PowerFlex DC Drive RPM output vs. analog input value.

[yam785]

Dick, the tach, which is geared off the press roll, is fed directly to the drive. There is no other feedback. The drive controls by this tach.

 

[yam785]

I found some pics, maybe help

Here are some pics, that may help understand the process. The red roller in the back is the presser roll. The tach is driven by the presser roll. Before the line starts, this roll moves forward, and rides against the threads being accumalated on the beam in front of it. This presser roll is driven by the surface speed of the beam. As the diameter of the beam increases, the speed of the of the presser roll increases, even though motor speed has remained steady, which increase voltage feedback from the tach to the drive. The drive reacts, and slows down. If I trended the output voltage of the drive to the motor, in Drive Executive, it would show a steady decrease in voltage, linearly.

 

[DickDV]

The tach, as described, is part of an external control loop on the drive, not part of the motor speed loop. Since there is no second tach, the motor must be operating as an armature voltage regulator.

For the above reason, it is very important that the drive have the exact motor nameplate data entered in the parameters.

It also appears that someone has decided to run these motors slightly field weakened (7.65/7.95amps). This will reduce available torque a little and shift the motor speed range slightly upward for any given armature voltage.

Have you reset the span calibration of the speed reference input? Did it get you the maximum speed you wanted?

 

[yam785]

I agree on armature voltage regulation, field voltage is pretty much constant. We are not doing field weakening, as we do not need that much speed. Both of these drives usually run about 3 something amps, and both drop back to I believe half their value when the drive has been stopped for a certain time period. This is good. Saves energy usage.

I might do the reference tuning today if they are done with the current run. I don't want any speed changes in the middle of a set. I will do it before the start of the next set.

We both agree setting my max reference = max speed, by analog in 1 tuning, is a good idea, correct?

 

[DickDV]

yes

 

[yam785]

Dick, thanks. One question is, the drive won't try to run, at top speed, when I do the analog in 1 tune, will it?

 

[DickDV]

It will only run if it has a start signal on its input terminal. Working with the analog input while the drive is stopped will not cause a start.

 

[yam785]

Dick. Okay. Thanks you very much. I should get a chance to do it next week. I'll let you know if it resolves the issue.