What are triple majority, triple average, and triple two-out-of-three in a DCS system?

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The last edit to this post was made by shh_Divine Eagle on 2024-9-3 at 10:05. In DCS systems, what are three-out-of-three, three-out-of-five, and two-out-of-three? In redundant configurations, \"two-out-of-three\" refers to a voting mechanism used in digital control; the same signal is evaluated using three redundant signals, and the condition is considered met if two of them satisfy it. Taking two out of three is intended to ensure accuracy and reliability in judgment, to prevent false operations, and is commonly used in protection circuits. Three-way averaging refers to the use of three redundant inputs for analog signals, with the average value of these being used as the actual value; this method is commonly employed in primary control loops. Generally, when the deviations between three measurement points at the same location are too large, it is necessary to identify the problem and address it safely and quickly; one must never rely on luck. In addition to the midpoint value, general function blocks also provide options: high selection, low selection, average, or one of the three. The average of three readings is also applied to analog values, with the average of these three numbers being taken to mitigate systematic errors to some extent; however, random errors caused by instrument failures are difficult to avoid. The difference lies in the use of a \"three-to-two\" logic for digital signals, primarily regarding the method of selecting protection signals. Analog quantities use the \"three-out-of-three\" or \"average of three\" method, and are generally used in control and regulation circuits; however, the average of several analog quantities should in principle not be used in critical regulation or protection circuits. Precautions in logical configuration for three-way selection: ① Take the intermediate value under normal conditions ； ②When a point is identified as defective or the deviation exceeds the limit, it is automatically removed, and the average of the remaining two points is taken ； ③A well-designed logic is capable of operating between any arbitrarily specified single value, median, or average. Three-out-of-three selection is still the most commonly used in control systems; it allows three signals to be used for mutual deviation checking, with one incorrect signal being discarded and an average value taken from the remaining two signals. If another signal fails, the third signal is automatically used. If all signals fail, the value corresponding to normal operation should be maintained, along with an alarm being issued. 02 A judgment can be added for the three values: when all three signals are normal, the average of the three is taken; when one signal is abnormal, the average of the two remaining values is used; and when two signals are abnormal, the value of the third normal signal is used. This method is the most widely used in automatic regulation. 03 For two-out-of-three or three-out-of-three voting, it is generally used for logical evaluation of the sampled signal; to ensure the reliability of the signal, logic operations such as quality assessment and rejection can be incorporated. For motion protection in three-choice scenarios, generally speaking, it is important to use appropriate signals, either for interlock protection or for regulatory control. So some judgment conditions and removal conditions will be added. In logical design, it is often necessary to have two or even three sets of switchable protection logic. Two-out-of-three, majority voting – these may be used in a protection logic.