1) MAXWELL Bridges: A Maxwell bridge (in long form, a Maxwell-Wien bridge) is a type of Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and capacitance . It is a real product bridge. 2) The Wien bridge is a type of bridge circuit that was developed by Max Wien in 1891. [1] The bridge comprises four resistors and twocapacitors. Bridge circuits were a common way of measuring component values by comparing them to known values. Often an unknown component would be put in one arm of a bridge, and then the bridge would be nulled by adjusting the other arms or changing the frequency of the voltage source. See, for example, the Wheatstone bridge. The Wien bridge is one of many common bridges. [2] Wien's bridge is used for precison measurement of capacitance in terms of resistance and frequency . [3] It was also used to measure audio frequencies. The Wien bridge does not require equal values of R or C. At some frequency, the reactance of the series R 2 –C 2 arm will be an exact multiple of the shunt R x –C x arm. If the two R 3 and R 4 arms are adjusted to the same ratio, then the bridge is balanced. The bridge is balanced when: [4] and The equations simplify if one chooses R 2 = R x and C 2 = C x ; the result is R 4 = 2 R 3 .

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2) TheWien bridgeis a type ofbridge circuitthat was developed byMax Wienin 1891.[1]The bridge comprises fourresistorsand twocapacitors.Bridge circuits were a common way of measuring component values by comparing them to known values. Often an unknown component would be put in one arm of a bridge, and then the bridge would be nulled by adjusting the other arms or changing the frequency of the voltage source. See, for example, theWheatstone bridge.The Wien bridge is one of many common bridges.[2]Wien's bridge is used for precison measurement of capacitance in terms of resistance and frequency.[3]It was also used to measure audio frequencies.The Wien bridge does not require equal values ofRorC. At some frequency, the reactance of the seriesR2C2arm will be an exact multiple of the shuntRxCxarm. If the twoR3andR4arms are adjusted to the same ratio, then the bridge is balanced.The bridge is balanced when:[4]andThe equations simplify if one choosesR2=RxandC2=Cx; the result isR4= 2R3.In practice, the values ofRandCwill never be exactly equal, but the equations above show that for fixed values in the2andxarms, the bridge will balance at someand some ratio ofR4/R3.

3) HAY bridge: Maxwell bridge is only suitable for measuring medium quality factor coils however it is not suitable for measuring high quality factor (Q > 10). In order to to overcome from this limitation we need to do modification in Maxwell bridge so that it will become suitable for measuring Q factor over a wide range. This modified Maxwell bridge is known as Hay's bridge.Or we say that Hay's bridge circuit is most suitable for high inductor measurement.

Advantages of Hay's Bridge(1) The bridge gives very simple expression for the calculation of unknown inductor of high value. The Hay's bridge require low value of r4 while Maxwell bridge requires high value of r4. Now let us analyse why should put low value of r4 in this bridge:

Consider the expression of quality factor, As r4 presents in the denominator hence for high quality factor, r4 must be small. Disadvantages of Hay's BridgeHay's bridge is not suitable for measurement of quality factor (Q