In a message dated 27/03/2006, Bobhelenmcclure@....... writes:
Place pairs on quarter-inch or thicker steel plates and hold the plates
apart with stove bolts. Assemble very carefully, using a thick shim to hold the
gap, and then jack the gap open with the bolts to release the shim. Wear heavy
gloves! For a gap of 0.250 inches, you get a field of 8000 gauss. A
rectangular coil of 1100 turns yields 85v-s/m output. You won't need separate damping
magnets. A shunt resistor will provide the damping.
Hi Bob,
What are 'stove bolts' please?
You may need rather thicker plate than 1/4" with two side by side 18 mm
x 6 mm thick magnets. The 5 mm plate that I used at first was only just thick
enough to take the flux of the 1/2" x 1/4" thick magnets.
Are you using a pair of magnets on one plate and then putting a bare
iron plate over the top, or do you use four magnets on two plates? I have found
using four magnets gives a more constant central field. It also allows a bit
more thread to fit the two central nuts.
The reason why I do not use this sort of damping is that I want the
damping and the sensitivity to be independent. The damping that you need is a
function of the period. Setting up a system where the sensitivity and the
damping are both a function of the period is a bit more difficult the second time.
I use the wide copper damping plate as a mechanical stop. The plate edge
can never move into the high field region at the edge of the magnets. If
your coil drifted off the magnet, the damping would go to zero. I have also had
some variable force effects when the copper wire is close to the edge of a
magnet. Not all copper wire seems to have the same diamagnetic properties.
Is the 85V/m/sec figure correct? It does not sound very high.
Regards,
Chris Chapman
In a message dated 27/03/2006, Bobhelenmcclure@....... writes:
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FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>
Place pairs on quarter-inch or thicker steel plates and hold the plat=
es=20
apart with stove bolts. Assemble very carefully, using a thick shim to hol=
d=20
the gap, and then jack the gap open with the bolts to release the shim. We=
ar=20
heavy gloves! For a gap of 0.250 inches, you get a field of 8000 gauss. A=20
rectangular coil of 1100 turns yields 85v-s/m output. You won't need separ=
ate=20
damping magnets. A shunt resistor will provide the=20
damping.
Hi Bob,
What are 'stove bolts' please?
You may need rather thicker plate than 1/4" wit=
h=20
two side by side 18 mm x 6 mm thick magnets. The 5 mm plate that I used=
at=20
first was only just thick enough to take the flux of the 1/2" x 1/4" thick=20
magnets.
Are you using a pair of magnets on one plate an=
d=20
then putting a bare iron plate over the top, or do you use four magnets=
on=20
two plates? I have found using four magnets gives a more constant central fi=
eld.=20
It also allows a bit more thread to fit the two central nuts.
The reason why I do not use this sort of dampin=
g is=20
that I want the damping and the sensitivity to be independent. The damping t=
hat=20
you need is a function of the period. Setting up a system where the sensitiv=
ity=20
and the damping are both a function of the period is a bit more difficult th=
e=20
second time.
I use the wide copper damping plate as a mechan=
ical=20
stop. The plate edge can never move into the high field region at the e=
dge=20
of the magnets. If your coil drifted off the magnet, the damping would=20=
go=20
to zero. I have also had some variable force effects when the copper wire is=
=20
close to the edge of a magnet. Not all copper wire seems to have the sa=
me=20
diamagnetic properties.
Is the 85V/m/sec figure correct? It does not so=
und=20
very high.
Regards,
Chris Chapman