Siemens simatic s7-400 FM 450-1, Руководство пользователя, Страница: 22 / 130

This is how the FM 450-1 counts
2.2 Gate functions
Counter module FM 450-1
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Manual, 02/2014, A5E03648739-02
2.2 Gate functions
Counting with gate functions
Many applications require that the counting process should be started or stopped at a
specifically defined point in time, depending on other events. In the case of the FM 450-1
starting and stopping the counting process like this take place via a gate function. If the gate
is opened, count pulses can reach a counter and the counting process is started. If the gate
is closed, count pulses can no longer reach the counter and the counting process is stopped.
Software gate and hardware gate
The module possesses two gate functions for each counter:
● A software gate (SW gate) which is controlled via the user program in the CPU.
● A hardware gate (HW gate) that is controlled via the 1I0 and 1I1 (counter 1) and/or 2I0
and 2I1 (counter 2) digital inputs on the module. When assigning parameters for the FM
450-1 you determine if the operation of the hardware gate is to be level controlled or edge
controlled.
Example
When the gate signal is set, the gate is opened and the count pulses are counted. If the gate
signal is taken away, the gate is closed and the count pulses are no longer picked up by the
counter. The counter status remains constant.
The figure shows a gate opening and closing and the pulses being counted:
Figure 2-4 Opening and closing a gate
Ending counting process with the gate stop function
You can end the counting process when counting with the SW gate and when counting with
the HW gate with the respective gate stop function. For this purpose you set the GATE_STP
input parameter of the FC CNT_CTRL.