Why use Net Communication with a VFD?

HI, -- Yesterday I asked a question about connecting a Power-flex 400 to a 22-comm-D (Device Net to DSI communication adapter) with the purpose of talking to the VFD over Device Net – obviously! Since then i have stepped back, and with new cost info, i have a different question.



Question: What benefit is obtained from using Device Net (or Ethernet/IP) with a VFD? That is, is there any PLC to VFD communication (beyond setup) that can’t be done with digital & analog output cards?

This really matters as the added cost of putting DeviceNet onto this system includes the following:
- 22-COMM-D "DeviceNet to DSI communication adapter (probably 1 for each of 2 drives)
- 1784-PCD (special pcmia card) for laptop to configure the adapter.
- PC Software "DriveExplorer Lite" - free
- 1788-EN2DN (brick to interface EtherNet/IP to DeviceNet)
This seems like an extra odinary complication to control start/stop and speed on a VFD. I really need a better reason for using DeviceNet! (or Ethernet/IP).
**narlin

It is my opinion that it is only really advantageous and desirable to put your VFDs on a network if you need the diagnostics capabilities and faster troubleshooting capabilities that a network can give you. Of course it just may save money in wiring if you have a lot of drives that are a long way from the controller.

It all depends on your needs. If you have a tight budget and you just need to do start,stop and speed ref for speed control then Digital and analog i/o is fine.

Many people here deal with large systems. Every line that i have has anywhere from 20-300 drives. That is a lot of wiring using digital and analog i/o for controls.

Many times you want parameters from the drive like voltage,torque,torque current,dc bus voltage,direction status,fault status,preset speeds,accel times.decel times,amps,and on and on and on.

Getting all those parameters is difficult when using non networked controls.

Network controls make maintenance easier,reduces wiring and system complexity,less points of failure,and provides more data and granular control.

Maybe not relevant but if you already have Ethernet/IP why not use the 22-COMM-E? Then at least the PC adapter card and the interface aren't needed. But with communications you can get a lot of drive status information, though you may need to perform individual messaging to get it. Depending on the application it may be really important.

In some cases we have 15 drives in a control cabinet. Many of which we need to specify different speeds for recipes. That can chew up a lot of I/O in just controlling the drives. Consider 15 forward/reverse commands, a few outputs each for drive speeds and possibly an input back for each to get something like drive faulted. Then the time to program them all.

Throw them on a network and I can change the speed to anything I want, I get all kinds of things back like drive ready, fault, at speed, I can use multiple accels/decels. I can also reset a drive fault from something like an HMI (nobody has to get into the cabinet).

OK. I am convinced there is a reason to network drives - at least in some places. I wouldn't want to run wires more than a few feet without networking.

As for DeviceNet vs Ethernet/IP, i would prefer Ethernet/IP. Next step is to convince my customer to accept it. Currently, he has neither but has expressed the desire for DeviceNet while insisting on CompactLogix with Ethernet.

Originally posted by Narlin:

As for DeviceNet vs Ethernet/IP, i would prefer Ethernet/IP. Next step is to convince my customer to accept it. Currently, he has neither but has expressed the desire for DeviceNet while insisting on CompactLogix with Ethernet.

Click to expand...

Generally speaking that discussion is just an exposure/education discussion. Once you perfom control over Ethernet/IP compared to DeviceNet you seldom go back. But this might take a little demonstration for them.

Keith

One thing I didn't like about drives on Ethernet/IP is they seem to take a lot longer than DeviceNet to come online and communicate.

Also you have to pay close attention to network design when you start putting a lot of control stuff on Ethernet/IP.

could you go more in depth about why you have to be careful how much control stuff you put online?

rob

The more items you put on a network, the more traffic is generated that needs to be regulated. If you just have a HMI talking to a PLC and a couple of drives, there isn't much to worry about.

But imagine a network with many drives, multiple HMI's, Ethernet I/O, PLC's sharing data, SCADA, and so on. The amount of traffic can overwhelm it if it is not regulated. This is where you need to know about the appropriate hardware (managed switches and their advanced features.

Narlin said:

OK. I am convinced there is a reason to network drives - at least in some places. I wouldn't want to run wires more than a few feet without networking.

As for DeviceNet vs Ethernet/IP, i would prefer Ethernet/IP. Next step is to convince my customer to accept it. Currently, he has neither but has expressed the desire for DeviceNet while insisting on CompactLogix with Ethernet.

Click to expand...

If they have insited on CompactLogix with Ethernet, then get a 1769-SDN (compact logix devicenet scanner). Then you wont need to get a 1784-PCD or Or the 1788-EN2DN, You can just comunicate to deviceNet network via compact logix ethernet port.

Devicenet is great when you have 9 or more drives, or they're remotely located and you
need the diagnostics.

No chance net-storming the business LAN with it, boots fast, updates fast, devicenet is good stuff once you make the investment in software and skills.

Find the devicenet bible or whatever its called.
Joe the Plumber duty is calling me...

Paul