Analysis and Modeling of State-Dependent Delay in Control Valves

Pneumatic control valves are deployed in a wide variety of industrial applications and plants. The plethora of valve applications has a great span in required operational accuracy and time scales, from precise medical dosing valves to large valves used for level control in offshore separation tanks. It is common for these valves to have inherent position control deployed by the manufacturer, and as a result, these valve systems often receive a wanted opening degree, where the inherent position control drives the actual valve opening towards the wanted opening degree. From previous works utilizing pneumatic control valves for offshore produced water treatment, an inconsistent input-output delay was observed. This work presents experiments to detect and describe these delays, such that the model may be incorporated in the design of improved control solutions that account for these behaviors. A pin-cart model with state-dependent delay is proposed, validated using data from a continuously actuated valve, and compared to commonly used existing valve models. The proposed model exerts the state-dependent input-output delay successfully.