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From: firstname.lastname@example.org (Ken Smith)
Subject: Re: Meter movements
Date: Sun, 24 Nov 2002 03:32:09 +0000 (UTC)
Organization: a2i network
References: <3DD47F82.14E8608@videotron.ca> <email@example.com>
NNTP-Posting-Date: Sun, 24 Nov 2002 03:32:09 +0000 (UTC)
X-Newsreader: trn 4.0-test76 (Apr 2, 2001)
Originator: firstname.lastname@example.org (Ken Smith)
In article ,
Winfield Hill wrote:
[... lots snipped ...]
>. IN __ ____
>. ----|+ \ R2 | | R1
>. | >--/\/\--| / |--+--/\/\--,
>. ,--|-_/ ==== | |
>. | | gnd
This circuit works a lot better with a capacitor across the meter and/or
one from the op-amps output to its inverting input.
A capacitor across the meter protects it somewhat from mechanical shock.
The other thing that the capacitors do is prevent oscillation of the
op-amp. The coil of the meter movement is inductive enough to make a fair
phase lag in the feedback at high frequencies. Depending on the op-amp
you use, this could lead to oscillation.
You can also add a series RC combination across R1. This was typically
done in galvo. pen motor based chart recorders. If you use the right
values you can put an electrical zero where the mechanical pole is. This
sharpens up the edge when a step is input.
email@example.com forging knowledge
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