# Wheatstone Bridge

Wheatstone Bridge

Electronic measuring instruments like electronic scales detect and measure resistance change of sensor material. In order to increase the sensitivity of measuring instruments, it is necessary to precisely measure changes in minute resistance values.
In this case, the main circuit used is the "Wheatstone Bridge" circuit, which consists of four resistors.
When used as a sensor, replace one of the four resistors with the sensor material and measure the potential difference between the resistors. The Wheatstone Bridge circuit can measure the resistance value with high accuracy because the output voltage "V G" changes drastically with subtle changes in resistance value.

$V_{ G }={ V }_{ 0 }(\frac { { R }_{ 3 } }{ { R }_{ 1 }+{ R }_{ 3 } } -\frac { { R }_{ 4 } }{ { R }_{ 2 }+{ R }_{ 4 } } )$

Equilibrium condition of Wheatstone Bridge

When the voltage "VG" applied to both ends of the galvanometer "G" becomes "0", it is be in equilibrium. Equilibrium condition is as follows.

R1 × R4 ＝ R2 × R3

If you do not know the resistance value of any one of the four resistors, you can easily calculate it by using the above equation.