In brief
A safety controller is a programmable controller that processes a machine’s safety functions in a fail-safe manner and shuts down in the event of faults.
Contents
What is Safety controller?
A safety controller evaluates signals from emergency stop buttons, light curtains, guard door switches or enabling switches and controls safe outputs. Unlike a standard PLC, it has an internally multi-channel design, monitors itself and continuously tests its inputs and outputs. Compared with individual safety relays, many functions can be linked in one device by software. If the machine or the safety concept changes, the logic can be adapted without rewiring.
There are compact, freely configurable safety modules, modular systems with expansion cards, and controllers that combine standard and safety logic in one CPU. They often communicate via safe protocols on Ethernet-based fieldbuses with distributed inputs and outputs or drives. Key ratings are the number and type of safe inputs and outputs, communication interfaces and the achievable performance level to EN ISO 13849-1 or SIL to IEC 62061.
For maintenance, the safety program counts as well as the hardware. Without a backed-up project file and matching firmware, a defective device often cannot be replaced in a meaningful way. Many systems store the configuration on a removable memory module that can be transferred to the replacement device.
In practice: maintenance and procurement
For every safety controller, keep the manufacturer part number, firmware version, project file with checksum and storage medium documented and ready. In a spare parts enquiry, it should be mentioned whether an identical device with compatible firmware is required, because a successor model may require the safety functions to be validated again.
Synonyms and abbreviations: safety PLC · fail-safe controller · safety CPU · programmable safety controller
Frequently asked questions
What is the difference between a PLC and a safety controller?
A standard PLC controls the production process but is not designed to reliably detect its own faults. A safety controller works redundantly, tests its inputs and outputs and switches to the safe state in the event of an internal fault. Only it may execute safety functions such as emergency stop or guard door monitoring. Some devices combine both tasks in separate program sections.
What must be considered when replacing a safety controller?
In addition to the right device, you need the valid safety program, ideally with a documented checksum, and a compatible firmware version. After the replacement, the safety functions are usually tested. If the replacement device differs in type or firmware, validation may have to be repeated. Responsibility lies with the person in charge of the safety of the machine.
Which standards apply to safety controllers?
For assessing safety functions on machinery, EN ISO 13849-1 with the performance level and IEC 62061 with the safety integrity level are mainly used. IEC 61508 is fundamental for the functional safety of electronic systems. Which requirements apply in an individual case results from the risk assessment of the machine.