main and auxiliary circuits
Thread Content
How to distinguish between primary and secondary circuits in a flowchart
Cascade control? It is applied to the secondary circuit of CAS and the primary circuit of auto, with the output of the primary circuit serving as the set value for the secondary circuit. It seems so.
The main circuit is the one that regulates the primary parameters, while the auxiliary circuit is used for regulating secondary parameters. You need to determine what should be controlled using what mechanism; for example, temperature is used to control the liquid level. In this case, the temperature circuit is the main circuit. However, it’s possible to use two temperature points, such as those from two different locations within a tank, and by using these two temperatures to calculate a cascade error, PID control can be applied to enable proactive adjustment. You can think of it this way: the secondary circuit acts first. It’s based on my personal experience.
The main loop is the outer control loop that aims to achieve the desired adjustment parameters, while the secondary loop is the auxiliary control loop located within the cascade control structure. The output of the secondary circuit is used to control the valve, while the output of the primary circuit is used to change the setpoint of the secondary controller. In fact, it’s quite clear just by looking at the direction of the arrow on the instrument signal line in the PID (except in cases where it’s shown randomly or horizontally).
In the flowchart, the sub-circuit boxes have output signal lines from the main circuit boxes, whereas the main circuit boxes do not.