Hello Mr. Nordgren;

The question I have is thus:

Is that coil right for the magnets or,
Should it be rectangular in shape with the
two vertical sides of the rectangle outside the magnetic flux ?

I figure I may need like 1206 feet of 36 AWG(B&S) copper enameled wire
for a 2100 turns 500 ohm coil ?

The 2100 turns are of enamled wire without a heavy coat of enamel.

Is 2100 turns enough ?

Would it be better if the coil had a copper or iron core ?

This would mean a custom coil rectangular instead of circular.

I think it may be possible to have two identical
coils center tapped in the middle with a single
rare earth magnet in the middle between the two
coils then you have the right setup for
a proper op amp differential circuit.

+COIL-  NmagnetS +COIL-

THE left coil - is connected to right coil +
which is then the ground.

Left Coil + goes to op amp +
and
Right coil - goes to op amp -

The relative motion is magnet fixed to ground
and coil fixed to device.

Coil is stable and magnet moves right and left
between the coils.

Possibly +/- 2mm of range of motion.

Each coil having 1050 to 2100 turns
custom wound to be exactly the same.
"Which I know is not possible."
Close enough for civilian work is all I can expect.

As you can tell, I'm not very learned on these affairs.

Best regards,
geoff

----- Original Message ----- 
From: "Brett Nordgren" 
To: 
Sent: Saturday, July 17, 2010 8:49 PM
Subject: Re: Velocity Sensor Question ?


> Geoff.
> 
> Looks reasonable to me.
> 
> Based on your photo, see http://bnordgren.org/seismo/magnet1.pdf
> 
> The voltage in the coil depends on how many wires cut how many 
> magnetic lines how fast.
> 
> With the magnets arranged as shown, the magnetic lines go from left 
> to right in the top gap and right to left in the bottom gap.  And, if 
> the coil wires are going away from you in the top part of the coil, 
> they will be coming towards you in the bottom part.
> 
> All that means is that as you move the coil up or down, the voltage 
> generated in the wires of the top half of the coil as they cut 
> magnetic lines, will add to the voltage generated in the wires of the 
> bottom half, adding up to give the output voltage proportional to 
> coil velocity you were looking for.
> 
> Brett
> 
> 
> 
> At 10:22 AM 7/17/2010, you wrote:
> 
>>Hello PSN folks,
>>
>>Below Is A Velocity Sensor i had sitting
>>in the corner for the past few years
>>which has collected a lot of dust.
>>
>>"Please Excuse the Years of dust and, possibly, life forms present"
>>
>>I believe it to be a proper design
>>for motion along the plane of the faces
>>of the two magnets.
>>
>>The poles are N=>S TOP
>>                     S=>N Bottom
>>
>>I intend the coil to move vertically in this picture.
>>
>>http://gmvoeth.home.mchsi.com/100_0516.jpg
>>
>>Do any of you know for sure if this is
>>or is not the correct use of magnet and coil
>>as a sensor ?
>>
>>Please explain your response so I "MIGHT" understand.
>>
>>Best regards,
>>geoff
>>
>>
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> 
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