computer-engineering-drafting-and-design-modules.pdf

Lesson II: Block Diagrams and Flowcharts A Block Diagram – is a diagram of a system in which the principal parts or functions are represented by blocks connected by lines that show the relationships of the blocks. They are h...

Lesson II: Block Diagrams and Flowcharts A Block Diagram – is a diagram of a system in which the principal parts or functions are represented by blocks connected by lines that show the relationships of the blocks. They are heavily used in engineering in hardware design, electronic design, software design, and process flow diagrams. A Flowchart – is a type of diagram that represents an algorithm, workflow or process. The flowchart shows the steps as boxes of various kinds, and their order by connecting the boxes with arrows. This diagrammatic representation illustrates a solution model to a given problem What Is The Difference Between Flowchart And Block Diagram? FLOWCHARTS Process Flowcharts The main reason of using Process Flowchart or PFD is to show relations between major parts of the System. Process Flowcharts are used in process engineering and chemical industry where there is a requirement of depicting relationships between major components only and not include minor parts. Process Flowcharts for single unit or multiple units differ in their structure and implementation. Concept Draw PRO is Professional business process mapping software for making Process flowcharts, Process flow diagram, Workflow diagram, flowcharts and technical illustrations for business documents and also comprehensive vision for mac application. Easier define and document basic work and data flows, financial, production and quality management processes to increase efficiency of your business with Concept Draw PRO. Business process mapping software with Flowchart Maker Concept Draw PRO includes extensive drawing tools, rich examples and templates, process flowchart symbols and shape libraries, smart connectors that allow you create the flowcharts of complex processes, process flow diagrams, procedures and information exchange. 1 Process Flowchart Solution is project management workflow tools which is part Concept Draw Project marketing project management software. Drawing charts, diagrams, and network layouts has long been the monopoly of Microsoft Visio, making Mac users to struggle when needing such vision alternative like vision for mac, it requires only to view features, make a minor edit to, or print a diagram or chart. Thankfully to MS Visio alternative like Concept Draw PRO software, this is cross-platform charting and business process management tool, now vision alternative for making sort of vision diagram is not a problem anymore however many people still name it business process vision tools. Basic Flowchart Symbols and Meaning Flowcharts are the best for visually representation the business processes and the flow of a custom-order process through various departments within an organization. Concept Draw PRO diagramming and vector drawing software extended with Flowcharts solution offers the full set of predesigned basic flowchart symbols which are gathered at two libraries: Flowchart and Flowcharts Rapid Draw. Among them are: process, terminator, decision, data, document, display, manual loop, and many other specific symbols. The meaning for each symbol offered by Concept Draw gives the presentation about their proposed use in professional Flowcharts for business and technical processes, software algorithms, well-developed structures of web sites, Workflow diagrams, Process flow diagram and correlation in developing on-line instructional projects or business process system. Use of ready flow chart symbols in diagrams is incredibly useful - you need simply drag desired from the libraries to your document and arrange them in required order. There are a few serious alternatives to Visio for Mac, one of them is Concept Draw PRO. It is one of the main contender with the most similar features and capabilities. 2 Types of Flowcharts A Flowchart is a graphical representation of process, algorithm, workflow or step-by-step solution of the problem. It shows the steps as boxes of various kinds and connects them by arrows in a defined order depicting a flow. There are twelve main Flowchart types: Basic Flowchart, Business Process Modeling Diagram (BPMN) Cross Functional Flowchart Data Flow Diagram (DFD) IDEF (Integrated Definition) Flowchart, Event-driven Process Chain (EPC) Diagram Influence Diagram (ID) Swimlane Flowchart, Process Flow Diagram (PFD) Specification and Description Language (SDL) Diagram Value Stream Mapping Workflow Diagram. 3  Using the Flowcharts solution from the Diagrams area of Concept Draw Solution Park you can easy and quickly design a Flowchart of any of these types. This solution offers a lot of special predesigned vector symbols for each of these widely used notations. They will make the drawing process of Flowcharts much easier than ever. Pay also attention for the included collection of ready Flowchart examples, samples and quick-start templates. This is business process improvement tools. If you are looking for MS Visio for your Mac, then you are out of luck, because it hasn't been released yet. However, you can use Visio alternatives that can successfully replace its functions. Concept Draw PRO is an alternative to MS Visio for Mac that provides powerful features and intuitive user interface for the same. Cross-Functional Flowchart Use of Cross-Functional Flowchart is a clear way of showing each team member’s responsibilities and how processes get shared or transferred between different responsible people, teams and departments. Use the best flowchart maker Concept Draw PRO with a range of standardized cross-functional flowchart symbols to create the Cross-Functional Flowcharts simply and to visualize the relationship between a business process and the functional units responsible for that process. To draw the most quickly Cross-Functional Flowcharts, Cross Functional Process Maps, or Cross Functional Process Flow Diagrams, start with a Cross-functional flowchart samples and templates from Concept Draw Solution Park. The Concept Draw Arrows10 and Rapid Draw technologies will be also useful for you in drawing. Concept Draw PRO supports designing both types - horizontal and vertical Cross-functional flowcharts. A vertical layout makes the accents mainly on the functional units while a horizontal layout - on the process. If you need a Visio alternative in Mac OS X, try Concept Draw PRO. Its interface is very intuitive and it’s actually much easier to use than Visio, yet somehow it’s just as powerful if not more so. Concept Draw PRO performs professional quality work and seamless Visio interaction. Functional Flow Block Diagram You need to draw a Functional Flow Block Diagram? You are an artist? Now it doesn't matter. With Block Diagrams solution from the "Diagrams" area for Concept Draw Solution Park you don't need more to be an artist to design the Functional Flow Block Diagram of any complexity. 4 UML Block Diagram Use Case Diagram Taxi Service UML. This sample was created in ConceptDraw PRO diagramming and vector drawing software using the UML Use Case Diagram library of the Rapid UML Solution from the Software Development area of ConceptDraw Solution Park. This sample shows the work of the taxi service and is used by taxi stations, by airports, in the tourism field and delivery service. Basic Diagramming 5  “Functional Flow Block Diagram”, or “FFBD” – is a time- sequenced and “step-by- step” flow diagram, with the helpof which it is convenient to describe some system’s functional flow. The “Functional Flow Block Diagram notation” was developed in the 50s, and it is quite widely used in classical systems engineering. “Functional Flow Block Diagrams” are the ones, used in the classic business process while modelling different methodologies, as well as flow charts, control flow diagrams, so-called “PERT” diagrams, “IDEF”, “Gantt” charts and flow charts. “Functional Flow Block Diagrams” can be also known as “Functional Flows”, “Functional Flow Diagrams” or “Functional Block Diagrams”. “Functional Flow Block Diagrams” are usually made using a number of different levels. With their aid it is simpler to show the same tasks, which are identified through functional decomposition and so to display these tasks in their logical and sequential relations. These diagrams can be used for developing the requirements and for identifying the profitable trade studies. This kind of diagram helps incorporate the alternate as well as contingency operations and, as a result, to improve the probability of the particular mission success. Using the flow diagrams, it is simpler to provide an understanding of some operation of the system in general. These diagrams can be used as a basis for development of both contingency and operational procedures. The pinpoints areas can be also mentioned on the flow diagrams and with the help of them it is also possible to represent different means of satisfying some function, but it is important to take into consideration, that each of the functions which are described with the aid of “FFBD” should be separated and so represented in a way of a single box. Function numbering: Each stage should have an according number scheme and provide the data regarding function origin. These numbers establish identification and relationships that will carry through all Functional Analysis and Allocation activities and facilitate traceability from lower to top levels. 