detect rise and fall times of modulated signal

[Kev2016]

Hello, 

I am trying to find the rise time and fall time of the signal shown in the attached image. This is a signal that is coming from a modulated light source. those narrower peaks are related to the 240Hz refresh rate of the source. I want to find the rise time and fall time of the ON/OFF transition of the light source while ignoring those narrow peaks that are related to the refresh rate. I tried using transition measurement vi but this VI always detects the rising and falling times of those smaller peaks that I want to ignore. 

I know that I can filter out the 240 Hz but t will change the shape of the ON/OFF transition peak and this will give out no so accurate rising and falling times. Is there any other way to do it? I want to only calculate the rising and falling times f the edges marked in red. 

Thank you so much !!

[GerdW]

Hi Kev,

it really would help to provide a VI with some typical data embedded inside and showing your effort of what you have tried so far!

(And it always helps to deonconvert to LV2021 or older in case you already use LV2022…)

[NIquist]

As Gerd said, it would really help to have an array of data to play with.

One question I have is since the light source is modulated, won't there be a range of rise times caused by the modulation cycle sometimes being in sync with the ON transition, making the rise time faster, and vice-versa for when it's falling.  Or is the modulation synchronized to the ON/OFF cycles?

[Kev2016]

HI Gerd W and Nyquist, 

Thank you for taking the time to look into this. Sorry for not including a VI with the post. I couldn't attach it because the VI is big and I acquire data sample by sample using NI DAQ. The acquisition is random and not synced with the light source. What I know is the frequency of the light source ( 240hz) and the ON/OFF period (100ms). 

One way I was thinking about doing this is to detect the voltage where lower peaks occur, cut off the waveform horizontally from that level, and then detect the main peak when there is only the main peak available, as shown in the attached image.   Any thoughts?  But how can i recognize the lower-level peak value from an array of data? using peak detection VI will output both higher and lower peaks

Thank you 

[LLindenbauer]

Run your acquisition, then paste the data to a new VI. The DAQ part is not relevant to the problem.

What you could try:

• Demodulate the 240Hz signal
• A Low-Pass filter (may distort your rise time)