Using a Blower to Eliminate Refraction
Certain conditions can cause refraction and
scintillation to occur inside the pipe, with the
laser dot appearing to be dancing all around the
target.
The laser light passes through a medium – air.
Anything that disturbs the air will cause the light
to scintillate (dance). The two main causes of
disturbed air are temperature difference and glue
used to connect the pipes.
Before being put in the ground, the pipe lies
around the job site in the sun and heat of the day.
The pipe is placed into the ground, which is much
cooler than the road or dirt surface. The pipe has
heated air and will continue to heat the air until it
cools off. The turbulent flowing air in the pipe will
cause the laser dot to dance.
A solution is to use a blower to move cool air through the pipe. Set the blower at about 5 mph.
A dangling dollar bill placed at the outflow end of the pipe will be at a 45° angle in 5 mile per
hour of flow – sufficient to cool the pipe in about 20 minutes.
Glue, as it dries, gives off vapors. These vapors are a different density, and possibly different
temperature, than the air. This also causes the dancing dot. You will need to wait until the glue
is dried enough so that the laser dot is fixed for a good reading.
OPTIONAL EQUIPMENT
Blower for Refraction Control
Minimizes laser drift for long pipe runs where there is more than a 20º F temperature difference
between the trench top and bottom. P/N 1-08915
Target Panel
For 12” and 15” (300-400mm) pipe. Can be used with standard frame. P/N 1-11254
Large Target Assembly
For 15” (375mm) and larger pipe. P/N 1-11217
Tall Leg Set
For 15” to 24” pipe:
Order 2 side legs (9-09622) and 1 center leg (9-09623).
Metric, for 375-600mm pipe:
Order 2 side legs (9-09606) and 1 center leg (9-09607).
Optical Instruments for Checking Elevation
Digital Level and Bar Code Rod
One push of a button provides digital elevation and distance. Eliminates rod reading errors.
P/N 1-16612
AL26-C Automatic Level
High accuracy, wire hung magnetic compensator with 26X magnification. P/N 1-16613
20
AGL Blower
1-08915
12VDC
