Siemens FM 450-1 - Page 18

Continuous counting
If when counting in the up direction a counter has reached the high count limit and a further
count pulse comes, then the counter jumps to the low count limit and begins to total the count
pulses; thus, it counts continuously.
Counter status
Time
Lower count limit
Upper count limit
Figure 2-1 Continuous counting in the up direction
If when counting in the down direction a counter has reached the low count limit and a further
count pulse comes, then it jumps to the high count limit and then goes on counting down from
there.
Single counting
For single counting the counter starts from the load value. If when counting up a counter has
reached the high count limit and a further count pulse comes, then the counter jumps to the low
count limit and comes to a halt even if further count pulses come.
Counter status
Time
Load value
Upper count limit
Lower count limit
Figure 2-2 Single counting in the up direction
If when counting down a counter has reached the low count limit and a further count pulse
comes, then the counter jumps to the high count limit and comes to a halt even if further count
pulses come.
This is how the FM 450-1 counts
2.1 Basics
Counter module FM 450-1
18 Equipment Manual, 03/2022, A5E03648739-AC