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Title: Programmable%20Logic%20Controllers


1
Programmable Logic Controllers
  • LO1 Understand the design and operational
    characteristics of a PLC system

2
Unit 22Learning Outcomes
  • LO1 Understand the design and operational
    characteristics of a PLC system
  • LO2 Understand PLC information and
    communication techniques
  • LO3 Be able to apply programmable logic
    programming techniques
  • LO4 Understand alternative implementations of
    programmable control

3
Learning Outcome 1
  • LO1 Understand the design and operational
    characteristics of a PLC system
  • 1.1 evaluate the design characteristics of
    typical programmable logic devices
  • 1.2 describe different types of input and output
    device
  • 1.3 evaluate the different types of communication
    link used in programmable logic control systems
  • 1.4 describe the internal architecture and
    operational characteristics of the CPU of a
    typical programmable logic device

4
Learning Outcome 1
  • 1.1 Evaluate the design characteristics of
    typical programmable logic devices
  • unitary modular rack-mounted
  • 1.2 Describe different types of input and output
    device
  • mechanical switches non-mechanical digital
    sources transducers relays

5
Learning Outcome 1
  • 1.3 Evaluate the different types of communication
    link used in programmable logic control systems
  • twisted pair coaxial fibre-optic networks
  • 1.4 Describe the internal architecture and
    operational characteristics of the CPU of a
    typical programmable logic device
  • central processor unit (CPU) arithmetic logic
    unit (ALU) storage devices memory
    opto-isolators input and output units flags
    shift registers
  • scanning performing logic operations continuous
    updating mass input/output (I/O) copying

6
What do we meanby Controller?
  • A controller might be something you want
  • to control a sequence of events,
  • to maintain some variable constant, or
  • to follow some prescribed change

7
Controlling aSequence of Events
  • Drilling a hole in an engine block
  • Start lowering the drill when the work-piece is
    in position
  • Start drilling when the drill reaches the
    work-piece
  • Stop drilling when the required
    depth is reached
  • Retract the drill
  • Switch off and wait for the next workpiece

8
Maintaining aVariable Constant
  • Controlling the number of items to be packaged
  • Items are counted using some sensor
  • After a defined constant level has been reached,
    the controller is required to do something such
    as rotate the next packaging container into
    position

9
Follow some prescribed change
  • A controller might be used to follow a prescribed
    change for example
  • tracking an object as it moves from point A to
    point B, or
  • tracking the level of water as a tank fills from
    one level to another

10
Types of Controller
  • Essentially three types
  • Hard wire controlled systems
  • Microprocessor-controlled systems
  • Programmable Logic Controller

11
Hard Wire Systems
Motor
Switch
Relay to switch on large current to motor
Low Voltage
12
Deficiencies withHardwired Systems
  • Hardwired (traditional) control systems suffer
    from the fact that the rules governing the
    control system is determined by the wiring
    itself.
  • Thus when the rules i.e. the control needs to
    be changed, the wiring needs to be changed!

13
MicroprocessorControlled Systems
  • Instead of hardwiring each control circuit for
    each control situation, the same basic
    arrangement of relays and sensors can be used,
    but we can write a programme to instruct the
    microprocessor how to react to each input signal.
  • By changing the instructions in the programme we
    can use the microprocessor to control a variety
    of different situations.

14
A Washing Machine microprocessor control card
15
ProgrammableLogic Controllers (PLCs)
  • A Programmable Logic Controller (PLC) is a
    special form of microprocessor based controller
    that uses programmable memory to store
    instructions and to implement functions such as
    logic, sequencing, timing, counting and
    arithmetic in order to control machines and
    processes.

16
The ProgrammableLogic Controller
PROGRAMME
PLC
INPUTS
OUTPUTS
17
The ProgrammableLogic Controller (PLC)
  • A PLC is designed to be used by engineers who
    may have limited knowledge of computers or
    computing languages
  • Programming is primarily concerned with
    implementing logic and switching operations.
  • Input and output devices to be controlled in the
    system are connected to the PLC.
  • The controller then monitors the inputs and
    outputs according to the programme and carries
    out the rules for which it has been programmed.

18
The ProgrammableLogic Controller (PLC)
  • PLCs are similar to computers computers being
    optimised for calculation and display tasks PLCs
    optimised for control tasks in the industrial
    environment. Thus PLCs are
  • Rugged, being designed to with stand vibrations,
    temperate, humidity and noise.
  • Have interfacing for inputs and outputs inside
    the controller
  • Are easily programmed and easily understood
    programming language that is primarily concerned
    with switching and logic operations

19
Different Types PLC
  • PLC Systems
  • There are essentially three types of mechanical
    design for a PLC system a single box (Unitiary),
    the modular and the rack-mounted type.

