PC-Based Control Sytem replaces legacy DCS system
Joe Machetta
Plant Engineering
PaperPak Products, Inc.
Tommy Roberson
Mill Maintenance Supervisor
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PaperPak is a worldwide industry leading supplier of hygienic absorbent products that are used in the health care and food packaging industries. Our products range from absorbent meat pads for poultry and meat packaging, to disposable adult briefs and hospital underpads. All of the products rely on some combination of highly absorbent tissue, non-woven material, and film, to create a final consumable product with the desired absorbency. In our Washington facility, the manufacturing process starts by creating a highly absorbent raw material produced on a Beloit tissue machine. This material is then wound into large rolls, and subsequently processed on converting machinery that shape and cut the product into its final form, prior to shipment to the customer.
Our tissue machine in Washington , Georgia is over 30 years old, and although it functioned mechanically, the process control system was of an older generation and becoming unreliable. Spare parts were expensive, had long lead times, and caused us significant down time. Even worse, although the system was programmable, it was difficult to make changes ourselves since most of the programming required knowledge of high-level computer languages. It was also difficult to get service when needed since there was no local knowledge base in Georgia . As our market share grew, and we entered new markets with new products, we needed tighter control of our process to provide the desired absorbency required by these new products. It eventually became obvious that we needed to replace our old DCS control system.
We decided we wanted to purchase a turnkey system, so that we were not distracted from our daily production requirements during the switchover. We narrowed our search to a couple of traditional distributed control products, as well as a PC-based control product. We ultimately contracted an Atlanta-based systems integrator, Hegwood Electric, for the turnkey package. Their recommended system was based on Think & Do Software, a fully integrated PC-based control and HMI package, with distributed Ethernet I/O from Automationdirect.com (formerly PLCDirect). At first we were skeptical that a PC software package could perform all the required functions, but we felt we had to give it serious consideration, since Hegwood was strongly recommending it, and they had successful installations to support their recommendation. After reviewing the entire system and associated costs, we directed Hegwood to install and program the Think & Do-based control system.
The control system configuration consists of two computers running Think & Do Software. An industrial touch screen computer, installed on the factory floor, performs all control and operator interface for stock preparation. This PC is linked to the control room PC, which is located in the operator control room, and controls all other functions of the operation. The operators use this second console to monitor process parameters without going to the machine floor. As an added benefit, the second PC can act as a back-up control system, although we have not seen the need for it, since the system has now been up and running fault-free for 9 months.
The Think & Do software uses flowcharts for logic, sequencing and PID functions. We use the flowcharts to control water, stock and steam pressures and temperatures, tank levels of all process chemicals, valve positions, and also to perform all functional logic for the machine. The HMI editor within Think & Do uses the same database as the control, so any parameter used in the flowcharts is immediately accessible to the operator.
The Ethernet I/O from Automationdirect.com provided substantial cost savings, both in initial cost and installed costs. Since the system has over 400 I/O points, and the field devices were already wired and terminated, we wished to keep our distributed I/O as close to the original configuration as possible. The DL205 Ethernet I/O is modular, and allowed us to create nearly a one for one exchange with our existing I/O. Overall, we only had to change a few field devices to accommodate the new I/O from Automationdirect.com. Using standard Ethernet cable reduced material cost, and installation was quite easy.
Overall, we saved 80% on the initial cost of the hardware and installation. Although Hegwood Electric performed all up-front programming and services, the system is extremely easy to use and understand. Since our maintenance and engineering staff can understand flowchart logic, we were able to make modifications and additions to the program immediately after Hegwood turned the system over. In less than nine months, we have already added two bases of I/O to accommodate new functions, and have made all program changes ourselves. Our performance on parameter control is much tighter since the scan time of the Think & Do system is faster than our old DCS. Where our previous system allowed variances on certain pressures of 3-4 psi, those variances are now less than 0.5 psi. We are now in the planning stages of linking the PC control system to our business system. Overall, we are very pleased with the selection of the Think & Do Software and the Ethernet distributed I/O from Automationdirect.com.
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