Most determine direction of rotation, speed, and angular position of their rotating targets by generating a series of pulses. Tachometer generators and many other conventional rotation monitors require a physical connection to the driving element. Proximity sensors, in contrast, do not.
In many cases proximity sensors directly monitor rotating parts of a machine such as shafts, gears, or cams. They need no special actuators or additional connecting elements. A caveat is that the gap or air space between targets must equal or exceed the diameter of any proximity sensor used to sense rotation.
The time needed to acquire a value for rotation speed depends on how fast the sensor generates pulses. A single-lobe cam needs enough time to complete one revolution before a sensor can determine its rotational speed. However, a cam with four equalspaced lobes only needs to complete one-quarter of a revolution.
Mild steel targets demand that sensors be positioned at half the nominal sensing range. Nonferrous targets require the use of correction factors. Neither statement applies for Factor 1 sensors that sense all metal at the same distance.
Turck Inc. (turck.com) provided information for this column.