Dual Redundant Safety Relays for Maximum Functional Safety

Fire protection is a high-priority issue, especially for process plants in the chemical industry. When flammable or even explosive process media are involved, extensive constructive measures must be taken into consideration to prevent fires from occurring, but this alone is not enough. If a fire breaks out, appropriate measures and processes must be established to extinguish it as quickly as possible. Only then has the plant operator taken all precautions to minimize personal injury, property damage, and environmental damage. 

Time saved is the decisive factor in efficient firefighting. Temperature gages, smoke detectors, gas detectors, and cameras are common sensor technology for detecting fires as early as possible and for initiating the necessary defense measures. All components used must be part of a coordinated and reliable alarm system that responds quickly and automatically when a fire is detected. Detected fire situations must be reported to a control panel, which in turn triggers automatic fire-extinguishing devices, and simultaneously activates audible and visual warning devices.

By definition, this is a low-demand mode. Nevertheless, the entire system for detecting and fighting fires must function with absolute reliability in any situation. 

A prerequisite for reliable alarm signaling in the event of a fire outbreak is safe signal transmission supplemented by galvanic isolation between the control and field circuits. The ETS safety relays (energized-to-safe) from Pepperl+Fuchs are designed precisely for this purpose. The KFD2-RSH-1.2E.L safety relay is an example from this series. It meets the requirements for integrated safety according to SIL 3 and is used for the safe energizing of devices. Periodic diagnostic and proof tests are carried out to check the proper functioning of connected devices to ensure that both a fire alarm and automatic firefighting measures are reliably triggered in the event of a fire.

Safety relays from Pepperl+Fuchs are equipped with dual redundant contacts. With this sophisticated “one out of three” (1oo3) architecture, it is sufficient if only one of these contacts is functioning. This mechanical architecture ensures maximum reliability and functional safety when fire alarms and automatic firefighting equipment are triggered. In contrast to force guided contacts, corrosion or pollution of contacts is virtually irrelevant.

Diagnostics are achieved using time-delayed switching of elementary relays. The result is extremely long proof times. The maintenance effort for the devices is negligible.

KFD2-RSH series safety relays offer comprehensive line fault transparency (LFT). Short circuits and line breaks are detected at the field level and the control side and are assigned to a specific signal circuit. It is therefore not necessary to monitor the relay using an additional fault indication output and the associated wiring effort.

The safety relays have an input filter, which reliably filters out incoming test pulses from the control system. As a result, the controller can perform all required diagnostics freely without creating an unintended circuit.

• Safe triggering of fire alarms and automatic extinguishing system with ETS safety relay
• Galvanic isolation of the control circuit and field circuit
• The effects of pollution and corrosion on the switching contacts are largely eliminated
• 1oo3 technology, integrated diagnosis, and line fault transparency
• Test pulse filters protect against faults caused by control diagnostics