In a message dated 06/08/2005, JohnJan@........ writes:
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size=3D2>http://jclahr.com/science/psn/wooden/
Hi John,
You may need to bend a bit of wire straight at=20=
both=20
ends of the spring and clamp it. One of the problems with spring suspensions=
is=20
noise from the loop ends. You could bore a small hole through the 'mass' bol=
t=20
just under the head and clamp the wire between two washers? Put a similar cl=
amp=20
bolt on the frame? Noise can also be minimised by bending the wire to a=
V=20
instead of a loop end and using a slightly sharper V of hard metal=
=20
with a slightly rounded edge, like they do in weighing scales.
You may get better results from the=20
suspension if, instead of points, you use a couple of stainless steel b=
all=20
bearings on the base column and either a square polished lathe tool or a=20
glass microscope slide on the end of the arm. 1/4" beari=
ngs=20
should do fine. If you just want to 'try it out' you should be able to buy=20
several sizes of ordinary ball bearings from a cycle shop. You do need=20=
to=20
place a drop of thin oil at the contact point to inhibit corrosion.
I would be tempted to use a U magnet for the ma=
ss,=20
like in the AS-1 and either a relay or a miniature transformer coi=
l.=20
Larry sells relay coils. To get good signals, you really need a high gradien=
t=20
magnetic field and lots of turns, preferably on a square section coil.
Mouser sell a range of small transformers. You=20
remove the I strips from both ends of the yoke, free up a central E str=
ip=20
on both sides with a knife blade and then push it out using blocks=
and=20
a vice. You can then peel off and extract the remaining E strips to lea=
ve=20
you with a nice square sensor coil on a plastic former. I use them for dista=
nce=20
sensors with all the E strips replaced on one side, in the same way tha=
t=20
Sean Morrissey did.
If you use a single vertical magnet, you w=
ill=20
likely pick up a lot of magnetic noise from the power wiring in your house,=20=
from=20
fridges, central heating, electric cookers, from bikes, cars, lorries, train=
s=20
and from the earth's field. You will still pick up noise with a U magnet, bu=
t it=20
will be less. Both N & S poles face downward and you are not sensitive t=
o=20
side to side forces. A totally soft iron shielded Neo quad array would proba=
bly=20
be too heavy. The best way is still to put the coil on the end of the arm wi=
th a=20
brass weight and sit the magnet array out of harm's way on the floor!
I notice that you mentioned damping magnets. Co=
uld=20
you make an air damper with two different sizes of drinks cans, or one drink=
s=20
can and an open topped tin set on the ground? The airflow=20
resistance would come from the small circular but long air gap in between th=
e=20
cans? Maybe this is not too practical. It could be quite sensitive to air=20
pressure variations. Just an off the cuff idea.
You can get quite significant damping by=20
drilling a round copper bar and sliding one pole of a cylindrical Neo=20
magnet just inside it.
I have tried every combination that I can think=
of=20
for 'flat' magnetic damping systems. BY FAR THE MOST EFFECTIVE SYSTEM is to=20=
use=20
rectangular Neo magnets mounted on two mild steel plates held apart by=20=
mild=20
steel bolts. I use 3.5" x 2" x 1/4" bright mild steel plates and 1/4" m=
ild=20
steel bolts. On one inner face you place a N and a S Neo bar magne=
t=20
pair, with the long sides together. Facing this on the other face is a S=20
and a N Neo bar magnet pair. The poles are on the flat faces of the=20
magnets. You suspend an Al or Cu damping blade in the central gap so th=
at=20
it moves at right angles to the long magnet join and overlaps the=20
magnets by maybe 3/8". This avoids edge force effects between the=20
blade and the magnets. The fields from the rear of the magnet pairs are clos=
ely=20
linked by the soft iron, so that most of the mmf drives the fields in t=
he=20
central gap. This system gives a very sharp rate of change of field at=20=
the=20
central join, allowing strong damping on a cental moving Cu /=20
Al plate.
Have fun!
Regards,
Chris Chapman