Industrial networking expands PLC functionality

08/09/2013


Combining networking and PLCs in the field

Remote I/O: The oil and gas industry deals with hazardous work environments and depends on precision and reliability. For an application that not only needs dependable performance, but also must adapt to changing requirements and increasing demands, traditional control solutions are not ideal, and instead require a modular solution that enables disassembly and transportation. For oil and gas industries, it is essential to use innovative connectivity solutions that allow for communication across great distances without sacrificing performance or being susceptible to environmental elements. These demands require a reliable marriage of control devices, such as PLCs, and networking protocols. 

With these plants, the challenge is overcoming the widespread design of the facility, which requires the network to accommodate a large number of signals and still reduce the wiring footprint while maintaining spare floor capacity. Using distributed I/O systems that feature a hazardous area quick disconnect wiring system provides a cost-effective answer to a complex problem. The easy-to-configure systems deliver remote I/O functionality for processing applications. A single Ethernet cable is capable of handling high traffic volume, transferring as many as 150 signals back to the PLC from the various remote sections of the plant.

Using a sophisticated connector system to terminate process instruments in the field consolidates those signals at a junction box for enhanced efficiency. Further, by implementing twisted shielded pair cables for signal transfer from the junction blocks to the PLC cabinet, and armored single twisted pair cables to connect the junction block to the instruments, there is no longer the need to run all the cables back to the PLC individually. Instead, what used to be eight wires has been combined into one single cable. Because of the small size of the home run cable receptacles, the size of the PLC cabinet, where all the signals eventually terminate, was also reduced. This results in additional cost savings.

Additionally, to meet the individual needs of the oil and gas market and its hazardous locations, these devices must be properly mounted. Options are available that include Ethernet protocols with Division 2/Zone 2 approval, consolidating temperature, 4-20 mA, and discrete signals and sending them at high speeds to the PLC. 

Enhanced automation: A coal production plant has extensive transportation systems that run through the entire facility to transport the coal from its repository to the coal mills. This transport system must be reliable at all times to promote continued plant productivity. Consequently, automation is an obvious choice, but this requires countless sensors and actuators to be installed through the plant that must be managed and maintained. 

Figure 4: In this coal processing plant example, each conveyor belt features its own control cabinet that incorporates connectors, motor-circuit switches, and distributed I/O. The modular I/O stations transfer all the analog and digital signals to higherTo meet these specific demands, using a modern fieldbus system for the signal transmission between the PLC and sensors/actuators can provide the necessary level of automation, control, and durability. Implementing a proper fieldbus system, one that features a modular design and offers rugged protection, will not only provide interference-free communication between all devices, but also a high degree of data integrity, protection against vibration, and extensive diagnostic functionality. 

Consider an example of a coal plant that incorporates two transport stations, two coal mills, and a coal bunker from which the coal dust is blown into kilns. Among these stations, coal is transported via multiple conveyor belts, so it is crucial to keep detailed records as the product moves through the various steps. Each conveyor belt features its own control cabinet that incorporates connectors, motor-circuit switches, and distributed I/O (see Figure 4). The modular I/O stations transfer analog and digital signals to higher level PLCs—which reflect the transport system’s status including parameters such as rate of feed, offset, distension, cracks, or fill level data—through a networking protocol, such as DeviceNet. After evaluating the obtained data, the PLC submits the plant’s status to the management information system. All this control can be implemented with just two fieldbus networks.

Manufacturers are assured of continuous transportation of coal because of the reliable, efficient, and flexible fieldbus technology that provides error-proof production. Using an IP67-rated fieldbus system, this solution meets the high demands of the coal production industry, with simple maintenance and fast diagnostics, combined with easy and error-free installation and low wiring costs—ultimately, ensuring efficient and safe plant operation—even in harsh environments. 

Conclusion

No two manufacturing environments are the same. However, manufacturers share a common drive to produce a high-quality product while maximizing efficiency, productivity, and profitability. The integration of control devices such as PLCs and advanced enterprise networks offers a proactive strategy for achieving these objectives. 

Today’s networking technology delivers fast, secure, and reliable factory-wide data transfer. PLCs deliver increased diagnostic and communication functionality, providing an intelligent, low-maintenance system that delivers significant benefits. Now manufacturers can improve accuracy, provide faster production speeds, and minimize errors, as well as save on material and labor costs.

Randy Durick is director of the Networks and Interfaces group and has 11 years of experience at Turck; Chris Vitale is senior product manager, Networks and has 13 years of experience at Turck; and Matt Boudjouk is product manager, Networks and Interfaces group and has five years of experience at Turck.

This article appears in the Applied Automation supplement for Control Engineering and Plant Engineering


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Don , , 09/19/13 10:29 AM:

Well put together PLC article Randy. Interesting
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