## 2 Materials and Methods  
### The Principle of Oil Extraction in a Pumping Unit  
The pumping unit achieves oil extraction through the coordinated operation of the prime mover, sucker rod, and pump [11]. Any malfunction in these components will cause variations in the dynagraph card curve, making it meaningful to have an understanding of the working principles of the pumping equipment for dynagraph card classification.  
A typical beam pumping system, which is the mainstream sucker rod pumping system, consists of three main components [12]. Firstly, there is the surface unit of the pumping unit, which is connected to a high-power prime mover. It includes components such as a gearbox, electric motor, connecting rod, walking beam, and crank, providing power for the system [13]. Secondly, there is the sucker rod, which connects to the pumping unit and the downhole pump, responsible for transmitting power. The sucker rod drives the pump to perform oil extraction and plays a vital role in the pumping process. Lastly, there is the downhole pump, which receives power and drives the pump to perform oil extraction. It mainly consists of components such as a pump barrel, valve, and plunger [14].  
Through the power transmitted by the pumping unit, the sucker rod undergoes a continuous reciprocating motion, creating a stroke that causes the pump barrel to move up and down. During the upward stroke, the fluid column's resistance forces the traveling valve in the pump barrel to close, while the hydraulic pressure of the fluid column opens the standing valve, allowing crude oil to be collected into the pump barrel [15]. Conversely,during the downward stroke, the force on the fluid column reverses, leading to the closure of the standing valve and the opening of the traveling valve. This allows the crude oil to be pumped out of the pump barrel and into the production tubing for collection. The uninterrupted movement of the sucker rod ensures a constant transportation of fluid from the wellbore into the pump barrel, thus completing the oil extraction process. The structure of a pumping unit well is depicted in Figure 1.  
From the above oil extraction process, it is evident that the pump and sucker rod are critical components that work underground and are prone to failure. During the pumping process, the sucker rod is influenced by the up and down loads, which can result in a wavy pattern in the paragraph card curve. Additionally, the inertia load can cause a clockwise rotation in the paragraph card, and the opening and closing of valves can affect stroke losses. Therefore, the sucker rod is susceptible to failures such as bending, deformation, or even fracture under different loads. The traveling valve and standing valve of the pump constantly open and close to collect crude oil, but they may experience failures due to impurities in the oil or limitations in the lifespan of valve connections.  
To quickly and accurately locate the faults in the pumping unit, it is essential to professionally collect paragraph card data [16]. The paragraph card describes the displacement and load conditions of the sucker rod, thus assisting in analyzing the working state of the pumping unit and identifying potential faults. Through an analysis of the dynagraph card, faults can be promptly identified, and corresponding maintenance measures can be taken to improve the operational efficiency and reliability of the pumping unit.