Application Cases

Experiment Name: Application of Voltage Amplifier in Pressure Detection of Hydraulic Pipelines Using Acoustoelastic Properties of Ultrasonic Guided Waves

Research Direction: Ultrasonic Testing

Experiment Objective:
To achieve non-intrusive pressure detection in the hydraulic systems of agricultural machinery, a controllable hydraulic pipeline pressurization testing system was built. This was based on an analysis of the acoustoelastic-sensitive guided wave modes and excitation frequencies suitable for pressure detection. Pressure detection experiments were conducted on hydraulic pipelines using a designed magnetostrictive sensor. The influence of temperature and the transmission medium on the propagation characteristics of ultrasonic guided waves was analyzed. The relationship between the acoustoelastic time delay and pressure was established for the excitation frequencies of the detection modes. The accuracy of pressure detection was evaluated through multiple repeated experiments. This research aims to lay the foundation for subsequent studies and engineering applications of non-intrusive pressure detection technology based on the acoustoelastic properties of ultrasonic guided waves.

Testing Equipment: Signal generator, ATA-2041 high-voltage amplifier, oscilloscope, magnetostrictive sensor, hydraulic pipeline under test, controllable hydraulic pipeline pressurization system

Figure 1: Ultrasonic Guided Wave Pressure Detection Test System for Hydraulic Pipelines

Experimental Procedure:
A function generator produced a modulated sinusoidal signal with a specific number of cycles required for the experiment. This signal was amplified by the power amplifier and then input to a magnetostrictive sensor that excites either the longitudinal mode or the torsional mode. This generated guided waves of the longitudinal or torsional mode in the hydraulic pipeline. A receiving magnetostrictive sensor at the other end of the hydraulic pipeline captured the signals and sent them to an oscilloscope for real-time display. After adjusting the hydraulic pressurization device to stabilize the pressure of the hydraulic pipeline at a predetermined value, the hydraulic pump was turned off to avoid interference from the motor and other equipment on the signal acquisition. The pressure was maintained by an accumulator. The oscilloscope acquired and averaged the signals to reduce noise, and the acquired signal data were saved to a computer for processing.

Experimental Results:

Figure 2: Longitudinal L(0,2) Mode Excitation and Received Signals

The longitudinal mode pressure detection experiments used the test system shown in Figure 1. The longitudinal mode magnetostrictive sensors were operated in a pitch-catch configuration for data acquisition. Figure 2 shows the longitudinal L(0,2) mode excitation and received signals. The received signal diagram shows that the direct wave signal was affected by factors such as pipeline interfaces, resulting in waveform superposition. To minimize the influence of other factors as much as possible, the waveform enclosed by the circle in the figure was selected as the data for experimental analysis.

During the experiment, the pipeline pressure was first increased from 0 MPa to 20 MPa and then decreased back to 0 MPa. A data collection point was set at every 2 MPa pressure interval, and at each point, data were acquired five times repeatedly. During both the pressure increase and decrease processes, one set of data was collected at each pressure point. Using the mean of the five signals acquired at 0 MPa as a reference, cross-correlation calculations were performed for the signals at the other pressure points to obtain the relationship between pressure and time delay. Cross-correlation calculations were also performed on the five repeated data acquisitions at each pressure point to obtain the error value for that pressure point. Figure 64 shows the calculated relationship between the time delay value and temperature.

Figure 3: Experimental Results of the Influence of Pressure on the Propagation Characteristics of Longitudinal Mode Guided Waves

The results shown in the figure indicate that the time delay value gradually decreases with increasing pipeline pressure. This means that the propagation velocity of the L(0,2) longitudinal mode decreases as pressure increases. This finding is in good agreement with theoretical and numerical simulation results. The linear fitting results for each pressure point during the pressurization and depressurization processes showed good consistency. Specifically, the time delay value per MPa of pressure was approximately -49.8 ns. Compared to the temperature-induced time delay of -28.9 ns, the effect of 1 MPa of pressure is roughly equivalent to the effect of a 17°C temperature change. However, during the pressurization and depressurization processes, there was a significant difference in the intercept of the linear fitting results. This is manifested as a substantial time delay difference between the initial 0 MPa pressure state and the final 0 MPa pressure state after the pressurization-depressurization cycle. The primary reason for this phenomenon is likely the temperature rise of the hydraulic oil during the experiment, leading to a temperature difference between the two 0 MPa states. Additionally, the possibility that the fundamental properties of the hydraulic oil, such as its viscosity, might also change during this process cannot be excluded, contributing to this initial error. Examining the error distribution at each pressure point during the pressurization-depressurization cycle, it was found that the error at some points was relatively large. Specifically, the error magnitude at these points was equivalent to the effect of a 10 MPa pressure change. Furthermore, from the results of the linear correlation analysis, it is evident that the fitting results also exhibit a significant deviation from the theoretical predictions.

Figure: Specifications of the ATA-2041 High-Voltage Amplifier