For a standard M4 threaded (4mm diameter) inductive proximity sensor, the typical rated sensing distance (Sn) ranges from 0. This limited range is due to the small physical size of the sensor head. The effective or "real" sensing distance in operation, however, is. With built-in focal lenses, longer sensing distances can be achieved up to 5 times longer compared to conventional sensors. The sensing distances for E3NX-FA are. The M4 optical sensing instrument is an economic commercial grade interrogator, featuring 4 monitoring channels. For custom fit, most plastic filament cables can be cut to length.