Subject: AS-1 Type Sensor



=20
I would appreciate any comments regarding my AS-1 type sensor. It's close t=
o the original design. I did not like the knife edge aluminum boom attached=
 to a score mark in the aluminum mast, so I modified the boom to mast attac=
hment. I am using two razor blades. One on the boom and one on the mast. Ha=
rdened steel on steel. Friction is much less. Free running oscillations hav=
e a much longer duration. Does anyone have a better suggestion? I would lik=
e to hear from you.
=20
See my pic's here:  http://picasaweb.google.com/cfi2fly/MyPictures#
=20
Also, Chris, if you read this, if I reversed the coil and magnet, would the=
 effort be worth the results?
=20
Hi Richard,
=20
    I agree about the original design, The arm needs to be held fairly rigi=
dly to prevent it from rotating about it's long axis, or swinging from side=
 to side. You can use a twin wire suspension in tension as shown on http://=
www.oregonshakes.com/temp/DesignDrawings4.pdf or an old type double edged s=
afety razor blade, in compression. This involves clamping one blade to the =
beam and the other to the vertical post. I blunt the blades on an emery sto=
ne first to avoid handling accidents. The two loop ends of the blade do the=
 flexing. I have broken the ends of blades. The edges are fairly sharp, but=
 I have never observed a section 'flying off'. You can only use this suspen=
sion for a vertical sensor.
=20
    The horizontal arm on the AS-1 is a very hard non magnetic alloy, nol a=
n Aluminum alloy.

    The ends of the spring should ideally be straightened and clamped. Loop=
 ends fixed by an eyelet tend to be noisy. You could also try gluing the lo=
op ends in position? Two component Acrylic glues are much better structural=
 glues than Epoxies. They set strong and tough and have a short setting tim=
e, rather than strong but brittle with a long setting time.
=20
     The benefits of reversing the coil and the magnet depend on how much n=
oise you are picking up. The Alnico U magnets do not have a very strong fie=
ld, the coil is a bit bulky and the output is not very high. You would do m=
uch better to use a quad NdFeB magnet block. See the designs at www.jclahr.=
com/science/psn/chapman/lehman/index.html You can get 10x the voltage outpu=
t this way without any difficulty. Also, the 1/4" mild steel backing plates=
 provide an effective electrostatic and magnetic screen for the pickup coil=
.. I suggest that you use a brass mass. There is also a design for an AS-1 m=
agnetic damper on the website.
=20
     I hope that these comments are helpful.

     Regards,
=20
    Chris Chapman


































=
Subject: AS-1 Type Sensor


=


 




 


I would appreciate any comments regarding my AS-1 type sensor. It's cl=
ose to the original design. I did not like the knife edge aluminu=
m boom attached to a score mark in the aluminum mast, so I modifi=
ed the boom to mast attachment. I am using two razor blades. One on th=
e boom and one on the mast. Hardened steel on steel. Friction is much less.=
 Free running oscillations have a much longer duration. Does anyone have a =
better suggestion? I would like to hear from you.


 


See my pic's here:  http://picasaweb.google.com/cfi2fly/MyPicture=
s#


 


Also, Chris, if you read this, if I reversed the coil and magnet,=
 would the effort be worth the results?


 


Hi Richard,


 


    I agree about the original design, The arm needs to=
 be held fairly rigidly to prevent it from rotating about it's long axis, o=
r swinging from side to side. You can use a twin wire suspension in te=
nsion as shown on http://www.oregonshake=
s.com/temp/DesignDrawings4.pdf or an old type double edged =
safety razor blade, in compression. This involves clamping one blade t=
o the beam and the other to the vertical post. I blunt the blades on an eme=
ry stone first to avoid handling accidents. The two loop ends of the b=
lade do the flexing. I have broken the ends of blades. The edges are f=
airly sharp, but I have never observed a section 'flying off'. You can only=
 use this suspension for a vertical sensor.


 


    The horizontal arm on the AS-1 is a very hard non m=
agnetic alloy, nol an Aluminum alloy.


 


    The ends of the spring should ideally be straighten=
ed and clamped. Loop ends fixed by an eyelet tend to be noisy. You could al=
so try gluing the loop ends in position? Two component Acrylic glues a=
re much better structural glues than Epoxies. They set strong and toug=
h and have a short setting time, rather than strong but brittle with a long=
 setting time.


 


     The benefits of reversing the coil and the ma=
gnet depend on how much noise you are picking up. The Alnico U magnets do n=
ot have a very strong field, the coil is a bit bulky and the output is=
 not very high. You would do much better to use a quad NdFeB magnet block. =
See the designs at www.jclahr.com/science/psn/chapman/lehman/index.html&nb=
sp;You can get 10x the voltage output this way without any difficulty. Also=
, the 1/4" mild steel backing plates provide an effective electrostatic and=
 magnetic screen for the pickup coil. I suggest that you use a brass mass. =
There is also a design for an AS-1 magnetic damper on the website.


 


     I hope that these comments are helpful.


 


     Regards,


 


    Chris Chapman