rotary encoder A, AB, ABZ

[unsaint32]

I am learning how to use a rotary encoder. Here is how much I know about A, B, Z pulses. Feel free to correct me. AB pulses together are used to indicate angular position (absolute) A:0 B:0 = 0 deg, A:0 B:0 = 90 deg, A:0 B:0 = 180 deg, A:0 B:0 = 270 deg. Am I right? Obviously I do not understand clearly, because a rotary encoder's AB pulses can be up to 2000 pulses per revolution. And what is the Z pulse? Isn't it the incremental pulse? Is it 1 pulse per revolution then? Thanks.

 

[mendonsy]

Making the assumption that you are talking about a rotary encoder, not a linear model .....
The A and B pulses are phased 90 degrees to indicate distance and direction. There can be a large number of pulses (50k for example) per revolution depending on the encoder.
The Z pulse is the zero reference. There is normally (but not always) one Z pulse per revolution.
Here's a good reference:
http://www.beiied.com/news/BEI_industrial_encoders_for-dummies_2nd_Edition.html

 

[bernie_carlton]

Unsaint32, you are asking EXCELLENT questions. Your grasp of one cycle of the A/B pulses is correct.

But now put more end - to - end. Because of the quadrature relationship of the A/B pulses the direction can be determined and sufficiently fast electronics can maintain an accurate count of position, even in the face of possible 1 pulse backward and forward jitter.

The Z pulse is an added assurance that precisely 1 revolution has taken place. The Z pulse usually occurs in sync with the first A pulse of the revolution.

In systems with ABSOLUTELY unidirectional movement then possibly one of the phases is all that's needed. Systems which have major changes in speed and especially those which may change direction need more of the information - A+B, Z.

Have fun with delving into the theory of motion measurement.

 

[unsaint32]

1. Can I somehow change my encoder's number of A pulses per revolution, or it that number fixed?

2. So, each complete revolution should generate one Z pulse? I tried this with a PLC program. I hooked up the Z output to a PLC input, then XIC for the input going to a CTU instruction. When I went online the CTU ACC became 1, and as the motor turned, the ACC stayed at 1. What am I not understanding?

Thanks.

 

[bernie_carlton]

Does the input have an indicator? Does it blink?

If you need specify exactly the encoder, the PLC and a diagbram of your wiring.

And the number of A pulses per revolution is (except in some very expensive models) fixed.