Table 3 - Uncertainty budget of calibrating the clamp transducer at 350 A dc Uncertainty Sources Repeatability of the DVM readings Uncertainty due to calibration of the reference DVM Accuracy of the DVM based on specification Drift of the reference calibrator Uncertainty of the reference calibrator system Combined Uncertainty Effective degree of freedom Expanded Uncertainty at confidence level 95% (k=2) Standard uncertainty (%) 6.1 × 10−4 3.5 × 10−4 2.2 × 10−4 1.3 × 10−4 0.15 Probability distribution Normal Type A Normal Type B Normal Type B Rectangular Type B Normal Type B Divider 1 1 1 3 1 Sensitivity Coefficient (Ci ) 1 1 1 1 1 Uncertainty contribution (%) 6.1 × 10−4 3.5 × 10−4 2.2 × 10−4 7.5 × 10−5 0.15 0.15 ∞ 0.3 Second Setup: Automatic Calibration of AC High Current Fig. 1. First setup: dc high current automatic calibration. Fig. 2. Second setup: ac high current automatic calibration using MJTVC. 32 IEEE Instrumentation & Measurement Magazine In contrast with the acdc transfer standards, calibrating the ac high current requires comparison with the corresponding standard dc high current that was calibrated in the first setup. Hence, the 1VMJTVC is utilized in the second setup to the clamp transducer output for the detection of high current in terms of low voltage (Fig. 2). High currents from the HCS are applied in sequence; ac, dc+,dc-, ac for optimum measurement of the ac-dc transfer difference [15]. As ac-dc transfer measurements require large amount of data acquisition and calculations at various frequencies, automation is a necessity. Consistent measurements of ac-dc transfer differences are automated by using a LabVIEW program. The sequentially applied high currents were sensed by the clamp transducer in May 2022