6  There are a few principles, which is always better to follow in terms of creating the functional flow block diagrams. First of all, each of the diagrams should contain a reference to other functional diagrams in a way of using some particular functional reference. Secondly, the lines, created within such diagrams, (those, which show the connections between different functions) should indicate a function flow, but not an intermediate activity. Also these diagrams should be laid out for the flow direction to go from the left side to the right one. There are often arrows used within such diagrams and they are there for indicating the different functional flows. A circle also can be used while making such diagram and it can be used for denoting a summing gate. “Bar G” and “G” are used for denoting such conditions as “go” and “no-go”. On such block diagram a function should be represented in a way of a rectangle which contains the function’s title as well as its unique decimal delimited number. A horizontal line can be used too and it is usually there for separating the number from the title itself. The basic logic symbols for making any “Functional Flow Block Diagram” can be: “AND” (shows the condition when all of the succeeding or the preceding paths are required; this symbol may contain an input with a few outputs or a few inputs with a single output, but never mixed multiple inputs and outputs), “Exclusive OR” (described a condition, when only one of the multiple succeeding or preceding paths is required, but never all of them; this symbol may contain an input with a few outputs, or a few inputs with an output, but never mixed inputs and outputs) and “Inclusive OR” (describes a condition when a few or all of the multiple succeeding or preceding paths are being required). Every “Functional Flow Block Diagram” should contain a name of the person or an organization, which created this diagram, a date, showing when this diagram was created, a unique number of the function, which is diagrammed, and also a unique function name of that function, which is being diagrammed. There are so many other block diagrams as well as “flow” ones, apart from the Functional Flow Block Diagram and you can always make any wanted with the help of ConceptDraw DIAGRAM as this software allows you to make the needed chart, flowchart, scheme, plan, schematics, drawing, diagram, including any of the existing “flow diagrams” and “block diagrams” within only a very short period of time as the Block Diagrams solution from the "Diagrams" area for ConceptDraw Solution Park, which can be found on this site and so downloaded for using, provides the necessary tools, including the examples of Functional Flow Block Diagrams of any complexity which can be used for making your own great looking diagram in ConceptDraw DIAGRAM 7  Having ConceptDraw DIAGRAM software as well as the needed solutions can simplify your work with making any needed drawing as well as save your time as it is well known that “time is money”, so getting the convenient and very useful application can save both — your time and your money. Try it as well as solutions and see the difference with any other applications you ever used. You need to draw a Functional Flow Block Diagram? You are an artist? Now it doesn't matter. With Block Diagrams solution from the "Diagrams" area for ConceptDraw Solution Park you don't need more to be an artist to design the Functional Flow Block Diagram of any complexity. 8 Example 1. Functional Flow Block Diagram - Total Solution Process Block Diagrams Solution includes 5 libraries with 190 vector objects which will allow to draw any Functional Flow Block Diagram: Block Diagrams Raised Blocks Blocks with Perspective Callouts Connectors 9 Example 2. Block Diagrams Library Design Elements Don't forget to use the colors, to make color accents — they help to make your diagram bright, beautiful, attractive, and certainly successful on various conferences, in publications, etc. 10 Example 3. Functional Flow Block Diagram — Six Markets Model The Functional Flow Block Diagrams you see on this page were created in ConceptDraw DIAGRAM using the tools of Block Diagrams Solution. They are included in Block Diagrams Solution and available from ConceptDraw STORE. An experienced user spent 5-10 minutes creating every of them. Example 4. Block Diagrams Solution Use the Block Diagrams Solution for ConceptDraw DIAGRAM software to create your own professional looking Functional Flow Block Diagram fast and easy, and then successfully use it in your work activity. All source documents are vector graphic documents. They are available for reviewing, modifying, or converting to a variety of formats (PDF file, MS PowerPoint, MS Visio, and many other graphic formats) from the ConceptDraw STORE. The Block Diagrams Solution is available for all ConceptDraw DIAGRAM or later users. 11  Assessment/Activity No.2: BLOCK DIAGRAM AND FLOWCHARTING OF CPU PROCESS Objectives: The activity aims to design a block diagrams and flow chart using AutoCAD software. This activity also provides student’s knowledge and skills on designing the process of CPU. Intended Learning Outcomes: 1. Create a block diagram and flow chart using AutoCAD software. Materials: AutoCAD software Activity Process: 1. Create the diagram process of CPU. 2. Students should pass their individual Diagram Drawings on how a CPU work does when it turn – on with its components. 12  Lesson III: Electrical, Electronic and Logic Components This standard contains definitions and general information applicable to most of the commonly used Electrical and Electronics Diagrams. It also includes detailed recommendations on preferred practices for use in the preparation of Electrical and Electronics Diagrams. The recommended practices covered by this standard are ground rules designed to eliminate divergent Electrical and Electronics Diagram drafting techniques. The illustrations shown represent good drafting practices. They are not intended as engineering design guides. Integrated Circuit Every electronic appliance we use in our day-to-day life, such as mobile phones, laptops, refrigerators, computers, televisions and all other electrical and electronic devices are manufactured with some simple or complex circuits. Electronic circuits are realized using multiple electrical and electronic components connected with each other by connecting wires or conducting wires for the flow of electric current through the multiple components of the circuit, such as resistors, capacitors, inductors, diodes, transistors, and so on. Circuits can be classified into different types based on different criteria, such as, based on connections: series circuits and parallel circuits; based on the size and manufacturing process of circuit: integrated circuits and discrete circuits; and, based on signal used in circuit: ana0log circuits and digital circuits. Integrated circuit or IC or microchip or chip is a microscopic electronic circuit array formed by the fabrication of various electrical and electronic components (resistors, capacitors, transistors, and so on) on a semiconductor material (silicon) wafer, which can perform operations similar to the large discrete electronic circuits made of discrete electronic components. 13  Integrated Circuits As all these arrays of components, microscopic circuits and semiconductor wafer material base are integrated together to form a single chip, hence, it is called as integrated circuit or integrated chip or microchip. Electronic circuits are developed using individual or discrete electronic components with different sizes, such that the cost and size of these discrete circuits increase with the number of components used in the circuit. To conquer this negative aspect, the integrated circuit technology was developed – Jack Kilby of Texas Instruments developed the first IC or integrated circuit in the 1950s and thereafter, Robert Noyce of Fairchild Semiconductor solved some practical problems of this integrated circuit. Different Types of Integrated Circuits There are different types of ICs; classification of Integrated Circuits is done based on various criteria. A few types of ICs in a system are shown in the below figure with their names in a tree format. 14  Different Types of ICs Based on the intended application, the IC are classified as analog integrated circuits, digital integrated circuits and mixed integrated circuits. Digital Integrated Circuits The integrated circuits that operate only at a few defined levels instead of operating over all levels of signal amplitude are called as Digital ICs and these are designed by using multiple number of digital logic gates, multiplexers, flip flops and other electronic components of circuits. These logic gates work with binary input data or digital input data, such as 0 (low or false or logic 0) and 1 (high or true or logic 1). 15 Digital Integrated Circuits The above figure shows the steps involved in designing a typical digital integrated circuits. These digital ICs are frequently used in the computers, microprocessors, digital signal processors, computer networks and frequency counters. There are different types of digital ICs or types of digital integrated circuits, such as programmable ICs, memory chips, logic ICs, power management ICs and interface ICs. Analog Integrated Circuits The integrated circuits that operate over a continuous range of signal are called as Analog ICs. These are subdivided as linear Integrated Circuits (Linear ICs) and Radio Frequency Integrated Circuits (RF ICs). In fact, the relationship between the voltage and current maybe nonlinear in some cases over a long range of the continuous analog signal. Analog Integrated Circuits The frequently used analog IC is an operational amplifier or simply called as an op-amp, similar to the differential amplifier, but possesses a very high voltage gain. It consists of very less number of transistors compared to the digital ICs, and, for developing analog application specific integrated circuits (analog ASICs), computerized simulation tools are used. Mixed Integrated Circuits The integrated circuits that are obtained by the combination of analog and digital ICs on a single chip are called as Mixed ICs. These ICs functions as Digital to Analog 16 converters, Analog to Digital converters (D/A and A/D converters) and clock/timing ICs. The circuit depicted in the above figure is an example of mixed integrated circuit which is a photograph of the 8 to 18 GHz self-healing radar receiver. Mixed Integrated Circuits This mixed-signal Systems-on-a-chip is a result of advances in the integration technology, which enabled to integrate digital, multiple analog and RF functions on a single chip. General types of integrated circuits (ICs) include the following: Logic Circuits Logic Circuits 17  These ICs are designed using logic gates-that work with binary input and output (0 or 1). These are mostly used as decision makers. Based on the logic or truth table of the logic gates, all the logic gates connected in the IC give an output based on the circuit connected inside the IC- such that this output is used for performing a specific intended task. A few logic ICs are shown above. Comparators Comparators The comparator ICs are used as comparators for comparing the inputs and then to produce an output based on the ICs’ comparison. Switching ICs Switching ICs Switches or Switching ICs are designed by using the transistors and are used for performing the switching operations. The above figure is an example showing an SPDT IC switch. 18 Audio amplifiers Audio amplifiers The audio amplifiers are one of the many types of ICs, which are used for the amplification of the audio. These are generally used in the audio speakers, television circuits, and so on. The above circuit shows the low- voltage audio amplifier IC. Operational amplifiers Operational amplifiers The operational amplifiers are frequently used ICs, similar to the audio amplifiers which are used for the audio amplification. These op-amps are used for the amplification purpose, and these ICs work similar to the transistor amplifier circuits. The pin configuration of the 741 op- amp IC is shown in the above figure. 