With the MSI safety relays, individual safety sensors can be integrated quickly and easily into the safety circuit of machines and systems. The MSI contact extensions are used both as an output extension for OSSDs and for contact multiplication for evaluation units and safety controls.
Areas of application
Evaluation of individual safety sensors: Available in the Safety product range are both evaluation units that are specifically tailored to various sensor types and technologies as well as units that can be used universally. Relay models with time delays up to 3 seconds as well as up to 30 seconds are used for applications with stop category 1.
The contact-extension relays are suitable as simple output extensions for OSSDs and also for contact multiplication for evaluation units or safety controls.
Safety relay as part of the safety function
The safety function ensures that the drive can be shut down safely at all times – when the sensor is triggered and if a fault is detected. Here, the safety-related part of a control system (SRP/CS) in accordance with ISO 13849-1 is the central component necessary for execution of a safety function. This component evaluates signals coming from the sensors, detects cross-circuits on the sensor side and faults in the contactor. It also ensures safe shutdown of the drive. A safety sensor alone cannot fulfil these tasks – safety sensors are always just part of a safety function. In the simplest case, a safety relay performs the necessary tasks. The safety function is usually triggered by a person. Here, the technology of the safety relay recognizes the signals coming from the sensor and, via the shutdown paths, disconnects the supply voltage to the contactor – and the contactor in turn disconnects the power supply to the drive.
Monitoring functions of a safety relay
Evaluation of the sensor outputs
In the case of sensors with electro-mechanical contacts, cross-circuit detection by the safety relay is necessary.
EDM monitoring of external devices
The EDM function monitors correct operation of the contactor. This allows jamming of the switching contacts to be detected before a hazardous situation can occur. If the EDM function is not used, the maximum achievable performance level is PL c.
Configuration of the safety function with a safety relay
Prevention of an automatic restart
If it is possible for a person to be located undetected inside the danger zone behind the access guard, the machine is not allowed to restart automatically. In this case, the safety relay takes over monitoring of a manual reset command.
Use of the shutdown paths
Safety relays offer multiple shutdown paths, the use of which directly influences the achievable performance level (PL). With 1-channel operation, the maximum performance level is PL c and with 2-channel operation it is PL e.
Safety control or safety relay?
When selecting the appropriate evaluation unit, there are various requirements that need to be taken into consideration. Classic safety relays offer the simplest and most economical solution when using a small number of sensors. As the number of safety sensors increases and the more complex safety functions become, the strengths of the safety controls become clearly apparent: they offer space and cost advantages and their configurable safety functions allow them to be flexibly adapted to various requirements.