Safety relays

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.
Banner mit Sicherheitsrelais für die Arbeitssicherheit

Safety relays

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.

Advantages for you

  • Compact and safe
    For the fast integration of individual safety sensors into the safety circuit of systems and machines, the safety relays offer the right solution.

  • Diverse application possibilities
    The application possibilities range from the monitoring of simple components such as E-Off, through to the integration of optoelectronic sensors.

  • Flexible installation and replacement
    The pluggable screw and spring-cage terminals allow the safety relays to be installed flexibly and replaced quickly.


Areas of application

Evaluation units

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.


Contact extensions

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.

Erklärung der Funktionsweise von Sicherheitsrelais

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.

Sicherheitsrelais mit Anschluss für Betriebsspannung

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?

Erklärung zur Unterscheidung von Sicherheitsrelais und Sicherheitssteuerung als Grafik

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.


To the safety controls


Selecting the correct safety relay


Anschließen von Sicherheitssensoren an Sicherheitsrelais

Evaluation of individual safety sensors

For correct execution of the safety function, safety sensors must be integrated into the machine circuit using safe control components in accordance with the requirements defined in ISO 13849-1.

The reliable MSI safety relay functions allow individual safety sensors to be connected quickly and easily to the safety circuit of machines and systems. Depending on the model, the relays are tailored to specific applications or can be used universally. 

Ein Sicherheitsrelais überwacht gleichzeitig zwei Sicherheitssensoren

Evaluation of two safety sensors with one safety relay


If two safety sensors act on a common shutdown path, they are to be integrated in the machine circuit by means of an economical and space-saving safety relay.


The MSI-SR5B safety relay can monitor two safety sensors simultaneously. The common, two-channel shutdown path ensures the safe shutdown of a dangerous movement up to PL e in accordance with ISO 13849-1.

Kompakte Sicherheits Lichtschranken sind an externe Auswerteeinheit mit Testung angeschlossen

Evaluation of single light beam safety devices through periodic testing


Compact single light beam safety devices of type 2 and type 4 in accordance with IEC 61496-1/2 do not usually have internal testing. To satisfy the requirements of electro-sensitive protective equipment, cyclical testing by an external evaluation unit must take place. 


The MSI-TRM evaluation units in combination with the SLS 46C type 4 single light beam safety devices are already certified as AOPD and achieve PL e in accordance with ISO 13849-1 and SILCL3 in accordance with IEC 62061. The MSI-TR1/TR2 evaluation units are optimized for the evaluation of type 2 single light beam safety devices. As a result, PL c and SILCL1 can be achieved.

Safety - Product overview (PDF, ~7 MB)
MSI - Safety controls and safety relays - Product information (PDF, ~4 MB)
MSI - Safety relays - Selector (PDF, ~2 MB)