A signal moves from a Distributed Control System (DCS) to a valve via a number of processes that include signal production, transmission, and actuation. Here’s a thorough breakdown of the procedure:
Signal Generation in DCS
Control Output
The DCS produces a control output signal, usually in the form of a 4-20 mA current loop. This signal indicates the desired position (or) flow rate for the valve. Ex: A 12 mA signal indicates a 50% open state.
Signal Characterization
To verify that the valve responds adequately over its working range, signal characterization can be used within the DCS. This method comprises linearizing the valve’s installed flow characteristic in order to increase control accuracy and reaction time.
Signal Transmission
Wiring
Wiring is used to convey the 4-20 mA signal to the valve actuator, which can be coupled to an electronic positioner or a pneumatic actuator.
Position Feedback
Many systems include feedback mechanisms, which include position sensors on the valve, which send real-time data to the DCS. This feedback enables modifications & corrections in control signals depending on actual valve position against desired position.
Actuation of the Valve
Actuator Response
When a control signal is received, the actuator (electric, pneumatic, or hydraulic) moves the valve to its designated position. For example, an electrical signal may trigger a motor that regulates the valve’s opening, or a pneumatic signal may control air pressure to move a diaphragm.
Final Control Element
The valve is the final control element in process control loop, regulating fluid flow in response to DCS orders and sensor data.
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