Signal conditioning
Safe firefighting on ships
Reliable safety relays are required to ensure that signals are transmitted safely in fire protection systems on ships. The KFD2-RSH series from Pepperl+Fuchs has an architecture requiring only one of the three contacts to be functioning, ensuring reliability when it is needed the most
F
ire protection on ships is a critical issue. A fire must be quickly detected and immediately extinguished, because the
escape options for the crew are limited. The consequences for nature and the environment would also be devastating. In the engine room alone, there is a constant risk of fire. The surfaces of the machines can become so warm that leaking fuel evaporates immediately. In the event of a fire, time is a critical factor.
Therefore, all firefighting and safety measures must be initiated immediately, for example sprinkler systems. However, oxidising factors such as the fuel lines leading to the fire source must also be shut down. This means turning off the fuel pumps as well as activating the sprinkler system. In addition, alerting the crew is an important part of the evacuation process. This means activating warning sirens and lamps in all rooms and cabins on the ship. The fire
alarm triggers and transmits these signals. A safety relay with a high degree of reliability in case of emergency is required to ensure that the signals are transmitted safely.
THe SoluTion The safety relays from Pepperl+Fuchs have a sophisticated “One out of three” (1oo3) architecture that uses two redundant relays to ensure reliability. This architecture only requires one of the three contacts to be functioning. It is available for both ETS (Energise-to-safe) and DTS (De-energise to safe). For example, this architecture is particularly advantageous when used for ETS applications in process automation, making it the only safe variant. In the process technology industry, safety loops can remain unused for years, meaning the contacts are not maintained by frequent switching processes. This can lead to dirty or corroded contacts closing, despite the fact that the resistance is so high that no current can flow. If contacts are force guided, this poses the additional risk of misinformation stating that a conductive connection has been established. In addition to increased
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reliability, the safety relays in the KFD2-RSH series also provide a unique diagnostics function that saves the user any additional test effort. The integrated diagnostics function switches the three contacts successively with a time delay during each switching operation. During the delay period, the device checks whether this contact closes or opens the circuit accordingly. Defective contacts are detected, and a fault is reported to the control system. After switching three times, the relay module is fully tested without any additional effort. The modules in the KFD2-RSH series also provide comprehensive line fault transparency (LFT). Short circuits and lead breakages are detected on the field and control sides and assigned to a specific signal circuit. In conventional modules, it would only be possible to monitor the field side by connecting an additional fault indication output. LFT means that wiring in this connection is no longer required. The safety relays also have an input filter, which reliably filters out incoming test pulses from the control system. As a result, the control system can perform all diagnostic functions freely without creating an unintended circuit.
Pepperl+Fuchs
www.pepperl-fuchs.com August 2020 Instrumentation Monthly
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