Then Cargill opened its Nutri-Products plant in the late 1990s, there was no inexpensive way for the Minneapolis food giant to automatically grab information from heat trace controllers that kept liquid process ingredients from solidifying. At the Iowa plant where Cargill produced vitamin E from soybean oil, a team of electricians and engineers took clipboards and trekked around the plant, recording data from the plant’s power meter and heat trace controllers.
“A team member would pour over the heat trace figures and issue work orders if we found problems with circuits,” explains Tom Shaw, automation manager at Cargill Nutri-Products Inc. “We manually entered power meter data into a spreadsheet for internal billing.” According to Shaw, this labor-intensive work was actually cheaper than automated systems. That changed recently.
After three years of manually gathering data to enter into spreadsheets, Cargill sought an automated alternative. “Nothing standard existed when the plant was built in 1997,” says Shaw. “OPC (OLE for Process Control) didn’t exist. We had to buy a whole central processing unit to do what now can be done with OPC software.” OPC is an open standard designed to provide business applications with a common local or remote access to industrial plant floor data.
Pitch the clipboards
To automate the collection and storage of data from the devices, Cargill turned to Paris-based Schneider Electric SA, an industrial control and automation company. Cargill installed an OPC factory server (OFS) to interface with its Modbus devices, which were already being provided by Schneider. “We provide both the software and the hardware,” explains Haroon Rashid, product marketing specialist at Schneider. Cargill’s clipboards were quickly discarded, as the OFS software grabbed data directly from the Modbus controllers.
The OFS interface with the Modbus devices was Cargill’s first experiment with OPC technology, but Shaw felt it was worth the risk of implementing an unfamiliar system, since the efficiency payoff promised to be significant. “While it was a bit of a gamble, it was the most efficient way to get dissimilar systems talking to each other,” explains Shaw.
According to Shaw, the key to the system’s success was bringing Modbus to Ethernet. “The uniqueness of our installation comes from the way we communicate with the Modbus devices,” notes Shaw. “Instead of using a programmable logic controller and a Modbus network, we used a simple and inexpensive Modbus-to-Ethernet bridge that converts Modbus TPC/IP to an Ethernet-based network.”
Cargill’s risk was mitigated with a relatively inexpensive implementation. “With a conservative initial investment, our team now can easily interface more than 7,000 Modbus TCP/IP registers,” says Shaw. The integration of the OPC software and Modbus devices will also keep upgrades inexpensive going forward.
According to Schneider’s Rashid, manufacturers use the collected information both for real-time system monitoring as well as later analysis. “Companies like to use the data to visualize the factory floor, not only in real-time, but also to analyze the data and run reports.”
Difficulties in the implementation mostly involved the use of Schneider’s software, which had recently been developed at the time of the Cargill implementation. “It was new software,” explains Rashid. “They were worried about learning new software, and there are always a few bugs in new software.”
For Shaw, the integration between the devices and the software meant a quick return on investment. “We had all these devices that already communicated via Modbus and we recognized that if we could use OPC/Ethernet technology to interface them, we could get a wealth of information very inexpensively.” The integration provides a major leap from the manual system of clipboard data collection. “We can now call up our information from our data historian just like the rest of our process data,” explains Shaw. “To do that in 1997, there wasn’t enough money in the bank. Today, it’s a walk in the park.”
