Instrument Valve: An analog regulator that uses an analog signal, also known as an analog instrumentation valve. It works by comparing the measured value of a controlled parameter in analog form with the setpoint and then generating an analog output signal based on a specific control rule to actuate the actuator, thereby eliminating the deviation and keeping the controlled parameter close to the desired value or following a predetermined pattern. In automated instrumentation, these valves are commonly used to combine signals from various instruments, allowing for precise control of industrial processes. Parameters such as temperature, pressure, flow rate, liquid level, and composition are often adjusted using this technology.
Instrument valves can be categorized based on the energy source into pneumatic valves, hydraulic valves, and electric instrumentation valves. Depending on their structural principles, they can also be classified into self-operated valves, local control devices, simple adjustment valves, unit combination valves, and assembled integrated control systems (as shown in the diagram). Furthermore, they can be divided into proportional valves, PI valves (proportional-integral), PID valves (proportional-integral-derivative), and feedforward valves.
Self-operated instrument valves automatically adjust the energy of the medium being controlled or after a simple conversion to drive the regulating valve. For example, a float-type level controller (like a toilet tank) uses the buoyancy of the float to operate the valve. These valves do not require external power and are locally adjustable. They are simple in structure, easy to maintain, and ideal for single-parameter control systems with low precision requirements. Their design is similar to that of pneumatic actuators and are often considered a type of actuator.
Base instrumentation valves are recording instruments equipped with an additional adjustment mechanism. They receive signals from sensors and use the indicating and recording mechanisms to drive the adjusting components, sending control signals to the actuator for automatic regulation. This includes dynamic indicating adjustment instruments, electric or pneumatic recorders with built-in regulators, and are widely used in controlling individual production units.
Simple instrumentation valves are designed to directly receive signals from sensors without a pointer mechanism, featuring a specialized function and a straightforward design. They can also accept signals from transmitters. Non-indicating regulators and temperature alarms are examples of such devices, commonly used in small and medium-sized enterprises.
Unit combination instruments consist of a set of standard units with independent functions, offering flexibility and adaptability for large-scale process control. They allow for complex multi-loop control and are widely used in industrial applications.
Assembled integrated control devices, also known as "assembled instruments," are custom-built control systems that integrate various functional components according to the specific needs of a large unit or process. They offer high flexibility and can be tailored to meet user requirements, making them highly adaptable in modern industrial environments.
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