Count Signals - Siemens SIMATIC ST-1500 Function Manual

2.3.4 24 V count signals
Count signals of 24 V incremental encoders
The 24 V incremental encoder returns the 24 V signals A and B to the technology module.
The A and B signals are phase-shifted by 90°.
The figure below shows an example of the time profile of the signals of an 24 V incremental
encoder:
The technology module detects the count direction by evaluating the sequence of edges of
the A and B signals. You can specify an inversion of the count direction.
Signal evaluation
The two phase-shifted signals of an incremental encoder are evaluated four times. With
quadruple evaluation, the positive and negative edges of signal A and signal B are
evaluated.
Whether count pulses are generated in an upward or downward direction depends on the
edge direction of the one signal and the level of the other signal in the meantime.
The figure below shows an example of the quadruple evaluation of 24 V count signals:
Count signals of 24 V pulse encoders
The encoder, for example, a proximity switch (BERO) or a light barrier, returns only a count
signal that is connected to the digital input of a counter.
You can count the positive or the negative edges of the signal.
Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG
The basics of counting, measurement and position detection
2.3 Basics of counting (TM Timer DIDQ)
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