Make safety a part of control design

MANUFACTURING has always been a dangerous industry. Engineers have tried to design safeguards and unions have tried to educate members about the importance of safety, but yet as late as 10 years ago it was not unusual to walk around a factory and see guards taken off machines and safety switches "defeated".

It is of no secret that safety is an extremely urgent concern - with care of plant personnel being of primary importance. No one who comes to work in manufacturing should be put in any risk. All employees should be well trained for situations where some risk is involved. Furthermore, injuries cause lost production, can impact quality, and can bring unwanted attention from regulatory agencies.

Les Ogden, general manager of Siemens Automation and Drives group (Australia and NZ), says safety concerns must be addressed up front, when engineers are planning a product, system or plant.

“Using integrated intelligence from sensors and drives, safety becomes part of the process' function, rather than an afterthought when disaster hits.

"Right now," Mr. Ogden says, "conventional safeguarding for machines is separated from the technical evolution of standard automation. Patching together safety after-the-fact is slow and onerous, requiring parallel wiring, special engineering tools, and redundant efforts.

“Addressing safety during planning and development saves time and money, and simply works better. Safety technology has to be integrated into standard controls-we call that 'Safety Integrated.'"

What Mr. Ogden points out applies today and in the future. Current safety control systems require hard wiring components rather than putting safety sensors and control on an existing industrial automation network. This dedicated safety system makes sense from more than just a legal view.

Safety control must be as failsafe as possible. Safety relays contain redundancy to assure proper operation even under abnormal circumstances-like a cut wire. Industrial control networks will need some further development and refinement along with extensive testing to become accepted for safety requirements.

Under Siemens' Safety Integrated concept, the company claims everything can be integrated from sensor systems, through evaluation and monitoring, up to the control and tripping level.

A key player in the success of Safety Integrated is Siemens' Siguard control and signalling devices. This includes emergency off switches, cable operated switches or switching strips, position switches, signal columns, light curtains and light arrays.

Siemens' emergency off control devices and Signum 3SB3 with positive latching, conform to international safety requirements. They can be used in every safety category, as they can be equipped with different contacts, including various NO and NC contact combinations.

Using Siguard cable-operated switches, operators can safely stop equipment along the cable. A single switch can secure application ranges of up to 100m. Operating optically Siguard safety switch strips protect dangerous edges from crushing parts of the human body.

Siguard light curtains and grids are type 4 active optical protective devices, which are compliant with Australian and European standards. These devices provide personnel protection for machines up to Category 4. Depending on the particular application, there are light curtains with 14, 30, 50 and 90mm resolution as well as 2, 3, or 4 beam light grids.

Typical applications for type 4 light curtains include hydraulic and mechanical presses, punches used in the metal, leather and plastics industry, welding and assembly lines and in robots.

Siemens' relay safety combinations are accommodated in a single enclosure. This means that the customer can use a single unit as certified combination to Category 4, without having to internally connect it up.

A single device can handle the emergency off functions and protective door monitoring as well as the press control. They can be controlled, either through one or two channels, they detect cross-circuit and ground faults in the feeder cables, as well as contact faults of the signal transmitters.

The relay safety combinations can be used in ambient temperatures up to 70°C when mounted in-line without any intermediate clearances between them.

In low-voltage technology, switching devices are becoming smaller and there is a trend to distributed peripheral devices. With Siemens' development of the ET 200S system, the demands for a modern, distributed, communications-capable I/O system and motor starters have been fulfilled when it comes to technology, functionality and user-friendliness.

There is no doubting that the range of safety products available on today's market can effectively protect hazardous working environments. As a global player, Siemens has a comprehensive range of products and the company embraces the safety issue with its Safety Integrated concept.

"The key message here is that safety is the number one issue, and therefore it must be part of planning in control engineering environments," Mr Ogden said. "There are many products out in the market, so there is no excuse these days to not have a fail-safe workplace. Legally, ethically, and financially it's just smart business." Siemens 03 97217387.