What PLC Settings Are Needed for Air Actuated Valves?
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In the field of modern industrial automation, air actuated valves are widely used in various fluid control systems due to their simple structure, fast response, and high cost-effectiveness. However, the operation of these valves cannot be separated from the effective control of programmable logic controllers (PLC). As the control center of the automation system, PLC requires a series of settings to ensure that the air actuated valve operates accurately according to process requirements. Therefore, this article will take an in-depth look at the key PLC settings required to drive air actuated valves and the logic behind them.
The most basic setup for controlling the action of a air actuated valve involves the digital output (DO) module of the PLC. The switching of air actuated valves is usually controlled by one or more solenoid valves (Solenoid Valve), which receive signals from the PLC DO point. When the PLC program needs to open the valve, it will drive the corresponding DO point to output an electrical signal. This signal will energize the solenoid valve coil, change the air path, introduce compressed air into one side of the air actuated actuator, and push the valve to open. On the contrary, when the valve needs to be closed, the PLC will cancel the output signal of the DO point, reset the solenoid valve after losing power, cut off or switch the air source path, and rely on spring force or introduce gas to the other side to close the valve. Therefore, in the PLC, the address of the DO point associated with each air actuated valve must be accurately configured, and these output points must be correctly set (Set) or reset (Reset) in the control logic.
Status feedback and confirmation settings
It is not enough to just issue a switch command, the PLC also needs to know whether the valve has actually reached the expected position. This requires a status feedback setup such as a limit switch or position sensor mounted on the air actuated actuator. These sensors are connected to the PLC's digital input (DI) module. When the valve moves to the fully open or fully closed position, the corresponding limit switch closes and sends a signal to the PLC. The addresses of these DI points must be configured in the PLC program and logic must be written to monitor these input signals.
Logic Timing And Delay Settings
In complex industrial processes, the opening and closing of valves often need to be coordinated with other equipment or steps in a specific sequence. The timer and sequence control logic inside the PLC play a key role at this time. For example, before starting a pump, you may need to ensure that its outlet valve is open; or after closing the feed valve of a reactor, you may need to wait for a period of time to ensure that the flow of material has stopped before opening the discharge valve. Therefore, the PLC program needs to set appropriate timers to provide the necessary delays, such as the timeout time to wait for the valve feedback signal after the instruction is issued, or the waiting time between steps in the process flow.
Interlocking And Safety Protection Settings
Safety is the primary consideration in industrial control. The PLC program must contain the necessary interlocking logic to prevent misoperation or operation of air actuated valves under hazardous conditions. Interlock settings are logical conditions defined based on process requirements and safety regulations that determine whether the valve is allowed to operate. For example, a tank's discharge valve may be interlocked, allowing it to open only when the liquid level falls below a certain safe height, or when the downstream processing unit is ready; or, two valves with conflicting functions (such as simultaneous feed and discharge) must be interlocked to ensure that they cannot be opened at the same time. These interlock conditions are written in the PLC program to continuously monitor relevant parameters (such as liquid level, pressure, other valve status, etc.), and forcibly prevent dangerous actions of the valve when the conditions are not met.
Diagnostic And Alarm Handling Settings
The PLC setting should also include diagnosis of the operating status of the air actuated valve and alarm processing of abnormal situations. In addition to the basic timeout failure alarm, the PLC can also monitor the number of valve actions (for predictive maintenance), detect feedback signal anomalies (for example, the fully open and fully closed signals appear at the same time, indicating sensor failure), etc. When any abnormality is detected, the PLC should be able to trigger corresponding alarm information, display it to the operator through HMI, and record event logs to facilitate troubleshooting and analysis.
