Hi experts. I would like to use sine sweep of 0-10KHz to excite a 2" pipe with two supports and measure it's response using a single axis accelerometer. Every time i repeat the experiment, I get different values of natural frequency even if the condition are same. why is that? also what are the optimum sweep parameters to determine the natural frequencies of a structure like sweep time, sweep direction (up or down), sweeping increment?

Please pour your insights. Thanks !!