User Guide
14
Figure 4 - Near Field Target
6mm
1mm
2mm
3mm
4mm
5mm
6mm 6mm 6mm
SCANNING
The depth of the dead zone may be measured as follows:
1. Apply coupling gel to the scanning surface or ll the water trough with tap
water.
2. Position the transducer above the near eld resolution target and per-
pendicular to the wires. (The wires should appear as dots, not lines).
3. Adjust the instrument settings (gain, TGC, output, etc.) to maximize reso-
lution in the near eld. Record these settings for use on subsequent test-
ing.
4. Freeze the image while the near eld targets are clearly displayed.
5. Measure Dead Zone distance using one of these two methods:
• Count how many wires of the near eld target you can see.
Subtracting this number from the total number of targets gives
you the dead zone measurement. For instance, if 3 targets are
visible, the dead zone distance = 2 mm (5mm-3mm).
• Use the electronic calipers to measure the distance between the
transducer face and the closest wire target to be resolved from
the reverberation. If the rst target to be resolved is at 4 mm,
then the dead zone distance is “something less than 4 mm”.
6. Record this distance and compare with baseline measurements.
The near eld group consists of parallel, 100 micron diameter, nylon, monolament
wires horizontally spaced 6 mm apart from center to center (Figure 4, page 13). Ver-
tical distance from the center of each wire to the top edge of the scanning surface
ranges from 5 mm down to 1 mm in 1 mm increments.
DEAD ZONE ASSESSMENT CONTINUED