## 3 Fault Classification for CPSs
The aggregate metering and discharging are controlled by the control system, and the accurate measurement of each aggregate is achieved by the sensor arrangement on the weighing hopper. In contrast to the aggregate metering system, a metering system such as cement and fly ash adopts a full sealing device. Multiple sensors are arranged on the weighing bucket to complete the accurate measurement of the pneumatic butterfly valve discharge. Metering systems such as water and liquid admixtures generally use a control system to control the pump, discharge water, and admixtures, and these systems use sensors to accurately measure liquid materials such as water and admixtures. In summary, each metering system is controlled by the microcomputer control system, which controls the arc door, cylinder, pump, and other components. The microcomputer control system also meters each material by the sensor. In the process of batching and metering, the electrical system is prone to problems such as line faults and power supply instabilities. The sensor is prone to problems such as damage and poor contact. The door is prone to problems such as opening and closing problems and control unit faults. The pump is prone to problems such as valve and solenoid valve faults. Common fault manifestations mainly include 1 load cell faults, 2 line faults, 3 power supply voltage fluctuations or poor grounding, 4 digital weighing instrument faults, 5 metering bin doors becoming stuck, and 6 material door solenoid valve faults. The basic structure of the batching metering system is shown in Figure 3.  
Figure 2: Material handling system structure. Class C: Pneumatic system fault  
Most of the mechanisms in the CPS are driven by air pressure, and the air pressure drive has the characteristics of being low cost and producing no pollution. The automatic control system of the concrete mixing building uses a programmable controller to issue control commands to control the relay action, the relay controls the action of each electromagnetic reversing valve, and the electromagnetic reversing valve controls the movement of each cylinder and gas valve of the executing component. Thus, the CPS completes the automatic metering, automatic transmitting, and automatic feeding of the finished material in the concrete mixing building. The pneumatic system plays an important role in the entire automatic cycle, and its structure is shown in Figure 4. Common fault manifestations mainly include 1 air source faults (such as air compressor faults, pressure relief valve faults, and pipeline faults), 2 the pneumatic execution of the original (cylinder) faults, 3 reversing valve faults, 4 pneumatic auxiliary original (such as oil mist and muffler) faults, and 5 mechanical faults (such as the cylinder-driven shaft door becoming stuck and the cylinder-driven flap butterfly becoming stuck). Figure 3: Batch metering system structure diagram. Class D: Mixer fault  
A concrete mixer is the main piece of equipment for the preparation of concrete. Raw materials such as sand, cement, water, and admixture can be uniformly stirred in the mixer to form finished concrete with a good construction performance (workability) and specified strength requirements. Concrete is mixed in two ways. One mixing method is to use the fixed vane on the rotatable mixing drum to bring the concrete material to the top of the cylinder for free-fall mixing. In the other mixing method, the charging drum does not rotate, and the rotation of the blade fixed on the shaft drives the concrete material to be mixed. The former method is widely used to mix concrete with a certain degree of slump; the latter method is used to mix dry and hard concrete. The main performance indicator of the mixer is its working capacity in L or m\({}^{3}\). Common fault manifestations of the mixer mainly include 1 the jamming door becoming stuck, 2 the mixer feed port being blocked, 3 gearbox mechanical faults, 4 mixer waste agglomeration, and 5 the mixer boring machine tripping.