Manufacturing Design

1. UNIT V-
INSTRUMENT DESIGN AND
MANUFACTURING TECHNIQUES
M.Selvam
Assistant Professor
Department of ECS
SKASC,CBE-08

2. TOPICS TO BE COVERED
• Grounding
• Shielding
• Elements of Design
• Product life cycle
• Circuit Design
• Circuit Layout
• Assembly and inspection
• Testing and calibration
• Power distribution
• Wiring and cabling
• Enclosures
• Integrated testing
• Documentation
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3. Grounding
• The term ground in electrical circuits refers to a current return path through
the earth.
• The electrical symbol for earth ground is shown in fig.
• The symbol represents a current return path through the earth to the low
potential (voltage) side of an energy source.
• Early developers of electrical systems theorized that the earth was an
electrically neutral body, i.e. an equal number of negative and positive charges
are distributed throughout the earth at any given time.
• Being electrically neutral, earth is considered to be at zero potential and
establishes a convenient reference frame for voltage measurements.
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4. The Concept of "Earth" Ground
• Noting that voltmeters read only the difference in potential between two
points, absolute measurements can be made by using earth as a reference.
• A true earth ground, as defined by the National Electrical Code, physically
consists of a conductive pipe or rod driven into the earth to a minimum depth
of 8 feet.
• Figure 2 shows this concept, where the earth is used as the conductive current
return path to the lowest potential point of the generating system.
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5. Examples of Current Return Path Symbols
• A current return path to an energy source is not necessarily, and frequently
isn't, earth ground. It can be a simple wire or a metal chassis or enclosure on
which the circuit is mounted. Because the return is the point of lowest
potential for all these cases, it is a convenient reference for circuit voltage
measurements.
• Figures 5a, 5b, and 5c illustrate the symbols commonly used to represent the
power supply common (a direct wire connection to the negative supply
terminal) or floating return, the chassis ground, and earth ground returns,
respectively. When more that one ground is required, the schematic circuit
diagram will generally define the meaning of each symbol.
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6. Examples of Current Return Path Symbols
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7. Grounding Considerations
• The most common noise problem encountered in large scale electronic
systems stems from a lack of good grounding practice. Grounding is a major
concern to practicing design and systems engineers.
• If several points are used for ground connections, differences in potential
between the points can cause troublesome "ground loops" which will cause
errors in voltage readings. This is illustrated in Figure 8, where two separated
chassis grounds are used.
• Vg represents a voltage existing between signal ground and the load ground. If
voltage measurements are made between the load ground and the input
signal, Vs, an erroneous voltage, (Vs + Vg) will be indicated.
• A common sign that a ground loop(s) exists, or that a ground is missing, is the
presence of induced power line (60 Hz) noise in the circuit.
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8. Grounding Considerations
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9. Basic Grounding Practices
a. Circuit Grounding
The ideal " single point ground " concept insures that no ground loops are created. As
the name implies, all circuit grounds are returned to a common point. This concept is
shown in Figure 9.
it is usually not practical. Even the simplest circuits can have 10 or more grounds, and
connecting them at a common point becomes a physical challenge. The next best
thing is a ground bus.
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10. Basic Grounding Practices
b. Ground Bus
• Bus bars are available or can be constructed to serve as an adequate substitute
for single point ground.
• The bus bar is simply a heavy wire or copper bar of low resistance which can
carry the maximum sum total of the load current back to the power supply.
• The bus can be extended along the length of the circuitry so that convenient
connections can be made at various points. The use of a ground bus is shown
in Figure 10.
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11. Basic Grounding Practices
c. Grounding Practice for Protoboards
• Most protoboards provide 2 or 3 lines of connected terminals extending along
the length of the board. One of these continuous strips should be dedicated as
a circuit ground bus. All circuit grounds should be tied directly to this bus. A
word of caution - with use, terminal contacts on the board can spread apart to
the extent that intermittent contact may be made with an inserted wire. This
could appear as noise in the circuit. Care should be taken that a good contact is
made to the ground bus.
d. Analog/Digital Grounds
• In general, analog and digital grounds should be kept separated and connected
together only at one single point.
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12. Shielding
• Shielding either prevents noise from energy from coupling between circuits or
supresses it. shielding can be anything from using a coaxial or shielded cable
to a sealed conductive chamber for circuit isolation.
• Shielding serves a reciprocal purpose: it protects the circuit it is shielding from
outside noise or unwanted signals.
• Shielding is mostly used to block electrostatic or ‘E’ Fields(faraday shield) and
electromagnetic interference (EMI) from lightening, discharges , radio and
television transmitters and high frequency circuits.
•
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13. Elements of Design
• Every electronic instrument (or a product) is a system of components and
interactions and also a part of a large system. Each component is a system unto
itself as well.
• The development of electronic instruments is a systematic system engineering
effort.
• System engineering provides a path from concept through design and test, to
delivery and documentation.
• System engineering encompasses :
• The technical efforts related to development,manufacture,verification ,
deployment,operations,support,disposal .
• The translation of the system definition into work breakdown structures.
• Gathering and analysis of information for management decision making.
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14. Product life cycle
• The idea of product life cycle acknowledges the fact that designing and selling
a product .
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15. Product life cycle
• Need Opportunity: The product starts with a need or opportunity in the
marketplace. In embedded applications, this need has historically been a goal
of reducing cost or increasing the functionality of an existing
electromechanically controlled system by inserting computer technology. An
example is digital engine controllers for automobiles, which were virtually
required to meet tougher emission controls that could not be handled by
mechanical engine controllers.
• Concept development: Once a need or opportunity is defined, a concept for a
product is created. The progression of elements within concept of
development. The first step is to define the product, taking into consideration
the following points.
• Consumer Objectives
• User needs
• Mission or regions of operations
• Constraints
• Regulation and Standards
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16. Product life cycle
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Modelling
• Analysis
• Simulation
• Prototyping
Feasibility Analysis
Characterization of
solution
Elements and iterative nature of concept development

