## 2 Design and Methods
### Vibration Test  
#### 2.3.1 Test Details and Methods  
The designed vibration sensor shown in Figure 2 was used in the tractor vibration test. The test location was Luoyang, China. The tractor was the newly assembled tractor (model size: LX2204) of China Yto Group Corporation (Luoyang, China). The tractor was equipped with an engine power of 162 kW, and the speed range of the tractor during the idle stage was 700 r/min to 1200 r/min.  
It is well known that the engine acts as the primary source of vibration excitation in a tractor. Conventional-wheel tractors are not equipped with spring shock absorbers or suspension systems. Consequently, the vibration from the engine is transmitted to the various components by a rigid connection. There are two vibration transmission routes: forward transmission to the front axle and backward transmission to the rear axle, as shown in Figure 3. The front and rear axles of the tractor are the terminals of the tractor vibration transmission, and can indicate whether there is a defect in the vibration transmission route.  
Figure 2: The wireless vibration sensor.  
It is important to note that the vibration characteristics of the tractor can be reduced by tires. The structure and mass of the tractor are symmetrical to the axis between the two wheels. To verify the effectiveness of the proposed vibration detection method and test the performance of the developed wireless vibration acceleration sensor, the wireless vibration acceleration sensor is symmetrically distributed on the tractor component surface. The symmetrical distribution is essential for obtaining accurate and reliable vibration data, which can identify any anomalies in the vibration transmission routes.  
Due to the symmetrical structure of the tractor, the wireless sensor was placed symmetrically in the middle position between the front and rear axles of the tractor, as shown in Figure 4. The orientation of the vibration sensor's data collection was defined as follows: The X-axis direction of the vibration sensor was the forward movement direction of the tractor. The Y-axis direction was oriented to the left side of the driver's position when seated in the tractor. The \(Z\)-axis direction was the forward direction of the vertical tractor, capturing vertical vibrations.  
The tractor was parked at the designed testing station, as shown in Figure 5a. The vibration sensor and the PC were connected wirelessly through the wireless router, as shown in Figure 5b. The wireless vibration sensor was carefully placed in the intended  
Figure 4: The distribution positions of vibration sensors.  
Figure 3: Tractor vibration transmission routes.  
test location, as shown in Figure 5c. When the tractor engine speed in the idling state stabilized at 800 r/min or 1000 r/min, the initial data of the vibration sensor were set to zero by the acquisition terminal software. The vibration data acquisition on the vibration characteristics of the tractor in the idling state were collected. The software was responsible for acquiring and storing the collected data. The vibration test result of the tractor in an idling state was be displayed on the collected software, as shown in Figure 5d. The visual of the test results facilitated a clear understanding of the vibration behavior of the tractor, enabling the identification of any issues that might affect its performance.  
When the vibration characteristic of the tractor at 800 r/min idle speed was tested, the tractor idle speed was accelerated to 1000 r/min. After the engine speed was stabilized, the vibration characteristics of the tractor were collected at an idling speed of 1000 r/min.