Expanded use of automation and the changing makeup of the industrial workforce are resulting in new workplace safety challenges. OSHA holds that employers are responsible for providing a safe and healthful workplace. Regulations, standards, and common sense, then, dictate machine safeguarding methods and applications.
Switches, relays, and controllers
Machines should not be operated without physical guards in place. Electrical interlocking to ensure that the guard is closed or in position is usually accomplished using safety limit switches, such as Banner Engineering’s SI Series Safety Limit Switches.
“The difference between a standard limit switch and a safety limit switch is the design of ‘positive opening’ normally closed (safety) contacts that are not dependent on springs,” says Mike Carlson, Banner’s safety products manager. “This forced opening of the normally closed contact reduces the possible unsafe failures that could result in loss of the switching action.” He adds: “Using redundant, individually mounted and monitored safety limit switches is recommended for applications that have a high risk of injury.”
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The new Sirius 3SK2 safety relays from Siemens offer as many as six safety functions that are configured with drag-and-drop Safety ES software. Complex safety applications, such as noncontact-area access monitoring through muting, can be easily implemented with the 3SK2 system. Device connectors allow for rapid expansion – for instance, via additional failsafe outputs or 3RM1 motor starters – without the need for additional control wiring.
“The 3SK2 system represents a solution for those applications where a simple safety relay is not quite enough, but a safety PLC is overkill,” says Glenn Symonds, product manager at Siemens Industry. “3SK2 offers simple configuration of safety functions through free assignment of inputs and outputs, selectable time delay, and automated user documentation, all through the Safety ES software.”
