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Understanding Smart Sensors - Nomads.usp

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Control Techniques 155consisting of logic gates and flip-flops. These dedicated controllers can beeither synchronous or asynchronous and can be implemented in hardware orsoftware.7.3 Fuzzy LogicFuzzy logic control theory is an alternative to lookup tables and algorithm calculationsthat is easier to develop and has performance advantages in manyapplications. Fuzzy logic can be defined as a branch of logic that uses degrees ofmembership in sets rather than a strict true/false membership [9]. Fuzzy logic isfinding acceptance in consumer, automotive, industrial, and even decisionmakingapplications [10]. Table 7.3 gives examples of existing applications offuzzy logic.In contrast to PID control, which models the system or process beingcontrolled, fuzzy logic focuses on the human operator’s behavior [11]. Fuzzylogic defines a partial set membership, not the strict one normally associatedwith the Boolean logic used in MCUs and DSPs. Rules stated in natural languageestablish membership to the fuzzy sets.Figure 7.4 shows an example of fuzzy logic membership for a pressure (orvacuum) input. The fuzzy set allows membership with different grades, eachexpressed by a number in the interval [0, 1]. In that example, membershipfunctions and rules are established for the five pressure ranges of very low, low,normal, high, and very high. The membership value for intermediate locationsis some number between 0 and 1. A rule for the very high pressure could bethis: If the pressure is very high, then decrease the power greatly, with a weightTable 7.3Applications of Fuzzy LogicConsumer Automotive Industrial Decision SupportVCRs Air conditioning Extruding Building HVACCamcorders Transmission control Mixing Medical diagnosticsTelevisions S<strong>usp</strong>ension control Furnace controls TransportationVacuum cleaners Cruise control Temperature controls Elevator controlsClothes dryersConveyor controlsWashing machinesHot water heaters

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