# Wheatstone Bridge Analysis

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Wheatstone bridge is a device used to measure unknown resistance by passing current through the resistor . Wheatstone bridge is made up of a power source and galvanometer that joins the two-parallel circuits which contains two resistors each. It is very useful in finding small resistances and is used in various applications such as strain gages. The following figure shows the arrangement of a Wheatstone bridge.

Figure 1: Arrangement of a Wheatstone Bridge 
Importance of Wheatstone bridge when measuring strain: Wheatstone bridge is useful in measuring strain because it is useful in finding small resistances or small variations in resistance . Whenever, a strain is applied to a particular material it changes the resistance of elements
It has two active elements with each one mounted to each (top and bottom) side of the bending strain . It is sensitive only to the bending strain. The following equation is used to calculate strain using half bridge type 2.

3. Full bridge: This arrangement is further divided into three arrangements.
a) Full bridge type 1: This arrangement measures only bending strain and has four active strain-gauge elements in which two active elements are mounted on each side of the bending strain . It is highly sensitive to bending strain. The following equation is used to calculate strain using full bridge type 1.

b)

Full bridge type 2: This arrangement only measures bending strain and also has four active strain-gauge elements . However, one active element is mounted in the direction of bending strain on each side and remaining two are mounted perpendicular to the principal axis of strain on each side. The following equation is used to calculate strain using full bridge type 2.

a) Full bridge type 3: This arrangement measures only axial strain and has four active strain-gauge elements with same orientation as full bridge type 2 . The following equation is used to calculate strain using full bridge type 3.

2.0 Applications of the Wheatstone bridge to measure tensile and bending