Design sketches and Engineering drawings

Design sketches

Engineers and designers frequently use quick hand-drawn sketches to illustrate design concepts as well as features associated with a particular product or process. In fact, being able to use sketches to illustrate your ideas is an essential part of becoming an engineer! Sketches are also an excellent way of communicating your ideas to other engineers and designers without having to resort to words or formal engineering drawings. When producing a design sketch there are no `hard-and-fast' rules other than ensuring that the sketch is clear and unambiguous (i.e. not liable to be misinterpreted) and that it is adequately labelled.

Activity 2.20

Produce a design sketch for an entry-level digital camera. The camera is to incorporate an in-built flash unit and an LCD screen. The battery is to be powered by two AA batteries and is to have a USB connection for downloading images to a computer. Make sure that all of these features are identified in your sketch. Present your work in the form of hand-drawn sketches and hand-written notes.

Engineering drawings

Like the graphs that we have just considered, there are many different ways of representing and communicating technical information. To avoid confusion, such information should make use of nationally and internationally recognized symbols, conventions and abbreviations. These are listed and their use explained in the appropriate British Standards. Such standards are lengthy and costly, but a summary is available for educational use. This document is entitled `Engineering drawing practice for schools and colleges' and it has the British Standards reference number PP 8888. The document is abridged from the earlier British Standard BS 308.

Block diagrams

These show the relationship between the various elements of a system. Figure 2.24 shows the block diagram for a simple radio receiver. This sort of diagram is used in the initial stages of conceptualizing a design or to provide an overview of the way in which an engineering system operates.

Activity 2.21

Construct a block diagram showing the arrangement of the braking system of a car. Label your drawing clearly.

Present your results in the form of a printout from a simple drawing or technical illustration package.

Flow diagrams

Flow diagrams are used to illustrate a sequence of events. They are used in a wide variety of applications including the planning of engineering processes and the design of computer software. Figure 2.25 shows a flowchart for the process of drilling a hole. The shape of the symbols used in this flowchart have particular meanings as shown in Figure 2.26. For the complete set of symbols and their meanings you should refer to the appropriate British Standard BS 4058.

Activity 2.22

Your bicycle tyre is flat and may have a puncture or may simply need reinflating. Draw a flowchart for checking the tyre and, if necessary, replacing the wheel. Figure 2.27 will provide you with a starting point. Present your results in the form of a printout from a simple drawing or technical illustration package.

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.

On-line services, directories and other reference sources

On-line services, directories and other reference sources

On-line services are services that add values to the World Wide Web. Originally, these services built and maintained trunk networks that could be used by their customers. They also added their own content (such as extensive databases, news and weather reports, software libraries, etc.) to the Web. Users who are prepared to pay for the service can access this material. Customers still pay for some on the on-line services but the trend, in recent years, has been to make added value services free.

Web directories such, as Yahoo, offer an editorially selected, topically organised list of Web sites. To accomplish that goal, these sites employ editors to find new Web sites and work with programmers to categorize them and build their links into the site's searchable index. To make things even easier, all the major search engine sites now have built-in topical search indexes, and most Web directories had added keyword search facilities.

Web-based business directories provide access to companies within a wide range of sectors. Using a business directory makes it easily possible to locate companies in a particular sector and in a specific location (e.g. a chemical supplier in the West Midlands).

In addition, on-line reference sources, such as Wikipedia, provide an excellent source of information which can be freely accessed and even edited and updated by users. A typical reference source Web page is shown in Figure 2.12. A word of caution is necessary here: when searching for information on the Web it is advisable to consult several sources and then compare your results before placing reliance on the information that you find. The reason for this is that almost all can place information on the Web, but not all of them are accurate and some of them can be deliberately misleading!

Intranets

Intranets work like the Web (with browsers, Web servers and Web sites) but companies and other organizations use them internally. Companies use them because they let employees share corporate data, but they are cheaper and easier to manage than most private networks because nobody needs any software more complicated or more expensive than a web browser, for instance. They also have the added benefit of giving employees access to the web. Intranets are closed off from the rest of the Net by firewall software, which lets employees surf the Web but keeps all the data on internal Web servers hidden from those outside the company.

Test your knowledge 2.11

List TWO advantages and TWO disadvantages of a catalogue supplied on CD-ROM compared with one that is published on the World Wide Web.

Extranets

One of the most recent developments has been that of the extranet. Extranets are several intranets linked together so that businesses can share information with their customers and suppliers. Consider, for example, the production of a European aircraft by four major aerospace companies located in different European countries. They might connect their individual company intranets (or parts of their intranets) to each other, using private leased lines or even using the public Internet. The companies may also decide to set up a set of private newsgroups so that employees from different companies can exchange ideas and share information.

