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Three - position pneumatic actuators are
controlled by several components and systems working in tandem:
Control Valve: This is a key component that
regulates the flow of compressed air to the actuator. It can be electrically,
pneumatically, or manually operated. Electric - operated control valves are
often used in automated systems and receive signals from a programmable logic
controller (PLC) or a distributed control system (DCS). The control valve opens
and closes ports to direct air into specific chambers of the actuator, thereby
controlling the movement of the piston or diaphragm.
Position Sensors: These are used to provide
feedback on the position of the actuator. Common types include limit switches
and proximity sensors. Limit switches are activated when the actuator reaches a
specific position, such as fully open, fully closed, or an intermediate
position. Proximity sensors use magnetic or inductive fields to detect the
position of a target on the actuator. The signals from these sensors are sent
to the control system, which compares the actual position with the desired
position and makes adjustments as needed.
Control System: This could be a PLC, DCS,
or a simple manual control panel. In an automated process, the control system
sends out control signals based on the process requirements and the feedback
from the position sensors. It calculates the necessary adjustments to the
control valve to move the actuator to the desired position. For example, in a
process where the flow of a fluid needs to be precisely controlled, the control
system will adjust the actuator - controlled valve to maintain the desired flow
rate. In a manual control setup, an operator can directly adjust the control
valve to set the actuator position according to the process needs.
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