Level Sensor Safety Proof Testing

Backing up your computer or server is a waste of time if restoring the backup fails when you need it. Good practice is to test these backups on separate test systems periodically to make sure they restore properly. Similarly, safety instrumented systems (SISs) need to assure that each safety instrumented function (SIF)/safety loop does what it’s intended to do to bring the plant to a safe state in the event of a demand.

Proof testing is the way to do this. In a PCN Europe article, Proof-Testing: An Effective Way to Increase Safety, the author explains how digital technologies in instrumentation have enabled remote proof testing in addition to the traditional manual testing performed locally at each instrument or back in the shop. These remote proof tests help to extend the time required for full proof testing.

The article opens contrasting manual and remote proof testing:

Traditionally, proof-testing has been performed with multiple technicians in the field and one in the control room, verifying the safety system reaction. This requires a considerable amount of time and effort, can pose safety risks to workers who need to climb tanks to perform the test, could take the process offline for an extended period, and can be prone to errors. However, technological advances in modern smart devices are now enabling proof-testing to be performed remotely, making the process much quicker, safer and more efficient.

The goal of these tests is to spot undetected failures that would affect the SIF from operating as it should.

Testing frequency directly impacts regulatory compliance and safety calculations, such as Safety Integrity Level (SIL). Obtaining a high-quality proof-test performed at regular intervals is critical in meeting SIL and regulatory requirements. Devices and systems across the process are involved.

Partial proof testing performs the test with the sensor or final control element still in service. These tests allow the time intervals between full stroke tests to be extended.

For level measurement devices used in atmospheric bulk liquid applications, the:

API 2350 standard outlines the minimum requirements… Its main purpose is to prevent overfills and improve safety. API 2350 does not compete with other, more generic, safety standards, but is intended to complement them. For the process industry, the standard for designing a SIS is IEC 61511.

The article shares two examples of remote partial stroke testing for a Rosemount 2140 Vibrating Fork Level Detector and a Rosemount 5400 Non-Contacting Radar Level Transmitter.

Emerson’s Rosemount HART vibrating fork level detector, for example, can be remotely proof-tested by issuing a HART command. Upon receiving the command, the device then enters test mode. This cycles the output through wet, dry and fault states, then returns into normal operation. The process is continually monitored during this time and any change will be reported immediately on test completion.

Emerson’s Rosemount 5400 non-contacting radar level transmitter can be remotely proof-tested using dedicated Radar Master software. This enables an operator to perform the proof-test simply by inputting a straightforward sequence of settings and commands from their interface.

Read the article for more on ways to test guided wave radar (GWR) transmitters and how this change from local and manual to remote partial proof testing helps plants operate more safely, efficiently and reliably.

You can connect and interact with level measurement and functional safety experts in the Level and Safety Instrumented Systems groups in the Emerson Exchange 365 community.

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