WHEAT STONE BRIDGE INSTRUMENTATION AND MEASUREMENTS FMPE-501 PRESENTED BY: SEHR FATIMA 16-ARID-4780

WHAT IS WHEATSTONE BRIGE ?  a simple circuit for measuring an unknown resistance by connecting it so as to form a quadrilateral with three known resistances and applying a voltage between a pair of opposite corners.

WHEATSTONE BRIDGE

CONSTRUCTION:  THREE KNOWN RESISTANCE  ONE UNKNOWN RESISTANCE  SENSITIVE GALVANOMETER  CONNECTING WIRES  BATTERY

WORKING  It is mainly used to convert a resistance change to a voltage change of a transducer.  To find unknown resistance it is compared with known resistances.  In WS bridge null or balanced condition is used to find the resistance.  For this bridge balanced condition voltage at points C and D must be equal. Hence, no current flows through the galvanometer.  For getting the balanced condition one of the resistors must be variable.

WORKING  VARY THE RESISTANCE UNTIL THE DEFLECTION IN GALVANOMETER BECOMES ZERO(BALANCED CONDITION) I-E- VOLTAGE DIFFERENCE BETWEEN POINTS B & D BECOMES ZERO  WHEM WS BRIDGE IS BALANCED THE CURRENT FLOWING THROUGH ;  ARMS AB & BC IS I 1  ARMS CD & DA IS I 2 WHEN WHEATSTONE BRIDGE IS BALANCED AB & BD ARMS HAVE SAME VOLTAGE DROP I-E V AB = V BD I 1 R 1 = I 2 R 3 (1)

WORKING  SIMILARLY V BC = V CD I 1 R 2 = I 2 R X (2)  DIVIDING 1&2 R 1 /R 2 = R 3 /R X

APPLICATIONS AND USES OF WS BRIDGE  The Wheatstone bridge is used for measuring the very low resistance values precisely.  Wheatstone bridge along with operational amplifier is used to measure the physical parameters like temperature, strain, light, etc.  We can also measure the quantities capacitance, inductance and impedance using the variations on the Wheatstone bridge.