HOW TO SET SLOPES (FALLS/GRADES)
18
Working Example 1
The following description in this guide, explains the general principles of setting a Slope (Fall/
Grade) when using the FRE-203XR.
Equipment
You will need the FRE-203XR laser level, a surveying tripod, measuring staff (rod) with mm scale
and a laser detector/receiver. Its not essential but having the remote control for the laser level is
preferable. (Without a remote control, having another person to assist you, is essential).
Site Conditions
There are many diff erent work site scenarios. As an example, we are assuming that you are
outside on a site with a clear fi eld of view and planning to set drainage falls.
All above ground and below ground drainage pipes should be laid to an adequate gradient. The
fall in a pipe is defi ned as the vertical height by which the pipe drops over a known distance. e.g.
a 2.5% gradient is a fall of 1m over 40m or 1:40. (1 in 40).
Typically, surface water or foul water drainage pipes are set between 1:40 to 1:80.
If a gradient is too steep i.e. steeper than 1 in 40, the liquid may run faster than the solids in a
foul water pipe thus leaving the solids stranded, which could then block the pipe. Conversely,
if a gradient is not steep enough (usually less than 1 in 110), then the pipe may still block, if the
solids slow down and become stranded.
Procedure
Place the FRE-203XR horizontally on the surveying tripod, switch it ON and allow it to auto (self)
level. Note the X-axis / Y-axis markings on the top cover of the laser.
Setting a 1:40 gradient:
Position the measuring staff at 10m away from the tripod, held
vertically and move the laser detector (receiver) along the staff to fi nd the set level position,
usually by giving a continuous audible tone. By proportion, a 1m fall at 40m is only 250mm
at 10m, so carefully noting the set level dimension on the rear of the staff , move the detector
down
by 250mm and clamp tight.
Using the remote control (from the staff location) or a colleague at the laser, press the Manual
Override button and have the axis to be adjusted facing the measuring staff .
Hold the “down arrow” button on the remote control or laser’s keypad, to slope the laser beam
down the measuring staff until it gives a continuous tone again, having found set level on the
detector.
This has now set a 1:40 fall.
Return the laser detector to the original set level dimension on the staff .
Dig out ground & lower staff until the laser detector picks up the laser beam again.
Important note:
All “grade facility” rotary lasers revert back to the auto (self) level condition if
switched
Off
without retaining the gradient set. So its recommended to complete the ground-
works before switching the laser Off .
