In a message dated 2006/12/12, tchannel@.............. writes:

> Chris, I was very pleased with the coil/magnet arrangement you suggested, 
> the one which sandwiched the four magnets between two plates. It was simple 
> and effective. If I were to make another sensor, this time a vertical like the 
> AS1, would you suggest the same approach, but modified for vertical rather 
> than horz? Or to use the horseshoe magnet and coil? I am sure both would work, 
> but I would like opinions on it.

Hi Ted,

       Entirely up to you. I am not quite sure what you want as 'an opinion'?

       Quad 1" square NdFeB magnets on mild steel backing plates are likely 
to give you a much higher magnetic field than a U form Alnico magnet. They are 
almost certainly cheaper. Large new Alnico magnets are now quite expensive. 
       If you wind a rectangular form coil, you can get a highly linear 
output and you won't need more than ~3,000 turns. Also, you get very little 
external stray field. Put the coil on the arm and the magnet assembly on the 
baseplate. 
       Don't put any ferromagnetic material or a magnet on a seismometer arm 
- this makes the system very noisy.

       Just an opinion..... You have my drawings....

       Chris Chapman
In a me=
ssage dated 2006/12/12, tchannel@.............. writes:



Chris, I was very pleased with=20=
the coil/magnet arrangement you suggested, the one which sandwiched the four=
 magnets between two plates. It was simple and effective. If I were to make=20=
another sensor, this time a vertical like the AS1, would you suggest the sam=
e approach, but modified for vertical rather than horz? Or to use the horses=
hoe magnet and coil? I am sure both would work, but I would like opinions on=
 it.




Hi Ted,



       Entirely up to you. I am not quite sure=
 what you want as 'an opinion'?



       Quad 1" square NdFeB magnets on mild st=
eel backing plates are likely to give you a much higher magnetic field than=20=
a U form Alnico magnet. They are almost certainly cheaper. Large new Alnico=20=
magnets are now quite expensive. 

       If you wind a rectangular form coil, yo=
u can get a highly linear output and you won't need more than ~3,000 turns.=20=
Also, you get very little external stray field. Put the coil on the arm and=20=
the magnet assembly on the baseplate. 

       Don't put any ferromagnetic material or=
 a magnet on a seismometer arm - this makes the system very noisy.



       Just an opinion..... You have my drawin=
gs....



       Chris Chapman