Re: s626 output voltage at zero crossing

On Tuesday 14 February 2006 04:14 am, Nico Mock wrote:
> Dear  Gianluca, dear all,
>
> since you are the one, who wrote the comedi-stuff for the sensoray s626
> I've did a cc to you directly. Many thanks by the way.
>
> I've managed to get a sensoray s626 card up an running with
> rtai-3.2/2.4.27-kernel/scilab/scicos ..., but I encounter a strange
> problem.
>
> The output voltage of the DA - converter exhibits a very funny ripple
> whenever the output crosses the zero-voltage line.
>
> To me it looks like a step response to a reasonable well damped second
> order system. Since the cables are fairly short and no inductance,
> capacitance or whatsoever is included in the measurement chain, I was
> wondering, if this might be a driver problem .

It looks to me like the board really has 13 bit analog outputs that can 
either be set to 0 to 10V, or -10V to 0V ranges.  The driver, however, 
treats it as a 14 bit ao with a -10V to 10V range.  My guess is a glitch 
happens due to the output first changing polarity and then slightly later 
changing output value.  If that's the case, the driver could work around 
it by temporarily setting the output to zero before changing polarity 
whenever the polarity changes.

-- 
Frank