Principle of Strain Gages

Each metal has its specific resistance. An externaltensile force (compressive force) increases(decreases) the resistance by elongating (contracting)it. Suppose the original resistance is R and a straininitiatedchange in resistance is Δ R. Then, thefollowing relation is concluded:

where, Ks is a gage factor, the coefficient expressingstrain gage sensitivity. General purpose strain gagesuse copper-nickel or nickel-chrome alloy for theresistive element, and the gage factor provided bythese alloys are approximately 2.

Types of Strain Gages

Types of strain gages include foil strain gage, wirestrain gage, and semiconductor strain gage.

Structure of Foil Strain Gage

The foil strain gage has metal foil photo-etched in agrid pattern on the electric insulator of the thin resinand gage leads attached, as shown in Fig. 2 below.

The strain gage is bonded casino spiele to the measuring objectwith a dedicated adhesive. Strain occurring onthe measuring site is transferred to the strainsensing element via the gage base. For accuratemeasurement, the strain gage and adhesive shouldmatch the measuring material and operating conditionsincluding temperature.