Automatic Calibration System For Sound Level Meter Based On PXI Bus Technology

Sound level meter (SLM), which is the basic acoustics instrument, has been widely used for measuring sound level. It's significant important to ensure the accuracy of SLM and currently manual calibration is widely applied. But manual calibration has the shortcoming of heavy workload, long hours, and heavy demanding on professional workers, so it's unsuitable for the increasing workload, and in this way, it's important to introduce a automatic calibration system for SLM.Currently, some engineers has been done some researches in this area, but all those researches has some deficiencies, such as incomplete functions and limited usage, therefore, this paper presents a novel automatic calibration system based on PXI bus.In this system, PXI device, which is used to replace signal generator, preamplifier and voltmeter, is set as the core. This reduces the number of the instruments, and ensures the accuracy of the signal. Meanwhile, PXI device charge the subsidiary instruments in the system, in this way, manual operation is limited and automatic flow is ensured.In the software structure, modular design principle is introduced. And the software structure is divided into 3 layers:common module, calibration module and system module. In which common module contains the functions of hardware management, data acquisition and processing, file management, database management, etc. And it's the base of the automatic calibration system. And the calibration module which contains calibration process is the main module of the system. System module controls the calibration of each SLM, it's the core of the system. In each layer of the software framework, each independent function is encapsulated as sub-module, and this decreased the coupling of the system.In the calibration system, it's important to get the response of the SLM. In former research, engineers tend to get the response by electrical output port. But thanks to the inconsistent definition of those ports, this method has great limitation. Therefore in this paper, image recognition is introduced. To realize the accuracy recognition to the SLM reading, this paper divides the whole recognition process into locating and recognition according to the features of recognition process. In the locating process, multiple frames difference is used to get the row position, and connected domain is used to get the column position, the combination of the results is the finally locating result. And in the recognition process, this paper use pre-processing to eliminate excrescent objects, and get the single digit. Then zip the digit to the array of 6*10 as the feature of the digit. At last, get the recognition results by template matching. The experiment shows this arithmetic has a satisfying recognition rate.The system can simplify the operations and improve the efficiency, reduce the demand on professional workers. The experiment proves the calibration result of the system is effective, and accordant to the contrasting system. Therefore this system is suitable to use in the daily calibration.