## Measurement of Self Inductance By Hay's Bridge:

The

**Hay's bridge**is a modification of Maxwell's bridge. The connection diagram and the phasor diagram for**Hay's Bridge**are shown in the below figure.**Hay's****bridge**uses resistance in series with the standard capacitor (unlike Maxwell's bridge which uses resistance in parallel with the capacitor).
Let L1 = unknown inductance having a resistance R1

R2, R3, R4 = known non-inductive resistance,

and C4 = standard capacitor.

**Must Read:**

The expressions for the unknown inductance and resistance contain the frequency term. Therefore it appears that the frequency of the source of supply to the bridge must be accurately known. This is not true for the inductance when a high Q coil is being measured as is explained below:

For a value of Q greater than 10, the term (1/Q)² will be smaller than 1/100 and can be neglected.

Therefore the above equation reduces to

L1 = R2 R3 C4

which is the same as for Maxwell's bridge.

### Advantages of Hay's Bridge:

**Hay's****bridge**gives a very simple expression for unknown inductance for high Q coils and is suitable for coils having Q > 10.- Hay's bridge also gives a simple expression for Q factor.
- If we examine the expression for Q factor

Q = 1/Ï‰C₄R₄

We find that the resistance R4 appears in the denominator and hence for high Q coils its value should be small. Thus

**Hay's****bridge**requires only a low-value resistor for R4, whereas Maxwell's bridge requires a parallel resistor, R4, of very high value.### Disadvantages of Hay's Bridge:

- The
**Hay's bridge**is suited for the measurement of high Q inductors, especially those inductors having a Q greater than 10. - For inductors having Q values smaller than 10, the term (1/Q)² in the expression for inductance L1 becomes rather important and thus cannot be neglected.
- Hence
**Hay's****bridge**is not suited for measurement of coils having Q less than 10 and for these applications Maxwell's bridge is more suited.

**Conclusion:**

In this, we have learnt

**Measurement of Self Inductance By Hay's Bridge**. You can download this article as pdf, ppt.

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