Gate Functions - Siemens FM 450-1 Equipment Manual

Periodic counting
For periodic counting the respective counter starts from the load value. If when counting up the
counter reaches the high count limit and further count pulses come, then the counter jumps to
the load value and starts totalizing the count pulses.
Upper count limit
Load value
Lower count limit
Figure 2-3
If when counting down a counter has reached the low count limit and a further count pulse
comes, then the counter jumps to the load value and then continues counting down from there.
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:
Counter module FM 450-1
Equipment Manual, 03/2022, A5E03648739-AC
Counter status
Periodic counting in the up direction
This is how the FM 450-1 counts
2.2 Gate functions
Time
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