19 Timer ICs Timer ICs Timers are special purpose integrated circuits used for the purpose of counting and to keep a track of time in intended applications. The block diagram of the internal circuit of the LM555 timer IC is shown in the above circuit. Based on the number of components used (typically based on the number of transistors used), they are as follows Small-scale integration consists of only a few transistors (tens of transistors on a chip), these ICs played a critical role in early aerospace projects. Medium-scale integration consists of some hundreds of transistors on the IC chip developed in the 1960s and achieved better economy and advantages compared to the SSI ICs. Large-scale integration consists of thousands of transistors on the chip with almost the same economy as medium scale integration ICs. The first microprocessor, calculator chips and RAMs of 1Kbit developed in the 1970s had below four thousand transistors. Very large-scale integration consists of transistors from hundreds to several billions in number.(Development period: from 1980s to 2009) Ultra-large-scale integration consists of transistors in excess of more than one million, and later wafer-scale integration (WSI), system on a chip (SoC) and three dimensional integrated circuit (3D-IC) were developed. All these can be treated as generations of integrated technology. ICs are also classified based on the fabrication process and packing technology. There are numerous types of ICs 20 among which, an IC will function as timer, counter, register, amplifier, oscillator, logic gate, adder, microprocessor, and so on. The conventional Integrated circuits are reduced in practical usage, because of the invention of the nano-electronics and the miniaturization of ICs being continued by this Nano- electronics technology. However, the conventional ICs are not yet replaced by nano-electronics but the usage of the conventional ICs is getting diminished partially. For improving this article technically, please post your queries, ideas and suggestions as your comments in the below section. Transmitters A transmitter consists of a precise oscillating circuit or oscillator that creates an AC carrier wave frequency. This is combined with amplification circuits or amplifiers. The distance a carrier wave travels is directly related to the amplification of the signal sent to the antenna. Other circuits are used in a transmitter to accept the input information signal and process it for loading onto the carrier wave. Modulator circuits modify the carrier wave with the processed information signal. Essentially, this is all there is to a radio transmitter. NOTE: Modern transmitters are highly refined devices with extremely precise frequency oscillation and modulation. The circuitry for controlling, filtering, amplifying, modulating, and oscillating electronic signals can be complex. A transmitter prepares and sends signals to an antenna that, in the process described above, radiates the waves out into the atmosphere. A transmitter with multiple channel (frequency) capability contains tuning circuitry that enables the user to select the frequency upon which to broadcast. This adjusts the oscillator output to the precise frequency desired. It is the oscillator frequency that is being tuned. [Figure 11-84] As shown in Figure 11-84, most radio transmitters generate a stable oscillating frequency and then use a frequency multiplier to raise the AC to the transmitting frequency. This allows oscillation to occur at frequencies that are controllable and within the physical working limits of the crystal in crystal-controlled oscillators. 21  Figure 11-84. Block diagram of a basic radio transmitter. Receivers Antennas are simply conductors of lengths proportional to the wavelength of the oscillated frequency put out by the transmitter. An antenna captures the desired carrier wave as well as many other radio waves that are present in the atmosphere. A receiver is needed to isolate the desired carrier wave with its information. The receiver also has circuitry to separate the information signal from the carrier wave. It prepares it for output to a device, such as speakers or a display screen. The output is the information signal originally introduced into the transmitter. A common receiver is the super heterodyne receiver. As with any receiver, it must amplify the desired radio frequency captured by the antenna since it is weak from traveling through the atmosphere. An oscillator in the receiver is used to compare and select the desired frequency out of all of the frequencies picked up by the antenna. The undesired frequencies are sent to ground. A local oscillator in the receiver produces a frequency that is different than the radio frequency of the carrier wave. These two frequencies are mixed in the mixer. Four frequencies result from this mixing. They are the radio frequency, the local oscillator frequency, and the sum and difference of these two frequencies. The sum and difference frequencies contain the information signal. 22  The frequency that is the difference between the local oscillator frequency and the radio frequency carrier wave frequency is used during the remaining processing. In VHF aircraft communication radios, this frequency is 10.8 MHz called the intermediate frequency, it is amplified before it is sent to the detector. The detector, or demodulator, is where the information signal is separated from the carrier wave portion of the signal. In AM, since both sidebands contain the useful information, the signal is rectified leaving just one sideband with a weak version of the original transmitter input signal. In FM receivers, the varying frequency is changed to a varying amplitude signal at this point. Finally, amplification occurs for the output device. [Figure 11-85] Figure 11-85. The basic stages used in a receiver to produce an output from a radio wave. Over the years, with the development of transistors, micro transistors, and integrated circuits, radio transmitters and receivers have become smaller. Electronic bays were established on older aircraft as remote locations to mount radio devices simply because they would not fit in the flight deck. Today, many avionics devices are small enough to be mounted in the instrument panel, which is customary on most light aircraft. Because of the number of communication and navigation aids, as well as the need to present an uncluttered interface to the pilot, most complicated aircraft retain an area away from the flight deck for the mounting of avionics. The control heads of these units remain on the flight deck. Transceivers A transceiver is a communication radio that transmits and receives. The same frequency is used for both. When transmitting, the receiver does not function. The push to talk (PTT) switch blocks the receiving circuitry and allows the transmitter circuitry to be active. In a 23 transceiver, some of the circuitry is shared by the transmitting and receiving functions of the device. So is the antenna. This saves space and the number of components used. Transceivers are half duplex systems where communication can occur in both directions but only one party can speak while the other must listen. VHF aircraft communication radios are usually transceivers. [Figure 11-86] Figure 11-86. VHF aircraft communication transceivers. Basic Components Used in Electronics & Electrical In any electronic circuit, we come across two types of electronic component: One which response to the flow of electrical energy and either store or dissipate energy. These are the Passive Components. They can be linear components with a linear response to the electrical energy or nonlinear components with a nonlinear response to the electrical energy. One which supplies energy or controls the flow of energy. These are the Active components. They require an external power source to be triggered and are generally used to amplify an electrical signal. Let us see every component in detail. 3 Passive Linear Components: Resistor: A resistor is an electronic component that is used to resist the flow of current and cause a reduction in potential. It consists of a low conductive component joined by conducting wires at both ends. When current flows through the resistor, the electrical energy is absorbed by the resistor and dissipated in the form of heat. The resistor thus offers a resistance or opposition to the flow of current. The resistance is given as R = V/I, where V is the voltage drop across the resistance and I is the current flowing through the resistor. The power dissipated is given by: 24  P = VI. Laws of Resistance: The Resistance ‘R’ offered by a material depends on various factors: 1. Varies directly on its length, l 2. Varies inversely on its cross-section area, A 3. Depends on the nature of the material specified by its Resistivity or Specific Resistance, ρ. 4. Also depends on the temperature 5. Assuming that the temperature is constant, the Resistance (R) can be expressed as R = ρl / A, Where R is resistance in ohms ( Ω ), l is the length in meters, A is an area in square meters and ρ is Specific Resistance in Ω-mts A resistor’s value is calculated in terms of its resistance. Resistance is the opposition to the flow of current. Two methods to measure resistance values: Using color code: Each resistor consists of a 4 or 5 color band on its surface. The first three (two) colors represent the resistor value, whereas the 4th (third) color represents the multiplier value and the last one represents the tolerance. Using Multimeter: A simple way to measure resistance is by using a Multimeter to measure the resistance value in ohms. 25 2 Types of Resistors: Fixed Resistors: Resistors whose resistance value is fixed and are used to provide an opposition to the flow of current. They can be carbon composition resistors which are made up of a mixture of carbon and ceramic. They can be carbon film resistors which consist of carbon film deposited on an insulating substrate. 26 A Carbon Resistor They can be metal film resistor which consists of small ceramic rod coated with metal or metal oxide, with the resistance value being controlled by the thickness of the coating. Metal Resistors They can be a wire-wound resistor which consists of an alloy wrapped around a ceramic rod and insulated. They can be surface mount resistors which consists of resistive material like tin oxide deposited on a ceramic chip. Variable Resistors: They provide a variation in their resistance value. They are generally used in voltage division. They can be potentiometers or presets. The resistance can be varied by controlling the wiper movement. The variable resistor or variable resistance, which consists three connections. Generally used as an adjustable voltage divider. It is a resistor with a movable element positioned by a manual knob or lever. The movable element is also called as wiper; it creates a contact with a resistive strip at any point which is selected by the manual control. 