Automating Manufacturing Systems - Process Control and ...

plc timers - 9.11
go
TON
t_1
delay 4 sec
go
RTO
t_2
delay 4 sec
go
TOF
t_3
delay 4 sec
go
RTF
t_4
delay 4 sec
t_1.DN
done
reset
RES
t_1
reset
RES
t_2
reset
RES
t_3
reset
RES
t_4
Figure 9.11
A Timer Example
A timing diagram for this example is shown in Figure 9.12. As input go is turned
on the TON and RTO timers begin to count and reach 4s and turn on. When reset becomes
true it resets both timers and they start to count for another second before go is turned off.
After the input is turned off the TOF and RTF both start to count, but neither reaches the
4s preset. The input go is turned on again and the TON and RTO both start counting. The
RTO turns on one second sooner because it had 1s stored from the 7-8s time period. After
go turns off again both the off delay timers count down, and reach the 4 second delay, and
turn on. These patterns continue across the diagram.
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