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ELECTRICAL AND ELECTRONIC DRAFTING

BLOCK DIAGRAMS

A block diagram uses blocks and lines to show the related functions of parts of an electric circuit

or system. Such a diagram shows the normal order of progression of the signal through a circuit.

A system is an assembly of parts (components) connected together to perform a stated function.

The system may be comprises of:

A number of individual components connected together

A number of smaller units called subsystem.

o Each subsystem itself consists of individual parts

In general, a block represents:

(1) It may represent a stage of the system

(2) It may indicate a complete subsystem within a system.

(3) The complete system

A stage is considered to be that part of a circuit from the point where the signal is introduced

(input) into one functional unit such as a tube or transistor to the point where leaves (output) that

section and is introduced to the next. For example,

a block diagram may be used to show the operation of a large electronic system. In such a

case, a block would represent a complete and removable chassis, such as a preamplifier,

multivibrator, or modulator.

However, another block diagram may be used to facilitate the operational understanding

of a multistage amplifier, for example. In this case each block would represent a "stage."

Figure 7-1.depicts the block diagram of a transistor radio chassis. In a typical amplifier, a stage

would extend from the signal grid of one tube to the signal grid of the next tube in the circuit.

A signal may be introduced via any of the three element of a transistor.

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Figure 7-1 shows that the signal comes through the antenna (usually portrayed by a

symbol rather than a block)

It then progresses through the mixer circuit, the intermediate stages, and finally to the

output stage and speaker.

The oscillator, which is an auxiliary circuit, is appended to the main circuit; and since it

is a frequency generator, its output is fed into the signal train as shown by the arrow.

Another circuit, labeled AGC for automatic gain control, is correctly shown below the

main circuit.

o The purpose of automatic gain control is to prevent fluctuation in speaker volume

when the audio signal at the antenna is fading in and out.

Principles to be followed in preparation of block diagrams.

The following rules for their construction can be listed:

1. The signal path should be made to go from left to right, if possible.

In large drawings, the input should be at the upper left-hand comer, and output at the

lower right, if possible.

2. Blocks should be drawn in one of three shapes: square, rectangular, or triangular. (The triangle

is sometimes used to indicate an amplifier, especially in microwave drawings; also it is used to

indicate a repeater in telephone circuits.)

3. Once a rectangle (with fixed dimensions) is chosen, it is usually used throughout the diagram.

The size of the rectangle bears no relation to the importance of the component(s) it

represents.

4. A single line, preferably heavy, should be used to show the signal train from block to block.

(Occasionally two lines are drawn from block to block, but such a practice invites

confusion.)

5. Arrows should be used to show the direction of signal flow.

Figure 7.1 Block Diagram of a Typical Transistor Superheterodyne Radio

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6. Some components, usually terminal ones such as antennas and speakers, are shown by means

of standard symbols rather than by blocks.

7. Descriptions of the components or stages represented should be placed within the blocks.

Aside from the above-listed rules, no standardized procedure exists for the preparation of block

diagrams. For example, in Fig. 7-1 squares are used for blocks, and the signal flow is represented

by heavy lines on each of which is an arrow touching the "next" block. In Fig. 7-2, blocks are

represented by rectangles, with special depth effect, instead of by squares, and the directional

arrows are placed alongside the lines which depict the signal path.

The diagram of an industrial television circuit shown in Figure 7-3 is more complicated than the

first two diagrams. More layout planning is required. For instance:

Dotted lines have been added to enclose and separate the camera and monitor (receiver)

areas.

At various places in the drawing the signal path goes up, down, and from right to left,

because drawing the signal flow in the conventional left-right direction at all times would

have produced an unwieldy diagram.

Additional symbols have been added to show the interlace, and many of the blocks have

more than one line going into or leading away from them.

Such complications are the rule, rather than the exception, in diagrams for large circuits or

systems.

Figure 7-2. Block diagram of cosine equalizer test set.

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Diagram for subordinate circuit.

Sometimes a complicated circuit may be broken down logically into several subordinate circuits

and separate block diagrams made of each subcircuit. Figure 7-4 illustrates the concept. it

represents an engineer's way of solving the presentation of an unusual circuit. Note that:

the first and second video IF stages are in d-c series as are the first sound IF and third

video IF stages. This arrangement, made to conserve power, is very difficult to follow in

the schematic diagram, hence the preparation of this power distribution block diagram.

