V20 seems not to reach setpoint value

Good day to all,

First of all, i am greatfull for having this forum, every time a have a question, i get the right help!

I am commissioning a machineline which stretches a rope in continuous motion. The amount of stretching (elongation) is set by the operator and calculated by a PLC. the PLC sends the desired motorspeeds for both pull-mangel-motor and hold-mangle-motor to the V20's.

The machine can be set for 1 meter/minute to 14 meter/minute. While i was testing the machine i found the elongation gets lost at 1m/min. reading the displays i saw the actual output from the V20 pull-mangle did not reach the setpoint. That causes loss of elongation because at 1m/min the actual value of V20 pull-mangle is under the value of the V20 hold-mangle.

I did read the V20 manual and carefully looked at each parameter but i can't get the clue. If i select >2m/min the elongation is correct, cause the actual pull value is greater than the hold value.

I also installed the wifi connection in order to look at parameters and have easy monitoring possibility's. The monitoring also shows the set value is correct, just above the value for the hold mangle resulting in elongation. To be more precise; while the set value is at 3,18Hz the actual value is 2,95Hz  I also took advantage off the wifi by downloading the parameters to share with you in the attachment of this topic.

It becomes more strange ; we have the same production line running with same setup so i copied the parameter set from the V20 which is running well in all speed settings. To my supprise the V20 keeps behaving like discribed above! 

So i would like to assume there's no parameter fault. Since the set value's are also correct at 1m/min i am out of options right now.

Thank you for reading, best regards Jan

EDIT; since the PULL and HOLD motor terminals are close to each other i swopped the HOLD motor to the PULL inverter and vica versa.

The problem is still there so i suppose there is no fault in the motor or cable, because the PULL inverter is stil not outputting the value the setpoint is asking for.

From now on i try to concentrate on the V20 itself since change of motor and change of parameterset (from good running production line ) did not solve the problem.

Today i got the feeling something could be wrong with the setpoint signal. So i hooked up the scope and found the signal gets a distorsion, specially at lower setpoints. Apart from the distorsion (wich can be 'eliminated" by the V20) there is also a certain amount of dampening. the dampening increases by lowering the setpoint so causing the troubles at the lowest speed of 1m/min or 3,16Hz.

So i'm gonne re-wire the original un-shielded cables to shielded cables as prescribed by the manufacturer of the D/A converter.

If this would solve the case i will come back and show some scope readings to show the amount of dampening and distorsion.

Still wonder why the monitoring software was indicating the supposed setpoint while scope was pointing out the dampening, maybe some kind of averaging in the software?

But i will not jump to conclusions right now, first try shielding....

regards, Jan