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[AMPS] How to control a vacuum C ??

To: <amps@contesting.com>
Subject: [AMPS] How to control a vacuum C ??
From: wc6w@juno.com (Radio WC6W)
Date: Wed, 31 Oct 2001 10:09:47 -0800
On Wed, 31 Oct 2001 17:48:28 +0100
=?iso-8859-1?Q?Verner_Tops=F8e-Jensen_OZ5TG?= <oz5tg@post2.tele.dk>
writes:
>
>I am trying to build a controlcircuit for a major PA with an YC156.
>I am using a pair of Jennings 10-1000PF motordriven capacitors.
>
>Problem :
>The integrated DC-motors requires 18volt to work reliably, but the
>end-to-endtravel takes only about 3 seconds i.e. 330PF/sec.
>The controlcircuit has a delay at about 25mSec i.e. the cap. stops
>8 - 10 PF off the wanted value. No problem on 160, but on 10, it
>is a matter of success or failure.
>
>The controlcircuit using variable resistors, cannot, even with a very 
>little
>hysteresis, stop the motors without overshoot. 
>
>I have tried to chop the DC for the motors. That was an improvement,
>but far from enough.
>
>Any ideas about how to slow down the RPM and maintain the torque ?
>
>I checked the Jennings URL, but they do not have any information about 
>
>how to do.
>
>
>Any help, any idea is welcome.
>
>
>OZ5TG, Verner
>

Hi Verner,
   When you tried PWM did you include a catch diode(s) across the drive?

   PWM is the best you are going to do without building a real servo
system, including velocity feedback, which will allow for the slow RPM &
hi torque you're seeking.

  Velocity feedback can come either from a tach connected to motor shaft
or if that is not easily implemented by calculating the motor speed from
the voltage & current seen at the motor terminals.

  Take a look at the National LMD18200 data sheet -- perhaps on line at: 
www.national.com

73 & Good evening (by you),     
   Marv  WC6W









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