Output Fail

[ccdubs]

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?

[support]

What are the output numbers that did not turn ON even though their online status shows as ON?

If they are output 5,6,7,8 then check if these are also double-defined as PWM or stepper motor output? A physical output that is defined as special function output will not work as regular output even if the corresponding "output" bit is ON.

If the output that are not behaving correctly are output 1 to 4 then these are linked to the expansion I/O signal as well as the 3 status LEDs. When you power cycle the PLC did any of the 3 status LED (one green, two red) turns on for half a second and then went off? If the status LED did not light up when you had the problem with the outputs then it is likely a hardware problem. You may like to replace it with a new unit and send the faulty unit in for an RMA inspection and repair.

[ccdubs]

All of the outputs showed the fault.

I didn't take note of the 3 LED's apart from noticing that the RTC Fault LED didn't turn on so it does sound like a hardware issue to me.

[support]

If all the output bits behave similarly then the problem is likely not with the PLC but with the SCADA or the communication.

What kind of SCADA are you using? Perhaps the SCADA software highlight the output bit that is SUPPOSED to be turned ON when you click on it instead of displaying the ACTUAL output bit data that it reads back from the PLC? I suspect at that moment your SCADA was not actually communicating with the PLC but it didn't tell you .

You should use the i-TRiLOGI software to connect to the PLC to examine the output status when this happen again. i-TRiLOGI will highlight an output only if the actual output bit it reads back from the PLC is turned ON (assuming that the output was not defined as a special output such as PWM or Stepper motor).

[ccdubs]

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.