Internet PLC Forum

Hi,

Is the Fx2424 PLC backwards compatible with T100MD2424? I have had a bunch on inputs (including high speed counters) fail on an old T100MD2424 and was looking to replace with a Fx2424 but don't want to have to reinvent the wheel, reprogramme, commission, etc.

Thanks

Thanks Gary. Now I'm really confused as I have used these PLC's a lot and haven't changed any of my software between changing from T100MD to FMD88 and the analogues have always read fine in my SCADA with a max scale of 4095?

Regarding the wiring, the only difference with the way I have the connections configured is that the pins allocated "future #D/A3 and #D/A4" are connected to 0V all other pins (apart from A/D#1-4) are not connected.

Hi, I have had to swap an old T100MD888 with a new FMD88 but had an issue with the analogue input values I was reading. From what I can see from the connection wiring the only difference is that our application connects the future D/A's #3 and #4(pins 10 and 11)  to 0V as that is what these pins were on the T100MD888.

Would this be the cause of the spurious analogue input readings I now get? If not, are there other differences (software and hardware) that I should be made aware of when swapping a MD888 with a FMD88?

Thanks.

Hi,

I have a FMD88-10 (Rev 3) which is showing something unusual. Digital outputs 1-4 aren't working correctly and when energised in the code, they don't turn on (sometimes they flicker) but the RTC error light flickers.

Any ideas what the cause may be?

Thanks

The PLC's are polled at 10 minute intervals so it is hard to know how intermittent the fault is. I haven't seen the values at 0 for longer than one poll. When the error happens all inputs fall to 0.

I am using DAQFactory and I am sure that there is no way that the SCADA can falsely show status as the screen display is directly mapped from the MODBUS reading from the PLC.

I was monitoring the status with Trilogi but unfortunately can't remember what it showed and I haven't been able to repeat the error since.

I have had a situation with an FMD88 where I could still communicate via ethernet and monitor the status of inputs but when I tried to activate outputs through my SCADA interface, the physical outputs didn't turn on but the status read back from the PLC showed that they were activate. This would imply that the code was still functioning as there is logic that maps SCADA commands to outputs but the physical outputs didn't trigger.

I re-powered the PLC multiple times and it made no difference. After leaving the PLC off for 30 minutes or so and turning back on again, it seems to be functioning correctly. I have not been able to replicate the issue since.

I can't say for sure but I don't think the RTC Error light was on while I had the problem. Any ideas?

Well it has been a while but I can now provide an update.

Gary: if you are still there, the RF chokes helped but didn't solve the problem.

Support: you were right. After a lot of trial and error testing we found the noise to be coming from the switch mode DC-DC converter. It wasn't that easy to find and we were mislead by the fact that unplugging the PLC made the noise go away...this still isn't really explained. Perhaps the noise from the DC-DC converter is load dependent (i.e., PLC small load is enough) or perhaps there is an interaction between the two that amplifies the noise to the radio.