Controlling water use and runoff helps protect
the environment and "the bottom line"

By Larry Lawver, PLC-EOI System Consultant, Rexel Orlando
Steve Young, Irrigation Systems Manager, Cherry Lake Tree Farm
Karen Perlbachs, Marketing Manager, Data-Linc Group

Abstract- A prime concern of Cherry Lake Tree Farm which occupies 1200 acre near Orlando, Florida, is water usage and the impact of water usage on the aquifers and any irrigation overflow's effect on the lake environment. Cherry Lake's legacy system was not reliable which increased threats to the environment as well as an increase in operating costs due to manual data collection and “misuse” fines. Installing Data-Linc modems to interface with Rockwell equipment produced a trouble-free, reliable and cost-effective system for monitoring and control of water usage and overflow, benefiting both the environment and the bottom line. (Download the 4.5 MB PDF print quality version.)

CHALLEENGES

For over six years, workers drove to each remote site to monitor and adjust the irrigation system.

The Cherry Lake Tree Farm, a supplier of standard and ornamental trees to landscape design firms for use on commercial real estate, occupies a 1200 acre site in Groveland, Florida near Orlando. According to Steve Young, Cherry Lake's Irrigation Systems Manager, the farm requires a significant amount of irrigation water which 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 and any fertilizer. 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 2.4GHz 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 controller locations and an RSView32 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- but 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 they 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 PLAN

Steve needed a cost-effective, reliable automated monitoring and control system. Enter Larry Lawver, a PLC-EOI System Consultant from Rexel Orlando, who proposed a better solution. The maximum range between irrigation stations and central control was only two miles with a change in elevation about 200 feet, but 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 Allen-Bradley MicroLogix controller locations and an RSView32 workstation at the office. Since the A-B MicroLogix controllers were all DF1 communicators, Larry strongly recommended eliminating the Ethernet feature and using wireless serial modems. He knew the MicroLogix were reliable and was convinced that Ethernet (and 2.4GHz) commercial grade modems were a significant part of the problem. Because of his experiences with Data-Linc modems, 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. And because he also knew that Data-Linc custom configures its modems and cables, he trusted that the installation would be straightforward.

In spite of the prior disappointing experience with wireless communications, Cherry Lake agreed to try Data-Linc's robust SRM6000 serial radio modems capable of supporting a range of 35 miles,with an RF data rate of 144 Kbps and an operating temperature of -40 to +167 degrees Fahrenheit (-40 to + 75 degrees Celsius)- performance specifications, even with a very generous operating margin, well beyond those required. Plus, these industrial grade modems came with 10 years of demonstrated, field-proven reliability ensuring that year-round, weather conditions would not impede operation.

THE DESIGN

The system controls irrigation valves and monitors a number of parameters, one of the most important of which is irrigation pipe pressure to insure that there is no water leakage. 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 Allen-Bradley MicroLogix controllers, (primarily ML1200s) and a total of 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's RSLinx software 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 the SRMs at the modem end.

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 per Data-Linc User Manual instructions, 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 ten Remotes. “We quit adjusting when we (quickly!) got to zero comm errors in RSLinx at each node,” said Larry. And after two days of field support, Cherry Lake found the installation process so uncomplicated that they proceeded with the project without further outside assistance

Layout of the Cherry Lake Tree Farm which occupies a 1200 acre site in Groveland, Florida near Orlando, and grows standard and ornamental trees requiring critical reporting, monitoring and control of runoff and irrigation water.

SUCCESS

According to Lawver, as soon as the system was installed it worked. “After dealing with the legacy commercial grade 2.4GHz modems that had been problematic for six years, the Data-Linc modems worked without errors and system time-outs immediately.”

Young stated that the SRM6000 radios have functioned flawlessly since they were installed over a year ago. As a result, Cherry Lake's water management is much more efficient and the potential for costly fines has been virtually 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.

LESSONS LEARNED

“The real lesson learned,” stated Larry, “is 'Don't over specify!'” Ethernet was not needed for this installation, as 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 over-heating 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 leaks and other conditions that could otherwise result in damage to the environment, the trees or excessiver usage fines. Using SRM serial modems made the project very cost effective. “After the 2.4GHz Ethernet modems had failed to perform for six years, the Data-Linc 900MHz serial modems simply worked as soon as they were installed,” said Larry.

Carefully examining the customer needs and system-performance requirements before selecting a data transfer option was critically important to this success story. The problematic, commercial Ethernet 2.4 GHz modems in the first system were not only data rate overkill, but also inherently unreliable since they weren't designed for the specific challenges of the operating environment. The Data-Linc SRM6000 modems afforded long range, full industrial temperature span radios with 10 years of field proven operation. And knowing Data-Linc's reputation for quoting conservative specifications to ensure trouble-free operation, Lawver knew their use would eliminate the costs involved in having to re-do a system installation because the modems couldn't perform. Lawver, Young and the others at Cherry Lake have been pleased with the trouble-free Rockwell/Data-Linc solution. They can be added to the long list of customers who state: “Why Data-Linc modems? Because they simply work!”

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