Electric encoder

by John Lewis, Regional Technical Editor -- Design News, March 11, 2002


Inherently insensitive to magnetic fields and internally shielded againt electrostatic fields, electric encoder technology is also available in two-plate rotary and linear versions.

The Sine/Cosine Rotary Electric Encoder™ relies on the physics of electricity instead of using the magnetic or optic principles applied in most encoders. The design combines both the accuracy and range of optic and magnetic encoders, however it is manufactured using pc-board assembly and injection molding techniques. As a result, it offers a simple, compact package that allows engineers to more easily tailor the sensor to suit the machine in high volume OEM applications that require non-contacting, full-rotation, absolute output at an economical price.

Electric position sensing differs from optic and magnetic sensors in that it uses a dielectric rotor attached to a rotating shaft. As the rotor moves with respect to a stationary, time-modulated, space patterned, field transmitter and stationary field receiver, angular displacement influences a patterned electric field that is continuously measured to provide position feedback. The output is a continuously varying voltage proportional to the sine and cosine of the measured angle.

Instead of using a local read head, as in optical encoders, the electric encoder averages the interaction between the field and the rotor over the whole area of the rotor. Consequently, the speed/resolution trade-off is virtually eliminated up to 30,000 rpm. Moreover, the design is less sensitive to mechanical mounting inaccuracies, vibration (15g @ 0 to 2,000 Hz), temperature (-55 to 125C), and humidity (to 100%, condensing).

Rogerio Marx, Netzer Precision Motion Sensors Ltd., 7550 Kirby Dr., Ste. 812, Houston, TX 77030 ; Tel: (713) 661-3833; Fax: (713) 661-3395; E-mail: netzerdesk@aol.com.

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Submit your ideas and rough drawings for this section to John Lewis, Designer's Corner, Design News, 275 Washington St., Newton, MA 02458

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