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What is the attenuation ratio and residual of the regulating valve

Update:06-05-2019
Summary:

The regulating valve is a throttling device and belongs […]

The regulating valve is a throttling device and belongs to the moving component. Compared with the detecting component, the transmitter and the controller, in the control process, the regulating valve needs to constantly change the flow area of ​​the throttle member, so that the manipulated variable changes to adapt to the load. Change or change in operating conditions. Therefore, higher requirements are placed on the sealing, corrosion, and withstand voltage of the regulating valve valve assembly. For example, the seal will increase the friction of the regulating valve, and the dead zone of the regulating valve will increase, resulting in poor control quality of the control system. It is installed in various production processes. The operating conditions such as high temperature, low temperature, high pressure, large flow rate and small flow rate require various functions of the regulating valve. The regulating valve can adapt to the requirements of different applications.

What is the significance of the attenuation ratio during the transition of the automatic valve system? The attenuation ratio n is a dynamic indicator for measuring the stability of the transition process. It is defined as the ratio of the amplitude of one wave to the amplitude of two waves of di in the same direction. If B is used to start the amplitude of one wave and B' is the amplitude of the two waves in the same direction di, the attenuation ratio is n = B / B'.

It is clear that for attenuating oscillations, n is always greater than one. The smaller n is, the more intense the oscillation process of the control system is, and the lower the stability is. When n is close to 1, when the transition process of the control system is close to 1, the transition process of the control system is close to the equal-amplitude oscillation process; otherwise, the more n Large, the stability of the control system is also higher. When n tends to infinity, the transition process of the control system is close to the non-oscillation process, and the attenuation ratio is appropriate. There is no exact conclusion, according to the actual operational experience, to maintain Sufficient stability, it is generally desirable to have two waves in the transition process, and the corresponding attenuation ratio is in the range of 4:1 to 10:1.

What is the definition of residual C during the transition of the regulating valve automatic control system? When the transition process is over, the deviation between the new steady-state value and the given value reached by the adjusted parameter is called the residual, or the residual is The residual deviation at the end of the transition process, the value of the deviation can be positive or negative. The given value in the production process is a technical indicator of production, so the closer the adjusted parameter is to the given value, the better, that is, the smaller the residual, the better.

However, in actual production, it is not required that the residual of any system of the regulating valve is very small. For example, the liquid level adjustment requirement of the general storage tank is not high. Such a system often allows a large variation range of the liquid level. The rest can be bigger. Another example is the temperature regulation of the chemical reactor, which is generally required to be high, and the residual should be eliminated as much as possible. Therefore, the requirements for the size of the residual must be combined with the specific system for specific analysis, can not be generalized. The adjustment process with residuals is called differential adjustment, and the corresponding system is called differential system. The adjustment process without residuals is called no-difference adjustment, and the corresponding system is called the dead-end system.

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