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© Copyright Brian Brown, 1992-2001. All rights reserved.

Plotters
These devices are similar to printers, but are generally vector based in the way that they draw lines and information on the paper. Vector based means from point to point, in comparison to the way that the majority of CRT displays are drawn, which is pixel based. Vector based tends to give must crisper lines and graphics.

There are two different sorts of plotter, one where the paper moves, the other where the paper is stationary. The majority of plotters use a serial connection to the computer.

The diagram on the left shows the Hewlett Packard HP7475A plotter, a 6 color pen plotter capable of printing up to paper sizes of A3. The pen moves across the paper, and the paper is moved backwards and forwards.

Most printers use a special language, the most popular being HP-GL, invented by Hewlett Packard. Early printers such as the HP7475A used pens, mounted in a carousel. The required pen was selected, and then across the paper to the desired spot. When positioned correctly, the pen was moved down to make contact with the paper surface.

At this point, either the pen or paper was moved to draw the information. At the end of the sequence, the pen was moved up to stop drawing, then positioned at the next co-ordinates.

Video of plotter operation

Paper Sizes
Pen plotters were offered in a range of different sizes, capable of printing on a wide variety of different paper sizes. For larger printing, continous drum plotters allow very large drawings to be done.

For drum rolls, paper was available in 24" and 36" width rolls.

Summary
Modern plotters made by HP are implemented using either DeskJet or LaserJet technology. The prime are of use for plotters has been in computer aided drafting, generating plans and drawings.

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© Copyright Brian Brown, 1992-2001. All rights reserved.