A magnetic speed sensor uses a magnetic field to sense the approach of a
ferrous metal target, which can be a gear tooth, fan blade, rotor blade, wheel spoke, etc. The magnetic speed sensor
will detect the presence or absence of the target. The signal amplitude will vary with how fast the target is moving,
which is how the magnetic speed sensor is able to relay the speed.
Learn About Our Magnetic Speed Sensors
There are a number of different technologies used for a magnetic speed sensor. The most basic is the variable
reluctance speed sensor, which will provide a sine wave output. However, there are also a number of options using
more sophisticated technologies, such as an amplified magnetic speed sensor, a Hall Effect Sensor or a
magnetoresistive sensor, which provide the user with a digital square wave output.
Design
A variable reluctance (VR) magnetic speed sensor is comprised of several elements, including the coil winding and
magnet. Due to the size of most magnetic speed sensors, the magnet wire used is extremely fine (38 to 44 AWG) and
requires special handling. Most high volume producers of magnetic speed sensors have automated this process, however
for custom requirements it is often necessary and more efficient to build the sensor by hand. Motion Sensors utilizes
a combination of methods depending upon design configuration and volume.
The VR magnetic speed sensor also includes a magnet. Magnet selection is based upon the geometry
of the sensor and the desired gauss strength, which is dictated by airgap and signal strength requirements, as well
as potential drag issues (common in "low-flow" turbine flowmetering applications).
There are specifications to consider when selecting magnetic speed sensors in order to ensure that
the desired signal strength is achieved. This will depend in part upon application considerations, not just the
magnetic speed sensor, for example airgap (the distance between the sensing front and the target), target/gear
geometry, number of teeth/targets, target material, and the speed at which it is moving. In addition, other criteria
such as external noise sources which may interfere with the speed sensor output should be considered in order to
achieve optimal performance.
Application Considerations
Magnetic speed sensors are typically incorporated into tachometers or used as gear tooth speed sensors. Industries
that use a wide range of speed sensors include automotive, turbine flowmetering, aerospace, and rail and transit.
Each industry has its own unique characteristics and requirements. Many times, speed sensors used in the automotive
industry will be epoxy encapsulated, while those in aerospace may be hermetically sealed for resistance to moisture
and environmental conditions. In applications such as the rail and transit industry, the magnetic speed sensor is
oftentimes mounted on the underside of the rail car, so it is designed with special cables and tubing to protect the
sensor from damage. Explore the different types of magnetic speed sensors:
For more information regarding magnetic speed sensor design and selection, please contact
us at eng@motionsensors.com or 252-331-2080. |
