Difference in amplitude of Octave analysis between monitoring and playback

[cyutljr]

Hello:

I tried to write a program to analysis traffic induced vibration. The hardware I used is a NI-9234 with an IEPE accelerometer. The software I used is LabVIEW SignalExpress. The acceleration and Velocity of during monitoring and playback are about the same. However, the amplitudes of Octave analysis between monitoring and playback are quite different. The screenshots are attached.  Can someone tell me what went wrong? Your help is deeply appreciated.

Regards,

JR Lai

[dsb@NI]

The dB reference is the difference. In the Monitor-Record screenshot, your reference is 1u. In the Playback screenshot, your dB reference is 1. That explains the 120 dB difference you are observing. I don't know why the dB reference is different between the two projects. Did the dB reference get saved to the log files?

[dsb@NI]

It is going to be hard to help with SignalExpress or the Sound and Vibration Assistant. These products are no longer shipping nor supported. Are any of these options for you: FlexLogger, LabVIEW, or even the Dynamic Signal Analyzer Soft Front Panel (SFP)? 

[cyutljr]

Dear Doug:

Thank you very much for your reply. I noticed the difference in the dB reference level between recording and playback. In LabView, there is a reset dB reference value function to reset the value. However, there is no such  such function in Signal Express. I browsed through the discussion forum and someone told that I can run an external VI in the  Signal Express step to reset the dB reference value. I just don't know how to save the reset dB reference value function into a VI that can be run in the  Signal Express step.

I can write a LabView VI to play back the recorded signal.  It would be nice if I can reset the dB reference level during play back in Signal Express.

Again, thank you very much for your time.

Best Regards,

Jiunnren Lai