The E3JK-RR11 2M sensor works in retroreflective mode, meaning it needs a reflector placed opposite to the sensor. The beam goes from the sensor to the reflector and then comes back; when an object interrupts that beam, detection occurs. Because of this setup, E3JK-RR11 2M can achieve much longer sensing distances — up to ~7 m with a standard reflector (E39-R1) and even ~11 m when using a better reflector (E39-R2).
On the other hand, E3JK-DR11 2M uses diffuse reflection: the sensor emits light, and it senses the light reflected off the surface of the target itself. This method doesn’t require an external reflector, but its effective sensing distance is much shorter (≈ 2.5 m under ideal reflection conditions) because the reflected signal is weaker and depends on the reflectivity of the object’s surface.
Because both are within the E3JK family, they share many core specifications: the same power range (24–240 V AC/DC), relay outputs, selectable Light-ON / Dark-ON operation, and environmental tolerances (temperature, humidity, protection class).
In real-world use, you’d pick E3JK-RR11 if you need longer reach in a relatively unobstructed path (with space for a reflector). E3JK-DR11 is more suitable when detection distance is short and you can’t align a separate reflector, or the object’s surface reliably reflects light back.
For full specs of the DR11 model, see Omron E3JK-DR11 2M Photoelectric Sensor — and for RR11, see Omron E3JK-RR11 2M Photoelectric Sensor.