Measure the amplitude of an analog input signal (daqmx)

[Moobe]

Hi there,

I am using a daq (NI USB-6009) to acquire an analog voltage input from a microphone. The signal is bipolar.

I want to measure the amplitude of the signal accurately.

I tried using the "Amplitude and Level measurements" and "Amplitude and Levels" functions, but the result is different from the amplitude of the signal plotted on the chart.

How can I measure the amplitude accurately?

And what value should I trust? The amplitude of the "Amplitude and Levels" function, or the value on the chart?

Thank you,

Moobe

[OKors]

Are you looking for RMS amplitude across the whole signal or just greatest min/max? In the Statistics Step there's a Min/Max signal output option.

I use this quite a bit while measuring things like strain in high frequency vibration analysis.  

There's also a option to output the MEAN but I've never used that.

See if that works for you.

If you're running an unlicensed version you'll have to unhide the licensed steps. Statistics is right under Amplitudes and Levels.

[Moobe]

Hi OKors,

I am looking to get the peak to peak value, since it's a bipolar signal +peak + abs(-peak).

I tried the statistics function, but it gives the same values as the amplitude and levels, which are different from the values seen on the graph chart.

So what could the reason for this difference in values?

[OKors]

What differences are you seeing exactly?

Have you checked the Hold Peaks option in the Configuration tab in Amplitudes and Levels?

Then select Export Peak-Peak. You may need to stop and restart your logging to re-acquire new valid peaks.

If that doesn't work try posting your .seproj file so we can have a look.

[Moobe]

HI OKors,

It seems to get accurate +peaks when I checked Hold Peaks, however if the following is smaller it won't measure it. So how can I restart the logging to re-acquire new valid peaks without stopping the program?

Thank you