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Sonic Tracker and SAS Setup
Sonic Tracker Placement
48
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
Placement in Relation to the Screed
As a tracker is moved closer to or further away from the screed, the response of the screed to an elevation
correction changes. A rule of thumb is to place the tracker about 1/ 3 to 2/ 3 the length of the tow arm forward
of the screed pivot point (Figure 83 on page 48).
Figure 83: Correct Tracker Placement in Relation to Screed
If the tracker is not placed between these points, then incorrect screed responses could result. The following
examples describe the possible, incorrect placements and the errors that would occur.
Example 1: Tracker Placed I ncorrectly at Screed Pivot Point
If the tracker is placed directly at the screed
pivot point (Figure 84), you can see exactly where the screed is relative to the grade reference. However, there
is no feedback from the tow point cylinder, which is used to make the grade control changes.
Figure 84: I ncorrect Placement at Screed Pivot Point
If the tracker gets closer to the reference, it sends a raise correction signal to the valve and the tow point
cylinder begins to move up. Because the screed floats, it does not react immediately to the tow point movement,
so the tracker continues to send raise correct signals to the valve. By the time the screed gets to grade
(approximately 3 tow arm lengths), the tow point cylinder has moved too far, causing the screed to continue
raising. The tracker senses this over correction and sends a lower signal to the tow point cylinder, repeating the
whole process in the other direction. Therefore, with the tracker mounted at the screed pivot point, long waves
in the mat are produced because there is no feedback from the tow point cylinder to the screed (Figure 85).
Figure 85: Tracker at Screed Pivot Point Causes Erroneous Corrections
Example 2: Tracker Placed I ncorrectly at Tow Point
At this point, where grade corrections are being made,
the Laser Receiver is kept at an exact distance from the grade reference (Figure 86 on page 49). Any tracker
elevation changes cause the tow point cylinder to move immediately. The problem with the tracker placed here
is the lack of feedback from the screed.
Desired Grade
Grade
Reference
1/32/3
Sonic Tracker II
Screed Pivot Point
Grade
Referen
ce
Sonic Tracke r II
Incorrect Placement
Sonic Tracker II
Grade
Reference
Average profile of mat with Sonic Tracker
TM
mounted at Screed
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