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Behind automation: How industrial networking elevates PLC functionality

31-08-2010
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Behind automation: How industrial networking elevates PLC functionality

How to improve production quality and reduce operating costs

By Cameron Dwyer – Managing Director of TURCK Australia

The days where manpower served as the brain and brawn in manufacturing are long gone – human-machine interaction has become commonplace on the factory floor.

One prime example of this is the Programmable Logic Controller (PLC), which has been taking on the role of the workhorse in automation and manufacturing industries across the board.

By interfacing with everything from sensors and machine guards to motion control devices, PLCs ensure operations run smoothly.

Through the flexibility offered with PLCs, manufacturers can manage multiple machines at once, achieving a higher level of integration and process automation machines and improving production quality and cost of operation.

The benefits of the PLC are well known with their contribution towards efficiency enhancement and the behind the scenes support of industrial Ethernet, making this heightened control possible.

Together, these technologies make communication between man and machine a seamless, profitable combination. Consisting of various protocols, industrial Ethernet was developed with deterministic capabilities to provide a cost-efficient alternative to legacy automation systems.

With the advanced capabilities, sophisticated functionality and simplistic installation, PLCs are a cornerstone of modern manufacturing.

However, to effectively utilize these devices, users must understand the crucial role networking plays and the individual requirements that must be considered for an effective solution.

Together, they form a unified infrastructure that can extend from the administrative to the control- and floor-level networking that offers inherent scalability to continue to meet growing industry demands. 

PLC technology breakdown

Since their inception, PLCs have become a keystone of industrial automation, often serving as a vital link between human and machine.

As control architecture continues shifting and network technology keeps advancing, these changes support integrated HMI-PLCs that leverage an established and portable programming environment.

As a universal controller, PLCs can be programmed to perform a variety of tasks, from switching on and off a motor to mathematical computing operations, through its memory input.

With the processing power, data storage and communication capabilities of today’s modern computers, PLCs offer an intelligent, rugged solution that offers field-level application control. PLCs are designed to act as miniature computers that can deliver reliable operation in a variety of challenging environments, such as extreme temperatures, electrical noise, vibration and shock.  

During operation, PLCs read data from devices and equipment they are connected to. Utilizing input interfaces, PLCs perform the control program that was stored through user-defined parameters.

Typically, these programs are created in ladder logic, which is a language that closely resembles a relay-based wiring schematic. Finally, based on the program, the PLC "writes", or updates output devices via the output interfaces.

This process, also known as scanning, continues in the same sequence without interruption, and changes only when a change is made to the control program.

PLC advantages

Implementing PLCs offer numerous performance and benefits, such as reduced hardware requirements, increased efficiencies and less waste.

With today’s technology, PLCs are highly customized solutions that can be tailored to individual control applications, while consuming less real estate on the factory floor.

As a built-in controller, PLCs offer a simplified installation that utilizes less cabinet space to free up valuable space.

Further, its visual display offers unparalleled opportunities for machine/operator interaction that increases production efficiency with display instructions for machine operators and data entry that can provide alarm monitoring or recipe management via an easy-to-use interface.

Designed for easy maintenance and troubleshooting, repairs are reduced to simply replacing modular, plug-in components.

The likelihood of faults and the time needed to fix these errors is significantly reduced, eliminating the need to rewire panels and devices.

Now, errors can be corrected by retyping the logic. Additionally, fault detection circuits and diagnostic indicators, incorporated in each major component, can tell whether the component is working properly.

With the programming tool, any programmed logic can be viewed to see if input or outputs are on or off.

Expanding PLC functionality with networking

Though PLCs opened the door for on-the-floor visual communication, it was their integration with networking devices that offered manufacturers a whole new level of visibility and control by combining real-time Ethernet with visualization, control and communication capabilities.

To meet the growing operation needs of industrial automation, networks continue to expand, offering monitoring and control capabilities in areas not previously possible. Device networks are now utilizing fieldbus-to-Ethernet integration to develop enterprise-wide control networks.

Merging networking functionality with PLCs enables users to off-load main processor tasks for distributed control in the field, placing control-level devices closer to the action.

Additionally, by combining control with distributed I/O, manufacturers lower their total cost of operation by streamlining data acquisition, communication and factory-wide connectivity.

Networking

First and foremost, in order for PLCs become a networking tool, users must have the necessary bandwidth that allows real-time industrial Ethernet.

Since connection and communication requirements are expanding, PLCs are required to increase support for multiple network technologies. 

While there is no “one size fits all” industrial network for all of the advanced I/O solutions, by accommodating multiple protocols, PLCs can connect the enterprise layer to the plant for as needed. Since network protocols add functionality, PLCs are a necessary component to drive and support these additional functions.

One key component to ensuring these integrated system continue functioning, is maintaining the industrial automation networks.

A reliable network is paramount; therefore, maintaining network availability is crucial.

This requires the system to support the necessary bandwidth and high data transmission rates to meet application specifications, as well as data protection during maintenance operations and fast recoveries post connection failure.

Along with speed and availability, redundancy is important for continued performance and reliability.

As prolonged periods of unplanned system downtime can become a potential threat to plant productivity, redundancy technologies not only provide millisecond-level network recovery, but they can also substantially reduce costs for deployment.

