Design And Implementation Of Heating Source System For Large-size Infrared Thermal Imaging Nondestructive Testing

Active infrared thermal imaging non-destructive testing technology requires an external heat source to heat the test piece,obtain the temperature field distribution of the material surface,and extract and locate defect information from it.Uniform and effective thermal excitation can reduce the interference of background noise,obtain infrared heat maps with high signal-to-noise ratio,and help improve the accuracy of defect detection.Therefore,the heating source technology is one of the key technologies of the active infrared thermal imaging nondestructive testing technology,and it is an important subject in the research of related technologies.A heating source system with uniform heat generation,stability and efficiency is independently designed for large-size specimens in this paper.The system consists of two parts: hardware design and software design,which work together to heat large size specimens effectively and uniformly.The whole device is composed of six modules:mechanical structure,heat lamp array,control board,upper computer software,radiant illumination acquisition board and programmable AC power supply.With the exception of programmable AC power supply,the rest of the modules are self-designed and completed.The mechanical structure is assembled by welded steel tubes and threaded joints for the support and fixation of the system.An adjustable structure is designed between the heat lamp array and the specimen.By adjusting the spacing between them,it helps to form a relatively uniform temperature field on the specimen surface.The array of heat lamps is composed of 25 infrared heat lamps distributed symmetrically,which increases the radiation area,improves the heating power and reduces the spatial gradient of temperature field.The programmable AC power supply supplies power to the heat lamp array,and the output mode of the power supply is controlled by the upper computer software to realize the multi-mode output of the heating source system.The upper computer software is developed based on the Qt framework,which provides a window for man-machine interaction and realizes three functions :(1)remote setting of the operation parameters of the programmable AC power supply and controlling the voltage output;(2)Control the switching state of each heat lamp on the heat lamp array;(3)Receive the measurement results returned by the irradiance sensor and build a closedloop system to complete heat wave tracking.The control board is a microcontroller system based on STM32 MCU :(1)It is responsible for receiving and analyzing the control instructions sent by the host computer,and switching the switching state of each heat lamp through the control relay;(2)Complete the acquisition configuration,data processing and result return of the irradiance sensor.The irradiance acquisition plate measures the irradiated energy(irradiance)on the surface of the specimen in real time and tracks the change of thermal wave on the surface of the specimen,which provides the hardware foundation for the closed-loop control of the system.Aiming at phase-locked thermal imaging technology,a closed-loop control scheme based on sensor feedback,Simulink parameter calculation and virtual serial communication is designed.The upper computer and Simulink run on the same computer,and they communicate through the virtual serial port.The measurement data of the sensor is sent to Simulink,and the error between the sensor and the reference signal is used as the input signal of the PID controller.The output of the PID controller is used as the control word of the programmable AC power supply to control the voltage output and supply power to the heat lamp array.In this way,a closed loop is formed,and the heat lamp array outputs a heat wave that follows the change of the reference signal.Compared with the sinusoidal heat wave output by controlling the electric power,this method improves the accuracy and fidelity of the sinusoidal heat wave.The heating source system designed in this paper can realize multi-mode output,provide thermal excitation for PT,ST and LIT imaging,and has the characteristics of convenient operation,stable and efficient,uniform heating and so on.Through experimental verification,the large-size carbon fiber honeycomb sandwich material of100cm×100cm can be uniformly and effectively stimulated,and the defect information inside the material can be accurately detected with the help of infrared thermal imaging nondestructive testing technology.