Adding nodes to the DH485 network

[Oliascobra]

Hi all:

I am connecting nodes to a DH485 network without using an AIC module as follows:

SLC5/03 DH485 port (RJ45-style jack) using a 1747-C20 cable to connect to the wide DH485 jack in a PV600, PN 2711-K6C3, which has both a wide AB jack and a RJ45 DH485 jack. I then connect another 2711-K6C3 to the first PV600 using another 1747-C20 cable. Then I connect my laptop through a PIC (which has only the wide DH485 jack) using yet another 1747-C20 cable into the second PV600.

Long-winded, I know, but here's the point. I use this setup for programming and testing in my lab and it works fine. Now I have a special application where instead of using the 1747-C20 cable to connect the first and second PV600s, I need to use a standard pin-to-pin CAT5e cable with an RJ45 plug on each end. This means that I must connect each PV600's RJ45 DH485 port to either end of the cable. This setup also works, but now I cannot connect my laptop to the second PV600 because AB does not make a wide DH485 to wide DH485 connector cable.

Now when speaking to AB, they don't explain why they don't make that cable configuration, and further, they say that I cannot connect more than 2 nodes to the DH485 network without a 1747-AIC module. Yet I am, and the fact that the standard ethernet cable works to connect the second PV600 to the DH485 network seems to imply that the wiring for the 1747-C20 is simply straight through pin-to-pin. They won't provide me with a wiring diagram for the 1747-C20 cable.

I manufacture an instrument that uses the SLC and PV600s. If I use the ethernet cable to connect the PV600s, will I be making a mistake and perhaps installing an unreliable system? AB won't comment other than "that is not a supported configuration", meaning, I believe, that they don't understand the specifics of their network themselves.

Thanks!

P.S. Is there a formal name for that "wide DH485 connector"?

[jimbo3123]

I think the wide connector you're talking about is a 6 pin phoenix connector (the kind with the bumps on one side), like a big version of a DH+/RIO plug.

BTW, you can connect multiple 6 pin connectors.
Here is the manual that explains how to do it:
http://www.ab.com/manuals/cn/1770622.pdf

[Ken Roach]

I've promised myself for years that I'd start diagramming pinouts so those damn cables made sense, but I never have. Most A-B people call the "wide DH-485 connector" the "AMP connector" after the manufacturer name that's stamped onto it. I have never seen an aftermarket supplier for these shielded, modular, 8-pin connectors.

What you are describing is a non-isolated, unshielded RS-485 network. While this will work fine for many simple installations, it's not as noise-immune or reliable as an isolated, shielded RS-485 network and that's why A-B won't back it.

In the matter of "why do RS-485 networks need all this extra stuff", I defer to the master: http://www.robustdc.com

The whole weird world of different-ended DH-485 cables and 1747-AIC modules has to do with isolation and power. In that way, it's a lot like Napoleon. I can't explain him either.

[Gerry]

Hypothetical system:

• SLC 503 connected to PV1000 with 1747-C20
• 1747-UIC connected to PV1000 with standard ethernet RJ45 cable

Will a PC connected to the UIC be able to access both the SLC and the PV1000?

[PhilipW]

Part of the mystery of DH-485 cable configurations is in understanding the isolation and power supply requirements.

PV's with part numbers ending in 2 have 2 DH-485 ports which are isolated from the PV's internal electronics, but are powered from the SLC DH-485 port instead.

This is a nice way of getting a isolation between the SLC and the PV, but of course there is a limit on how many ports the SLC processor will power up in this manner.

In your configuration you are powering TWO PanelView ports and a PIC (which is isolated from your PC serial port too). On the 24 v line the PIC draws about 105 mA, and I think the PV ports will draw a similar amount, so the your total current draw is up around 300mA. Clearly it is working on the bench BUT:

The upper limit on the SLC CPU +24 supply line is nominally 200 mA and if the total chassis PSU is heavily loaded on the +24 V line, ie lots of analog or relay O/P modules, there may not be enough current left to drive both your PanelViews and PIC.

The ability of the 5/03 and 2711-xxx2 PanelView to create a simple 2 node network with no AIC module but still obtaining isolation is a nice feature. More than one commissioning tech has been greeted with smoke because a non-isolated RS-232 network was wired at different earth potentials.

However for a bunch of reasons, one of which is the power supply limitations outlined above, more than two nodes demands the use of AIC modules to be certain of reliable operation.

[Gerry]

Philip,

Not sure if you were answering my question or someone else's.

I mentioned a 1747-UIC, which, according to the literature, is powered from the PC's USB port.

Also, I'm unaware of any PV's with part no. ending in '2'. I was considering one that ended in '3' (for DH485).

[Ken Roach]

I think Philip was answering the original post, so I'll answer your related question, Gerry.

YES, you can connect an SLC-5/03, 2711-xxx3 terminal, and a 1747-UIC all together and have them work properly. I configured and am running just such a configuration right now on my desk.

If you have separate power supplies or separate grounds for the PanelView and the SLC, post again and we'll debate whether it's advisable to go with an isolated network. Same if the cable between the PanelView and 1747-UIC is longer than 20 feet.

2711-xxx2 is DH-485 only communications
2711-xxx3 is DH-485 communications with printer port
2711-xxx5 is DH-485 (RS232) communications
2711-xxx9 is DH-485 (RS232) communications with printer port

[attachment]

[Gerry]

Thanks, Ken

The SLC and PV will be in the same cabinet and the UIC connection would be occassional for programming access, most likely with a 3-metre (10 ft) cable.

Since I was only looking at PV1000, I could only find '3' and '9' DH485 options - I see that the other options are available for the PV550 and PV600.

[Oliascobra]

Thanks, folks. I expect I've just been lucky having it work the way it's currently connected. I will add an AIC module. If anyone can post the details of the 1747-C.. cable, that would be great.