It makes no difference which hole it is inserted into, because there is no distinction between the two fibers for a Through-beam Fiber Unit.
With Coaxial Diffuse-reflective Fiber Sensors (such as the E32-C31), the holes that the fibers are inserted into are set for the receiver and transmitter.
With Coaxial Diffuse-reflective Fiber Sensors (such as the E32-C31), the holes that the fibers are inserted into are set for the receiver and transmitter.