Distributed control

Using distributed control allows parts of the automated system to be decentralized and dispersed through the system. This means that certain portions of the system are be controlled via separate controllers that are located close to the area of direct control.

This allows multiple different form factors for a wide variety of application requirements.

Further, by spreading the I/O data across the application as appropriate (either in-cabinet or on-machine), manufacturers are able to reduce their footprint and the number of components necessary, and ultimately, provide the most cost effective solution.

Distributed control enables users to implement a flexible modular design with the exact amount of I/O expansion to be added when necessary, providing an inherent scalability for fast, cost-effective updates for future expansion.

Distributed intelligence reduces any additional load on the PLC, and also allows the system to accommodate future functional requirements—enabling expansion while still using the same PLC to control automated applications.

This means users can enrich their systems by expanding the size and functional capabilities, and still be standardized on PLC systems.

During off-loading, some of the control functions from the main processor (either PLC or PC-control) to the distributed I/O, which are located either on-machine or in-cabinet, reduce network traffic.

This occurs because through the distributed I/O, the main processor does not need to ‘make requests’ of the remote I/O for status of inputs or to initiate an output, as the distributed I/O system with control/programmable functionality can handle certain tasks, relegating communications to supervisory or status data to the main processor.

By enabling remote I/O configurations, manufacturers can achieve high-level connectivity with only a few I/O points required—even in widespread areas—providing a cost-effective control solution for diverse industries and applications. In large facilities where extensive monitoring and control is necessary, it is not practical or cost-efficient to have a controller at each site.

This would require a tedious and expensive installation process that would require each I/O point to be hardwired with cable running over long distances.

For example, remote I/O systems can be used in acquiring data from remote plant or facility locations. Information such as cycle times, counts, duration or events, etc. then can be sent back to the PLC for maintenance and management reporting. Additionally, hardwiring increases the likelihood of errors, such as mis-wiring, which can cause excessive downtime to correct.

Advanced I/O capabilities

Networking technology has expanded beyond standard DI, DO, AI, AO to advanced I/O such as identification technologies like RFID, SSID for motion and serial inputs, for example, for datalogging or barcode/2D matrix identification systems.

Smarter, more advanced I/O produces greater amounts of data and higher-lever diagnostics that integrated PLCs must be able to deal manage.

Now, typical factory environments are looking for tighter control of their manufacturing process, which results in a need for more than discrete I/O. T

his means that PLCs are experiencing more bandwidth consuming advanced I/O types like analog, temperature and RFID. 

For example, PROFINET uses three different communication channels to exchange data with Programmable Controllers and other devices. The standard TCP/IP channel is used for parameterization, configuration and acyclic read/write operations.

The Real Time (RT channel is used for standard cyclic data transfer and alarms. RT communications bypass the standard TCP/IP interface to expedite the data exchange with Programmable Controllers.

The third channel, Isochronous Real Time (IRT), is the high-speed channel used for motion control applications.

Combing Networking and PLCs in the Field

Remote I/O

Dealing with hazardous work environments, the oil and gas industry 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 an modular solution that enables disassembly and transportation.

For oil and gas industries, it is essential to utilize 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.

Utilizing 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 to 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, but 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 an additional cost saving.

Additionally, to meet the individual needs of the oil and gas market and their hazardous locations these devices must be mounted.

Options are available that include Ethernet protocols with Division 2/Zone 2 approval, consolidating the temperature, 4-20mA and discrete signals and send them at high speeds to the PLC.

Enhanced automation

In a coal production plant, there are extensive transportation systems that run through the entire facility in order to transport the coal from its repository to the coal mills. This transport system must be reliable at all times in order to promote continued plant productivity.

Due to this, automation is an obvious choice, but this requires countless sensors and actuators to be installed through the factory that must be managed and maintained.

In order to meet these specific demands, utilizing a modern fieldbus system for the signal transmission between the PLC and sensors/actuators can provide the level of automation, control and durability necessary.

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 involved, but also a high degree of data integrity, protection against vibration and extensive diagnostic functionality.

In a coal plant that incorporates two transport stations, two coal mills and a coal bunker from which the coal dust is blown into the burning kilns. Between these stations, the coal is transported through multiple conveyor belts, so it crucial to keep detailed records as the product moves though the various steps.

Each conveyor belt features its own control cabinet that incorporates connectors, motor-circuit switches and the distributed I/O.

The modular I/O stations transfer all the analog and digital signals to higher level PLCs that reflect the transport system’s status, 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 (MIS).

All this control can be implemented with just two fieldbus networks.

Manufacturers are assured continuous transportation of coal, with the reliable, efficient and flexible fieldbus technology that provides error-proof combustible production.

Using a n 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 the efficient and safe plant operation necessary, even in harsh environments.

Conclusion

No two manufacturing environments are the same, but share the common drive to produce a high quality product while maximizing efficiency, productivity and profitability.

The integration of control devices like PLCs and enterprise networking capabilities offers up a proactive strategy for achieving these objectives.

Today’s networking technology delivers fast, secure and reliable data transfer factory-wide, and 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 minimise errors, as well as achieve substantial cost savings from both a material and labor standpoint. 

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