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General/Basics

Rotary Measuring Technology – Incremental Encoders

Number of channels:Encoders with one output channel Encoders with one output channel are usedwhere no direction sensing is needed, e.g. Encoders with two output channels Applications, where the direction of a rota-tion should be sensed, e.g. positioning, require encoders with two channels A andB being shifted 90° out of phase. By detecting the phase shift, the directioncan be located. • Shaft turning clockwise, top-view of shaft• Inverted signals available • 0-pulse is linked to AND with channel Aand Btr = rise time tf = fall time speed control or length measuring.
90° + 20° Encoders with three output channels In addition to the two channels A and B there is a zero signal available, that appears once per turn. This can be used e.g. as areference signal during the first revolutionafter power up. • Shaft turning clockwise, top-view of shaft• Inverted signals available • 0-pulse is linked to AND with channel Aand Btr = rise time tf = fall time
90° + 20° Multiplication of pulses: The resolution of a two channel encoder can be multiplied by two or four using a special edge detecting.An encoder with physically 5000 pulses perrevolution can generate 20000 pulses per revolution using this technique. Inverted signals: When used in environments, with a lot ofelectrical noise and/or if very long cable distances are required, we recommend touse encoders with inverted (complementa-ry) signals. These signals are always available with output circuits of the RS 422type and sine wave outputs. Kübler also offers them for push-pull outputs. Resolution: Example: An encoder is equipped with a measuring wheel. Every revolution corre- sponds to a distance of 200 mm (circumfer- ence). The accuracy should be 0.1 mm.What is the required resolution (ppr)?Given:Circumference of the measuringwheel: U = 200 [mm]Accuracy of the system: G = 0.1 [mm]Wanted: Resolution of the encoder: A = ?[pulses/resolution] resolution =CircumferenceAccuracy =UG The required resolution would be 2000 ppr(pulses per revolution).
20 www.kuebler.com 1/2008