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Intelligent electric control valves and intelligent pneumatic control valves can both be referred to as intelligent control valves. How to determine whether a control valve is an intelligent control valve? Definition of intelligent control valve: An intelligent control valve is a control valve equipped with a microprocessor, enabling intelligent control functions. The intelligentization of control valves usually takes the following forms: a. Pneumatic control valves equipped with intelligent valve positioners ； b. Intelligent electric control valve ； Pneumatic control valve equipped with a fieldbus intelligent valve positioner. The ‘intelligent control function’ mainly includes the following: a. Easy modification of the flow characteristics of control valves. b. Perform PID control calculations. c. Implement other operational functions, such as setting the range for step control and performing nonlinear compensation calculations. d, Change the forward and reverse operating mode of the control valve. e. Establish communication with the host computer to achieve information sharing. L enables fault diagnosis and alarm for control valves. g. Achieve self-locking of the control valve. h. For tasks such as managing the status information of control valves, the advantages of using intelligent valve positioners are as follows. a. Reduce the installation, calibration, and commissioning time of the control loop. b. Utilize the diagnostic function to enable the use of the control valve. Life span is extended, and operational status can be monitored in a timely manner. c. Reduce the skill requirements for instrument maintenance personnel. Intelligent control valves can be roughly divided into intelligent electric control valves and intelligent pneumatic control valves: Pneumatic control valves equipped with intelligent valve positioners. The structure of these control valves is the same as that of ordinary control valves; however, the presence of an intelligent valve positioner endows them with intelligent functions. The main differences between intelligent valve positioners and ordinary valve positioners are as follows: 1. The way in which the flow characteristics of the control valve are achieved is different. The feedback section of the intelligent locator uses linear feedback, and the flow characteristic required of the control valve is achieved within the setting circuit. The feedback element of a conventional positioner is a cam of different shapes, and the flow characteristics of the control valve desired are achieved by changing the shape of the cam. 2. The input and output methods are different. Typically, intelligent valve positioners are intelligent electrical valve positioners. Compared to conventional electrical valve positioners, the input signal of intelligent electrical valve positioners is a standard 4–20mA or 1–5V electrical signal, which must be converted via analog-to-digital conversion before it can be used as an input signal for the microprocessor. While the input signal for ordinary electrical valve positioners is typically a 4–20mA or 1–5V electrical signal, it does not require analog-to-digital conversion; it can be sent directly to the electromagnetic coil to generate an electromagnetic force, thereby achieving force balance. The output signal of an intelligent valve positioner is a digital signal, which is usually sent to a piezoelectric valve assembly; the opening and closing of this valve assembly is used to regulate the air pressure acting on the diaphragm of the control valve. In general, the output signal of an electrical valve positioner is an air signal that has been amplified by a pneumatic amplifier. 3. Different control methods are used. Similar to ordinary computer control devices, intelligent valve positioners use discrete control, so the opening degree of the control valve remains unchanged during the sampling interval. During operation, the opening degree of the control valve changes in a stepped manner. Typical valve positioners use a continuous control mode; therefore, throughout the control process, the change in the opening degree of the control valve is continuous (except for the jumps caused by dead zones). 4. The detection and processing of feedback signals are different. In intelligent valve positioners, the feedback signal from the control valve must be converted from analog to digital form before it can be processed by the microprocessor; whereas in conventional valve positioners, the feedback signal is used directly as a feedback force (torque), without the need for an analog-to-digital conversion into an electrical signal. Some intelligent valve positioners use standard analog signals as their input signals; at the same time, HART digital signals are also transmitted over the same wire, resulting in intelligent valve positioners that utilize mixed signals. Such devices do not belong to the category of fieldbus intelligent valve positioners, but they still remain intelligent valve positioners. Intelligent electric control valve: These control valves are composed of an intelligent servo amplifier, a digital operator, a reduction mechanism, a valve position detection and transmission device, and an electric control valve. The main difference from ordinary electric control valves is the use of a servo amplifier with intelligent functions. An intelligent servo amplifier is a compact computer that receives standard analog current or voltage signals, converts them into digital signals through analog-to-digital conversion. The microprocessor compares the input signals with setpoints and performs calculations according to certain control rules; the resulting output signal is then converted back to an analog form in order to drive the corresponding electric control valve. Similar to the working principle of pneumatic control valves equipped with intelligent valve positioners, the main difference in intelligent electric control valves is that they use electric actuators; thus, the output signal is sent to an electric motor (which can be single-phase or three-phase), and after passing through a reduction mechanism, it adjusts the opening degree of the electric valve. Intelligent electric valves also utilize the nonlinear characteristics of the setpoint circuit to compensate for the nonlinear characteristics of the controlled system, thereby avoiding instability in the control system caused by the nonlinearities in the feedback circuit. At the same time, since nonlinear compensation is implemented digitally, the positions of each polyline point in the nonlinear compensation circuit can be determined based on the pressure drop ratio of the control valve and the required flow rate characteristics. Pneumatic control valve with fieldbus intelligent valve positioner. Compared to ordinary intelligent valve positioners, the valve positioners used in these control valves have the following characteristics. a. The input signal is not a standard analog current or voltage signal, but rather a digital signal from the fieldbus device. b. It has communication capabilities, allowing for easy communication with a host computer to enable data exchange and sharing. c. It can operate in either direct power supply mode or intrinsically safe mode, in compliance with the relevant standards for field buses. d. It can implement functions related to open system interconnection, such as interchangeability and interoperability. e. Fully digital, two-way communication.