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A home position limit switch is a mechanical device that is usually not repeatably accurate enough for the application.The encoder reference or marker pulse has much greater repeat accuracy and is therefore a better reference point to establish a starting point for subsequent measurements. The home limit switch is required to signal the control that the next marker pulse signal received is "Home" in multi-turn encoder applications. Typical Marker Pulse Applications A unique shaft position can be identified by using the reference pulse output only, or by logically relating the reference pulse to the A and B data channels. Thus it is most frequently used in positioning and motion control applications as an electronic starting point of known position (a "reference" pulse) from which counting or position tracking begins. In long travel or multiple turns of the encoder, the reference pulse is sometimes used by the control to initiate an electronic check on the total count received from the encoder. For example, each time a reference pulse is received by the control, the total count received from channels A and B should be an even multiple of the encoder's pulses per revolution.
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The reference pulse (sometimes called a Marker or Index Pulse) is a once-per-revolution pulse that occurs at precisely the same mechanical point in a 360° revolution of an encoder shaft. The pulse appears on an output separate from the specified pulse train. The duration of the reference pulse is usually the same pulse width as the output pulse. However, the reference pulse width may be different and is dependent on the specific encoder design.
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