The JOURNAL
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From Irrigation Disaster to Success
Tree farm plugs up leaks in its irrigation monitoring and control system by going wireless.
By Jim Garrard, Southeast Regional Sales Manager, Data-Linc Group; Larry Lawver, PLC-EOI System Consultant, Rexel Orlando; and Steve Young, Irrigation Systems Manager, Cherry Lake Tree Farm
Occupying 1,200 acres in Groveland, Fla. near Orlando, Cherry Lake Tree Farm must adhere to strictly enforced water regulation that can bring significant fines for water overflow and usage outside their allotment. The tree farm's legacy system was unreliable, which increased operating costs because of manual data collection and "misuse" fines. Therefore, Cherry Lake installed wireless modems from to produce a trouble-free, reliable and cost-effective system for monitoring and controlling water usage and overflow.
The farm requires a significant amount of irrigation water that Florida strictly regulates, assessing significant fines for any water used in excess of the allotment or for any water released into lakes on the property, according to Steve Young, Cherry Lake's irrigation systems manager. Careful water management, therefore, is crucial for both environmental and financial concerns.
Several years ago, Cherry Lake attempted to deploy an irrigation monitoring and control system using commercial-grade 2.4 GHz Ethernet radios with Ethernet-to-serial converters at each programmable logic controller (PLC) location. The project required data to be reliably transmitted among the Allen-Bradley® MicroLogix™ controllers from Rockwell Automation and a Rockwell Software® RSView®32 workstation at the office. The original consultant added thousands of dollars worth of serial-to-Ethernet converters to the MicroLogix controllers, reaching for near real-time performance using commercial wireless Ethernet modems.
However, that system never worked, despite huge consulting fees and extensive antenna work. The modems overheated, and growing trees obstructed line-of-site data transmission. It was so disastrous that Cherry Lake went an entirely different direction, exploring wire and fiber optic options. Both proved to have prohibitively expensive installation costs.
The "successful" work-around during the six years of total failure of the commercial wireless Ethernet system involved workers in pickup trucks driving to the remote sites to observe, record and modify.
The Move to Wireless
Young needed a cost-effective, reliable automated monitoring and control system. Larry Lawver, a PLC-EOI System Consultant from Rexel Orlando, proposed the solution.
The maximum range between irrigation stations and central control was only two miles, with a change in elevation of about 200 feet. However, they needed to consider the impact of foliage on wireless transmission as the trees grew.
Cherry Lake's project required only small amounts of data to be reliably transmitted among the MicroLogix controller locations and RSView32 workstation. Since the controllers were all DF1 communicators, Lawver recommended eliminating the Ethernet feature and using wireless serial modems. He knew the MicroLogix controllers were reliable, and he was convinced that Ethernet (and 2.4 GHz) commercial grade modems were a significant part of the problem.
Because of his experiences with modems from Data-Linc, a participating Encompass™ Product Partner in the Rockwell Automation PartnerNetwork™, Lawver was confident that Data-Linc's 900 MHz SRM serial radio modems would be able to handle data transfer without errors or performance degradation. In addition, because he also knew that Data-Linc custom configures its modems and cables, he trusted that the installation would be straightforward.
Cherry Lake agreed to try Data-Linc's SRM6000 serial radio modems. They can support a range of 35 miles, with a radio frequency (RF) data rate of 144 Kbps and an operating temperature of —40°F to +167°F (-40°C to +75°C) — performance specifications, even with a very generous operating margin, well beyond those required. Also, weather conditions would not impede modem operation.
Setting Parameters
The system controls irrigation valves and monitors a number of parameters. One of the most important is controlling and monitoring irrigation pipe pressure to ensure that water doesn't leak. The only change to the legacy system was abandoning the entire field Ethernet structure and connecting everything by serial DF1.
The new system design involved 10 remote stations with MicroLogix controllers, (primarily ML1200s) and 11 SRM 900 MHz serial radio modems — one master and 10 remotes.
The control station in the main office included the SRM modem configured as a master with a PC server running Rockwell Software RSLinx® and RSView32. This station communicated via the remote modems, configured to transfer data using DF1 half duplex, with the MicroLogix PLCs located throughout the tree farm property. Both the modems and the PLCs are encased in weatherproof enclosures with the antennas mounted on poles to achieve line-of-sight.
Because of central Florida's severe and frequent electrical storms, the design specified the installation of lightning arrestors between the antennas, topped by lightning rods, and on the SRMs at the modem end.
Easy Installation
Because of their former experience with the commercial grade modems, Cherry Lake asked for help with the initial deployment. Lawver had recently attended Data-Linc distributor training. He installed the master according to user manual instructions, and then went methodically through the remotes. He reconfigured the RSView32 nodes to DF1 half-duplex.
As he worked, he trained the folks at Cherry Lake on reconfiguration and modem setup. Using an earlier site survey, they planned for clear lines of sight using the tall antenna at the master to communicate with all 10 remotes.
"We quit adjusting when we — quickly — got to zero comm errors in RSLinx at each node," says Lawver. In addition, after two days of field support, Cherry Lake found the installation process so uncomplicated that they proceeded with the project without further outside assistance.
Instant Success
As soon as the system was installed, it worked. "After dealing with the legacy commercial grade 2.4 GHz modems that had been problematic for six years, the Data-Linc modems worked without errors and system time-outs immediately," Lawver says.
The SRM6000 radios have functioned flawlessly since they were installed, says Young. As a result, Cherry Lake's water management is much more efficient, and the potential for costly fines has been eliminated. The data update every few seconds from all remote locations is a vast difference from data collected via workers traveling by truck to each station.
Serial Was the Answer
"The real lesson learned," states Lawver, "is 'don't over specify!'" Ethernet wasn't needed for this installation because the operation required the transfer of small amounts of data. Serial was the answer, and the industrial grade SRMs could get the data through without overheating like the legacy commercial grade modems.
Specifying serial rather than Ethernet saved money, and the robustness of the network saved personnel troubleshooting time and ensured rapid response to potential leaks and other conditions that could otherwise could damage the trees or incur state water usage fines.
Carefully examining the customer needs and system-performance requirements before selecting a data transfer option was critical. The problematic, commercial Ethernet 2.4 GHz modems in the first system weren't only data-rate overkill, but also unreliable because they weren't designed for the specific challenges of the operating environment.
For more information about Data-Linc Group, visit www.rockwellautomation.com/go/p-datalinc.