Intelligent control valve
The intelligent control valve is a control valve with a microprocessor that can realize intelligent control functions.Control valveThe intelligence of the usually takes the following forms:
a.Pneumatic control valve with intelligent valve positioner;
b.Intelligent electric control valve; pneumatic control valve with fieldbus intelligent valve positioner.'Intelligent control functions' mainly include the following
a.Conveniently modify the flow characteristics of the regulating valve.
b.Realize PID control operation.
c.Realize other calculation functions, for example, the range setting of split-range control, nonlinear compensation calculation, etc.
d. Change the positive and negative action modes of the regulating valve.
e.Realize the communication with the host computer,-realize the information sharing. L realize the fault diagnosis and alarm of the regulating valve.
g.Realize the self-locking of the regulating valve.
h.achieveControl valveThe advantages of using intelligent valve positioner are as follows.
a.Reduce the installation, verification and debugging time of the control loop.
b.Adopt the diagnostic function to enable the use of the regulating valve.The service life is prolonged and the operation status can be monitored in time.
c.Reduce the skill requirements for instrument maintenance personnel.
Pneumatic control valve with intelligent valve positioner
The structure of this kind of regulating valve is the same as that of ordinary regulating valve. The main difference between the smart valve positioner and the ordinary valve positioner is as follows: 1. The flow characteristics of the regulating valve are realized in different ways.The feedback part of the intelligent positioner adopts linear feedback, and the required flow characteristics of the regulating valve are realized in the setting loop.The feedback part of the ordinary positioner is cams of different shapes, and the required flow characteristics of the regulating valve can be achieved by changing the shape of the cams.See section 5.3 for details.
2. Different input and output methods.Generally, the smart valve positioner is a smart electric valve positioner.Compared with the general electric valve positioner, the input signal of the intelligent electric valve positioner is a standard 4-20mA or 1-5V electric signal, which needs to be converted from analog to digital as the input signal of the microprocessor.Although the input signal of the general electric valve positioner is 4-20mA or 5-XNUMXV electric signal, it does not need to be converted from analog to digital, and can be directly sent to the electromagnetic coil to generate electromagnetic force to achieve force balance.The output signal of the intelligent valve positioner is a digital signal, which is usually sent to the piezoelectric valve group, which is adjusted by the switch of the piezoelectric valve group.Control valveThe air pressure of the membrane head, generally the output signal of the electric valve positioner is the air signal amplified by the pneumatic amplifier.
3. Different control methods are adopted.The intelligent valve positioner is similar to a general computer control device, and adopts a discrete control method. Therefore, within the sampling interval, the opening of the regulating valve does not change.During operation, the opening of the regulating valve presents a stepped change.Generally, the valve positioner adopts continuous control mode. Therefore, during the whole control process, the change of the opening degree of the regulating valve is continuous (except for the jump caused by the dead zone).
4. The feedback signal detection process is different.The feedback signal of the regulating valve in the intelligent valve positioner needs to be converted from analog to digital and then sent to the microprocessor for processing. However, the feedback signal of the general valve positioner is directly used as the feedback force (torque) and does not need to be converted into an electrical signal by analog to digital.Some intelligent valve positioners use standard analog signals as input signals, and transmit HART digital signals on the same wire to form a mixed-signal intelligent valve positioner. It is not a fieldbus intelligent valve positioner, but it is still an intelligent valve positioner.
Intelligent electric control valve
This kind of regulating valve is composed of intelligent servo amplifier, digital operator, deceleration mechanism, valve position detection sending device and electric regulating valve.The main difference from the general electric control valve is the use of a servo amplifier with intelligent functions.The intelligent servo amplifier is a miniature computer. It receives standard analog current or voltage signals and converts them into digital signals through analog-to-digital conversion. The microprocessor compares the input signal with the set signal, and operates according to a certain control law to output the signal. Drive the corresponding electric control valve after digital-to-analog conversion.Similar to the working principle of the pneumatic control valve with intelligent valve positioner, the main difference of the intelligent electric control valve is that the electric control valve is used. Therefore, the output signal is sent to the motor (can be a single-phase or three-phase motor) and changed after the deceleration device The opening of the electric valve.The intelligent electric valve also uses the non-linear characteristics of the setting loop to compensate the non-linear characteristics of the controlled object, therefore, avoiding the instability of the control system caused by the nonlinearity of the feedback loop.At the same time, because the digital method is used to realize the nonlinear compensation, the position of each broken line point in the nonlinear compensation link can be determined according to the pressure drop ratio of the regulating valve and the required working flow characteristics.
Pneumatic control valve with fieldbus intelligent valve positioner
Compared with the general intelligent valve positioner, the characteristics of the valve positioner of this kind of regulating valve are as follows.
a.The input signal is not a standard analog current or voltage signal, but a digital signal from a fieldbus device.
b.With communication function, it can communicate with the host computer conveniently to realize data exchange and data sharing.
c.It can be operated in direct power supply mode and intrinsically safe mode, in line with the requirements of relevant fieldbus standards.
d. Relevant functions of open system interconnection can be realized, such as interchangeability and interoperability.
e.All digital, two-way communication.