Eddy Current Linear Position Sensors

Eddy current linear position sensors use a reference coil to produce a magnetic field in a target and monitor the field in an adjacent sensing coil to determine distance from target. As the target gets closer to the sensor, the magnetic field gets disrupted and this is sensed by the second coil. They also measure variations in the field due to the presence of nearby conductive objects. Field generation and detection information is provided in the kHz to MHz range. Because eddy current linear position sensors operate by their magnetic field being interrupted, it is possible to have magnetic or nonmagnetic targets, ferrous or nonferrous.

The most important specification for eddy current linear position sensors is the range they are to measure.  Another important specification is sensing frequency. Sensing frequency is the frequency range over which the device operates. Also important is static resolution. Resolution is the smallest increment of the quantity that can be recognized. It tells you how much change in a quantity is required for the sensor to detect the change. For very small changes in position you would want a sensor with a very tight (small) resolution. Nonlinearity is deviation from a purely linear response in the measuring region; lower linearity deviation values denote more accurate reading throughout the measuring range. Temperature compensation, another important specification, is the ability to maintain output stability during fluctuating or changing ambient temperature conditions.

Electrical output can be digital, computer signals, whether parallel or serial, or analog voltage, current or frequency. Eddy current linear position sensors can have such features as shielding, weld field immunity and ratings for intrinsic safety. Weld fields are similar to EMI/RFI noise. These devices can be as simple as a raw sensor element, a sensor/transducer, a gauge with only visual and no electrical output or as complex as an instrument with local displays and controller functionality.

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