Design Of Auto Calibration System For Field Bus Intelligent Instrument

Field bus is an interactive communication net which is used on the field of process automation and manufacturing automation in the recently years. This technology already became the hot spot in the automation field. In the three structures of the field bus, its core part is the field bus intelligence observation and control-measuring appliance. The precision had not determined before the measuring appliance export or the precision has the displacement after a period of time, the instrument needs to carry on the examination and calibrate again to determine its reliability and safety. Therefore the calibration of the field bus instrument is essential and it is an extremely important work.This article comes from the present situation of the field bus instrument calibration technology and summarizes that there is massive manual controls in the technology and exist a big limitation. Therefore, this topic based on an already widespread application and basic mature control system -SHCAN2000 Field Bus Control System and designed a kind of Auto Calibration System to use in this intelligent instrument. Regarding the mature SHCAN2000 field bus system, it has already developed many kinds of series and type scene measuring appliance control system and this kind of automatic calibration system aims at SHCAN2000's each kind of measuring appliance. The AI AO DI and DO are the common problems, and we design a kind the auto calibration system which various types are all use in common.This auto calibration system didn't increase any hardware, and used the data transfer function adequately, carried on the data between the two slave machines and used the RS232 serial port, the CAN protocol conversion controller to complete the configuration downloading from the host machine and the data uploading from the slave machine .The auto calibration was realized by the linear principle. This system has used the field bus technology communication function and the real-time processing technology adequately, finally completed the auto calibration of the field bus series instruments. The system also designed the breakdown localization function, the system can locate the unqualified measuring instrument's breakdown accurately, moreover it can identify the wrong type automatic, and the user can see the error message on the monitor. This calibration system can set up the precision request nimble, the user may establish voluntarily to satisfy respective request.Experiment showed that, comparing to the traditional intelligent instrument's calibration system, this system enhanced the working efficiency greatly, reduced the manpower consumption, achieved the universal 3‰precision request need, realized the each series field bus instrument calibration by the least measuring appliance resources.