AC bridge is used for measureing the unknow impedence where as DC bridge used for measuring unknow resistance.
AC components are present in the arm ( resistive or reactive ) in DC bridges the arm contain resistiv3e components only maxewell bridge is madiflication to the wheatstone bridge , used to measure unknown impedence in terms of collibrated resistance and induction or resistance and capacitor.
The bridge circuit measure and inductance by comparison with a variable standard self inductance with respect to diagram.
1) R1L1 are unknown parameters.
2) R2 is the coil resistance/ decand resistance.
3) R2 & L2 are variable resistance and inductance respectively.
4) R3 & R4 are fixed resistance a normally R3 & R4 are a selection of values from 10 , 1000 & 10,000Ω
★ Maxewell inductance capacitance bridge.
Maxewell inductance capacitance bridge here unknown self inductance to be determine is compared with standard unknown capacitor.
The Maxwell inductance bridge, also known as the Maxwell-Wien bridge, is a type of bridge circuit used for measuring inductance. It was developed by the Scottish physicist James Clerk Maxwell and the German physicist Wilhelm Eduard Weber in the 19th century. This bridge configuration is particularly useful for accurately determining the value of an unknown inductance in terms of known resistance and capacitance values.
The Maxwell inductance bridge consists of four arms or branches: two ratio arms, one of which contains a variable resistance (R) and an unknown inductance (L), and the other containing a fixed resistance (R') and a fixed capacitor (C). The remaining two arms consist of a known resistance (R1) and a known capacitor (C1) connected in series.
The primary principle behind the Maxwell inductance bridge is based on the balance condition, where the ratio of the impedance of the L-C branch to the impedance of the R-C branch is equal to the ratio of the resistances in the ratio arms. When the bridge is balanced, the voltage across the galvanometer connected between the two junction points of the ratio arms becomes zero.
By manipulating the variable resistance (R) in one of the ratio arms and observing the null indication on the galvanometer, the unknown inductance (L) can be determined. At the balanced condition, the inductance (L) can be calculated using the formula:
L = R' * C * (R1 / C1)
Where R' is the fixed resistance, C is the fixed capacitor, R1 is the known resistance, and C1 is the known capacitor.
The Maxwell inductance bridge is a highly accurate method for measuring inductance because it eliminates the need for precise calibration of the bridge components. By adjusting the variable resistance, the bridge can be balanced regardless of the absolute accuracy of the resistors and capacitors used.
Overall, the Maxwell inductance bridge provides a practical and reliable means of measuring unknown inductance values in various applications, including electrical engineering, electronics, and physics research.
★ Advantage of using standard capacitor.
1) low cost compared to the stable and accurate standard inductor.
2) Capacitors used here are loss less and their is less possibility of loosing energy.
3) Capacitors are independent of external magnetic field.
W.R.T diagram :-
1) L1 is the unknown inductance to be measure.
2) R1 resistance of unknown inductor.
3)R2 &R3 are R2 & R3 each can be selected to 10, 100, 1000, 10,000Ω
4) R4 standard non inductive variable resistance.
5) C4 standard capacitance variable.
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