Test your knowledge 2.12

Briefly explain what is meant by a URL. Give an example of a URL for a UK-based engineering company. What is the URL of the Web page shown in Figure 2.9?

E-mail

Like ordinary mail, e-mail consists of a message, an address and a carrier that has the task of conveying the message from one place to another. The big difference is that e-mail messages (together with any attached files) are broken down into small chunks of data (called packets) that travel independently to their destination along with innumerable other packets travelling to different destinations. The packets that correspond to a particular e-mail message may travel by several different routes and may arrive out of order and at different times. Once all the packets have arrived, they are recombined into their original form. This may all sound rather complicated but it is nevertheless efficient because it prevents large messages hogging all of the available bandwidth. To put this into context, a simple page of A4 text can be transferred half-way round the world in less than a minute! Figure 2.13 shows a typical e-mail message written using Microsoft Outlook Express.

what is Databases

Databases

A database is simply an organized collection of data. This data is usually organized into a number of records each of which contains a number

of fields. Because of their size and complexity and the need to be able to quickly and easily search for information, a database is usually stored within a computer and a special program - a database manager or database management system (DBMS) - provides an interface between users and the data itself. The DBMS keeps track of where the information is stored and provides an index so that users can quickly and easily locate the information they require.

Test your knowledge 2.5

A manufacturer wishes to distribute a set of data sheets on a conventional CD-ROM. Each data sheet consists of an Adobe Acrobat file having a size of 2.8 Mbytes. In addition, the manufacturer has included an index and other files amounting to a total of 80 Mbytes. Approximately how many data sheets can be included on a single CD-ROM?

The database manager will also allow users to search for related items. For example, a particular component may be used in a number of different products. The database will allow you to quickly identify each product that uses the component as well as the materials and processes that are used to produce it.

The structure of a simple database is shown in Figure 2.6. The database consists of a number of records arranged in the form of one or more tables. Each record is divided into a number of fields. The fields contain different information but they all relate to a particular component. The fields are organized as follows:

Field 1 Key (or index number)

Field 2 Part number

Field 3 Type of part

Field 4 Description or finish of the part

CD-ROM

CD-ROM

Compact disks can provide storage for around 650 Mbytes of computer data. This is roughly equivalent to 250,000 pages of A4 text. It is, therefore, hardly surprising that the compact disk has now become firmly established as a storage medium for a variety of different types of information, including text, drawings, sound and video (i.e. multimedia). The latest PCs offer CD-ROM drives that can be used to store data on recordable CDs (CD-R) or rewritable CDs (CD-RW). High-end PCs now also have DVD (Digital Versatile Disk).

Application notes and technical reports

Application notes and technical reports

Application notes are usually brief notes (often equivalent in extent to a chapter of a book) supplied by manufacturers in order to assist engineers and designers by providing typical examples of the use of engineering components and devices. An application note can be very useful in providing practical information that can help designers to avoid pitfalls that might occur when using a component or device for the first time.

Technical reports are somewhat similar to application notes but they focus more on the performance specification of engineering components and devices (and the tests that have been carried out on them) than the practical aspects of their use. Technical reports usually include detailed specifications, graphs, charts and tabulated data.

Typical section headings used in application notes and technical reports include:

Summary                    A brief overview for busy readers who need to quickly find out what the application note or technical report is about.

Introduction                 This sets the context and background and provides a brief description of the process or technology - why it is needed and what is does. It may also include a brief review of alternative methods and solutions.

Main body                   A comprehensive description of the process or technology.

Evaluation                   A detailed evaluation of the process or technology together with details of tests applied and measured performance specifications. In appropriate cases comparative performance specifications will be provided.

Recommendations      This section provides information on how the process or technology should be implemented or deployed. It may include recommendations for storage or handling together with information relating to health and safety.

Conclusions                This section consists of a few concluding remarks.

References                 This section provides readers with a list of sources of further information relating to the process or technology, including (where appropriate) relevant standards and legislation.

Technical reports, on the other hand, provide information that is more to do with whether a component or device meets a particular specification or how it compares with other solutions. Technical reports are thus more useful when it comes to analysing how a process or technology performs than how it is applied.

Activity  

Write an application note that explains the use of AA-size NiMh batteries as replacements for the conventional alkaline batteries used in a digital camera. You should carry out some initial research before starting to write your application note but the following are possible headings (these can be combined or expanded if you think it necessary):

• Executive summary
• Introduction
• Basic requirements for batteries used in digital cameras
• Comparison of three battery types (NiCcl, NiMH and conventional alkaline types)
• Battery life and charging arrangements
• Analysis of costs
• Suitability
• Recommendations
• Reference data (including a list of manufacturers and suppliers).

Use a word processor to present your work in printed form.

