Displacement sensors use magneto-inductive technology

Paul Boughton

Micro-Epsilon is introducing an innovative range of displacement measurement sensors that combine the robustness and proven measurement performance of eddy current sensor technology with the latest printed coil and permanent magnet technologies. The new Mainsensors family of magneto-inductive displacement sensors not only benefits from having an extremely compact design relative to the measuring range, but the sensors also offer designers an attractive price-performance ratio for mid- to high-volume applications.
At the core of this new sensor technology is Micro-Epsilon's proven eddy current sensor technology, which provides the new sensor with robustness, high speed and high-resolution measurements. However, it is how Micro-Epsilon has applied and combined this proven technology to the new sensor that provides users with several technical advantages. As well providing a new, simplified displacement measurement technique, the new sensor also offers extremely high basic sensitivity and excellent temperature stability (low thermal drift).
Chris Jones, Managing Director at Micro-Epsilon (UK), comments: "The magneto-inductive sensor was originally developed by Micro-Epsilon as a high-volume, low-cost solution for load detection in washing machines. Since then, the technology has been developed further, resulting in an industrial-grade family of standard displacement measurement sensors which will prove invaluable in many mid-to-high volume OEM applications, including hydraulics, automotive, off-highway vehicles and special-purpose machines.
"Due to simplified electronics, Micro-Epsilon is now able to produce low-cost versions of the sensor with printed circuit boards and basic analogue outputs, or we can combine this version with a microprocessor to create a digital output sensor, including PWM, Canbus and other digital interfaces. The electronic circuit design and production is undertaken in-house at Micro-Epsilon's PCB production facility, allowing full design flexibility of the electronic layout combined with complete quality control over the product. This enables Micro-Epsilon to offer a genuine competitive advantage to its customer base. We now have in-house capabilities to produce more than three million sensors per year."

Micro-Epsilon is keen to point out that Mainsensor is not a Hall-effect sensor, as Jones explains: "Although the new sensor uses a permanent magnet as the target, unlike Hall-effect sensors, it does not suffer from relatively low sensor accuracy or high-temperature drift."
In contrast to the Hall-effect, the Mainsensor uses Micro-Epsilon's patented measuring method that is based on a linear relationship between the position of the permanent magnet and the output signal.
The underlying functioning principle of the sensor is based on a coil that is supplied with alternating current, resulting in a primary magnetic field. According to the Maxwell formula, this magnetic field induces eddy currents in the electrically conductive material arranged opposite the coil. In the field of the eddy current sensor is a special film that attenuates the eddy current sensor, depending on the strength of the magnetic field. Using this method, a linear relationship can be established between the distance to the magnet and the output signal. As printed coils can be used inside the sensor, manufacturing does not rely on any semiconductor processes.
Thomas Birchinger, Mainsensors product manager at Micro-Epsilon, describes the benefits of the new technology: "The sensor has an extremely high basic sensitivity, which enables a very simple and consequently low-cost evaluation circuit. With an eddy current sensor as the technological core, both very fast and very high resolution versions of the sensor can therefore be produced. A pulse width modulated signal is available as an output signal, which can be easily read by a microcontroller using a time measurement, which opens up a wide range of potential applications."
The first standard industrial sensor in the Mainsensors family is the MDS-40 M30, which has a 40mm measuring range and an M30 cylindrical, barrel-type stainless steel housing. The alternative to this is the OEM version, the MDS-40MK, a miniature flat rectangular PCB version with a plastic housing and a 40mm measuring range. The signal output provides 4-20mA or 2-10V DC.
For more information, visit www.micro-epsilon.co.uk