Linearity and Sensitivity Error in the Use of Single Strain Gages with Voltage-fed and Current-fed Circuits

Summary The purpose of this article is to draw attention to the fact that the linearity and sensitivity of straingage measurements cannot be assessed solely from the relation betweenchange in resistance and change in electrical signal; the transmissibility between strain and change in resistance must also be taken into account. However, one important proviso to the relationships developed in the article is that they are only precisely valid for ideal strain gages applied ideally. In reality the transmissibility of ‘strainlchange in resistance’ is adversely affected by many factors such as less-than-ideal backing materials and adhesives and multiple-axial stress fields in the grid of the strain gages. Such factors are usually unsystematic and, therefore, cannot be dealt with in a universally applicable form. Moreover, their effect cannot be calculated either for the voltage-fed circuit or the current-fed circuit. This is the reason for comparing the linearity and sensitivity error of the two types of circuits on the basis of systematic, calculable relationships. The general conclusion can be drawn that, for the use of strain gages in quarter-bridge connection, the voltage fed bridge circuit is superior to the current-fed circuit in many ways, primarily because of better linearity by several powers of ten and similarly better sensitivity stability under conditions of initial detuning.