BECKHOFF EL1904 - Manual (Page 27)

Operation
EL1904 25
EL1904 pin assignment
Terminal
point Input Signal
1 1 Input 1+
2 Input 1-
3 3 Input 3+
4 Input 3-
5 2 Input 2+
6 Input 2-
7 4 Input 4+
8 Input 4-
Note
Configurable inputs
The inputs 1 to 4 can be occupied as you want with normally closed contacts or
normally open contacts. The corresponding analysis is carried out in the safety PLC.