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Getting the best out of PLCs

09 September 2015

PLCs are something of an industry giant, so why is there still apprehension when engineering issues arise? Food Processing investigates.

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Bosch’s IndraLogic XLC
Bosch’s IndraLogic XLC

A programmable logic controller, or PLC, is a digital computer used for automation on the production line. They can be found in every type of food and drink factory around the globe, and yet they still hold an air of trepidation for engineers on the line. 

The PLC is something of a workhorse in the automation industry. In the 47 years or so since they were first developed, the PLC has not only changed the way assembly lines are controlled and sequenced, but they’ve also made the manufacturing process much more efficient. 

“The PLC was created to simplify assembly line processes and make them more productive,” says Jonathan Wilkins, Marketing Director of European Automation. “Before the PLC came about, manufacturing control was operated by specialist hardware such as relays and drum sequencers. This meant that if there was a technical failure, or even a necessary upgrade, it would be cost and time intensive to attend to. When Richard Morley proposed the first PLC to General Motors in 1968, there was a loud sigh of relief from manufacturers everywhere, and an even louder groan of disappointment from the electricians paid to rewire the relays. The PLC introduced an efficient way of controlling processes, one that was sleeker, didn’t guzzle energy and was easier to repair and update.”

So the question remains, if repairing PLCs are not as cost or time consuming as manually rewiring hundreds of pieces of specialist hardware, why is there still apprehension surrounding PLCs when something goes off plan?

Perhaps the problem lies with how intricately woven into the fabric of the production line PLCs have become. While PLC issues are relatively easy to diagnose, because PLCs are relied on for a wide range of responsibilities and functions, these problems can cause the whole production line to come to a grinding halt, costing the business money as they fight against downtime.

“For some issues, a simple rewiring might be enough,” says Wilkins. “For others, you may be looking at improving the shielding of the device. There are a range of things that could put our dependable friend the PLC out of action, but luckily troubleshooting is very easy to do once you look beyond the black box. And it shouldn’t take long for the production line to be operational again. The good news is that even when a PLC is beyond repair, it is relatively easy to replace. In fact, older and obsolete models are not too difficult to get hold of, if  you work with the right supplier.”

Wilkins’ advice is continuous maintenance for PLCs: “The best measure is to regularly make sure that your PLC is properly maintained, and that any potential risks are highlighted and dealt with as soon as possible. Continuous maintenance and testing is essential and although its time consuming, it’s a more sustainable approach and it avoids costly downtime, should the PLC break without warning. Most PLCs are designed to endure the most extreme industry conditions and control processes in spite of noise, temperature and vibrations. Due to being cost and energy efficient, it is the industrial control choice of many. For all the disadvantages of wiring and potential hold-up times if something goes wrong, there are many more advantages.”

The black box
PLCs have developed something akin to a black box reputation, which is an unfair assessment according to Hugh Tasker, Product Manager - Micro PLC & Visualisation at Mitsubishi Electric. “As the programming environment has changed and more of the interaction with them has become more visual and modular rather than endless code on screen, there is less to fear when installing and fault finding,” he says. “But it’s not just the technology that has evolved over the years. There have been many other changes in automation, notably the quantity and skill sets of the engineering staff required to successfully implement PLC systems. By and large, the hardware has evolved over a predictable course with continuous, incremental improvements meaning that each generation of products is smaller, faster and more powerful than the one before.”

The evolution of software has been more subtle, as early PLCs changed from needing experts in coded programs to exploit their benefits, becoming more open and accessible through the development of ladder programming, which allowed anyone with a basic electrical knowledge to become an effective programmer. 

Mitsubishi's MELSEC iQ-F series compact PLC
Mitsubishi's MELSEC iQ-F series compact PLC

“More recently now though the demand for structured programming has been pushed and pulled by two forces,” explains Tasker. “Firstly, the fact that we have ever more capable and powerful PLCs means that the only way to manage their programs is to segment them into logical sections that can be easily debugged whilst also employing a choice of languages afforded by IEC 61131-3 (ladder, function block, structured text, instruction list and sequential flow card). Secondly, there is the skill set of new entrants to the workforce for whom ladder logic is an alien language and who are far more adept at using the likes of C# and therefore more comfortable with structured text and flowchart programming styles.”

For Tasker, another factor that comes into play is the de-skilling and de-manning within many of the PLC’s end users, meaning that they are becoming beholden to third-parties to support vital parts of their manufacturing or other processes. “The answer could be addressed with better training and support, but such aspects of a business are often the poor relations and are frequently underfunded and under resourced,” he says. “What we see more and more now is the deployment of remote access to offer 24/7 support for critical processes, and whilst this requires yet another field of expertise (IT, webserver technology, etc), the end results can take away the stress of managing a system. The inclusion of web-servers in HMIs is one of the main reasons why most PLC systems are sold with an HMI these days as this is a simple cost-effective way to give secure access to remote users and engineers.”

