In a message dated 29/12/2006, tchannel@.............. writes:

1.  I have made an adjustable magnetic  damper, which I can slide in and out 
to increase or decrease the effect.   Chris, gave me a very good example of 
how to adjust the damper on the Horz  Lehman, I finished a few months ago.  It 
was something like, "move the  arm 10mm and release it, it should move past 
center and extend 5mm past  center, it then should return to center and stop;"   
Would it be the  same for a vertical spring sensor?

Hi Ted,
 
    Correct damping is when you get ~ 0.5 mm overshoot,  NOT 5 mm, from a 10 
mm deflection! 
 
    It is the same for both sorts of sensor, but the  vertical damping 
usually has to be stronger - the damping force required is  inversely proportional 
to the period.

2.  The coil measures 847 ohms.  If I  were to use a resistor to act as a 
damper, what would the ohms value be for  the resistor?
     Is there a  formula?


    Yes, but it may be easier to just measure and see.  You need a closely 
coupled coil with a fairly intense magnetic field. Remember  that drawing off a 
damping current both reduces the output voltage and increases  the circuit 
noise. The resistance also depends on the mass, the set pendulum  period and the 
magnetic field. More mass - lower resistance, greater period  - higher 
resistance, higher field - higher resistance.  Remember that  most amplifiers have an 
input resistor which needs to be 'taken into  account'.
 
    Regards,
 
    Chris Chapman





In a message dated 29/12/2006, tchannel@.............. writes:
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1.  I have made an adjustable magnet=
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  damper, which I can slide in and out to increase or decrease the effect.&n=
bsp;=20
  Chris, gave me a very good example of how to adjust the damper on the Horz=
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  Lehman, I finished a few months ago.  It was something like, "move th=
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  arm 10mm and release it, it should move past center and extend 5mm past=20
  center, it then should return to center and stop;"   Would it be=
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  same for a vertical spring sensor?
Hi Ted,
 
    Correct damping is when you get ~ 0.5 mm oversh=
oot,=20
NOT 5 mm, from a 10 mm deflection! 
 
    It is the same for both sorts of sensor, but th=
e=20
vertical damping usually has to be stronger - the damping force required is=20
inversely proportional to the period.
<=
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  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
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2.  The coil measures 847 ohms. =
; If I=20
  were to use a resistor to act as a damper, what would the ohms value be fo=
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  the resistor?
  
     Is there a=20
  formula?

    Yes, but it may be easier to just measure and s=
ee.=20
You need a closely coupled coil with a fairly intense magnetic field. Rememb=
er=20
that drawing off a damping current both reduces the output voltage and incre=
ases=20
the circuit noise. The resistance also depends on the mass, the set pendulum=
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period and the magnetic field. More mass - lower resistance, greater pe=
riod=20
- higher resistance, higher field - higher resistance.  Remember t=
hat=20
most amplifiers have an input resistor which needs to be 'taken into=20
account'.
 
    Regards,
 
    Chris Chapman