Magneto-inductive displacement sensors feature low thermal drift

First shown at the 2010 Hanover Trade Fair in Germany, and now available in the UK, Micro-Epsilon's mainSENSORs not only benefit from having an extremely compact design relative to their measuring range, but they also offer OEMs 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 technology within 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).

Standard range and customisation

Chris Jones, Managing Director at Micro-Epsilon (UK) Ltd, 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."

Jones is keen to explain that the mainSENSOR is not a Hall-effect sensor: "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."

How it works

In contrast to the widely used Hall-effect measuring principle, 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. Micro-Epsilon produces the complete sensor in-house.

The underlying functioning principle of the sensor is based on a coil, which is supplied with alternating current to establish 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 between the distance to the magnet and the output signal can be established. 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 (PWM) 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."

Industrial sensor

The first standard industrial sensor in the family is the mainSENSORs 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 miniature, flat-profile MDS-40MK PCB version with a plastic housing and a 40mm measuring range. The signal output provides 4-20mA or 2-10V DC.

As Jones states: "Micro-Epsilon does not just manufacture sensors, we have more than 40 years of experience in providing sensor solutions to OEMs, so we understand the importance of providing complete solutions and supporting our customers. Many of the companies we have worked with view us as a consulting, development and application partner that provides sensor solutions for complex, customer-specific measurement, inspection and automation. We do not sell sensor products; we have a firm belief in always selling technical advantage to our customers. The mainSENSOR is a perfect illustration of this."

Follow the link for more information about Micro-Epsilon's mainSENSORs Magneto-inductive displacement measurement sensors.