Each safety instrumented function (SIF) including its sensor, logic solver and final control element must be periodically tested to make sure it will perform as designed in the event of a safety demand. These “proof tests” help to uncover and failure conditions which may have developed since the last proof test or safety demand.
A new whitepaper, Reducing the Complexity of Proof-Testing with New Generation Point Level Detectors, compares the traditional and modern approaches for proof-testing critical point level and overfill prevention instrumentation.
In the whitepaper, proof tests are defined as:
…operational tests conducted in accordance with the safety manual of an individual installed device to evaluate its ability to perform its safety function and to uncover random hardware failures. These are failures that prevent the device from performing its primary function and which would otherwise remain undetected by its built-in diagnostics during normal operation.
…place high importance on regular proof-testing with recommended schedules and procedures for inspection and testing of gauging equipment and high-level instrumentation and related systems…
The traditional approach for proof testing point level detectors has been:
…carried out by multiple technicians in the field, with another worker stationed in the control room to verify the reaction of the system. This method can involve workers having to climb tanks to access instruments and perform the proof-test, within a potentially hazardous environment with increased safety risks.
The test requires either the removal of the level detector to conduct an immersion test or to adjust the tank’s liquid level to reach the detector—which introduces additional risk.
In addition to a comprehensive (full) proof test, partial proof tests can be performed to increase the time interval between tests. This time interval is based upon the instrument’s probability of failure on demand (PFD) average and level of risk being mitigated.
The Rosemount 2140:SIS Level Detector enables partial proof-tests to be remotely initiated by an operator issuing a command from the control room, without the need to install a separate switching unit in the control panel. This partial proof test:
…exercises the processing and output electronics of the device, and since it is performed in-process, it takes only minutes to complete the test cycle, thereby providing a significant time reduction compared to other proof-testing methods.
Download the whitepaper for more on how this method reduces complexity compared with other remote proof testing approaches which require external switching units and additional space as well as a case study on how these devices were used in a fleet of compressor stations. Visit the Rosemount 2140 Level Detector section on Emerson.com for more on how this vibrating fork technology works and how it addresses your overfill prevention and safety instrumented system applications.
You can also connect and interact with other level measurement experts in the Measurement Instrumentation group in the Emerson Exchange 365 community and/or at the September 23-27 Emerson Exchange conference in Nashville.