What is the difference between the REFLEX mode and the POLARISED REFLEX mode on photo-electric sensors?
Both systems work by sensing the interruption of the beam which is normally seen by the sensor receiver on being bounced back from the reflector. An object passing through the beam blocks the reflection and triggers the sensing signal.
REFLEX mode sensors may not be suitable for detecting reflective objects, as a shiny target may bounce the beam back to the sensor in the same way as the reflector and the sensor can not tell the difference between the target and reflector and will therefore fail to detect the object. For maximum effectiveness the targets should be opaque or near opaque and should not be highly reflective in nature. However, the advantage of reflex mode sensors is that they give relatively long sensing distances.
POLARISED REFLEX mode sensors have polarising filters over both the transmitter and receiving sensor. The filters are at 90 deg to each other which means that the receiver cannot see the transmitted beam as it will be blocked by the receiver filter. The reflector turns the polarised light waves through 90 deg so that the receiver can see them. Light bouncing of other objects is not rotated so it will not trigger the sensor. This means that the polarised reflex can be used to detect very reflective surfaces, even mirrors, polished metal and semi transparent materials. However, the sensing distance is shorter than REFLEX.