*2.4. PID Control Method*

The PID control systematic is a classic control systematic. Figure 4 shows its operating system picture. The difference between the actual output signal of the controlled object and the given signal and tracking is the primary PID control method. The control rate (u) of the proportional (P), integral (I), and differential (D) systems was used as the main index for the analysis of the performance of liquid manure spraying. When the flowmeter feeds back the actual flow to the PID controller, the PID controller first reflects the difference between the actual flow and the demand flow in proportion. The output u (t) is directly proportional to the input deviation e (t), which can quickly reflect the deviation and thus reduce the deviation. Then, the function of the differential link can reflect the change trend (change rate) of the deviation signal, and can introduce an effective early correction signal into the system before the value of the deviation signal becomes too large, in order to speed up the action speed of the system and reduce the adjustment time. Finally, the integration link is used to eliminate the static error and improve the error-free degree of the system. The setting parameters of PID are provided by experience, through which the opening of the electromagnetic proportional regulating valve can be adjusted quickly. Through the feedback value of the flowmeter, the opening of the electromagnetic proportional valve is continuously adjusted to realize the PID control of liquid manure spraying. However, owing to the influence of nonlinearity and time delay in the process of liquid manure spreading, the precision of utilizing the classical PID dominant method to adjust liquid manure spreading is poor. Tracking variations in the application amount cannot be performed well with liquid manure spreading [20].

**Figure 4.** PID dominant method block diagram.
