BECKHOFF KL1904 - Manual (Page 30)

Operation
28 KL1904
Parameter
To connect these sensors please set the following parameters for the KL1904 in the TwinCAT System
Manager:
 Connect the two sensor signals either to channels 1 and 2 or channels 3 and 4 and activate the
two-channel evaluation for the two inputs used.
 Set the KL1904 sensor test for the two inputs used to not active.
CAUTION
No simultaneous sensor self-test with two-channel evaluation
The sensor self-test must not set the two channels for two-channel evaluation to LOW
simultaneously!