Consultation on SIS systems
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1. In the safety design section, the furnace flame out signal is incorporated into the SIS system (classified as SIL1). Is it necessary for the flame detection device to have a SIL certification? Should we still use SIL-certified relays for the flame monitoring signal circuit? 2. The fault signals from the furnace supply fan are also incorporated into the SIS system. Is SIL certification required for the motor, or is control circuit certification sufficient?
1. When designing a SIS (Safety Instrumented System) system, if a certain safety function is classified as SIL1 (Safety Integrity Level 1), then all the critical components and systems on which that function relies must meet the corresponding safety integrity requirements. For flame detection devices, if they are a critical component upon which safety functions depend, then in theory, such devices should have an SIL certification to ensure that they can operate reliably at the required safety level. However, in practice, sometimes the components of the entire flame detection system (such as sensors, logic solvers, actuators) can be certified for SIL separately, or the entire system can be certified as a single unit. As for whether relays with only SIL certification can be used, it depends on the design and certification process of the entire system. It is recommended to consult relevant certification bodies or safety engineering experts for more precise guidance. 2. In the case of incorporating fault signals from the furnace blower into the SIS system, generally, the motor itself does not undergo SIL certification, as it is not an electronic device that performs safety-related functions but rather a mechanical device. What usually needs to be certified is the control system that monitors the motor status and takes appropriate action when a fault is detected. This means that the entire control loop needs to meet SIL1 requirements, including sensors, logic solvers, and any relays or other actuating components. In short, the focus is on ensuring that the entire process, from detecting a fault to carrying out a safety response, meets the SIL1 requirements. .
Currently, there are flame probes available on the market that come with SIL certification; to avoid future problems, it is recommended to go for those from the start； Motors are electrical devices and cannot undergo effective SIL certification. In addition to the above equipment, it is advisable that the remaining equipment in the SIF loop also have SIL certification.