regression area under the curve

[heang]

hello
i was trying to get the area under the curve. mathematically the integration can b done directly from 'numeric integration' vi. but what my problem is i cant define the time t1 to t3( as i need to set the threshold level to eliminate noise). what i previously did was defining the threshold level, find the 2 point of t1 and t2. but i left out the coloured portion. using regression will it help to get t3?if yes. how this will b done?


thanks
regards

[NathanT]

Hello Heang,
       To clarify, you just want to get the area of the curve that is not blue, correct?  One method would be to just go through your data and find out where the y value crosses your threshold level and use that as your t1, and do the same thing to find out where the curve crosses the threshold value again for t2.

If your data is already in a waveform, you can use "Search Waveform" to find the time value of the intersections.  You could also come up with your own array calculations to calculate the time values.

Cheers,

NathanT

[altenbach]

This has been going on for a while:

http://forums.ni.com/ni/board/message?board.id=170&message.id=226483#M226483

http://forums.ni.com/ni/board/message?board.id=MathScript&message.id=145#M145

http://forums.ni.com/ni/board/message?board.id=170&message.id=227008#M227008

If I understand this correctly, you use a threshold to find the peak, but then you want the entire area, including the "wings".

As I said before, if you pick the baseline right, your integration boundary does not need to be exact and can be significantly outside because the areas outside the peak will average to zero.

If you have a mathematical model for the peak (e.g. gaussian), you can fit it and calculate the area from the fit.

[heang]

hello
sorry i was making error statement. when i set threshold level. i modify the vi of basic level trigger. it helps me to get the 2 locations which are t1 and t2. but what i cant get is t3. how to define t3?as i need t3 to determine the portion i left out from t1 to t3.

thanks

[heang]

---

hello
sorry
i forgot to mention that it might have 4 curves in one graph. i need to determine each area with respect to each curve.
using numeric integration, i can find the area if only one curve exists. if i do not define the time t1, the integration result will be much different, if i am not mistaken.

regards

[altenbach]

Since the real start and end is buried in the noise, you have to make some assumptions on the shape of the peak. Are all four peaks well seperated or can they overlap?

[heang]

hello
these 4 curves are separated and not overlapping. what i did previously is define the threshold level, getting the trigger location, get the t1-t2, then  it will be added with a certain constant(i assume t3 to t1).it then feed as the input of extract portion of signal. then numerical integration is done.

the result i get is not so accurate as i have comparison result.

what assumption should i make?is it wrong to assume certain constant over t1 to t3?

thanks
regards