The CT2 and 2430 combination enable us to detect the effects of a few picofarads. The lowest impedance measurable is about 0.1 ohms - the insertion impedance of the current probe. Range could be extended somewhat with various de-embedding techniques or additional hardware, but in our work we found these techniques unnecessary. A significant portion of program code is used to determine the frequency of the 2430 - acquired waveforms. In such bursts, one has only a few cycles to work with, and the frequency must be determined by interpolating zero crossings.
Several problems can crop up when using the zero - crossing approach.
One interesting phenomenon is that amplitude measured at a quarter of the sampling frequency can be quite unstable when only a few cycles are averaged. This instability is probably due to the way the system interpolates non - repetitive processes. When frequencies differ between bursts, repetitive or averaging modes cannot be used. A more serious problem that occurs when the DUT itself adds higher - order harmonics to the waveforms impressed across it. FFT techniques can get around these nuisances if sufficient cycles are available.