Studio 5000 & PF 525, Ethernet Comms, Encoder FB, Using Motor RPM as speed reference

[AutomationTechBrian]

Studio 5000 & PF 525, Ethernet Comms, Encoder FB, Using Motor RPM as speed reference

I'm trying to figure out how to send a speed reference in RPM over the Ethernet connection between a Contrologix L71S and a Powerflex 525. I can send a speed reference in Hz to the PF 525, but I would like to be more precise and use RPM, since there is an encoder on the motor giving feedback to the VFD. The application has 4 spinning drums, with different circumference and different gear ratios. I can easily do the math in the controller to give the correct motor RPM to use as either the speed reference, or setpoint, if a PID loop is the correct technique. I just need a little help from someone who has done this before. Can I set the speed reference up as RPM? Or do I need to set up a variable set point to achieve this control? What would you do?

A note of frustration... I tried asking Rockwell (Tech Connect automation contract) but the "basic guys" had no idea what to do. They kept on telling me that I should use a scale function for my 4-20ma signal. I had to explain to them more than once that the Ethernet connection doesn't use an analog output, and that I was looking at communication tags in the PLC to use. (Wow...!) They realized this was out of their level of expertise, and tried to send me to the "Motion" guys. But they said my "Automation" contract didn't include that.

I'll keep looking for info online. Example setups are great. I'm hoping I'll stumble across one.

 

[Jmeadows7676]

To my knowledge I don't think this is possible with the PF 525. It doesn't have selectable Speed units like the 700 and 750 series.

 

[AutomationTechBrian]

Thanks, that explains why I wasn't finding much. Seems weird that I have OutputRPM as one of my feedback tags. I'll see how a scaling function works using 0-60 Hz (0 to 6000) and see if I need more accuracy.

 

[L33er]

You can do it, indirectly.

 

[Ken Roach]

PowerFlex 525 always uses 0.01 Hz as the reference units over any network connection.

It's simply as close to the physical thing you're controlling as possible. Everything else is known to the user (or is part of the motor and feedback tuning).

As the user manual says, the OutputRPM value is basically for convenience, and is calculated with the Hz and the number of poles.

 

[AutomationTechBrian]

PowerFlex 525 always uses 0.01 Hz as the reference units over any network connection.

It's simply as close to the physical thing you're controlling as possible. Everything else is known to the user (or is part of the motor and feedback tuning).

As the user manual says, the OutputRPM value is basically for convenience, and is calculated with the Hz and the number of poles.

Well, that makes it simple. I'll do a scale block for each roll, and just to satisfy my curiosity, I'll dust off my tach wheel and double-check the results when it's done.

My thoughts about accuracy stem from the differences in the slip of the motors. They are all 4-pole, but with different nameplate RPM values, 1,720 and 1,745. And because I'm a "Tech", I think about the day when the motors are replaced... the motors might be slightly different. So using actual RPM would have given me a constant that doesn't change.

Also, the habit of erroring on the side of greater accuracy dictates that I include that small difference in the calculation. But realistically..... the gear ratios are so huge that the actual difference would be very small.

OK, I'm over it. Thanks, guys.

 

[JeremyM]

^ I provide a block that handles reconfiguration of the 525, including those parameters. You can tie Cfg_ and Val_ tags to an HMI for your sets and actuals.