ONLINE ELECTRICAL ENGINEERING STUDY SITE

Maxwell Bridge Inductance Capacitance Bridge

This bridge is used to find out the self inductor and the quality factor of the circuit. As it is based on the bridge method (i.e. works on the principle of null deflection method), it gives very accurate results. Maxwell bridge is an AC bridge so before going in further detail let us know more about the AC bridge.

AC Bridges

AC Bridges consist of a source, balance detector and four arms. In AC bridges, all the four arms consists of impedance. The AC bridges are formed by replacing the DC battery with an AC source and galvanometer by detector of Wheatstone bridge.They are highly useful to find out inductance, capacitance, storage factor, dissipation factor etc. Now let us derive general expression for an AC bridge balance. Figure given below shows AC bridge network: maxwell bridge Here Z1, Z2, Z3 and Z4 are the arms of the bridge. Now at the balance condition, the potential difference between b and d must be zero. From this, when the voltage drop from from a to d equals to drop from a to b both in magnitude and phase.

Thus, we have from figure e1 = e2

From equation 1, 2 and 3 we have Z1.Z4 = Z2.Z3 and when impedance are replaced by admittance, we have Y1.Y4 = Y2.Y3. Now consider the basic form of an AC bridge. Suppose we have bridge circuit as shown below, maxwell bridge In this circuit R3 and R4 are pure electrical resistances. Putting the value of Z1, Z2, Z3 and Z4 in the equation that we have derived above for AC bridge.
Now equating the real and imaginary parts we get
Following are the important conclusions that can be drawn from the above equations:
  1. We get two balanced equations that are obtained by equating real and imaginary parts this means that for an ac bridge both the relation (i.e.magnitude and phase) must be satisfied at the same time. Both the equations are said to be independent if and only if both equation contain single variable element. This variable can be inductor or resistor.
  2. The above equations are independent of frequency that means we do not require exact frequency of the source voltage and also the applied source voltage waveform need not to be perfectly sinusoidal.

Maxwell's Bridge

Under this we going to study about the following
  1. Maxwell's inductor bridge
  2. Maxwell's inductor capacitance bridge

Maxwell's Inductance Bridge

Let us now discuss Maxwell's inductor bridge. The figure shows the circuit diagram of Maxwell's inductor bridge. maxwell induction bridge In this bridge the arms bc and cd are purely resistive while the phase balance depends on the arms ab and ad. Here l1 = unknown inductor of r1. l2 = variable inductor of resistance R2. r2 = variable electrical resistance. As we have discussed in AC bridge according to balance condition, we have at balance point
We can vary R3 and R4 from 10 ohms to 10,000 ohms with the help of resistance box.

Maxwell's Inductance Capacitance Bridge

In this Maxwell Bridge, the unknown inductor is measured by the standard variable capacitor. Circuit of this bridge is given below, maxwell-inductance-capacita Here, l1 is unknown inductance, C4 is standard capacitor. Now under balance conditions we have from ac bridge that Z1.Z4 = Z2.Z3
Let us separate the real and imaginary parts, the we have,
Now the quality factor is given by,

Advantages of Maxwell's Bridge

Advantages of Maxwell's bridge are showing below
  1. The frequency does not appear in the final expression of both equations, hence it is independent of frequency.
  2. Maxwell's inductor capacitance bridge is very useful for the wide range of measurement of inductor at audio frequencies.

Disadvantages of Maxwell's Bridge

  1. The variable standard capacitor is very expensive.
  2. The bridge is limited to measurement of low quality coils (1 < Q < 10) and it is also unsuitable for low value of Q (i.e. Q < 1) from this we conclude that a Maxwell bridge is used suitable only for medium Q coils.
The above all limitations are overcome by the modified bridge which is known as Hey's bridge which does not use an electrical resistance in parallel with the capacitor.




Closely Related Articles Wheatstone Bridge Circuit Theory and PrincipleKelvin Bridge Circuit | Kelvin Double BridgeAnderson′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 Electrical Measuring Instruments | Types Accuracy Precision Resolution SpeedErrors in Measurement | Classification of ErrorsPermanent Magnet Moving Coil Instrument or PMMC InstrumentMoving Iron InstrumentElectrostatic Type Instruments Construction Principle Torque EquationRectifier Type Instrument | Construction Principle of OperationThermocouple type Instruments Construction Principle of OperationProtection of MetersDigital Frequency MeterOhmmeter Working Principle of OhmmeterPotentiometer Working Principle of PotentiometerInduction Type MetersWhat is Low Power Factor Wattmeter ?Energy Meter with Lag Adjustment DevicesElectrodynamometer Type WattmeterMeasurement of Three Phase PowerVarmeter | Single Phase and Polyphase VarmeterMegger | Working Principle Types History Uses of MeggerWeston Type Frequency MeterPower Factor Meters | Electrodynamometer Type Power Factor MeterPhase Sequence IndicatorAmmeter Working Principle and Types of AmmeterDigital MultimeterInsulation Resistance Test and Polarization Index TestTan Delta Test |Loss Angle Test | Dissipation Factor TestElectronic DC VoltmeterWorking Principle of Voltmeter and Types of VoltmeterDigital Voltmeters Working Principle of Digital VoltmeterMeasurement of Electrical EnergyEnergy Meter TestingAC PotentiometerConstruction of AC Energy MeterWatt Hour MeterCapacitance MeterVector Impedance MeterHow to Use a Digital Multimeter?Transducer | Types of TransducerRadiation Pyrometer | Types Working PrincipleResistance Temperature Detector or RTD | Construction and Working PrincipleStrain GaugeTemperature Sensor Temperature Measurement | Types of Temperature SensorSensor | Types of SensorOptical Pyrometer | Construction and Working PrincipleBimetallic Strip ThermometerPiezoelectric TransducerThermistor Thermometer | Thermistor Temperature Sensor | Construction and Principle Thermocouple Temperature MeasurementInductive TransducersTemperature TransducersLinear Variable Differential Transformer LVDTOscillator TransducerThermistor Definition Properties Construction Characteristics and Applications Hartley OscillatorColpitts OscillatorClapp OscillatorRC Phase Shift OscillatorWien Bridge OscillatorGunn OscillatorCrystal OscillatorMonostable MultivibratorBistable Multivibrator555 Timer and 555 Timer WorkingWhat is an Oscillator?Astable MultivibratorVoltage Controlled Oscillator | VCOCathode Ray Oscilloscope | CROLissajous Patterns of CRO or Cathode Ray OscilloscopeFrequency Limitation of an OscilloscopeSignal GeneratorMeasurement of Voltage Current and Frequency by OscilloscopeDigital Storage OscilloscopeDouble Beam OscilloscopeSampling OscilloscopeNew Articles Voltage in ParallelVoltage in SeriesVoltage Regulator 7805How to Use a Digital Multimeter?Vector Impedance MeterVoltage Follower