Safety instrumented system (SIS) is a system designed to monitor dangerous conditions in a plant (operation unit) and take action in the event of a dangerous condition or a condition where if no action is taken it will cause danger.
This system will produce output that will prevent danger or reduce the consequences. In general,SIS consists of sensors, logic solver or also called safety control and final element, as shown in the following figure:
The sensor functions to measure and detect the presence or absence of a deviation. Deviation is an industrial process means that all deviations from the measured process parameters, such as low-level high-level, low-pressure high-pressure, low-flow high. Sensors are the front guard in the safety system.
Logic Solver is a part that is vital enough to play a role in processing data sent by sensors into a command. For example, if there are two flow sensors that both detect low flow and a set point is reached, then the logic solver will order the final element to close.
Final Element functions as an end in a safety instrument system, which is an active role to protect and maintain process safety by opening, closing (if a valve), running or shutting down if it is another (motorbike or other device).
How the Safety Instrumented System works?
The process in the safety instrumented system is controlled by a distributed control system namely (DCS) by monitoring process values, temperature, pressure, or flow and manipulating the end of elements such as valves, actuators.
If the value exceeds the acceptable level process, the alarm is issued by the operator to take action. However, if the operator’s actions are not successful in handling the process under control, the safety instrumented system automatically works, the process moves to be safe to prevent the possibility of an accident.
Safety Instrumented System function:
- Safety instrumented systems function as protectors if there are unexpected events that cause fatal accidents, environmental pollution, and accidents in an industrial instrumentation process. Safety instrumented systems are designed and built to reduce the risk of accidents in process control that can threaten life and environmental safety.
- SIF is a function implemented by SIS aimed at achieving or maintaining a safe condition of the process by referring to a specific hazardous event. So this SIS will have many SIFs, each SIF must be designed and tested to meet the SIL (Safety Integrity Level) target.