A new linear encoder combines high performance almost equal to that of optical encoders with the lower cost and ruggedness of magnetic models. Engineers at Danaher Controls (Gurnee, IL), who designed the unit, say it is ideally suited for applications using linear motors.

Known as the LR/LS Inductive Linear Encoder, it employs a unique sensing method. Unlike magnetic encoders, which sense magnetic targets, Danaher's magneto-resistive sensors detect the variable reluctance of a target. As a result, the unit senses the presence or absence of metal in a magnetic field.

Because it uses the unique inductive technique, the LR/LS offers sensing resolution of up to 0.25 microns (0.00001 inch) for sine/cosine outputs, and up to 5 microns (0.0002 inch for quadrature outputs. At the same time, it offers the lower cost and ruggedness of conventional magnetic sensors. Danaher Controls' engineers say that the LR/LS encoder typically costs about one-third as much as competing optical sensors, filling a gap on the price/performance curve.

For that reason, Danaher engineers believe the LR/LS could play an important role in the growth of linear motors. "It's definitely an enabler for linear motor technology," notes Paul Schildhouse, encoder product manager for Danaher Controls. Currently, he says, the speed and positioning capabilities of linear motors are often dependent on the use of high-cost sensors.