Amplify the hell out of it.

[John Popelish]

"Gregory L. Hansen" wrote:

In article <4216219E.E375B008@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

I also emailed the seller and verified that this interpretation is
correct. After you have yours on the way, I may order one to play
with.

Somehow it seems bigger than it looked in the pictures. The can is five
inches in diameter, almost three inches high, the sensors mounted on the
lid which has two arrows oriented with the two horizontal sensors and a
spirit level in the middle. The large screws (5/16"?) on the bottom allow
mounting to something. And the two fittings are rubberized compression
seals that would allow wiring through conduit.

I haven't had the chance to plug it in to anything yet, but from the
physical inspection I like it.

Thanks for the report. That is about how big I expected it to be.
But since talking with you, I have sort of gotten my heart set on
making my own sensor coils and an Lehman type long period
seismometer. I have a bunch of magnets selected for purchase, and am
getting a quote from a machinist tomorrow, for the iron pole pieces.
I think I can achieve quite a multiple of the signal to noise ratio
(50, perhaps) compared to any sensors I have seen that hobbyists
build. It has a hum bucking coil design that cancels the effect of
large fields, like power line hum, lightning and variations in the
geofield caused by aurora. And the whole coil sits in an
approximately 10,000 gauss field. It would make one hell of a linear
motor.

My goal is to be able to lie down on the concrete, next to my unit,
and monitor my heart beat above the noise. If it will do that, I
should be able to pick up any significant quake on the planet. Like
the geophone pickups, this will be a velocity output.

If I get that to work, I want to add an optical detector that goes
down to DC so the unit effectively becomes a tilt meter. I have no
idea how sensitive I can make that, compared to the magnetic unit.
Connecting them in a feedback loop, to hold the magnetic bob
stationary with respect to the Earth will make the coil current
proportional to acceleration.

I am very interested to hear how your amplifier works with the unit
you have purchased. I need to get a few of those LT1007 opamps for
the front end of mine.

After you get a signal, I would like to talk with you about filtering
possibilities to reduce high frequency (road traffic) noise and extend
the low frequency performance, if these things interest you.

--
John Popelish

 

[Gregory L. Hansen]

In article <421FEB95.6324E018@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

"Gregory L. Hansen" wrote:

In article <4216219E.E375B008@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

I also emailed the seller and verified that this interpretation is
correct. After you have yours on the way, I may order one to play
with.

Somehow it seems bigger than it looked in the pictures. The can is five
inches in diameter, almost three inches high, the sensors mounted on the
lid which has two arrows oriented with the two horizontal sensors and a
spirit level in the middle. The large screws (5/16"?) on the bottom allow
mounting to something. And the two fittings are rubberized compression
seals that would allow wiring through conduit.

I haven't had the chance to plug it in to anything yet, but from the
physical inspection I like it.

Thanks for the report. That is about how big I expected it to be.
But since talking with you, I have sort of gotten my heart set on
making my own sensor coils and an Lehman type long period
seismometer. I have a bunch of magnets selected for purchase, and am
getting a quote from a machinist tomorrow, for the iron pole pieces.

That's quite a project. Where did you find the magnets?

I think I can achieve quite a multiple of the signal to noise ratio
(50, perhaps) compared to any sensors I have seen that hobbyists
build. It has a hum bucking coil design that cancels the effect of
large fields, like power line hum, lightning and variations in the
geofield caused by aurora. And the whole coil sits in an
approximately 10,000 gauss field. It would make one hell of a linear
motor.

What's a hum bucking coil? I had thought of making two identical coils
connected in opposite senses with the magnets for each coil in different
directions, so that e.g. line noise would be (approximately) equal and
opposite in the two coils, but the pickup EMF adds together. But I went
with the geophone instead.

My goal is to be able to lie down on the concrete, next to my unit,
and monitor my heart beat above the noise. If it will do that, I
should be able to pick up any significant quake on the planet. Like
the geophone pickups, this will be a velocity output.

If I get that to work, I want to add an optical detector that goes
down to DC so the unit effectively becomes a tilt meter. I have no
idea how sensitive I can make that, compared to the magnetic unit.
Connecting them in a feedback loop, to hold the magnetic bob
stationary with respect to the Earth will make the coil current
proportional to acceleration.

You should do a web page.

I am very interested to hear how your amplifier works with the unit
you have purchased. I need to get a few of those LT1007 opamps for
the front end of mine.

After you get a signal, I would like to talk with you about filtering
possibilities to reduce high frequency (road traffic) noise and extend
the low frequency performance, if these things interest you.

I think I mentioned before that I might move kind of slowly on it. Partly
because I'm learning as I'm going. I'm just starting to read about active
filters in my Horowitz and Hill. And partly it's just hard to work
around the fact that I'm living in a rented room on a student's budget.
It's hard to build up much of a workshop.

I don't have the special op-amps yet, but I've been to Radio Shack to pick
up miscellaneous electrical things. It doesn't seem too bad to spend 99
cents on an op-amp, 69 cents on a pair of sockets, $2.50 for a switch,
etc. But when you run through a parts list, those nickels and dimes can
add up. I wanted to try wire wrapping this one. They had a wrapping
tool, but no sockets. Oh, well.

--
"A nice adaptation of conditions will make almost any hypothesis agree
with the phenomena. This will please the imagination but does not advance
our knowledge." -- J. Black, 1803.