Safe Coupling Relays
What is a safe coupling relay?
Safe coupling relays ensure the integrity of a safety chain by transmitting signals redundantly and self-monitoring. Simple coupling relays cannot be used here, as the safety chain would be interrupted and safe shutdown in the event of danger could no longer be guaranteed. This problem is solved by using safe coupling relays. Safe coupling relays enable standard-compliant coupling of safety-related signals up to SIL 3 / PL e.
What are the characteristics of safe coupling relays?
- Safe signal coupling: They enable the transmission of safety-related signals up to SIL 3 / PL e without interrupting the safety chain.
- Galvanic isolation: The relays safely isolate digital 24V signals from 230V networks in order to decouple different voltage levels.
- Contact amplification: They serve as power amplifiers for safety PLC outputs, which often have only limited output power.
- Test pulse filtering: The devices filter out the test pulses sent by safety controllers to prevent faulty switching or fluttering.
- Redundancy and monitoring: Their redundant design and self-monitoring functions ensure safe shutdown in case of danger.
- Certified according to international safety and design standards: The devices meet the functional safety requirements of IEC 61508 (Parts 1-2, 4-7), IEC 61511-1, DIN EN ISO 13849-1, and EN 62061, as well as the specific standards EN 60204-1, EN 50156-1, EN 746-2, and EN 81-20/50:2014.
What are the areas of application for safety coupling relays?
- Mechanical engineering: They are used for the safe coupling of control signals to the peripherals of machines.
- Process industry: In process engineering plants, they are used for reliable signal transmission in compliance with high safety standards.
- Firing systems: The relays are specially designed and certified for use in firing systems in continuous operation.
- Shipping: With approvals such as those from Germanischer Lloyd, they have proven themselves in the demanding maritime environment.
- Safety-oriented sensor technology: They reliably couple signals from sensors, such as pressure monitors, to the higher-level control system (PLC).
- Safety controllers (safety PLC): The relays act as necessary contact amplification for outputs from safety controllers with low switching capacity.
| Type | Safety contacts / outputs (NO) |
Auxilliary contacts / outputs (NC) |
1 / 2 channel wiring | Width in mm | Reaction time | Approvals | |
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Safe coupling relay
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1 | 1 | 1 | 6.8 | < 20 ms* |  |
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3 | 1 | 1 | 22.5 | < 50 ms |  |
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3 |
1 |
1/2 |
22.5 |
< 20 ms* |
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3 | 1 | 1/2 | 22.5 | < 7 ms* |
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3 | 1 | 1/2 | 22.5 | < 7 ms* |
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3 | 1 | 1/2 | 22.5 | < 20 ms* | |
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5 | 1 | 1 | 22.5 | < 50 ms |  |
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7 | 6 | 1 | 45 | < 20 ms* |
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7 | 6 | 1 | 45 | < 20 ms* |
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Coupling relay with forcibly guided contacts
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3 | 1 | 1 | 17.5 | < 40 ms |  |
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2 change over | 15,5 |   |
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Non safe coupling relays |
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1 change over |
1 | 6.2 | 15 ms | |
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2 change over |
1 | 17.5 | < 40 ms | |
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2 change over |
1 | 17.5 | < 40 ms | |
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4 |
1 | 31.5 | < 20 ms | |
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4 independent |
1 | 22.5 | |
*< 20 ms:
Applies for wiring via the safe inputs S14 & S12
Product Information:
Our safe coupling relays are not only suitable for furnaces in continuous operation, but also fulfil all current requirements of the relevant standards and are type-tested and certified by independent testing institutes such as TÜV-Rheinland.
The coupling relays, which are used for safe contact reinforcement, contact multiplication and safe signal isolation, are tested in accordance with ISO 13849-1. Our relays with their coupling function have also proven themselves in the process industry and shipping (Germanischer Lloyd).
The safe coupling relay SD1K impresses with its extremely slim design. With a width of only 6.8 mm, the SD1K meets all normative requirements for the safe coupling of safety-directed signals up to SIL3/PLe.
The ultra-slim SD1K requires only one-third of the space in the control cabinet compared to standard coupling relays with a 22.5 mm design – with the same level of safety. Whether in new installations or retrofits, this leads to space and thus cost savings.
In addition to its application in general mechanical engineering, the SD1K is also suitable for continuous use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
The safe coupling relay SK3D comes in a classic 22.5 mm wide housing, features 3 safe relay contacts, and is available in three voltage variants: DC 24 V, AC 115 V, and AC 230 V. It meets all normative requirements for applications up to SIL3 / PLe.
The SK3D is not only perfect for coupling functions and contact multiplication but can also safely couple 115/230 V high-voltage signals, e.g., from pressure monitors, to the control system thanks to its various voltage variants.
In addition to its application in general mechanical engineering, the SK3D is also suitable for continuous use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
Our safety relay SR3D comes in a classic 22.5 mm wide housing, features 3 safe relay contacts, and is available in three voltage variants: DC 24 V, AC 115 V, and AC 230 V. It meets all normative requirements for applications up to SIL3 / PLe.
It is designed as a fast coupling relay for the process industry and is used where fast response times are required, which cannot be achieved with a classic coupling relay.
In addition to its application in general mechanical engineering, the SR3D is also suitable for continuous use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
Our safety relay SR3D comes in a classic 22.5 mm wide housing, features 3 safe relay contacts, and is available in three voltage variants: DC 24 V, AC 115 V, and AC 230 V. It meets all normative requirements for applications up to SIL3 / PLe.
It is designed as a fast coupling relay for the process industry and is used where fast response times are required, which cannot be achieved with a classic coupling relay.
In addition to its application in general mechanical engineering, the SR3D is also suitable for continuous use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
Our safety relay SR3C comes in a classic 22.5 mm wide housing, features 3 safe relay contacts, and is available in three voltage variants: DC 24 V, AC 115 V, and AC 230 V. It meets all normative requirements for applications up to SIL3 / PLe.
It has been developed for general mechanical engineering and is at home in all applications where fast response times are required, which cannot be achieved with a classic coupling relay.
The safe coupling relay SK5C comes in a classic 22.5 mm wide housing, features five safe relay contacts, and meets all normative requirements for applications up to SIL3 / PLe.
The SK5C is perfect for coupling functions and contact multiplication where three relay contacts are not sufficient, but space is also limited.
In addition to its application in general mechanical engineering, the SK5C is also suitable for use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
Our safety relay SR7D comes in a 45 mm wide housing, features 7 safe relay contacts, and meets all normative requirements for applications up to SIL3 / PLe.
The SR7D is used when standard coupling relays reach their limits. With seven safe relay contacts, massive contact multiplication can be realized and reliably monitored through four signaling contacts and two semiconductor signaling outputs.
In addition to its application in general mechanical engineering, the SR7D is also suitable for continuous use in firing systems and the process industry due to its special certification according to EN 50156-1, EN 746-2, and IEC 61511.
The safe coupling relays SK3D and SD1K are especially designed for this application and enable the coupling of safety-related signals up to SIL 3 / PL e applications with a minimum width of 6.8 mm or 22.5 mm.
Aside from the use according to IEC61508 and IEC 61511, the recognised standards for furnaces were also taken into account. Both relays are type approved for the use in furnaces in continous operation according to EN 50156-1 and EN 746-2.
