VOLUME
25, NO.
1, J A N U A R Y
distance can be recorded by two marks on a piece of paper (an analog of the original distance) or by a series of figures on a piece of paper. The precision of the first process is low, because the paper expands and contracts with humidity changes, or if it is crumpled; the precision of the second (digital) remains fixed even if the record is a sixplace number written in pencil on the back of an old envelope in an inventor's pocket. Like the number on the envelope, digital methods for recording and handling information lose no precision, although of course they cannot improve on the accuracy of the original information. As digital methods come into greater use in computation, converters are being developed to change experimental observations such as pressures, positions, and the like, into digital form. In most cases the measured quantities are first represented by analogous electrical quantities; these are then compared with a series of electrical standards until a match is found. The known value of the matching standard is next put in the form of a number, or digit, which can be punched in a tape or card or recorded magnetically. Converters of this kind can take data up to 100,000 times per second, that is, to give 100,000 consecutive figures in a second, representing the changes of some quantity, such as light intensity. They can do this with precisions better than one per cent; greater precision is possible with lower speeds. Another form of converter often needed is that which translates the position of a rotating shaft into a number representing the extent of its rotation from a zero position, as the position of the hour hand of a clock represents the degree of its departure from twelve. Applications are found in the control of positions of radar antennas, antiaircraft guns, airplane control surfaces, precision lathes, and the like. Far higher accuracy is possible with such digital systems than with voltageoperated devices. Several different conversion methods are available ; again,. however, high precision entails lower speeds of operation. Often, of course, high precision is not necessary, even though digital methods make it possible. It is not difficult to imagine situations where experimental data having an accuracy not better than five per cent are fed into an expensive and complicated digital data-handling system with a precision of 0.1 per cent or better, and then used to design a structure with an arbitrary safety factor of 200 per cent. Careful study of complete data-handling systems in the initial stages, however, can lead to material savings in scarce engineering manpower, as well as in construction costs, and can greatly speed the long and tedious engineering phases of both defense and industrial production.
1953
17 A
A Complete Line of Visual Polarimeters UTILITY POLARIMETER NO. 50 reading accuracy 0.1 degree an all purpose instrument for educational a n d use
where
the
above
accuracy
is
industrial
sufficient.
ROUTINE POLARIMETER NO. 60 reading 0.05 a rigidly
built
accuracy degree
instrument
f o r class-
room w o r k a n d routine measurements in the Control L a b o r a t o r y .
LABORATORY POLARIMETER NO. 62 reading accuracy 0.02
degree
similar t o No. 6 0 but with a scale o f l a r g e r diameter g r e a t e r measuring
to
o b t a i n the
accuracy.
PRECISION POLARIMETER NO. 70 reading accuracy 0.01 degree suitable
for
macro
and
micro work in research a n d general polarimetry.
HIGH PRECISION POLARIMETER NO. 80 reading accuracy 0.001
degree
recommended f o r macro a n d micro
work
where
greatest
accuracy is r e q u i r e d .
FOR FURTHER INFORMATION WRITE TO
O. C. R U D O L P H & SONS Manufacturers of OPTICAL RESEARCH AND CONTROL INSTRUMENTS P. O. BOX 446
Associate Editor
CALDWELL, N. J.
