Example Gate Installations
When Reclamation began designing and installing low-cost canal automation systems in 1994, there was very little enthusiasm among commercial manufacturers to make and sell 12- and/or 24-VDC (volts direct current) gate actuators. For this reason, Reclamation designers developed several prototypes that can be retrofitted onto slide gates on existing structures.
"Do-It-Yourself" Model
While developing a low-cost solar-powered gate actuator, Reclamation staff determined it that is relatively easy to attach a 12-VDC gear motor to an existing slide gate. This can be accomplished with a chain and sprocket[2]. What is more complex is measuring gate position and installing limit switches. Measuring gate position is important because it provides necessary information on the state of the automation system (and can also be used to estimate flow). The limit switches are critical because they protect the gate from being closed too tightly or opened too wide.
Frank Woodward, of Reclamation's Provo Area Office staff, has developed two prototypes which measure gate position and provide limit switches ()http://www.uc.usbr.gov/progact/ca/index.html. The first prototype mounts over the gate stem and is designed for a gate system where the stem moves up and down in sync with the gate (see Fig. 2). As the gate stem moves, a potentiometer tracks gate position. The limit switches are triggered as the gate moves toward its extremes.
Figure 2. The first prototype is mounted over the gate stem and houses the gate position potentiometer and limit switches.
The second prototype (see Figs. 3 and 4) was designed for gates where the stem does not move up and down. On this unit, a gear box is attached to the gate stem lift nut with a chain and sprocket. The gear box is connected to a disk which activates the potentiometer and triggers the limit switches. Because there is increasing interest in integrating image monitoring into gate control systems, the first prototype (which covers the gate stem: a useful visual monitoring point), may not be appropriate for systems that include a camera. In addition, the first prototype is visually obvious and, for this reason, susceptible to vandalism. The second prototype overcomes these two problems.
Figure 3. The second prototype (center left) attaches to the gate stem lift nut with a chain and sprocket and also includes a gate position sensor and switches.
Figure 4. The 12-VDC motor and second prototype are attached to the brass lift nut on the gate stem.
Typical of the solar-powered field sites currently in operation is the diversion structure on the Sevier Valley/Piute Canal, Richfield, Utah, USA (see Fig. 5). The structure has four large slide gates (each is 2-meters square) which are moved up and down by fractional-horsepower 12-VDC motors. A 40-watt solar panel charges two deep-cycle (130 amp-hr) batteries which provide ample power for: four gate actuators, a radio telemetry system, sensors, and a data-logger/controller. The solar-powered automation system was retrofitted onto the existing structure using the first prototype described above.
Figure 5. The diversion structure for the Sevier Valley/Piute Canal illustrates the successful implementation of a solar-powered canal automation system.
The automation system operates in automatic remote control (the canal manager makes frequent changes in the flow target from his office or home). The gates adjust automatically to maintain a near-constant flow in the canal; they can move any time of the day or night. They are controlled by a modified-PI algorithm.
Over the last 7 years, Reclamation has installed over 25 solar-powered automated gate structures similar to the one in Fig. 5. They have proved to be very reliable.