27 Potentiometer The potentiometer divides the voltage into different proportions depending on its movable positions. It is used in different circuits where we require less voltage than the source voltage. Practical Application of Variable Resistors: Sometimes it is necessary to design a variable dc bias circuit that should be able to very precisely get some specific voltage to say 1.5 volts. Thus a potential divider with a variable resistor is so chosen that one can vary the voltage from 1 volt to 2 volts from a 12 volt DC battery. Not from 0 to 2 volt but 1 to 2 volt for a specific reason one can use a 10k pot across a 12-volt dc and can get that voltage but it becomes very difficult to adjust the pot as the full arc angle of about 300 degrees. But if one follows a circuit below he can get easily that voltage because the entire 300 degree is available for just 1volt to 2 volts to be adjusted. Shown in the circuit below 1.52 volts. This how we get a better resolution. These onetime set variable resistors are called preset. 28  Capacitors: A capacitor is a linear passive component that is used to store an electrical charge. A capacitor generally provides reactance to the flow of current. A capacitor consists of a pair of electrodes between which there is an insulating dielectric material. The stored charge is given by Q = CV where C is the capacitive reactance and V is the applied voltage. Since current is the rate of flow of charge. Therefore, the current through a capacitor is: I = C dV/dt. When a capacitor is connected in a DC circuit, or when a constant current flows through it, which is constant with time (zero frequency), the capacitor simply stores the whole charge and opposes the flow of current. Thus a capacitor blocks DC. When a capacitor is connected in an AC circuit, or a time-varying signal flows through it (with non-zero frequency), the capacitor initially stores the charge and later offers a resistance to the flow of charge. It can thus be used as a voltage limiter in the AC circuit. The resistance offered is proportional to the frequency of the signal. 2 Types of Capacitors Fixed Capacitors: They offer a fixed reactance to the flow of current. They can be the Mica capacitor which consists of mica as the insulating material. They can be nonpolarized 29 ceramic capacitors which consist of ceramic plates coated with silver. They can be electrolyte capacitors that are polarized and used where a high value of capacitance is required. Fixed Capacitors Variable Capacitors: They offer capacitance which can be varied by varying the distance between the plates. They can be air gap capacitors or vacuum capacitors. Capacitance value can be either read directly on the capacitor or can be decoded using the given code. For ceramic capacitors, the 1st two letters denote the capacitance value. The third letter denotes the number of zeros and the unit is in Pico Farad and the letter denotes the tolerance value. Inductors: An inductor is a passive electronic component that stores energy in the form of a magnetic field. It generally consists of a conductor coil, which offers a resistance to the applied voltage. It works on the basic principle of Faraday’s law of inductance, according to which a magnetic field is created when current flows through the wire and the electromotive force developed opposes the applied voltage. The stored energy is given by: E = LI^2. Where L is the inductance measured in Henries and I is the current flowing through it. 30 Inductor Coils It can be used as a choke to offer resistance to the applied voltage and store the energy or used in combination with a capacitor to form a tuned circuit, used for oscillations. In AC circuits, the voltage leads the current as imposed voltage takes some time to build up the current in the coil due to opposition. 2 Passive Non-Linear Components: Diodes: A diode is a device that restricts current flow in only one direction. A diode is generally a combination of two differently doped regions forming a junction at the intersection such that the junction controls the flow of charge through the device. 6 Types of Diodes: PN Junction Diode: A simple PN junction diode consists of a p-type semiconductor mounted on an n-type semiconductor such that a junction is formed between the p and n types. It can be used as a rectifier that allows current flow in one direction through proper connection. A PN Junction Diode 31  Zener Diode: It is a diode made up of heavily doped p region compared to the n-region, such that it not only allows current flow in one direction but also allows current flow in the opposite direction, on the application of sufficient voltage. It is generally used as a voltage regulator. A Zener diode Tunnel Diode: It is a heavily doped PN junction diode where the current decreases with increasing forward voltage. The junction width is reduced with increasing impurity concentration. It is made from germanium or Gallium Arsenide. A Tunnel Diode Light Emitting Diode: It is a special type of PN junction diode made from semiconductors like Gallium Arsenide, which emits light when a suitable voltage is applied. The light emitted by the LED is monochromatic, i.e. of a single color, corresponding to a particular frequency in the visible band of the electromagnetic spectrum. 32  A LED Photo Diode: It is a special type of PN junction diode whose resistance decreases when light falls on it. It consists of a PN junction diode placed inside a plastic. A Photodiode Switches: Switches are devices that allow the flow of current to the active devices. They are binary devices, which when completely on, allows the flow of current and when completely off, block the flow of current. It can be a simple toggle switch which can be a 2-contact or a 3 contact switch or a push-button switch. 2 Active Electronic Components: Transistors: Transistors are devices which generally transform resistance from one part of the circuit to another. They can be voltage controlled or current controlled. A transistor can work as an amplifier or as a switch. 33 2 Types of Transistor: BJT or Bipolar Junction Transistor: A BJT is a current controlled device that consists of a layer of n-type semiconductor material sandwiched between two layers of p-type semiconductor material. It consists of three terminals – The emitter, base, and collector. The collector-base junction is less doped compared to the emitter-base junction. The emitter-base junction is forward biased whereas the collector-base junction is reverse biased in normal transistor operation. A Bipolar Junction Transistor FET or Field Effect Transistor: A FET is a voltage-controlled device. The ohmic contacts are taken from the two sides of the n-type bar. It consists of three terminals – Gate, Drain, and Source. The voltage applied across the Gate-Source and the Drain-Source terminal controls the flow of current through the device. It is generally a high resistance device. It can be JFET (junction Field effect transistor) which consists of an n-type substrate, on the side of which a bar of the opposite type is deposited or a MOSFET (Metal Oxide Semiconductor FET) which consists of an insulating layer of silicon oxide between the metallic Gate contact and the substrate. 34  MOSFET TRIACS or SCR: An SCR or Silicon Controlled Rectifier is a three-terminal device which is generally used as a switch in power electronics. It is a combination of two back to back diodes having 3 junctions. The current through the SCR flows because of the voltage applied across anode and cathode and is controlled by the voltage applied across the Gate terminal. It is also used as a rectifier in AC circuits. An SCR So these are some of the important components in any electronic circuit. Apart from these active and passive components, there is one more component, which is of vital use in the circuit. That is the Integrated Circuit. 35 What is an Integrated Circuit? A DIP IC An Integrated Circuit is a chip or a microchip on which thousands of transistors, capacitors, resistors are fabricated. It can be an Amplifier IC, a timer IC, a waveform generator IC, a memory IC or a Microcontroller IC. It can be an analog IC with a continuous variable output or a Digital IC operating at a few defined layers. The fundamental building blocks of Digital ICs are the logic gates. It can be available in different packages like Dual in Line Package (DIP) or Small Outline Package (SOP) etc. A Practical application of resistors – Potential Dividers Potential dividers are frequently used in electronic circuits. Therefore it is desired that a thorough understanding of the same would greatly help in designing electronic circuits. Instead of deriving the voltages mathematically by applying Ohm’s law, the following example by assessing in ratio way, one would be able to quickly get the approximate voltage while attending to the R&D nature of work. When two resistors of equal value (e.g. 6K both for R1 & R2) are connected across a supply, the same current will flow through them. If a meter is placed across the supply shown in the diagram it will register 12v concerning ground. If the meter is then placed between the ground (0v) and the middle of the two resistors it will read 6v. The battery voltage is then divided in half. Thus voltage across R2 for ground =6v 36 Similarly 1. If the resistor values are changed to 4K (R1) and 8K (R2) the voltage at the center will be 8v for ground. 2. If the resistor values are changed to 8K (R1) and 4K (R2) the voltage at the center will be 4v for ground. 37  The voltage at the center is better determined by the ratio of the two resistor values, though one can go by Ohms law to calculate to arrive at the same value. Case-1 the ratio was 6K: 6K = 1:1=6v:6v , Case-2 ratio 4k:8k= 1:2 =4v:8v and Case-3 ratio 8k:4k= 2:1=8v:4v Conclusion:-In a potential divider, if the upper resistor value is lowered then the voltage at the center goes up (concerning ground). If the lower resistor value is lowered then the voltage at the center falls. Mathematically but the voltage at the center can always be determined by the ratio of the two resistor values which is time-consuming and is given by the famous Ohms law formula V=IR Let us see the example-2 V = {supply voltage / (R1+R2)} X R2 V= {12v / (4K+8K)} R2 =(12/12000) x 8000 V = 8v 38  Assessment/Activity: LED LIGHTS CIRCUIT DRAWING Objectives: The activity aims to design a LED Circuit using AutoCAD Software. This experiment also provides students’ knowledge and skills on Electrical and Electronic system. Intended Learning Outcomes: The students shall be able to create a LED circuits using AutoCAD Software. Discussions: The LED (Light Emitting Diodes) is a semiconductor diode that emits visible lights or near infra-red radiation when it is forward. Inside the LED is a semiconductor which is encased in a transparent epoxy resin which could be either diffused or clear lens. The LED, unlike a normal bulb, has a limited viewing angle between of 30 degree to 90 degrees. Procedures: Make a LED Light Circuit in a AutoCAD and in an circuit board showing the Electrical and electronics parts. Assessment/Data Results: Output must be submitted in terms words. They expressed their learnings in this activity into words definition and explanation. 