# fibre optic TCP/IP or not, Modicon and others

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Thread Starter

#### Ranjan Acharya

Dear List,

We have a customer with an Modicon 984 that is communicated to via an analogue modem link (Gandalf modems at 9600bps to be precise).

There are actually three sets of modems for the various communications signals (HMI, programming and ancillary data channel).

The HMI gets to the PLC via a Bridge Mux BM-85.

The Modicon 984 is to be replaced with a Quantum PLC. The analogue link is to be replaced with a fibre-optic link.

My question is which would be a better approach:

Approach 1:
Add Modbus over TCP/IP to the Quantum PLC and switches at either end.
Obviously some re-jigging of the communications because the Mux is being by-passed. Other ancillary traffic would be routed through the TCP/IP fibre link by TCP/IP - Serial protocol converters. There is some concern about traffic between the HMI and other devices attached to the Bridge Mux that would need to be re-routed. Perhaps a protocol converter would also be required to keep that aforementioned link.

Approach 2:
Do not add Modbus over TCP/IP to the Quantum PLC and just use fibre-optic modems. Obviously one trunk line per system and new modems. Everything
else remains the same.

I would appreciate any opinions on why we would prefer Approach 1 over Approach 2. Approach 2 appears to be cheaper and involve a little less engineering, but we are keen to add Ethernet TCP/IP and make use of the diagnostic capabilities of the Quantum PLC that are available via Ethernet.

I would be interested from hearing from Quantum users who started at the 984 and added Ethernet.

Thanks

RA

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#### Rafael N. Jacomino

We have a similar customer who just upgraded a centralized Modicon 984-685e with a Quantum PLC with Momentum Distributed I/O (ModBus Plus). The new system has an NOE77110 Quantum Ethernet module (FactoryCast unit) with 10/100Base T/FL
connectivity. Its built-in fiber connectivity, speed, and DHCP compatibility allowed them to link the system to a 30 node Ethernet network without a traffic/collision glitch (1 year running). Now I DO NOT want to start a FUD
Industrial Ethernet "thread," suffice it to say that you can quickly, cheaply, and COMPLETELY solve any latency issues with a switch. This application has 5 users "surfing" the Process without problems.

Once start-up ended, it got interesting! They just removed their proprietary $12k ControlView HMI and replaced it with$168 MS-FrontPage! The Quantum PLC now "hosts" 38 screens-worth of HMI written in standard HTML code accessible from anywhere in their intranet. To the point that their Purchasing Department can check raw-material inventories right from their MS-InternetExplorer equipped PCs. Read-between-the-lines and reach your own conclusions.

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#### Lynn Linse

Ranjan Acharya wrote:
> There are actually three sets of modems for the various communications
> signals (HMI, programming and ancillary data channel).
> ....
>
> Approach 1:
> Add Modbus over TCP/IP to the Quantum PLC and switches at either end.
> ...
>
> Approach 2:
> Do not add Modbus over TCP/IP to the Quantum PLC and just use
> fibre-optic [3 pair] modems [to run the 3 serial lines](Lynn added [] comment)
> ...
>
> I would appreciate any opinions on why we would prefer Approach 1 over
> Approach 2. Approach 2 appears to be cheaper ...

Considering the cost of your fiber, #2 may not be much cheaper. #1 would allow a 4-core fiber (2 used + 2 spare) while #2 will require an 12-core
fiber (not sure 8-core are commonly available & 6-core with no spare is not wise). Maybe your fiber is short and indoors, but if this is a direct burial cable in the 1Km range, my last exposure to cable costs would mean #1 would save many thousands of $- the$2K-4K range.

Considering the future options a fiber-based Ethernet at this remote site would offer - for me it would have to be a pretty BIG cost difference or this site is really loosing money and on management's sh*t list before I'd think Approach #2 is a wise investment.

For example - with the Ethernet you could:
1) Add a second HMI as backup with no added cost
2) Could "tunnel" dozens of serial ports thru this one fiber-pair at from $190 to$700 per port, so you could add future serial products
there cheaply.
3) Add future Ethernet products at this site for free (at least no added infra-structure costs).

Best regards

Lynn August Linse, Senior IA Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected] www.lantronix.com
Tel: (949)279-3969 Fax: (949)453-7152

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