Device Net questions...

I have a few questions about a DeviceNet setup that I am going to be possibly building sometime soon.

Ok, everything in our plant is Allen Bradley, so I'm sticking with that. The setup is simple...I'll have either a 1769-L32E or 1768-L42 Compact Logix controller. Throught the DeviceNet I will be controlling 10 PowerFlex 4 VFD's. I have done a ton of reading on AB's website, but I thought I would ask the gurus to see what their input was. My question is, what do I need to make this work?

Besides the VFDs and PLC themselves...I know I need a "1769-SDN" module to go in the PLC (right?), I belive I need a "22-COMM-D" module for each VFD. Of course I need the physical DeviceNet wiring...I see round, KwikLink, and KwikLink Lite on AB's website. Has anyone tried these and what is your opinion on the best way to wire this?

Would it be better to use PowerFlex 40's that are already ready for DeviceNet, or to go with the 4's and 22-COMM-Ds like I said earlier? And any suggestions on anything else I'm forgetting?

Yes, you need a 20 or 22 commD for each drive and unless there has been a change in the last week then the PF40 does not come equipped for devicenet, it still needs a 22Comm-D.
If the drives are in the switchboard I would be tempted to use the thin round cable.
Look up the AB website and get Bob Laws "Devicenet Book of Knowledge" (previously called the DNet Bible in less politically correct times)
Regards Alan Case

As Alan recommended, the "devicenet bible" is a good point to start.
I only use thin round cable i tried to use thick round cable but it was difficult to handle, never use flat cable.
Do not forget your rsnetwork for devicenet software, try downloading some examples from rockwell web page.

Thanks guys. I will look up the "DNet Bible". And widelto, I do have NetWorx for DeviceNet already. Just out of curiosity, why do you not prefer flat cable? Just trying to learn...

widelto said:

As Alan recommended, the "devicenet bible" is a good point to start.
I only use thin round cable i tried to use thick round cable but it was difficult to handle, never use flat cable.
Do not forget your rsnetwork for devicenet software, try downloading some examples from rockwell web page.

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Each cable type has it's place. Blanket statements to "never" use one type without explanation aren't very useful.

My personal preference for trunk cable is the flat in most situations. The ability to add new nodes quickly without disrupting the trunk is a strength the other cables can't match. If your area is wet get the connectors with the o-ring. This configuration seems to reject water better than thick or thin with tees. The only real "problem" I've had with flat trunks is electricians moving a connector on the trunk. Once the vampire taps are screwed in, that connector is there for good. Never remove one and attempt to reuse it.

The tee connections for the thick round trunk cable are a challenge for many electricians to assemble correctly and the cable itself is stiff and awkward to work with in tight spaces. If assembled and installed correctly, it's reliable. It's just easy to do it badly.

For short networks with only a few nodes (like in a drive panel), daisy chain with thin round cable is reasonable.

However, I still prefer the flat cable with a drop to each drive in these cases. Eliminating screw terminal connections on the trunk makes for a more robust network in my opinion. Adding new nodes is much easier too.

Unless something has changed since the last time I checked, the PF4 would not work on a 22COMMD. You had to use one 22COMMD and an AB RS484 converter and run the PF4 on RS485.

I have not checked lately to see if that was still the case.

Sorry, maybe my statemet was not the best, I meant i have never used flat cable. Maybe one day I use it.

widelto said:

Sorry, maybe my statemet was not the best, I meant i have never used flat cable. Maybe one day I use it.

Click to expand...

I certainly misunderstood, but thanks for clearing it up. I get it now.

I have an OEM who started using DeviceNet and PF40 drives with the thin cable daisy-chain and later switched to KwikLink flat cable to improve integrity of the cable system. The with just 10 devices on the network, only one of 40 screws needs to come loose or break a wire to disable the network.

A-B uses Kwiklink flat cable as the trunk in our MCCs. It's very well shielded (behind the wireway cover) and I've had very few problems with connectors or noise in those networks.

The PowerFlex 4 drives are physically too small to mount a 22-COMM-D interface onto; you have to use an external mounting box (I think it's called a 22-XCOMM) and run the RS485 daisy-chain cable to between 1 and 5 drives per 22-COMM-D.

The choice between 1 DNet module per drive and multiple drives per DNet module is generally one of speed, which is application dependent. If you can tolerate 100 ms reaction times from your drives, you can economize by using one 22-COMM-D and daisy-chaining it to multiple drives. With only 10 drivess, you might actually do better using a couple of 1769-SM2 serial modules instead of DeviceNet.

The only other general comment I would have to add is that I think on the L32E, bridging between the Ethernet port and the DeviceNet network is not supported. I think you have to step up to the L35E processor to get that feature. Of course none of this is an issue if you have a DeviceNet interface for your laptop.

If you are used to the 1756 ControlLogix line, this can be a supprise if you were expecting that functionality.

Hopefully Ken will speak up if I have stated that incorrectly.

Darren

Slightly related Compact DeviceNet details

The MicroLogix 1500 and the CompactLogix 1769-L20 and -L30 controllers do not allow bridging from a controller serial port to the DeviceNet connected to a 1769-SDN scanner.

The 1769-L20 and -L30 were both not very popular and have been not been produced for about 5 years.

An interesting tidbit on the MicroLogix 1500; neither the 1769-LSP nor the 1769-LRP controllers support bridging from a controller port to DeviceNet, but the 1769-LRP does support bridging from the network to the controller. I can connect to the DeviceNet using a 1761-NET-DNI or a 1770-KFD or 1784-PCD or 1784-U2DN and go online with the MicroLogix controller over the DeviceNet.

All current CompactLogix controllers, from the lowly 1769-L31 to the 1768-L45, do support bridging from their serial port or network ports to the DeviceNet via the 1769-SDN. This includes the two most popular CompactLogix, the 1769-L32E and 1769-L35E.

Hmmm.. Maybe it was an issue on older firmware (like around V13), but I know we bought an L32E and could not bridge between the ethernet and DeviceNet networks. We had to return the unit for a L35E to get that functionality.

Just curious, why DN? Ethernet is much easier. CN is more robust.

Another good bet its download and install the IAB Software from Rockwell Automation website, it is in the IA Tools section, is a good tool to develope your new project becouse you can change the configuration of dnet media and configure anytime you want it, and delivers detailed BOM List and validates your designed devicenet network, hope it will help you

robertmee said:

Just curious, why DN? Ethernet is much easier. CN is more robust.

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I agree, switch to Ethernet. DN is clunky. Also, and I am sure I am in for it for this, but DO NOT address the card's memory block directly. Use the Device Net Tag Generator Tool. That way if someone clicks on AutoMap, you don't have a lot of time ahead of you remapping the IO. Plus if you have the newer EDS files, the tool will create UDTs with named extensions.. such as:

DNET1_EXAMPLEN01_INPUT.FAULT

However, If you do use Ethernet, I recommend an additional ethernet card to keep the HMIs and IO off the same network.