What is meant by Rotary Incremental Encoder Index Pulse "Gating"?
May 7, 2020
An INDEX PULSE is a digital signal generated from an incremental encoder on an individual output channel, once per revolution. This unique pulse may be used for several purposes:
- In conjunction with a counter, it can be used to track the total number of shaft rotations.
- It may be used to reset a counter if it must be reset to zero once per encoder shaft revolution.
- Most commonly, it is used in servo motor applications that require total system synchronization. It is in effect a position verification pulse used to ensure that sensor feedback, motor controller and the related equipment are all working together properly to control speed, acceleration or the position once per revolution.
- The pulse can be used to return a system to a known physical alignment position.
- The pulse can be used to improve encoder and system accuracy.
The width of the index pulse, also referred to as the Z channel, relative to the A and B channels can vary from 360 electrical degrees 90 electrical degrees. An index pulse should never be wider than two rising edges of either the A or B channel pulses.
An ungated index is the widest option for an index pulse. This pulse is typically referred to as 360 electrical degrees and has a maximum width of 540 electrical degrees.
A gated index pulse is used to improve system accuracy but also requires the system to be able to read the Z channel at a faster rate. Gating is the truncating of the Z pulse’s width. Gating comes in either 180 or 90 electrical degrees. Users have many options how the Z pulse is gated to the A and/or B channels. Index gated to 180 degrees is either linked to A or B in their high state or to A or B in their low state. Index gated to 90 degrees has the options of gating Z pulse to A and B in their high state or A and B in their low state.