17. Product life cycle
• Product Design: Concept development proposes various approaches to design.
• Top –Down: The requirements completely drive the design
• Bottom-UP: The solution is synthesized from current design and available
technology
• Outside –In: System interfaces drive the system
• Inside –out : The design is driven by developing Technology
• Hybrid : The combination of approaches is used.
Prototyping and testing:
 bench test development board
 Beta test
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18. Manufacturing Process design
•Production
•Deployment
•Support
•Upgrades
•Retirements and disposal
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19. Circuit Design
• The first step of circuit design is to finalize requirements/Specifications of the
system.
• The general requirements are Performance, Reliability and maintainability
User interface safety and failure modes, operational regimes and logistical support.
Performance:
range
speed
throughput
size
weight
Power consumption
test Levels- EM interference-Vibration and shock- thermal Cycle
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20. • Reliability:
• Failure Rate
• User Interface:
• Response Latency
• No of operations per sequence
• Ease of Use
• Intuitive operation
• Logistical Support
• Maintenance interval
• Personal Expertise
Along with these electrical specifications are important while design a circuit.
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21. Circuit Design- General Issues
• General issues involved in circuit design are
• Selection of Technology
• Reliability
• Fault Tolerance
• High Speed Design
• Low Power Consumption
• Noise and error budgets
• Selection of Technology
The right choice of technology reduces the part counts, PCB size, power cost, and
reliability of systems.
• Reliability
The durability of working period with the failures.
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22. Circuit Design- General Issues
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Bathtub Curve

23. Circuit Design- General Issues
• Fault Tolerance
It is a measure of continuous operation of the system in the event of problem.It
has 3 distinct areas,
1. Careful design- Probability of failure can be reduced by design techniques.
2. Testable Architecture- The process of testing and dragonising failures within
systems.
3. Redundant Architecture
• High Speed Design
In High speed clocking circuits (>1MHz) transmission lines are must be care fully
designed due to the effect of Harmonics.
A careful design can avoid the problems associated with the transmission lines
such as bandwidth limitation, Decoupling, ground bounce, cross talk,
impedance match and timing screw or delay.
• Low power design- used for portability, isolation and low heat dissipation and
low power consumption.
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24. Circuit Layout
PCB’s are necessary elements in the complex process of developing a functional
product. To achieve a good circuit layout the following procedures and practices
are adopted .they are
1. Component Placement
2. Routing signal traces
3. Grounds ,returns ,Shielding
4. Connectors
Component Placement: Placing the components in PCB is plays a vital role in
avoidance of wrong connections. After the placement the components may
grouped as high current Circuits, High frequency Circuits, and analog and digital
circuits.
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25. Circuit Layout
Routing signal traces: Proper routing of traces(tracks)
increases trance density, minimizing trace impedance
,reduces the effects of noise and crosstalk and EMI.
Grounds ,returns ,Shielding – Proper grounding and Shielding
are reduces the effect of noise and EMI
Connectors – the Mechanical and electrical interface between
a PCB and Cable.The metal to metal contact within connectors
raises several concerns as
• contact force and resistance
• Gastight Fit
• Life cycle
• Keying and Polarizing
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26. Testing and Calibration
• Testing can be performed by Several ways,3 Common methods are
1. Scan tests
2. Functional tests
3. Built in Test
• Scan Test: Simulates the points within a chain of circuitry , records of the
results and compares them with expected or calibrated data.
• Functional test: Exercise a subset of all the operations that circuit may
generate.
• Built in Test: BIT usually dedicates circuitry for the testing the remainder of the
system. It can Implement the Scan or Functional Tests.
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27. Power Distribution
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• Transmission and distribution of Power within an instrument and
between modules is an important step in the instrument design
• There are two configurations of power distributions
• Centralised power Supply
• Distributive Power Supply
Centralised Power Supply: It Converts ,regulates and transmits
power from single location.
Distributive Power Supply: It Transmits unregulated power to each
subsystem local converters then regulates the power within each
subsystem.

