BACKGROUND & THEORY The circuit diagram of a Wheatstone bridge is shown in the f

Question

BACKGROUND & THEORY The circuit diagram of a Wheatstone bridge is shown in the figure below. The resistor Rk is known and the two resistors RI and R2 have a known ratio R2/RI, although their individual values may not be known. The unknown resistor is RX. A DMM measures the voltage difference VAB between nodes A and B. Either the known resistor Rk or the ratio R2 RI is adjusted until the voltage difference VAB is zero and no current flows through G. When VAB 30, the bridge is said to be "balanced".

Explanation / Answer

wheat stone bridge used as a transducer for the purpose of measuring changes in temperature, pressure . this is calculated by calculating the value of unknown resistor.

1.The Wheatstone bridge is based on a simpler circuit element called the voltage divider.

There are two basic concepts needed to understand how these circuit elements operate .

1. Ohm’s Law (I=V/R)

2. Kirchoff’s Circuit Laws

2.DERIVATION:

   SINCE VAB =0 THE VOLTAGE DROP FROM C TO A IS MUST EQUAL TO THE VOLTAGE DROP BETWEEN C TO B.

SO VCA =VCB

  SIMILARLY WE HAVE VDA =VDB.

BY THIS WE CAN WRITE

IAR1 = IBRK --------------------(1)

  IAR2   = IBRX ------------------(2)

BY DIVIDING 2 BY 1 WE HAVE

( R2/R1 ) = ( RX /RK )

RX = ( R2 /R1) * RK

3. VOUT = (VA -VB)

VA = (R2 / (R1+R2)) * V0

VB=(R4 / (R3+R4)) * V0

I= V0 / (R1+RK)

THROUGH VOLTAGE DIVIDE RULE WE CAN FIND OUT THE AMOUNT OF VOLTAGE AT EACH POINT.

BY MULTIPLING THE I AND V VALUES WE CAN FIND OUT WHAT IS THE POWER OBSORVED BY EACH RESISTOR.

BY SUMMING ALL POWER DISSIPATION VALUES WE CAN GET TOTAL POWER DISSIPATION VALUE.

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