PS-RL4-NS2B-PHOTO SENSOR STD RT 4.2M NPN TEACH M8 20.The PS-RL4-NS2B-PHOTO SENSOR STD RT 4.2M NPN TEACH M8 20 is a high-performance photoelectric sensor with a 4.2m range and NPN output. Easy calibration makes it ideal for industrial automation activities such as item identification and packing.