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Siemens AG
Entry type: Application example Entry ID: 109485648, Entry date: 09/19/2016
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Access monitoring using a light curtain with two-hand operation and emergency stop to SIL 3 or PL e with a 3SK2 safety relay

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To monitor access to an open danger zone, so-called non-contact protective equipment such as a light curtain can be used. If the light beam is interrupted, a shutdown signal is triggered.

To enable safe operation of the actuator, two-hand operation is used. This prevents the operator from reaching into the danger zone during operation.

 


Access monitoring using a light curtain with two-hand operation and emergency stop to SIL 3 or PL e with a 3SK2 safety relay

 

Operating principle

The light curtain consists of a send unit and a receive unit. Between the two is the protective zone. If the light beam is not interrupted, outputs OSSD1 and OSSD2 carry voltage and are evaluated by the safety relay. When the light beam is interrupted, the two outputs switch off and the safety relay opens the enabling circuits, switching off the power contactors in a safety-related manner.

In addition, simultaneous actuation of the two-hand operation console prevents the operator from reaching into the danger zone. The 3SK2 safety relay only switches the enabling circuits when both signals are active within 500 ms, the light beam of the light curtain is uninterrupted, and the feedback circuit is closed.

If one of the two pushbuttons is released, the 3SK2 safety relay immediately switches the machine off in a safety-related manner.

The four-channel design in the two-hand operation console ensures that possible welding of one of the contacts is detected immediately.

The plant is also switched off in a safety-related manner after operation of both emergency stop command Units.

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