Monday, December 22, 2008

Found out today that the data from some seismic accels I calibrated was erroneous. The problem was that I used a reference accel that was not good down to the low frequencies that the seismic accels were good to. Thus, the ref accel rolled off and the seismic accels did not, causing an increase in the FRF at low frequencies. "THIS SHOULD HAVE BEEN A RED FLAG"!! Make sure it is in the future!!!!!! I needed to either use an accel that was rated to low freqs or use a coupler with a very low frequency high pass filter.

Also, I found out that an excel spreadsheet I wrote to calculate the natural frequency of a tube or pipe was incorrect. The problem is that E, the elastic modulus, is in lbf/in2, while the specific weight, rho, was in lbm/in3. I needed to convert from lbm to lbf in order for the units to work out. Once I did, I got the correct answer. ALWAYS MAKE SURE UNITS CHECK OUT!!!! I didn't do this the first time so I didnt catch this mistake until now!!!!!!!!!!