Hi Chris,
Your reference to capacitive linear position sensor was very instructive.
Thank you. It took a few minutes for me to understand, but I get it now. The
text in Randall Peters description
http://physics.mercer.edu/hpage/new-z.html "A picture of the prototype
instrument that was built and tested is shown in the figure below. The
instrument can be adjusted to have a natural period of at least 20 s-the
prerequisite for high teleseismic sensitivity. To operate at that period for
variable temperature/pressure requires force-feedback, components of which
are not pictured. The feedback is not one of `hard' force-balance, but
rather `soft' type, based on a long time constant response to mean position
changes." suggests feedback. So it seems that if one wants a 20 second
resonant period, some means of feedback is required (not shown). Any idea
what Randall has used for the feedback scheme. Also what is the typical
signal frequency used in the capacitive linear position sensor. But why go
to this more complicated method compared to your simple rare-earth magnet
assembly with compact coil design concept. I suppose the answer has to do if
feedback is used and then one can get a DC voltage proportional to position.
Gary
From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of ChrisAtUpw@.......
Sent: Sunday, August 24, 2008 6:52 PM
To: psn-l@..............
Subject: Re: Vertical Seismometers
In a message dated 2008/08/25, gel@................. writes:
My first inclination would be to go with the Sean Thomas Morrissey's
concept. It would sure be nice to have a vertical with an equivalent 50ft
beam length in a 2 sq. ft space. But the design detail and drift issues
would seem to be a problem.
Hi Gary,
It takes a bit of sorting out, but it is all there.
As a few mentioned, the Randall Peters design
http://physics.mercer.edu/hpage/new-z.html looks interesting. But I have a
few questions:
1. What is a capacitive linear position sensor.
Exactly what it says it is.
See http://physics.mercer.edu/hpage/rpend.html
2. If feedback is used
I don't see any feedback. There could be a magnetic damper behind the
sensor plates. The horizontal had a magnet damper around the tongue on the
end of the shield plate. The apparatus in the photo looks more like a
construction to demonstrate the principles involved.
Also have a look at http://jclahr.com/science/psn/hill/index.html
Regards,
Chris Chapman
Hi Chris,
Your reference to capacitive linear position =
sensor was
very instructive. Thank you. It took a few minutes for me to understand, =
but I
get it now. The text in Randall Peters description http://physics.mercer=
..edu/hpage/new-z.html
“A picture of the prototype instrument that was built and =
tested
is shown in the figure below. The instrument can be adjusted to have a =
natural
period of at least 20 s-the prerequisite for high teleseismic =
sensitivity. To
operate at that period for variable temperature/pressure requires
force-feedback, components of which are not pictured. The feedback is =
not one
of `hard' force-balance, but rather `soft' type, based on a long time =
constant
response to mean position changes.” suggests feedback. So it seems =
that
if one wants a 20 second resonant period, some means of feedback is =
required
(not shown). Any idea what Randall has used for the feedback scheme. =
Also what
is the typical signal frequency used in the capacitive linear =
position sensor.
But why go to this more complicated method compared to your simple =
rare-earth
magnet assembly with compact coil design concept. I suppose the answer =
has to
do if feedback is used and then one can get a DC voltage proportional to
position.
Gary
From:=
psn-l-request@.............. [mailto:psn-l-request@............... On =
Behalf
Of ChrisAtUpw@.......
Sent: Sunday, August 24, 2008 6:52 PM
To: psn-l@..............
Subject: Re: Vertical Seismometers
In
a message dated 2008/08/25, gel@................. writes:
My
first inclination would be to go with the Sean Thomas Morrissey's =
concept. It
would sure be nice to have a vertical with an equivalent 50ft beam =
length in a
2 sq. ft space. But the design detail and drift issues would seem to be =
a
problem.
Hi Gary,
It takes a bit of sorting out, but =
it is
all there.
As a few mentioned, the Randall Peters design
http://physics.mercer=
..edu/hpage/new-z.html
looks interesting. But I have a few questions:
1. What is a capacitive linear =
position
sensor.
Exactly what it says it is.
See
http://physics.mercer.edu/hpage/rpend.html
2. If feedback is used
I don't see any feedback. There =
could be a
magnetic damper behind the sensor plates. The horizontal had a magnet =
damper
around the tongue on the end of the shield plate. The apparatus in the =
photo
looks more like a construction to demonstrate the principles =
involved.
Also have a look at
http://jclahr.com/science/psn/hill/index.html
Regards,
Chris Chapman