Display:
"What's "4.2% per 100 inhabitants"

I recently came across a mail from someone trying to kill a project, asking for various calculations before it could go on, that had to take into accounts some powers expressed in kW.h/h.

I mentioned in passing that it simplified nicely as kW and that it did not bode well for the person's competence.


Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi

by Cyrille (cyrillev domain yahoo.fr) on Thu Nov 19th, 2009 at 07:48:25 AM EST
[ Parent ]
That's not always exactly the same thing: kW is more "instant power" whereas kW.h/h is "average power".

You can achieve 10 kW.h/h with 10 kW during one hour, or 600 kW during one minute and then 0 kW during the following 59 minutes...

Europeans think a hundred miles is a long way. Americans think a hundred years is a long time.

by Bernard on Thu Nov 19th, 2009 at 08:31:45 AM EST
[ Parent ]
Well, he called it power, not average power. And the relevant period was not an hour.

And average power should still be expressed in kW.

Anyway, I know you're trying to catch me ;-)

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi

by Cyrille (cyrillev domain yahoo.fr) on Thu Nov 19th, 2009 at 09:50:00 AM EST
[ Parent ]
I don't think this is true.  Reciprocal units represent derivatives (instantaneous), powers represent integrals: All units are integral operators.

If one wants to denote average power over some time frame, one should specifically say so.  Also, different kernels (weighting functions) result in different output - the naive 'sum of previous n values/n' rectangle filter is very lumpy in frequency space (sinc function), instead it's better to use something monotonic like the exponential weighting function (each average is a convex combination of the current value and the previous average).

(The thing about nitpicks is that there is always someone more pedantical than you :)

by njh on Thu Nov 19th, 2009 at 04:03:13 PM EST
[ Parent ]

Display:
Login
. Make a new account
. Reset password
Occasional Series