I have a question regarding Bessel filtering. I recently moved from LabView 8.6 to 2013 and by chance noticed a difference between filter results on the same prerecorded data between the two versions – 2013 seems to pass more of the original signal.
The original data is from an impact test of a shock absorber recorded at 8000 Hz through a SCXI-1520 with 1K hardware filter fed to a 6052-E DAQ card. The reporting routine filters the force and travel info through a low pass Bessel 4 pole filter at 125 Hz and then reports max force and travel and the energy delivered and absorbed.
After a bit of digging, I found that the call to lvanlys.dll for the Bessel coefficients returns slightly lower forward and reverse values in 2013. I then moved the 8.6 lvanlys.dll to the 2013 machine and parked it in a different directory ( not resource ) and created my own call to that dll for the coefficients. The results were closer but still passed a bit more signal. The energies are closer the theoretical values ( good ) but Engineering and Sales do not like the shape of the 2013 force – travel curves. More precisely, more “ripple” most noticeable at the beginning of the impact.
. Does anyone have an explanation? One would expect that the same coefficients would be returned.
