Views: 5 Author: Site Editor Publish Time: 2019-03-29 Origin: Site
Center pivot irrigation is a form of overhead sprinkler irrigation including a pivot base structure, there can be one to fifteen or more towers on each system. Towers are usually
identified by number starting with the tower closest to the pivot base or the linear move engine/pump assembly. Thetowers should always follow the same tracks through the field. Equipment crossings and problems with traction aswell as runoff from the compacted, wet wheel tracks are sometimes serious concerns. Keeping linear move and center pivot machines in good alignment is critical to proper operation. Substantial damage can occur to the equipment and the crops if the alignment system fails. Alignment sensors are located on the pipeline at each tower causing the tower motor to start or stop . Alignment is controlled by electronic strain gauges, radio or laser controlled sensor systems. Often the first tower (closest to primary controls) will have an additional adjustable timer that will turn off the entire system if that tower does not move at least once every two to five minutes for extra protection against alignment system failures. Inadequate traction at a tower will often cause alignment problems.
Generally, the tower farthest from the pivot point controls the movement of the entire machine. Minimum rotation
times (maximum speed) are commonly between 14 and 20 hours (2 to 3 m/min at the outer tower). Special high
speed gear boxes can be installed on each tower to reduce rotation times to less than 12 hours (i.e., 4.3 m/min at the
outer tower) which is often desirable on sandy or cracking clay soils. Timing controls at the control panel
determine the relative average speed of the outer tower. The on-off cycle time of the outer control tower is usually
about 1 minute (i.e., on a 50% speed setting, the outer motor is on 30 seconds in every minute.) A 100% setting
causes the machine to travel at maximum speed (minimum rotation time) whereas a 50% setting results in the outer
tower moving at half the maximum speed. Of course, the slower the rotation speed, the greater the amount of water
applied. All the other towers try to stay in alignment with the end tower as regulated by the alignment system.
However, tower movement in the interior of the system is somewhat random and start and stop times of 1 to 3
minutes may occur. Thus, because of the start-stop action the uniformity coefficients in the direction of travel are
largest near the pivot and the end tower and the smallest near the center of the irrigation system.