=
e 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 con=
crete
> 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.&n=
bsp;
> 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 <=
br>
> 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.
=
&nb=
sp;
=
I don't fol=
low Larry Cochrane's point about the two 100muF capacitors. There aren't =
FONT>
=
any in his circuit - assuming =
that you are using his board ?
=
I hope that=
this helps,
=
Regards, =
FONT>
=
Chris Chapm=
an
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