We have an 800xa ABB DCS since commissioning we are bothered with modbus communication between third party equipments like compressors, bently nevada vibration system and others. We have program written in FBD but how to establish or what checks to be done for communication.

Please help...

 

In my personal opinion 800xA Modbus can be challenging from what I saw a couple of years ago, when I was doing some work on ABB. I observed much struggle. I suggest Get Profibus DP 800xA card and then buy third part Profibus DP to Modbus bridge. The third part guys do a good job. Example check PROSOFT. ABB likes Profibus so it will be simple that way. Profibus is a standard so you should be able to just load up the PROSOFT GSD File into ABB standard Profibus blockware. Let me know how it worked out.. V. Newman

 

Is the equipment connected directly to a controller or to an interface on the operator consoles..?? This is very important to know.

Vance Newman vnewman1963 [at] gmail.com

 

I have to disagree with others on the "difficulty" of Modbus links on AC800M controllers.

1. Check the help files for the Modbus communication library.

2. You need one MB_Connect block for each PLC and one or more MB_Read and MB_Write blocks for each block of data you want to fetch / send to that PLC. Don't make the code overly complex.

3. Check the help files for information on setting adresses.

4. As with almost every Modbus link, theres a 50/50 chance that the PLC address space starts at either 0000 or 0001, so you might have to adjust the addresses by one.

5. Its modbus, it isnt that complex. Check you have blinky lights on the com ports, check your baud rate and parity settings, check your cable terminations and check your code for errors. If you get desperate, put a test client on the end of the cable instead of the remote PLC.It either works or it doesn't.

Remember that Modbus communication is quite slow. If you have multiple PLCs on one link, then you have to talk to each plc in turn and then modbus speed can become an issue - especially if one of the PLCs fails and you have to wait for the retry and timeout periods to elapse before you can talk to the next. In this case you can either split the PLC's onto multiple links or go for the Profibus solution suggested previously.

Rob
www[.]lymac.co.nz

 

Hi Rob!

If you make already a modbus communication with AC800 with other PLC, can you pleas share the example in simple text. Will be greatly appreciated . I need to make that kind of connection with S7-300 PLC, but never used Modbus FB in Control Builder.

Thanks in advance and best regards from Stefan.

 

Contact us off forum through our web site. I should have a simple example I can send you

Rob
www[.]lymac.co.nz

 

I have sent you a email before some days...i hope it's not so irritating for you to be bothered again .

my email is stefanov [at] starteng.com..

Thanks for your patience Rob ..Cheers!

 

It has been connected to the controller only, via CI853 Dual RS232-C INTERFACE CARD.

 

Are you connecting over a serial link?

It might be worth considering if the equipment at the far end is DCE or DTE. IF you are DCE to DCE, you will need a cross in the serial cable between Tx and Rx. If you are DCE (800M)to DTE (remote) then you don't need the cross. Sometimes the software's not the issue...