Hi, I'm carrying out some tests by sending in sound waves through a tube and measuring the response from the microphones. I have 8 loudspeakers and 8 microphones. At low frequency forcing of my loudspeakers (about 100Hz), the response of the system is small. Therefore the microphone amplitudes are small as well. The attached figure (low_f.png) shows the response of the microphones and the loudspeaker forcing. The problem I'm having is, in this plot the amplitude difference between microphone 8 (MP8) and microphone 1 (MP1) is much larger than the amplitude difference between other consecutive microphones. However, when I measured the signal on the oscilloscope the amplitude difference between these two microphones were comparable to the difference between other micrphones (which is what I expect). Therefore, there is an apparent inconsistency from the measured signals on the oscilloscope and that from LabVIEW. At higher frequencies the system response is large and therefore the amplitude read by the microphones are large as well. In this case the results between the oscilloscope and the LabVIEW results agree. So I think the error in the LabVIEW readings might be due to a property of the DAQ board I'm using. I'm using PCI-6229 board with BNC-2090A terminal block to measure the analog inputs. I use the first 8 channels (ai0-7) to measure the microphone signals, in which I connect microphone 1 (MP1) to ai0, microphone 2 (MP2) to ai1 and so on. The next 8 channels (ai8-15) is used to measure back the signals I send to the loudspeakers. I was wondering whether the inconsistency might be due to the time lag between the signal measurement from the DAQ board, since the amplitude difference is observed for the channels which are the farthest apart (i.e. ai0 and ai7). But then again, if it was a time lag problem I guess I should have the same problem at higher amplitudes as well. Also, why don't I observe this at higher frequencies (i.e. higher amplitudes). Is it something to do with the d.c. of the board? Note that when plotting this figure I have removed the DC Offset of my microphones (by finding the DC component using an FFT). I did plot the signal including the DC offset and I still observed the same problem, i.e. I don't think it's something to do with the DC of the microphones.

Multifunction DAQ

Inconsistency between oscilloscope and LabVIEW readings

This thread is 9 years old...

+20m ?? what? Watt? Volt?

-30 milliseconds ??

How do you generate the sine signal?

How do you measure it?

Self test? Last self calibration ? Last calibration?

Zero (shortcut) offset voltage?

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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Multifunction DAQ

Inconsistency between oscilloscope and LabVIEW readings

Re: Inconsistency between oscilloscope and LabVIEW readings