A spiral chronograph for long time intervals

THE F R A N K L I N INSTITUTE LABORATORIES FOR RESEARCH A N D DEVELOPMENT. The following are abstracts of papers printed in technical journals other than the JOURNAL OF THE FRANKLIN INSTITUTE, but written by members of the staff of The Franklin Institute Laboratories for Research and Development• A Spiral Chronograph for Long Time Intervals ( The Review o f Scientific Instruments, Vol. 19, No. 7 ) . - - A spiral chronograph has been developed for measuring the time between any pair of a series of transient events that occur within a period of 12 milliseconds. The maximum error in the measurement of such an elapsed time is :t: 6 microseconds• The chronograph differs basically from those of Emrich and Moran as follows: (1) it measures time periods up to 12 milliseconds; (2) a logarithmic spiral is developed; (3) the spiral is generated by a circuit which avoids a modulating network. The spiral trace is presented on the screen of a cathode-ray tube. The trace is modulated by a crystal-controlled oscillator to provide accurate time markers. Each transient event produces a momentary radial deflection of the spiral trace. Elapsed time between any two events is determined by counting the time markers between the corresponding signals. The accuracy of determining elapsed time between signals is primarily limited by errors involved in reading the photographic records since the absolute error in crystal frequency is less than 0.01 per cent. When using 10-microsecond time markers and a sweep speed of 2 miUiseconds per revolution, each signal may be located within 4-3 microseconds so that the maximum error in measuring elapsed time between signals is 4-6 microseconds. Using the same time markers, the peripheral distance between them will increase as the sweep speed is increased, thereby resulting in increased reading accuracy. This will be gained at the expense of the total time of duration of the spiral. H . D . WARSHAW. High Accuracy Contour Cams (Product Engineering, August, 1948).--A contour or tapewheel cam is a logarithmic spiral shape. Pairs of contour cams rotate without sliding; a condition of pure rolling• Recently they have been used in computing and control equipment. In these, they have been applied for certain computing problems requiring great accuracy. Unlike other cam and follower combinations, contour cams are reversible; hence when one function is mechanized, its inverse may be obtained. Although contour cams are difficult to make and cannot be used for nonmonotonic functions, their use is justified by their distinct advantages. The author develops, in the article, the basic formulas for the contour cams, also those for the points of inflection which may occur. In addition, the formulas are given for the center of the c u t t e r used for cutting such cams. An example is developed to illustrate the applications of the formulas. There is a n admitted difficulty in designing and cutting contour cams; T0ut their use for computations may be justified by the superior accuracy that is possible. Friction problems are not critical in contour cams since the cam shafts may rotate in ball bearings. I t appears that a combination of many pairs of contour cams in a more complicated computing problem would still yield satisfactory results, with little cumulative lost motion or other adverse effects. In the problem solved here, addition and subtraction are accomplished by the use of differentials; multiplication and division are performed by means of addition and subtraction, using a logarithmic scale on contour cams. Although this type of cam is suitable only for limited types of function, nonmonotonic functions being eliminated, it has the distinct a d v a n tages of being quite accurate, and of being reversible. R.O. YAVNE. I71