Abstract: A carousel receives a plurality of removable reagent containers, a turntable receives a plurality of sample fluid containers and a rotatable cuvette assembly holds an annular array of reaction and test cuvettes. A robotic arm carrying a fluid transfer needle coupled to a pair of syringes picks up one or more reagents and sample fluid for deposit into a cuvette. As the arm moves the needle tip exterior is washed and contaminants sent to a waste collector. At the end of a test cycle, the needle core is flushed and cleaned. A colorimetry photometric test is performed on the reacted fluids in each cuvette by a system employing ten interference filters, corresponding diode detectors and amplifiers employing two identical multiplexers providing identical filtered signals for logarithmic calculation of absorbance.

Abstract: A generally spherical bead on the floor of a compartment is prevented from lying in the path of insertion of an elongated member into the compartment when the compartment is located at a site. A drive mechanism first moves the compartment relatively slowly and a small distance away from the site so that the inertia of the bead causes it to move with the compartment away from the insertion path. The compartment is then moved relatively quickly back to the site so that the inertia of the bead prevents it from moving with the compartment, to thereby position and maintain the bead away from the insertion path. The compartment has a relatively planar floor integral with side walls. When the compartment is at the site, a first side wall is adjacent to the insertion path and a second opposed side wall is remote from the insertion path.