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Automating Manufacturing Systems - Process Control and ...

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continuous sensors - 23.6<br />

sensors read across<br />

a single radial line<br />

relative encoder<br />

(quadrature)<br />

absolute encoder<br />

Figure 23.4<br />

Encoder Disks<br />

When using absolute encoders, the position during a single rotation is measured<br />

directly. If the encoder rotates multiple times then the total number of rotations must be<br />

counted separately.<br />

When using a relative encoder, the distance of rotation is determined by counting<br />

the pulses from one of the rings. If the encoder only rotates in one direction then a simple<br />

count of pulses from one ring will determine the total distance. If the encoder can rotate<br />

both directions a second ring must be used to determine when to subtract pulses. The<br />

quadrature scheme, using two rings, is shown in Figure 23.5. The signals are set up so that<br />

one is out of phase with the other. Notice that for different directions of rotation, input B<br />

either leads or lags A.<br />

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