The Augusta, Ga., facility of specialty chemical manufacturer Ratgers Organics produces more than 750,000 pounds per year in bulk solids for its industrial customers, ranging from agriculture to pharmaceutical. During the installation of a new solvent recovery mixer several years ago, the company learned that digital fieldbus technology could not only reduce wiring and installation costs, but also improve remote troubleshooting, calibration and diagnostics capabilities.
Using traditional cabling to wire up the hot oil system on the solvent recovery mixer, with the usual assortment of pressure and temperature transmitters and valves, is very labor-intensive and time consuming. As a contract manufacturer, Ratgers has to maintain a flexible operation that can change as customer requirements do, while paying close attention to the bottom line.
After months of research, Ratgers decided on a network topology that included an Ethernet backbone, Profibus DP and PA for field devices and an AS-Interface bus for binary devices.
Ratgers selected SIMATIC PCS 7, a flexible and cost-effective control system from Siemens Energy & Automation, Alpharetta, Ga. The facility already had a Siemens APACS+ system for other operations. The control architecture of these newer hybrid systems, as opposed to distributed control systems (DCS), lends itself to the quick-change characteristics of contract manufacturing.
Using a basic PC in an adjacent office next to the plant, Ratgers engineers can perform all system programming, configuration and diagnostics, as well as process monitoring and control.
An Ethernet switch connects the PCs to the mixer's main operator console and controller, and Profibus DP over a fiber optic cable joins the main controller to small remote I/O cabinets through a Siemens Optical Link Module. A combination of Profibus DP to PA converters ," and Profibus DP to AS-I masters in the I/O cabinets ," then makes connections with respective devices. Redundancy is built into the network, as is circuit protection to make sure the bus always is available.
Extensive use of Profibus (PA) and AS-I shielded armorflex cable for wiring the Profibus and AS-Interface devices yielded immediate savings over traditional cabling, which would have required additional conduit and man hours for installation. The new wiring, combined with the easy installation and commissioning of the devices on the network using SIMATIC's Process Device Manager application, saved the company approximately $25,000.
Ratgers was able to install the entire mixer control system after just two days of on-site training and some tech support provided over the phone by Siemens. Instruments first were deployed according to a system plan, and engineers then followed the configuration guidelines for both AS-Interface and Profibus.
Installation was accomplished between batches. With all devices in place and ready to go, engineers had a 12-hour window to get the system up and running.
In many batch-processing operations, recovery is the bottleneck. Because Ratgers could implement process and control modification easily, it was able to reduce processing time by 12 hours to 14 hours. The ability to record temperature, pressure and valve cycles in a precise and timely manner contributed to decreased process cycles. The new bus technology is helping to save more time by allowing engineers to add a transmitter or a control valve easily. Because the bus is already there, all that is needed is a simple connection.
In addition to sensor failure, Ratgers can monitor and control remotely things such as calibration drift (which can be time stamped), feedback linkage wearing on a control valve, valve travel and sticking valves. The company also can determine whether or not a valve is completely open or closed.
