Diagnostics for Final Elements in Safety Applications

At the Emerson Exchange Americas virtual series, Emerson’s Mike Hoyme and Stanley Af demonstrated diagnostics in the final elements within a safety instrumented function. Here is their presentation abstract:

In this demonstration we will show how to use the FIELDVUE DVC6200 SIS to perform diagnostics on SIS final elements. This device can run full stroke testing, partial stroke testing (PST), solenoid valve (SOV) health monitoring, and log triggered events in the event of a trip. These diagnostics can help improve diagnostic coverage for final elements to assist with SIL compliance and the proof provided by a triggered event can be used as a proof test which can prevent the need to perform an addition full stroke proof test.

Mike opened showing the demonstration final element components used.SIS Final Element Components

He showed how the piping was configured for these components.SIS Final Element Piping Schematics

Stanley first showed a partial stroke test to verify movement in the safety valve. Limits being applied during the test includes actuator pressure and travel movements. If either limit is violated the test fails and the diagnostics report the likely cause. The graphs displayed show when the movement begins in response to actuator pressure and when the movement completes. Based on the lags the partial stroke test will indicate success or failure.

These tests can be performed automatically with notifications sent out to the staff responsible for maintaining the safety valves. Safety instrumented systems supporting HART commands, such as DeltaV SIS, can schedule the automatic partial stroke tests. Stanley showed parameters that can be configured by the safety engineer to identify different issues that may or may not be relevant for the application of the valve.

Local control panels, such as the LCP 200, can also be used to initiate partial stroke tests. Stanley also showed a valve signature measuring the valve travel versus the actuator pressure to identify possible issues in the travel of the valve. These signatures can be compared over time to the original factory valve signature to identify problems.

A travel deviation alert during a proof test can spot a failed solenoid valve (SOV) by measuring the actuator pressure versus it’s travel. A last demand stroke time diagnostic compares the actual time during the test versus what the safety instrumented function requires to take the process to a safe state.

The DVC6200 digital valve controller can test the solenoid valve by pulsing the solenoid and the DVC6200 registers the change in pressure. The test can be done from the safety instrumented system logic solver if it supports HART commands, or directly from the DVC6200 through a discrete output.

Visit the Digital Valve Controllers section on Emerson.com for more on the advanced diagnostics to support your SIS final elements across the IEC 61511 safety lifecycle.

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