How to Select Magnetoresistive Linear Position Sensors and Switches
Image Credits: Balluff Sensors, ifm efector, Measurement Specialties
Non-contact magnetoresistive linear position sensors and switches measure a magnetic object's distance and movement, or whether it has approached within a set distance.
How Magnetoresistive Linear Position Sensors and Switches Work
Magnetoresistance is a material property which reflects its change of resistance when exposed to a magnetic field. These sensors measure the angle direction of a field from the magnet (as opposed to the strength of the magnetic field). They provide an absolute reading from the moment they
are turned on; they do not need to be zeroed to an external reference.
Types of Magnetoresistive Linear Position Sensors and Switches
Anisotropic magnetoresistance (AMR) depends on the angle between the electric current and the magnetization direction. The resistance is maximum when the magnetization direction is parallel to the current direction and minimum when the magnetization is perpendicular to the current.
A giant magnetoresistance (GMR) device consists of two or more layers of ferromagnetic metal separated by an ultra-thin non-magnetic metal spacer. When the magnetic layers are aligned in the same direction, electrical resistance decreases; if the magnetizations are opposing, electrical resistance increases. The 10-15% change in resistance found in GMR far exceeds that of AMR devices.
Tunneling magnetoresistance (TMR) is similar to GMR except that it uses an ultra-thin insulating layer to separate two magnetic layers. Electrons pass from one layer to the other through the insulator by quantum mechanical tunneling. The ease of tunneling (the electrical resistance) is modulated by the angle between the magnetization vectors in the two layers.
Specifications and Features
Device packaging may be a simple transducer or a fully self-contained sensor system.
Body styles include barrel, limit switch, rectangular/block, slot, or ring.
Sensor operating distance varies (e.g., 1.97 to 300 inches) or may be field-adjustable.
Repeatability (e.g., no more than 4 mils) is how quickly the device senses.
Devices can tolerate certain temperature ranges (e.g., -4 to 176 F).
Resistance value range is an indication of the full range of output values expected for the full range of input values.
Resistance tolerance is the "resolution" of the measured resistance value.
Digital interface options are serial, parallel, or other.
Analog, digital, and/or video display options exist.
Controls options include analog, digital, or computer.
Sensors may include a fixed cable, integral connector(s), terminals (screw or clamp down), and/or plastic or metal housing.
Sensors can be shielded (protected against EMI and RFI), weld field immune, short circuit protected, and/or intrinsically safe (cannot cause ignition of atmospheric mixtures).
These sensors boast maintenance-free, wearless operation; large permissible air gaps between sensor and target; precise linear measurement with high resolution; high bandwidth for monitoring dynamic processes; reliable and safe use in difficult operating conditions.
Finding the Right Sensor for Linear Displacement
How Magnetoresistive Sensor Works
Linear Position Sensing Using Magnetoresistive Sensors
Magnetoresistive Sensors for Nondestructive Evaluation
Related Products & Services
Capacitive Linear Position Sensors
Capacitive linear position sensors are devices that sense position / displacement using capacitance technology.
Eddy Current Linear Encoders
Eddy current linear encoders detect the distance from a target by using magnetic fields generated by a reference and sensing coils.
Linear Variable Differential Transformers (LVDT)
Linear variable differential transformer (LVDT) linear position sensors have a series of inductors in a hollow cylindrical shaft and a solid cylindrical core. These devices produce an electrical output proportional to the position of the core
Optical Linear Encoders
Optical linear encoders use fiber optic technology to sense position and displacement.
Optical Triangulation Position Sensors
Optical triangulation position sensors use reflected waves to pinpoint position and displacement. The source of these waves may be a light emitting diode (LED), infrared (IR) light, or laser.
String Potentiometers are used to measure the movement and displacement of objects. A cable or wire is attached to an object, and as the object moves, the transducer produces an electrical signal proportional to the wire's linear extension.
Ultrasonic Linear Position Sensors and Switches
Ultrasonic linear position sensors and switches use ultrasonic waves in combination with light and frequency readings for position and displacement sensing.