Figure 12-7.—Laser-level rod equipped with a laser detector.
consequent electrical impulses drive servomotors that
automatically level the base and make the axis of the
laser vertical. The laser beam is emitted at an angle
90 degrees to the axis of the laser by an optical train,
and the optics rotate to form a horizontal reference
plane. This device also can be side-mounted so the
axis of the laser is in a horizontal position, and a
vertical plane can be formed by the rotating beam. An
electronic sensing device, parallel to the axis of the
laser, allows self-plumbing of the rotating beam. The
instrument is self-leveling and self-plumbing within a
range of 8 degrees. Beyond 8 degrees, it will not
operate. This is a safety feature. The tolerance
specified for the position of the reference plane with
respect to true level or true vertical is 20 seconds of
arc. Thus, in a distance of 330 feet, a deviation of 0.03
feet is possible.
Laser Rod
A laser rod equipped with a laser detector (fig.
12-7) contains a sliding battery-powered sensor on
the front face of the rod. When within 0.45 feet above
or below the rotating laser beam, this sensor locks
onto the beam and emits a beep that indicates that a
reading should be taken. The operator then reads the
rod directly to the nearest 0.01 feet.
There are two modes for the sensor: the lock
mode and the float mode. The lock mode means the
sensor will seek the beam, average the position of the
beam, and then lock onto it, giving a beep to alert the
operator to read the scale. The float mode enables the
sensor to fix on the laser beam and continue reading
the beam, as the rod is moved up and down. The lock
mode is used for normal leveling and determination
of elevation or position. The float mode is useful when
forms or stakes must be adjusted. The sensor is
controlled by a mode switch at the top of the rod.
Uses and Advantages of
the Laser Plane
Some uses and advantages of the laser plane
areas follows:
1. The laser plane replaces the horizontal line of
sight of the engineer’s level, and the laser beam
replaces a string line.
2. The operation of setting a grade stake to a
given elevation is the same as using an engineer’s
level, except that there is no need for instructions
from the operator of the instrument.
3. It is not necessary to have an operator
stationed at the instrument when you desire to get on
line or obtain a rod reading.
4. When a laser target is properly attached to a
machine used in operations, such as grading, paving,
12-7
