10. High-speed Input/Output Design Examples 10.6 PWM - Sprayer Valve Control Program 100% X2 X3 X4 25% 50% X1 START STOP X0 Control Purpose: z Controlling the sprayer valve opening degree as 25%, 50% and 100% by adjusting the t on /t off value of PWM technique (24V) . For reducing the energy lost during the gradual shut-down/start-up process, we apply the switching method which performs immediate turn-on and turn-off of the current valve. The switching method is somewhat like cutting off the current, and is therefore called a Clipper. However, in the practical application we apply a transistor between the power and the motor for representing the function of the clipper.
Pulse signal will be applied to the base of the transistor so as to yield a pulse current between the base and the emitter. The input voltage of motor is in proportion to the t on /t off value. Therefore, the motor voltage could be adjusted by modulating t on /t off value. There are various methods to modulate this value and the most common one is to adjust the ON time (t on ) rather than adjusting the ON times within specified time period. The method is called PWM (Pulse-Width Modulation). Devices: DVP-PLC Application Examples 10-9 Device Function X0 X0 = ON when the button START is pressed X1 X1 = ON when the button STOP is pressed. X2 25% opening button. X3 50% opening button.
X4 100% opening button. Y1 Controlling the opening degree of the valve D0 Storing the valve opening degrees