Automating Manufacturing Systems - Process Control and ...

plc timers - 9.16
I/1
I/2
I/3
C5:1/DN
CTU C5:1
preset 3
CTD C5:1
preset 3
RES C5:1
O/1
I/1
I/2
I/3
C5:1/DN
O/1
Figure 9.16
A Counter Example
The timing diagram in Figure 9.16 illustrates the operation of the counter. If we
assume that the value in the accumulator starts at 0, then the I/1 inputs cause it to count up
to 3 where it turns the counter C5:1 on. It is then reset by input I/3 and the accumulator
value goes to zero. Input I/1 then pulses again and causes the accumulator value to
increase again, until it reaches a maximum of 5. Input I/2 then causes the accumulator
value to decrease down below 3, and the counter turns off again. Input I/1 then causes it to
increase, but input I/3 resets the accumulator back to zero again, and the pulses continue
until 3 is reached near the end.