What is SSV in instrumentation?

Excuse me, as a fellow professional in the field of finance with an interest in the intricacies of instrumentation, I was wondering if you could clarify what the acronym "SSV" stands for in the context of instrumentation? I've encountered it in a few technical documents but have yet to find a concise explanation. Is it related to a specific type of sensor or perhaps a certain type of validation procedure? Clarifying its precise meaning would be of immense assistance as I continue my research into various instrumentation systems. Thank you for your time and expertise in this matter.