Sensors include: Variable Reluctance Sensors (VRS) also know as Magnetic Speed Sensors, Magnetic Pickups or Passive Magnetic Sensors. Completely self powered, they are simple rugged devices that do not require an external voltage source for operation. Referred to as Passive Magnetic Sensors because they do not need to be powered, but are self generating. These sensors convert mechanical motion into an AC Voltage without mechanical linkage when positioned near a gear, rotor, shaft or other regular moving devices.
Other Speed Sensor designs include: Hall Effect and Digital Speed Sensors which require a supply voltage and create a square wave output signal.