Safety relays

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Safety relays - risk reduction

Safety relays are devices used for safety-relevant control systems of electric motors and industrial machines. They usually have two redundant contacts which are switched on by two independent lines of safety circuits. When both contacts are closed at the same time, the enable circuit coil is closed.

The role of the safety relays is to monitor functions and supervise the safety system with a machine start or stop permit. This also includes the control of other safety-related functions. They monitor specific processes, and in the case of connection with other devices, they allow for the construction of a complete machine protection, referred to as a safety system. Safety relays are devices with configurable control parameters. They ensure the safe operation of machines, thanks to which they are used in everyday use, in many different applications, allowing for function monitoring and fault detection.

Safety relays - application

The safety relay is designed to protect people and machines. In addition to the typical emergency stop function, they monitor safety doors, two-handed buttons, light curtains (barriers), pressure mats, drive parameters, time delay and other safety functions. In the event of an emergency, it is necessary to use appropriate steps to reduce the risk to an acceptable level. The safety standard IEC / EN 60 204 defines the parameters and hardware configuration for machines requiring special safety supervision.

Risk reduction takes place through the correct design and implementation of the machine (e.g. with protective measures controllers of the relevant safety functions).

Given the intended use and reasonably foreseeable misuse, the selected technical and additional protective measures can be readily applied to reduce the risk as long as the hazard cannot be eliminated or the associated risk cannot be reduced by an inherently safe design.

Types of safety relays

Depending on the type, the safety relays may differ in terms of supply voltage ranges, the number of safety contacts and the number or possibility of connecting wires through detachable plugs.

Single-function safety relays are the most economical solution for smaller machines.

Configurable modular safety relays is a solution used in places where there is a need for a large number of various protective devices and where there is a need for at least zone control. Configurable control systems require a software tool to configure.

Safety relays - construction

Typical relays in their design have a coil and positively guided executive contacts for the enable and signaling circuits. Many safety relays contain electronics. Then the electronic device allows for greater immunity to errors, which does not lead to a dangerous condition in the circuits important in terms of safety (e.g. transverse short circuit in the emergency shutdown circuit).

The safety relays are designed so that device faults and external faults do not limit the safety functions, provided that they are correctly connected.

Main advantages of safety relays

The main functionalities of the relays include setting the operating mode and the time of switching on and off (advanced time programming functions), as well as high loads allowing for the protection of high-power devices. Ease of configuration of the systems thanks to the modular structure.