What Are Magnetic Targets?

What Are Magnetic Targets?

Magnetic Targets, as they relate to industrial applications, are the means by which a hall effect sensor is triggered.

Magnetic Targets are available in a wide variety of configurations. They can range from a single magnet to multiple magnets embedded in a disk or ring, or hundreds of alternating magnetic fields on a magnetic strip.

Magnetic Targets  are attached to a shaft or some other point of measurement on a machine to measure speed or to indicate a stalled (stopped) condition. Magnetic Targets are also used for positioning – to indicate when a moving or moveable portion of a machine is in a certain or proper position.

There are two fundamental configurations to Magnetic Targets. One is where each magnet presents the same pole (usually the negative or south pole) to the sensor and one where successive magnets present alternating poles (north and south poles).

The quantity of magnets embedded in a Magnetic Target is usually determined by the frequency required by an application. For example, if an application has a Magnetic Target containing 1 magnet and is operating at a speed of 1 RPM (rotations per minute), the hall effect sensor will detect the magnet once every 60 seconds. If the same application has a Magnetic Target containing 60 magnets and is operating at 1 RPM, the hall effect sensor will detect a magnet once per second.

The Magnetic Target is most effective when mounted on the load side of an application, as opposed to the drive side of said application. If mounted on the drive side of an application and the coupling between the drive motor and load breaks, (such as a belt, chain, etc.), there might not be a noticeable change in the frequency output of the hall effect sensor (unless the motor is driving a heavy load) as the motor will continue operating. When the Magnetic Target is mounted on the load side of the application and the same breakage occurs, the frequency slows or stops and is indicated by the output signal of the hall effect sensor.

Magnetic Targets are secured to a shaft usually in one of three ways:

  1. Bolted onto the end of the shaft
  2. Slid onto the end of the shaft and secured with set screws
  3. Clamped around a shaft

Individual magnets can be secured with a screw(s) or an adhesive. Magnetic strips are typically secured using an adhesive.

Further Reading

Ferromagnetic Materials

Geartooth Sensing Architecture

Hall Effect Sensor Voltage Regulation and Power Management