SIRIUS Coupling Relays and Signal Converters

SIRIUS coupling relays and signal converters provide I/O and PLC isolation, signal boost and level conversion to extend reach and protect devices.

When controllers with standard inputs/outputs reach their limits, coupling relays and signal converters provide electrical isolation, signal amplification and conversion between voltage levels or signal types.

Choose from a wide selection of products that support diverse applications. Our SIRIUS 3RQ4 coupling relays are suitable for all relevant coupling functions and with their compact design, they are ideal for space-optimized use in the control cabinet.

Integrate the coupling relays into controller systems with verified compatibility between SIMATIC and 3RQ4 relays. A modular architecture and uniform design simplify installation, configuration and consistent system performance.

Support reliable plant operation with integrated relay outputs designed for signal continuity and operational stability. Verified B10d values support safety planning and help meet functional safety requirements.

Safely couple signals to and from PLCs while supporting functional safety up to SIL 3/PL e. Force-guided contacts and compatibility with 3SK safety relays help maintain dependable signal switching in safety-critical applications.

Operate across 24 V to 240 V AC/DC with large terminal capacity and real load contacts, including NC circuits. Meet international standards for demanding industries such as rail, shipbuilding, and heavy industrial automation.

Reduce installation and service time with features such as removable terminals, push-in or screw connections, exchange relays and integrated connection combs. Clip-on labeling and isolation plates support fast configuration.

A coupling relay is mainly used for electrical separation and voltage transformation, for example, from 24 V DC to 230 V AC. It is also used to amplify weak signals and can be used for general relay controls and for overvoltage and EMC protection of controls.

The utilization categories for coupling relays are defined in IEC 60974-5-1 and stipulate the characteristic operating conditions. The most common are AC-15 and DC-13.

AC stands for the utilization categories for alternating voltage. The typical application for AC-15 is control of electromagnetic load (for alternating voltage).

To switch very small currents, e.g. at control inputs, hard gold-plated contacts are used.

For silent, fast and frequent switching, semiconductor contacts can also be used.

According to the standard IEC 60947, it is defined as the number of switching cycles without load that is achieved or exceeded by 90% of all devices under test, without repair or replacement of any component.

Simple selection and worldwide standardization, e.g. a 3RQ1/2 coupling relay with a voltage of 24 V AC/DC to 240 V AC/DC can be used both for the US market (110 V AC) and for the CE market (240 V AC) or also with a 24 V power supply.

Functional safety defines a state in which the risk of damage is reduced to a tolerable level, or that can be regarded as risk-free. This definition consequently applies to the functional safety of persons, machines and the environment.

Functional safety is intended to ensure equal protection of people and the environment in all countries with internationally harmonized standards. Apart from that, many countries have laws that mandate compliance with safety aspects. This obligation can often be met by applying the standards. In particular, the following standards must be applied to factory automation: IEC 61508. IEC 62061 and EN ISO 13849.

Safe coupling relays are used for the same purpose as standard coupling relays (see “What is a coupling relay used for?”) and usually have positively-driven contacts and safety certification.

In mechanically linked operation according to IEC 60947-5-1 (IEC 61810-3), the contacts of the installed relays are connected to each other so that NO contacts and NC contacts are never closed at the same time. In this way, opening failures are reliably detected and maximum safety is ensured.

They are used as a coupling link for signals, e.g.: for fail-safe control and output expansion (SIL 1-3) for safety relays with direct control of actuators and signaling elements.

The SIRIUS 3SK1 safety relays and the force-guided SIRIUS 3RQ1 coupling relays offer such a possibility. This means both the number of contacts and the switching capacity of the fail-safe control can be increased and amplified up to 10 A.

You will find more information in this FAQ: https://support.industry.siemens.com/cs/de/en/view/76676971

The IEC 62061 standard “Safety of machines –Functional safety of electrical, electronic and programmable electronic control systems” defines comprehensive requirements. It includes recommendations for the development, integration and validation of safety-related electrical, electronic and programmable electronic control systems (SRECS) for machines. For the first time, the standard covers the entire safety chain, from the sensor to the actuator. The “Safety Integrity Level,” or “SIL” for short, is defined as the application parameter for this standard. The standard does not specify performance capability requirements for non-electric — e.g. hydraulic and pneumatic — safety-related control elements for machines.

The standard EN ISO 13849-1 “Safety of machines – Safety-related components of control systems, Part 1: General principles for design” superseded EN 954-1 at the end of 2011. It takes into consideration the complete safety chain with all the devices involved in its performance. EN ISO 13849-1 also makes a quantitative analysis of the safety functions. The standard describes how to determine the “Performance Level,” “PL” for short, for safety-related parts of control systems on the basis of architectures specified for the intended service life. When several safety-related parts are combined to form a complete system, the standard explains how to determine the resulting PL. It can be applied to safety-related parts of control systems (SRP/CS) and all types of machines, regardless of the technology and energy used, e.g. electrical, hydraulic, pneumatic or mechanical.

The B10d values (means: the number of switching cycles during which 10% of the relays can fail under defined conditions) are important for functional safety according to ISO 13849-1 and IEC 62061. They are often used to calculate PFHD (Probability of Dangerous Failure per Hour) or MTTFd (Mean Time to Dangerous Failure) in safety-related controllers.

Use of B10d values for coupling relays: Determination of the MTTFd (Mean Time to Dangerous Failure) The MTTFd is calculated from the B10d value, the operating frequency, and the number of switching contacts:

MTTFd = (B10d)/(0.1 x n x switching frequency per hour x 3600)

n = Number of dangerous errors per cycle (usually 1)

The operating frequency must be realistic.

Calculation of PFHD (Probability of Dangerous Failure per Hour) If necessary, the PFHD value required for SIL (Safety Integrity Level) according to IEC 62061 can be calculated from the MTTFd and other factors.

Evaluation of the Performance Level (PL) according to ISO 13849-1 The MTTFd value is used in conjunction with other safety parameters such as DC (Diagnostic Coverage) and the structure (Category B, 1, 2, 3 or 4) to determine the Performance Level (PL) of the safety circuit.