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Log in with Facebook Log in with Google. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. AC Bridges. Eshwar Munna. Related Papers. Digital electronics. Dasar-dasar Elektronika. Circuit Analysis Theory and Practice. EEC Instrumentation 1-Theory. Section 1 Electrical Principles. High Voltage engineering CL Wadhwa 1.
Bridges Resistances can be measured by direct-current Wheatstone bridge, shown in Fig. As shown in Fig. Bridges that for balance relations, the phase balance depends on the remaining two arms. Hence, we conclude that an inductive impedance may be measured in terms of another inductive impedance of equal time constant in either adjacent arm Maxwell bridge or the unknown inductive impedance may be measured in terms of a combination of resistance and capacitance of equal time constant in Fig.
It is important, however, that in each case the time constants of the two impedances must be matched. The bridge is balanced by varying L4 and one of the resistances R2 or R3. Alternatively, R2 and R3 can be kept constant and the resistance of one of the other two arms can be varied by connecting an additional resistance in that arm Ex.
Resistive and reactive terms balance independently and the conditions are independent of frequency. This bridge is often used for measuring the iron losses of the transformers at audio frequency. The balance condition is shown vectorially in Fig. The currents I4 and I3 are in phase with I1 and I2. This is, obviously, brought about by adjusting the impedances of different branches, so that these currents lag behind the applied voltage V by the same amount.
Example The arms of an a. Find the resistance and inductance of the coil. Nagpur Univ. The a. The unknown inductance then becomes known in terms of this capacitance. Let us first find the combined impedance of arm 1. Bridges Example If balance is obtained under these conditions, find the value of the resistance and the inductance of the branch CD.
The bridge is shown in Fig. The conditions of balance have already been derived in Art. Anderson Bridge Fig. In this method, the unknown inductance is measured in terms of a known capacitance and resistance, as shown in Fig. As seen from Fig. The alternating current source is connected to A and C and the telephone receiver to E and D. A balance is obtained when resistances of arms CD and BE are 50 and 2, ohm respectively.
Calculate the resistance and inductance of arm DA. Draw the vector diagram showing voltage at every point of the network. Measurements, Pune Univ. The circuit diagram and voltage vector diagram are shown in Fig. As seen, I2 is vector sum of IC and I3. IC is at right angles to V2. Draw the vector diagram for the voltages and currents in the branches of the bridge at balance.
B Summer Solution. The network is shown in Fig. It is seen that, in this case, a comparatively smaller series resistance R1 is used instead of a parallel resistance which has to be of a very large value. If the supply frequency is 50 Hz, determine the inductance and the resistance at the balance condition.
Sec B, Solution. The bridge circuit is shown in Fig. The Owen Bridge The arrangement of this bridge is shown in Fig. In this method, also, the inductance is determined in terms of resistance and capacitance. This method has, however, the advantage of being useful over a very wide range of inductances with capacitors of reasonable dimensions.
AC Bridge Circuits. Related Papers. Digital electronics. Op-amp for e one. Electrical Circuit. Circuit Analysis Theory and Practice. EEC Instrumentation 1-Theory. So Why A Bridge Circuit? DC meter movements can be used if the AC is rectified. Like DC null detectors, its only required point of calibration accuracy is at zero. Or, they can be "nonsymmetrical," using parallel impedances to balance series impedances, or even capacitances balancing out inductances. The frequency-sensitive types may be used as frequency measurement devices if all component values are accurately known.
Unbalanced Wheatstone Bridge The value of the parameter being measured can be determined by the amount that the bridge is unbalanced. Tiny changes in transducer resistance will unbalance the bridge, thereby providing a measurement reading. For example, in the circuit below, the unknown capacitance Cx has an internal resistance Rx. To balance out the Rx, the known variable capacitance Cs is connected in parallel to a known variable resistance Rs.
Vout is then equal to 0V and the bridge is balanced. P is a standard 1 kohm resistor and Cs is a standard 0. Calculate the range of measurement of Cx and rx. These types of bridges are very sensitive to bridge changes and susceptible to external noise. A single-ended AC bridge has the output voltage referenced to ground. These types of bridges are not as sensitive to bridge changes compared to differential-ended AC bridges but are less susceptible to external noise.
Principles of analog signal conditioning, pp. Resonance Classroom. Allabout AC. AC Bridges. Electrical circuit theory and technology second edition revised edition john bird by censored. Electical circuit analysis sadiku. Op Amps For Everyone. Chp A. Introduction to instrumentation and measurements 2 edition by robert b northrop. If balance is obtained under these conditions, find the value of the resistance and the inductance of the branch CD.
The bridge is shown in Fig. The conditions of balance have already been derived in Art. Anderson Bridge Fig. In this method, the unknown inductance is measured in terms of a known capacitance and resistance, as shown in Fig.
As seen from Fig. The alternating current source is connected to A and C and the telephone receiver to E and D. A balance is obtained when resistances of arms CD and BE are 50 and 2, ohm respectively. Calculate the resistance and inductance of arm DA. Draw the vector diagram showing voltage at every point of the network. Measurements, Pune Univ. The circuit diagram and voltage vector diagram are shown in Fig.
