Any time a relay is required and must be used in a SIF, it must conform and adhere to IEC 61508 and to the relevant industry standards (i.e. IEC 61511).
Typical cases :
- Controller cannot meet power requirement (V or A)
- Multiplication of contacts is required
- Controller Safety Function must be inverted
SIL certified relays are used in Oil & Gas or petrochemical industries and are also a must in many other industries (railways, automotive, power distribution), and any time a failure of the relay can cause a serious accident.
SIL certified relays are used for critical loops where careful consideration should be given to Line and Load Monitoring. In a de-energize to safety application a wire/coil failure leads to a safety status.
In an energize to safety application line failures leads to a dangerous status. In both cases failure detection is important, if not essential.
Other diagnostics applications are monitoring the load status to prevent spurious trips or to verify the condition of the individual coil in a redundant coil SOV. In F&G system line diagnostics is a must and regulated by NFPA 72 code.
Control system diagnostic capabilities are designed to work when no device is interposed between the control system and the load. If a relay is placed in the loop, the diagnostic function stops at the relay input circuit (coil). To perform line monitoring from field device to controller, a SIL relay with built-in diagnostic circuit is required.
GM International relays will perform diagnostics of the load, wire, power supply and internal coils in all operating conditions, providing an independent alarm contact as well as transparently transferring the fault indication to compatible DO cards.