Keeping on top of technology
With the wide use of PLCs in factory and machine control systems, forming an integral part of a food manufacturer’s operation and hosting a wide range of functions designed to enable seamless automation and enhance plant production, the full benefits of PLCs are not always realised by operators. With apprehension still surrounding PLCs, there are a number of steps that food manufacturers can implement to overcome any barriers they may have relating to the use of PLCs to achieve the best possible results.

“Technology surrounding PLCs is ever changing, however food manufacturers often miss out on the benefits new technology can offer as they apply the ‘if it isn’t broke, don’t fix it’ approach,” explains Gary Provis, Product Manager, Industry Automation at Siemens UK & Ireland. “By not staying abreast of the latest PLC technology and identifying the right system for their plant, manufacturers could be missing out on the opportunity to increase productivity and efficiency, which can have a real impact on their cost models in the long term.”

Another issue is a lack of skills within the business. Most sites have in-house maintenance services, but they do not always have dedicated in-house engineers, relying instead on third parties to troubleshoot and resolve issues as businesses continue to outsource their skill sets. The result can be that operators feel as though they don’t have any real control over their PLCs, and feeling out of touch with their system will only add to concerns and bring into question the true value of the system. 

“Key to overcoming these challenges is the adoption of a true partnership approach with the solutions manufacturer or distributor,” says Provis. “PLC technology is complex – indeed it’s designed to deal with the most complex of plant processes – and by working with a trusted expert, operators can strike the right balance between maintaining a suitable system and realising the full potential of effective use of PLCs, such as energy efficiency and enhanced productivity.

“For example, at Siemens we work with food manufacturers to develop comprehensive internal strategies and operation standards to meet the individual needs of plants. One of the benefits in a partnership approach such as this is that our experts are able to remotely access systems, enabling off-site diagnosis and resolution which greatly drives down plant costs and reduces onsite inventory. What’s more, working closely with their solutions provider enables them to tap into a read-made pool of industry knowledge and make more informed decisions about possible technological enhancements or plant modernisation.” 

For Bosch Rexroth, one of the biggest issues still facing PLCs is the lack of standardisation across the industry. The huge array of PLCs available on the market are manufactured with different programme interfaces, which can lead to confusion and apprehension from operators when engineering issues arise.

“This lack of understanding can lead to users not utilising PLCs to their maximum functional capacity and they therefore continue to use the product in a traditional, one-dimensional manner,” explains Mark Thomas, Processing and Packaging Sector Sales Manager at Bosch Rexroth. “A modern PLC sits at the heart of most industrial automation systems and is no longer just memory capability and size, but functionality and an ability to integrate into different machinery, functions and processes play equally important roles. With differences in PLC installations, it’s vital to understand how to obtain the best performance from your controller.”

Siemens Simatic S7-1500
Siemens Simatic S7-1500

A common platform
For an automation system to perform efficiently for a business, it’s imperative to link the functions of automation technology to key performance levers. A shared platform that caters for all possible control applications throughout the production process, from inbound to primary, secondary and outbound, allows built-in integration of the automation system within the business systems and production environment.

“The PLC plays a major role in the control element of the system, as well as the collection, distribution and management of data; and process and system diagnostics,” says Thomas. “System diagnostics are now part of the PLC as standard and can be initialised when necessary, such as during the system installation or commissioning phase, helping to reduce project time and allowing the manufacturer to get product to market quicker.”

A PLC gathers vast amounts of data from all areas of the automation system, which can be evaluated to help improve production and maintenance efficiencies. The PLC acts as a control hub for connecting different devices throughout the automation system. As automation systems become more intelligent and that intelligence is distributed around the production environment, this information is available to help engineers when carrying out installation, commissioning and maintenance works, helping to provide higher machine and plant availability. The information can also be stored, analysed and displayed for production and operation managers to monitor key performance indicators and energy usage.

“Previously, PLC memory was at a premium, limiting the capability of the controller,” explains Thomas. “But now higher-speed processors and large memory capacity have opened up the possibility of implementing new functionality in automation systems such as vision system integration, motion control and simultaneous support for multiple communication protocols, whilst still maintaining much of the simplicity that makes the PLC so attractive.”

Getting the best out of PLCs
“Like a loyal pet, the humble PLC is dependable and will deliver what you expect and need from it,” says Wilkins. “All you have to do is ask it nicely and keep it healthy. So even when they break down, there’s no need to panic about PLCs. They’ve been a fundamental part of the manufacturing process for almost half a century, and with good reason. Of course, it’s easy to forget that when your production line stops and you’re left verbally abusing it!”

For Provis, it’s about staying connected: “Often there is too much reliance on PLCs without the partnerships to back the systems up and this is where uncertainty can rise. But by embracing an ongoing partnership approach and utilising the knowledge and skills of their solutions provider or distributor, food manufacturers can ensure their plants are equipped to meet industry challenges now and in the future through an effective and reliable PLC system that delivers optimum productivity.”

“The headaches of implementing and supporting systems will never go away,” says Tasker. “However we can be sure that the solutions on offer will continue to evolve in order to match the needs of both developers and users alike.”

“The PLC still sits at the heart of automation and is a key delivery component,” Thomas concludes. “If used to its maximum ability, a PLC can not only improve end-user functionality, but also provide significant production savings.”

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