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WHEATSTONE BRIDGE Maram Odeh Anwaar Haimoor Bridges A bridge circuit is a type of electrical circuit in which two circuit branches (usually in parallel with each other) are "bridged" by a third branch connected between the first two branches at some intermediate point along them. 2 A bridge circuit is a type of electrical circuit in which two circuit branches (usually in parallel with each other) are "bridged" by a third branch connected between the first two branches WHY DO WE USE THEM?? The bridge was originally developed for laboratory measurement purposes and one of the intermediate bridging points is often Why do we use them ?? adjustable when so used. 3 EXAMPLES : Diode bridge Kelvin bridge Maxwell bridge H bridge 4 WHEATSTONE BRIDGE:1) the best-known bridge circuit . 2) is used for measuring an unknown resistance. 3) it minimize the error measurement (precise system). 5 TO MEASURE AN UNKNOWN RESISTANCE …. First we can try measuring a resistor connected to a battery ,using ohms law…. 6 CURRENT MEASUREMENT Based on ohms law :The current is directly proportional to the voltage and inversely proportional to the resistance. Current measurement 7 SO … the primary benefit of a Wheatstone bridge is its ability to provide extremely accurate measurements (in contrast with something like a simple voltage divider) 8 Rx : is the unknown resistance to be measured. R1,R2 and R3 : are resistors of known resistance. r2 is adjustable 9 MEASUREMENT USING WHEATSTONE BRIDGE: A Wheatstone bridge as shown below can be used to measure the resistance of the resistor “R”: 10 IN MOST CASES the Wheatstone bridge is unbalanced and it is so called when some current is flowing through the galvanometer. 11 BUT in the case, when no current flows through the bridge galvanometer ; this state is called the balanced state of Wheatstone bridge. 12 APPLICATION OF WHEATSTONE BRIDGE: * Measuring the value of an unknown resistor. * It is also used in electrical sensors like temperature sensor , light sensor etc. 13 Some Wheatstone bridge designs include two variable resistors to improve the sensitivity of the system. (vg) is proportional to the difference in the transducers’ resistance values relative to the reference resistance in the bridge configuration 14 The design of the circuit reduces the effects of noise on the output voltage. 15 IF the input voltage varies, it does not influence the output voltage since it is related to the ratio of the resistances. 16 Also, a variation in temperature affects all the resistor elements equally and therefore cancel each other out. therefore, this circuit greatly suppresses electrical noise and thereby improves the signal to noise ratio. 17 When the Wheatstone bridge is used in a pressure sensor, the resistors are oriented such that R1 and R4 are variable under the stress of a flexible membrane on which they are made. 18 The resistors in the Wheatstone bridge are made of a piezoresistive material, a material which changes its resistance when mechanical stress is applied. 19 . A change in pressure creates a deflection of the diaphragm. This deflection causes the variable resistors of the bridge to expand, increasing circuit resistance indicating a change in pressure 20