Pneumatic Pressure Control Using on-off Valves with Pulse Width Modulation

Servomotor-controlled valves are widely used in industry for pressure control of pneumatic systems. However, as a first stage, they can cause significant hysteresis that can result in loss of pressure or flow control accuracy at the second stage level. To reduce this effect and improve accuracy, a possible solution relies on the use of on-off switching valves controlled by Pulse Width Modulation (PWM). This approach is studied, firstly by analytically determining how the PWM parameters have to be tuned according to the on-off valve characteristics, secondly by ensuring that these characteristics provide the desired behavior of the system, and finally by experimentally verifying whether the PWM control can successfully reduce hysteresis, without decreasing the application range.