Encoder Signals; 24 V And Ttl Count Signals - Siemens SIMATIC ST-1500 Function Manual

2.2 Basics of counting, measuring and position input (TM Count, TM PosInput, Compact CPU)
2.2.13

Encoder signals

2.2.13.1

24 V and TTL count signals

24 V and TTL incremental encoder count signals
The 24 V incremental encoder returns the 24 V signals A, B, and N to the technology
module. The A and B signals are phase-shifted by 90°. You can also connect incremental
encoders without an N signal.
A 24 V incremental encoder uses the A and B signals for counting. If configured accordingly,
the N signal is used for setting the counter to the start value or for saving the current counter
value to the Capture value.
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.
24 V and TTL pulse encoder count signals without/with direction signal
The encoder, for example an initiator (BERO) or a light barrier, returns only a count signal
that is connected to terminal A of the counter.
In addition, you can connect a signal for direction detection to terminal B of the counter. If
your encoder does not return a corresponding signal, you can specify the count direction
with the user program using the control interface.
The figure below shows an example of the time profile of the signals of a 24 V pulse encoder
with direction signal and the resulting count pulses:
Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG
The basics of counting, measurement and position detection
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