The Joe Mullins Reverse Osmosis Water Treatment Plant in Melbourne, Florida, processes water drawn from three Floridian Aquifer System wells, close to 850 feet underground. The Reverse Osmosis membrane system removes salts, metals, and minerals from the water and produces up to 6.5 million gallons of safe, drinkable water per day.
Ethernet technology was chosen for a recent network infrastructure upgrade because it was cost effective and would be able to support future expansions. But from the perspective of Instrumentation Technician Vaughn Curry, the significance of Ethernet technology in this application was speed.
"10 Mbps versus 1900 baud rate for hard wired," said Curry. "That was the primary reason."
Curry administers the control software and is responsible for equipment integration to the server. During the upgrade, he worked with the City's Information Technology (IT) department.
"IT provides the hardware and software upgrades for all the PCs at the plant. We budget the money to IT to maintain our PCs. We employ GE Cimplicity Software to control and monitor the treatment process which runs on servers dedicated to this end. The GE Fanuc PLCs monitor flow, pressure, pH, etc. and through the use of Ladder Logic makes auto-adjustments in the process."
However, Curry and the IT department disagreed when choosing what Ethernet equipment to install. The IT department wanted Curry to use an office-grade Ethernet hub purchased from CompUSA, but he preferred an industrial-grade device.
"The process required constant 24/7 monitoring so the operators had complete control of the plant at all times," he said. "I didn't believe the office-grade hub could tolerate the heat and provide the reliability to prevent losses in downtime. Also, the office-grade hub didn't have any hooks; it had four rubber pads so this hub literally sat on the PLC in the cabinet. As expected, the heat caused the hub to fail. As a consequence, the operator became virtually blind to the process, and all the data that populated the Cimplicity screens went blank."
He remembered reading about Contemporary Controls in a trade magazine; a manufacturer of industrial-grade Ethernet products in Downers Grove, Illinois. Curry bought the company's eight-port Ethernet hub marketed under the CTRLink® trade name. The virtue of this EI8-100T hub is to extend a 10BASE-T system beyond two nodes or to increase network distance beyond the 100-meter segment limit of the 10BASE-T specification. Each twisted-pair can be as long as 100 m.
This hub measures 7.6" H x 1.8" W x 6.0" D and can operate in the industrial temperature range between 0° to +60°C. The MBTF is calculated at 70 years, allowing for solid reliability. The results of these calculations are very conservative. These calculations were produced with the use of the Telcordia standard: Method I - Case I - Quality Level I. The hub also follows the standards for IEEE 802.3 repeater units. These standards include preamble regeneration with symmetry and amplitude compensation. Repeaters must retime signals so that jitter, introduced by transceivers and cabling, does not accumulate over multiple segments. This product detects runt packets and collisions and reacts by generating a Jam signal. It automatically partitions jabbering ports to maintain network operability.
Shielded RJ-45 connectors accommodate either UTP or STP cabling. The Link Integrity function is supported-confirming that a functioning adapter or hub is on the other end of the segment. Hubs can be cascaded using a crossover cable. This unit also operates from a wide-range, low-voltage AC or DC power source. Provisions exist for redundant power connections.
For more accurate troubleshooting, the EI8-100T incorporates LED indicators. Besides one common Collision LED, each port has a pair of LEDs to indicate link status and port activity. It is suited for easy panel or DIN-rail installation unlike office-grade equipment.
Curry installed the device in his system last year, providing a more convenient and neater wiring scheme. "It allowed me to mount the device away from the heat sources in the cabinet, PLCs, power supply, etc," he said. "With eight ports, I was able to connect the one hub to the four PLCs to the Main and backup Cimplicity server. One of the connections was used to attach a switch that transfers data across the street to another control network at the surface water treatment plant."
Curry said Contemporary Controls' hub matched his application perfectly. "It has performed without any problems. Reliability is a concern and can pose a critical situation if the system is unable to maintain connections to the software. We monitor input pressure and the PLCs. If the input pressure is too high or if differential pressure is not monitored, it can cost $1 million to replace the membrane tubes reverse osmosis in one train. The PLCs control the injection of chemicals into the process. For example, they calculate the amount of pH with sulfuric acid. If the PLCs malfunction, the amount of chemicals would be inaccurate."
"I've won my battle!" Curry said. "The IT department is even satisfied because the hub aides in troubleshooting the network. The indicators on the hub's front panel allow the operators to see who's talking and who isn't. It is easier to locate problems. The system includes notifications to operators for alarm events, high and low levels. I do not have to babysit this part of the system which leaves me free to stomp out other fires. That's a good thing."