Abstract: A monobeam system for determining concentration changes of chromophore substance in a sample includes a flash lamp for passing a light beam through a sample containing the analyte. The values of absorbance by the sample at multiple wavelengths are measured and the optimum linear combination of absorbance values is determined to obtain a measure of chromophore concentration. Extinction coefficients for a chromophore is measured employing Deming's method and eigenvector transformations. A matrix reflecting the noise pattern of the system is determined. This matrix and the extinction coefficients are used in determining the coefficients for the optimum linear combination. An electronic module converts analog intensity data into digital data for five wavelengths. This is processed into absorbance values and concentration determinations.

Abstract: Apparatus for establishing a "home" position for a load element driven axially along the lead screw. A position sensor includes a first sensor element attached for axial travel with the load element and a second sensor element attached for rotation with the lead screw. The pair of sensor elements is operatively aligned at a predetermined relative axial and rotational position establishing the "home" position.

Abstract: A shutter assembly for a radioactivity measuring apparatus having a sample counting chamber, the assembly having a bulky solid lead cylinder with a sample access port extending therethrough for alignment with the sample chamber. The cylinder is rotated by a Geneva wheel arrangement having a drive wheel with a plurality of equi-angularly disposed pins perpendicular to the surface thereof engaging radially extending open-ended slots in a driven wheel secured to the lead cylinder for concurrent rotation therewith. The drive wheel is rotated at a constant speed with the driven wheel accelerating as a pin traverses the slot from the open end toward the driven wheel center and then decelerating as the pin traverses the reverse direction to provide precise positioning with adjacent pins engaging the open ends of adjacent slots in the stop position of the cylinder.