Improved system for the automatic calibration of standard resistors in the meg-ohm range

An automated measuring system has been developed to improve the calibration of high value standard resistors in the meg-ohm range at the National Institute for Standards (NIS), Egypt. This system is suitable for the calibration of the standard resistors from 100 kΩ to 100 MΩ using the DMM-based method by the substitution technique where the unknown resistor and the standard resistor are indirectly compared in the same position using a dummy resistor as a short-term reference standard. The system operation is automatically controlled by using a Lab VIEW program which is especially developed for this purpose. The uncertainty for the high value standard resistors measurement of this system is estimated. The performance of this system is also evaluated by comparing the measurement results obtained from this technique with those obtained by the direct comparison DMM-based method. It is found that the measurement uncertainty of with this method spans from 4.1 × 10−6 to 27 × 10−6, while it spans from 40 × 10−6 to 110 × 10−6 for the direct comparison method. The relative differences of the deviation from nominal values of the working standards resistors measured by the two methods are found to be within their expanded uncertainties.