Magnetostrictive transducer with digital interface

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June 2005 Sensors & Transducers

Balluff GmbH has further developed its magnetostrictive, wear- and maintenance-free BTL6 series transducers for use on injection moulding machines by introducing a version with the digital P-111 interface. This gives the user the functionality of a magnetostrictive displacement sensor with a fieldbus interface, but at a significantly lower price and without any of the disadvantages.

The new universal pulse interface combines not only the functions of the Balluff P and M interface, but for the first time uses DPI/IP (digital pulse interface/integrated protocol) for bi-directional communication between the controller and the transducer. Thanks to 'plug-and-play' there is no more time-consuming, error-prone manual entering of the sensor parameters. The matching high-speed controller, the C-DIAS programmable controller module, is supplied by Sigmatek GmbH & Co. KG from Austria.

Each time the injection-moulding machine is started up, the serial number, ultrasonic gradient, manufacturing date and the stroke length of the transducer are checked to ensure the proper transducer is connected. The active travel zone can be stored in the controller, so that an 'out of range' error message is output as soon as the magnet is moved out of the zone.

Both the machine builder and the end user benefit. The time-consuming and error-prone manual entry of sensor parameters (when the machine is first placed in service or when a transducer is replaced) is now eliminated. By unscrewing the transducer, connecting the cable, the system is ready to go again.

If there are several moves associated with a single axis, the BTL6 can be equipped with multiple magnets to detect several position changes at one time. All that is needed is the appropriate mechanical linkage accommodated in the machine design.

Rugged and precise

With a resolution of <10 µm and repeatability of < 20 µm the Micropulse AT exceeds all the requirements placed on transducers in injection moulding machines. The same applies to the non-linearity of just 200 µm at a nominal stroke length of 500 mm, or 0,02% of full scale at lengths over 500 mm.

BTL6 transducers with IP67 protection consist of an hermetically sealed, round extruded housing made of anodised aluminium, protecting the waveguide from exposure to contamination and moisture and providing a high degree of shock and vibration resistance. The measuring point is marked by a non-contacting magnetic element attached to the moving member of the machine, with stroke lengths of between 50 mm and 1,5 m available.

The transducers with the digital P-111 interface are insensitive to external magnetic fields, making them quite suitable for use on high-precision injection moulding machines - such as those used for manufacturing DVDs - in production locations outside of Europe with their current fluctuations and voltage spikes in the AC supply network.

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Magnetostrictive transducer with digital interface

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