Sometimes, achieving significant efficiencies in plant operation requires taking a calculated risk. Such was the case when our automation team at Cargill Nutri-Products' vitamin E plant sought to optimize labor utilization. With help from Schneider Electric, we successfully deployed OPC (OLE for Process Control) server software and a simple, inexpensive Modbus-to-Ethernet bridge to do what would have been too expensive to achieve just a few years ago.
The plant was built as a joint venture between Cargill Foods and a leading global pharmaceutical company to form Cargill Nutri-Products, Inc. It turns out natural vitamin E from co-products of soybean oil. Cargill Foods' soybean processing plants throughout the United States supply the feedstock. The plant sells all its output to our pharmaceutical partner, which targets the growing worldwide market for antioxidant vitamins.
When the plant opened in 1997, Cargill Nutri-Products committed to achieving supply chain efficiency and to employing state of the art technology to optimize productivity. Ensuring that this commitment became reality fell, in part, to the 5-person automation team.
One of our obvious opportunities was interfacing the plant's Square D POWERLOGIC® power meter and eight heat trace controllers, which weren't connected to the plant's distributed control system (DCS). The heat trace controllers use electric heating cables to keep liquid process ingredients from solidifying in piping systems and holding vessels and to prevent stagnant water from freezing during winter.
Making the upgrade would eliminate the laborious task of manually recording power data. But to interface devices from different vendors was cost-prohibitive when the plant first opened.
So, for more than three years, our electricians and engineers took clipboards and pens in hand and trekked around the plant, recording data from the power meter and heat trace controllers. We recorded voltage, current, power factor and energy usage at the meter. At the heat trace controllers we monitored the temperatures of all 40 circuits in each panel. A team member would then pore over the heat trace figures and issue work orders if we found problems with circuits. We manually entered power meter data into a spreadsheet for internal billing.
We were looking for an economical solution to so much manual data collection. But when the plant was built, we would have had to do a custom interface because nothing standard existed -- OPC didn't exist. We'd have had to buy a whole CPU to do what now can be done with OPC software.
OPC is a standard, non-proprietary technical specification. OPC software is designed to provide business applications with a common local or remote access to industrial plant floor data. Using the OPC open standard helps integrate communication and databases.
We installed OFS -- OPC Factory Server -- software from Schneider Electric to interface simple Modbus devices. With our system, just a few mouse clicks collect data, compile it into a spreadsheet, and feed it to our data historian for tracking.
It was our first experiment with OPC. While a bit of a gamble, it was the most efficient way to get dissimilar systems talking to each other. Schneider Electric supplied the OFS software and POWERLOGIC circuit monitors, part of a power quality analysis system that includes meters, circuit monitors, software, and hardware for managing power.
In our application, circuit monitors are talking on Ethernet through a gateway. The OPC server goes out and identifies those registers in a meter, pulls them in, then serves them up to our batch control system. The OPC server is essentially a conduit between the two devices. It lets the registers be communicated in a standard format that the DCS can understand.
Bridging Modbus to Ethernet was a key step for our team. The uniqueness of our installation comes from the way we communicate with the Modbus devices. Instead of using a PLC and a Modbus network, we used a simple and inexpensive Modbus-to-Ethernet bridge from Schneider. The bridge converts Modbus to ModbusTCP/IP on an Ethernet-based network.
Having used the bridge to convert to Modbus TCP/IP, we connected the equipment using standard Ethernet cabling to an Ethernet switch. Using the OPC software, we were able to easily configure the Modbus TCP/IP devices and test the configuration. After we finished those steps, completing the rest of the project was a breeze.
That entailed configuring communication software points in the plant's DCS and using OPC mirror software to pipe the Modbus TCP/IP registers to the communication software points. The actual configuration was simple. When we start the mirror software, the program asks us to define a pipe. We configured the pipe by selecting OFS as the source OPC server and our other server as the destination server.
After completing that step, we browsed the Modbus TCP/IP registers and the communication software point attributes, then dragged and dropped the pipe from the correct Modbus TCP/IP register to the correct communication software point attribute. Finally, we configured the points in the plant's data historian.
With a conservative initial investment, our team now can easily interface more than 7,000 Modbus TCP/IP registers. We also can enhance the plant's OPC interface in the future at a fraction of the initial investment.
We had all these devices that already communicated via Modbus and recognized that if we could use OPC/Ethernet technology to interface them, we could get a wealth of information very inexpensively. We can now call that information up from our data historian just like the rest of our process data. That's where the real savings are -- doing with software what we used to need hardware to do. To achieve that in 1997, there wasn't enough money in the bank. Today, it's a walk in the park.
