Mitsubishi FX2 Communcations problem

Hi All,

I have a problem with a Mitsubishi FX2n PLC, the system is set up and has been operating for over 10 years in the following configuration.


SCADA (MX32) comms via RS232 to two FX2n PLC's using a FX2n-485-BD card to effect communications, the station numbers are 0 and 1, and the communications bits are:

Hex: H6097
Binary: 0110 0000 1001 0111

Station 0 is an FX2N-64MR, interrogation of this station using GX Developer shows a communications error 'PLC/PP Comm error' further investigation shows M8062 set to 1 (Error Present) and the value of D8062 is 6201.

All cabling has been checked and is without fault
I have replaced the FX2N-485-BD card on both stations as part of the fault finding routine

The SCADA system has intermittant communication with station 1 but no communication with station 0

Soft and hard reset of the complete system has been tried, the fault on station 0 will not clear. The fault appears to have occured during a period of electrical storm activity, and I am no looking at replacing the PLC as that is the only part left.

Any advise or wise words would be appreciated

Thanks in advance
Mark Bolton

Presumably no one has altered the code in the plc ?

From memory the 485 card is like the 232 card and requires an initialisation to be sent to it on first power up basis.

For a 232 card the code would look something like this

This code is within the PLC and operating correctly to set both D8120 and D8121

Thanks for the question this has had me scratching my head for a couple of days now

You could try disconnecting the scada, connecting a cable between the 2 FX2N's and write a bit of code to pass some date between them ?

If no errors are present then its the cable/scada and not the FX2N's

Has the Scada had any updates ?

I did a job with an FX2N 232 BD talking to a redlion G3 HMI last year and even though the G3 showed comms good and they talked away without any problems i found that when going online i would get a 'PLC/PP Comm error' every minute or so on the FX but this didnt affect anything.

There are some example progs in the FX Comms Manual

You could also try upping the Retry Count and Comms Time out Values (Although if it has worked for 10 years then this shouldnt matter!)

Hi Dave,

I have tried the inter-PLC communications Station 0 will not clear it's fault at all, which is making me think that it is something within the PLC, all the code is good and has not been altered, I am getting the RX Led lit on the 485 comms card but the station is not replying due to the continuous 6201 PLC/PP comms error.

Processtech said:

The fault appears to have occured during a period of electrical storm activity, and I am no looking at replacing the PLC as that is the only part left.

Click to expand...

Another idea swop the PLC's and programs over to see if station 0 still remains faulty.

Hi Dave,
Unfortunately the PLCs are different types otherwise I would have tried this one is a 64 and the other is much larger, I am 90% sure that it is an internal PLC problem but am checking here and with Mitsi for any other ideas

Regards
Mark

Processtech said:

Hi Dave,
Unfortunately the PLCs are different types otherwise I would have tried this one is a 64 and the other is much larger, I am 90% sure that it is an internal PLC problem but am checking here and with Mitsi for any other ideas

Regards
Mark

Click to expand...

I think (and this is from memory) that the io count doesnt matter on the FX's you can run a 128 IO program in a 64 IO plc (or vice versa) so you could still try swopping them, you will just have extra wires hanging in the panel.

For Information:
Talked to Mitsi tech support, they believe the PLC has Probably been spiked and recommend next step in fault finding is replacement of the PLC

From Memory, and a very old one at that, there are some errors in the FX series that need to be reset in the program, no matter what else you do.
try using a dummy bit to RST both M8062 and D8062, force the dummy bit on then off, and see if that helps.

Like I said, this is a very old memory, I may be way off, but it sounds like you are getting desperate enough...

isn't the BD card the plug in one on the processor front?.

If so you could swap the 485 cards & see if it's the card, this would be cheaper than replacing the whole plc.

parky said:

isn't the BD card the plug in one on the processor front?.

If so you could swap the 485 cards & see if it's the card, this would be cheaper than replacing the whole plc.

Click to expand...

I agree, the BD boards are relatively inexpensive and can fail. I've only had one go belly up, but it's definitely a place to start.

Processtech said:

I have replaced the FX2N-485-BD card on both stations as part of the fault finding routine

Click to expand...

@ Parky & RBergmann

Processtech has already been down this route and replaced both 485bd cards!