see my comments beside your questions below -- Jan M
Jan Marshall
jandmarshall@............
www.cableone.net/jandmarshall
Nampa, ID
-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@.................
Behalf Of ChrisAtUpw@.......
Sent: Sunday, September 29, 2002 3:24 PM
To: psn-l@..............
Subject: Re: New Lehman on line (almost)
In a message dated 29/09/02, jandmarshall@............ writes:
Please visit my web site www.cableone.net/jandmarshall and choose the
Seismic Page to view my project.
Problems I note right off
1 - I have a 4-5 hz oscillation in the pendulum.
2 - I seem to have a lot of environmental noise -- I can not
correlate it with actions in the house
3 - Am I damped enough?
Hi Jan,
The photos are a great help.
What is the weight of the seismic mass on the end of the arm? right
at 5 pounds
What undamped oscillation period are you getting? about 12 - 14 sec
Only you can check the damping. Deflect the beam a very small
amount, maybe by putting a screwdriver etc near it, let it go and observe
it. The pendulum should swing back to the zero position, but it should not
go beyond zero and come back, or show any actual oscillations. OK -- I am
not damped enough -- It oscillates about 4-5 times
The bearings, general construction etc look fine. Check for
electrical activity in the house / movement of magnetic materials, even cars
/ trains outside etc to search for the environmental noise. Does the seis
react when the fridge / cooker / central heating switches on / off? It is
more usual to put both magnets on the baseplate and the coil and damping
plate on the arm. With unscreened magnets on the arm, it can and will pick
up any small changes in the local environmental magnetic field. I will
consider this
From the photos, I can't see where the pick up coil is in relation
to it's magnet. The centre line of the coil should be roughly on the end
face of the magnet with your setup. See the 6th picture down --
The 5 Hz could be due to the whole arm system nodding up and down or
side to side. Try tapping the end post with your finger and see if you get
this sort of frequency response. With your coil system as shown, you will
likely pick up both vertical and horizontal movements of the arm. I lowered
the right end a tiny bit -- the LF oscillations appear to have stopped
What amplifier / filter / A/D system are you using? What is the
cut-off frequency of the filter? I am using Larry Cochran's Serial A/D
board and his Filter/Amp both stock as I received them -- I am using his
coil also
Regards,
Chris Chapman
see my=20
comments beside your questions below -- Jan M
Jan=20
Marshall
jandmarshall@............
www.cableone.net/jandmarshallNampa,=20
ID
-----Original Message-----
From: =
psn-l-request@.................
[mailto:psn-l-request@...............On Behalf Of=20
ChrisAtUpw@.......
Sent: Sunday, September 29, 2002 3:24 =
PM
To: psn-l@..............
Subject: Re: New =
Lehman on=20
line (almost)
In a =
message dated=20
29/09/02, jandmarshall@............ writes:
Please visit my web site =
www.cableone.net/jandmarshall and=20
choose the Seismic Page to view my project.
Problems I note =
right=20
off
1 - I have a 4-5 hz oscillation in the =
pendulum.=20
2 - I seem to have a lot of environmental =
noise -- I=20
can not correlate it with actions in the house =
3 - Am=20
I damped enough?
Hi=20
Jan,
The photos are a =
great help.=20
What is the weight of the =
seismic=20
mass on the end of the arm? right at 5=20
=
pounds
Wha=
t=20
undamped oscillation period are you getting? about 12 - =
14=20
sec
Only you =
can=20
check the damping. Deflect the beam a very small amount, maybe by =
putting a=20
screwdriver etc near it, let it go and observe it. The pendulum should =
swing=20
back to the zero position, but it should not go beyond zero and come =
back, or=20
show any actual oscillations. OK -- I am not damped enough -- It =
oscillates about=20
4-5 =
times
The =
bearings, general construction etc look fine. Check for electrical =
activity in=20
the house / movement of magnetic materials, even cars / trains outside =
etc to=20
search for the environmental noise. Does the seis react when the =
fridge /=20
cooker / central heating switches on / off? It is more usual to put =
both=20
magnets on the baseplate and the coil and damping plate on the arm. =
With=20
unscreened magnets on the arm, it can and will pick up any small =
changes in=20
the local environmental magnetic field. I will consider =
=
this
From =
the=20
photos, I can't see where the pick up coil is in relation to it's =
magnet. The=20
centre line of the coil should be roughly on the end face of the =
magnet with=20
your setup. See=20
the 6th picture down=20
=
--
T=
he 5=20
Hz could be due to the whole arm system nodding up and down or side to =
side.=20
Try tapping the end post with your finger and see if you get this sort =
of=20
frequency response. With your coil system as shown, you will likely =
pick up=20
both vertical and horizontal movements of the arm. I lowered =
the right=20
end a tiny bit -- the LF oscillations appear to have=20
=
stopped
Wh=
at=20
amplifier / filter / A/D system are you using? What is the cut-off =
frequency=20
of the filter? I=20
am using Larry Cochran's Serial A/D board and his Filter/Amp both =
stock as I=20
received them -- I am using his coil=20
=
also
Regar=
ds,=20
Chris Chapman=20