Theoretical Research And Equipment Development Of Magnetostrictive Ultrasonic Guided Wave Distributed Temperature Measurement

The interior of large high temperature equipment is characterized by large volume,long depth,multi-temperature layer and harsh environmental conditions(including a lot of dust and smoke).In the process of industrial production,it is very necessary to monitor the temperature of different positions inside the structure of the equipment for the normal and efficient operation.Conventional temperature measurement technologies are limited by the above equipment conditions,and their measurement methods and accuracy can not meet the requirements of measurement,with certain limitations.In view of the current situation of temperature measurement of large-scale high temperature equipment,an ultrasonic temperature measurement technology with fast response speed,non-contact coupling energy conversion,multi-stage measurement and strong environmental adaptability is proposed.Based on the principle and method of ultrasonic temperature measurement,this paper deduces the ultrasonic temperature measurement model and designs the ultrasonic temperature measurement scheme.By simulating the temperature measurement model and the key parameters of the transducer,the temperature measurement experiment and the optimization design of the transducer are theoretically guided and mutually verified.Subsequently,the temperature sensor is developed and the system platform is built.The signal processing algorithm is designed for the collected experimental data,the experimental calibration of sensors is accurately completed,and the static performance index of sensors is evaluated.Focusing on common problems such as reducing signal attenuation,improving signal strength and accurate inter-signal delay,a series of researches are carried out to achieve accurate temperature measurement.The main research contents of this paper are as follows:(1)The internal depth of large high temperature equipment is about 20 meters,and the sensor body is matched with the same length for indirect temperature measurement.Acoustic attenuation and dispersion effects become more obvious with long distance propagation.In order to solve the above problems and effectively ensure the acoustic measurement information,the formation mechanism and propagation properties of guided waves are studied in this paper.By calculating dispersion curves,the propagation process of cylindrical guided waves under different modes is analyzed,and the longitudinal mode guided waves with fast excitation propagation speed and long detection distance are determined.At the same time,in order to overcome the dispersion effect of longitudinal modal guided waves and take into account the subsequent section design,the diameter of the waveguide wire is determined to be 1.6mm.(2)The principle of ultrasonic temperature measurement is based on the relationship between ultrasonic sound velocity and temperature in the measured medium.The sound velocity is very sensitive to the temperature change of the medium and highly temperature-dependent.According to the research background of the measured environment,a number of distributed intercept sensors are designed to measure the temperature,and a functional relationship is established between the sound velocity of the guided wave and the temperature in the measured medium.The temperature of the waveguide and the surrounding environment is measured by measuring the sound velocity or the transit time of the guided wave.On the basis of studying the principle and method of temperature measurement,the temperature measurement model is further deduced.The acoustic and temperature characteristics of materials are studied by multi-physical field finite element simulation.(3)In the long-distance propagation process of guided wave signals,besides reducing signal attenuation,it is necessary to optimize signal excitation and receiving process to realize signal enhancement.Therefore,a magnetostrictive transducer suitable for guiding wave excitation and receiving in ultrasonic temperature measurement sensor is studied and designed.By optimizing the structure parameters of permanent magnet,the axial relative distance between permanent magnet and coil edge is studied to flexibly adjust the superposition matching between dynamic magnetic field and static bias magnetic field,determine the optimal magnetization point and obtain the optimal magneto-acoustic energy conversion efficiency;The copper ring is used to accurately control the dynamic magnetic field range to avoid the influence of the electromagnetic field diffusion effect of the excitation coil to enhance the signal amplitude;The double-section receiving coil is used to effectively stack the received signal and improve the SNR.The optimized design scheme of energy exchange is obtained to provide high quality signal for subsequent temperature measurement.(4)Large high temperature equipment needs to effectively monitor the thermal layer of different depths,so the sensor of single point temperature measurement is no longer suitable for this research background.In this paper,ultrasonic distributed temperature measurement is carried out to measure multiple regions of interest.According to the actual monitoring requirements,three temperature measurement areas are set up,and the main body of the sensor is designed through theoretical calculation.In the process of building the overall experimental system,a transmitting and receiving circuit with a frequency of 160k Hz double pulse excitation signal is developed to complete signal sending and receiving,followed by data acquisition and post-processing of the superior computer.In signal processing,zero phase filter algorithm is used to eliminate echo signal noise and phase offset.At the same time,a recursive cross-correlation algorithm based on template signal is proposed to calculate the transit time increment accurately.The template signal is designed to reduce the error caused by synchronization and improve the accuracy and repeatability of the recursive process to calculate the increment of transit time.(5)An ultrasonic temperature sensor based on ferrochrome aluminum alloy is developed.The temperature of the sensor is calibrated in the range of 20?to 900?,and the corresponding relationship between temperature and delay increment is established.Fitting the function relation between the above two variables T=a?~4+b?~3+c?~2+d?+e,the higher order polynomial function fully considers the nonlinear trend of partial temperature interval,better fits the experimental data,and improves the fitting accuracy.Test sensor related performance indicators,including:range input and output,resolution,sensitivity,sample standard deviation,repeatability error,hysteresis and lag,and uncertainty analysis.Through model building,theoretical simulation,system building and engineering experiment,the measurement of ultrasonic temperature sensor is effectively completed.It lays the foundation and provides the reference for the temperature test of large high temperature equipment.