6.3 HAY'S BRIDGE

HAY'S BRIDGE

• Also called "Opposite Angle Bridge"

• It is a modification of Maxwell's Bridge and have the same function: to measure unknown inductance & resistance.

• Hays Bridge Circuit differs from Maxwell's bridge by having a resistance R₁ in series with a standard capacitor C₁ instead of a parallel.

• Hay's bridge is more convenient for measuring inductance and resistance of coils with high-Q value. (Q> 10)

• Otherwise the Maxwell Bridge is used for measuring low Q coils (Q < 10).

Advantages of Hay’s Bridge

-The bridge gives very simple expression for the calculation of unknown inductors of high value.

-Bridge gives a simple equation for quality factor.

-The bridge requires a low value of r4.

Disadvantages of Hay’s Bridge

-Not suitable for measurement of quality factor (Q<10)

HAY'S BRIDGE THEORY

Let,

L1 – unknown inductance having a resistance R1.

R2, R3 and R4 – known non-inductive resistance.

C4 – standard capacitor

At balance condition,

Separating the real and imaginary term, we obtain

Solving the above equation, we have

The quality factor of the coil is