I think the original post stated the measurement was dc. Inrush current, to my mind, implies nothing about ac vs. dc. Because an inrush waveform has a spectrum of components, it is clear that the measurement device, whatever its nature, must have a flat response from the power frequency to whatever frequencies make up the transient. If power is dc and you don't already have a dc probe, the simplest and cheapest way to do that is with a resistive shunt.
I must have missed some of the postings - I recall 100 Amps from the original post, and I don't understand where the AWG 18 or 16 numbers come from. > From: Rich Nute <[email protected]> > Date: Tue, 17 Feb 2004 15:45:12 -0800 (PST) > To: [email protected] (Ken Javor) > Cc: [email protected], [email protected] > Subject: Re: DC Current Probes > > > > > Hi Ken: > > >> My understanding is that this is a dc measurement, hence the discussion of >> waveform potential and phase doesn't apply. If it were an ac measurement, >> this would be a very important consideration, but it doesn't bear on the >> current probe shunt selection. > > If the measurement is inrush current, then it is a > line-frequency measurement over several cycles. > > It is an AC measurement of an exponentially > decaying series of near sine-squared pulses of > which you want to know the peak value of the > first pulse. > > You don't need a big window for the current probe > because you are measuring a #18 or #16 AWG wire. > But, you need a probe that will handle the current, > i.e., won't saturate the core. Usually, this is > a larger current probe with an associated larger > window. > > On 120 and 230-volt power systems, the inrush > currents will range from 40 amps to as much as > 120 amps (for the first 1/2 cycle, with switch-on > optimized for maximum inrush current). On a test > bench using a really low source-impedance power > source, inrush current could be more than 120 > amps. > > Retracting my previous statement, certainly a > current shunt can be used in place of the current > probe. > > On the other hand, if the EUT is a dc-operated > device, then the inrush current is still an ac > waveform, starting with some sort of step function > followed by an exponential decay to the steady- > state current. > > > Best regards, > Rich > > > > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