39  Lesson IV: Designation, Standards and Abbreviations INTRODUCTION This drawing standards manual establishes the conventions to be adhered to by engineering and drafting personnel in the preparation, revision, and completion of engineering drawings. This manual sets forth the minimum requirements acceptable at GSFC for the preparation of engineering drawings for flight hardware and ground support systems. The requirements specified herein are essential to the standardization of practices and to a uniform interpretation of drawings. A system, payload, or component assembly shall be completely defined by means of drawings, including lists, schematics, wiring diagrams, and specifications, to ensure that components fabricated are in accordance with the design. The documentation information shall serve as a permanent record. 40 Engineering drawings are defined as those drawings that communicate the requirements for the manufacture of the end-product items, their assembly, and their installation in the end product. DRAWING ELEMENTS Drawing Sizes – The following table defines the standard drawing sizes, and their letter designations to be used at GSFC: Notes: (a) Lengths for “J” roll size to be in ll-inch increments. (b)Not inclusive of added protective margins of at least 2 inches on both ends of roll size drawings. Multi-sheet Drawings – Multi-sheet drawings are permitted in all sizes. a. The first sheet of a multi-sheet drawing shall always contain the complete Title block, List of Material, Revision Block, and general notes. b. All sheets of multi-sheet drawings shall be of the same letter size. Use of multi-sheet drawings shall be found to be advantageous for certain types of schematics and diagrams. c. The sheets of “J” size drawings may be any of the above-noted lengths and may be intermixed in different lengths. d. Sheet numbering for all first sheets shall include the total number of sheets, as “SHEET 1 OF 1,” “SHEET 1 OF 2,” etc. Numbering of continuation sheets shall be limited to 41  stating the specific sheet number (e.g., “SHEET 2,” “SHEET 3”) without specifying the total number of sheets. Zoning Vertical and horizontal zoning – may be used if necessary to provide orientation to the field of drawings. Zoning is mandatory for multisheet drawings “D” size and larger and single-sheet drawings “E” size and larger. Zones shall be identified by alphabetical (uppercase) and numerical entries in the margin spaces as indicated in Figure 1. Zone sizes shall be 8½ inches (width) by 11 inches (length) for “E” and “J” size, 7 inches (width) by 10 inches (length) for “F” size, and 5½ inches (width) by 8½ inches (length) for “D” size. Title Block and Revision Block Title blocks and revision blocks – shall be prepared and completed as follows: The Title block of single-sheet drawings, first sheets of multisheet drawings, and revision blocks shall appear as shown in either Figure 2a on page 5 (dimensional system/inches) or Figure 2b on page 6 (dimensional system/millimeters). The information required in the Title block shall be as specified or referenced by items 1 through 28, below. The Title block of continuation sheets for multisheet drawings shall contain information listed in items 1, 2, and 4 through 11. 42 DRAWING NO. : See page 60. SH OF : Enter sheet number as applicable. Indicate total sheets only on sheet 1. WT : Enter unit weight calculated at time of design if required. TITLE : For selection and arrangement of drawing title. SCALE : Enter scale. CODE : For drawings prepared by the Goddard Space Flight Center (GSFC) with an official GSFC drawing number, enter the three- digit GSFC code identifying the group responsible for the drawing. For drawings prepared by a contractor with a contractor drawing number and format, the contractor's code number from the Commercial and Government Entity (CAGE) Publication H4/H8 (formerly Federal Supply Code for Manufacturers (FSCM) H4 and Federal Supply Codes for Non-Manufacturers (FSCNM) H8) shall appear. DATE : Enter date of initials. DESIGNER : Enter designer's printed name and initials. DRAWN : Enter draftsmen printed name or if drawn by the designer, the designer’s printed name may be repeated. CHECKED : Enter design analyst's printed name. This name shall be an independent name from all other names on the drawing. It represents that the drawing has been checked against the parameters of this drawing manual and, where possible, to form, fit, function, and feasibility. The checker must have a thorough understanding of the methods and practices of geometric tolerance and be able to specify such practices in accordance with ANSI Standard Y14.5M-1982, Dimensioning and Tolerancing. APPROVED : Enter the printed names of GSFC personnel assigned to approve the drawing. Project requirements for drawing names shall vary from program to program, but each name shall be identified. For 43  example, after each approval name, note the following: “ENG” for engineer, “STRESS” for stress engineer, “QA” for quality assurance engineer, “MATL” for materials engineer, “ELEC” for electrical engineer, etc. All names in line items 8 through 11 must be legible. The hand-written initials on the paper original are the official approval of that document. USED ON : Enter acronym name of program and acronym name of subsystem or experiment where applicable. X-673-64-1F REV 001 DEC. ‘94 GODDARD SPACE FLIGHT CENTER, Greenbelt, Maryland 8 ENGINEERING DRAWING STANDARDS MANUAL. NEXT ASSY : Enter drawing number on which the part is next utilized, modified, or assembled. In the case of tooling drawings, in the Next Assembly block refer to a general note that states “This drawing is used to fabricate (drawing number).” Installation drawings should reflect a top configuration drawing number as the next assembly. When a configuration drawing is not being produced, the installation drawing shall indicate by note “The installation forms a part of the configuration for program (project name).” EXAMINATION : The appropriate “Non-Destructive Examination (NDE) required” block shall be checked off, and the addition of the applicable code or “see note XX” shall be added where required. Refer to Testing and Inspection Notes of the general notes section paragraph 2.4.4.6 on page 20. FLIGHT HARDWARE and HARDNESS TESTING : The Flight Hardware block must be checked off when the part is used in actual flight configurations. The appropriate Hardness Testing block shall be checked off regardless of whether the part is flight hardware or not. On CAD-produced drawings, add a 3.5-inch-long by 0.88-inch-high block as follows : THIS DRAWING WAS PRODUCED USING: SOFTWARE: (a) VERSION: (b) FILENAME: (c) Notes: 44  (a) Software used (example: “AUTOCAD”) (b) Version of software (example: “10c7”) (c) Filename (example: “GSFC1234”) METRIC/HYBRID METRIC-INCH : Add “X” to type of drawing block. ITEM NO. : Enter item numbers when more than one type of material or part is required, and coordinate drawing callouts on the drawing field. Parts made of the same material, condition, and specification shall be assigned only one item number, even though the part may be required in various sizes and thicknesses. The quantity for such items in the List of Material (L/M) shall be stated as “A/R” with the specific sizes spelled out in the field of the drawing. Refer to Figure 3 on page 10, Figure 34 on page 80, and Section 8.6, Find or Item Number System of Identification, on page 79. Do not skip item numbers on new drawings. REQD : Enter quantity of parts required only for the parts of an inseparable assembly or assembly drawing. PART NO. : Enter identifying part numbers when required (Government, contractor, vendor, or other). On new drawings, group like items together. X-673-64-1F REV 001 DEC. ‘94 GODDARD SPACE FLIGHT CENTER, Greenbelt, Maryland ENGINEERING DRAWING STANDARDS MANUAL 9 DESCRIPTION : Enter material description (plate, etc.) or a part name title if it is another drawing. Enclose reference information such as fastener sizes in brackets. MATERIAL : Enter the material from which the part is fabricated. Examples: “AL ALY”; “CRES”; “BE CU.” MATERIAL SPEC. : Enter the applicable material specifications, number, and final condition. Examples: “QQ-A-250/11 6061-T6” for AL ALY plate; “ASTM A582 303 COND A” for CRES bar. The information required in the revision block shall be as specified or referenced by items 24 through 28, below, and in accordance with “Drawing Revisions,” paragraph 7, page 68. 45 REVISIONS – SYM : Enter revision symbol. REVISIONS – ZONE : Enter zone (where used). REVISIONS – DESCRIPTION : Enter description of the revision (refer to Section 7, “Drawing Revisions”). REVISIONS – DATE : Enter date approved by authorized signer(s) in block. REVISIONS – APPROVAL : Enter signature of GSFC person assigned to approve. If change was by approved EO, drawing only needs approval of the draftsman or person incorporating the change, and the checker. If changes made are not covered by an EO, then approval must include the engineer. Drawing Format – The drawing format for the drawing sizes listed on page 3, including zoning, drawing numbers, security classification, etc. 1. NOMENCLATURE Drawing Title General – Information for the selection or development of a drawing title is as follows: a. The title should be as brief as possible but should contain sufficient information to categorize the part properly and to distinguish it from other similar parts. b. The drawing title shall consist of the following: 1. Identifying noun or noun phrase. 2. the most significant modifier or modifying phrase. 3. The next most significant modifier or modifying phrase. The noun or noun phrase establishes a basic concept of an item. The modifiers serve to narrow the area of concept established by the basic name. A modifier is separated from the noun or noun phrase by a comma and from any preceding modifier by a comma. The type designator and/or any additional modifiers required to further identify an item are separated from the first part of the title by a dash. Where applicable, the word “ASSEMBLY” shall be used as the last word of the noun phrase. 