Measuring signals with incremental encoders

Encoders are transducers for rotary movements. In combination with mechanical converters such as gear racks, measuring wheels or threaded spindles, they are also suitable for linear measurements. A pulse is output for each position step.

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During optical conversion, a rotatably mounted "reticle" made of metal, plastic or glass interrupts the infrared light beam of a gallium-arsenide transmitter diode. The number of lines determines the resolution, i.e. the measuring points within one revolution. The interruptions of the light beam are picked up by the receiving element and processed in an electronic unit. At the output, they are available as a square wave signal.

Output signals

The encoders supply two 90° electrically phase-shifted square pulses A and B. In addition, a reference pulse N (zero signal) is generated.

To suppress interference pulses, certain output circuits (RS 422 and push-pull antivalent) generate inverted signals (A, B, N), e.g. with the types RI30, RI 36, RI 58, RI 58-H, RI 58-D, RI 76 TD.

The value between two pulse edges of A and B is defined as the measuring step.

evaluation

In the subsequent electronics, the resolution of a two/three-channel encoder can be doubled or quadrupled. Thus, the resolution of an encoder with 2500 lines/revolution can be electronically increased to 5000 or 10000 pulses/revolution (see sketch below).

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