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 nois e in such sensors has been observed to increase with light power: Fibe r bundle design was investigated to determine the effect of light flux on the precision of measurement. It was found that the signal noise f or a diffuse reflectance sensor in milk as measured by the standard de viation of the signal, increases with the flux of light emitted at the distal end of the fiber bundle. The precision of measurement, as meas ured by the signal output divided by the standard deviation of the sig nal, increased as light power increased but there was a large differen ce between fiber bundles. The data suggests that signal noise is reduc ed with larger total fiber area and decreased light flux. The precisio n of determination of t(max) was found to be 10 s. Thus, the predicted cutting time for uniform milk and constant processing conditions base d 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 I minute for a n objective method of predicting cutting time of coagulum.