Gathering Potato Data with HMIs and PLCs

PLC driver software helps potato processors go from manually separating and weighing their products to an HMI/PLC system that delivers Web-based production information on-demand.

Despite low-carb trends, Americans love their potatoes and—from roasted redskins to fries, wedges and chips—and food makers keep coming up with new ways to use them. According to www.potatogoodness.com, food processors saw a 30 percent volume increase in the demand for such specialty potatoes between 2011 and 2012. To keep up with demand, potato processors have turned to automation to help streamline operations and reduce human error. 

Potato grading facilities purchase spuds from growers who are paid according to what kind of product can be made them. Each facility sorts and grades potatoes using a system that includes a weigh scale and conveyors. The system must meet the requirements of the U.S. Department of Weights and Measures, with the USDA acting as a neutral third party in the inspection and grading process.

Traditionally, operators manually separate out the dirt and rock from each dump, weigh and inspect the potatoes, and then place them on the appropriate conveyor. Personnel write all the data on a clipboard and then walk to an office to enter the information into the USDA certificate. This manual provides many opportunities for human error and inefficiency.

One processor tasked Basic Engineering with developing a better strategy. The engineering firm does everything from machine design and line layout to process automation, electrical engineering and database programming. It also makes BasicSafe software, a Web-based database management system for safety-related information and regulatory compliance reporting.

The firm decided to borrow an idea from the world of industrial automation and automate the system via a programmable logic controller (PLC) and human machine interface (HMI). The PLC would control the process by running the gates and scales, capturing data about the potatoes and zeroing the scales after each dump. The HMI would display the process production data as well as let technicians control certain operations. The task at hand was developing a cost-effective and efficient way for the HMI application to communicate with the PLC and the underlying database.

“We were already familiar with manufacturers who had written their own HMI applications for a similar purpose using a Windows-based software application development environment,” said Kevin Showmaker, president of Basic Engineering. “But to cover all the bases, we evaluated proprietary software from large HMI suppliers including General Electric, Siemens and Allen-Bradley [Rockwell Automation]. Some packages lacked the flexibility we needed for the design.”

There were other constraints, said Showmaker. Such a proprietary approach would result in licensing and annual maintenance fees of tens of thousands of dollars. Also, proprietary software can’t be modified by users. But most of it is written in Microsoft Visual Basic or Visual Studio.NET, he said, and “these packages are highly familiar to many Microsoft programmers. So they can easily and quickly code HMI/SCADA, data communications and SQL database applications.”

Basic Engineering opted to build custom operator interfaces for the new system using PLC driver software from CimQuest Ingear. The company's  Net.Logix software contains a library of drivers for Rockwell Automation ControlLogix, CompactLogix, SoftLogix and Micro850 PLCs and programmable automation controllers (PACs). These drivers let Visual Studio.Net programmers create HMI applications by providing direct access to the controller memory, data bases, I/O and communications.

Potato handling via touchscreen

In this case, the automated system can be thought of as “analogous to a typical machine tool HMI, but for a broader use,” says Showmaker. At its heart is a Rockwell Automation Allen-Bradley 1769 CompactLogix PLC and a total of nine Rockwell Automation Panel View Plus HMIs on the facility floor. Because the facility is a food-grade environment, the HMIs are waterproof NEMA 4X touchscreens in stainless steel or fiberglass enclosures that can be pressure washed.

The PLC connects to load cells hooked to the scale for measuring the weight of potatoes, as well as to output devices like pneumatic cylinders that open and close gates to direct a potatoes to the correct conveyor for grading. It also hooks to various motor starters and relays, and even zeros out the scales after each dump. Capturing weights and other data, and displaying production rates, requires polling the PLC.

According to CimQuest Ingear, its software lets programmers obtain the information they need from the controller, process it in a PC, and send commands back to the device for control; it does not require third-party components, drivers, APIs or tools such as OPC servers. The Ingear libraries contained all the necessary Rockwell Automation software drivers.

According to Showmaker, the software allowed Basic Engineering’s programmers to develop applications that had the same functionality as those written in proprietary software. Better yet, the software costs only a few hundred dollars and has no runtime fees.

According to the programmers, setting up the PLC to communicate with the HMI was just a matter of defining the necessary commands upfront, and then making one call to the PLC to retrieve all the information required.

The custom interfaces built using Visual Basic let operators run the entire potato handling process from the HMI touchscreens. “A panel displays information on weight, the status of the production process, data on the lot being graded, and other production metrics, all in real-time. Users can also create certificates and production reports as well as manipulate the data in any other useful way,” says Showmaker.

Web-based access to information

As part of the system, Basic Engineering developed a Web application that resides on a server. Ingear libraries are used to collect the weights and other data through the PLC from the field locations. This data is used to populate an SQL database on the server, which is running on Apache open source server.

Basic Engineering has built similar systems for several of the almost 50 potato-grading facilities in North America. “The Web application calls up the data collected by Ingear that is placed in the database and serves it to clients or to screens that are on the server video display,” explains Showmaker. “In effect, all the information becomes available on the facility intranet.” This means users just need any browser running on a PC, Mac or mobile device with wireless or 3G/4G data capabilities to view data, see data forms and reports or edit data, he says.

According to the processing facility, the new system has made it easy to gather plant floor data, move it into a database, and then make the information available to all qualified personnel. This has reduced errors, streamlined operations and cut facility costs.

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