7i95T spindle control via Modbus RS485 and SPINX1A

I was able to start the spindle, direction works fine, but I have a problem with the speed.
My lathe max speed is 3000 rpm, when I set this speed, the pwm value is 0.999 so almost 1, which I think is correct.
When I set 700rpm, I get 0.23 on the pwm.value, which is also correct, however, the voltage measured between SP- and SPV is 5.8V so it spins way faster than it should.
How can I scale the value of the potentiometer so that between SP- and SPV I get the correct voltage.
Between SP- and SP+ I have 10.75V so this would mean 3000 rpm, so for 1500rpm, between SP- and SPV, I should have 5.37volts or smth like this.

Normally, you would set the PWM scale to the spindle RPM
at SPV+ (so if the spindle RPM is 3000 at 10V, you would set
the PWM scale to 3225 (3000*10.75/10)

Then the PWM value is set directly in RPM.

If you have issues with non-linearity, check
that SPV+ is constant at different spindle settings.
Other possible causes of non-linearity are PID settings
or incorrect PWM frequency

pwm frequency is set to 5000
I've set the scale to 3225, it doesn't seem to make any difference.
I was not using PID for spindle speed, I was using lincurve.
However, I think that as long as PWM value is correct, the problem is somehwere else. I think the PWM value should go between 0 and 1, at max speed its 0.999, at 1500 rpm is almost 0.5, which seems correct to me.

I don't know what else to check :/

Is this with a SPINX1A?

The SPINX1A should have better than 1% linearity

Does the 10,75V vary?
 

Yes its SPINX1A, the 10.75 voltage comes from the VFD, I have a delta VFD,and I have wired this way:
+10v -> spinx SP+
ACM -> spinx SP-
AVI -> spinx SPV

Between SP+ and SP-, I measure 10.75

If I reduce the RPM at 100 rpm, the pwmgen value is correct, but the voltage between SPV and SP- is still 5.45

That sounds like either the SPINX1A is damaged or perhaps the wiring is incorrect.

I would verify SPINX1 operation by running SPV+ and SPV- from 5V and GND from the
7I95 to verify its operation independent of the VFD

Also SPINX1A PWM frequency should be 20 KHz (though this should just affect ripple)

The problem was that I had pwmgen.00.offset-mode set to 1
Once I set this to zero, now the voltage is correct.
I've set the pwm_frequency to 5000 initially, then after your last comment, I increased it to 20000, but didn't noticed any difference.
Not sure what this does exactly and why would it matter if its higher.

Thanks for your help so far!

The SPINX1A has a 2 pole ~ 100 Hz RC filter to average the PWM signal.

Too low a PWM frequency will let noticeable ripple through the filter.
Too high a PWM frequency will result in poor linearity, (as the switcing
time of the OPTO becomes a significant part of the cycle time)

For the SPINX1A, 20 KHz is about the optimum compromise between ripple and linearity.