Freeze and Frequency Analysis

[Gregory88]

Hey,

I am new in Labview and for my project i have to do a FFT analysis. I use a NI SCB68a and a MEMS Adxl335 sensor for vibration and frequency analysis.

I tried around with while- and for-cases, but i cant solve it and so I have 2 Questions to you:

How can i get my signal visable in a graph-chart for e.g. 10 seconds? Now its just for some milliseconds, played arround with the rate and the samples but no change. Then i got the plan to make it with a loop but i dont now how.

Plan is:  push the trigger for recording the measurements. so far its working (for some milliseconds)

and after the vibration measurement like 10 seconds, with an FFT i wanna analyse the graph manually.

Thanks a lot for you help. 

[Duffy2007]

Hello Gregory88,

you can set the chart histroy length, this defines how many samples are stored inside of the diagramm.(right click on the diagramm)What i recommend is tu use a produce consumer structure and making the FFT in the consumer.

Hope it helps.

[Gregory88]

hey duffy,

thanks for the reply.

i think it´s because you´ve labview '16 i can´t open your recommend VI 😕 is it possible to make it run under my '15?

ok i found the chart history length, but if i play arround with it nothing changes... i mean the more important chart is the one below cuz i thought i could make there the FFT.

[Duffy2007]

Hello Gregory88,

saved down to 2015

[Gregory88]

hey alex,

thank you, also for the VI, now i can open it but it isn´t working 😞

I setted everything and i in the DAQmx i could see my signal, but not if run the VI. 

And a Question: this makes a FFT over the whole time like 10seconds? Or is it also possible to analyse the signal at a peak or over a time like 2 seconds, you know, to be variable/flexible.

But therefore i think must be created cursors right?

[Duffy2007]

Hello Gregory88,

this example makes an FFT every 10 seconds over the complete signal. In the singal chart you only see the last second.

If you want to have a variable analyse system, where you see the 10 seconds and select what region should be analysed you can use the cursor function to select the regions.

[Gregory88]

This would be the one i am looking for. Do you know if NI provides such a VI?

[Duffy2007]

Hello Gregory88,

there is no ready to run function. Attached an idea from my side

[Gregory88]

😕

Thank you again for the VI.

I got a error - 200279: "The VI cant keep up with the hardware recording.

Maybe the problem can be solved trough increasing the buffer, read out more often the datas, or set a special number of the samples."

[Gregory88]

I wanna use labview like in the following example. Like a normal oscilloscope.

https://www.youtube.com/watch?v=vkEg7P3oPvs

I tried to rebuild the VI but doesn´t work at all. 😞