SUPERVISORY CONTROL AND DATAACQUISITION SYSTEM FOR SITE-SPECIFIC CENTER PIVOT IRRIGATION

A distributed control and data acquisition network was developed for implementing variable rate water application to irregularly shaped areas under a center pivot irrigation system. The control network was designed to meet system requirements for variable rate irrigation. The control network utilizes power line carrier technology for communicating over the three-phase 480 VAC center pivot power cable and multiple network nodes in a master-slave configuration distributed along the center pivot lateral. The network was implemented on a commercial 392 m (1285 ft) center pivot system and field tested during the 1996 irrigation season. The supervisory control and data acquisition network was used to withhold water from non-cropped areas of the field and minimize system operating pressure according to distributed pressure measurements by controlling the speed of the water supply pump using a 111 kVA variable speed motor controller. A description of the control network hardware, software, system implementation, and preliminary operational performance are presented.