23 Jun
2004
23 Jun
'04
11:05 a.m.
On Wednesday 23 June 2004 17:47, Jules Richardson wrote:
Ok, here's a couple of examples:
Given an RMS meter reading of 600, what's the peak voltage of the signal
(a simple sine wave) to ground, for judging how thick insulation should
be on a HV line.
Estimate the power usage in W (assuming a purely resistive load) on a
208V 3phase VAX 8800 if the load is 25A on each phase.
The first is, of course 600*sqrt(2) = or about 1.4*600=840. I can do
that quickly and easily in my head.
The second can be done two ways. Either (knowing that each phase is
120V, assuming a Y configuration) 120V * 3 * 25A, or 208 * sqrt(3) *
25A. If you're dealing with a delta or weird voltages where you dont
have V/sqrt(3) memorized (208/sqrt(3) = 120), it's helpful to know that
sqrt(3) is approximately 1.7.
I'd say sqrt(2) and sqrt(3) are the two most important roots to know the
value of, at least in an elect(ron)ic context.
Pat
--
Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/
The Computer Refuge --- http://computer-refuge.org
How many even
know the square root of 2 and 3?
Now I'd say there's a difference between the two there - in that the
first is an example of a general skill which could be useful (and no,
I don't believe I've ever been taught how to do it!). The second is
just a specific of the first though and I'm not sure how useful
memorising specific numbers is (someone convince me, though)