21
HOW TO SET SLOPES (FALLS/GRADES)
Working Example 2 (when you do NOT know the % grade to set)
The following description explains the general principles of setting a Slope (Fall/Grade) using
your Spectra laser, when you do
NOT
know the % grade to set.
Equipment
You will need the Spectra laser level, its remote control, a surveying tripod, measuring staff (rod)
with mm scale and a laser detector/receiver.
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.
See Diagram 1
A
is a manhole cover with surveying tripod and attached Spectra laser level.
B
is a second manhole cover at a lower position, located at distance of “
D
” apart and by a fall of
“
F
”.
The planned sitework is to set a slope on the laser level to assist in digging a drainage channel to
join
A
to
B
.
Procedure
First measure distance “
D
”.
Next, attach the laser level on the surveying tripod, switch it ON and allow it to auto (self) level.
The tripod height is unimportant. Face keypad (Y axis) towards cover
B
.
Position your extended measuring staff on the ground next to the laser & clamp the detector to
pick-up the rotating beam to give a continuous tone on the detector.
Note & record the mm height from the scale on the measuring staff .
To determine & set fall F:
Before moving position from cover
A
, press the laser’s Manual Override button to disable the
auto (self) levelling. On the LL100N, this is only found on the remote.
Do NOT un-clamp detector. Move position and place extended measuring staff over the
centre of cover
B
, holding it vertically (
see diagram 2
). Un-clamp detector and move it up the
measuring staff to pick-up the laser beam with a continuous tone. (
see diagram 3
). Record the
new height value. The site Fall “
F
” is this value minus the value taken before at cover
A
.
Return the detector down to the lower position again & clamp tight. See diagram 2.