Safety switchgear
A safety switching device implements safety functions in machines and systems, especially those with electrical drives . They monitor dangerous functions and are intended to reduce the risk to operating personnel to an acceptable level by taking suitable measures. A safety switching device is not required for the functioning of a machine, it only serves to guarantee the safety function.
Security functions
Typical safety functions are:
- Emergency off / emergency stop
- Guard door monitoring
- Photoelectric barrier
- Safety mat
- Two-hand control
Basis for safety switching devices
Machine controls must be designed and built in such a way that hazardous situations do not arise. In particular, controls must be designed and constructed so that
- they withstand the expected operational stresses and external influences.
- a defect in the hardware or software of the control does not lead to hazardous situations.
- Errors in the logic of the control circuit do not lead to hazardous situations.
- Foreseeable operating errors do not lead to hazardous situations.
Neither an error in the device nor an error in externally connected sensors or actuators may lead to the loss of the safety function.
If these requirements cannot be met by adequately designing the machine, further measures must be taken, such as B. Use of safety switching devices.
Layout and function
Safety switching devices differ in their technical implementation:
- Classically based on relay technology with contacts .
- With electronic evaluation and contact-based potential-free outputs.
- Fully electronic devices with semiconductor outputs.
Increased safety for switches with contacts
A conventional switching relay uses a wire coil and the mechanical movement of the metal contacts that it causes to switch the load on and off. The metal contacts can weld after repeated switching cycles or in the event of errors. If that happened and the operator hit the kill switch, the machine would keep running. This would create a dangerous state for the operator. The safety standards therefore provide for the use of relays and contactors with forcibly guided contacts instead of simple relays or contactors .
Relevant standards
- Machinery Directive 2006/42 / EC of the European Parliament and the Council
- EN ISO 13849-1, Safety of machines - Safety-related parts of control systems - Part 1: General principles for design
- EN 62061, Safety of machines - Functional safety of safety-related electrical, electronic and programmable electronic control systems
Individual evidence
- ↑ The Safety Compendium, Pilz
- ↑ a b Directive 2006/42 / EC (Machinery Directive)