Measurement precision for a fiber optic diffuse reflectance sensor

The fiber optic bundle design for a diffuse reflectance sensor used to determine cutting time in cheese manufacture was analyzed. Signal noise in such sensors has been observed to increase with light power. Fiber bundle design was investigated to determine the effect of light flux on the precision of measurement. It was found that the signal noise for a diffuse reflectance sensor in milk, as measured by the standard deviation of the signal, increases with the flux of light emitted at the distal end of the fiber bundle. The precision of measurement, as measured by the signal output divided by the standard deviation of the signal, increased as light power increased but there was a large difference between fiber bundles. The data suggests that signal noise is reduced with larger total fiber area and decreased light flux. The precision of determination of t(max) was found to be 10 s. Thus, the predicted cutting time for uniform milk and constant processing conditions based on this precision of determination of t(max) and a beta of 1.5 to 2.0 implies that the standard error of prediction of cutting time would be 30 to 40 s. This is within the precision criteria of 1 minute for an objective method of predicting cutting time of coagulum.