ANALOG COMPUTERS: CHARACTERISTICS, COMPONENTS, TYPES - TECHNOLOGY - 2024

The analog computers are a type of computer that uses continuously changing aspects of physical phenomena, such as electrical quantities, mechanical or hydraulic, to model the problem being solved.

That is, they are computers that operate with numbers represented by directly measurable continuous values, such as pressure, temperature, voltage, speed, and weight. In contrast, digital computers represent these values ​​symbolically.

Source: X-15_Analog_computer By How it's made - https://www.youtube.com/watch?v=PW1NAcZLDgs, Public Domain, Analog computers can have a very wide range of complexity. The simplest are slide rules and nomograms, while the computers that control naval guns and large hybrid digital / analog computers are among the most complicated. At the time, they were the first computer machines developed.

Process control systems and protection relays use analog computing to perform control and protection functions.

In the 1960s, the main manufacturer was the American company Electronic Associates, with its 231R analog computer, with vacuum tubes and 20 integrators. Later, with his 8800 analog computer, with solid-state op-amps and 64 integrators.

Replacement by digital computers

In the 60s 70s digital computers, based first on vacuum tubes, and later on transistors, integrated circuits and microprocessors, became more economical and precise.

This led to digital computers largely replacing analog computers. However, analog computers continued to be used in scientific and industrial applications, because at that time they were commonly much faster.

For example, they continued to be used in some specific applications, such as the flight computer in airplanes.

More complex applications, such as synthetic aperture radar, remained under the dominance of analog computing well into the 1980s, as digital computers were insufficient for the task.

Research is still ongoing on analog computing. Some universities still use analog computers to teach the theory of control systems.

characteristics

Analog data processing

An analog computer is used to process analog data, such as voltage, temperature, pressure, speed, etc. It continuously stores this data of physical quantities and performs calculations with the help of these measurements.

It is quite different from the digital computer, which uses symbolic numbers to represent the results.

Analog computers are great for situations that require data to be measured directly, without converting it to numbers or codes.

Using analog signals

The analog computer uses the analog signal, which can be represented as a continuous or sine wave, which contains values ​​that vary over time.

An analog signal can vary in amplitude or frequency. The amplitude value is the intensity of the signal related to its highest point, called the crest, and its lowest points. On the other hand, the value of the frequency is its physical length from left to right.

Examples of analog signals are sound or human speech through electrified copper wire.

Analog computers do not require any storage capacity because in a single operation they measure and compare quantities.

Limited precision

Analog representations have limited precision, commonly to a few decimal places.

The accuracy of an analog computer is limited by its computing elements, as well as the quality of internal power and electrical interconnections.

It is mainly limited by the precision of the reading equipment used, which is generally three or four decimal places.

Programming

Programming in an analog computer involves transforming the equations of the problem into the analog computer circuit.

What are analog computers for?

They are used to represent data by measurable quantities, such as voltages or gear rotation, in order to solve a problem, instead of expressing the data as numbers.

Monitoring and control

In monitoring and control systems they are used to determine a control formula and to calculate process parameters, such as efficiency, power, performance and others.

If you can assign a mathematical expression that defines the association of a parameter with the coordinates of an object, the analog computer can solve the corresponding equation.

For example, analog computers are widely used to evaluate the economic efficiency of power systems, and can serve as automatic regulators.

They are often used to control processes such as those in oil refineries, where continuous flow and temperature measurements are important.

Advanced analysis

By repeatedly solving the system of equations that describes a controlled process, an analog computer can scan a large number of alternate solutions in a short time. To do this, it uses different values ​​in the parameters subject to change during the process.

The required quality can be guaranteed by means of control signals announced by the analog computer.

The values ​​determined by the computer are transmitted to a regulating device, which adjusts the control points.

Determination of disturbing or useful signals

The magnitude of a disturbing or useful signal is determined using differential equations that describe the dynamic system, the values ​​of the initial conditions, in addition to the changes determined in the statistics that measure noise and signal.

An analog computer can also be used to build instruments that automatically record disturbances and produce a control signal, which will depend on the character and quantity of the disturbances.

Dynamic systems simulation

The simulations can be carried out in real time or at very high speeds, thus allowing to experiment with repeated runs with the altered variables.

They have been used extensively in aircraft simulations, nuclear power plants, and also in industrial chemical processes.

Components

Operational amplifier

Most electrical analog computers work by manipulating voltages or potential differences. Its basic component is the operational amplifier, which is a device whose output current is proportional to its input potential difference.

By causing this output current to flow through the appropriate components, more potential differences are obtained and a wide variety of mathematical operations can be performed, including addition, subtraction, inversion, and integration.

An electrical analog computer consists of many types of amplifiers. These can be connected to generate a mathematical expression of great complexity and with a multitude of variables.

Hydraulic components

Key hydraulic components could include pipes, valves, and containers.

Mechanical components

There can be rotary shafts to transport data within the computer, differential gears, disk, ball or roller integrators, 2-D and 3-D cams, mechanical resolvers and multipliers, and servo-torques.

Electrical and electronic components

- Precision resistors and capacitors.

- Operational amplifiers.

- Multipliers.

- Potentiometers.

- Fixed function generators.

