Image Credits: Keyence and Panasonic
High performance, noncontact, eddy current linear position sensors measure the position and motion of conductive targets.
How Eddy Current Linear Encoders Work
These sensors use a reference coil to produce a magnetic field in a target. As the target gets closer to the sensor, the sensor and target magnetic fields distort each other. The image below shows the fields.
Image Credit: Lion Precision
This video illustrates the operation:
Video Credit: National Instruments
Types of Eddy Current Linear Encoders
Although they sometimes share the “inductive” designation, eddy current sensors should be distinguished from inexpensive inductive sensors. The latter sensors, such as those used in inexpensive proximity switches, are not suited to precision metrology applications. In contrast, eddy current sensors have very linear outputs, high resolution, and are stable with temperature.
Specifications and Features
Range of measurement varies (e.g. 0.04 to 0.62 inches).
Sensing frequency can vary (e.g. at least 3 to at least 34 kHz).
Static resolution (e.g. better than 6.5E-7 to better than 9.6E-5) indicates much change in a quantity is required for sensor detection.
Nonlinearity (e.g. better than 5% to better than 0.5%) indicates the deviation from a purely linear response in the measuring region. Lower deviation values denote more accurate reading throughout the measuring range.
Output electrical signals can be analog (current, voltage, or frequency) or digital (serial, parallel, or other).
Packaging can be a raw sensor element or a housed transducer. Self-contained instruments or meters display output at or near the device. Gauges/indicators have an analog display and no electronic output.
Devices can tolerate maximum shocks, maximum vibrations, and certain temperature ranges (e.g. -60 to 300°F).
Targets can be magnetic or nonmagnetic, ferrous or nonferrous.
Sensors can be shielded (embedded in metal and not side-sensitive), weld field immune (will not false-trigger in the presence of extreme electromagnetic fields and produced by resistance welders), and/or intrinsically safe (incapable of releasing sufficient electrical or thermal energy to cause ignition of hazardous atmospheric mixtures). They also may have temperature compensation (ignore ambient temperatures).
Eddy current linear encoders have high resolution and are tolerant of dirty environments. They are used to measure position (automation, machine tools, disk drives) and dynamic motion (drive shaft monitoring, vibration measuring).
Related Products & Services
Capacitive Linear Position Sensors
Capacitive linear position sensors are devices that sense position / displacement using capacitance technology.
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.
Photoelectric sensors use emitters and receivers to detect the presence, absence, or distance of target objects.
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.