How to make one Digital Output driven by two PLC with out any relay's
Is there any way to make the output driven by two PLC's ?
You can simply connect both outputs if:
- you want a logic OR operation (the actor operates as soon one of the PLC powers the output)
- both PLC outputs are driven by the same power source and voltage level. If not there are possible high currents equating the voltage levels through the PLS outputs! In permanent environments it is even required to have both output power sources on the same fuse, but as a short time solution it may be a acceptable risk to mix circuits on different fuses.
- the ground have to be connected
- the outputs do not make a "pull down". I never seen a PLC digital output doing this.
Summary, there are many things to take care of, if you make a direct connection. Not recommended, but possible.
You can also use 2 diodes to connect both outputs if:
- logic OR operation
- DC current
- a voltage loss 0.5 to 0.7V is acceptable
This is much saver than the direct connection, but requires diodes and an extra connection point.