DeviceNet for links to HMI?

[Wordman 0]

Someone left mid-project and it got dumped in my lap. It's a devicenet controlled network using a SLC5/04, and the HMI has a devicenet slave module, so I'm assuming that was how he was planning on talking to the SLC 5/04. The HMI is in a control room, quite some distance from the rack itself. I am wondering why someone would do this. I thought devicenet was a decent fieldbus to talk to devices, but i didn't know you should use it this way as well. It seems there are limitations on the length of network, and message size regarding devicenet. Has anyone ever done this and has some insight into why this instead of just using rs232 or ethernet and keeping the field devices' network seperate?

[Ken Roach 194]

What sort of HMI is it ? Some have only a polled I/O object for interface, but others can do some pretty nifty explicit messaging directly to other devices on the network instead of just to the PLC. I only use small PanelView terminals on DeviceNet when I need to communicate directly with things like AC drives and E3 overloads. You can put in a repeater (B&B Electronics and Western Reserve Controls make them) to get extra distance and isolation from the main machine trunkline.

[Wordman 0]

Actually E3's are what i'm talking to as well. It's a Pro-face (GP675 Series), i think these were formerlly QuickPanels. I haven't had time to play with it yet, but the module is just a DeviceNet Slave Module. I haven't seen an Object classification yet either, but intuitively, it seems like a headache to set up data viewing that would be simple under SIO. What sorts of advantages do you have by using your Panelview Terminals to initate explicit messaging instead of the PLC. And what advantage would I have using DeviceNet over SIO to view data on the PLC. Regards, Andy

[Ken Roach 194]

PanelView Standard DeviceNet terminals have two very neat features; UCMM explicit messaging, and Listen-Only DeviceNet connections. Listen-Only helps reduce the amount of traffic on the network, as you can read the status and feedback of an E3 overload directly from its connection to the 1747-SDN. There's no need to include the data in the PanelView's I/O connection. UCMM Explicit Messaging allows the PanelView to display any parameter in an E3 or a drive directly, without learning how to program explicit messages in the PLC. That's especially handy for the 1747 and 1771 scanners, in which explicit messaging is complicated. E3/E3+ devices with V3 firmware support UCMM messaging; there's no need to even have them in the 1747-SDN scanlist to have them talk to the PanelView. Drives have supported UCMM from the beginning. But all this stuff is, I find, only useful in local control panels. I wouldn't use DeviceNet for a big supervisory HMI tool, such as the one you describe being in the control room. If there is a serial port on your HMI that can use DF1 protocol, and the DeviceNet wiring is already run up to the control room, you could use a pair of 1761-NET-DNI modules to provide a DF1 path between the control room and the Channel 0 serial port of the SLC controller.