Safety has undergone a major change since the start of the decade. Integrated safety has become the new watchword following a change to U.S. safety standards that eliminated the requirement for dedicated, hardwired safety architectures.
In 2002, the standards that dictate industrial safety in the U.S. were revised, allowing safety to be designed into controllers. That change from dedicated, hardwired safety systems marked a huge change in system design. This allowed for harmonizing the U.S. safety design with machines built in other countries around the world and now it’s transforming the full spectrum of manufacturing equipment.
“People no longer paste safety on at the end of the machine design,” says Tim Parmer, Siemens’ Automation Consultant. “The benefits are now starting to roll in at all phases of system design cycle, especially when it’s considered as part of the system architecture.”
That provides major benefits for system integrators and others who install hardware. Now, they can install straight forward wiring connections without worrying about changes in the safety requirements. Those modifications are now simply made in the safety software.
“Safety is now integrated into standard wiring, reducing costs, simplifying installation and improving reliability” Parmer says. “At the same time, integrators can choose the safety controls they need, including safety I/O modules where they’re needed.”
That flexibility extends to software. Programs can now include any functions within the equipment, something that wasn’t possible when external hardwiring carried safety signals. Equipment designers can include safety in the early stages of design and simulation, making it more efficient without sacrificing protection.
On the plant floor, integrated safety can save floor space while also reducing installation times. Floor space requirements decline because safety-related hardware can more easily be housed inside the machine, eliminating the need for external safety enclosures. Space savings also come in the elimination of crowded wiring channels.
When new machines are first turned on, diagnostics are also simplified. Technicians only have to analyze one set of software, and they don’t have to test separate wiring harnesses or dedicated electro-mechanical safety systems.
Another plus is that the ladder logic now used to program the safety interlocks on many machines is self documenting. Maintenance personnel look at functional logic that matches the real status of the safety design instead of the engineering drawings that often do not get updated when changes are made. Together, these advances mean that installations and equipment commissioning will be interrupted far less often.
Installations may also be more efficient since integrated technologies offer more freedom. For example, I/O modules can be distributed so they are close to input devices. Putting an I/O rack close to switches saves wiring while also improving efficiency; by fitting in the automation architecture and providing superior troubleshoot aids.
The benefits continue throughout the lifetime of equipment. Downtime can often be reduced considerably because diagnostic data is readily available to operators, showing up on the main control panel. Alerts can be far more focused leveraging the capabilities of controllers and modern networking schemes like Ethernet, which provide far more information than hardwired safety networks.
“Now an operator will get a message saying the machine won’t start because door four is open instead of just an alert saying a safety interlock failed. It’s much quicker to close door four than to search all the doors and all other interlocks around the machine,” Parmer says. He also noted that networking diagnostics make it easier to find loose or broken wires, shortening the time traditionally required to correct these problems.
Reconfiguring and expanding production lines will also be simpler. That’s largely because adding or moving equipment tied to a network is far easier without hardwired interconnections in safety networks.
“Throughout the machine’s life cycle, owners will save a lot of man hours because they don’t have to do the complex engineering required to customize the wiring connections and contactor requirements to physically create the safety functions. In the past, every change took an excessive numbers of man hours,” Parmer says.
Though integrated safety is fairly new to the U.S., its reliability has been well proven. These techniques have been developing in the process industry and in Europe since the late 1980s, so we have experience in designing programmable electronic products that protect operators and other equipment.
“Meeting the highest level of safety requirements (as defined by IEC 61508 and IEC 62061 through Safety Integrity Levels), SIL 3 sets a very high level for safety. To put this into perspective, the required protection level is set so high that a dangerous failure is limited to a timeframe of around once in 11 centuries,” Parmer says.
A key aspect of this long timeframe is to ensure that all safety relevant signals are acted on and any failure is dealt with safely. When components fail, an inevitability with any type of control systems, the system must move to a de-energized safe state. For example, a moving arm must stop or move to a position where it no longer poses a threat. “The processes must run a continuous level of diagnostics that detects any single point of failure and maintains a safe state,” Parmer says.
Adopting another emerging technology, wireless networking, will now create the possibility of extending safety shutdowns to an object in motion, where hardware systems were impossible. Sending all signals over the same network simplifies the overall architecture. Embedding the safety protocol like PROFISafe into the standard network means the network components need no special safety rating.
The intelligence protecting the safety integrity is embedded in both ends of the communications path so wireless networks, routing safety signals through the air, don’t compromise safety integrity levels since any failure in the communication will cause a shutdown to a safe state.
Integrated safety gives design engineers and users more safety and more versatility. It can also enhance safety over a product’s entire lifetime.
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::Design World::
Filed Under: Factory automation, INDUSTRIAL SAFETY SYSTEMS