Automating Manufacturing Systems - Process Control and ...

plc timers - 9.11
I/1
TON T4:1
delay 4 sec
I/1
RTO T4:2
delay 4 sec
I/1
TOF T4:3
delay 4 sec
I/1
RTF T4:4
delay 4 sec
T4:1/DN
O/1
I/2
RES T4:1
I/2
RES T4:2
I/2
RES T4:3
I/2
RES T4:4
Figure 9.11
A Timer Example
A timing diagram for this example is shown in Figure 9.12. As input I/1 is turned
on the TON and RTO timers begin to count and reach 4s and turn on. When I/2 becomes
true it resets both timers and they start to count for another second before I/1 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 I/1 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
I/1 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.