A few months ago, I attempted to clear up some misconceptions about the use of digital valve controllers in safety applications in a post, Clarifications on the Use of the DVC6000 SIS in Safety Applications. It addressed misconceptions about references to the obsolete DIN 19250 standard, failsafe DVC 6000 SIS, SIL 3 suitability not being limited to the pneumatic portion of the positioner, and the use of solenoids in safety functions.Emerson’s Riyaz Ali shared some additional detail and another misconception that he’s heard. The misconception is that the DVC6000 SIS is the same design as the DVC6000 used for control valves. Riyaz notes that although it shares the same hardware components of the DVC6000, the DVC6000 SIS is intended for on-off use, and includes functionality unique to safety instrumented system (SIS) applications, such as partial valve stroke, and SOV test recording capabilities. The DVC6000 SIS has undergone a certified design process to ensure that it adheres with the functional safety requirements of the international IEC 61508 safety standard.
On the use of external hardware, a misconception is that uncertified hardware is required to be used in the partial stoke test (PST) application. Riyaz clarifies that this is not true. The DVC6000 SIS can perform partial stroke testing without the use of additional hardware to initiate it. It can be initiated by push button, by the device itself, or via HART command. Once a PST test has been performed, ValveLink software is required to view the test results. These diagnostics do not affect the safety function of the final control element and therefore, may reside in the Basic Process Control System (BPCS). Riyaz references IEC 61511-1, 11.3 for more detail on this approach.
Is there anything you’ve heard about the use of digital valve controllers in safety instrumented functions? If so, add a comment below or start a new thread in the valve controllers & positioners track in the Emerson Exchange 365 community.