Download - Wien’s bridge
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Wien’s bridge and applications
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AC BRIDGES• Ac bridges are the bridges which are formed by
network of four impedances with a ac source supply to the bridge
• These impedances may be various reactance
1. Capacitive2. Inductive3. Resistive
• Under balanced condition (when the current across the detector is zero)
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Wien’s bridge
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• Under the balanced condition this bridge involves frequency as a function of capacitances and resistors let us see?
Operation of Wien’s bridge
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applications• The wien’s bridge is primarily known as a frequency determining bridge but it can be applicable
in audio oscillators as frequency determining devices
• Wein’s bridge operation range is (100Hz-100KHz)
• It is used in total harmonic distortion analyser(THD) as a notch filter
Which discriminates unwanted frequencies of a given response of a system
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Wien’s bridge oscillator• The Wien-bridge oscillator is a unique circuit
because it generates an oscillatory output signal without having a sinusoidal input source
• Instead, it uses capacitors with initial voltages to create the output.
• Here Wien bridge is a lead-lag network. The phase’-shift across the network lags with increasing frequency and leads with decreasing frequency. By adding Wien-bridge feedback network, the oscillator becomes sensitive to a signal of only one particular frequency. This particular frequency is that at which Wien bridge is balanced and for which the phase shift is 0°
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• This oscillator is similar to the previous one
• if we examine the gain of the oscillator is dependent on resistors R5 and R6
• The gain is
A=R3 + R4 / R4
Under practical conditions R3 = 2 R4 in wien bridge
The gain must be A=R3 /R4 +1 so the gain must A=3 is ideal condition to work as an oscillator
operation of oscillator
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Time
0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(R5:2)
-4.0V
0V
4.0V
Time
0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(R5:2)
-4.0V
0V
4.0V
Time
0s 100us 200us 300us 400us 500us 600usV(R5:2)
-20V
0V
20V
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ADVANTAGES OF WIEN’S BRIDGE DISADVANTAGES OF WIEN’S BRIDGE
• As the bridge is frequency sensitive it is difficult to balance the bridge for non sinusoidal waves
• Bridge is not balanced for any harmonics present in applied ac voltages
• This bridge is not cost effective since a perfect variable capacitor is expensive
• This bridge is suitable for measuring of frequencies
• It has accuracy ranging from 0.1 to 0.5 per cent
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