Control valve, also known as control valve, controls the final control of process parameters such as medium flow, pressure, temperature and liquid level by means of power operation by accepting the control signal output from the regulating control unit in the field of industrial automation process control element. Generally by the implementing agencies and valves. According to the characteristics of travel, the control valve can be divided into straight-stroke and angular travel; according to the power of the actuator used, can be divided into pneumatic control valve, electric control valve, hydraulic control valve three; according to their function and characteristics For the linear characteristics, such as percentage characteristics and parabolic characteristics of three. Regulating valve for air, water, steam, all kinds of corrosive media, mud, oil and other media. Electric control valve is used to regulate the flow of media, pressure and liquid level. According to the PLC system control signal, to adjust the valve opening, and feedback a current value to the PLC system, PLC system will be given signal and feedback signal for comparison, when there is a deviation signal and then determine whether it is positive or negative deviation, determine the motor Forward rotation or reverse rotation, until the given signal and the feedback signal, stop the motor drive. The media flow, pressure and level are adjusted to achieve the desired preset value for the PLC system. Circulation capacity Cv value is one of the main parameters of the electric control valve, the electric control valve flow capacity is defined as: When the electric control valve is fully open, the pressure drop across the valve is 0.1MPa, the fluid density of 1g / cm3 hourly Flow through the electric control valve flow number, known as the flow capacity, also known as flow coefficient, in Cv, said t / h. The flow characteristics of the electric control valve is the relationship between the relative flow of the medium through the electric control valve and its opening under the condition that the pressure difference between the two ends of the valve is kept constant. Electric flow control valve features a linear flow characteristics, such as percentage characteristics and parabolic characteristics of three. The significance of the three kinds of fluency features are as follows: (1) Equal Percentage Characteristics (Logarithmic) The relative and relative flow rates of equal percentage characteristics do not have a linear relationship, and the change of the flow rate caused by the unit stroke change at each point of the stroke corresponds to this point Of the traffic is proportional to the percentage of traffic changes are equal. So it has the advantage of small flow, small changes in traffic, traffic flow, the flow changes, that is, in different degrees, with the same regulation accuracy. (2) Linearity (Linearity) Relativeness and linearity of linearity are linear. Changes in unit stroke caused by changes in the flow is unchanged. When the flow rate is large, the relative value of the flow rate changes little, and when the flow rate is small, the relative value of the flow rate changes greatly. (3) Parabolic characteristics The flow rate varies proportionately with the two sides of the travel, and generally has the intermediate characteristics of linear and equal percentage characteristics. From the analysis of the above three characteristics can be seen, in terms of its regulatory performance, with equal percentage characteristics for the best, stable regulation, good regulation performance. The parabolic characteristics than the linear properties of the regulatory performance is good, according to the different requirements of the occasion, select any one of the flow characteristics.
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