Rapid precision interferometry for the analytical ultracentrifuge. III. Determination of period of rotation, frequency of rotation, and elapsed time.

The approaches presented in this series of papers make possible rapid gathering, reduction, and analysis of data from the Rayleigh interference optical system of an analytical ultracentrifuge. Instrumentation described in this paper provides some of the timing and measurement circuits necessary for a microprocessor or minicomputer to determine the rotor frequency, rotor period, and elapsed time of an experiment. It includes simple but effective circuits to generate precise rotor timing pulses that are useful for synchronization of pulsed light sources. Circuits to control photographic operations in the ultracentrifuge are described briefly. All of these circuits are interfaced to a simple microcomputer address/data bus. An adapter between this bus and a Q-bus (for a DEC LSI-11/2 or LSI 11/23 microcomputer) is also described. The circuits presented have been used in this laboratory over a 3-year period. They have proven reliable and form an integral part of the real-time data acquisition systems that have been constructed.