- Joined Oct 29, 2013
Someone please catch my mistake. I'm trying to measure RMS ripple current at a capacitor that is filtering noise on a DC supply line. The AC component looks like a sawtooth wave with somewhat random period and amplitude. There is a series fuse to the capacitor that measures 0.2 ohm. My true RMS fluke 87V multimeter measures ~50mV RMS AC across the fuse. The math says I should have about 250mA ripple current. But this is not true because an automotive style 2A fuse blows in less than one minute, so I know the ripple is something more than 2A. Is the error in my method or in my measurements? I'm trying to resist lugging my scope out to where the circuit is, but maybe the multimeter isn't giving me accurate RMS AC voltage?