Data sheets and data books

Data sheets usually consist of abridged information on a particular engineering component or device. They usually provide maximum and minimum ratings, typical specifications, as well as information on dimensions, packaging and finish. Data sheets are usually supplied free on request from manufacturers and suppliers. Collections of data sheets for similar types of engineering components and devices are often supplied in book form. Often supplementary information is included relating to a complete family of products. An example of a data sheet is shown in Figure 2.3.

Test your knowledge 2.2

Refer to the extract from the Howard Associates data sheet shown in Figure 2.3 and use it to answer the following questions:

(a) What is the date of issue of the data sheet?

(b) Who owns the copyright of the data sheet?

(c) How many independent logic gates are contained in the device?

(d) What do the letters `NC' mean?

(e) How many pins are there on an 'FK' package?

(f) Which two devices are suitable for operation over the `military temperature range'?

(g) What is the absolute maximum supply voltage for these devices?

(h) What is the storage temperature range specified for these devices?

 (i) What does the manufacturer specify as typical values of supply voltage and operating free-air temperature for these devices?

Information and information sources

Information and information sources

The dictionary definition of `communication' usually mentions something like `the means by which we convey information'. There are, of course, many different ways of conveying information. You might consider, for example, the different ways that you could let your tutor know that you will not be attending college next week. You could speak to him in person, telephone him, leave a message on his answering machine, put a note on his desk, send him an e-mail message, or even write a letter and post it to him.

The method that you chose depends on a number of factors (not the least of which might be how friendly he is!). To be certain that he gets the message you might decide to speak to him in person (this might not be so easy if you do not have a good reason for not attending!). Alternatively, your college may require that you explain your absence in writing and they may have a form that you must complete. In deciding how to convey a simple message like this you probably need to think about several factors, including:

• How important is the information?
• How will I know that the information has been conveyed and understood?
• Do I need to keep a record of the information?
• How well do I know the person or persons with whom I am communicating?
• How urgent is the information?
• Is this a 'one-off' message or is it part of something much bigger?

Forms of communication

The forms of communication that we use in everyday life can be broken down into four main types, namely:

• Written
• Graphical
• Verbal
• Other (non-verbal).

Each of these main types of communication can be further subdivided. For example, graphical communication can take the form of drawings, sketches, block diagrams, exploded views, graphs, charts, etc.

Some of these can be further divided. For example, there are many different types of graph and chart.

In everyday life, we usually convey information by combining different forms of communication. For example, when we speak to other people we often combine verbal with non-verbal (body language) forms of communication. Body language can help add emphasis to our words or can be used to convey additional meaning.

Presentations to groups of people usually involve verbal communication supported by visual aids such as overhead projector transparencies, handouts or flipcharts. Technical reports invariably combine written text with diagrams and photographs.

Throughout this unit there are numerous opportunities to develop your own skills in obtaining, processing, evaluating and presenting information. In order to do this, you should be prepared to make use of appropriate technology (i.e. hardware and software). For this reason, we will not study hardware and software as a separate topic. Instead, we will assume that you will acquire familiarity with its use as you progress through the topics in this book.

Activity 2.1

From the types of communication shown in Figure 2.1, identify (with reasons) methods of communication that you consider most appropriate in each of the following situations:

(a) Making an appointment to see a doctor.

(b) Apologizing for forgetting your sister's birthday.

(c) Directing a friend to a restaurant in the next town.(d) Selling your car.

Present your work in the form of a brief set of hand-written notes.

Activity 2.2

Complete the table shown below by placing a tick against the applicability of different forms of communication in relation to fitting a plug to the electric cable on a portable appliance:

Information sources

Engineers use a wide variety of information in their everyday lives. This information is derived from a variety of different sources including:

• books
• application notes
• technical reports
• data sheets and data books
• catalogues
• engineering drawings
• CD-ROM
• databases
• websites.

Books

Books, whether they are paper-based publications or one of the new generation of electronic books (eBooks), provide information on an almost infinite number of subjects and a good technical library can be invaluable in any engineering context. All books contain summary information. This typically includes:

• the date of first publication
• the date(s) of any reprint(s) (with or without corrections)
• the date(s) of any subsequent edition(s)
• the date(s) of any reprint(s) of subsequent editions (with or without corrections)
• information concerning copyright
• British Library Cataloguing data
• an ISBN number
• other library (e.g. Library of Congress) cataloguing data
• information relating to the printing and binding of the book.

Test your knowledge 2. 1

Take a look at the information that appears in the first few pages of this book and then answer the following questions:

1. What was the year of first publication?

2. Is this book a reprint?

3. Who owns the copyright?

4. What is the book's ISBN number?

5. Who has published the book?

When using a book as a source of information it is important to ensure that it is up to date. It is also necessary to ensure that the content is reliable and that there are no omissions or errors. Book reviews (often published in the technical press) can be useful here!

