If a Safety Instrumented Function (SIF) has a process safety time of 2 seconds, with a sensor response time of 300 milliseconds and a logic solver response time of 800 milliseconds, what is the required response time of the final element?

If a Safety Instrumented Function (SIF) has a process safety time of 2 seconds, with a sensor response time of 300 milliseconds and a logic solver response time of 800 milliseconds, what is the required response time of the final element?

• A. 300 milliseconds
• B. 2 seconds
• C. The SIF cannot meet the process safety time
• D. 900 milliseconds

Answer: (D)

To determine the required response time of the final element in this scenario, it is important to understand how the components of a Safety Instrumented Function (SIF) interact within the overall safety time. The process safety time is the total time available before a hazardous event occurs, within which the SIF must operate to ensure safety. In this case, the process safety time is 2 seconds (or 2000 milliseconds), while the response times of the other components are given as follows: the sensor response time is 300 milliseconds and the logic solver response time is 800 milliseconds. To ensure the SIF can operate effectively within the 2 seconds, we first need to calculate the cumulative response time of the sensor and logic solver. This total is computed by adding the sensor response time and the logic solver response time: 300 milliseconds (sensor) + 800 milliseconds (logic solver) = 1100 milliseconds. This means that there are 1100 milliseconds already accounted for by the sensor and logic solver. To determine the maximum allowable response time for the final element, we subtract the cumulative time from the total process safety time: 2000 milliseconds (process safety time) - 1100 milliseconds (sensor + logic solver) = 900 milliseconds

To determine the required response time of the final element in this scenario, it is important to understand how the components of a Safety Instrumented Function (SIF) interact within the overall safety time. The process safety time is the total time available before a hazardous event occurs, within which the SIF must operate to ensure safety.

In this case, the process safety time is 2 seconds (or 2000 milliseconds), while the response times of the other components are given as follows: the sensor response time is 300 milliseconds and the logic solver response time is 800 milliseconds.

To ensure the SIF can operate effectively within the 2 seconds, we first need to calculate the cumulative response time of the sensor and logic solver. This total is computed by adding the sensor response time and the logic solver response time:

300 milliseconds (sensor) + 800 milliseconds (logic solver) = 1100 milliseconds.

This means that there are 1100 milliseconds already accounted for by the sensor and logic solver. To determine the maximum allowable response time for the final element, we subtract the cumulative time from the total process safety time:

2000 milliseconds (process safety time) - 1100 milliseconds (sensor + logic solver) = 900 milliseconds