A Method to Calibrate Metal Length Measuring Rulers by Mechanical Comparison

Abstract

A Length measuring stick (length measuring ruler) is a very fundamental length measuring tool uses in many sectors such as construction industry, material processing industry, Apparel industry testing and calibration industry, and household. These measuring sticks are manufactured by different manufactures across the world and uses different references to mark the length on the sticks. Therefore, confirmation of maintaining the measurement traceability of length measuring sticks to the primary standard before their use is very essential. Even though sophisticated calibration systems are available globally for the calibration of length sticks, purchasing such a system became difficult due to high costs. As a solution, a low-cost mechanism for the calibration of industrial metal length measuring sticks is proposed here. The proposed method determines the length of the intervals of an unknown length stick (test ruler) in comparison with a pre-calibrated reference standard rule. The difference in length between test and reference ruler is measured by a mechanical movement of the reference standard ruler until coinciding the scale mark of the reference ruler with the corresponding scale mark of the test ruler. The linear movement of the reference ruler is measured by a dial gauge. The length of the test ruler is calculated by considering other factors such as the length of the standard stick and overall temperature correction as well. A calibration system was developed to determine length of the length intervals of test rulers in compliance to the proposed method. The combined uncertainty was calculated for the length determined by the proposed system using the proposed method and was ±0.33 mm at k =1 level corresponds to 68% confidence. The results from the proposed method were compared with the results from existing calibration methods and in compliance when the results are considered with above quoted uncertainty.