Looking to learn more about DeviceNet. Still have many mental blocks .

Good Morning ,

I admit , I have so many mental blocks when it comes to DeviceNet.
I have a question you guys may be able to help me with.

- We have a SLC 500 PLC with Devicenet ( 1747-SDN ) and 6) Powerflex 70
Drives on this network. We need to upgrade the Motor and Frequency
Drive. I would like to replace the Powerflex 70 with a PowerFlex 525. I would
like to take this new drive off of Devicenet. My plans are to eliminate
Devicenet all thru the plant. A few questions ......

We don't have the scanlist for this machine. I guess we can't just remove
the Devicenet from this drive without faulting out the whole Devicenet
system I guess ?

How difficult is it to replace a drive with a totally different drive on
Devicenet ?

Thanks so much for your help ,

You need to think through how you will be controlling the new drives. Since they are currently on Devicenet, I would think you are sending the start/stop and speed reference for each drive over the Devicenet. Powerflex 525's are intended for Ethernet IP networks. You can't do implicit EIP I/O with a SLC controller of any kind.


As for the Devicenet scanlist, you need to get some software and an interface to upload that from the current network. The software is RSNetworx for Devicenet. There is a USB to Devicenet cable available from Rockwell for the physical interface part. Once you have both of these items, you can connect to the Devicenet network from your laptop and upload the scanlist from the master (1747SDN). Once you have that uploaded and saved, you are better prepared to make any changes to the network.

Go to google and download:
DeviceNet Book of Knowledge

Cydog said:

Good Morning ,

I admit , I have so many mental blocks when it comes to DeviceNet.
I have a question you guys may be able to help me with.

- We have a SLC 500 PLC with Devicenet ( 1747-SDN ) and 6) Powerflex 70
Drives on this network. We need to upgrade the Motor and Frequency
Drive. I would like to replace the Powerflex 70 with a PowerFlex 525. I would
like to take this new drive off of Devicenet. My plans are to eliminate
Devicenet all thru the plant. A few questions ......

We don't have the scanlist for this machine. I guess we can't just remove
the Devicenet from this drive without faulting out the whole Devicenet
system I guess ?

Click to expand...

Normal .. or should I say 'normal' implementation of devicenet is to have the scanner talk to each drive. The drives can technically talk to each other and to pushbuttons and other devicenet stuff. But that is rare in my experience.

Turning off or removing the powerflex drive will give you an error 77 (not found) on your scanner for the devicenet address that the drive is.

You can use the HIM (keypad) to go through the configuration of the drive and figure out how many datalinks are configured on devicenet and what parameters they are. That gives you an idea of what information is passed to the SLC and commands are received from the SLC

RSNetworx for devicenet will read the scanlist for your devicenet network, and let you change it. You don't need the computer backup files, but you will need EDS files for each drive on the network and for your scanner.

How difficult is it to replace a drive with a totally different drive on
Devicenet ?

Thanks so much for your help ,

Click to expand...

As long as you have the EDS file for the new drive, RSNetworx for devicenet, and the SLC program you should be able to use a different drive. It's easier to replace a powerflex drive with a newer powerflex drive than if you use a Schneider or some other brand.

You will need to learn how to configure the new drive for:
- the devicenet interface (start, stop, speed reference)
- the control scheme (vector or v/hz, accel and decel times, minimum and maximum speeds, etc)
- any specialty control that is used (encoder, electronic shear pin, stall prevention, dynamic braking, dc braking, holding torque, etc)

Moving to ethernet, as had been mentioned, has additional things to consider. Ethernet does a lot of stuff well. But it is not a direct replacement for Devicenet, or Controlnet.

It sounds like you don't have a lot of experience with either devicenet or ethernet. Perhaps you can get a local PLC contractor to help you through your first conversion. Once you have that experience, and a bit of an example on what can be done and what is not-so-easy to do ... that makes the next one much easier

In my experience, asking for help on the first one ... of pretty much anything ... seems expensive until you work through some potential problems. And you realize how badly you could have messed things up without a bit of guidance.

I'll do my best to respect your decisions and not be defensive because I sold, supported, and promoted the technology for so many years !

You can happily remove a DeviceNet node while the network is running. Obviously you can't break the daisy-chain and expect it to keep going, which is why trunk/drop architecture was recommended.

Disconnecting one drive will just make the 1747-SDN report that it can't communicate with that drive. All the others will keep working.

Since you have an SLC-500, what network are you going to use to connect to the PowerFlex 525 ? Or are you going to give it start/stop/reference over discrete and analog signals instead of a network ?

Because drives are relatively complex and flexible devices, it's not super easy to replace one model with another on any network. DeviceNet tried to make it easier by offering standard I/O Assemblies that had the same data size and format, but sometimes a device is just too different to use those Assemblies.

There's a Rockwell (Access Level: Everyone) Knowledgebase document (117297) that describes migration of various RA platform drives on DeviceNet, and includes the PowerFlex 70 to 525 migration. Check your drives to see if they're the Standard Control versions, or the 70EC Enhanced Control.