Electronic books are presented in electronic rather than paper format. The book actually comprises of a number of files which can either be downloaded into a PC, laptop, or pocket reader device or which can be supplied on a CD-ROM. In order to convert the files that make up the book into something that can be read on the screen, the PC, laptop or pocket reader requires appropriate software such as Adobe's Acrobat Reader or Microsoft's Reader. 

Communications for Technicians

Communications for Technicians

Effective communication skills are essential for anyone working in engineering. This unit will help you develop skills in using and interpreting information in a wide variety of forms. It aims to provide you with experience of speaking, reading and writing as well as graphical means of communication including drawing and sketching. These skills are essential not only for employment in engineering, but also as a basis for further study. The unit also gives you a variety of techniques used for obtaining, evaluating, processing and presenting information.

This unit is often assessed by means of a portfolio of evidence that you build as you progress through the course. You must ensure that you include a variety of sufficient and appropriate evidence within your portfolio. Assessment may also involve assignments and case study work carried out in conjunction with other units (such as Project and Business Systems) as well as sketches and drawings, presentations, data sheets, technical reports and letters that you have produced. You should begin to work on your portfolio as soon as you start the unit and then continue to collect evidence systematically as you progress through the unit. You should also cross-refer the evidence in the portfolio to the individual learning outcomes and the list of evidence requirements. Your tutor will be able to help you with this.

This unit has strong links with the Project and Business Systems core units. Wherever possible, you should apply the techniques that you have developed in this unit to work undertaken in the Project and Business Systems units. There are also links to the optional unit on Engineering Drawing.

Being able to present your work and demonstrate proficiency in your own communications skills is an important aspect of this unit. To do this, you will need to have access to appropriate presentation and graphics software (such as Microsoft Power Point, Visio, Corel Draw, etc.) and spreadsheet software (such as Microsoft Excel) as well as hardware including scanners, laser and ink-jet printers, optical character recognition and speech recognition software, digital cameras and bar code readers. Your school or college will normally be able to supply you with everything that you need as well as guidance and help with its use.

Magnetic Reluctance

   Magnetic Reluctance

Magnetic reluctance or "magnetic resistance", is analogous to resistance in an electrical circuit (although it does not dissipate magnetic energy). In likeness to the way an electric field causes an electric current to follow the path of least resistance, a magnetic field causes magnetic flux to follow the path of least magnetic reluctance. It is a scalar, extensive quantity, akin to electrical resistance.

   Definition

The total reluctance is equal to the ratio of the "magnetomotive force” (MMF) in a passive magnetic circuit and the magnetic flux in this circuit. In an AC field, the reluctance is the ratio of the amplitude values for a sinusoidal MMF and magnetic flux. (see phasors)

The definition can be expressed as:

where

(“R”) is the reluctance in ampere-turns per weber (a unit that is equivalent to turns per henry). "Turns" refers to the winding number of an electrical conductor comprising an inductor.

("F") is the magnetomotive force (MMF) in ampere-turns

Φ ("Phi") is the magnetic flux in webers.

It is sometimes known as Hopkinson's law and is analogous to Ohm's Law with resistance replaced by reluctance, voltage by MMF and current by magnetic flux.

Magnetic flux always forms a closed loop, as described by Maxwell's equations, but the path of the loop depends on the reluctance of the surrounding materials. It is concentrated around the path of least reluctance. Air and vacuum have high reluctance, while easily magnetized materials such as soft iron have low reluctance. The concentration of flux in low-reluctance materials forms strong temporary poles and causes mechanical forces that tend to move the materials towards regions of higher flux so it is always an attractive force (pull).

The reluctance of a uniform magnetic circuit can be calculated as:

where

l is the length of the circuit in metres

μ₀ is the permeability of free space, equal to  henry per metre

μ_r is the relative magnetic permeability of the material (dimensionless)

A is the cross-sectional area of the circuit in square metres

The inverse of reluctance is called permeance.

Its SI derived unit is the henry (the same as the unit of inductance, although the two concepts are distinct).

3.6.2          Applications

§        Air gaps can be created in the cores of certain transformers to reduce the effects of saturation. This increases the reluctance of the magnetic circuit, and enables it to store more energy before core saturation. This effect is also used in the flyback transformer.

§        Variation of reluctance is the principle behind the reluctance motor (or the variable reluctance generator) and the Alexanderson alternator.

§        Multimedia loudspeakers are typically shielded magnetically, in order to reduce magnetic interference caused to televisions and other CRTs. The speaker magnet is covered with a material such as soft iron to minimize the stray magnetic field.

Reluctance can also be applied to:

§         Reluctance motors

§         Variable reluctance (magnetic) pickups