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Challenge: Extending Proof Test Intervals while Maintaining High Levels of Safety

Functional Safety systems are critical elements to the safe operations of a process facility. The periodic proof testing of these systems is essential to ensuring that the system will perform when needed the most, but can also be time consuming and costly. Finding the optimal interval for when the proof test should be performed is a challenge facing safety engineers today. On one hand you want to perform the test often enough to significantly reduce the risk of the system being unavailable in the case of a safety incident, while also doing your best to limit the downtime of your process.

Emerson instruments provide you with several tools you can use to extend out intervals between proof tests, while ensuring that you maintain the highest levels of safety for your facility. The first tool is by providing multiple levels of proof tests for each instrument, with some being able to be performed without physically removing the instrument from the process. By performing partial or in situ proof tests more frequently, you can extend the time interval between when the instrument needs to be removed from the process to better align with your turnaround schedule. A second step that can be taken is by utilizing the diagnostic capabilities of your instruments. The Rosemount 3051S pressure transmitter has Power Advisory diagnostics that, when turned on, move 12 failures that were previously considerd dangerous undetected to the dangerous detected category, allowing a significant improvemnet in the probability of failure on demand for the instrument. The 3051S also has the ability to detect plugged impulse lines, which you can use to proactively maintain the device and ensure that it will be able to detect potential unsafe conditions.

Do you use any of these technologies in your safety functions? How do you optimize the proof test intervals at your facility? Please comment if you have any questions or feel free to reach out to me directly for any additional information on these technologies.

2 Replies

  • Interesting. What are the 12 failures detected?

    Diagnosing failure in the 4-20 mA loop should be a requirement for every 4-20 mA circuit, and integrity check to know the signal is not being affected by ground loop current or increased resistance due to corrosion which may develop over time. Particularly for safety functions. Alternatively use digital signal transmission with error checking.
  • When taking credit for a standard (non-sis) process control interlock or a PFD of .1 on a LOPA, what impact does the testing interval have on this number? What is the assumed testing interval for the interlock to carry a .1 PFD?