Servo analog command, PID and El5101

Hello 
I run the follow configuration el4034 to command analog servo drive.
I have a glass scale wired to an EL5101 device. 
I saw several posts regarding pid tuning but I have the feeling (or I understood that way) the velocity was mandatory.
On the mesa, for each encoder we have the velocity available but it's not the case for the EL5101. 
How is it possible to generate it? 

Thank you in advance 
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If you do not connect the pid.N.feedback-deriv pin, the PID component will calculate
the velocity (for the D term)  via D/DT of position, so its not required to generate
and independent velocity signal. This may not be quite as good as velocity estimation
but it should be pretty good if the scale resolution is high.
 

You can also investigate if it is possible to wire the glass scale directly to the servo drive.
The servo drive will then use the glass scale instead of the servo's encoder.

It's possible for my specific servo but there is not point to do this as my servo is not piloted by position but with analog (no ethercat drive)