Calculating integral from data over time - solved

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

[Mathieu NOE]

hello

so what are your experimental data look like and what code have you already produced ?

[Robert Mama]

Sorry, didn't see that I answered whole topic :D

Answer 1

[Robert Mama]

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