1. PLC Concepts Example 8 - Oscillating Circuit An oscillating circuit with cycle ΔT+ΔT Y1 Y1 Y1 T T In the first scan, Y1 turns on. In the second scan, Y1 turns off due to the reversed state of contact Y1. Y1 output status changes in every scan and forms an oscillating circuit with output cycleΔT(ON)+ΔT(OFF) Example 9 – Oscillating Circuit with Timer An oscillating circuit with cycle nT+ΔT X0 Y1 X0 T0 Y1 Y1 When X0 = ON, T0 starts timing (nT). Once the set time is reached, contact T0 = ON to enable Y1(ΔT). In next scan, Timer T0 is reset due to the reversed status of contact Y1. Therefore contact T0 is reset and Y1 = OFF. In next scan, T0 starts timing again.
The process forms an oscillating circuit with output cycle nT+ΔT. T T n Example 10 - Flashing Circuit The ladder diagram uses two timers to form an oscillating circuit which enables a flashing indicator or a buzzing alarm. n1 and n2 refer to the set values in T1 and T2 and T refers to timer resolution. T2 X0 T n2 T1 Y1 Example 11 - Trigger Circuit In this diagram, rising-edge contact X0 generates trigger pulses to control two actions executing interchangeably. Y1 T n1 M0 X0 X0 Y1 Y1 M0 T M0 Y1 M0 Y1 Example 12 - Delay OFF Circuit If X0 = ON, timer T10 is not energized but coil Y1 is ON. When X0 is OFF, T10 is activated.
After 100 seconds (K1000 Ч 0.1 sec = 100 sec), NC contact T10 is ON to turn off Y1. Turn-off action is delayed for 100 seconds by this delay OFF circuit. X0 Timer Resolution: 0.1 sec Y1 100 seconds 1-15 TMR T0 Kn X T X TMR T1 Kn1 TMR T2 Kn2 TMR T10 K1000 T10 Y1 TMR T10 K1000