Machine safety and safety certified networks

Do you remember when PLCs came out in the early 1970s – were there any communication networks available at that time? What is pier to pier? Fishing?

08/07/2012


Networked functional safety architecture showing PROFIsafe-enabled devices in yellow: controller, IO, drive, and process instrument. Courtesy: PI North AmericaDo you remember when PLCs came out in the early 1970s – were there any communication networks available at that time? What is pier to pier? Fishing? Who knew much or anything then about industrial communications networks?

 

 

Control Engineering recently ran three articles on Safety Certified Networks.

CIP Safety: Fail-safe Communication Between Nodes

PROFIsafe: Networked Functional Safety

Safety At Work Tutorial On Networked Safety Strategies

 


Boy, have we come a long way since the late 1970s when communication networks were introduced by the likes of Allen-Bradley, Modicon, and a few others. Today, automation and controls engineers use words like “packets” as frequently as “tweet.” In the late 1970s packets (or satchels, envelopes, boxes, etc.) were used to gather several messages to be hand carried across town by a courier service.

 

Diagram shows how safety data is routed between DeviceNet and EtherNet/IP in CIP Safety applications. Courtesy: ODVAIn the 1980s and 90s communication networks contributed significantly to the rapid acceleration and adoption of PLC automation. Until 2002 machine safety controls were excluded by codes and regulations from participating in this transition from electromechanical controls to PLC automation. Likewise, machine safety was excluded from the benefits of communication networks. Now, since NFPA 79, 2002, the entire control system for a machine can include machine safety and can potentially be programmed by a single platform on one computer. And, communication networks can include PLC to PLC as well as machine to machine via communication protocols known as pier to pier clearly having nothing to do with fishing.

 


Having said that, let’s get back to the term packet. I talk about packets in the general sense on the subject of communication networks. Today there are standard packets and safe packets and both can be on the same safety certified network at the same time. I explain it this way. Imagine a safety network with a combination of standard components and safety certified components. A safety certified network (wired or wireless) allows the mix of standard packets and safe packets and the safe packets can only be communicated between safety certified components.

 

This is a medium-size, stand-alone safety system where the safety controller handles all safe-rated operations but also controls standard outputs like the e-stop illumination and indicator LEDs on protective door switch. There are a surprising nThe standard components are not equipped to engage a safety packet so they essentially fly by a standard component. Additionally, safety packets are redundant to meet the higher reliability requirements for safety applications. So, in this day and age, packets still carry messages but these packets are on a safety certified network.

 

In summary, the safety network articles referenced here are great examples of how far machine safety has advanced over the past ten years. I recommend that you take the time to read all three. In my opinion, safety automation has accomplished in ten years what standard automation accomplished in 30 years.

Are safety certified networks your helping hand to advance your business?

 

Your comments or suggestion are always welcome so please let us know your thoughts. Submit your ideas, experiences, and challenges on this subject in the comments section below. Click on the following text if you don't see a comments box, then scroll down: Machine safety and safety certified networks.

 

JB Titus, CFSE

Related articles:

CIP Safety: Fail-safe Communication Between Nodes

PROFIsafe: Networked Functional Safety

Safety At Work Tutorial On Networked Safety Strategies

 

Contact: www.jbtitus.com for “Solutions for Machine Safety”.



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