micrologix slow to communicate with powerflex drive

[braxton357]

To preface, these are the parts the guy had setup to use so its what I have to work with--ml1400 to switch to powerflex 525. Using msgs to communicate.
I'm having a hard time with this drive and this whole setup. The commands work but take 5-10 seconds to execute. As in a start, stop, or freq change. What can I look at? Thanks.

 

[Ken Roach]

A MSG instruction from a MicroLogix to a PowerFlex 525 should take 10's of milliseconds to complete at the most.

Post the logic you're using in the MicroLogix to trigger these messages. Screenshots are fine, but ZIP and attach the *.RSS file is better.

Are you using EtherNet/IP, or Modbus RTU over RS-485 wiring ?

Your previous posts suggested that here was a malfunction or mis-wiring in your system that was seriously damaging the MicroLogix when the system was powered up. Did you find the root cause of that problem ?

 

[braxton357]

A MSG instruction from a MicroLogix to a PowerFlex 525 should take 10's of milliseconds to complete at the most.

Post the logic you're using in the MicroLogix to trigger these messages. Screenshots are fine, but ZIP and attach the *.RSS file is better.

Are you using EtherNet/IP, or Modbus RTU over RS-485 wiring ?

Your previous posts suggested that here was a malfunction or mis-wiring in your system that was seriously damaging the MicroLogix when the system was powered up. Did you find the root cause of that problem ?

EthernetIP. And yeah that ended up being a bad ground and high leg 3phase issue. This whole thing was just as a favor and I'm very much regretting it, so I really appreciate the help. Anyway the only thing I'm at all concerned about is getting the "belt drive" operating.

 

[braxton357]

I've gone back now and hardwired the run fwd, run reverse, and jog inputs to discrete plc outputs but would still need to control speed and speed feedback to the hmi.

 

[Ken Roach]

Thanks very much for posting that RSS program.

I am a notorious curmudgeon on the topic of PCCC messaging to control AC drives, so please don't take any criticism personally. I'm friendly and helpful; just ask my dog.

One issue is that all of the MSG instructions were programmed in the classic "fanning the trigger" mode where they run independently and as fast as possible, re-triggering as soon as each one finishes by un-latching the .EN bit whenever the .DN or .ER appears.

This works for simple testing, and can be necessary when you're really pounding on MSG instructions to get data between controllers fast.

But I recommend strongly against it for this sort of control. Recycling timers and more careful MSG sequencing is better for the PLC's comms bandwidth.


Another issue that might be responsible for the 5-10 second time between commands appearing to take effect is that I believe that the PowerFlex might not accept 1-word writes to N41:0,1,2. It might be that it was accepting it once every time the PCCC command function timed out. Because your logic was re-triggering the MSG instruction as fast as possible, you never got the opportunity to visually see the .ER bit or the .ERR error code.

The proper way to do it is to write to N41:0, Length 3. That unused N41:1 word doesn't hurt anything, and the Command bit word and the Reference word arrive in one packet.

In addition, I noticed that you used Copy Word to move the Feedback value to a FLOAT type data table. That's going to give you a weird result because CPW copies the raw bit pattern, rather than automatically converting from Integer to Floating Point.

The PowerFlex 525 uses Reference and Feedback values in units of 0.1 Hz, so the value "123" represents 12.3 Hz. You can handle them in those units, or just divide by 10.0 and put the result in a FLOAT, or do any scaling to RPM, inches/second, or furlongs per fortnight.

I'll post the amended RSS file in a few minutes. There's plenty of room for me to have made a mistake because I don't have a MicroLogix 1400 or PowerFlex 525 to test on, so I'd like your feedback about whether the modified logic works.

 

[Ken Roach]

Attached is an example of my recommendations for the Belt PowerFlex 525 drive, in Rungs 0-4 of the LAD3 routine.

I did not modify the logic that controls the Start and Stop bits, but I'll mention that it looks like you're intending to hold them True for a certain amount of time so that he drive "sees" them like it would a discrete input.

The bits do need to be held true long enough for the MSG logic to cycle through and send them, but I generally don't use Timers. I hold the START bit true until I see the feedback bit telling me the drive is running, and I hold the STOP bit true until I see the feedback bit telling me the drive is not running.

Let us know if this amended logic works better for you, or if you have more questions.

 

[braxton357]

Worked well! And thanks for the notes.