One analogue of a desktop, the TR-48 ticks away

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One of the Museum’s galleries is dedicated to the less well-known, analogue computers and includes an exhibit of a working TR-48 desk top analogue computer (c1961) available for our visitors to see.

Sheridan, a volunteer at TNMOC, was once a Scientific Officer using analogue and digital computers to model the flight of unguided rockets while working for the Ministry of Defence's Royal Armament and Research Development Establishment (RARDE).

Along with other volunteers in the museum, he is available at times to tell visitors more about this unusual computer.

A digital computer program involves breaking a problem down into a sequence of steps which are executed by the computer one at a time. The results of calculations and decisions are represented by stored numbers and states. But constructing an analogue computer program involves creating a mathematical model of a problem, and then ‘plugging up’ an electronic circuit, which simulates the system represented by the mathematical model. This is achieved by techniques such as summing, integrating, and applying other functions to create changing voltages within the computer.

The plugged up wires (shown right) are the equivalent to the digital computer program and are the means of changing the task that the analogue computer performs.

Our TR-48 is ‘plugged up’ to simulate a mass – spring – damper system, which could enable one to design a system to give a car a smooth ride or a racing suspension, depending on the requirements. The wiring and computer circuitry is an analogue of the mathematical model (a differential equation) of the real world system. The parameters of the equation can be varied by changing voltages inside the computer by turning the knobs on the right hand side of the control panel. In this way the output of the ‘program’ can be varied by changing variables such as the mass, the springiness of the spring or the time taken to dampen the oscillation.

The output from this analogue computer is not what you would expect.

On the top of the machine is an oscilloscope providing a means to examine the output as a trace on the screen. The scope shows the desired trace and the operator can read off the values of the knobs that have been set and that is the answer to the problem!

The fully transistorised PACE TR-48 was manufactured in the USA by Electronic Associates Incorporated (EAI) and sold as a ‘desktop’ computer from 1961 for around $25,000. It was used in applications for aerospace, bio-medical, chemical engineering and food technology. British Aerospace at Bedford produced the first aircraft automatic landing systems using the TR-48.

Find out more about analogue computers here.

The National Museum of Computing has one of the widest ranges of functioning computers in the world. Come see the TR-48 for yourself as well as many other machines demonstrating the development of computing through the last 60+ years.

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