powerflex 700 VC speed problems

I've got a machine with several powerflex 700 VC drives. Two of the drives are configured nearly the same way except for the rated amps. The are receiving the same DPI Port 5 speed reference from the PLC 5/40C via controlnet on two separate output addresses. The speeds should always match on both drives. Well, they don't. One drive seems to be scaled properly, but the other drive is running too fast for the reference it's being given. I went into the controlnet adapter parameters and slowed it down to 70% to get it more in line with the other drive, but that's just a workaround.

What can cause the feedback speed not to match the reference? I've gone through all the parameters and everything that would affect the speed seems to match between the two drives.

Is this a machine you're bringing back into operation, or one that's been running for a while ?

When you say that one drive isn't running at the speed you expect: what are you using to read the output frequency or RPM ?

Can you capture an output frequency or RPM and correlate it to the actual Reference value being sent over ControlNet ?

What exact parameters did you change in the 20-COMM-C module configuration to change the output/reference scaling ?

Is there any chance the two motors have different gear ratios . . .

But 'somebody' loaded the same 'program' into both drives when the programs should be different?

(Or somebody changed the motor with something different . . .)

Mad Poet.

If you scaled the reference by a percentage, then the above answer sounds logical. When you say the speeds are different, what is different? Output Frequencies are different, or motor RPMs are different, or the "final" shaft speed/surface speed different?

Output frequencies different = programming (scaling or some other setup)

Output frequencies the same and motor RPMs are different = possible motor name plate differences?

Output frequencies and motor RPMS are the same, and your driven shaft/rollers/sheaves/etc speeds are different, then likely a gear ratio difference between them.

I spent a couple of days questioning my grip on basic math while troubleshooting a conveyor system at a sawmill, because two conveyors that should have been running at the exact same speed were significantly different. I glared and scowled at the PLC-5 and 1336+II drives extensively, and put my excellent Shimpo tachometer to use on the motor shaft and the conveyor belts again and again.

Finally I decoupled the conveyors and turned the gearboxes by hand.

One of the gearboxes had been assembled at the factory with the wrong gearset but the correct nameplate.

MOST other issues eventually succumb to the scientific method.

That is assuming you are sending a speed reference as an expected frequency and not a motor RPM.

This machine has been in operation for a long time. The drive has been in operation for several months and has had the same problem since day 1.

The speed reference sent to both drives is the same, but the feedback speed is different.

I will get answers to the rest of the questions when I go in to work tonight.

Some details.

The parameter on the 20-COMM-C I used to adjust the speed is #27 Ref Adjust. I set it to 70% to get the speeds close to what they need to be on the problem device.



Here is the process display window pulled up on CCW showing the Port 5 reference (note the 70 percent difference from using the 20-COMM-C Par#27.

Also note that the commanded speed from Parameter 2 is nearly the same. I assume there should be a 70% difference in the commanded speed. If I change the 20-COMM-C back to 100% of the reference, the problem device speed goes way up beyond what it should be.

Both drives are using HZ and not RPM. I've checked twice.

Here is the process display with 20-COMM-C parameter 27 at 100%. The commanded speed does not match up to the reference.

I believe I just got it figured out. Parameter 299 was set to MAX FREQ instead of MAX SPEED.

Parameter 299 was set to MAX FREQ instead of MAX SPEED.

Click to expand...

Outstanding sleuthing, Jason.

I think that was another thing that the PowerFlex 700VC and PowerFlex 70 EC introduced; all drives prior to that always had max ref = max frequency. I had a little cheat sheet for the 1336+ that I used every time I set one up.