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|October 30th, 2005, 01:21 PM||#1|
Lifetime Supporting Member + Moderator
DH485 networking... best route?
I'm venturing into the world of PLC networking and hoping that some of my questions can be answered here.
We have a process with one ML1200, one SLC 5/03, and a PanelView 600 (I haven't purchased the PV yet so I can still choose the protocol). Each device is in a different panel. The wiring will need to be routed from the SLC to the PanelView (about 30 feet), then from the PV to the MicroLogix (about 20 feet). I'd also like to have the ability to program all three devices from either the PV or ML panel. I'm not transferring much data, maybe 5 words from the ML and 20 words from the SLC.
The requirements of this application (plus the hardware already in place) led me to DH-485, but I had the following concerns:
1. I know that I'll need a 1761-NET-AIC at the MicroLogix, but do I need a 1747-AIC at the SLC? I have read some posts on this subject but am not clear on when the isolator is necessary. A-B seems to say that you should always use one when connecting to a DH485 network, well if that's true why don't they just build the isolation into the CPU?
2. The PanelView 600 with RS485 has two 485 ports (RJ45 plus 8-pin flat). Can I daisy-chain through these ports without an isolator? I think I read that someone here has done that successfully.
3. I already ran about 30 feet of Cat5 cable from the SLC's RS-485 port to the PanelView cabinet, where I've been using a 1747-UIC for programming. This has worked fine, but should I swap that out for shielded cable before extending the network? It is currently run through conduit and wire trough with 24VDC control lines.
4. With the 1761-NET-AIC at the MicroLogix, can I also plug my PC into it (Port 1, RS232 DB9) and access all three devices for programming?
As I was pondering this issue I started thinking about the future. Someday we might want to add this small network to a larger one--probably on ethernet. The data transfer requirements would still be fairly low. Is there a way to interface between DH485 and ethernet? I am hesitant to use ethernet right now due to the cost (5/05 processor $$$).
Sorry for being long-winded... I'd appreciate any help from the gurus out there.
|December 29th, 2005, 08:12 AM||#2|
Lifetime Supporting Member + Moderator
Well I never got any responses to my post so I just forged ahead and set up the system. I thought I'd post some of my observations in case anyone has similar issues in the future.
Here is the network I set up. The image is out of the AIC+ user manual but I added the SLC node. Note that I actually used a PV600 and ML1200.
This setup does in fact work. One of my concerns was whether I could daisy-chain through the two DH485 ports on the PV600, as I didn't see any references to doing that in the AB manuals. Well it doesn't seem to be a problem, although I'm not sure about the isolation.
When I first set everything up, I didn't put the 1747-AIC link coupler on the SLC. That most definitely did not work... very erratic operation (not to mention no isolation).
The cable running from the 1747-AIC to the PanelView is about 30 feet of regular unshielded Cat5 ethernet cable, running through conduit with other 24vdc wiring. As of yet this has not been a problem.
I am able to connect my laptop to port 3 of the AIC+ and see all 3 devices in RSLinx, although I found that I have to use a 1747-UIC USB converter. I think that is because port 3 is RS232 DH485, not DF1. I believe Linx does have a driver for directly connecting to the AIC+ (same as the PIC driver), but it is outdated and only supports COM ports 1-4.
Overall I am glad everything is working but the speed leaves a little to be desired (although acceptable for this application). Changing machine settings on the PanelView can take several seconds to respond. I think I will consider ethernet for my next project.
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