The typical sensing height is 2/3 of the shortest leg of a loop (in feet). Therefore a 4’ x 8’ loop typically
has a detection range of 2.6’.
The inductance of a conventional four-sided loop can be estimated using the formula:
L = P x (T
2
+ T) / 4
Where L = Loop Inductance in microHenries
P = Loop Perimeter in feet
T = Number of turns of wire in saw slot
Therefore a 4’ x 8’ loop with 3 turns would be:
L + (4 + 8 + 4 + 8) x (3
2
+ 3) / 4
L = 24 x (9 + 3) / 4
L = (24 x 12) / 4
L = 24 x 3
L = 72 microHeneries
NOTE: Loop feeder cable typically
adds 0.22 microHeneries of inductance
per foot of cable.
The following are suggested guidelines for
loop installation:
1. Make sure the pavement surface in the
area that the loops are to be installed is
dry and free of debris.
2. Design the loop geometry considering the
area of detection, the type of vehicles to
be detected and the distance between the
loop and the loop dectector.
3. The outline of the loop(s) should be
marked on the pavement in such a way
that the lines can be followed easily by
the saw operator and not be erased by the
water feed from the saw.
2“
Sealant
Backer Rod every
2 (two) feet.
Loop Wire / 3 turns
1/4” Saw Slot
Pavement Surface
SAW SLOT CROSS SECTION
Loop
Perimeter
6’ to 12’
13’ to 20’
21’ to 60’
61’ to 240’
240’ & Up
# of
Turns
6
5
4
3
2
Loop wires must be twisted together - 6 twists per
foot from the end of the saw slot to the detector.
Loop Installation Guidelines