Full question: for the Schneider XCSRC1, I have two systems, both with four sensors, and in both systems the last sensor with the resistor fails. The RD LED (received/output LED) flashes twice, and the TR LED (transponder state LED) is off, and the other three switches in both systems work perfectly. Plus, the transducer is placed according to the instruction. The error starts as soon the power turns on. Why is this?

The problem is because all the switches are reversed. Please see the IN & OUT markings on the switch body. You can resolve this just by changing the orientation of each switch.

Discover photoelectric sensors on Think Hub