According to the nature of mathematical operations

Linear

Linear components perform the operations of addition, integration, sign changes, multiplication by a constant, and others.

Non linear

Function generators reproduce non-linear relationships. There are computer components designed to reproduce an assigned function, from one, two, or more arguments.

It is common in this class to distinguish between devices that reproduce single-argument discontinuous functions and multiplier divisor devices.

Logical

Among the logic components are analog logic devices, designed to separate the larger or smaller quantity between various quantities, discrete logic devices, relay switching circuits, and some other special units.

All logical devices are generally combined into one, called a parallel logical device. It is equipped with its own patch panel to connect individual logic devices to each other and to the other analog components of the computer.

Types

Mechanical computers

They are built from mechanical components, such as levers and gears, rather than electronic components.

The most common examples are adding machines and mechanical counters, which use the turning of gears to perform additions or counts. More complex examples could carry out multiplication and division, and even differential analysis.

The most practical mechanical computers use rotating axes to transport variables from one mechanism to another.

In the Fourier synthesizer, which was a machine for predicting tides, cables and pulleys were used that added the harmonic components.

It is important to mention the mechanical flight instruments in the early spacecraft, which showed the calculated result not in the form of digits, but through displacements of the indicator surfaces.

Manned Soviet spacecraft were equipped with an instrument called the Globus. This showed the figurative movement of the Earth through the displacement of a miniature terrestrial globe, in addition to indicators of latitude and longitude.

Electric Computers

They are more common because they have a substantially wider passband and are convenient for connecting to other computers and to device control elements.

They use electrical signals that flow through various resistors and capacitors to simulate physical phenomena, rather than mechanical interaction of components.

The design of the analog elements of the computer is based on direct current electronic amplifiers. These have high gain in open circuit mode.

Depending on the structure of the input circuit and the feedback circuit, an op amp performs either a linear or a non-linear mathematical operation. Also a combination of these operations.

This type of analog computer was widely used in computer science and military technology in the mid-20th century, such as in aircraft and missile tests.

Differences with digital

Signal transmission

Digital signals have two discrete states, off or on. The off state is zero volts and the on state is five volts. This is why digital computers use binary number data, in the form of 0 and 1.

Analog signals are continuous. They can be anywhere between two extremes, such as -15 and +15 volts. The voltage of an analog signal can be constant or vary over time.

That is, in analog computers, data is transmitted in the form of continuous signals. In digital computers they are transmitted in the form of discrete signals.

Circuit types

Analog computer circuits use operational amplifiers, signal generators, resistor networks, and capacitors. These circuits process continuous voltage signals.

Digital computers use a variety of on / off circuitry, such as microprocessors, clock generators, and logic gates.

That is, the digital computer uses electronic circuits, while the analog computer uses resistors for the continuous flow of the signal.

Precision

Analog computers must deal with a certain level of electrical noise in circuits, affecting their accuracy. The circuits of a digital computer also have electrical noise, although this has no effect on accuracy or reliability.

On the other hand, the analog computer cannot produce repeating results with an exact match. This means that analog computers are less accurate compared to digital computers.

Programming

Both analog and digital computers can be programmed, although the methods are different.

Digital computers use complex sequences of instructions, such as comparing or multiplying two numbers, or moving data from one place to another.

To program an analog computer, different subsystems are electrically connected with cables to each other. For example, a signal generator is connected to a control knob, to vary the intensity of the signal.

Examples

Castle clock

This famous computer was capable of storing programming instructions. Standing over three meters high, the device displayed the time, the zodiac and also the orbits of the sun and the moon.

The computational part of the device thus allowed users to set the variable length of the day depending on the season. Described in 1206, this computer was very complex for its time.

Slide rule

One of the simplest and most recognizable mechanical analog computers is the slide rule. This is a device to approximate basic mathematical calculations.

Users slide a marked rod to align it with various marks on another rod, thus reading the device based on the alignment of those various marks.

Differential analyzer

This mechanical analog computer was capable of solving differential equations. With a design as old as the early 1800s, the differential analyzer was perfected in the 1930s and used until the mid-20th century.

It is considered the first modern computer. It weighed 100 tons and contained 150 motors, plus hundreds of miles of cables connecting relays and vacuum tubes.

By today's standards, the machine was slow. In fact, it was only about a hundred times faster than a human operator using a desktop calculator.

Other examples

- Predictor Kerrison.

- Librascope, balance and weight computer of an aircraft.

- Mechanical integrators such as the planimeter.

- Nomogram.

- Norden bombardment visor.

- Computers related to fire control.

- Water integrators.

- MONIAC, economic modeling.

The Simulation Council was an association of analog computer users in the United States.

The Simulation Council newsletters from 1952 to 1963 are currently available online. They show the technologies at that time and also the common use of analog computers.

References

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4. Encyclopaedia Britannica (2019). Analog computer. Taken from: britannica.com.
5. John Papiewski (2019). 10 Differences between Analog & Digital Computers. Taken from: techwalla.com.
6. The Free Dictionary (2019). Analogue Computer. Taken from: encyclopedia2.thefreedictionary.com.
7. Encyclopedia (2002). Computer, Analog. Taken from: encyclopedia.com.