Siemens simatic s7-400 FM 450-1, User Manual, Page: 98 / 130

Encoder signals and their evaluation
9.5 Signal evaluation
Counter module FM 450-1
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Manual, 02/2014, A5E03648739-02
24-V pulse encoders without/with direction signal
Encoders such as proximity switches (BERO) or light barriers return only a count signal
which you wire to terminal A* of the front connector.
in additional, you can wire a signal for direction detection to terminal B* of the relevant
counter. If your encoder does not return a corresponding signal, you can wire a
corresponding ID signal you generate within the user program, or use a corresponding
process signal.
The diagram shows the time profile of the encoder signals, and the resultant count pulses
Figure 9-3 Signals of a 24-V pulse generator with direction signal
Programming the encoder inputs
The count direction is defined by programming the encoder inputs. The diagram shows a
change of the count direction based on parameter settings.
Table 9- 2 Count direction determined by input parameters
Programming Terminal B* Count direction
current sourcing, push-pull not wired Up
24 V connected Down
current sinking not wired Down
Short-circuited to ground Up
Set the "24 V pulse and direction" parameter for the selected encoder.
You can not reverse the direction of these count signal by inverting the B* signal.
Note
This type of evaluation may cause the count value to "drift off" at the edges if count signal
oscillates, as all signals are added.