7i97 wrong Analog output for Spindle

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13 May 2022 19:35 #242905 by 5_Zylinder
Hi,

I need a +/- 10v signal for my spindle inverter.
If I specify a speed in Linux CNC, e.g. 750rpm, an incorrect analog value comes from the mesa card.
The max speed is 6000rpm.

10V/6000rpm = 1/600 [v/rpm]

1/600 [v/rpm] * 750rpm = 1.25V.

But I always measure a factor of 2 at the analog output, also 2.5V.
I can transfer the whole thing to all other speeds, so that the analog output is 10V at 3000rpm instead of at 6000rpm. The reversal of the direction of rotation works, depending on the direction of rotation (M03/M04) the analog output is +/- V.

Maybe someone can tell me the error in the configuration.

Regards
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13 May 2022 22:29 #242914 by tommylight
Is this a double post?
I am sure i have read this same question before.
It is much more useful to attach the config files used, more details about the hardware used, etc, than making several post with the same content. This also makes it harder to follow what has already been answered.

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14 May 2022 03:39 #242935 by PCW
What do you get if you set P to 0?

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14 May 2022 04:04 #242936 by 5_Zylinder
I described the problem in my Hurco thread, but I wasn't sure if I could reach people that way. Maybe someone has a similar problem and finds this thread easier.
I found a similar thread but it doesn't solve my problem.
I only have a Mesa 7i97, hal and ini are attached. I've already used another analog output, same result, so I think the hardware is ok.

@PCW I'll test it later.

Thank you.

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14 May 2022 11:17 #242947 by 5_Zylinder
Yes this was the problem.
I set P to 0 and the Mesa card give me the right analog output.

I try to set P to 1 and 2 because i want to know what happend.

0-> 1,25V
1->2,5v
2->3,75V

Thank for your fast help.

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14 May 2022 13:10 #242949 by PCW
Yes, if feedback is not working and the only non-zero PID terms are FF0
and P, the PID output with FF0 = 1 will be commanded RPM +P*Error.
Error will be the commanded RPM if the feedback RPM is 0.

This is why you get double the expected output when P=1,
The PID component is trying to do the right thing...

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