20
The Unitary Type
  • A unitary type (sometimes called a brick) is
    commonly used for small programmable controllers
    and is supplied as an integral compact package
    complete with power supply, processor, memory and
    input / output units
  • Typically such a PLC might have 6, 8, 12 or 24
    inputs and 4, 8, or 16 outputs and a memory that
    can store some 300 to 1000 instructions

21
The Single Box(Compact) PLC
  • The Mitsubishi MELSEC FX3U

22
The MitsubishiCompact PLC Range
Type FX3U-16M_ FX3U-32M_ FX3U-48M_ FX3U-48M_ FX3U-64M_ FX3U-80M_ FX3U-128M_
Integrated inputs/outputs 16 32 48 48 64 80 128
Power supply 24 V DC / 100-240 V AC 24 V DC / 100-240 V AC 24 V DC / 100-240 V AC 24 V DC / 100-240 V AC 24 V DC / 100-240 V AC 24 V DC / 100-240 V AC 100-240 V AC
Integrated inputs 8 16 16 24 32 40 64
Integrated outputs 8 16 16 24 32 40 64
Output type Relay / Transistor (source type) Relay / Transistor (source type) Relay / Transistor (source type) Relay / Transistor (source type) Relay / Transistor (source type) Relay / Transistor (source type) Relay / Transistor (source type)
Power consumption 25 W / 30 VA 30 W / 35 VA 35 W / 40 VA 35 W / 40 VA 40 W / 45 VA 45 W / 50 VA 65 VA
Weight (Kg) 0.6 0.65 0.85 0.85 1.0 1.2 1.8
Dimensions in mm (WxHxD) 130x90x86 150x90x86 182x90x86 182x90x86 220x90x86 285x90x86 350x90x86
23
Extending BrickPLCs to add capacity
  • Some brick systems have the capacity to be
    extended to cope with more inputs and outputs by
    linking input / output boxes to them

OMRON CPM1A PLC
24
The Modular Type
  • Systems with larger numbers of inputs and outputs
    are likely to be modular.
  • The modular type consists of separate modules for
    power supply, processor and input and output
    cards (interfaces).
  • You can pick--mix modules to fit the
    requirements of the job.
  • Thus the mix of modules required for a particular
    purpose is decided by the user and the
    appropriate ones then plugged in to the rack.

25
The Modular Type
  • To add further I/O connections, modules can
    simply be added into the rack.
  • To add additional memory, a memory module can be
    clipped to the PLC directly.

26
The Rack Type
  • The Rack type PLC consists of individual elements
    (Power supply, CPU, I/O modules etc)that are
    clipped into the rack the engage into copper
    conductors in the backplane of the rack (a bus).
  • To add further I/O connections, modules can
    simply be added into the rack.
  • To add additional memory, a memory module can be
    added to the rack.
  • When the modules are clipped into the rack the
    engage into copper conductors in the backplane of
    the rack (a bus).

27
Allen-Bradley PLC-5
1771 I/O Back-panel mounted
1771 I/O rack mounted
28
Possible Modules for theAllen-Bradley PLC-5
  • Power Supply Module
  • Processor Module
  • Communications Module for communication to
    computers, I/O adaptors and other PLC processors
  • I/O adaptor Module for connecting the backplane
    to the processor at another location
  • I/O modules to provide the means to convert input
    signals to backplane levels and backplane signals
    to output circuit levels.

29
The criteria behind theselection of a particular
type of PLC
  • Safety
  • The PLC must be safe to operate in the
    environment for which it is to be designed i.e.
    can it function effectively in an explosive
    environment? (i.e. dust!)
  • Functionality
  • It probably goes with out saying the PLC needs to
    fit for the purpose i.e. it needs to perform the
    function required to meet the specification of
    the particular job task in question. (i.e. the
    number of I/O required, comms cards, ADC, etc)

30
The criteria behind theselection of a particular
type of PLC
  • Communication
  • How will the PLC communicate with other devices
    in the system such as computers, HMIs, etc.
    (Clearly all equipment must be compatible.)

31
The criteria behind theselection of a particular
type of PLC
  • Compatibility
  • A particular company when ordering a PLC system
    may specify particular manufacturers equipment
    this might be for reasons such as that employees
    may already be familiar with the kit and so this
    may reduce the need for training, etc.
  • Additional Programming equipment need not
    necessarily be purchased.
  • Contrast the needs of the procuring company and
    that of the PLC system builder!!!!!

32
The criteria behind theselection of a particular
type of PLC
  • Environment
  • The PLC must be suitable for the working
    environment heat, dust, vibration, moisture,
    electrical inference, magnetic fields, etc)
  • Reliability
  • Consider the use in a nuclear power plant. Back
    up systems? What would be the cost of a
    breakdown?
  • Cost

33
Exercises
  • Handout 1
  • Handout 2
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