Design And Modelling Of Pressure Measurement System Based On TDC

Pressure vessels are widely used in many areas of industrial production and daily life and its total number is numerous.As a typical pressure equipment,pressure vessels are often filled with flammable,explosive,toxic or corrosive medium,which will lead to serious accidents and economic losses in case of failure.Overpressure is the main cause of safety accidents in pressure vessel.Therefore,it is very important to detect and control the inner pressure of pressure vessel in real time.Pressure measurement methods can be divided into two types:invasive and non-invasive.Based on the study of non-invasive pressure measurement technology,a set of online ultrasonic pressure measurement equipment is designed to realize low-cost and online measurement of pressure in this paper.Meantime,in view of the non-linearity of the low pressure section,pressure measurement models based on Response Surface Method are proposed.To avoid the vulnerability of the measurement system to the installation of the probe,the temperature,the coupling agent and the signal processing circuit,pressure measurement based on time-intervals between neighboring longitudinal waves are proposed.The main work and innovations in this paper include:(1)Pressure measurement model based on Response Surface Method is proposed.Due to the influence of residual stress and temperature,the relationship between pressure and travel time shows nonlinear in the low pressure zone.In order to improve the accuracy of measurement,a multi-nonlinear pressure measurement model based on Response Surface Method and multi-wave fusion theory is adopted.The model structure is optimized according to the significance of variables to the model.The experimental results show that the model can achieve high measurement accuracy,with the fit goodness of 0.998,the root mean square error of 0.1MPa and the average relative error of 3.3%.(2)A new measurement method based on the Time-interval change between neighboring longitudinal waves is proposed.Considering the ability of TDC to measure three signals simultaneously in a single measurement cycle,multiple longitudinal waves(critical refracted longitudinal waves or reflected longitudinal waves)generated by the same excitation signal can be acquired.This method can overcome the inconsistency of ultrasonic probe onset time,coupling agent,ultrasonic excitation and receiving circuit and the probe fixing characteristics,which can improve the pressure measurement accuracy.The experimental results show that the time delay obtained by this method has better repeatability,the root mean square error of pressure measurement is within 0.165MPa and the average relative error is less than 3.61%.(3)A set of ultrasonic pressure measurement equipment based on TDC-GP22 is designed.According to acoustoelastic effect and shell theory,the pressure in the vessel can be determined by the measurement of travel-time change.In this paper,MSP430F149 and TDC-GP22 are employed to design high-precision,high resolution,low cost and online pressure measurement equipment.The device mainly includes:a power module,a control module,a driving module,a signal conditioning module,and a data processing and display module.(4)A pressure measurement system is set up to test equipment and modeling method.Experiment results show that the pressure measurement equipment designed in this paper is applicable.The model optimization method and measuring method proposed in this paper can further improve pressure measurement accuracy and simplify the system.