Page 887 - Basic Electrical Engineering

Solution:

Output resistance of the potentiometer under set condition

Resistance of the potentiometer per unit length

Change in resistance due to displacement

Displacement of the object

12.8 STRAIN GAUGE TRANSDUCER

We have known that the resistance of a metallic wire is dependent upon its

length and cross-sectional area. If a long resistance wire is stressed and
strained, i.e., its dimensions are changed, its resistance value will change. A
strain gauge converts strain into change in resistance of the wire under strain.

The basic principle of a strain gauge is that when a resistance wire is
stressed within its elastic limit, its dimensions change, and hence its

resistance change. This change in resistance can be used as a measure of the
stress and strain of the object on which the strain gauge is attached or
embedded. In civil engineering and mechanical engineering, field strain

gauges are used extensively to measure stress on structures.
A strain gauge transducer is made of thin wires of diameter varying from

0.02 to 0.04 mm cemented (permanently fixed) in a zig-zag pattern on a thin
flat paper. The zig-zag pattern of winding reduces the inductance and