Designer's Corner

Protensive potentiometer

In harsh environments, output signals from contacting potentiometers can start degrading after only 50 thousand cycles. Thanks to a heavy-duty bearing arrangement and a non-contacting potentiometer design, the Model 155 position sensor achieves a 20-million cycle minimal rotational life. By combining an integrated Hall-effect magnetic-field sensor and a patent pending magnetic circuit, the three-terminal, voltage-output device resolves rotation up to 180° with near-zero-hysteresis capability between shaft position and voltage output.

To generate a 0.5 to 4.5V output, the magnet rotates around a Hall effect IC or Melexis chip at the center of a 7/8-inch diameter metal housing. Standard electrical angles are at 60, 75, 90, 105, 120, 135, and 150°, and standard linearity is 62%. Special linearity to 60.25% can be achieved, and users have the option of programming the potentiometer's voltage-output slope and its offset in order to electronically compensate for tolerance stack-up in mechanisms such as pedal and throttle linkages.

Model 155 requires 5V dc input, but offers a second input voltage option that operates from an unregulated 5.5 to 24Vdc source. Operating temperature range is from -40 to 150C. The sensor is EMC compliant to Class C, 200 V/m to 1 GHz. Typical applications for this position sensor include off-road vehicles, industrial controls, marine equipment, and material handling.

A bronze sleeve bearing supports the stainless steel shaft, and all circuitry and components are encapsulated in epoxy to protect against dirt, dust, lubricants, water, shock, and vibration.

Judy Winner, Spectrol Electronics Corp., 4051 Greystone Dr., Ontario, CA 91761; Tel: (800) 624-8902; Fax: (909) 923-6765; E-mail: jwinner@spectrol.com.   

Ring-bearing sensor

Rotary tables on machine tools typically require a separate measuring system to provide position feedback. Adjacent construction elements for such bearing/measuring system arrangements add to the section height, consume available machining space, and require precision fitting and careful alignment. Series YRTM axial/radial bearing with integral measuring system provides position feedback from a compact bearing unit without such hassles.

A magnetizable galvanic coating made up of several metallic layers is electroplated on the bearing shaft washer to provide a magnetic dimensional scale. As the scale moves, two diametrically opposed magnetoresistive sensors on the measuring heads detect the small magnetic fields and generate 90° phase-shifted sine signals with 500(micron)m cycle lengths. An electronic evaluation system uses vector addition to calculate the effective angle value and provides 1 Vss output signals.

Although the angle measuring system measures incrementally, another magnetic track applied every 15° provides absolute reference when the sensor moves over two adjacent references. The integral design achieves high positional accuracy of a few angular seconds, saves on overall installation space and cost, and is available in 200-, 260-, and 325-mm bore diameters.

Scott Hart, INA Corp. U.S.A., 308 Spring Hill Farm Rd., Fort Mill, SC 29715; Tel: (803) 548-8500; E-mail: hartsot@usa.ina.com.