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Date: Fri, 23 Dec 2011 20:30:12 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Re: Automatic Variometer adjustment at DK7FC
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Hi Andy,

Thanks for the hint.

I intended to use a hard drive since the motor does not rotate when=20
supplied with < 4 V DC. So it would always stop before the resonance is=20
reached. That problem may be reduced by increasing the gain of the input=20
stage but then i expect oscillation problems and small currents running=20
through the motor all the time...

73, Stefan

Am 23.12.2011 20:24, schrieb Andy Talbot:
> Stefan..
>
> An idea.  You have implemented a bang-bang driver with a dead zone.
> Switched hard on in either direction,  or stopped close to the middle.
>
> Change the circuit so you linearly amplify the output from the phase
> detector, and make youself a bidirectional bridge driver, using say an
> op-amp and NPN-PNP pair - as in audio amplifiers.  Or it may even be
> possible to use an audio amplifier chip if the gain can be brought
> down low enough..
>
> Now, the motor will automatically slow as the phase error is reduced,
> and you 'shouldn't' have to include any dead zone.
> You may have to compensate the loop to prevent overshoot or high
> frequency instabilities if there is too much mechanical lag in the
> system or inertia, but that is something that can be done pure with CR
> networks.
>
> Andy
> www.g4jnt.com
>
>
> 2011/12/23 Stefan Sch=E4fer<Stefan.Schaefer@iup.uni-heidelberg.de>:
>   =20
>> Jim,
>>
>> Another thought:
>>
>> Am 23.12.2011 12:17, schrieb James Moritz:
>>     =20
>>> [...] I guess the inertia of the motor and gearbox will produce some
>>> hysteresis, moving the variometer to a very slightly over-adjusted po=
sition
>>> after the motor drive is removed, which will also help to prevent the=
 system
>>> continuously searching around the correct tuning point.[...]
>>>       =20
>>
>> This effect can be compensated by choosing the dead band treshold valu=
e.
>> Then the motor gets stopped a bit before the resonance point and will
>> exactly land on it. As good as having an infinitesimal small dead band=
 ;-)
>> Anyway we are talking about phase angles which are very very small, mu=
ch
>> below that what could become critical for a PA.
>>
>> 73, Stefan/DK7FC
>>
>>     =20
>   =20