Design Of Universal VME Bus Calibration System For Analog I/O Modules

The analog I/O modules are essential components of automatic test systems(ATSs).However,hardware limitations and complicated working environment in practical applications could dramatically weaken the performances of analog I/O modules.Presently,the calibration system for analog I/O modules varies from interfaces to interfaces,which requires more human interventions and has the disadvantages of strong specificity,single function and cumbersome in operation.For these reasons,this thesis studies on the design of a universal VME bus calibration system for analog I/O modules based on the requirement of field calibration.As a result,this paper designs and implements a calibration system that could realize automatic control of standard equipment,automatic calibration,error analysis,visual interaction and reports generation,which is of great significances to improve the working accuracy of analog I/O modules and ensure the reliability of ATSs.After analyzing the functional requirements of the calibration system and the error sources of analog I/O modules,the least square fitting method is adopted as the calibration model and several calculations of relevant parameters during the calibration process are deduced.The system schemes,including hardware and software solutions,are proposed based on the equipment and VME test system within the lab.The hardware system consists of a VME embedded computer,a VME chassis,standard instruments,a VME calibration carrier board,cables and a module to be calibrated.The VME calibration carrier board that is designed based on FPGA to achieve interface conversions between VME bus interface,local bus interface and M module interface respectively,is the core part of the hardware design.In addition,we adopt the theories of layered and object-oriented to design the software with functions including instrument communication,raw data acquisition,automatic calibration,parameters write-back,reports generation,and visualization interaction.The software is designed by Qt/Embedded,which is a powerful graphical user interface(GUI)development tool with abundant APIs.In this thesis,the control of standard instruments is achieved by employing the technologies of bus,serial,and network programming;Multi-thread technology is applied to achieve raw data acquisition,data processing,and data preservation;After calibration,it is required to generate a report as a guideline of the following works;the calibration interface is used to achieve friendly human-computer interaction and display calibration results and status information.Finally,a calibration test platform is set up to perform functional tests of the calibration software and calibration tests of modules.The test results show that the calibration interface is simple,beautiful,and friendly.The calibration system which is characterized by high efficiency and reliability could achieve universal automatic calibration for four types of modules with M module interface or local bus interface.The analog I/O modules after calibration can meet the requirements of accuracy.