Windows

 

You can define windows before a spectrum is computed. A window applies a shaping function to the waveform signal before the analyzer computes the spectrum, and helps to prevent leakage in a spectrum. The Hanning and Uniform options are available for most measurements. Force/Exponential is available for Impact mode.

Option Description
Hanning Smooth out end effects and reduce leakage in the spectrum. Use the Hanning window for normal analyzer operation.
Uniform Does not apply any shaping and is subject to leakage and amplitude errors. Use Uniform when you analyze transient signals that are contained within the analysis time record length.
Force/Exponential The Force/Exponential window is the default for Impact mode. Impact testing normally requires two window types. The analyzer applies a Force window to the hammer channel, and an Exponential window to the response channel. The Force/Exponential window automatically applies these window types to the appropriate data.
Configure the following parameters.
  • Start Time - Should be equal to or slightly less than the percent pre-trigger in the Set Trigger menu. Recommended default values are 10 percent for Pre Trigger and 9 percent for Start Time, until other window parameters are determined.
  • Force Width - The duration of the force signal as a percent of the overall sampling time. It requires initial test measurements to determine the actual force duration relative to the overall sampling time. Recommended value is 10 percent.
  • COS Taper - Reduce leakage and smooth the leading edge of both the Force and Exponential window and the trailing edge of the force window. 10 to 20 percent is recommended.
  • Expo Decay - The value when amplitude has decreased by 1/e, where e = 2.7182, which should occur at 1/4 of the total time record. A value of 20 to 25 percent is recommended, and 98 percent is the maximum. Enter 0 to prompt the machine to automatically calculate a decay value.