By Jim Montague, Executive Editor
How healthy is your network? No, I don't mean is your refining process filling its tanks, or are your machines spitting out products? What I want to know this time is how healthy are the managed Ethernet switches and gateways moving all of the critical operating information?
This is a crucial difference. It's important because many network devices can pass along important production values and alerts, but users sometimes forget to check on the switches themselves. Some switches can pass along lots of process data, but they can't deliver information on their own status and well-being. Unfortunately, if a network switch goes down or is overwhelmed, then vital process data won't get through—just as if the application had unexpectedly shut down.
Evaluating a network once meant plugging in a handheld device and checking voltages and analog signal levels, but these tools evolved into network sniffing capabilities and network software that uses the simple network management protocol (SNMP) and other protocols to check pre-defined parameters and thresholds on switches and network segments, collect and view these indicators in on-screen displays and manage their networks from more central or remote locations. So while you can never take your eyes off essential process values, you must also find a way to check on the switches that support them.
Of course, many network management tools originated on the information technology (IT) side, but now they're employed and adapted for the plant floor. This is necessary because many manufacturers are realizing they have hundreds if not thousands of Ethernet switches, signal converters and other devices to monitor. Fortunately, there are lots of software tools for examining and managing industrial Ethernet networks. As always, you just have to choose and use the right one.
Orange County Overhaul
Orange County Utilities (www.ocfl.net) in Orlando, Florida., pumps 35-40 million gallons per day (mgd) of drinking water to more than 140,000 users in the county's mostly unincorporated areas. The utility operates 15 water production sites, re-pumping stations, elevated tanks, several 600-hp pumps and other facilities (Figure 1). These sites are coordinated by a central control facility, which is usually manned by just one or two operators.
"We monitor pressure, fluoride, residual chlorine, pump status and many other values, and test for lead, copper, bacteria and other contaminants," says Robert Doyon, SCADA supervisor at Orange County Utilities. The operators monitor water production and seek out bad equipment trends by keeping manual and computer logs and also using HMI/SCADA software from GE Intelligent Platforms.
Besides being supplied almost 100% by groundwater, Doyon reports that Orange County Utilities also is almost 100% Ethernet in its well houses, processing areas, generators and other areas. The utility began building its Ethernet network about five years ago and installed a fiberoptic backbone, consisting of 12 pairs of cables, which always has four loops active and serves about 7,000 I/O tags and three databases at the main control facility. Where it used to have PLCs linked by Modbus Plus, it now uses Schneider Electric's PLCs and GarrettCom's managed Ethernet switches, and all of these devices run on Modbus TCP/IP Ethernet protocol.
"Once this whole network was out there and the PLCs were talking to each other, we needed to identify process areas where the equipment wasn't talking," says Donyon. "We wanted software that could look at the whole network. Also, when we converted from Modbus Plus to Modbus TCP/IP, we had some bandwidth problems. As a result, with all the processes we have going on, if they all tried talking at once, we'd just get more traffic from all the repeats and retries, and this would really use up our bandwidth." The utility had slowdowns in PCs polling PLCs for data in each process area, including its wells, chlorine and fluoride feeds and CO2 injection station for reducing pH. "Some of the older modules on the serial side were slow because they ran at 1.5 Mbps on Modbus Plus," explains Donyon. "Now we're scanning at 100 Mbps. Whenever you go from one communication system to another, you're going to have issues like jitter, lost data packets and some failed communications. But we still need to know what's going on at our wells, so we know how much chlorine to feed and have the right concentration at the furthest point in the system."