Measuring magnetic field

[John Popelish]

eromlignod wrote:
(snip)

So it acts sort of like a relay buzzer. Each time the string is pulled
into the beam, the switch turns the coil back off and releases the
magnetic pull on it. Then it bounces back out of the beam and the
cycle repeats.

My large coil takes enough current that I need an intermediate
transistor, since the little fork switch can't handle it alone. I
would like to reduce the power consumption of the coil so that I can
switch it with the sensor directly. Obviously, I would also like to
reduce the coil cost.

Are you using the pull of one end of a solenoidal coil? If so, you
can greatly increase the force by putting the coil along side the
string, and use the poles at both ends to attract the string. This
gets rid of a lot of air in the magnetic field path. Even better
would be to use a small E core lamination stack with the center pole
and two other end poles all lined up along the string.

 

[eromlignod]

John Popelish wrote:

Are you using the pull of one end of a solenoidal coil? If so, you
can greatly increase the force by putting the coil along side the
string, and use the poles at both ends to attract the string. This
gets rid of a lot of air in the magnetic field path. Even better
would be to use a small E core lamination stack with the center pole
and two other end poles all lined up along the string.

This is interesting, John. Do you think that I might be able to use
PCB-mount axial chokes (look like little green resistors) as my coils?
Or will ferrite cores give me much pull? Maybe some other standard
(cheap) inductor?

Don
Kansas City

 

[John Popelish]

eromlignod wrote:

John Popelish wrote:

Are you using the pull of one end of a solenoidal coil? If so, you
can greatly increase the force by putting the coil along side the
string, and use the poles at both ends to attract the string. This
gets rid of a lot of air in the magnetic field path. Even better
would be to use a small E core lamination stack with the center pole
and two other end poles all lined up along the string.



This is interesting, John. Do you think that I might be able to use
PCB-mount axial chokes (look like little green resistors) as my coils?
Or will ferrite cores give me much pull? Maybe some other standard
(cheap) inductor?

I doubt it. You need a form that has the core extending out to the
edge of the coil, so it is close to the string. Something like these
might work:
http://www.jwmiller.com/pdf2/6000.pdf
Especially if you cut he shrink tubing off.
However supporting an axial version like these may be easier:
http://rocky.digikey.com/WebLib/API%20Delevan/WEB%20DATA/4590.pdf

 

[Rich Grise]

On Thu, 21 Jul 2005 08:03:39 -0700, eromlignod wrote:

My large coil takes enough current that I need an intermediate
transistor, since the little fork switch can't handle it alone. I
would like to reduce the power consumption of the coil so that I can
switch it with the sensor directly. Obviously, I would also like to
reduce the coil cost.

I just took a look at Digi-Key, and they have some reed relays for
$1.19 in 100's. So I'm sure you can get coils cheap, now just look
for some long E-cores, like Spehro suggested, and you might be
done!

Good Luck!
Rich

 

[Dan Major]

"eromlignod" <eromlignod@aol.com> wrote in news:1121877843.165642.68820
@g14g2000cwa.googlegroups.com:

Hi guys:

I'm working on an application where I need a simple DC coil that
provides a particular magnetic field strength.
(snip)
Is there a simple way to do this without expensive equipment?

How much influence does a magnetic field have on an (iron/steel) object?
One way to measure the field strength would be to suspend an iron weight on
a string. The deflection from vertical would give the force (do some
simple vector analysis).