Principles of Strain Gages

Principles of Strain Gages

If external tensile force or compressive force increases or decreases, the resistance proportionally increases or decreases. Suppose that original resistance R changes by ΔR because of strain ε: the following equation is set up.

Where, Ks is a gage factor, expressing the sensitivity coefficient of strain gages. General-purpose strain gages use copper-nickel or nickel-chrome alloy for the resistive elements, and the gage factor provided by these alloys is approximately 2.

Types of Strain Gages

Types of strain gages are classified into foil strain gages, wire strain gages, and semiconductor strain gages, etc.

Structure of a Strain Gage

The foil strain gage has metal foil on the electric insulator of the thin resin, and gage leads attached, as shown in Fig. 1 below.

Base length,Example of KFGS gage,Grid length,strain sensing part,Gage length,Laminate,Base width,Base,Center mark
,Base,Metal foil,Laminate film,Bonded surface,Solder,Gage lead,Gage length

The strain gage is bonded to the measuring object with a dedicated adhesive. Strain occurring on the measuring site is transferred to the strain sensing element via adhesive and the resin base. For accurate measurement, the strain gage and adhesive should be compatible with the measuring material and operating conditions such as temperature, etc.