Description

What is the difference between a safe and a non-safe electromechanical relay?

With a non-safe switching relay, the metal contacts can weld together after multiple switching cycles. If the machine operator presses the emergency stop button in this case, the machine will not stop. This results in a non-safe state. This may lead to the operator being harmed or the machine becoming damaged.

The relays installed in the safety relay module are based on relay technology with force-guided contacts in accordance with EN 50205, and they reliably monitor functions in machines and systems. Thanks to redundant structures, a safe state is always ensured for the machine operator.

National and international norms and standards prohibit the use of non-safe relays in dangerous machines and systems. Safety relay modules certified in accordance with the relevant safety standards and norms must be used here instead.

Safety functions

Safety relay modules are ideal if a machine or system requires few safety functions and logic operations to be implemented, such as in the following examples:

• Emergency stop
• Monitoring of movable guards, e.g., safety doors
• Electro-sensitive protective equipment
• Two-hand control devices up to type IIIC
• Zero-speed monitoring and speed monitoring

Proven safety with force-guided contacts

In a safety relay module with integrated monitoring, the forced guidance property is used for fault detection. This ensures that serious faults, such as contact welding, are reliably detected and a high safety level is achieved.

How does it work?
The N/O and N/C contacts of an elementary relay are connected to one another mechanically through forced guidance. This prevents N/O and N/C contacts from closing at the same time. In conjunction with a suitable circuit, failure to open can be reliably detected. This is the most reliable way to ensure maximum safety for both people and machinery.

Relevant standards and certifications for safety relay modules

All safety relay modules from Phoenix Contact are TÜV-certified in accordance with EN ISO 13849 up to performance level e or IEC 61508 up to SIL 3.

The safety relay module is a subsystem that forms the logic part of a safety function, and must therefore correspond to the new safety requirements. As part of the certification process, the following features of the switching devices are checked, evaluated, and validated, among others:

• Correct design
• Mean time to dangerous failure (MTTFd)
• Diagnostic coverage (DC)
• Common cause failure (CCF)

Your advantages

The advantages of PSR safety relay modules at a glance:

• A suitable product is available for all safety functions
• Compact safety relay modules can be installed in the smallest of spaces
• Simplified wiring with Push-in connection technology
• Approvals for all markets and industries, such as GL, UL, TÜV, maritime, and combustion technology
• Innovative relay technology for more diagnostic options and maximum safety