Online Electrical Engineering
Moving Iron Instrument
Temperature Sensor Temperature Measurement | Types of Temperature Sensor
Anderson′s Bridge | Advantages Disadvantages of Anderson′s Bridge
Maxwell Bridge Inductance Capacitance Bridge
Hay′s Bridge Circuit Theory Phasor Diagram Advantages Applications
Owens Bridge Circuit and Advantages
Schering Bridge Measurement of Capacitance using Schering Bridge
Heaviside Bridge Circuit
De Sauty Bridge
Electrodynamometer Type Wattmeter
Induction Type Meters
Energy Meter with Lag Adjustment Devices
Electrical Measuring Instruments | Types Accuracy Precision Resolution Speed
Errors in Measurement | Classification of Errors
Permanent Magnet Moving Coil Instrument or PMMC Instrument
Electrostatic Type Instruments Construction Principle Torque Equation
Thermocouple type Instruments Construction Principle of Operation
Rectifier Type Instrument | Construction Principle of Operation
What is Low Power Factor Wattmeter ?
Megger | Working Principle Types History Uses of Megger
Transducer | Types of Transducer
Sensor | Types of Sensor
Varmeter | Single Phase and Polyphase Varmeter
Blavier Test | Murray Loop Test | Varley Loop Test | Fisher Loop Test
Measurement of Three Phase Power
Weston Type Frequency Meter
Power Factor Meters | Electrodynamometer Type Power Factor Meter
Phase Sequence Indicator
Insulation Resistance Test and Polarization Index Test
Resistance Temperature Detector or RTD | Construction and Working Principle
Tan Delta Test |Loss Angle Test | Dissipation Factor Test
Radiation Pyrometer | Types Working Principle
Optical Pyrometer | Construction and Working Principle
Bimetallic Strip Thermometer
Thermistor Thermometer | Thermistor Temperature Sensor | Construction & Principle
Thermocouple Temperature Measurement
Cathode Ray Oscilloscope | CRO
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 BridgesAC 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:
Here Z1, Z2, Z3 and Z4 are the arms of the bridge.
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,
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: (a) 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. (b) 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 BridgeUnder this we going to study about the following (a) Maxwell's inductor bridge (b) 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. 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 BridgeIn this Maxwell Bridge, the unknown inductor is measured by the standard variable capacitor. Circuit of this bridge is given below, 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,