We have a Modicon 984 series PLC.

We are having following problems in our PLC.

1. The 'Comm error' indication in Remote I/O processor is ocassinally blinking.

2. In the 'PLC stat' diagnostic pages we are getting alignment error and end-of-frame error for Cable A & Cable B (redundant cables between Remote I/O and I/O processor card). We are getting CRC error occasionally. What are these things and how to rectify them?

3. Recently we have replaced a J890 I/O processor card with a J892 card for a drop which does not have ASCII communicaiton. how to set the ASCII address. Will there be any problem in the functioning of PLC?

4. In the 'PLCstat' diagnostic page, the Cable errors for all 5 drops which we are having displays counts for every few minutes. Will this trip the PLC?

 

What is the distance to the remote drop?

 

You have RIO cable installation problems.
CRC and Alignment problems are pretty much due to:
1. Improper termination of the cable
2. Improper design of the RIO network.
3. Lengths of cable below the recommended
minimum length.
4. Lengths of cable exceeding the maximum length.
The manual that spells out all the details can be found at
http://eclipse.modicon.com

"Modicon Remote I/O Planning and Installation Guide."
Click on Quantum link and then click on technical manuals.

Also Modicon (Schneider Electric) technical support can help.

Good luck

Frank Prendergast
Schneider Electric

 

The remote drops are in the same panel of controllers and in the adjacent panel.

my email: [email protected]

 

There is a spec on the MINIMUM cable length between taps. make sure you follow that spec.

Bob Peterson

 

> The remote drops are in the same panel of controllers and in the adjacent
panel. <

I don't believe that this is correct. Remote drops for a PLC typically refers serial communication connections to remote I/O which can be located in the same panel or some distance away in another panel. This opposed to local I/O which is in the same rack as the PLC CPU or is connected the main rack by a parallel communication connection.

For the Modicon, from the 984 System Planning and Installation Guide (GM-0984-003), that distance can be up to 15,000 feet(main trunk plus branches) but depends on the type of cable used. For example, the 15,000 feet is listed for CATV cable while it is only 5,000 feet for Type RG-6/U coax cable. As mentioned before in a previous post, there is a minimum distance which I don't believe is in the manual but the information would be available from Modicon. There are also a minimum bend radius for each type of cable.

Common cause of communication error in remote I/O of this type are too short of a cable, no termination resistor(s), termination resistors(s) in wrong place, reflections from line taps or splitter or cable terminations, too short of bend radius, mixed cable types, problems with the remote I/O adapter, cable damage, cables run close to something that can cause interference on the cable, etc.

One key question to ask if this is an existing system is if the errors began after something was changed.

I suggest that you get the latest 984 System Planning and Installation Guide that is applicable to your Modicon from Modicon and get the information from the horse's mouth.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected](b) [email protected](h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

 

been there!

I gather the system was working well before. Cables, the lengths from the taps to the drops, too short and you get refections. this is a common fault. correct termination and crimp at the F connectors. Taps, Check the Revsion number on the tap, check they are all within 1 revison of each other. The end resistors are in the right location and be weary of inline resistors. The j892 set the dip switch for that drop and this will eliminate any error from the controller checking the ASCII port. We have not had problems with this in the past.

good luck
G