FX2N PLC AND DRIVE COMMUNICATION (RS484) PROBLEM

[PLC DIGGER 0]

HELLO FRIENDS AND MASTERS, I M CARRYING OUT A PROJECT WITH 'FX2N' PLC. THERE ARE 16 DRIVES ON PROJECT. ALL ARE INITIALLY ON RS485 COMMUNICATION INITIALLY THROUGH 'FX2N 485 BD' . THE PROBLEM IS THAT AFTER CERTAIN TIME OF RUNNING PROPERLY THE DRIVES PUT UP COMMUNICATION. THE COMMUNICATION BEHAVIOUR BECOMES UNCERTAIN. AND THIS TIME DURATION IS IN BETWEEN 1 TO 1 & 1/2 DAY. IN STARTING IT COMMUNICATES PROPERLY. ALL DRIVES TAKING I/P FREQUENCY AND READING O/P FREQUENCY PROPERLY. PROBLEM STARTS AFTER ONE OR ONE AND HALF DAY. AFTERWARDS I CHANGED THE SCHEME , I SEPARATED DRIVES. TOOK 8 DRIVES ON PLC AND OTHER 8 DRIVES ON HMI (DUAL DRIVER). INITIALLY IT WORKED, BUT AFTER SOME TIME FEW DRIVES STOPPED READING FREQUENCY. THEY WERE TAKING I/P FREQUENCY PROPERLY. NOW HERE WHERE I CAN NOT LOCATE WHERE THE PROBLEM IS. AND THE REMEDIES WHICH I HAVE ALREADY IMPLEMENTED. ALL OF THE COMMUNICATION CABLES CHECKED AND REPLACED FAULTY ONES. CHECKED ALL DRIVES INDIVIDUALLY FOR COMMUNICATION. (WORKING PROPERLY) CHECKED PROGRAM THOROUGHLY, AND EVEN ARRANGED A SET UP AT OFFICE TO CHECK IT THE PROGRAM IS OK. SO PLZ HELP ME LOCATE PROBLEM.

[Veganic 8]

With that number of drives on 485 the problem is often not how to avoid comm problems but how to react to them. 1. If the HMI can handle all 16 drives try that. The protocol is written for you and you can concentrate on error checking in the PLC. 2. Are problems only on the ones connected to the PLC? 3. Increase time out parameters in the drives and HMI. 4. Reset the drives when a fault is detected. 5.Write to one drive at a time->check response->move to next drive. Use a index register to ensure this happens. 6. Post the program here.

[PLC DIGGER 0]

First of all thanks for reply. The problem is not fixed with particular drives. It occurs radomly. and Not only plc also with the drives on HMI. HMI drive communication set up is as below: From RS 232 port a 232 to 485 converter is taken and from 485 side there is connected all 8 drives. so problem is like it stops communicating after certain time. From the indicatros on converter I observed no sending and receving was occuring. and again when I downloaded the same HMI program again it started communicating. This problem happened thrice and stil persisting.This is regarding drives on HMI. Now with drives on plc same problem is there. And program I have made is the same like u suggested. first i communicated one drive , response came and then started for another drive. Even I have checked all drives individually. They are communicating perfectly. As they put together , then starts malfuctioning. And ya, the time out parameters are already selected so , as they dont come in picture. The prog has been already checked no. of times , even at office also I set the same set up as at the site and put under observation but here no problem was detected. Actually my confusion is the below mentioned point: 1. It should not communicate even once if there is problem in program, where as situation is like it runs properly for one or one and half day. The problem starts afterwards. Edited 15 May 2009 by PLC DIGGER

[Veganic 8]

That's rarely true. Are the drives, assmuming they are mitsu, giving a E.opr fault? I'm away for a few days so maybe someone else will be able to help.

[PLC DIGGER 0]

Drives are D700 mitsubishi. and none of them are giving this error.

[Veganic 8]

I've given the program a quick scan...so may have missed some of the finer detail: The com. part seems to have three sections: Writing frequencies, controlled by C0. Reading frequencies, controlled by C1. Fault response, controlled by M802. I can't see where you wait for M8123 during the writing. C0 just waits for a timer before moving on to the next drive. I can't see anywhere where you check for the correct response either. Edit: C0 increments on a time value of K45. C1 increments on a time value of K10. Increase the K10 value? Edited 19 May 2009 by Veganic

[PLC DIGGER 0]

ok..u got it correct. here frequency write is going ok. and for receiving completion confirmation, logic is like either m8123 or a timer whichever is earlier will move to next drive. this i have done because there were 16 drives and if few among all are on and others are off then the m8123 from drives which are off will not be recieved and sequence wont go further. so i have taken one timer also , which in case of particular drive off, will move to next sequence after some time.