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MAGNETIC AND OPTICAL MEASUREMENT PRINCIPLES

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MAGNETIC AND OPTICAL MEASUREMENT

Principles of magnetic measurement

Magnetic rotary encoders determine angular position using magnetic field sensor technology. A permanent magnet

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attached to the encoder shaft creates a magnetic field

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which is sampled by a sensor which then generates a single absolute position reading.

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Signal processing: the key to high performance

The technological leap that propels POSITAL’s IXARC magnetic encoders to the level of optical system performance is based on a new generation of these sensors. A customized Hall effect sensor associated with a complex signal processing device via a powerful 32-bit microprocessor, which allows to obtain a result, in resolution and in precision, considerably increased, with latency times of only a few microseconds. POSITAL has also implemented an incremental interface which makes it possible to cover the full range of its encoder offer.

Multiturn innovation

POSITAL IXARC multiturn rotary encoders use innovative technology to keep track of the number of rotations the encoder has made, even if they occurred when the system was not powered. To do this, the encoders generate electrical energy from the rotation of the shaft thereof. This technology is based on the “Wiegand effect”: when a permanent magnet rotates on the encoder shaft at a certain angle, the magnetic polarity of the “Wiegand wire” changes suddenly, inducing a brief voltage peak in a coil. surrounding the wire. This pulse marks a rotation of the shaft and supplies the electrical circuit which registers the event. The Wiegand effect occurs reliably even in very slow rotations and does not require backup batteries.

Advantages of magnetic encoders

  • Robust and durable
  • Mechanically simple and economical: no battery or gear
  • Compact design for installations in confined spaces
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Advantages of magnetic encoders

Principles of measurement

A key component of optical encoders is the encoder wheel

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mounted on the encoder shaft.

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This wheel is made of a transparent material that features a concentric pattern made up of transparent and opaque areas. Infrared light produced by LEDs

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shines through the encoder wheel on an array of photoreceptors.

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As the shaft spins, a unique combination of photoreceptors is illuminated or not depending on the pattern present on the wheel. For multiturn models, an additional set of encoder wheels is organized into a gear train.

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As the main encoder shaft rotates, these wheels are assembled together to spin like the wheels on an odometer. The position of each wheel is optically monitored and the result is a count of the whole number of rotations of the encoder shaft

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Principles of measurement

Features

POSITAL IXARC optical rotary encoders use highly integrated Opto-ASICs that provide resolution up to 16 bits (65,536 steps) per revolution, with incremental signals. For multiturn models, the measuring range is extended by the mechanical gear encoder wheel up to 16,384 revolutions.

Advantages of optical encoders

  • High resolution and precision with excellent dynamic response
  • For use in areas subject to strong magnetic fields
  • No risk that these devices lose their absolute position
  • No spare battery needed

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