A new test setup and method for the calibration of current clamps

Current probes are widely used to measure the common mode currents in electromagnetic compatibility (EMC) applications. Often, it is necessary to characterize the ratio of measured voltage to the common mode currents up to gigahertz (GHz) frequencies. Existing calibration methods for current probes suffer from the problem of not directly measuring the current within the current clamp. Instead they either reconstruct the current from measurements at other locations or they use assumptions regarding the geometry which allows them to use a current that is measured at a different location without applying a mathematical correction. For example, by maintaining a 50-Ω transmission-line impedance the current can be determined with low uncertainty. The proposed method overcomes these disadvantages by directly measuring the current at the center of the current clamp. This way the mechanical dimensions of the test setup are not critical any more, i.e., one setup can be easily used to measure a large variety of clamps. The method is primarily applicable for current monitoring probes in the frequency domain.