Calculating integral from data over time - solved

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Robert Mama
Robert Mama 2020-11-9
编辑： Robert Mama 2020-11-9
Meybe I'm stupid, but, cumtrapz give me a table, I used it for further calculation - meybe it will be F - I don't have time to stay in this point forever
Hi,
I am completely new to the matlab environment, but the current studies threw me into the deep water right away, and on the previous ones they did not even show us a pond.
I have problem like this. I have experimental data -just record of V(t) and I(t) (both around 1000 pints), frequency equals 4800 Hz and I think it is all that is needed for this question. All in AC regime.
I need to calculate
integral V(t) dt
, and to be honest, I don't even know how to start. I found out on the forum, that this integral is equal to:
integral V(t) dt = k * i(t)
Also my teacher mentioned in the email that I should get some integration constant from this and as I looked through further equations k will be needed.
I've been browsing forums and google for the third day, all trapz, cumtrapz are not useful for me, or I don't know how to get the data I need from them. Ordinary integrals do not work when I do not have a formula, and unfortunately, it cannot be derived from the data I have - the sensors simply have their measurement errors and the formulas do not agree with the graphs I got by calculating the time of subsequent measurements from period.
I would also like to add that in later calculations I multiply by the result of this integral, as long as the trapz did it here, because I got one number, not a table as in the case of cumtrapz, the result was completely different from the actual measurements I could find in the textbooks.
Please give me some tips on what I should be looking at or what I have missed.
Thanks in advance
  2 个评论
Mathieu NOE
Mathieu NOE 2020-11-9
hello
so what are your experimental data look like and what code have you already produced ?

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Robert Mama
Robert Mama 2020-11-9
So, as I mentained:
  • Data that I have is measured in AC regime, its Vrms oraz V(t) [on the left] and I(t) [on the right] - I'm not allowed to put all the data on the internet, so here is a fragment:
0.253689580213472 -0.0459724027807118
0.254260392503034 -0.0445915447659934
0.254704284548489 -0.0463669336420599
0.255190264136031 -0.0414352978752085
0.255951127982832 -0.0420270941672307
0.256796824531654 -0.0406462361525123
0.257451811905391 -0.039758541714479
0.258403384927277 -0.0391667454224569
0.258889364514819 -0.0359118658163349
0.259545009506401 -0.0368981929697052
0.259777148605728 -0.0358132331009979
  • I read data, create tables for Vrms and I
Data=dlmread('Data.txt');
I=Data(:,1);
Vrms=Data(:,2);
  • furter I add some constants and equations that are not related to the question, so I will skip that. Then I add frequency, calculate period from it just like T=1/f and than create timetable for every measured peak:
f=4800; %%Hz
T=1/f; %% s
t=linspace(0,T,height(Data)); %% calculation of t
t=t'; %% idk if this is needed but I do it for plots - I wanted to have data and time vectors looks same
  • Here I have plots and other calculations, but they are not needed to be mantained
  • further I need to calculate Y=x*integral V(t) dt - thats where I have problem, idk how to calculate this integral properly:
  1. My teacher says that I have to compute the indefinite time integral
  2. From this integral I should also recieve some integration constant for further calculations
  3. When I'm using trapz I feel likeit treats all measuring point like - first is in begining of integration, last at the end, interval is 1
  4. cumtrapz gives me table of numbers, I read that the last one should be solution, but idk
  5. Numerical integral functions ofc don't work for data - I'm not surprised here, but I checked anyway :D

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