The components shown in symbol form are hum filters, isolation resistors, and voltage

dividers, all of which are used for current stabilization.

Block diagrams can be expected to appear in printed form, not just as a blueprint

Figure 7.3 Block Diagram of an Industrial Television Installation

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The following procedures should be considered in making any block diagram:

1. The drawing should be made large enough that it can be reduced to half, or even less, of its

drawing size and still convey the idea which the designer expects it to communicate.

2. The drawing should be in ink, preferably on a white background or on tracing cloth.

3. Special attention should be given both to the quality and to the size of the lettering.

Use of mechanical lettering devices for drawings that are to appear in printed

publications appears to be the rule.

Figure 7.4 Power Distribution Block Diagram

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Figure 7-2. Block diagram of cosine equalizer test set.

Figure 7.1 Block Diagram of a Typical Transistor Superheterodyne Radio

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Figure 7.3 Block Diagram of an Industrial Television Installation

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Figure 7.4 Power Distribution Block Diagram

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FLOW DIAGRAMS

Definitions

A drawing that uses symbols interconnected with lines to represent the flow of

information

A process flow diagram that illustrates the successive steps in a process, procedure,

system or model.

A pictorial representation showing/describing all of the steps of a process being studied

or even used to plan stages of a project. Flow charts tend to provide people with a

common language or reference point when dealing with a project or process.

Purpose of Flow Charts

A Flowchart is used for:

1. defining and analyzing processes (example: What is the registration process for entering

freshmen students?)

2. building a step-by-step picture of the process for analysis, discussion, or communication

purposes (example: Is it possible to shorten the length of time it takes for a student to

complete the program?)

3. defining, standardizing, or finding areas for improvement in a process

By visualizing the process, a flowchart can quickly help identify bottlenecks or inefficiencies

where the process can be streamlined or improved

Process Flowcharting (Process Flow Mapping):

Involves creating a flow model that illustrates and analyzes the overall flow of activities in

producing a product or service. Sometimes called: Process Diagram, Process Flow Chart,

Process Flow Map or Process Map, Process Flow Document or Process Flow Documentation,

Process Flow Model or Process Design Model, Process Flow Analysis Chart or Process Flow

Analysis Map Model, Process Document or Process Documentation.

Business Flowcharting (Business Mapping):

Illustrates the activities in a business in order to understand and use knowledge more efficiently;

identify what processes may be needed to make improvements (e.g. increase productivity or job

satisfaction among employees); or mapping to profitability and success. Sometimes called:

Business Flow Chart, Business Map, Business Map Model, Enterprise Map, Enterprise Model,

Solutions Map, Decision Map, Decision Model or Decision Making Process Map.

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Concept Flowcharting (Concept Mapping):

Involves creating a flow model that contains a concept, item or question for exploring

knowledge, new information, new ideas, or relationships; to illustrate an individual's concept of

knowledge in a specific area; or to communicates complex ideas. Aka Concept Diagram,

Concept Map, Concept Model, Concept Module, Concept Flow Chart,

Conceptual Map or Conceptual Model.

Information Knowledge Mapping (Mind Mapping):

Similar to a concept map, it involves creating a flow model that explores knowledge, new

information, new ideas, or relationships; an illustration of one's knowledge in a specific area; or a

model that communicates complex ideas. Aka Information Map or Information Flow Model,

Mind Map, Inspiration Diagram, Brainstorm Map, Circle Map, Bubble Map, Thinking Map or

Thought Map.

BASIC FLOWCHARTING SHAPES AND SYMBOLS

Flowcharts use special shapes to represent different types of actions or steps in a process and

Lines and arrows show the sequence of the steps, and the relationships among them.

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Start/End The terminator symbol marks the starting or ending point the system. It usually

contains the word "Start" or "End."

Action or Process A box can represent a single step ("add two cups of flour),

or and entire sub-process ("make bread") within a larger process.

Document A printed document or report.

Merge Indicates a step where two or more sub-lists or sub-

process become one.

Collate Indicates a step that orders information into a standard

format.

Manual Loop Indicates a sequence of commands that will

continue to repeat until stopped manually.

