Flow level cascade control
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I would like to ask everyone: are the control methods for Figure 1 and Figure 2 the same? Is it all flow level control? Still, Figure 1 shows cascade control for the flow and level, while Figure 2 depicts a single-loop system. It’s difficult for me to tell which loops are shown in the PID diagram; do anyone have any suggestions? Is there also a control method like in Figure 1, where the flow rate is controlled by a valve as well? I know the liquid level must be high, so the valve needs to be opened wider. But what about the flow rate – does it decrease? Is there also a valve to control the flow rate? When the flow rate is high, the valve is closed slightly, and then there’s no need to adjust the liquid level
Both of these control schemes are level-flow cascade control systems. As for the principle, please refer to the cascade control system in the textbook.
Figures 1 and 2 differ in terms of control mechanism; Figure 1 is more appropriately referred to as i-series uniform regulation, as it is intended not only to control the liquid level but also to maintain a stable flow rate, although its structure is the same as that of series regulation. Figure 2 shows cascade control; since the flow rate output by the pump is not very stable, the flow rate is set as a secondary variable, but the ultimate goal is to stabilize the liquid level.
I can’t understand these diagrams. . . . . . .
The goal is the same, but the primary and secondary circuits are in opposite order
Actually, both diagrams are intended to stabilize the liquid level, right? But in Figure 1, why is the flow signal arrow directed at the level signal instead of directly at the valve? If it were directed directly at the valve, wouldn’t that be Figure 2? And how did you tell that the market was adjusting evenly? It’s certain that both are cascade, right?
? What does that mean? The liquid level is part of the main circuit, right? The flow rate is part of the secondary circuit, right?
The main controlled parameter is the liquid level; in Figure 1, the secondary loop corresponds to the outflow rate, while in Figure 2 it corresponds to the inflow rate.
The cascade control loop consists of a primary loop and a secondary loop, as shown in Figure 1. The FIC serves as the main controller, while the LIC acts as the secondary controller, though this configuration is not common. The main circuit is the control point of the entire system; in other words, whatever is the main circuit is what controls everything else. If we think in terms of this, then it must be that there is a very high demand for flow stability downstream
Of the two controllers, only one can act directly on the valve. In Figure 1, it is the LIC that acts directly on the valve, while the FIC acts on the LIC; in other words, the FIC sends signals to the LIC, or it issues commands to the LIC. Therefore, the FIC is the master controller. The ultimate goal of cascade control is still to eliminate disturbances. In a normal level-flow cascade control system, the flow rate is adjusted when it starts to change but the level has not yet reacted, thereby eliminating disturbances in advance; a setup like the one shown in Figure 1 has not been seen before. . . . . Better ask the research institute!