1. Truncate any part of the data that is not actually representative of the airflow measurements 2. Find the average value of the remaining data and subtract that from your signal 3. Take the running integral as before
Just a correction to my previous post : there is no real need to find the zero crossing point : the lung volume is simply the positive and negative maxs of the signal integral over several breaths. Sorry to have missed that ! The only thing that remains to be done is to remove the DC component when present, as in the last Burcu's example...
Chilly Charly (aka CC)
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Hi, My signal is airflow and unit is liters/second.I'm trying to calculate volume from this signal.I'm taking integral of this signal offline after saving airflow data.It is strange that I saved a data 1 as you can find as attachment and I can see a proper signal when I take the integral of it.
However, Ican't see the proper signal in my saved data called 2 as you can find in the attachment. Isaved these two data in the same ondiitons with the same vi. Why can I see with data 1 a proper volume signal while I can't see with data 2?
If you look at the 2.txt data you will see that there is a DC offset across your data of around 0,12. When you subtract the DC offset from the data, you get a good looking plot. There is a function called 'AC&DC Estimator' that will give you the number to subtract from your data. Add this to your program before you take the integral. Also, it wouldn't hurt to apply a lowpass filter as with your ECG data, you seem to have 50/60 Hz riding on your signal.
As for getting your data, you really need to start from a known state. If I were you, I would have your subject take as big a deep breath as he can and hold it until you start the acquisition and then exhale as much as he/she can. Have the subject repeat two or three more times (in the same acquisition) and then breathe in whatever way you want. The first few will give you a max/min reference for (assuming the exhale is the minimum volume or zero reference point) the rest of your analysis.
I am trying to acquire pressure signals from the parallel port in order to calculate flow and volume waveforms and some time data related to flow waveform. but i have some problems;
1- i need to automaticly measure and digitally display the inspiration time and expiration time which are related to flow waveform; inspiration time is the total duration of flow travilling on the positive side and expiration time is the duration of flow travelling on the negative side.
2- my sample rate is 200 Hz in the waveform graph. should i use and array to combine x and y values and should i use 0.005 value for x-axis.
3- when my pressure signal is zero at the input, i see 24 value on the inport at labview. how can i deal with it and pull the value to zero for zero input value. other vaules of input are accurate. when i send 255, i see 255 on inport function.
i am attaching an example flow graph, and i will send a screenshot of my block diagram at my next message.