46 EXAMPLES: “Beam, Hoisting, Guided Missile” “Cover, Protective, Rocket Motor—Forward Section” “Cabinet, Electrical Equipment—CY-147” “Transportation—Dolly Assembly, Earth Satellite” c. The noun, or noun phrase, is never abbreviated. Abbreviations are used in the modifiers only when space is limited. When used, abbreviations shall conform to Abbreviations, paragraph 2.2 on page 12. d.When one drawing supersedes another, the new drawing, when practical, has the same title. e. Parentheses are not used to enclose any portion of the drawing title. f. Program names (or abbreviations) should be added to the “Used On” block and not the Title block; exceptions are on the final or top assembly drawing. Abbreviations The purpose of this section is to provide a list of authorized abbreviations for use on drawings and associated documents. When used, abbreviations and acronyms shall be in accordance with GSFC STD-256-WE-1 and MIL-STD-12 (in that order of precedence). a. Uppercase Gothic letters shall be used. b. Abbreviations for word combinations (e.g., MMC—Maximum Material Condition) shall be used as such and shall not be separated for use singly. Single abbreviations may be combined when necessary. c. The same abbreviation shall be used for all tenses, the possessive case and the singular and plural forms of a given word. d. Abbreviations should be used only to save space or time, but never at the expense of clarity. e. Periods shall be used with abbreviations that spell entire words to provide clarity and to avoid misinterpretation. The following abbreviations are acceptable to use and are “industry-related” associations not found in GSFC STD-256-WE-1 or MIL-STD-12. AFBMA Anti-Friction Bearing Manufacturers Association, Inc. 1101 Connecticut Avenue, 47 NW Suite 700 Washington, DC 20036 AGMA American Gear Manufacturers Association, Inc. 1500 King Street Suite 201 Arlington, VA 22314 ANSI American National Standard Institute 1430 Broadway New York, NY 10018 ASME American Society of Mechanical Engineers 345 E. 47th Street New York, NY 10017 ASTM American Society for Testing and Materials 1916 Race Street Philadelphia, PA 19103 AWS American Welding Society, Inc. 550 N.W. Ledeune Road P.O. Box 351040 Miami, FL 33135 IEEE Institute of Electrical and Electronic Engineers, Inc. 445 Hose Lane P.O. Box 1331 Piscataway, NJ 08855-1331 ISO International Organization for Standardization/ (Organization International de Normalization) 1, rue de Varembé 1211 Geneve 20 Switzerland/Suisse NEMA National Electrical Manufacturers Association 2101 L Street, NW Washington, DC 20037 NSA National Standards Association, Inc. 1200 Quince Orchard Blvd Gaithersburg, MD 20878 NAS Aerospace Industries Association of America, Inc. 48 1250 I Street, NW Washington, DC 20005 SAE Society of Automotive Engineers, Inc. 400 Commonwealth Drive Warren dale, PA 15096 List of Material a. Requirements on the Body of the Drawing Each part listed in the List of Material (Parts List) must be identified at least once by an Item (Find) Number on the body of the drawing (except single item drawings and shown and opposite item drawings). Note: Parts shall be bracketed, indicating reference, when they are identified by number and are not noted in the List of Material. Such parts are shown in phantom. Repeated item numbers shall be indicated as reference either within brackets or by the word “REF.” b. Requirements in the List of Material a. The List of Material is a list of all parts and materials called out on the drawing. b. The quantity of parts noted in the List of Material is the number required to complete the noted assembly. c. When a new drawing is made, all parts in the List of Material should be grouped as to type, such as dash number (for shown and opposite assemblies), GSFC drawings (for detailed parts), MS parts, NAS parts, etc., and listed in this sequence. d. Quantities of Bulk Items and placement: Refer to notes (a) Through (e) on Figure 3 on page 10. e. Preferred parts lists for parts, materials, and processes can be found in an unofficial publication available for viewing in the Mechanical Engineering Branch. The “Design Selection Guide” contains a wide range of hardware, materials, design standards, and processes. It shall be noted that not all of the items in this reference guide are rated for space flight use. Note: All fasteners used in flight hardware and critical nuts and bolts used on ground support equipment, including all flight/GSE interfaces, must meet the specification GSFC Fastener Integrity Requirements, GSFC S-313-100, Materials Branch, Office of Flight Assurance. Notes on Drawings 49  Information other than pictorial views and dimensions necessary for completing a drawing is classified as “notes.” The two types of note forms are General Notes and Local Character Notes. Notes on a drawing take precedence over specification requirements; hence, notes conflicting with referenced specifications shall not be placed on a drawing unless they are necessary for deviations from certain provisions of the specification. a. Security Classification The security classification “Top Secret,” “Secret,” or “Confidential” shall be located on the drawing as noted in Figure 1 on page 4. Each sheet of a multisheet drawing shall be individually classified as to its contents. The security stamp on each sheet shall be that of the highest classification for any item shown on that individual sheet, not the general overall classification of the entire set of drawings or the end item. On roll-size drawings, the security classification shall be shown on the reverse side at both ends of the drawings next to the drawing number to enable the classification to be seen without unrolling the drawing. A warning note shall be included adjacent to the security classification located above the Title block and shall read as follows: THIS MATERIAL CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE OF THE UNITED STATES WITHIN THE MEANING OF THE ESPIONAGE LAWS, TITLE 18 U.S.C., SECTIONS 793 AND 794. THE TRANSMISSION OR REVELATION OF WHICH IN ANY MANNER TO AN UNAUTHORIZED PERSON IS PROHIBITED BY LAW. b. Note Location Notes of general character that do not require leaders to indicate where they apply, and for which provision has not been made in the supplementary blocks of the drawing format, shall be located in the following order of preference: a. Adjacent to the upper left border and to the left of all views. b. Immediately to the left of the revision block. c. Adjacent to the lower left border or below the revision block, space being left for extending the revision block downward. This location should be avoided whenever practical because the space required for revisions cannot be anticipated. c. Numbering of Notes 50  General notes are numbered consecutively downward. Note numbers may be identified on the field of the drawing by placing the note number in a pennant-shaped flag at the general note location and in the field of the drawing, or in the List of Material (Material Specification column), whichever location is more appropriate. d. Note Examples The following notes are listed as representative examples and should be used on Engineering Drawings when applicable. Significant information is to be inserted where blank(s) are indicated and, for most cases, the notations in parentheses are for information only. (When not applicable, do not use in note). Before using the referenced specifications, check the Department of Defense Index of Specifications and Standards Publications to ensure that the specification has not been cancelled or superseded. Use either of the following statements as main heading for notes: “Except as noted” or “Unless otherwise specified.” e. Dimension Notes ALL DIMENSIONS APPLY AFTER SURFACE TREATMENT. DIMENSIONAL LIMITS AND SURFACE ROUGHNESS DESIGNATIONS APPLY (state “BEFORE” or “AFTER”) PLATING. f. Local Character Notes Notes of local character, such as drill notes, thread notes, etc., that require leaders to indicate the features to which they apply, shall be located in the field of the drawing in positions adjacent to such features. Each note shall state the number of features to which it applies unless a leader is drawn to each feature. g. General Dimensional Tolerance Notes 51  The general tolerances entered in the supplementary portion of the Title block shall control all dimensions applied to the drawing, except those specifically labeled “Max,” “Min,” “Ref,” “Datum,” or “Basic,” or dimensions having tolerances applied directly thereto, or dimensions controlled by notes or documents invoked on the drawing. General tolerances may be changed to the prevalent tolerances that are required by the drawing type. This is done by striking through the tolerance and inserting the new tolerance beneath the old. In the case where metric tolerancing is required, see Section 10.2, subparagraph i, for general tolerances. Specification Callouts Normally, only the basic document number of a specification should be shown on the drawing, in which case, the latest issue in effect at the time of invitation to bid shall be imposed in all procurement actions. Changes to the specification occurring subsequent to the time of invitation to bid shall not be imposed in current procurement actions unless the drawing is revised to show the new issue by basic document number, revisions, amendment, and/or date and current procurement actions amended to specify the new drawing revision or Engineering Order (EO). If the basic document number, revision, amendment, and/or date of a specification are shown on a drawing, only that particular issue shall be imposed in all procurement actions. Changes to the specification occurring subsequent to the time of invitation to bid shall not be imposed in either current or future procurement actions unless the drawing is revised to show the new issue by basic document number, revision, amendment, and/or date and current procurement actions amended to specify the new drawing revision or EO. Regardless of whether a specification is shown on the drawing by basic document number only or by a particular issue, superseding specifications (new number) shall not be imposed in either current or future procurement actions unless the drawing is revised to show the new basic document number and, if applicable, issue and current procurement actions amended to specify the new drawing revision or EO. 2. DRAFTING PRACTICES General 52  These drafting practices are to be employed in the preparation of drawings by GSFC personnel to achieve commonality throughout and result in legible reproductions at the least cost from original drawings. Drawings must be complete and unambiguous in interpretation. Complete drawings contain or make reference to all data necessary for fabricating and installing the part and, when applicable, the necessary test requirements, procurement requirements, and source. Third-angle orthographic projection shall be used for mechanical engineering drawings. (Certain diagrams, schematics, etc., are accepted). Although other types of projection, such as isometric, perspective, etc., are not prohibited, their use must be confined to an auxiliary view on a drawing of a complex part when such a view shall aid in visualizing the part. Drawings need not have three views, (i.e., one or two views are permissible for objects that can be completely defined). Complementary notes or dimensions are acceptable in place of the additional views. The rule shall be that only those views shall be drawn that are necessary to convey the required characteristics of the part. Views, dimensions, etc., shall not extend into the margins of the drawing. A. Lines Acceptable quality of reproductions is dependent on the density and uniformity of line work (and lettering). Types of lines described herein are merely line conventions, but in every case, each type of line shall be opaque and of uniform width and shall be used on all drawings other than diagrams, such as schematics, etc. Ink Lines and Plotted Lines o Lines, whether hand-drawn or plotted, shall be opaque and of uniform width for each type of line. Two widths of lines, i.e., thin and thick, with their widths in the proportions of 1:2, shall be used. The actual width of each type of line shall be governed by the size and style of the drawing; the relative widths of the lines shall approximate those shown in Figure 4 on page 26. 