# Analog computer fundamental

an analog computer is a computing device that has two distinguishing characteristics:

* 1. Performs operations in a truly parallel manner. Meaning it can perform many calculations all at the same time.

* 2. And operates using continuous variables. Meaning it uses numbers that that change not in steps, but change in a smooth continuous manner.

By constrast, a digital computer can only perform sequential (one at a time) operations, and operates on discrete (noncontinuous) numbers.

Electronic analog computers may seem to be “simple” or “like a toy computer”, in fact they are powerful tools that were used during the 1950s and 1960s to design and test systems like ICBMs, supersonic aircraft and spacecraft. But the analog computer can be used to model any physical system that can be described by mathematical formulas, even more mundane ones from modeling the effects of pollution on the fish population in a river to fine tuning the suspension on a new car design. Analog computers will not only test a fixed design but also allows variables to be quickly changed to test “what if” conditions. By scaling time as an independent variable, physical processes that happen quickly can be stretched out, and processes that happen over a long period can be shortened to make the process easier to study. And it is very easy to study variables at any point in the program while it is running to find faults in the program design.

Although the electronic analog machine is correctly termed a computer, it does not perform its computations by numerical calculations as does the calculator or the digital computer. The analog computer performs mathematical operations on CONTINUOUS variables instead of counting with digits. Positive numbers are represented by positive voltages and negative numbers are represented by negative voltages, all scaled to the computer’s working range, usually -100 volts to +100 volts (vacuum tube) or -10 volts to +10 volts (transistorized), Thus the analog computer does not subtract 20 inches from 45 inches to obtain 25 inches but, rather, it subtracts 4 volts from 9 volts to obtain 5 volts. This 5 volts the operator reads as 25 inches in accordance with his arbitrarily specified “scale factor” of 1 volt equals (or is ANALOGOUS to) 5 inches.

The electronic analog computer is basically a set of building blocks, each able to perform specific mathematical operations on direct current voltages and capable of being easily interconnected one to another. Some of the basic operations include addition, subtraction, multiplication, division, inversion, and integration. By interconnecting these building blocks, mathematical equations are modeled. BUT an analog computer is a true PARALLEL computer that can solve one or one thousand equations at the same time. In fact, similar analog computers can be easily connected together to increase their computing power. When you think about the result of many equations being solved simultaneously and becoming the input to other equations, and sometimes these solutions are then fed back or looped back into the original equations with all of the variables changing CONTINUOUSLY with time, then you can get a brief glance into the incredible power of these computers. Output is usually a voltmeter, oscilloscope, or plotter.

Many universities today like Massachusetts Institute of Technology, University of Illinois, University of Notre Dame, and Purdue University offer classes or do research using analog computers, because they realize that the last chapter of the history of analog computers has not being written. It’s an ANALOG universe and analog computers are a natural way to study and understand it.

There are two distinct families of computing device available to us today, the all pervasive digital computer and almost forgotten analog computer. These two types of computer operate on quite different principles.

The digital computer is a sequential device, in general, operating on data one step at a time, in addition the digital computer represents data internally using a quite verbose but very robust form of representation called binary. Thus a single transistor in a digital computer can only store two states, on and off. Obviously to store a number to any sensible degree of precision, many transistors are required.

An analog computer operates in a completely opposite way to the digital computer. For a start, all operations in an analog computer are performed in parallel. Secondly, data are represented in an analog computer as voltages, a very compact but not necessarily robust form of storage (prone to noise corruption). A single capacitor (equivalent to the digital’s computer use of a transistor) in an analog computer can represent one continuous variable.

A computer that represents data in terms of physical measures or quantities and proceeds along a continuum constituted by its components. Analog computers are especially suited for the solution of complex non-linear equations and for the simulation of multi-dimensional, parallel and continuous processes.

The modern analog computer is based on an electronic circuit known as an operational amplifier. Early operational amplifiers (“op amps” for short) used vacuum tubes, since that was the only available technology. Modern op amps are constructed as semiconductor integrated circuits. Either way, the general theory is the same.

We will discuss the internal workings of op amps in a separate page. For the overall discussion of analog computer circuits and op amp behavior in such applications, we will make three assumptions about op amps:

1. They have infinite voltage gain.

2. They have infinite input resistance (or zero input current).

3. They have zero output resistance (infinite output current capability).

Although these assumptions aren’t really correct, they’re close enough that the circuit works well, so long as the electronic components connected to the amplifier to control its operation have reasonable values. For a discussion on typical IC op amps and their real-world characteristics

An analog computer operates in a completely opposite way to the digital computer. For a start, all operations in an analog computer are performed in parallel. Secondly, data are represented in an analog computer as voltages, a very compact but not necessarily robust form of storage (prone to noise corruption). A single capacitor (equivalent to the digital’s computer use of a transistor) in an analog computer can represent one continuous variable.

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