how do you integrate power to get energy?

legs11

hi folks,

im measuring the power consumption of WSN's. i have excel files with cells of power, current, time and voltage. how do i go about integrating the power which should get me a time vs energy consumed graph?

incisor71

I'm not sure if this is an Excel formula question or a physics question, seeing as you've already (effectively) answered your own question in the title.... but here goes, from both angles:

Energy refers to the total number of joules converted from one energy form to another. One Watt of power is one Joule consumed over one second, so.... if you have tabular forms of your power usage over discrete intervals of time, a running summation will do the trick. Bear in mind, though, if you're plotting graphs of other metrics alongside the energy, that its graph will be cumulative over time.

The required scaling factor is the reciprocal of the number of seconds between measurements, which I'm going to call T. In other words:

Energy = (1/T) * (SUM, from 1 to N, of Power values).

In Excel you would accomplish this by entering this formula into the top of the column where you want your energy values - let's say your column of power values starts in C5. Then enter your scaling value into some other fixed location, say F1. You would type in this formula:

=SUM(C$5,C5)/$F$1

Copy and paste this formula down the entire "Energy" column, and it will replicate itself to become:
=SUM(C$5,C6)/$F$1
=SUM(C$5,C7)/$F$1
=SUM(C$5,C8)/$F$1
....and will include more of the individual power values each time - effectively mimicking a running sum with an increasing value of N.

Hope this is of some small help.

legs11

hi mate

thanks for that tip.
so my excel file is like this., im not sure where i put the forumla for energy?


time(minutes) power

xx xxxx
xx xxx
xx xxx
xx xxx
xx
xx etc........ etc
xx
xx

incisor71

legs11 wrote:

hi mate

thanks for that tip.
so my excel file is like this., im not sure where i put the forumla for energy?

The energy column in your example would go to the right of time and power. So say you had one row for the headings, you use column A for time and column B for power, and cell D1 for your scaling factor, then your spreadsheet would look like this (with the first power value at B3):

   A     B        C                          D
1 time  power  energy                <scaling factor>
2 ====  ====   ======
3 x1    yyy1   =SUM(B$3,B3)/$D$1
4 x2    yyy2   =SUM(B$3,B4)/$D$1
5 x3    yyy3   =SUM(B$3,B5)/$D$1
6 x4    yyy4   =SUM(B$3,B6)/$D$1

etc........ hope this clarifies it sufficiently.

legs11

thats great, i will check that out soon.

good stuff:D