Figure 12-7.—Laser-level rod equipped with a laser detector.consequent electrical impulses drive servomotors thatautomatically level the base and make the axis of thelaser vertical. The laser beam is emitted at an angle90 degrees to the axis of the laser by an optical train,and the optics rotate to form a horizontal referenceplane. This device also can be side-mounted so theaxis of the laser is in a horizontal position, and avertical plane can be formed by the rotating beam. Anelectronic sensing device, parallel to the axis of thelaser, allows self-plumbing of the rotating beam. Theinstrument is self-leveling and self-plumbing within arange of 8 degrees. Beyond 8 degrees, it will notoperate. This is a safety feature. The tolerancespecified for the position of the reference plane withrespect to true level or true vertical is 20 seconds ofarc. Thus, in a distance of 330 feet, a deviation of 0.03feet is possible.Laser RodA laser rod equipped with a laser detector (fig.12-7) contains a sliding battery-powered sensor onthe front face of the rod. When within 0.45 feet aboveor below the rotating laser beam, this sensor locksonto the beam and emits a beep that indicates that areading should be taken. The operator then reads therod directly to the nearest 0.01 feet.There are two modes for the sensor: the lockmode and the float mode. The lock mode means thesensor will seek the beam, average the position of thebeam, and then lock onto it, giving a beep to alert theoperator to read the scale. The float mode enables thesensor to fix on the laser beam and continue readingthe beam, as the rod is moved up and down. The lockmode is used for normal leveling and determinationof elevation or position. The float mode is useful whenforms or stakes must be adjusted. The sensor iscontrolled by a mode switch at the top of the rod.Uses and Advantages ofthe Laser PlaneSome uses and advantages of the laser planeareas follows:1. The laser plane replaces the horizontal line ofsight of the engineer’s level, and the laser beamreplaces a string line.2. The operation of setting a grade stake to agiven elevation is the same as using an engineer’slevel, except that there is no need for instructionsfrom the operator of the instrument.3. It is not necessary to have an operatorstationed at the instrument when you desire to get online or obtain a rod reading.4. When a laser target is properly attached to amachine used in operations, such as grading, paving,12-7
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