8 - The Digital Differential Analyzer

Abstract

This chapter discusses the digital differential analyzer. Differential analyzers are analog machines. They are based on the observation that, in general, a physical system can be represented by a group of elements interconnected so that disturbances of one or more elements are coupled to other elements. This is the basis for the derivation of differential equations in the first place. The differential equation specifies the variables of interest in a system and the manner in which they are interrelated. It follows that if one has a set of idealized elements, analogous in behavior to the elements of a system to be investigated, one can use the differential equation of the system to indicate how these elements must be interconnected; two systems are considered analogous if their elements have similar physical and/or abstract attributes and the elements are similarly interrelated in each. Electronic analog differential analyzers use the integrating characteristic of a capacitor in conjunction with operational amplifiers to produce linearity. The accuracy of the electronic analog devices is also limited and involves long-term drift problems that are overcome only with highly engineered critical circuits.