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 engineers 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 engineers 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,

Figure 12-8.Grading machine controlled by laser level and laser detector.

5. The laser level shuts off when the laser beam deflects from horizontal.

6. It increases the number of rod readings, as each rodman can set elevations without waiting for the instrumentman, thereby increasing the area of survey within a given time frame.