Research On Key Technology Of Ultrasonic Guided Wave Temperature Measurement

China's aviation industry is developing with each passing day,so we put forward higher requirements on the performance of the aircraft engine.The temperature is one of the important parameter of the aircraft engine.It will directly affect the engine performance that whether the temperature of the engine combustor and the tail flame can be measured accurately.The temperature of the engine combustor and the tail flame is above 2000 degrees,and the traditional temperature sensor,such as thermocouple,can not meet the measurement requirements.Because the temperature limit of thermocouple is only 1800 degrees.Radiation thermometry has not measurement limit in theory,but the radiation thermometry need to modify the emissivity of material,increasing the difficulty of processing the result of measurement.In addition,the measurement of radiation thermometer is highly affected by the intermediate medium.Especially under the condition of industrial field,the environment is bad,and the result of measurement will be influenced greatly by intermediate medium.So the accuracy of measurement can not be guaranteed.A temperature sensor based on ultrasonic is built by ultrasonic defect detector,ultrasonic transducer,ultrasonic concentrator and waveguide rod in this paper.And the two key technologies of the sensor are analyzed in detail:one is ultrasonic coupling and amplification,the other is ultrasonic echo signal processing.The sensor has large measuring range and low measurement error.The present situation and progress at home and abroad of measuring temperature based on acoustic is studied in the paper,and two key technologies based on ultrasonic temperature measurement sensor is put forward: one is ultrasonic coupling and amplification,the other is processing of ultrasonic echo signal.In view of the problem that the amplitude of ultrasonic echo signal is small and can't meetthe requirements of data processing,the working principle of the ultrasonic concentrator is briefly discussed firstly in the paper.the exponential shape,the conical shape and the ladder type accumulator,The relationship between the area factor and the magnification of the three concentrators is gotten by frequency equation and amplification factor of coniform ultrasonic horn,exponential ultrasonic horn and stepped ultrasonic horn.In view of the magnification and the difficult degree of manufacturing,the conical concentrator is selected as the ultrasonic coupling and amplification device.Then,the geometrical design of coniform ultrasonic horn is was provided detailly in the paper.Combined with finite element simulation software comsol,the design of the concentrator is completed,which solves the problem of coupling and amplifying of ultrasonic.The hardware platform of ultrasonic data acquisition is set up,and the control software of ultrasonic data acquisition based on Labview is designed in the paper.Ultrasonic echo data acquisition system is formed with computer,high-capacity,high-speed data acquisition board,Ultrasonic defect detector and ultrasonic piezoelectric probe.The host computer indirectly controls the ultrasonic flaw detector to emit high voltage pulse to the ultrasonic piezoelectric probe to stimulate the ultrasonic wave.The ultrasonic wave is coupled to the waveguide rod through the concentrator,and the data acquisition card is used to collect and upload the ultrasonic echo signal.It is upper computer that completes the data storage,processing and display of the results.The change of temperature is directly related to the speed of sound,and the change of sound velocity will lead to the change of delay difference between node echo signal and end point echo signal.Therefore,the key to data processing is to calculate the delay difference of the two echo signals.Firstly,the ultrasonic echo signal is denoised by the moving average algorithm.Then,the node echo signal and the end echo signal are separated and reconstructed.After that,cross-correlation is made for the two echo signals,and the delay difference between two echo signal is gotten.Experimental results show that temperature can be measured quickly and accurately bytemperature measurement sensor based on ultrasonic.