Bingo,What I see now is that the input terminal 15, is a current sinking input. So the sensor needs to be a current sourcing sensor. That is quite possible if the emitter connection of the photosensor can be separated from the cathode of the LED and terminal X40-22 A resistor would be connected between X42-1 and X42-2 and the connection between X40-20and X42-1 would be opened. The emitter would be connected to terminal X40-20.
The input would be close to 24 volts except when the beam was broken, at which time it would be close to zero. So there would need to be a logic inversion added, but hopefully that is possible.
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