Thursday, 10 May 2018

AC bridge circuit

The bridge circuit :
                                  These are used for measuring component values, such as resistance inductance , capacitance etc. the bridge are compare the value of an unknown
components its measured accuracy is very high


Wheatstone Bridge :
                                      It is used for the measurement of d.c. resistance and a simple version the bridge has four resistor arms together with source of emf and null dector . The bridge is said to be balanced when the potential difference across the galvanometer is zero volts so there is no current through the galvanometer hence the bridge is balanced when R1 R4=R2R3

the Wheatstone widely used for precision measurement of resistance from approximately 1ohm to the low mega-ohm range


AC Bridge :
                     AC bridge are consist four arms a source of excitation and a null detector . The power source supplies an a.c. voltage to the bridge at the desired frequency . At higher frequencies. an oscillator generally supplies the excitation voltage . The null detector respond to an ac unbalance current and in its cheapest form consist of a repair headphone . other null dector maybe ac amplifier with an output meter or an electron ray tube indicator  the condition for bridge balances is 

ż1ż4=ż2ż3





Maxwell Bridge:
                          The Maxwell bridge is used to measures an unknown inductance in term of known capacitance . Once of the ratio arms has a resistance and capacitance in parallel. 

Maxwell bridge is limited to the measurement of medium Q-Coils (1<Q<10).  It is unsuit for the meaurement of coils with very low Q value (Q<1)


Hey Bridge circuit:
                                   It is different from Maxwell bridge is having R1 in series with standard capacitor C1 instead of being in parallel.
the value or Rs and Ls are given

Hey  Bridge is suited for the measurement  of high Q inductors having Q more then 10


Schering Bridge :
                                 It is used for measurement of capacitors particularly for measuring insulating properties .In other word for phase angle very nearly 90° . arm I has a parallel combination of a capacitor and combination of a resistor and a ca0acitor and standard arm contain only a capacitor



Wein Bridge :
                         The wein bridge has a series RC combination in one arm and a parallel RC combination in the adjoining arm. The frequecy of the applied voltage is
Wein bridge is used as a notch filter in harmonic distortion analyzer . 


It is used in audio and HF oscillator as frequency determining element
   

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