In all automated processes the use of sensors to provide information for the plc is of prime importance. Sensors supply the necessary signals on positions, end stops, levels or serve as pulse transmitters for counting jobs or for monitoring rotational speed. In industrial usage inductive and capacitive proximity switches are indispensable. As compared to mechanical switches they offer almost ideal conditions: non-contact, maintenance-free operation, high switching frequencies and switching accuracies as well as high protection against vibration, dust and humidity. Inductive sensors detect all metals without contact, capacitive sensors detect nearly all solid and liquid media such as metal, glass, wood, plastic, water, oil, etc... Both inductive and capacitive proximity switches are available in NAMUR versions. In conjunction with an NV0100/NV0200 amplifier the sensors can be used in zone 1 hazardous areas (the amplifier which contains Zener barriers as well as power supply and output must be mounted outside the hazardous area).