On 6/4/06, Lew Wolfgang <[EMAIL PROTECTED]> wrote:
Tracy R Reed wrote: > Can anyone recommend a simple device which can measure the amperage > used? Preferably without having to place it inline (I think some can > measure the EMF) but inline is doable if that is all there is. You can get clip-on ammeters, probably at Frys. They just clip around the power cord and measure the AC magnetic field. I've got an older one that only works if you clip around "one" of the wires, but modern ones don't care.
From the physical point of view, I don't see how this can work.
The external magnetic field of one conductor is essentially cancelled by the field of the other (running parallel) conductor. There are too many variables in the geometry to make this a practical measurement method. You can use a clamp-on ammeter at a master circuit-breaker box where the two wires of a circuit are available individually. I have a neat electronic gadget called the "Kill-A-Watt" (google for that name) which measures volts, amps, watts, power factor, etc. It comes with male and female standard 3-way AC connectors. To use it easily with computer equipment, I have made up a two-part extension cord that adapts the connection to the 3-way IEC plug/socket that computers use. Still requires pulling the cord from the back of the computer and inserting the Kill-A-Watt with its extension cord into the circuit. To comment on Tracy's original problem:
At work last month we had half of our servers go down because a power
strip
which was supposed to have blown its breaks at 15 amps blew it at half
that. Computer power supplies draw current in short high-amplitude pulses at the peaks of the AC input. The RMS value of the current, and thus the heating effect on a circuit breaker, is significantly higher than would be calculated from the DC power consumption of the computer. The magnitude of the effect can by calculated by a simple exercise in integral calculus, which I have done in the past, but not recently. For some education on this subject, look at < http://www.harmonicslimited.com/docs/tech/what_r.html >. And associated follow-on pages. carl -- carl lowenstein marine physical lab u.c. san diego [EMAIL PROTECTED] -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
