Abstract: A device comprising a set of fine, uniform, translucent fibers mounted on a suitable holder. When used in conjunction with appropriate neutral density optical filters, if necessary, on suitable particle sizing instruments, the device can easily and quickly be used to perform three important functions--namely, to accurately check the instrument calibration or response to particle size, to locate the limits of the optical depth of field in the particle illuminating beam, and to test the ability of the instrument to detect and register all validly sampled, single particle events.

Abstract: A control unit for automatically controlling the angular position of a reversible, motorized device, such as an antenna rotor, in response to a signal from an external sensor, such as a potentiometer coupled to the rotating shaft of a windvane. The unit includes integrated circuits and other electronic components for monitoring the windvane signal and for activating the rotor, as necessary, to maintain its alignment with the sensed wind direction. The unit also comprises means for providing: a no-response zone of adjustable width about the momentary, average wind direction; an adjustable, time delayed response to changes in wind direction; an automatic reversal of rotation if the rotor approaches the .+-.180.degree. position while searching for the wind direction; an automatic disabling of the rotor for windspeeds less than a selectable, threshold value.