I have had yet another discussion today on what it means to put something into bypass when an instrument is part of a multiple instrument voting arrangement. At its most basic level, when you logically put something into bypass, that should mean that the instrument is voting NOT to trip. While logical, many like to “improve” by creating elaborate voting tables. While these tables do have their merit, then can be confusing. For instance, if you have a voting table that says that when a sensor in a 2oo2 voting arrangement is put into bypass you revert to 1oo1 mode, that is counter to the physical functionality of how a bypass works. You are turning that “bypass” signal into a vote TO trip, which is logically the exact opposite of what you expect.

While there are merits to keeping it simple and also merits to advanced voting schemes, it is important that all people who interact with the SIS understand exactly how it works.