Introduction to DC Bridge
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Figure 1 : Example of Bridge Circuit
Bridge circuits are used for measuring component values such as resistance (for dc circuit), inductance and capacitance (for ac circuit).
The configuration of D.C bridge circuit consists of four resistor forming a diamond closed shape circuit, connected to a D.C supply and a galvanometer or null detector.
Bridge circuits will compare the unknown value of component with an accurately known value of component.
Working Principle of Bridge Circuit
Figure 2 : Bridge Circuit with Galvanometer
Current is generated from the dc source or dc supply and then flow through the cable all the way to terminal A.
The current is then split to 2 ways which are I1 and I2, and become I3 and I4 respectively after passing through the terminal D and B.
By using the Kirchhoff current law or Kirchhoff voltage law, the balanced condition in the circuit can be achieved when I1 = I3 and I2 = I4 or V1 = V2 and V3 = V4
Hence, a ratio of R1/R3 = R2/R4 can be obtained and this balancing equation can be used to determine the unknown value of resistor. (Note : the unknown resistor can be any one of the four)
The bridge circuit is said to be unbalanced if the balancing equation is unbalance.
Advantages of Bridge Circuit
The higher the supply voltage, the easier it is to detect the condition of unbalance between the four resistors with the null detector and also more sensitive it will be.
A higher supply of the voltage benefits to the possibility of increased measurement precision.
No fundamental error introduced. Lesser or higher power supply voltage unlike other types of resistance measurement schemes.
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