Research On Key Technologies Of International Comparison On Shock Acceleration Calibration By Laser Interferometry

Mechanical shock refers to a sudden change of force, displacement, velocity or acceleration. This sudden change is also regarded as an instant disturb to system affected. The measurement and control of mechanical shock acceleration is significant in various applications. Since mechanical shock is a typical dynamic process, accelerometers used for measurements of different purposes should be calibrated under similar shock excitation to obtain their dynamic specifications accurately, based on which international comparison can be possibly held for the unification of the quantity’mechanical shock’ worldwide. For the lack of low-g shock calibration system by laser interferometry, China has neither held nor participated in any international low-g shock comparison. Meanwhile, international comparison at high-g is not available for the fact that research on modeling of standard accelerometer based on parameter identification methods, Support Vector Machine (SVM) method, or dynamic error compensation algorithm is not efficiently carried out using real measurement data from high-g shock calibration system. Therefore, it is of great importance to carry out research on key technology of international comparison on shock acceleration calibration by laser interferometry.In this thesis, current status of key technologies of shock calibration by laser interferometry and of international comparison is introduced in details, based on which the former is further investigated at both low-g and high-g levels. The accurate primary shock calibration by laser interferometry is implemented by virtual instrument technology at the whole acceleration range with different shock excitation devices for low-g or high-g, and homodyne or heterodyne interferometers. The uncertainty estimation for dynamic shock calibration is demonstrated. Three feasible approaches for international shock comparison by laser interferometry are proposed based on research work on standard accelerometer’s linear modeling by parameter identification methods and nonlinear modeling by SVM, and on dynamic error compensation and uncertainty estimation. As a result, Asia Pacific Metrology Programme (APMP) held an international pilot comparison of low-g shock acceleration calibration by laser interferometry, with four primary labs as participants from China, Chinese Taipei, Thailand and Germany respectively. This comparison is piloted by National Institute of Metrology (NIM), China, and satisfactory results are achieved.Calibration of standard accelerometers by laser interferometry at low-g can be completed accurately on the basis of further investigation of shock excitation system, laser interferometry and virtual instrument technology. A novel low-g mechanical shock excitation system with wide acceleration range is proposed in this thesis. The working principle of this system is based on collision of high-precision air-borne rigid bodies which is motivated by either electromagnetic hammer or pneumatic hammer. The shock pulse produced by this excitation system is smooth, well-repeatable and precisely-controlled of its acceleration peak value and pulse duration. The low-g shock calibration system by laser interferometry with wide acceleration range is implemented on PXI platform with advanced Michelson homodyne laser interferometer and Mach-zender heterodyne laser interferometer. The accurate calibration of standard accelerometers can be conducted within (20-10000) m/s2, which means a promising application in the field of shock measurement.The high-g shock calibration system by laser interferometry is implemented with Hopkinson bar excitation system, Mach-zender heterodyne laser interferometer and virtual instrument technology. The dynamic calibration data of this calibration system is a good basis for research of dynamic specification of standard accelerometers, based on the fact that the minimum pulse duration is 10 us. In this thesis, both linear modeling methods and nonlinear modeling method of accelerometers are investigated. For linear modeling, Particle Swarm Optimization (PSO), Prediction of Error Method (PEM) and Least Square Method (LSM) for parameter identification are studied while SVM is studied for nonlinear modeling. A feasible solution for international shock comparison is proposed with modeling of standard accelerometer by LSM verified by calibration data of the high-g shock calibration system by laser interferometry.The dynamic error compensation of standard accelerometers and dynamic calibration uncertainty estimation for international comparison is investigated. A feasible and promising solution with wide comparison range is proposed based on dynamic error compensation system tailored with specific filter design for standard accelerometers, which is verified by calibration data of the high-g shock calibration system by laser interferometry.In short, the sensible and practical architecture of the low-g shock calibration system by laser interferometry ensures good measurement repeatability and reliability, and therefore, provides a novel implementation for accurate calibration of standard accelerometers at low-g with relative wide acceleration range. This low-g shock calibration system by laser interferometry at NIM, China was used to pilot APMP low-g shock international comparison which serves as a good example for a planned international key comparison at low-g shock with more participant metrology institutes worldwide. Two feasible solutions for high-g shock international comparison by laser interferometry are proposed based on dynamic modeling of standard accelerometers by parameter identification or dynamic error compensation of standard accelerometers.