Serial Communication Problems with a PLC and a PanelView


Thread Starter

Yannick Bouchard

I have problems with a serial communication (Rs-232) between a PLC(Control Logix) and a Panel View. The problem is the length of the cable because its greater than 50 feet. For resolve the problem I think to convert the protocol Rs-232 to Rs-422 at the out of my ControLogix PLC and after that convert the protocol Rs-422 to Rs-232 for communicate to the PanelView. It is a good solution and it is possible ? Please help me.

N.b. My panelView don't communic by a bridge RIO, DH+, DeviceNet, ControlNet and Ethernet.

Alok Varshney

If distance is the only consideration then you have no choice but to convert to 422 or 485. It is possible that your PanelView may accept 422 or 485 connection without the need to reconvert back to 232. Also it might be worth checking by using a better shielded cable on 232 and it may work.

Bob Peterson

Just because it is more then 50 feet of cable away does not mean RS232 will not work. This is just a rule of thumb. If its a reasonable distance (a few hundred feet) it will probably work fine, although you may have to run at lower baud rates.

Bob Peterson
50 feet of serial cable doesn't sound like too much.
I've personally run good cabling well over 100 feet.
I'd suggest looking for good shielded, twisted pair cabling, and ground one end. Otherwise your stuck with 485 which might cause all sorts of setup problems with your hardware.


Steve Myres, PE

Another option for long distance comms is a pair of fiber transceivers at either end of the run. I've done this over a distance of like 10K feet. Both of the devices are still connected via copper (to the transceivers), so they are none the wiser.
This is what you can do: You can try flashing the firmware of your panelview from a standard RS232(DF1) to a RS232(DH485) protocol, you do this by
selecting the panelview firmware that has a RS232(DH485) port on it, of course it will be a different catalog number than the one you have. This firmware is included on the cd-rom of the programming software.

Once the conversion is done, all you need is two NETAICs from A-B and you can go up to 4000ft between your PLC and the Panelview. Make sure that your CLX is compatible with the DH485 protocol on his RS232 port (if it is a 5555, your ok, if not, it won't work).

The other option is to try your chances and go up to 75-100 feet if you want to(use highly shielded wire), one of my collegues was telling me that there is no "specifications" on the length, but it is a matter of signal amplitude and baud rate, the 50 feet is a certainty but not a limitation. This collegue saw an application where they ran a 200ft long RS232 cable with a baud rate of 1200 Bps without any problems.

It's your call, good luck

Salut Yannick,

Voici ce que tu peux faire, tu peux flasher ton panelview (de rs232 à dh485, t'as juste à selectionner ton firmware pour RS232(DH485))donc tu demeureras RS232(mais avec le protocole DH485), tu pourras aller jusqu'à 4000 pi avec des
Net Aic. Bien sur il faut que ton CLogix (CPU) soit capable d'avoir le DH485 sur son port RS232.

L'autre option, un collegue me disait qu'il n'y avait pas de standard en tant que tel en RS232, donc le 50 pi est une certitude, mais n'est pas une limite. Le problème avec ces distances est la perte d'amplitude, donc une perte d'un bit. Essai à 9600 Bps jusqu'à 100. Ce même collègue a vu une distance de 200 pieds avec 1200Bps, sans problème.

À toi de juger, bonne chance

Michel A. Levesque, eng.

The RS-232 standard does not specify distances. It specifies capacitance: 2500 picofarads max. This gives you about 50 meters (not feet) at 19.2kb. You can use low capacitance cabling to push these distances up. We've used fibre optique transceivers (available from Phoenix) and we've used RS-422 and RS-485. There are no inherent problems with any of these solutions.
As for the PV and the CLX, make sure you are talking with the same protocols (DF1 is not DH-485). If you want to stay in the Rockwell world, use a 1747-NET-AIC (3000 ft max).
I believe that the length limit of a RS-232 cable currently is defined by the cable total capacitance less than 2,500 picofarads. Modern RS-232 cables can be much longer than 50 feet. Black Box's on-line catalog sells RS-232 cables good for 200 feet and I believe their paper catalog has cables as long as 500 feet.

Bill Mostia
William(Bill) L. Mostia, Jr. P.E.
P.O. 1129
Kemah, Tx 77565
Excellence in Dependable Automation
[email protected](b) [email protected](h) 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.