Uncertainty analysis of displacement measurement with Imetrum Video Gauge

Imetrum Video Gauge is a commercial image-based two-dimensional displacement measurement system which has been widely used. Its uncertainty analysis is presented in this paper. First, the procedure to use Video Gauge is introduced. Then, based on the measurement model, two major sources of uncertainty are identified: (1) the uncertainty associated with the calibration procedure u(C) which is composed of the uncertainty of the known length used in calibration u(L) and the uncertainty of the projection of the known length in the image u(D) and (2) the uncertainty associated with the measurement system itself u(P). Following the Guide to the Expression of Uncertainty in Measurement, the uncertainties can be quantified. In the end, 60 experiments are performed to analyze the relationship between the measurement uncertainty and the working parameters, which are working distance, acquisition frequency and focal length of the lens. In order to ensure the validity of the calculation, two calculation methods are used. The main results of this paper are as follows: (1) the displacement measurement uncertainty increases along with working distance and decreases with the increase of focal length. At the same time, the results indicate that using a longer known length in calibration can also reduce the measurement uncertainty. (2) u(C) is greatly influenced by the known length used in the calibration procedure. It can be reduced when u(L) is reduced. (3) Under the laboratory circumstances, reducing u(C) can greatly reduce the total measurement uncertainty. (4) The displacement measurement uncertainty is more sensitive to the measurement uncertainty of the known length used in calibration than the projection of the known length in the image. (5) As the working distance grows, the sensitivity to the known length is getting weaker and the sensitivity to the projection of the known length in the image is getting stronger. (6) When a longer focal length lens is used, the influence of the working distance to the sensitivity gets weaker. The reported results can help people better understand the characteristics of this system and better use the system for their own purposes.