Measurement System for Accurate Determination of Fast-Changing DC Currents Up To 900 A

Accurate measurement of fast-changing direct current (dc) is of great importance for high-power, high-resolution amplifiers generating fast-changing pulsed dc currents, for example, used in magnetic resonance imaging (MRI) systems. A setup and a comprehensive measurement method are developed for the accurate determination of fast-changing dc currents up to 900 A for evaluating these amplifiers. By using a comprehensive analysis method, the predominant factors and noise sources affecting the accurate determination of the amplifier current pulse reproducibility are studied. To further reduce the noise of the readout electronics in the measurement system, a noise reduction method based on correlation analysis is developed. Experiments have subsequently been carried out to prove the validity of the theoretical analysis and the design method. The experiments show that a single measurement channel achieves a current pulse reproducibility of around 1.1 mu As. Using two channels and the correlation analysis method gives around 80% improvement in the measurement noise, resulting in a current pulse reproducibility of around 0.25 mu As, which is more than a factor 20 improvement with respect to the state of the art. These results and the successful final application of the new setup in an actual high-power, high-resolution power amplifier confirm the effectiveness of this new measurement method.