Magnetic speed sensing: principles and applications

One of the most common sensed properties is the speed of a rotating shaft. While this can be accomplished through a wide variety of technologies, some of the simplest, least expensive, and easiest to apply are based on the ability to sense a magnetic field. Accidental magnetic fields are seldom significant, and the fields are relatively unaffected by environmental influences. The most common means of measuring shaft speed magnetically require the use of a special target attached to the shaft. Measuring the speed of the target then indirectly senses the shaft speed. Different targets require different sensing strategies. Some common types are ring magnets, metallic toothed gears, and stamped sheet metal vanes. This paper discusses the various types of targets that may be used for speed sensing, and what kinds of sensors are needed to detect them