Time Discrepency in Torsional Vibration Output

[EatClutch]

I am using LabView with the Sound and Vibration toolkit to calculate the torsional vibrations of a driveshaft.  I am using an analog tach sampled at 40960 Hz.  At the same time I am collected linear acceleration data at 2048 Hz.  The hardware is a CompactDAQ chassis.  I am trying to have the tach data and the linear accel data have the same time step.  In the SV OAT Torsional Vibration VI I have set the output step to 1/2048.  Unfortunately when I run my vi get the results shown in the attached plot.  The red line is the calculated torsional vibraiton from the analog tach.  The blue line is from a linear accel mounted to measure tangential acceleration on the shaft (using a telemetry system).  When I look at the waveform output of the VI it indicates the correct time step, but my overall time span for the calculated value is too short.  Does the VI truncate data in any way?

[BobRodge]

Hi EatClutch,

Are you performing any other data manipulation on your tach data besides the Torsional Vibration VI? I would check the length of the data before and after you input it into the Torsional Vibration VI with an Array Size VI. The VI may take a few revolutions to return data, but it should not truncate 20 seconds of data down to 3 seconds. I would check the length of data in LabVIEW and make sure you are getting the same amount in Excel.