Uncertainties Associated with Strain-Measuring Systems Using Resistance Strain Gauges

Resistance strain gauges have been used for the measurement of strain for more than 50 years; however, research to quantify the inherent uncertainty in a strain-measuring system has been scarce hitherto. Nevertheless, resistive strain gauges are the most widely used tool to measure strain owing to their simplicity, apparent accuracy, low cost, and ease of use. In spite of this, at times they are used improperly, and the sources of error are neglected. Every type of measurement has an uncertainty associated with it. As it is impossible to eliminate error completely, the goal must be to quantify it and to reduce it to a value that is acceptable for the purposes of the measurement being taken. The novelty of the present research is to put forward a new methodology for determining the uncertainty in a strain gauge measuring system. To achieve this, the principal sources of error that influence the measuring system are formulated in order to develop an error model. Subsequently, the law of propagation of uncertainty is applied, together with a type A and B evaluation approach to determine the combined uncertainty of the entire measuring system, taking into consideration the correlation between variables, when applicable. The new methodology is then applied to a series of strain measurements taken on an aluminium flat bar subject to a bending load, and the results are discussed.