ifm electronic Inductive Barrel-Style Proximity Sensor, M30 x 1.5, 10 mm Detection, PNP Output, 10 → 36 V dc,

Thread type M30 x 1.5 / overall length 81 mm
Set point adjustable by potentiometer; indication by yellow LED (= sensor suppressed) and green LED (= actual value ≥ set point, output is conductive)
Easy installation, problem-free operation

Simple, robust solution for monitoring minimum rotation speeds, impulses etc.
The compact speed monitor detects pulses without contact (e.g. from the cams of a shaft or a drive unit) and compares them to the preset value. If the rotation speed is in the acceptable range, the output is conductive.