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

2. Unit 22: Learning 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 unitary; modular; rack-mounted
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 mean by 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 a Sequence 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 a Variable 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 with Hardwired 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. Microprocessor Controlled 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. Programmable Logic 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 Programmable Logic Controller
PROGRAMME
PLC
INPUTS
OUTPUTS

17. The Programmable Logic 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 Programmable Logic 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. PLC Systems: Different Types PLC
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 Mitsubishi Compact PLC Range
Type
FX3U-16M_
FX3U-32M_
FX3U-48M_
FX3U-64M_
FX3U-80M_
FX3U-128M_
Integrated inputs/outputs 16 32 48 64 80
128
Power supply
24 V DC / V AC
V AC
Integrated inputs 8 24 40
Integrated outputs
Output type
Relay / Transistor (source type)
Power consumption
25 W / 30 VA
30 W / 35 VA
35 W / 40 VA
40 W / 45 VA
45 W / 50 VA
65 VA
Weight (Kg)
0.6
0.65
0.85
1.0
1.2
1.8
Dimensions in mm (WxHxD)
130x90x86
150x90x86
182x90x86
220x90x86
285x90x86
350x90x86

23. Extending Brick PLCs 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 the Allen-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 the selection 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 the selection 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 the selection of a particular type of PLC
Compatibility
A particular company when ordering a PLC system may specify particular manufacturer’s 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 the selection 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