Integrating safety in automation requires specialized knowledge

In a typical automation project, maximum efficiency is key. However, undertaking a safety automation project presents additional challenges. First, legal requirements must be met. Second, care must be taken to ensure and validate that the application is truly safe. For example, is safety ensured if the equipment is misused or fails? Are you ready? Do you need a risk assessment?

08/11/2010


In a typical automation project, maximum efficiency is key. However, undertaking a safety automation project presents additional challenges. First, legal requirements must be met. Second, care must be taken to ensure and validate that the application is truly safe. For example, is safety ensured if the equipment is misused or fails?

‘Muting’ a light curtain is accomplished with additional sensors. When the sensors detect a pallet, the safety light curtain is muted. This configuration is done with a safety PLC; a safe and pre-certified muting function block ensures safe suspension of the light curtain (Source: Sick).Many people—including health and safety engineers, consultants, and safety equipment suppliers—are involved in performing a risk assessment and creating a safety plan. Fewer have a role in determining, commissioning, and implementing safety technology. In fact, often it is up to the integrator alone.

During typical automation projects, PLC programmers must adapt the system to the real-world environment and makes changes “on the fly” to get the project up and running. They often use “OR” function blocks (parallel contacts in ladder logic) and active low sensors. Both are highly critical when doing safety programming.

Consider, for example, a safety application where material has to get out of a machine, but neither a person nor any material is allowed in. This arrangement can be accomplished by “muting” a light curtain using additional sensors. Muting refers to an automatic, temporary suspension of the safety device. When the sensors detect a pallet, the safety light curtain is muted.

This configuration can be done with a safety PLC. A safe and pre-certified muting function block ensures safe suspension of the light curtain (see the diagram). Assume that the muting sensor is a reflector switch where the output is “HIGH” when it sees a reflector and “LOW” when an object is in the light path. The muting function block needs to be “HIGH” on the sensor input to mute the light curtain.

An inexperienced integrator might see no problem with this situation, saying, “Let’s negate the signal by using a ‘NOT’ function block.” Although such a solution works well and appears safe, what happens if the common power supply for the two sensors breaks down? Both sensors will switch off and it will appear to the safety PLC that they both see the object. As a result, the light curtain will be suspended.

An unsafe situation can occur easily by adapting a safe concept (function block) to a real-world scenario. An integrator needs to know his/her determination methods will influence the application. In this case, use of active “HIGH” sensors in combination with additional control signals or time monitoring functions would be required.

Integrating safety technology in a practical way requires extensive knowledge, application expertise, and many years of experience. Just as you would carefully select a qualified integrator for an automation project, make sure to do the same for the safety portion of the project by keeping them separate. This approach will ensure that safety is left to the experts. Experienced safety integrators will reduce the likelihood of safety risks during all phases of a project. Making use of simple and easy-to- use tools for design, simulation, and test also will help validate the safety functions throughout the life cycle of a machine or project.

- Juergen Bukowski is safety program manager, Sick Inc., Minneapolis, MN. Edited by Jeanine Katzel, consulting editor, Control Engineering, www.controleng.com

www.sickusa.com

Also see the Control Engineering:

Machine Safety blog

Machine Control Channel

System Integration Channel



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 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...
2016 Engineering Leaders Under 40; Future vision: Where is manufacturing headed?; Electrical distribution, redefined
Strategic outsourcing delivers efficiency; Sleeve bearing clearance; Causes of water hammer; Improve air quality; Maintenance safety; GAMS preview
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Flexible offshore fire protection; Big Data's impact on operations; Bridging the skills gap; Identifying security risks
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Driving motor efficiency; Preventing arc flash in mission critical facilities; Integrating alternative power and existing electrical systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

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.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me