Subroutine Indicates a sequence of actions that perform a

specific task embedded within a larger process. This sequence of

actions could be described in more detail on a separate flowchart

Sort Indicates a step that organizes a list of items into a

sequence or sets based on some pre-determined criteria.

Decision A decision or branching point. Lines representing

different decisions emerge from different points of the diamond.

Input/ Output Represents material or information entering or

leaving the system, such as customer order (input) or a product

(output)

Connector Indicates that the flow continues where a matching

symbol containing the same letter) has been placed.

Flow Line Lines indicate the sequence of steps and the direction of flow.

Delay Indicates a delay in the process.

Basic Flowcharting Shapes

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Four particular types of flow charts have proven useful when dealing with a process analysis:

top-down flow chart

detailed flow chart

work flow diagrams

a deployment chart.

Each of the different types of flow charts tend to provide a different aspect to a process or a task.

Flow charts provide an excellent form of documentation for a process, and quite often are useful

when examining how various steps in a process work together.

When dealing with a process flow chart, two separate stages of the process should be considered:

the finished product

the making of the product.

In order to analyze the finished product or how to operate the process, flow charts tend to use

simple and easily recognizable symbols. The basic flow chart symbols below are used when

analyzing how to operate a process.

Loop Limit Indicates the point at which a loop should

stop.

Data storage Indicates a step where data gets

stored

Database Indicates a list of information with a

standard structure that allows for searching and

sorting.

Display Indicates a step that displays

information.

Off Page Indicates that the process continues off page.

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Steps for creating a flowchart are:

1. Familiarize the participants with the flowchart symbols

2. Brainstorm major process tasks. Ask questions such as "What really happens next in the

process? ", "Does a decision need to be made before the next step? ", or What approvals are

required before moving on to the next task?"

3. Draw the process flowchart using the symbols on a flip chart or overhead transparency. Every

process will have a start and an end (shown by elongated circles). All processes will have

tasks and most will have decision points (shown by a diamond).

4. Analyze the flowchart for such items as:

Time-per-event (reducing cycle time) 0 Process repeats (preventing rework)

Duplication of effort (identifying and eliminating duplicated tasks)

Unnecessary tasks (eliminating tasks that are in the process for no apparent reason)

Value-added versus non-value-added tasks

INSTRUCTIONS

Step-by-Step process of how to develop a flow chart.

Gather information of how the process flows: use a)conservation, b)experience, or

c)product development codes.

Trial process flow.

Allow other more familiar personnel to check for accuracy.

Make changes if necessary.

Compare final actual flow with best possible flow.

o Note: Process should follow the flow of Step 1, Step 2, ... , Step N.

o Step N= End of Process

CONSTRUCTION/INTERPRETATION tip for a flow chart.

Define the boundaries of the process clearly.

Use the simplest symbols possible.

Make sure every feedback loop has an escape.

There is usually only one output arrow out of a process box. Otherwise, it may require a

decision diamond.

Analyze flow chart of actual process.

Analyze flow chart of best process.

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Compare both charts, looking for areas where they are different. Most of the time, the

stages where differences occur is considered to be the problem area or process.

Take appropriate in-house steps to correct the differences between the two separate

flows.

Tips for Effective Flowcharts

1) Label each flowchart with a title identifying the process that it illustrates.

(For example: Entry Process").

2) Clearly indicate the starting and ending points of the process, using the standard

terminator symbols.

3) Keep the direction of flow consistent. Avoid confusion by keeping your flow lines

moving from top to bottom and left to right. Don't reverse the direction in the chart

unless the flow reverses itself in reality.

4) Break the steps down to a consistent level of detail. Don't include trivial sub-steps of

one task while treating another equivalent task as a whole. If one step or task needs to

be analyzed in detail, make a separate chart illustrating that sub-process.

You can hyperlink the shape representing a sub-process that, illustrates it,

allowing users to "drill down" for more detail.)

sequence of actions in

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5) Avoid crossing flow lines. In a well-designed chart, flow lines will not cross each

other. By rearranging a chart you can usually get rid of crossed lines. If two lines

must cross, use a "bridge" (also known as a "line hop") to show that the lines do not

intersect.

6) Make sure there are at least two no outcomes from every decision diamond.

7) Label your flowchart components. Use active verbs to label activity steps and

questions to label decisions. Clearly label the from a decision diamond in terms that

answer the question.