PID Setpoint

[zacslade]

Hi PLCs.net,

I'm new to using RSLogix5000. I want to set up a PID in ladder logic, but the setpoint field is read only. How do I give it a setpoint?

The application is: I have a 1769 L33 commanding a VFD/motor to put tension on a web for an unwinder. There is a load cell measuring tension on the web. So, if I understand this right, the tension feedback is my process variable, the commanded torque is my control variable, and I would like to put a calculated value into the setpoint, so that it will adjust torque to keep tension at the setpoint.

Thanks in advance,
Zac Slade

 

[Mickey]

Write to "My_PID.SP".

Where did you see its read only?

 

[zacslade]

Oh, is that all?

Typically these instructions seem to have their most important components on the block itself. On this ladder logic block it only has an indicator for the setpoint, so I made an inaccurate assumption.

Thanks for the help!

 

[osmanmom]

how you ramp up/down the unwinder motor

 

[zacslade]

The VFD is a PowerFlex 755, and i'll have the PLC conrtolling it via Ethernet.

The VFD will be set to torque mode, so the PLC will use the Reference output tag in the PF755 hardware profile to set the torque. The PLC can ramp the motor up or down, as I program it to, by changing the reference tag.

 

[osmanmom]

this link about unwinder/winder system,


https://www.google.com/search?q=Pow...UTF-8#q=plctalk+unwinder+site:www.plctalk.net