Two scada servers control one plc

[Kha2016 0]

What will be the issue if two scada system controlling one process plc through modbus tcp on same network? Can it be done? Worry about control write as both are using same output address..

I need some help/info on it as my client want to have 2 different scada running together...

[Gambit 326]

Both will overwrite the same addresses each time.

So the value used will depend who did the last write before a new scan starts.

[kaare_t 155]

@Gambit is correct, however: SCADA systems do not write until you explicitly tell the SCADA system to write one or more devices. In other words, they will poll the PLCs for information all the time, the "problem" only occurs if both systems would write to the same address at the exact same time. At regular operation, SCADA1 will write a device, then read it again at the same time as SCADA2 reads the newly updated device.