Ac bridges
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This document discusses several types of AC bridges used to measure unknown resistances, capacitances, and inductances. The Maxwell's inductance bridge uses two known impedances on one side and two pure resistances on the other to measure an unknown impedance. The Maxwell's capacitance bridge can measure unknown inductance by compensating the positive phase angle of inductance with the negative phase angle of capacitance. The Anderson bridge precisely measures unknown inductance over a wide range by using a known capacitance and resistance.
Ac bridges
- 1. A.C.Bridges By :- Ranjal Agrawal (0105EC131087) EC 3rd Sem.
- 2. ? A.C.Bridges are those circuits which are used to measured the unknown resistances, capacitance and inductance.
- 3. Maxwell¨s inductance Bridge ? In the Maxwell¨s inductance bridge ,there are two pure resistances used for balance relations but on other side or arms the two known impedances are used. ? The known impedances and the resistances make the unknown impedances as Z1 and Z2.Such a network is known as Maxwell¨s A.C.. Bridge. As shown in fig.
- 4. Fig. (R1 + jwL1 )R3 = (R4 + jwL4 )R2
- 5. Maxwell¨s Capacitance Bridge ? In the Maxwell¨s capacitance Bridge the positive phase angle of the inductance may be compensated by the negative phase angle of the capacitance impedance put in the opposite arm. ? The unknown inductance then becomes known in terms of the capacitance. As shown in fig.
- 6. Fig. R2 R4 + jwL1 R2 = R1 R3 + jwCR1 R2 R3
- 7. Anderson Bridge ? In the Anderson Bridge the unknown inductance is measured in terms of a known capacitance and resistance. ? This method is capable of precise measurements of inductance over a wide range of values from a few micro-henrys to several henrys and is the best bridge method.
- 9. Hay¨s Bridge ? It is also a modification of the Maxwell¨s Wien Bridge and is particularly useful if the phase angle of the inductive impedance is large. ? In this case a comparatively smaller series resistance R1 is used instead of a parallel r└sistance.( which has to be of a very large value) as shown in fig.
- 10. Fig L3= C1 R2 R4 R3= w C1 R1 R2 R4 1+w R1 C1 1+w R1 C1
- 11. Schering Bridge ? Schering bridge used for the measurement of capacitance and dielectric loss of a capacitor. ? It is a device for comparing an imperfect capacitor C2 in terms of a loss-free standard capacitor C1. As shown in fig.
- 12. Fig. C3 = C2 ( R1 / R2 ) R3 = R2 ( C1 / C2 )
- 13. Wien Series Bridge ? It is a simple ratio bridge and is used for audio-frequency measurement of capacitance over a wide range. As shown in fig.
- 15. Wien Parallel Bridge ? It is also a ratio bridge used mainly as the feedback network in the wide range audio- frequency R-C oscillators. ? It is may be used for the measurement of the audio-frequency but it is not as accurate as the modern digital frequency meters. As shown in fig.
- 16. Fig. C2 = R2 = R3 C1 R1 R4
- 17. THANK YOU