53 o Pencil Lines Pencil lines shall be opaque and of uniform width throughout their length. The line widths which are specified for ink lines do not apply to pencil lines. Cutting and viewing plane lines are the thickest lines on the drawing. However, the thick lines used for outlines and other visible lines shall be sufficiently prominent to immediately differentiate them from lines 54 used for other purposes. Hidden, sectioning, center, phantom, extension, dimension, and leader lines shall be thinner than outlines. In selecting the widths of pencil lines, consideration shall be given to the medium of reproduction involved to ensure proper reproduction and reduction of the thinner lines. Types of Lines 1. Center Lines Center lines shall be composed of long and short dashes, alternately and evenly spaced, with a long dash at each end. Center lines shall cross without voids. See Figure 5, below, and Figure 6, page 28. Very short center lines may be unbroken if there is no confusion with other lines. Center lines shall also be used to indicate the travel of a center. See Figure 6 on page 28. 55 2. Dimension Lines Dimension lines shall terminate in arrowheads at each end. They shall be unbroken except where space is required for the dimension. The proper method of showing dimensions and tolerances is explained in Section 1.7 of ANSI Y14.5M-1982. 3. Leaders Leaders shall be used to indicate a part or portion to which a number, note, or other reference applies and shall be an unbroken line terminating in an arrowhead, dot, or wavy line. Arrowheads should always terminate at a line; dots should be within the outline of an object. 4. Break Lines Short breaks shall be indicated by solid freehand lines. For long breaks, full ruled lines with freehand zigzags shall be used. Shafts, rods, tubes, etc., which have a portion of their length broken out, shall have the ends of the break drawn as indicated in Figure 7 on page 29. 56 5. Phantom Lines Phantom lines shall be used to indicate the alternate position of parts of the item delineated, repeated detail, or the relative position of an absent part and shall be composed of alternating one long and two short dashes, evenly spaced, with a long dash at each end. See Figure 5 on page 27, Figure 6 on page 28, and Figure 8, below. 6. Sectioning Lines Sectioning lines shall be used to indicate the exposed surfaces of an object in a sectional view. They are generally thin full lines, but may vary with the kind of material shown in section. 57 7. Extension Lines Extension lines are used to indicate the extension of a surface or to point to a location outside the part outline. They start with a short, visible gap from the outline of the part and are usually perpendicular to their associated dimension lines. 8. Hidden Lines Hidden lines shall consist of short dashes, evenly spaced. These lines are used to show the hidden features of a part. They shall always begin with a dash in contact with the line from which they begin, except when such a dash would form a continuation of a full line. Dashes shall touch at corners, and arcs shall begin with dashes on the tangent points. See Figure 5 on page 27 and Figure 8 on page 29. 9. Stitch Lines Stitch lines shall be used to indicate the stitching or sewing lines on an article and shall consist of a series of very short dashes, approximately half the length of dash or hidden lines, evenly spaced. Long lines of stitching may be indicated by a series of stitch lines connected by phantom lines. 10. Outlines or Visible Lines The outline or visible line shall be used for all lines on the drawing representing visible lines on the object; see Figure 5 on page 27. 11. Datum Lines Datum lines shall be used to indicate the position of a datum plane and shall consist of one long dash and two short dashes, evenly spaced. 12. Cutting-Plane/Viewing-Plane Lines The cutting-plane lines shall be used to indicate a plane or planes in which a section is taken. The viewing-plane lines shall be used to indicate the plane or planes from which a surface or surfaces are viewed. On simple views, the cutting planes shall be indicated as shown in Figure 9 on page 31. View shall be shown in back of the cutting plane (3rd angle). 58 3. Lettering and Numerals All lettering shall be uppercase (capital letters). Numbers shall be Arabic numerals. The lettering and numerals shall always be placed in a horizontal reading position as far as practicable. Other than this, lettering shall be in a horizontal reading position when the drawing is rotated 90° clockwise. Legible lettering is essential for reproductions. Letters and/or numerals shall not run together. When typewritten letters or digits are used on drawings or related data, nothing smaller than pica type is permitted. 59 1. Style Other than being uppercase Roman and placed in a horizontal reading position, the lettering is that of the individual's style. 2. Heights Lettering heights shall be as follows: 3. Scale Drawings Shall be made to full scale unless the parts (or assembly) are too large to permit it or so small and complex that drawing to an enlarged scale is essential for clarity. When the main views of large parts are drawn to a reduced scale, the detail views “taken” to clarify detail should be made to full scale whenever possible. When the part has been drawn to an enlarged scale for clarity, it is not necessary to make an actual-size view. a. The scales preferred for engineering drawings are full size 1/1, reduced 1/2, 1/4, 1/10, 1/20, and enlarged 2/1, 4/1, 10/1, 20/1. The computer data base for the format size shall be 1/1 at all times. EXCEPTION: Certain drawings or figures, by their very nature, cannot be drawn to a specific scale (for example, wiring and schematic diagram drawings.) The scale designation for these cases is “NONE.” See “b,” below. b. The scale, as noted above, or the word “NONE” must be entered in the Title block. Do not use the word “SIZE” following the ratio. The notations “1/4 & NOTED” or “1/2 & NOTED,” etc., apply to those drawings on which the main views are to a reduced scale and auxiliary views are to some other scale. 60  c. To maintain consistency with title block callout for scale, detail views shall be noted thus: DETAIL - A SCALE 1/1 Note: The scale of the view shall be stated only when it differs from that noted in the Title block, which represents the majority of views and sections. d. Original pencil drawings should be to scale within 0.03 inch. When changes to an existing drawing take place, it is required to indicate that a particular feature is not to scale by underlining the dimensions with a straight line. e. The geometry of CAD-produced drawings shall be entered into the electronic database at one-to-one (full) scale. 4. Positioning the Part on the Drawing Installations shall usually be positioned on the drawing as they would be seen when viewed from the left side or top side of the equipment with its forward end pointing to the left. If clarity can be greatly improved by a position that results in fewer hidden lines and foreshortened projections, then that position should be used, and the above rule should be disregarded. Such instances would be a door or door jamb which installs on the right side being drawn with the forward portion to the right, or a number of items installed on the forward side of a panel being drawn looking at the forward side. Parts and minor assemblies are not necessarily drawn in the position they assume in the equipment. They may be drawn with some surface, side, or reference line parallel or perpendicular to the lower border of the drawing. Lathe-turned parts are usually drawn with the larger diameters to the left. 5. Picturization i. Unnecessary detail shall be omitted from all views and sections if clarity is not sacrificed and if drafting time is reduced. See Figure 11 on page 34. 61 6. Sections a. A sectional view shall be made through an outside view and not through another sectional view. See Figure 12 on page 35. b. The location of a section is indicated by a cutting plane with reference letters and arrowheads showing the direction in which the section is viewed. c. Sectional views shall not project directly ahead of the cutting plane arrowheads and should be as near as practicable to the portions of the drawing that they clarify. d. The axes of sectional views should not be rotated; however, the cutting plane may vary in direction (see Figure 12). If views have to be rotated, the angle and direction of rotation must be given. 62 e. Visible and invisible outlines beyond the cutting plane should not be shown unless necessary for clarification. f. Shafts, bolts, nuts, etc., which are in a cutting plane should not be cross-hatched. g. The cross-hatching symbol for cast iron should be used regardless of material as shown in Figure 13. If essential for clarity, material from which the parts are made should be indicated by the conventions given in ANSI Y14.2M-1979. 63  h. When sections are remotely located, zone information shall be added to both locations (i.e., from where the section is taken and to the location where the section is shown). Views a. A view is used to enlarge or clarify a portion of the drawing. See Figure 14. b. Projected views which are shown along common center lines to their origin need not be identified. Views located directly ahead of viewing plane arrowheads are absolutely prohibited. c. “Transported” views or sections are those which are not direct projections. They must be identified where shown, by letters, and at their origin by the cutting plane lines and letters. d. Views should not be rotated; however, if views have to be rotated for a legitimate reason, the angle and direction of rotation must be given. Details A detail is a partial view which shows a portion of another view in the same plane and will usually depict greater detail. Details should not be rotated. See Figure 15. 