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NCSL International - Governance
Automatic Calibration of Precision Multifunction Calibrators
D.W.K. Lee, The Govt. of the Hong Kong SAR Standards and Calibration Laboratory
An automated system is developed at the Standards and Calibration Laboratory (SCL) for calibration of DC voltage and DC current functions of precision multifunction calibrators, namely Wavetek 4X0X series and Fluke 57XX calibrators. UUTs are calibrated automatically against laboratory standards, including Zener voltage reference and standard resistors, which have previously been calibrated by the Laboratory’s intrinsic primary standards, namely the Josephson Array Voltage Standard (JAVS) and the Quantized Hall Resistance Standard (QHRS). Measurement results obtained are traceable to the Laboratory’s electrical reference standards. Calibration is performed using a high precision Digital Voltmeter (DMM), Agilent 3458A, whose gain and linearity errors have been determined by the Laboratory’s JAVS. Measurement errors due to the system DMM are minimized by applying offset and gain corrections. The system comprises control software and a user-friendly graphical user interface written in Visual Basic. The system takes approximately 4 hours to calibrate the DCV (full range measurements from 100 mV to 1000 V and linearity test at the 10 V range) and DCI (full range measurements from 10 μA to 2 A and linearity test at the 1 A range) functions. The best measurement uncertainties better than 1/4 of the UUT’s 1-year accuracy specifications.
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