I am using a newy bought 34411A to measure AC current (f=1kHz-50kHz). It gives zero values at f>=30kHz. While an old 34401A gives reasonable reading up to 50kHz at least. I also checked their readings at 10kHz. Both of 34411A and 34401A show nearly the same values. Is 34401A superior to 34411A at AC current measurement? Or something wrong with my 34411A?