Importance of impulse calibrator output impedance and method of all-waveform compensation

The influence of the impulse calibrator output impedance on the measured waveform is often ignored because of the rather limited bandwidth of lightning and switching impulses and the short cable connection to the digitizer. A simple model defined by the output impedance of an amplifier-based calibrator, the characteristic impedance of the measuring cable and the input capacitance of the digital recorder is used to compensate the pulse distortion effects of the measurement setup with a significant influence on the front-time of lightning impulse waveforms. Evaluation of an all-waveform compensation is performed on recorded and simulated data. Investigations to transfer the compensation of the raw data into the curve fitting process resulted in a new no-added noise compensation method and application of the Shannon limit has been introduced as a performance indicator for the dependence of the waveform time parameters on the noise level and bandwidth of the calibration setup. The example presented in this paper, although centered on the topic of the calibrator output impedance, will serve as a pertinent entry point to the calibration of high-voltage dividers and impulse digitizers.