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Magnetic encoders now a viable alternative to optical encoders

27 July 2014

Recent improvements in accuracy and response times for the latest magnetic encoders mean that they are now a viable alternative to optical encoders in an increasing number of applications.

Until recently magnetic absolute rotary encoders typically offered accuracies of up to 1° to 0.5°, a maximum resolution of 12 bits, and cycle times over 600µs. Whilst reasonable, these values are often far exceeded by optical technology and for this reason, applications with more stringent requirements in terms of accuracy and dynamic range have used mainly optical rotary encoders.

However, tough environmental conditions such as dirt, vibrations, or extreme temperatures present major challenges for optical rotary encoder technology.  

To combine the high precision and broad dynamic range offered by optical rotary encoders with the value-added factors, extreme robustness, and compactness of magnetic rotary encoders, the engineers at Pepperl+Fuchs are developing magnetic rotary encoders to redefine the boundaries of technical feasibility. Boasting accuracies of up to 0.1°, a resolution of up to 16bits, and a cycle time of < 100µs, these encoders are taking flexibility and performance to new heights.

Absolute rotary encoders based on a magnetic detection principle have been part of the Pepperl+Fuchs product range for a number of years. Developed specifically for use in harsh environments, these encoders demonstrate their performance even in the most adverse application scenarios, such as in offshore wind turbines or in the mobile equipment industry.

The key advantage of magnetic rotary encoder technology is its noncontact detection principle, which means no mechanical gears to wear or incur maintenance and service costs. This technology, which is not subject to environmental influences, delivers reliable measured values. 

Pepperl+Fuchs absolute rotary encoders are based on a magnetic detection principle and use a two-axis Hall sensor, which generates a sine or cosine signal via a rotating magnetic field. This signal is processed via an internal processor that compares the process value with the output value of an absolute rotary encoder with optical scanning. This internal processor enables unique, compact single-turn absolute rotary encoders to be created in small construction volumes.

Combined with an additional Wiegand sensor, these single-turn absolute rotary encoders are converted into multi-turn absolute rotary encoders. A permanent magnetic field that is made to rotate by the Wiegand sensor generates a change in the direction of the magnetic field in the core of the Wiegand sensor, and in turn an induction voltage in the coil wrapped around the sensor. Energy is therefore always available during a change in the direction of the magnetic field, i.e., twice per revolution. This energy is used to electronically count the revolutions and to power the electronics

 An internal battery for supplying power to the electronics is not required. The rotary encoders supplied by Pepperl+Fuchs are therefore not affected by voltage failures. No data is lost and all position values are available after rebooting. The noncontact and non-wearing Wiegand sensor is therefore instrumental in increasing reliability and in reducing maintenance and service work.

In addition to high reliability and a long service life, multi-turn sensing technology enables more compact designs compared to conventional technology thanks to the Wiegand effect. The integrated Wiegand sensor replaces delicate mechanical gears, saving on the space required for these gears. This sensor enables the creation of uniquely compact absolute value encoders. The advanced magnetic field technology of these encoders is accommodated in small housings of 36 millimetres and up.

"Robust and compact magnetic rotary encoders are being developed predominantly with regard to electronics, using highly-precise production methods," explains Stefan Horvatic, the product manager responsible at Pepperl+Fuchs Drehgeber GmbH in Tuttlingen, Germany. In relation to these encoders, he alludes in particular to the state-of-the-art 14-bit Hall sensors, optimized magnet technology, and special software modifications that permit accuracies of up to 0.1° with multi-turn resolutions of up to 16 bit.

In a new range of magnetic absolute rotary encoders with accuracies of 1° to 0.1°, Pepperl+Fuchs will in future offer rotary encoder technology that delivers new prospects for general machine engineering scenarios and plant automation. Optimized precision and performance keep processes current, even in difficult industrial environments involving high loads. In this way, the revolutionary magnetic rotary encoder technology improves production reliability.

What's more, these rotary encoders ensure improved efficiency with performance matched to the application in question—not least because the sophisticated magnetic technology virtually eliminates maintenance and service costs, and prolongs the encoder's service life even in dusty, dirty environments and at extreme temperatures. Even in applications where compact housing designs play a role, magnetic absolute rotary encoders are opening up a surprising wealth of new potential uses, regardless of the sector.

The development of magnetic rotary encoder technology by Pepperl+Fuchs takes flexibility and performance to new heights for machine engineering and plant automation. Extremely precise, robust, and exceedingly compact, this revolutionary technology ensures greater process reliability and efficiency in all industrial environments through the implementation of custom modifications. 

Typical positioning tasks in automation require a high degree of accuracy, as well as high resolution and fast response. This, in turn, defines the requirements for devices that measure rotational movements, angular speeds, or the positions of moving parts. Rotary encoders are used in practically every area of general machine engineering or industrial automation.

Increasingly challenging environmental conditions, the trend for smaller and smaller housing designs, and growing demands on process reliability are shifting the focus to features, such as compactness, robustness, maintenance costs, and service life. Requirements for which non-contact magnetic detection principles offer the ideal opportunity for adding value. 


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