Logical problems
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This post was last edited by hby1224 on 2016-2-25 08:08. What is the difference between three-select and three-select-two? I understand that for a three-to-one selection, an analog value is chosen, while for a three-to-two selection, 0 and 1 are chosen; I’m not sure if this is correct. The SIS system should use a three-to-two configuration; however, I saw a diagram in which a three-to-three setup was used for safety interlocks, and it was a bit confusing. A three-to-three setup should be used for displaying values or for adjusting measurements, right?
The actual configuration is indeed formed in this way; it’s reasonable for AI to choose the middle option.
For example, in terms of the drum level, a two-out-of-three interlock is used to shut down the furnace; the middle value out of the three is utilized as the control signal for the main loop that regulates the level. The original poster is right – I’ve never heard of a middle-value interlock; there’s no such thing as an interlock of that kind; interlocks can only work with 0s and 1s