Improvement of Agilent 3458A Performances in Wideband Complex Transfer Function Measurement

Digital multimeters (DMMs) Agilent 3458A are valuable devices in accurate characterization of voltage transducers. Five selectable ranges, from 100 mV to 1 kV, high input impedance and accuracy make this device the state of the art. The paper focuses on the correction of the multimeter frequency response when used in Direct Current digitising mode (DCV), to allow post-correction of the errors introduced by the digitizers. To this end, two different approaches for the identification of the multimeter input complex filter function up to about 100 kHz are proposed. They are, respectively, based on the identification of the complex filter transfer function considering the input stage of the DMM as a black box and on the estimation of the parameter of the DMM input stage. The two methods are validated in a test case and equivalence of the results obtained is found. As a further verification, a deep investigation of DCV and direct sampling mode is performed when the zero level trigger mode is set.