31
•
Bandpass – Passes the frequencies between the left and right mark. This type of
pass-band can be used for Impact Echo data analysis if there is interference from
low frequency noise.
The following guidelines can be used for selecting appropriate filters:
1. When the expected concrete thickness is less than 3 inches, a bandpass filter of
10,000 to 50,000 Hz is appropriate
2. When the expected concrete thickness is between 3 inches and 6 inches, a
highpass filter of 6000 Hz is appropriate.
3. When the expected concrete thickness is between 6 inches and 12 inches, a
highpass filter of 3000 Hz is appropriate.
4. When the expected thickness is greater than 12 inches, a highpass filter of 1000
Hz is appropriate.
Figure 17 – Filter Panel
5.4 Windowing
Interactive time-domain windowing is implemented in this software. Two cursors (left
blue and right red) found on the top plot box can be dragged into the data to window the
front and back of the time domain waveform. This feature is useful to eliminate any front
interference from the solenoid (front end) and/or the interference from double hitting or
other noise (back end). Figures 18A and 18B show the effect on the frequency
spectrum before and after windowing is applied to a typical time domain data waveform
with noise present. Notice that the spectrum from the windowed time domain data in
Figure 18B is smoother than the un-windowed data in Figure 18A.
Left Mark – To set the high pass value
Right Mark – To set the low pass value
Filter Pass
