What is a strain gauge?

• A. It is a micrometer for measuring the differences in distance between the two webs of a crankshaft
• B. It measures oil pressure
• C. It measures fuel flow
• D. It measures air flow

Answer: (A)

A strain gauge is a sensor that detects how much a structure deforms under load by turning that deformation into an electrical signal. When a crankshaft web experiences stress, the distance between nearby points on the part changes by an incredibly tiny amount. A strain gauge bonded to the surface senses this stretch or compression and causes a change in its electrical resistance. That resistance change is then read out as a measure of strain. So describing it as measuring the difference in distance between two points on the part captures the essential idea: the gauge reports tiny changes in geometry caused by stress. It’s not used for oil pressure, fuel flow, or air flow, which are different physical quantities.