Although most engineers are familiar with non-contact eddy current displacement sensors, this article acts as a useful checklist of the factors that should be considered before specifying a sensor, as well as the benefits and limitations of this measuring principle.
The eddy current measuring principle occupies a unique position among inductive measuring methods. The principle is based on the extraction of energy from an oscillating circuit. This energy is required for the induction of eddy currents in electrically conductive materials. A coil is supplied with an alternating current, causing a magnetic field to form around the coil. If an electrically conducting object is placed in this magnetic field, eddy currents are induced, which form a field according to Faraday‘s induction law. This field acts against the field of the coil, which also causes a change in the impedance of the coil. This impedance can be calculated by a controller, which looks at the change in the amplitude and phase position of the sensor coil.
There are several distinct advantages of using eddy current measurement sensors. First, measurements are made on a non-contact basis and so are wear-free. Second, the principle offers high precision, high resolution and high temperature stability. The sensors can also be used on both ferromagnetic and non-ferromagnetic materials. The sensors also perform at high speed if required, with some sensor suppliers offering measurement speeds up to 100kHz. With high measurement accuracies and frequency response times, together with an extremely robust design, eddy current sensors enable measurements to be made in tasks where conventional sensors have reached their performance limits.
Eddy current sensors also perform well in demanding, harsh industrial environments where oil, dirt, dust, high pressures and high temperatures are present. Some suppliers, for example, offer robust eddy current sensors with increased protection (to IP67) for harsh environments and pressure-resistant versions that withstand pressures up to 2,000 bar.
It is also important to look for a supplier that offers …..
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