In the world of process safety, technology continues to advance to assist process manufacturers in their IEC 61511 safety compliance efforts. I saw a recent press release on enhancements to the Fisher DVC6000 digital valve controller. The news was:
…enhancements include manual reset, a stored safety demand event log, pass / fail status after a partial stroke test, and third party certification to SIL3, SIF loop.
I asked Riyaz Ali, whom you may recall from earlier posts, to simplify what this all means for me. The stored safety demand event log he likened to an airplane black box recorder. If a process upset condition triggers a safety demand on a valve controlled by the DVC6000 SIS (operated by 4-20mA input signal), it in turn automatically triggers an event log to capture the data into non-volatile memory locally in the digital valve controller.
This log keeps pre- and post-event data of the operating conditions surrounding the safety demand event. Examples of the type of data stored away in this event log include: travel, travel setpoint, output pressure with time in seconds, graphical representation of data points and date and time stamp of the trigger event for regulatory compliance.
Riyaz also described for me the partial stoke testing reporting. It now will provide pass/fail status and a signature curve of the valve stem movement. These partial stroke tests periodically diagnose the SIS valve to help ensure its availability. Also, a specially designed built-in relay provides protection against spurious trips which improves overall process availability. Other information provided back to the AMS ValveLink software includes diagnostics on stick slip, shaft integrity and maximum and minimum torque values.
For the DVC6000 SIS, the Fisher team achieved third-party certification for compliance to the IEC 61508 international safety standard for use in a SIL 3 safety instrumented function. This means that process manufacturers can use the DVC6000 SIS as part of the safety instrumented function in the SIL 3 loops they identify as part of their risk assessment and risk mitigation strategy.
Having all these digital valve controllers keeping logs of what’s going on especially around upset conditions can greatly assist root cause investigations and help avoid future abnormal situations. And the diagnostics coming from the partial stroke tests can help process manufacturers avoid these abnormal conditions in the first place.
