TLE 7 - LO3 prepare/ make changes on electrical/ electronic schematics and diagrams

Learning Outcome 3

Prepare/ make changes on electrical/ electronic schematics and diagrams

PERFORMANCE STANDARDS

Electrical/ electronic schematic diagrams are drawn and correctly identified.
Correct drawing are identified, equipment are selected and used in accordance with job requirements

What Do You Already Know?

Let us determine how much you already know about preparing electronic diagrams. Take this test.

What Do You Need To Know?

Read Information Sheet 3.1 very well then find out how much you can remember and how much you learned by doing Self-check 3.1.

Information Sheet 3.1

One of the features of a quality electronic diagram is its appearance with simplicity in design and easy-to-understand layout. To achieve this, you have to follow the following standards in laying out electronic diagrams.

Rules for Drawing Symbols

Recommended practices to be used in the application of symbols to a circuit diagram are listed below.

1. The position of a symbol on a diagram does not affect its meaning.

2. The weight of a line used in drawing a symbol does not affect its meaning. In some cases, a heavier line may be used to emphasize a particular symbol.

3. A given symbol may be drawn in any size that is suitable for use in any particular diagram. However, when a symbol is enlarged or reduced in size, it should be drawn in proportion to the rest of the drawing.

4. If necessary for contrast, some symbols may be drawn smaller or larger than other symbols on a diagram. However, for simplicity, it is recommended that not more than two different sizes of symbols be used on any one diagram.

5. In general, a connecting line should be brought to a symbol either vertically or horizontally, but a connecting line brought to a symbol at an angle has no particular significance unless otherwise noted.

6. The arrowhead of a symbol may be open ( ) or closed ( ) unless otherwise noted.

7. The standard symbol for terminal (o) may be added to any symbol. But when this is done, the terminal symbol should not be considered a part of the symbol itself.

Reference Designations

The symbols used to represent various components on a circuit diagram are most often accompanied by a combination of letters that identify the components but are not themselves a part of the symbol (Table 3-1).

Table 3-1. Reference Designations of Electronic Components

When more than one symbol of a specific type of component appears on a diagram, the letter (or letters) is followed by numbers that identify the components. These combinations of letters and numbers are referred to as reference designations (Fig. 3-1).

Fig. 3-1. Recommended methods of indicating reference designations and component values.

Numerical Values of Components

When details of the type, rating; or value of a particular component are to be given on a diagram, this information is placed adjacent to the symbol or is given by means of notes accompanying the diagram. For example, resistance and capacitance values are indicated as shown in Fig. 1-3. In this scheme, the symbol Ω for ohms and the abbreviations μF and pF for capacitance values are usually omitted and are instead replaced by notes such as the following:

1. All resistors expressed in ohms unless otherwise indicated.

2. All capacitors expressed in microfarads unless otherwise indicated.

A resistance value of 1,000 ohms or more is most often expressed in terms of Kilohm (K) or Meghm (M) units. Thus a resistance of 4,700 ohms is written as 4.7K, while a resistance of 270,000 ohms may be written as 270K or as 0.27M. The comma used when writing a 4-digit number such as 4,700 is not used when such a number is given on a diagram.

Capacitance values of 1 through 9,999 picofarads are usually expressed in picofarad units. Capacitance values greater than 10,000 picofarads should be expressed in microfarad units.

Suffix Letters

Suffix letters are used to identify separate parts of a unit upon a diagram when such components appear as a single, enclosed unit as shown in Fig. 3-2. C1A and C1B are the suffix letters used in the diagram.

Fig. 3-2. Two capacitors are enclosed in one unit.

Layout

The layout or form of a diagram should show the main features prominently. The parts of a diagram should be carefully spaced to provide an even balance between blank spaces and lines. Enough blank space should be left in the areas near symbols to avoid crowding any necessary notes or reference information (Fig. 3-3).

Fig. 3-3. Schematic diagram of an audio amplifier.

Line Thickness

As with other types of diagrams, a schedule of line weights or line conventions is used in drawing electrical and electronics diagrams. The standard line conventions used in the preparation of these diagrams are shown in Table 3-2.

Table 3-2. Line thickness

Connecting Lines

Lines connecting symbols and other parts on a diagram should, whenever possible, be drawn either horizontally or vertically. As a general rule, no more than three lines should be drawn to any point on a circuit diagram (Fig. 3-4A). This procedure reduces the possibility of line crowding that could make the interpretation of a diagram more difficult than necessary.

RECOMMENDED (A) AVOID IF POSSIBLE (B)

Fig. 3-4. Connecting lines. (A) recommended and undesirable methods of drawing lines to a point upon a diagram, (B) two “groups” of connecting lines drawn parallel to each other. When connecting lines are drawn parallel to each other, the space between them should be at least 1/16 inch when the diagram is reduced to a final size.

Interrupted Lines

Connecting lines whether single or in groups, may be interrupted when a diagram does not provide for a continuation of these lines to their final destination. When a single line is interrupted, the line identification can also indicate the destination (Fig. 3-5A). When groups of lines are interrupted, the destination of the lines is usually given in conjunction with brackets (Fig. 3-5B). In all cases, the lines should be located as close as possible to the point of interruption.

Fig. 3-5. Methods of identifying the destination of single and grouped connecting lines.

Dashed Lines

Dashed lines (------) are used on schematic and other types of diagrams to show a mechanical linkage between components or parts of components (Fig. 3-6).

Fig. 3-6. Dashed lines are used to indicate the mechanical linkage of a 2-pole, 3-position selector switch.

PARTS & TYPES OF AN ELECTRIC CIRCUIT Activity

How Do You Apply What You Have Learned?

Show that you learned something by doing this activity

Operation Sheet 3.1

I. Directions: Using your electronic template, redraw the schematic diagram of a six-input mixer shown below. Label all components using the values listed as parts list. Be sure to follow the rules in drawing symbols.

Parts list:

R1 – R6 = 22KΩ

R7 – R12 = 39K Ω

R13 = 100K Ω

R14 = 2.2KΩ

R15 = 6.8KΩ

R16 = 68Ω

R17 = 1KΩ

C1 – C6 = 10μF/16V

C7 – C8 = 47μF/16V

Q1 = 2SC945

II. Redraw the diagram of a 30-watt audio amplifier shown below applying the standard drafting practices. Label all components of the 30-watt audio amplifier using the values listed in the parts list.

III. DIRECTION: Shown in Fig. 3-7A is a schematic diagram of a 50-watt booster amplifier and in Fig. 3-7B is its pictorial diagram. Redraw the pictorial diagram and write in Table 3-3 the name of components/devices indicated by arrows and give their functions.

Fig. 3-7A. Schematic diagram of a 50-watt booster amplifier.

Fig. 3-7B. Pictorial diagram of a 50-watt booster amplifier.

Table 3-3. Name of components, devices and their functions.

IV. DIRECTION: Redraw the diagram of a discrete audio amplifier of a typical AM radio receiver shown below which is NOT properly drawn. Be sure to make your diagram more presentable by following the Standard Drafting Practices.