64 Identification of Sections, Views, and Details a. Identifying letters for sections, views, and details are assigned in alphabetical sequence as follows: For sections and such views as “A-A” in Figure 14 on page 36, use hyphenated letters. After “Z-Z,” begin: “AA-AA,” “AB-AB,” etc. b. For encircled details such as detail “A” in Figure 15, use single letters. After “Z,” begin: “AA,” “AB,” etc. c. The letters “I,” “O,” “Q,” and “X,” either as a single letter or as double-letter entries, shall not be used. A designated letter or combination of letters on a released drawing shall not be used for another section, view, or detail on the same drawing. Locating Sections, Views, and Details On zoned and/or multisheet drawings, a view, section, or detail and the portion of the drawing it clarifies shall be cross-referenced as follows: 65 TYPES OF DRAWINGS 1. Altered or Selected Vendor Part Drawing Altered vendor part or selected vendor part drawings shall be prepared on GSFC format when an existing vendor part cannot be used as is and it is desired to document and control the alteration or selection of the part. Preparation shall not be initiated until the vendor has been requested to make the alteration or selection, supply his number, and supply documentation. When the drawing is prepared by GSFC, it shall specify the part to be altered or selected by vendor number, name, and address and shall completely delineate the alteration or selection. In addition, the drawing shall specify reidentification of the part by the GSFC part number. An altered or selected vendor part drawing shall be identified by the words “Altered Vendor Part Drawing” immediately above the Title block. 2. An assembly drawing Shows two or more separable parts joined to form a stockable item, or a group of assemblies required to form an assembly of higher order. 3. Detail Drawing A detail drawing shows all the information necessary for fabricating an item, including the material from which it is made and those finishes, protective coatings, and processes required to fabricate the end product. Only one item (detail part) shall be presented per drawing. 4. Drawing Tree A drawing tree is used to control the development of drawings and their place in the overall scheme of the project. Although this type drawing is not a requirement for each project, when used properly and kept up to date, it can be a valuable management aid and can be contained in a configuration management database. 66 5. Electrical/Electronic Drawings Electrical/electronic drawings – are prepared to depict schematics, wiring diagrams, cable interconnections, and detailed cable assembly drawings. Electrical and Electronic Symbols Application: Symbols shall be in accordance with ANSI Y32.2- 1975, Graphic Symbols for Electrical and Electronic Diagrams (or later revisions), unless otherwise noted. Graphic electrical wiring symbols for architectural and electrical layout drawings shall conform to ANSI Y32.9-1972, Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction (or later revisions). Electrical and Electronic Diagrams Application: Diagrams shall be in accordance with ANSI Y14.15- 1966 (R-73) Electrical and Electronic Diagrams (or later revisions); ANSI Y14.15a-1971, Interconnection Diagrams, subsection 15-11; ANSI Y14.15b-1973, Electrical and Electronics Diagrams, subsections 15-1 through 15-10, and 15-12. 6. Inseparable Assembly Drawing An inseparable assembly drawing delineates items (pieces) which are separately fabricated and are permanently joined together (e.g., welded, brazed, riveted, nailed, bonded, etc.) to form an integral unit (part) not capable of being readily disassembled. An inseparable assembly drawing may be prepared in lieu of individual monodetail drawings for inseparable assemblies intended to be procured and replaced as a unit, where (except for standard hardware) the separate parts are of similar or compatible materials. An inseparable assembly drawing shall fully define the end product or detail assembly as assembled. Pieces of the inseparable assembly may be detailed either on separate detail drawings or on the inseparable assembly drawing itself. In the case of weldments, the parts shall not be individually detailed on separate drawings (due to the consumable material allowances that would have to be shown on detail drawings), except in cases where extensive machining might be necessary. 7. Installation Assembly Drawing An installation assembly drawing shows where and how parts and/or assemblies are installed relative to supporting structure or associated items. It shows locating dimensions, tolerancing, specifies attaching parts (such as rivets, bolts, or screws) and specific adjustments, assembly instructions, and processes required for completing and inspecting the installation. 67  a. That portion of the structure into which the installation is being installed shall be shown in phantom and identified by its part number. Such identifications shall be indicated as reference information by enclosure of the part number in parentheses or by use of the symbol “REF.” b. Applicable datum points or planes, such as center lines of structure, plane of symmetry, station planes, etc., shall be shown and identified. c. Parts may be detailed in place on installation drawings when convenient. Interface Control Drawing An interface control drawing shall be used to maintain compatibility of all physical and functional designs between different engineering design activities. The drawing shall communicate design criteria such as dimensions, hole and/or bolt sizes, hardware, and ultimate changes relative to cofunctioning systems. “Interface Control Drawing” shall be added directly above the Title block. No list of materials is permitted on this type of drawing; it is not to be used to manufacture parts. Matched-Set Drawing A matched-set drawing depicts parts that are machine-matched or otherwise mated and for which replacement as a matched set or pair is essential. The operating or mating characteristics of the matched parts (set) shall be indicated. The parts shall be uniquely marked with a serial number identification to indicate a matched set. Mechanical Schematic A mechanical schematic diagram drawing illustrates the operational sequence or arrangement of a mechanical device. Dimensions and relative sizes of items may be shown to indicate mechanical relationship. Modification Drawing Modification drawings delineate changes to delivered items, stockable items (e.g., Standard Part Drawing of honeycomb panel blanks), assemblies, installations, or systems. Drawings are prepared to add, remove, or rework items, equipment installations, or systems to satisfy the using activity's requirements. They also incorporate mandatory changes (e.g., safety, 68 reliability, or application extension) in delivered equipment. A modification drawing shall be identified by the words “Modification Drawing” immediately above the Title block. This type of drawing has also been known or referred to as a “Make from Drawing.” Outline Drawing An outline drawing is a drawing that defines the external contour of an item, usually by showing the projected views in two or three perpendicular planes. Two types of outline drawings are depicted in Figures 25a, below, and 25b on page 52. 69 Source Control Drawing A source control drawing shall be used to limit procurement of a vendor-designed and manufactured part (or assembly) to that source or sources that exclusively provide the performance, installation, and interchangeable characteristics of the part selected and tested for a specific application. In the event the vendor shall not provide drawings as described in paragraph 4.14.d on page 56, the source control drawing shall include the same description of the part as required on specification control drawings. If vendor drawings are made available, the content of the source control drawing shall be limited to vendor's part number, name, and address. In either case, the following note shall appear on the source control drawing: “Only the part(s) specified on this drawing and identified by vendor's name(s), address(es), and part number(s) has (have) been tested and approved by GSFC for use in name of item. A substitute part shall not be used without prior testing and approval by GSFC.” a. The source control drawing number is not a part number. The vendor part itself shall be identified by the vendor's identifying number. b. The assembly (or installation) drawing shall call out the part by source control drawing number. In the List of Material (parts list) of the drawing, the source control 70  drawing number shall be accompanied by the following note: “Vendor Part—see source control drawing.” A source control drawing shall be identified by the words “Source Control Drawing” immediately above the Title block. c. A source control drawing shall not upgrade a vendor's part beyond the vendor's stipulations. Specification Control Drawing Specification control drawings are prepared to record the characteristics of a vendor- designed and manufactured part (or assembly). This type of drawing may also be used to document GSFC parts that are sent to a unique vendor to perform a specific operation because of special equipment and/or hardware only available there. Such characteristics are size, shape, mounting dimensions, and other design requirements, including tests, when applicable, that could be obtained from the vendor's manufacturing drawings if they were made available. The vendor's part number, name, and address shall be included, either in note or table form. Standard Part Drawing Standard parts shall be selected from government and industry standards in that order of precedence. If neither of these contain a part satisfactory for the design needs, a drawing shall be prepared. Before preparation, it must be determined that the part shall be a GSFC standard part, in which case it shall be drafted on GSFC standard manual format. Tabulated drawing A tabulated drawing depicts similar items with differences in characteristics such as dimensions, material, finish, and other requirements. These differences are tabulated on the drawing, the fixed characteristics depicted once. Pictorial differences that are not clear should be shown in views or details and should be properly labeled. A tabulated drawing precludes the preparation of an individual drawing for each item. 71 Tooling Drawing Tooling fixtures and templates are production aids. The templates are not intended as engineering documentation of the final end item configuration. Composite Material Drawing A composite material drawing is an engineering representation of two or more materials in combination (reinforcing fibers and resin binder). The fiber and resin differ in form or composition, and are tailored to meet specific engineering properties. The drawing shall specify the multi-ply laminate configuration that defines the number of plies, the stacking sequence, the ply angle orientation, the prepare fiber-resin materials, and the physical dimensions. For the following requirements, refer to Figure 29 as an example of a compo