Re: [Emc-users] Mesa 7i77 encoder max count rate

[Peter C. W. <pc...@me...>]

On Tue, 22 Dec 2015, Marius Alksnys wrote:

> Date: Tue, 22 Dec 2015 05:06:43 +0200
> From: Marius Alksnys <mar...@gm...>
> Reply-To: "Enhanced Machine Controller (EMC)"
>     <emc...@li...>
> To: emc...@li...
> Subject: [Emc-users] Mesa 7i77 encoder max count rate
> 
> In my current linuxcnc, 5i25 and 7i77 setup I get 1MHz maximum encoder
> count rate. Is it possible to increase it?
>
> I want to run a spindle up to 10k RPM with resolver. There is a resolver
> to quadrature converter, giving 16384 counts per revolution. That's
> 5.461 MHz.
>
> Encoder velocity output goes crazy above 4000 RPM roughly. That's about
> 1 M counts / s.
>
> It might be not possible for Mesa 7i77 while using 4 channels. I will
> try to reduce output scale of the converter, but would like to get more
> from 7i77. Can't find how.
>
> Another approach would be to look at the index pulse width and if it is
> wide enough, count it with another encoder channel in count mode and
> make custom HAL component to switch between feedback devices. I need
> accuracy for slow moves and spindle orientation and velocity at higher
> speeds.
>
> Using probably the latest firmware for Mesa cards and updated LinuxCNC 2.7.
>

Did you try turning off the encoder filter bit?

The limitation is because the 7I77 encoders are muxed. You can push up the mux 
rate with rev 4 encoders because they allow adjusting the multiplexing skew
(from cable delays and switching times)


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Peter Wallace
Mesa Electronics

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