Simplified Safety: Rethink the Cost of Entry Using Safety PLCs

The bulk of safety projects industrial companies initiate today involve upgrading safety and control systems in existing production equipment.


Advanced Engineering develops control systems using equipment from many equipment providers, including Siemens and Allen Bradley. Picking the right hardware and software plays a huge role in a company’s machine safety programs. We provide our value added through knowing which issues are important, using unbiased information about safety hardware and software, and doing system integration.

Over the past few years, safety PLCs have become much more common, and hence more often included in customers’ integration programs. The benefits of a safety PLC-based architecture extend well beyond simplified wiring and the ability to alter safety to accommodate changing demands.

Most customers have machines that are already being used in production and they want to add safety to them. Typically, they’re adding safety to two or three machines per year. These machines will already have safety devices, such as e-stops and interlock switches, which the machine builder incorporated into the original design. The value we add is to develop a solution to bring the machine up to the safety level required by a risk assessment. More than likely, these upgrades will include a safety PLC and fail-safe drives.

Developing a safety solution

The first step required for the upgrade is for customers to perform a risk assessment. Risk assessment is a systematic means for quantifying risk levels in order to determine the scope of required safety systems needed to protect personnel and machines from possible injury and damage. The outcome of the risk assessment is that the customer learns the level of safety that is required to be implemented on their system to comply to the North American machine-safety requirements.

Based on the risk assessment and the level of safety required on the machine, Advanced Engineering puts together a safety solution for the customer that includes a safety controller, such as a safety PLC, and necessary fail-safe devices, such as e-stops and light curtains.

The first consideration is what automation platform is currently being used on the machine. The next step is to analyze the most beneficial safety solution for the customer. The solution should be easy to integrate with their existing platform, and provide the most cost-effective implementation. The prime goal is to avoid causing a hindrance to machine operators, while being compliant. We also wish to increase productivity of the system as a whole.

We analyze different manufacturers’ safety solutions. For example, Allen-Bradley products use a standard processor and a safety-partner PLC in combination in the same rack. No safety inputs and outputs are allowed in that rack. Instead, safety signals, such as from interlocks, go to a remote panel, where they are formatted and sent over the network to the safety-partner PLC in the central rack.

Siemens, on the other hand, does both standard and safety processing in one controller. This allows implementing standard control logic for normal machine operation, and safety logic for the safety system in one module with standard and non-standard I/O mixed, either in the main rack or as distributed I/O stations.

Several different network offerings are available depending on the chosen safety solution. These include either Ethernet (PROFINET from Siemens) or PROFIBUS, then, Ethernet (EtherNet/IP from ODVA) , or DeviceNet (ODVA). Customers have flexibility to do everything over the network, which might get them to switch to Safety PLCs.

Similar criteria hold true while selecting variable speed drives. Rockwell Automation offers safe-torque-off options on Allen-Bradley drives, but still uses a hard-wired configuration, with a wire from the PLC to the drive. Whereas, Siemens’ fail-safe drives have a network offering, so there is one network cable to the drive, and no hard-wired safety connection.

Another critical factor is the time spent getting the hardware up and running. Installation can be a huge factor. There may be a lot of machines running with safety relays and e-stop strings, and often there are people who haven’t even heard of safety PLCs. Installation and setup time may even trump the always-critical financial factor. Buyers should examine tradeoffs and ensure that they understand safety, ease-of-use, and monetary considerations. Cost may not make a difference, for example, if one option costs more, but takes less time to install. The cost of hardware may not be as great as the income lost when production lines are down.

Some of the first things Advanced Engineering looks at are the amount of time the system will be down, and general ease of use. If switching from a standard PLC to a safety PLC, how much wire will have to be pulled? When you’ve got people in there troubleshooting at 1:00 am, you want the equipment to be easy to use. That’s often one of the first things people compare after cost. Those cost considerations must also account for the problems that can arise if protective technologies aren’t installed or maintained properly. If equipment or products are damaged, it’s expensive, but if humans are injured, expenses soar and the possibility of legal action rises.

After developing the initial safety solution, we then review it with the customer, making changes per customer requests – such as changing from light curtains, say, to safety mats, and vice versa.

Multiple revisions are done based on customer functionality and requirements, then we ensure that the safety solution meets the safety levels as identified by the risk assessment. Only then do we finalize the drawings, write the code, and install the system.

Follow-up is critical

After the safety system is installed, the customer must do a follow-up risk assessment to evaluate its performance before signing off on it. This follow up risk assessment is critical to ensure that the upgraded machine achieves the required safety levels.

Risk assessment is an ongoing process, to be done every time there is a change made in the safety circuit or re-installation of the equipment. Safety is the most important part of the industrial environment, especially in the U.S.

System integrators always need to talk with their customers and do an evaluation based on the customers’ company-wide safety standards. When customer teams are analyzing these issues, their decision should shade more towards purchasing state of the art equipment. When people add safety, the latest and greatest safety technology solutions would be the wisest decision. They don’t want to be doing this all over again in a few years because they used obsolelete technology.

Tim Gidcumb, senior programmer, Advanced Engineering

This article was submitted for the Siemens Simplified Safety custom newsletter.

See other articles in the Siemens Simplified Safety newsletter.

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
Sister act: Building on their father's legacy, a new generation moves Bales Metal Surface Solutions forward; Meet the 2015 Engineering Leaders Under 40
2015 Mid-Year Report: Manufacturing's newest tool: In a digital age, digits will play a key role in the plant of the future; Ethernet certification; Mitigate harmonics; World class maintenance
2015 Lubrication Guide: Green and gold in lubrication: Environmentally friendly fluids and sealing systems offer a new perspective
Drilling for Big Data: Managing the flow of information; Big data drilldown series: Challenge and opportunity; OT to IT: Creating a circle of improvement; Industry loses best workers, again
Pipeline vulnerabilities? Securing hydrocarbon transit; Predictive analytics hit the mainstream; Dirty pipelines decrease flow, production—pig your line; Ensuring pipeline physical and cyber security
Cyber security attack: The threat is real; Hacking O&G control systems: Understanding the cyber risk; The active cyber defense cycle
Designing positive-energy buildings; Ensuring power quality; Complying with NFPA 110; Minimizing arc flash hazards
Building high availability into industrial computers; Of key metrics and myth busting; The truth about five common VFD myths
New industrial buildings: Greener, cleaner, leaner; New building designs for industry; Take a new look at absorption cooling; Offshored jobs start to come back

Annual Salary Survey

After almost a decade of uncertainty, the confidence of plant floor managers is soaring. Even with a number of challenges and while implementing new technologies, there is a renewed sense of optimism among plant managers about their business and their future.

The respondents to the 2014 Plant Engineering Salary Survey come from throughout the U.S. and serve a variety of industries, but they are uniform in their optimism about manufacturing. This year’s survey found 79% consider manufacturing a secure career. That’s up from 75% in 2013 and significantly higher than the 63% figure when Plant Engineering first started asking that question a decade ago.

Read more: 2014 Salary Survey: Confidence rises amid the challenges

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.