As seen, I2 is vector sum of IC and I3. IC is at right angles to V2. Draw the vector diagram for the voltages and currents in the branches of the bridge at balance.
B Summer Solution. The network is shown in Fig. It is seen that, in this case, a comparatively smaller series resistance R1 is used instead of a parallel resistance which has to be of a very large value.
If the supply frequency is 50 Hz, determine the inductance and the resistance at the balance condition. Sec B, Solution. The bridge circuit is shown in Fig. The Owen Bridge The arrangement of this bridge is shown in Fig. In this method, also, the inductance is determined in terms of resistance and capacitance. This method has, however, the advantage of being useful over a very wide range of inductances with capacitors of reasonable dimensions.
Heavisible-Campbell Equal Ratio Bridge It is a mutual inductance bridge and is used for measuring self-inductance over a wide range in terms of mutual inductometer readings. The primary of the mutual inductometer is inserted in the supply circuit and the secondary having self-inductance L2 and resistance R2 is put in arm 2 of the bridge.
The unknown inductive impedance having self-inductance of L1 and resistance R1 is placed in arm 1. The other two arms have pure Fig. Bridges Balance is obtained by varying mutual inductance M and resistances R3 and R4.
For balance, I1 R3 I 2 R A balancing coil or a test coil of self-inductance equal to the self-inductance L2 of the secondary of the inductometer and of resistance slightly greater than R2 is connected in series with the unknown inductive impedance R1 and L1 in arm 1.
A non-inductive resistance box along with a constant-inductance rheostat are also introduced in arm 2 as shown. Balance is obtained by varying M and r. Two readings are taken; one when Z1 is in circuit and second when Z1 is removed or short-circuited across its terminals. With unknown impedance Z1 still in circuit, suppose for balance the values of mutual inductance and r are M1 and r1.
With Z1 short- circuited, let these values be M2 and r2. Then Fig. The inductance of a coil is measured by using the Heaviside-Campbell equal ratio bridge. With the test coil short-circuited, balance is obtained when adjustable non-reactive resistance is When the test coil is in circuit, balance is obtained when the adjustable resistance is What is the resistance and inductance of the coil?
With reference to Art. Capacitance Bridges We will consider only De Sauty bridge method of comparing two capacitances and Schering bridge used for the measurement of capacitance and dielectric loss.
De Sauty Bridge With reference to Fig. For balance, points B and D are at the same potential. The simplicity of this method is offset by the impossibility of obtaining a perfect balance if both the Fig. A perfect balance can only be obtained if air capacitors are used.
Schering Bridge It is one of the very important and useful methods of measuring the capacitance and dielectric loss of a capacitor. In fact, it is a device for comparing an imperfect capacitor C2 in terms of a loss- free standard capacitor C1 [Fig. The imperfect capacitor is represented by its equivalent loss-free capacitor C2 in series with a resistance r [Fig. The junction between arms 3 and 4 is earthed.
Since capacitor impedances at lower frequencies are much higher than resistances, most of the voltage will appear across capacitors. Grounding of the junction affords safety to the operator form the high-voltage hazards while making balancing adjustment in arms 3 and 4.
The quality of a capacitor is usually expressed in terms of its phase defect angle or dielectric loss angle which is defined as the angle by which current departs from exact quadrature from the applied voltage i. For low power factors, therefore, dissipation factor is approximately equal to the power factor.
In a test on a bakelite sample at 20 kV, 50 Hz by a Schering bridge, having a standard capacitor of pF , balance was obtained with a capacitance of 0. Determine the capacitance, the p. Derive any formula used. Indicate the precautions to be observed for avoiding errors. Paper I, Indian Engg. Services Solution. C2 C1. A losy capacitor is tested with a Schering bridge circuit. The supply frequency is 50 Hz. Calculate from the equation at balance the equivalent series capacitance and power factor at 50 Hz of the capacitor under test.
Wien Series Bridge It is a simple ratio bridge and is used for audio-frequency measurement of capacitors over a wide range. 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 may be used for measuring audio-frequencies although it is not as accurate as the modern digital frequency meters. In the simple theory of this bridge, capacitors C1 and C2 are assumed to be loss-free and resistances R1 and R2 are separate resistors. In that case, the bridge has equal ratio arms so that Eq. Then, as seen from Eq. Determine i the value of R and ii the supply frequency at which the bridge will be balanced.
Bridges Solution. In Anderson a. For balance following data is obtained. The supply is 10 volt A. Find L and R. Derive the equations of balance and hence deduce the resistance and inductance of the inductor. Theory and Meas. London Univ. Calculate the resistance and the inductance of the arm DA. What would be the effect of harmonics in the waveform of the alternating current source?
Determine the values of unknown resistance R and inductance L. Madras Univ. Find the values Fig.
WebExample 1 Figure below show the schematic diagram of a Wheatstone bridge with values of the bridge elements. The battery voltage is 5 V and its internal resistance negligible. The . WebMaxwell�s bridge is an AC bridge having four arms, which are connected in the form of a rhombus or square shape. Two arms of this bridge consist of a single resistor, one arm . WebLecture 6,7&8: AC Bridges Do not publish it. Copy righted material. Dr. D. K. Pandey 2 A.C. Bridges: AC bridges are similar to Wheatstone bridge in which D.C. source is replaced .