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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of
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Measurement of the unknown inductance by using Hay’s bridge method.

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Aim:- Measurement of the unknown inductance by using Hay’s bridge method.
Apparatus:- Multimeter
LCR meter
Hay’s bridge kit,
Patch cords.
Circuit Diagram:-
Theory:-
The hays bridge is the modification of the Maxwell Bridge. This bridge uses a resistance
in series with the standard capacitor. The bridge has four resistive arms in which the arms
one is consists of the resister R1, Lx .The arm 2 is consists of the variable resistance
R3.The low value of the resistance is obtain by the low resistive arms of the bridge. The
value of R4 and C4 is the standard value of the capacitor and resistance.
By using the unknown inductance having a resistanceR1. R2, R3,R4-is the known
non-inductive resistance and C4 is standard value of the capacitor. The unknown value of
inductance and Quality factor of the Bridge is obtained by formula.
Lx = (R2R3C4) /(1+w2R4
2C4
2)_
Quality factor (Q)=(1/w2R4
2C4
2)
Basic AC bridges consist of four arms, source excitation and a balanced detector.
Commonly used detectors for AC bridges are:
(1) Head phones
(2) Vibration galvanometers
(3) Tunable amplifier detectors
Vibration galvanometer is extremely useful at power and low audio
frequency ranges. Vibration galvanometers are manufactured to work at various
frequency ranging from 5 KHZ to 1 KHZ. But one most commonly used between
200HZ.
Advantage-1) This Bridge gives very simple expression for unknown for High Q coil.
2) This bridge also gives a simple expression for Q factor.
Disadvantage-1)The hays bridge is suited for the measurement of the High Q inductor.
2)It is used to find the inductor having the q value of the smaller then 10.
.
Procedure:-
1) Study the circuit provided on the front panel of the kit.
2) Connect unknown inductance LX1 in the circuit. Make all connections to
complete the bridge.
3) Put the supply ON
4) Set the null point of galvanometer by adjusting variable resistance R3.
5) Note value of R2, R3, and C4 by removing connection by patch cords.
6) Calculate theoretical value of LX1 using L=R2R3C4
7) Measure value of LX2 by LCR meter and compare it.
8) Repeat process for LX2.
Result:- The unknown inductance is measured using Hay’s bridge and is found to
be___
Viva Questions:-
1)What is the Q factor of the coil?
2) Which bridges are used for measurement of inductances?

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