DH485 Network

[Noely 0]

I am thinking of using a dh485 network for an application that is coming up. I have two control panels that are going to be located about a 100mtrs away from each other, each controlling a different part of the plant.Going to use a Slc 5/03 in panel 1and a Slc 5/02 in panel 2processor along with a panel view 600 in panel 1. Couple of questions. 1 - Do you program the two slc's separatley as in do the two have their own program to control their own panel or will one program do both 2 - Is there any examples to look at 3 - Can the slc 5/03 see an input on the slc 5/02 I am new to DH485 and was thinking of trying it out to save using multicores for signals from one panel to the other. Thanx

[TimWilborne 108]

If you are new at DH485 then don't bother learning it. Go with something like Devicenet

[gravitar 3]

I respectfully disagree The small amount of time he'll spend learning the MSG instruction is time well spent. Its not like he wants to break down the DH485 data packet and write his own driver! DH485 capability is built-into the SLCs.. He'd need a NET-DNI or SDN at each node if he were to use devicenet, which would unnecessarily add to the cost and complexity. Anyway.. Let's take a stab at the questions. 1. Yes! A SLC is ALWAYS responsible for its own I/O and must have its own program to control it, totally independent of any other PLCs it is networked to. DH485 is strictly for passing messages back and forth, it is NEVER used for controlling I/O. 2. There are surely some examples here on MrPLC.com, click the "Download code" link and search this forum for past examples. The instruction set reference manual does a pretty good job explaining it too.. Click this link and go to chapter 12: http://www.theautomationbookstore.com/idc/...rm001_-en-p.pdf 3. Yes it can.. Although off the top of my head I'm not sure if you can put an I1 file element in the MSG insturction. But a simple workaround is to copy the input file to a B or N file and send that.

[TimWilborne 108]

Very good point. My main thing is you limit yourself to the variety of newer products you can add later. DH485 is not going anywhere but not as many new products will not be developed for this network in comparision with others. Rockwell even recommends using it only for existing applications.

[eemcclure 0]

Could you be more specific about the function of each of the PLC's and the amount and purpose of the "shared" information? You ask "Do you program two SLC's with their own program, or have one to control both panels?" That would depend on the the timing, functional, safey, etc. requirements of the process being controlled. The process should dictate whether you use two PLC's or one. Questions to ask yourself are: 1. Can process 1 function independently of process 2? If so do I want one process to continue if the other fails? If you want either process to function without the presense of the other then you must have two PLC's. If either process fails and you want both processes to stop, then you MAY want to use a single processor. 2. What is the I/O count and level of logical complexity of each process. If the I/O count is high and/or the logical complexity is such that you may have a number of scan-dependent issues related to the process you should use 2 processors. 3. There is no problem whatsoever sharing the status of any part of process 1 with process 2 as long as you understand a couple of important facts regarding the shared data. First the shared data is not sent or received synchronous with the program scan of either processor. Secondly, there can (will) be some finite transport delay, particularly if you are using an HMI (panelview) on the same network. You need to take these facts into consideration when you share data. That the data is asyncnchronous to the program scan and has some transport delay is not necessarily a problem, just data you need to properly understand how to use the data. Good Luck, Ed McClure