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With the development of industrial production, processes are constantly being improved, product varieties are continually updated, operating conditions are becoming more complex, and higher standards are placed on product quality. Single-loop control systems can no longer meet the requirements of the production process; therefore, we employ complex control systems in our engineering designs. What is a complex control system? Put simply, it is a control system that consists of circuits with two or more transmitters, controllers, or actuators. Such multi-variable control systems are known as complex control systems, or multi-loop control systems. Complex control systems include: cascade control systems, proportional control systems, ratio control systems, range control systems, automatic selective control systems, feedforward control systems, and three-input control systems, among others. This article first introduces cascade control systems and uniform control systems. 1) Cascade control system: As can be seen from the diagram below, it consists of 2 transmitters and 2 controllers; the output value of one controller serves as the setpoint for the other controller, with the two controllers connected in a cascade configuration. Regarding interference entering the secondary loop, the T2C secondary loop controller has a fast and strong ability to overcome such interference ； It can improve the characteristics of the generalized object of the main regulator and increase the operating frequency ； Eliminate the influence of nonlinear characteristics such as control valves to achieve more precise control of the control variable ； It possesses a certain degree of adaptability, enabling more flexible control methods. 2) Uniform control system: Uniform control is a type of control system named after its function. When a disturbance occurs, it is the parameters set by the regulator that ensure the controlled parameter does not change sharply, but rather changes slowly and uniformly within a certain control range, instead of being strictly maintained at a specific given value. Uniform control systems are divided into: simple uniform control systems, cascade uniform control systems, dual impulse uniform control systems, etc. The basic task of uniform control is to maintain two conflicting parameters, taking into account each other within the allowable range of fluctuations and enabling smooth changes. However, uniform adjustment does not mean an equal distribution of the controlled parameters across the front and back; rather, it determines the priority and order of importance for the uniform adjustment based on the significance of the parameters to be adjusted. Original link: https://www.sohu.com/a/308120508_120129629?sec=wd