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Roughly proportional to how fast the magnet is moving - give us aIf I had a flat, 2 foot by two foot coil lying flat, how far above it could
I reasonably expect the detect a rare earth magnet, perhaps the size of an
M&M?
On Thu, 3 Feb 2005 04:57:10 -0600, "Brian" <brian@w3gate.com> wrote:
If I had a flat, 2 foot by two foot coil lying flat, how far above it
could
I reasonably expect the detect a rare earth magnet, perhaps the size of an
M&M?
Roughly proportional to how fast the magnet is moving - give us a
clue.
d
Pearce Consulting
http://www.pearce.uk.com
A Hall Effect sensor is the only option for a stationary magnet. It issay it crosses the plane in 2 seconds.
Are there ways of detecting a stationary magnet?
A SQUID will work, as well. They work best when they are very cold.On Thu, 3 Feb 2005 10:41:03 -0600, "Brian" <brian@w3gate.com> wrote:
say it crosses the plane in 2 seconds.
Are there ways of detecting a stationary magnet?
A Hall Effect sensor is the only option for a stationary magnet. It is
also the best choice for such a slow moving magnet.
The magnitude of signal you get depends on stuff like how strong the
magnet is.
An ordinary inductive coil requires the magnet to be in motion and theIf I had a flat, 2 foot by two foot coil lying flat, how far above it
could
I reasonably expect the detect a rare earth magnet, perhaps the size of an
M&M?
Semi-seriously, you could use a compass and an led-phototransistorAh, flat statements are (almost ;-)) always wrong. What about a
fluxgate senor? Or a reed? Or magnetoresistive (eg. GMR) sensor?
There are probably others I've forgotton
"Brian" <brian@w3gate.com> wrote in message
news:VJadnZKl8qofnp_fRVn-tA@centurytel.net...
If I had a flat, 2 foot by two foot coil lying flat, how far above
it
could
I reasonably expect the detect a rare earth magnet, perhaps the
size of an
M&M?
An ordinary inductive coil requires the magnet to be in motion and
the
voltage induced is a function of the number of turns and the rate of
change
of the flux, dphi)/dt. Therefore the speed of a moving magnet is very
important. Practically you might be able to sense the magnet moving a
foot
away or so depending on the number of turns in the coil and the speed
of the
magnet. It is a signal to noise issue and power line interference
(hum)
would limit what you can detect.
However it is possible to detect small stationary magnetic fields
(DC) by
arranging and energizing coils in a device called a flux gate. These
things
can be designed to measure fields as low as 1/1000 of the earths
magnetic
field or even lower, less than a milligauss and could easily measure
your
magnet many feet from the fluxgate. Being DC, it's easy to get rid of
the
power line interference. There is also hall effect devices which has
been
mentioned but they are not particularly sensitive. Beyond that, there
is a
quantum mechanical device called a "squid" that can measure
extremely small
fields like the field from the iron in a single blood cell. These are
probably way beyond what you need or could pay for but it gives you
an idea
of the technology available. What are you trying to do?
Bob
Dang! Now I have to throw away my chunk of iron glued to a switch!A Hall Effect sensor is the only option for a stationary magnet.
I think 2 toroids inside two solenoids will work better.A fluxgate magnetometer (Google search terms) can probably be built easily
enough by the hobbyist. You need a high permeability material like
mumetal, a few solenoids, and electronics.
E.g. http://beale.best.vwh.net/measure/fluxgate/
A cow magnet? This would be a magnetized cow, possibly one that has aBTW: A good flux gate will detect a cow magnet up to about 100 feet. A
SQUID only improves on this distance by about a factor of 20.
Put a solenoid on a crank and spin it around.On Thu, 03 Feb 2005 16:45:05 GMT, the renowned donald@pearce.uk.com
(Don Pearce) wrote:
On Thu, 3 Feb 2005 10:41:03 -0600, "Brian" <brian@w3gate.com> wrote:
say it crosses the plane in 2 seconds.
Are there ways of detecting a stationary magnet?
A Hall Effect sensor is the only option for a stationary magnet. It is
also the best choice for such a slow moving magnet.
Ah, flat statements are (almost ;-)) always wrong. What about a
fluxgate senor? Or a reed? Or magnetoresistive (eg. GMR) sensor?
There are probably others I've forgotton
_Good Vibrations_ by the Beach Boys.There is a
musical instrument called a Theramin where the frequency of an oscillator is
varied by waving ones hand over an antenna. This is beat with another
oscillator producing an audio tone played through an amp and speaker. You
can hear these things in space movies and other places where weird etherial
music is used.
Easy - just run a cat past the dog house to see if he is home ... (alsoI am tryning to accomplish "mental exercise". Sometimes I see things and
it
just makes me ponder how to do it.
This "application" could be many, but is similar to RFID I suppose.
Tagging
something, but without identification and a completely passive tag. Could
be
to see if a box is on a pallet, or a dog is in his doghouse.
On Thu, 3 Feb 2005 10:41:03 -0600, "Brian" <brian@w3gate.com> wrote:
say it crosses the plane in 2 seconds.
Are there ways of detecting a stationary magnet?
A Hall Effect sensor is the only option for a stationary magnet. It is
also the best choice for such a slow moving magnet.
---I believe the principal of these coils is a tuned resonant tank that is
detuned by a large hunk of metal. I don't believe that the magnet
helps in this case but there are people out there that will swear that
they do work.
If I had a flat, 2 foot by two foot coil lying flat, how far above it
could
I reasonably expect the detect a rare earth magnet, perhaps the size of an
M&M?
No, for the ultimate try a low temperature SQUID. The have a noise ofOn Thu, 03 Feb 2005 16:45:05 GMT, donald@pearce.uk.com (Don Pearce) wrote:
On Thu, 3 Feb 2005 10:41:03 -0600, "Brian" <brian@w3gate.com> wrote:
say it crosses the plane in 2 seconds.
Are there ways of detecting a stationary magnet?
A Hall Effect sensor is the only option for a stationary magnet. It is
also the best choice for such a slow moving magnet.
Or a GMR sensor - more sensitive. NVE and Philips make them.
For ultimate sensitivity, try a fluxgate magnetometer.
The reaction depends on the dog. I think feeding the dog radioactive foodEasy - just run a cat past the dog house to see if he is home ... (also
counts
as a "cat scan" )
Those who have tried this have posted glowing reports.I think feeding the dog radioactive food and using automatic
radiation detector would work better: That would be
Radio-Active Dog Automatic Ranging (RADAR)