Halo! The project that i am dealing with is to replace an old plc with S7400 with ET200M and S7300 modules.I will use PCS7 for SCADA.

The problem is in digital inputs. The old plc uses 60VDC for input supply, but for signal 1 0VDC and for signal 0 60VDC (it uses 60VDC for common, it is a source input) (attachment).

What module can i use? I found that in siemens sourcing module digital inputs are:

63S7321-1BH50-0AA0 (24vdc source input) the SM 321 64DI,DC24V Sinking/Sourcing module i have read that is not working with PCS7.

Is it possible to use 63S7321-1BH50-0AA0 and to make a bridge between the common (0VDC) of the two power supplys (attachment)?

Thans in advance....