Presenting engineering information

Presenting engineering information

Engineers rely heavily upon graphical methods of communication. Drawings and charts produced to international standards and using international symbols and conventions suffer no language barriers. They are not liable to be misinterpreted by translation errors. Graphical communication does not replace spoken and written communication but instead is used to simplify, reinforce and complement other means of communication.

Having now established the need for communicating engineering information, let us look at the various methods of graphical communication available. We can broadly divide engineering information into two categories. That which is mathematically based and that which is technically based. We will start by looking at ways of representing mathematical data.

Graphs

Just as engineering drawings are used as a clear and convenient way of describing complex components and assemblies, so can graphs be used to give a clear and convenient picture of the mathematical relationships between engineering and scientific quantities. Figure 2.14a shows a graph of the relationship between distance s and time t for the mathematical expression s = ¹/₂at², where the acceleration a = 10ms^-1.

In this instance it is correct to use a continuous flowing curve to connect the points plotted. Not only do these points lie on the curve, but every corresponding value of s and t between the points plotted also lie on the curve.

However, this is not true for every type of line graph. Figure 2.14b shows a graph relating speed and distance for a journey. From A to B the vehicle is accelerating. From B to C the vehicle is travelling at a constant speed. From C to D the vehicle is decelerating (slowing down). In this example, it is correct to join the points by straight lines. This is because each stage of the journey is represented by a linear mathematical expression which is unrelated both to the previous and following stages of the journey.

Histograms

Histograms are used for plotting information where the change is discrete rather than continuous. To put this into context consider the number of National Diplomas awarded by a college over a 6-year period. The award of a National Diploma happens at the end of each academic year when a particular number of students achieve the qualification. This varies from year to year but, since it does not change on a continuous basis, it is inappropriate to illustrate the relationship using a line. Instead, we use a series of bars representing the number of National Diplomas awarded. Despite the fact that there is no line joining the bars together we can still clearly see a trend.

Test your knowledge 2.14

Use Figure 2.15 to answer the following questions:

1.   In which academic year were the least number of National Diplomas awarded?

2.   Assuming that the class size remained the same over all six years, in which year were the students most successful?

3.   How many National Diplomas were awarded in 1998/99?

4.   Expressed as a percentage, by how much did student achievement improve over the 2-year period, 1996/97 to 1997/98?

5.   What is the total number of National Diplomas awarded over the 6-year period?

6.   What is the average number of National Diplomas awarded each year for the 6-year period?

Activity 2, 14

The total number of machines manufactured by two competing engineering companies are shown in the table below:

Draw histograms to compare the performance of these two companies. What might you infer from these results?

Present your work in the form of hand-drawn histograms with a brief hand­written comment.

Bar charts

Like histograms, bar charts are also used for displaying statistical data, but are usually plotted horizontally. They are also often made to look more attractive by using 3-D drawing.

Test your knowledge '.15

Figure 2.16 shows how the speed of a PC has increased with successive generations of processor. Use this bar chart to answer the following questions (answers need only be approximate):

1.   How fast is a Pentium 3 when compared with the original 8086 processor?

2.   What is the relative speed of a Pentium 4 processor when compared with a Pentium 1 processor?

3.   What is the relative speed of a Pentium 1 processor when compared with an 80486 processor?

4.   What is the percentage increase of speed between a Pentium 1 and Pentium 2 processor?

Ideographs (pictograms)

Ideographs (or pictograms) are frequently used to simplify statistical data so that it can be made meaningful to the general public. A typical example is the number of cars produced by a car manufacturer, over a 4-year period, as shown in Figure 2.17. In this example, each symbol represents 1000 cars. Therefore in 1998, 4000 cars were produced (four symbols each representing 1000 cars makes a total of 4000 cars).

Some ideographs use the size of a symbol (rather than a number of symbols of identical size) to represent quantities. An example of this is shown in Figure 2.18.