The DI channels in our products support both dry and wet contacts and hence can be organized in groups such that all DIs in a group can share the same DI.COM (floating) channel. This design enables the use of a different sensor type (NPN/PNP) in each group.
However, if multiple DI channels in one group are used and all the DIs in a group are connected to the ground (GND) contact, the DI channels (including the unused channels) will turn ON. The reason is that all the DI channels in a group will be pulled down to a lower potential voltage because they are internally connected to the same DI.COM, which in turn affects the internal IO circuit and the status of the DIs, causing the unused DIs to also turn ON.
A real-world example for the ioLogik E2200 Series is given below:
The behavior of the IO circuit is indicated using the following lines:
To solve the issue of the unused DIs turning ON, connect an external power source to the DI.COM contact so as to maintain the internal voltage at the same level.
Source: ioLogik Series User Manuals