ONLINE ELECTRICAL ENGINEERING STUDY SITE

Wheatstone Bridge Circuit Theory and Principle

Wheatstone Bridge

For measuring accurately any electrical resistance Wheatstone bridge is widely used. There are two known resistors, one variable resistor and one unknown resistor connected in bridge form as shown below. By adjusting the variable resistor the current through the Galvanometer is made zero. When the current through the galvanometer becomes zero, the ratio of two known resistors is exactly equal to the ratio of adjusted value of variable resistance and the value of unknown resistance. In this way the value of unknown electrical resistance can easily be measured by using a Wheatstone Bridge.

Wheatstone-bridge

Wheatstone Bridge Theory

The general arrangement of Wheatstone bridge circuit is shown in the figure below. It is a four arms bridge circuit where arm AB, BC, CD and AD are consisting of electrical resistances P, Q, S and R respectively. Among these resistances P and Q are known fixed electrical resistances and these two arms are referred as ratio arms. An accurate and sensitive Galvanometer is connected between the terminals B and D through a switch S2.
The voltage source of this Wheatstone bridge is connected to the terminals A and C via a switch S1 as shown. A variable resistor S is connected between point C and D. The potential at point D can be varied by adjusting the value of variable resistor. Suppose current I1 and current I2 are flowing through the paths ABC and ADC respectively. If we vary the electrical resistance value of arm CD the value of current I2 will also be varied as the voltage across A and C is fixed. If we continue to adjust the variable resistance one situation may comes when voltage drop across the resistor S that is I2. S is becomes exactly equal to voltage drop across resistor Q that is I1.Q. Thus the potential at point B becomes equal to the potential at point D hence potential difference between these two points is zero hence current through galvanometer is nil. Then the deflection in the galvanometer is nil when the switch S2 is closed.
Now, from Wheatstone bridge circuit and Now potential of point B in respect of point C is nothing but the voltage drop across the resistor Q and this is Again potential of point D in respect of point C is nothing but the voltage drop across the resistor S and this is charles wheatstone Equating, equations (i) and (ii) we get, Here in the above equation, the value of S and P ⁄ Q are known, so value of R can easily be determined.
The electrical resistances P and Q of the Wheatstone bridge are made of definite ratio such as 1:1; 10:1 or 100:1 known as ratio arms and S the rheostat arm is made continuously variable from 1 to 1,000 Ω or from 1 to 10,000 Ω.
The above explanation is most basic Wheatstone bridge theory.

Video Presentation of Wheatstone Bridge Theory



Comments/Feedbacks








Closely Related Articles Kelvin Bridge Circuit | Kelvin Double BridgeSensor | Types of SensorMaxwell Bridge Inductance Capacitance BridgeTemperature Sensor Temperature Measurement | Types of Temperature SensorAnderson′s Bridge | Advantages Disadvantages of Anderson′s BridgeHay′s Bridge Circuit Theory Phasor Diagram Advantages ApplicationsOwens Bridge Circuit and AdvantagesSchering Bridge Measurement of Capacitance using Schering BridgeDe Sauty BridgeHeaviside Bridge CircuitBlavier Test | Murray Loop Test | Varley Loop Test | Fisher Loop TestMore Related Articles Cathode Ray Oscilloscope | CROLissajous Patterns of CRO or Cathode Ray OscilloscopeMeasurement of Voltage Current and Frequency by OscilloscopeDigital Storage OscilloscopeDouble Beam OscilloscopeSampling OscilloscopeMeasurement of ResistanceDigital Frequency MeterOhmmeter Working Principle of OhmmeterInduction Type MetersWhat is Low Power Factor Wattmeter ?Electrodynamometer Type WattmeterProtection of MetersBimetallic Strip ThermometerVarmeter | Single Phase and Polyphase VarmeterWeston Type Frequency MeterAmmeter Working Principle and Types of AmmeterDigital MultimeterElectronic DC VoltmeterWorking Principle of Voltmeter and Types of VoltmeterDigital Voltmeters Working Principle of Digital VoltmeterConstruction of AC Energy MeterWatt Hour MeterCapacitance MeterVector Impedance MeterHow to Use a Digital Multimeter?Flow MeasurementFlow MeterAir MeterWater MeterFrequency Limitation of an OscilloscopeSignal GeneratorHartley OscillatorColpitts OscillatorClapp OscillatorRC Phase Shift OscillatorWien Bridge OscillatorGunn OscillatorCrystal OscillatorWhat is an Oscillator?Voltage Controlled Oscillator | VCOPotentiometer Working Principle of PotentiometerAC PotentiometerDigital PotentiometersElectrical Measuring Instruments | Types Accuracy Precision Resolution SpeedTransducer | Types of TransducerErrors in Measurement | Classification of ErrorsPermanent Magnet Moving Coil Instrument or PMMC InstrumentCharacteristics of SensorsMoving Iron InstrumentElectrostatic Type Instruments Construction Principle Torque EquationResistance Temperature Detector or RTD | Construction and Working PrincipleEnergy Meter with Lag Adjustment DevicesRectifier Type Instrument | Construction Principle of OperationThermistor Thermometer | Thermistor Temperature Sensor | Construction and Principle Thermocouple Type Instruments Construction Principle of OperationThermistor Definition Properties Construction Characteristics and Applications Measurement of Three Phase PowerThermocouple Temperature MeasurementTemperature TransducersMegger | Working Principle Types History Uses of MeggerRadiation Pyrometer | Types Working PrincipleOptical Pyrometer | Construction and Working PrinciplePiezoelectric TransducerStrain GaugePower Factor Meters | Electrodynamometer Type Power Factor MeterInductive TransducersPhase Sequence IndicatorLinear Variable Differential Transformer LVDTOscillator TransducerInsulation Resistance Test and Polarization Index TestVoltage SensorTan Delta Test |Loss Angle Test | Dissipation Factor TestMeasurement of Electrical EnergyEnergy Meter TestingMonostable MultivibratorBistable MultivibratorAstable MultivibratorNew Articles Measurement of Insulation ResistanceAmpere's Circuital LawMechanical Equivalent of HeatTrees and Cotrees of Electric NetworkDifferentiatorIntegrator
electrical engineering app