Network Help

Ok here we go,

I have a SLC/504 which is currently connnected to our control room via DH+ and RS view etc. Ok so far.

I have 3 valves and 3 tank levels that I want to monitor/control. (A small number of I/O.)

The geography is from my PLC North 500m valve 1 and level 1. South from my PLC 400m valve 2 and level 2. Further South another 100m from valve 2, valve 3 and level 3.

Ok so my question is what type of network do I put in to control/monitor my valves and levels?

Now before you say I have not tried....

I contacted our local tech support (not mentioning names here) and the answer they came up with was to use Flex I/O. This was based on the understanding that my valves were 110v controlled and Flex I/O modules are obtainable that are digital 110v in/out. (I could fit interface relays here but thats another story.)
All is well until at 4.50.pm. when I look on AB's web site and find that the modules have to be series linked! Am I right? Like DH+?

Back to the geography that means that I have to go 500m north to valve 1, 900m back past my PLC to valve 2 and then 100m to valve 3.

Please tell me that there is a better way? Or am I being petty about the 500m extra DH+ cable?

Ben

1) Cable is cheap. You can't afford to do a lot of engineering for the cost of 400m of twisted pair.

2) If you have all this hardware installed already at the main panel, I would use the DH-485 link from the SLC 5/04 and put AIC modules with Micro-Logix 1000 at each remote location.

3) If you haven't already gotten the hardware you can probably do all of the control you are describing with a Micro-Logix 1500 and skip the SLC.

4) For the little bit of I/O you are using it is probably cheaper to pull the wires and use I/O on the SLC.

5) I'm not familiar with Flex I/O but with most serial links you can cheat on short runs and use a star topography instead of a multi-drop. You just need to watch your terminating resistors.

If you use DeviceNet, the scanner module does not have to be at the physical end of the network. You could still use Flex I/O if desired, but there are plenty of other options to hang 115 VAC devices on DeviceNet, from other vendors in addition to A-B. Go to http://www.odva.org

Just to make sure we all understand. You want to know if you can wire the Remote I/O (which is all Flex I/O is, with the PLC scanner in the middle, like this:

VALVE_1     SLC    VALVE_2     VALVE_3

    \_______/\_______/\___________/

or, do you have to put the SLC on the end, like this:

VALVE_1     SLC    VALVE_2     VALVE_3

   |\_______/   _____/\___________/

   |___________/ 

I'm fairly sure that the former is perfectly acceptable. (I don't have any manuals handy to confirm it though)

Still, it costs about the same to put one blue hose as two through the conduit. And the cost of the cable is probably cheaper than your time in sweating over it.

Make the connections as per Allen's first sketch - put the terminating resistors at Valve 1 and Valve 3. The electronics at each node are identical for all intents and purposes so wiring sequence doesn't matter.

I have read somewhere in AB literature that by placing the scanner in the middle like this, the blue hose can be up to 10,000 ft. on both sides (max. 20,000 ft end to end).

I don't think that's true Gerry. You can put it in the middle of the link, but it is still limited to 10,000ft.

Maybe you saw something where they had two remote i/o networks both starting at the cpu. 10,000 feet off each network headed in opposite directions would certainly look like 20,000ft.

OG

A basic thing so our friend the mysterious poster doesn't get caught unawares:

We're talking about Remote I/O networking, here, not DH+. You cannot connect up I/O modules to Data Highway Plus.

You'll need a 1747-SN Remote I/O Scanner Module in your SLC-5/04 chassis to do this application.

The wiring is identical, but the protocols are different.

Mysterious Poster

Thanks for all your input,

I was aware that you need a remote scanner in the SLC, but a was told that you can use standard DH+ cable to connect to the remote Flex I/O.

I have read the postings, we would not usually run conduit on site because the cable run is underground ducts and the cables mounted on cable tray. So I was thinking of S.W.A DH+ cable. (Steel wired armoured.) Also the cost of installing conduit in this country on those sort of runs would be v.high.

I am still unsure as to if I can run my small net work in a star format, however as mentioned already it is probably not worth loss of sleep for the extra 500m cable. Thread over?

On the subject of DH+ why do you need the termination resistor and where do you connect it? I am sure that the existing DH+ network we have does not have these. So it dosen't affect your network? I noticed that a recently purchased RIO card has two values of resistors in the package but the manual has no reference to them at all?!? Does this require a new thread I wonder?

Again thanks for all input.

Ben

Ben:

A 'star' connection will produce trouble but the suggested hook-up is a 'daisy-chain' connection. The terminating resistors belong at the physical extremities of the daisy-chain.

Data Highway, Data Highway PLus, and Remote I/O are electrically identical and use the same cable. DH and DH+ run at 57.6K and up to 3000 metres. RIO can run at 57.6K for 3000m, 115.2K for 1500m, or 230.4K for 750m. When running at 57.6 or 115.2, use the 150 ohm terminators, at 230.4, use the 82 ohm terminators.

Having said all that, I wonder if, given the geography, you shouldn't be considering a fibre-optic link. A ground strike (lightning) could roast anything on a wire link. (See A-B 1770-AF/AF1)

Not familiar with y'alls location BUT can testify that Gerry is correct when stating a ground strike ( lightning ) can destroy things...multiple items.

Gerry,

I cannot seem to find this card.

(See A-B 1770-AF/AF1)

Is it not 1771? A PLC5 card? I am using a SLC5/04.

Ben

1771-AF

Here is a link to the product profile for the 1771-AF from the AB web site.

http://www.ab.com/manuals/cn/1771290.pdf

OG

OOPS

I got the number wrong

The AF1 is a stand-alone version of the AF (which requires a 1771 chassis).

You'll find fiber converters WAY more expensive than cable, but if you're running a long distance in a lightning-prone location they can't be beat. We sell a lot of fiber to aluminum smelters, where the electromagnetic environment is, to put it mildly, complex.

I'll throw in my two cents: the 1771-AF and -AF1 have antiquated fiber optic connectors (they're SMA-905 type, threaded plastic) and I try not to use them when I get the chance because it's very hard to find cable tools for those connectors anymore.

You'll probably find a more modern and less expensive option through Phoenix Digital. I use and recommend them for all my DH+/RIO fiber optic applications.

www.phoenixdigitalcorp.com.

If you don't go fiber for long runs (particularly outdoors or away from metallic conduit) of DH+/RIO, be sure you at least put in a Transtector or similar lightning suppressor like the FSP-4002-MC.