In brief
A safety switch monitors the position of guard doors or covers and positively signals any opening to the machine’s safety evaluation unit.
Contents
What is Safety switch?
Safety switches, technically interlocking devices, ensure that a machine only performs hazardous movements when the guard is closed. If someone opens the door, the safety circuit is interrupted. Guard locking devices additionally keep the door locked until any run-down movement has come to a standstill. The term should be distinguished from the maintenance or main isolator switch, which is also colloquially called a safety switch.
Designs include mechanical switches with a separate actuator, hinge switches, position switches with positive opening and non-contact switches with a coded transponder or magnet. Requirements for design and protection against defeat are set out in EN ISO 14119. Key ratings are contact configuration, locking force, coding level, degree of protection, connection type and the achievable performance level in combination with the evaluation unit. Non-contact versions are less sensitive to tolerances in the door guide and are easy to clean, which is an advantage in hygienic areas.
Frequent failures are caused by bent actuators, door misalignment, contamination and cable breakage. Because tampering is a known problem, a faulty switch should be replaced promptly and not bypassed. Actuators and switches are often matched to each other and are best procured as a pair.
In practice: maintenance and procurement
For an enquiry, the manufacturer part numbers of switch and actuator, contact configuration, locking principle, supply voltage, connector type and, for transponder switches, the coding level are relevant. With high-coded switches, the replacement part may need to be taught in again.
Synonyms and abbreviations: interlock switch · safety interlock · guard door switch · safety position switch · guard locking device
Frequently asked questions
What is the difference between a safety switch and a guard locking device?
A safety switch only detects whether a guard door is closed. A guard locking device additionally locks the door mechanically and only releases it when a controller signals that the condition is safe. Guard locking devices are used when machine parts run down and immediate opening would be dangerous.
What information is needed to replace a safety switch?
The manufacturer part numbers of switch and actuator, the type of contacts or outputs, the supply voltage for electronic devices, the connection type, the degree of protection and, for guard locking devices, the principle, i.e. spring-applied or power-to-lock, are needed. For non-contact switches, the coding level is also important.
Why must safety switches not be bypassed?
A bypassed switch permanently signals a closed door to the controller, even though it may be open. This disables the protective function, and people can reach into running movements. Operators are obliged to prevent tampering; EN ISO 14119 describes measures that make defeating more difficult.