Research On Automatic Tele-Calibration System For Digital Temperature Indicating Meters

Digital temperature indicating meters are also called temperaturesecondary meters, which are used with thermal resistance or thermocouple toindicate the temperature. They are widely used and their stock is huge in the industryand agriculture.Digital temperature indicating meters must accept strickt calibrationto unify the value in their whole life cycle termly. There is low efficiency and largehuman error in the current verification for digital temperature indicating meterswhich are difficult to trace to the higher level standards.Combining with the remote calibratiom technology and machine visiontechnology, this paper proposes a automatic tel-calibration system for digitaltemperature indicating meters to improve the efficiency of the calibration and changethe traceability process. The main work shows the following five aspects:(1) Design scheme and technology route. According to the characteristics of thedigital temperature indicating meters calibration, this paper give up the schemewhich uses a computer as a communication protocol conversion media, and choosethe inexpensive communication module as the lower computer. The system adoptsthe machine vision technology instead of by means of standard interface to read themeters’ value, expanding the application range of the system.(2) Automatic tele-automatic calibration system hardware design. According torequirements of remote calibration, RS232/RS485to Ethernet module and Gigeinterface industrial CCD camera are chosen to realize data remote transmission.Meanwhile according to the actual needs of the automatic calibration, using PLC,step motor, photoelectric switch, etc device, a pipeline type calibration field platformis designed.(3) Based on visual servo system calibration cycle mode improvement. Aimingat the shortcomings of the existing calibration cycle, the paper puts forward ameasurement method of target depth in monocular vision. Combining with the fuzzyself-turning PID stepper motor control strategy, the scheme of the fast locating the indicating value of the meters, whitch is based on visual servo is designed and thecalibration cycle is improved. The efficiency of the digital temperature indicatingmeters calibration is improved further and calibration equipment is protected.(4) Automatic tele-automatic calibration system software design. According tothe user needs, an easy to operate remote automatic calibration software which has afriendly interface is designed. The system software put to use the modularizedsoftware design thought, and is divided into many function modules which areindependent encapsulated. The paper introdues the communication control moduleand character recognition module, and proposes an efficient feature extractionimproved algorithm of the seven-segment code character.(5) Uncertainty evaluation experimental verification.This paper adopted GUM and the grey evaluation to evaluate calibration resultsof FLUCK724and Yujia XMTD-3002at the same time. The results of two methodsshow that expanded uncertainty of the calibrated meters are no more than one-thirdof the allowable error, and the system to achieve the design specifications.