Lee-Long Han

Evaluation of dynamic performance of pressure sensors using a pressure square-like wave generator

In this study, we measured the dynamic characteristics of pressure sensors using a pressure square-like wave generator (PSWG). With high excitation energy, the PSWG can measure dynamic pressure and work more effectively in a high frequency range. Under the same experimental parameters (10 bar, 600 Hz), the performance of six pressure sensors of dissimilar design and structure was evaluated. The experimental results indicate that they all exhibited extremely different dynamic characteristics. The dynamic pressure sensors based on quartz plates and crystals possess larger overshoot, greater gain margin and shorter rise time in comparison with other sensors based on strain gauge and piezoresistive materials. Compared with other traditional methods, such as the hydraulic control method, the PSWG proves to be superior in that it can be employed to evaluate the dynamic performances of pressure sensors at high frequency of above 10 kHz.

The Measurement and Analysis of Pressure Square Wave Generator

Investigating the dynamic characteristics is a significant study for actual hydraulic pressure system because the dynamic environment is used more often than static one. A dynamic pressure generator is called pressure square wave generator (PSWG) that developed in our team and generate square-like waveform and change testing pressure and frequency form 0.1 to 5 MPa and 12 to 2 KHz, respectively. In this study, dynamic performance of PSWG was investigated under different testing tangent velocity of rotor of PSWG including detailed transient response of a pressure square-like wave, rise time and deviation of magnitude. Results show that the tangent velocity of the rotor of PSWG affects the transient response of pressure square-like wave form. The desired transient response can be obtained when the tangent velocity is larger than 0.5 m/s. Furthermore, the larger the tangent velocity used, the smaller the rise time will be.

Structural Reinforcement on a Superconducting Radio-Frequency Cavity

A pressure test on a liquid-helium vessel with the niobium cavity in a cryostat to the maximum allowable operational pressure is required as the main item for a safety test near 300 K, to prepare for application for a license to operate a superconducting radio-frequency (SRF) module. Because the niobium cavity has a shell structure and is part of the liquid-helium vessel, to prevent its buckling during test at high pressure becomes a critical issue in designing a 500-MHz SRF module. To meet the safety requirement, currently available 500-MHz SRF modules hence have a limit on the maximum allowable operational pressure that is marginally above the routine operational pressure. Safety devices such as relief valves are, correspondingly, chosen to meet the pressure limit at only 10 or 20 kPa above the operational pressure, thus causing operational inconvenience and a risk of damage of the shell-like cavity structure. A local reinforcement of the cavity is proposed herein to increase its buckling strength and thus its maximum allowable operational pressure. Illustrated with a 500-MHz SRF cavity of KEK type, detailed investigations of its elastic buckling modes and the corresponding strengths are computed with linear, 3-D, and finite-element models to determine an optimized geometry and the location of the reinforcement rings. Variations of the corresponding buckling modes and stress distributions are examined. Although the required tuning force is slightly increased but within an acceptable range from an engineering point of view, maximum allowable operational pressure of the 500-MHz SRF module can be effectively increased up to 200 kPa or even more when properly implementing one pair of reinforcement rings on the niobium cavity cell.

Volumetric effects on the dynamic pressure wave in hydraulic system

The dynamic characteristics of hydraulic system were commonly analyzed by the time domain response. The rise time and maximum overshoot are both significant specifications for presenting the dynamic chrematistics. A dynamic pressure generator, was called pressure square wave generator (PSWG), was used as an input source for exciting the response of hydraulic devices. The testing frequency and amplitude of PSWG was arbitrary and the testing range was employed between 16 and 300 Hz. The primary objective of this paper was investigating the volumetric effects on PSWG. The volume was the chamber of a hydraulic cylinder and changed by controlling the stroke in 50 mm incensement between 0 mm to 200 mm. Results show that the greater the chamber volume obtained the larger the rise time, smaller the maximum overshoot and the waveform tended to trapezoid-like shape.

Using pressure square-like wave to measure the dynamic characteristics of piezoelectric pressure sensor

Piezoelectric pressure sensors are commonly used to measuring the dynamic characteristics in a hydraulic system. The dynamic measurements require a pressure sensor which has a high response rate. In this paper, we proposed use of a pressure square wave to excite the piezoelectric pressure sensor. Experimental frequencies are 0.5, 1.0, 1.5, and 2.0 kHz at 10, 15, 20 bar, respectively. Results show that the waveform of time-domain and frequencydomain response are quite different under above testing conditions. The higher the frequencies tested, the faster the pressure-rise speeds obtained. Similarly, the higher the testing pressure, the shorter the rise time attained.

Study of Frequency Response of Control Components in a Pneumatic System

The study explores the frequency response characteristics of the control components in a pneumatic system, while developing a set of the most effective measurement methods and equipment that provides the closest dynamic characteristics of the pneumatic system. First, the study inputs square pressure wave signals, which have various frequencies and are generated by directional control valves, into the pneumatic system, which is comprised of an electromagnetic valve, pneumatic pipes, and pressure sensors. In addition, the study discusses the influences of the aforementioned electromagnetic valve, pneumatic pipes, and pressure sensors on the frequency responses of the pneumatic system through the analyses of outputted pressure signals. Next, the study replaces the electromagnetic valve with the square pressure wave generator developed in the study that emits pressure square waves with frequencies up to 500 Hz to be inputted into premeasured pressure sensors in the pneumatic system for testing the dynamic characteristics of the pressure sensors at high frequencies. The study proposes applying square pressure waves to the dynamic property analyses of pneumatic components, i.e., inputs square pressure waves into premeasured pressure sensors through the excitement method to the pressure sensor and utilizes spectrum analysis for analyzing the outputted voltage signals. The experimental results can be provided for designers of pneumatic systems as references for selecting components and rectifying the system properties.