Sonic Tracker and SAS Setup
Sonic Tracker Placement
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
Figure 86: I ncorrect Placement of Tracker at Tow Point
If any of the forces acting on the screed change, then the screed rises or falls without the tracker sensing the
movement. For example, if the amount of material in front of the screed was decreased, the head of material
force (“M”) also decreases and the screed would begin to fall (Figure 87). However, the Tracker would keep the
tow point cylinder on grade, but not the screed since there is no feedback.
Figure 87: Tracker at Tow Point Causes Erroneous Corrections
The best place for the tracker is in the 1/ 3 to 2/ 3 zone, but where do we position the tracker within that area?
That depends on what end result of paving you are trying to achieve. As the tracker is moved further back
towards the screed it becomes more reactive. At the 1/ 3 point a 1/ 4 inch correction at the tracker causes a 3/4
inch correction at the tow point (Figure 88). Another way to look at it is the “Net Tow Arm Length”.
A paver with a 9 foot tow arm and no Laser Receiver takes 27 feet (9 feet x 3 tow arm lengths) to see 96% of
the elevation change. I f a tracker is placed at the 1/ 3 point, or 3 feet in front of t he screed pivot point , t hen t he
paver must move 9 feet (3 feet x 3 tow arm lengths) for 96% of the elevation change. The tracker is measuring
the distance to the reference, so its position along the tow arm becomes the “net tow arm length”. A more
reactive screed would be beneficial for applications where it is important to match the reference, such as
tracking a curb and gutter or matching a joint.
Figure 88: Correct Placement of the Sonic Tracker
As the tracker is moved further forward the screed becomes less reactive. A tracker placed at the 2/ 3 point and
looking for a 1/ 4 inch correction only causes the tow point to move 3/ 8 inch. The net tow arm length is now 18
feet (6 feet x 3 tow arm lengths). This would be a better tracker position for applications where smoothness is
desired such as mainline paving or when using a mechanical or non-contacting (SAS) ski.
Sonic Tracke r II
Incorrect Placement
Desired Grade
Sonic Tracke r II
Incorrect Placement
"Net Tow Arm Length"
Sonic Tracker II
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