28. Power Distribution
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29. Wiring and Cabling
• Wires and cables are used to interconnects the modules
,connector, power supply etc. These were selected based on
current carrying capacity, mechanical strength, insulation
properties, shielding and environmental conditions.
• Types of Cables
• Coaxial cable
• Fibre optic Cable
• Power Cable
• Control and Signal Cable
• Twisted pair Cable- Unshielded /Shielded
• Ribbon Cable
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30. Wiring and Cabling
• General guidelines of Cabling:
• Cabling should be neat ,sturdy, and short.
• Easy to inspect and testing
• Prevent from damage to assembled parts
• It should be rout over sharp edges, screws or
terminals.
• Should allow reasonable bends
• Prevent strain on conductors, connectors and
terminals
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31. Enclosures
• Factors that affects electronic Instruments are
• Temperature and Cooling
• Vibration and Shock
• Humidity and Air Condition
• EMI
• Salt Spray or Corrosion
• Pressure and Altitude
• Radiation
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32. Enclosures
• Design of an enclosure must take into the following
considerations
• Cost
• Size
• Weight
• Material
• Cooling
• Aesthetics
• Ergonomics
• Serviceability
• Regulations and Standards
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33. Enclosures-Cooling
• Mostly, equipment are designed to operate in one of the following these
important ranges
• Commercial- 0ᴼC to 70ᴼC
• Industrial - -40ᴼC to 85ᴼC
• Military - -55ᴼC to 125ᴼC
Chips as they are used in electronic circuits need power in order to operate, by
Continuous usage exposed to high temperature .Thus need proper Cooling
arrangement is required to control the temperature of the devices and the
system as a whole. The several ways of cooling are
1. Passive cooling
2. Forced Air Cooling
3. Passive + Forced Air Cooling
4. Active Cooling
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34. Cooling
• Passive Cooling: -Heat Sinks
• Forced Air Cooling: Cooling Fan in CPU
• Active Cooling: Thermo Electric Cooler( Heat sink Paste)
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35. Aesthetics
• It governs the Appearance of an Instrument by Shape, Features, Finish and
Colour and tone.
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36. Ergonomics
• The term “ergonomics” is derived from greek word ergos means work and
nomics meaning law.
• It is classified into 2 types.
• Industrial ergonomics
• Occupational biomechanics
• It concentrates on the physical aspects of work and human capabilities.it is
some times referred as human factors.
• The benefits of ergonomics are
• Reduces the risk of unfavourable products
• Improve the quality of products
• Improves safety
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37. Integrated Testing
• An Instrument design procedure must have the following testing. They are
• Fit Check – Proper clearness between components and mechanisms and
cables.
• End to End test- Complete test to avoid mistakes
• Thermal Test - conforms the environmental requirements
• Vibration and Shock Test- improve the stability of the instrument
• EMI/RFI Test- reduces the radiation effects.
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38. Integrated Testing
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Fit Checks
Component Test
End to End test
Calibration
Thermal Test EMI /RFI Test Vibration Test Shock test

39. Documentation
• Documentation is an integral part of any product.It
provides the foundation of understanding the product
.Documentation is necessary for
• Operation
• Maintenance
• Repair
• Upgrades
• Fixes
• Legal Liabilities
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Thank
You