eddylab GmbH is a specialist in the field of high-precision measurement technology for linear displacement measurement and offers you detailed information about sensor technology.
This page explains the functionality of digital scales based on the magnescale principle. The sensors are mainly used in machine tools and in industrial applications with highest demands on accuracy and reliability. At the same time, they must be resistant to machine vibrations, coolants and lubricants, and contamination by chips. The devices guarantee the highest accuracy unaffected by temperature fluctuations and are extremely resistant to external interference fields caused by servo drives.
Digital Scales based on the magnescale principle have MR elements that operate according to the GMR (giant magnetoresistance) effect. The MR elements change their electrical resistance depending on the strength and direction of the magnetic field strength (flux density) of an external magnetic field.
The external magnetic field is formed by a permanently magnetized neodymium-iron-boron scale with alternating north-south pole division, which is guided past the MR elements by the external movement of the probe.
The resistance change in the MR element is based on the deflection of the direct current path by the magnetic field strength (flux density) due to the Lorentz force. Due to the magnetic field strength, the current does not flow in a straight line through the element on the shortest path, rather it runs in zigzag lines, which have an increased path and thus higher resistance. To produce a high change in resistance and thus high sensitivities of the MR elements, the individual MR elements of the Magnescale sensors are made of bismuth. This is a highly diamagnetic metal with the largest resistance change (over 100%) due to external magnetic fields compared to all elements. This allows highly accurate measurement of flux densities in the range of 0.0001...5 mT. Bismuth MR elements are therefore particularly well suited for sensor technology.
The three MR elements are arranged in such a way that the guided movement of the scale at the MR elements produces three sinusoidal signals offset by 120°. Simultaneous evaluation of the sine signals allows the direction of movement to be detected and particularly effective error correction (amplitude, phase and offset errors) to be performed. This guarantees maximum accuracy in the submicrometer range and offers significant advantages over conventional systems with only two sinusoidal signals offset by 90°.
An evaluation unit interpolates the sine signals to an incremental TTL output signal with specified resolution (transistor-transistor logic).
A cost-effective, simple and robust solution. It offers a resolution of 5 µm and a linearity of 10 µm. The SJ700A can be connected directly to digital multifunction displays.
This robust scale offers a very high resolution of 0.5 µm. The GB-ER provides you with a TTL signal with a good linearity of ±5 µm regardless of the installation situation.