1. CHAPTER 2: TYPES OF CONTROLLER
Digital Logic Controller
Fuzzy Logic Controller
Programmable Logic Controller
PLC Applications

2. DIGITAL LOGIC CONTROLLER

3. INTRODUCTION Lowest level controller Not flexible Many limitations
Digital values are in a binary format.
Binary means 2 states.
1 (logic “high”, or H, or “on”)
0 (logic “low”, or L, or “off”)

4. A good example of binary
a light
only ON or OFF
Binary systems
Need 2 inputs
to produce 4 states

5. BINARY AS A VOLTAGE Voltages used to represent logic values:
Voltage supply
Vcc or Vdd = 1
Zero Volts or ground
Gnd or Vss = 0

6. BASIC DIGITAL LOGIC based on 3 primary functions the basic gates: AND
all inputs high for high output OR
any input high for high output
NOT
output is opposite (compliment) of input

8. WHAT IS FUZZY LOGIC? a control method
to mimic human decisions making using
not only uses fixed mathematical formula
but can weight each rule as to its importance

9. WHY FUZZY? A logic based only on two truth values True and False
inadequate to describe human reasoning
Fuzzy logic
uses whole interval between 0 (False) and 1 (True)
Better to describe human reasoning
As a result, fuzzy logic is being applied in rule based automatic controllers

10. EXAMPLE:
To illustrate, consider a tank in a cement plant

11. CONSIST OF: a tank two level sensors HL (high level) LL (low level)
a magnetic valve
VL (valve)

12. OBJECTIVE: to control VL ON VL when level is low as LL Start refill
OFF VL when
level is high as LH
Stop refill

13. CONDITION STATUS VL=1 (valve open) VL=0 (valve close)
LL=1 (level above mark)
LL=0 (level below mark)
HL=1 (level above mark)
HL=0 (level below mark)

14. HUMAN REASONING An operator would describe the control strategy as:
if the level is LOW then open VL
if the level is HIGH then close VL

15. FUZZY LOGIC Fuzzy logic aims to mimic operator’s decisions
if the level is LOW then open VL
if the level is HIGH then close VL
(1)

16. BOOLEAN/ DIGITAL LOGIC CONTROLLER
it can be described as:
if LL switches from 1 to 0
Then VL=1
if HL switches from 0 to 1
Then VL=0
(2)

17. EXAMPLES IN TODAY’S APPLICATION
Video recorders
can differentiate wanted movement from unwanted movement
Thus stabilize the picture
Washing machines
Decide level of water
Rice cookers ?

18. PROGRAMMABLE LOGIC CONTROLLER

19. INTRODUCTION TO PLC user friendly electronic computer
used to control functions of
many types of outputs
Different levels of complexity

20. ADVANTAGES OF PLC

21. EASY WIRING
To substitute hard wiring using conventional relay which are
Complicated

22. INCREASE RELIABILITY
Once a program has been written and tested it can be downloaded to other PLCs.
Since all the logic is contained in the PLC’s memory, there is no chance of making a logic wiring error.

23. MORE FLEXIBILITY
It is easier to create and change a program in a PLC than to wire and rewire a circuit. End-users can modify the program in the field.
Original equipment manufacturers (OEMs) can provide system updates for a process by simply sending out a new program.

24. LOWER COSTS
Originally PLCs were designed to replace relay control logic. The cost savings using PLCs have been so significant that relay control is becoming obsolete, except for power applications.
Generally, if an application requires more than about 6 control relays, it will usually be less expensive to install a PLC.

25. COMMUNICATION CAPABILITIES
A PLC can communicate with other controllers or computer equipment.
They can be networked to perform such functions as: supervisory control, data gathering, monitoring devices and process parameters, and downloading and uploading of programs.

26. FASTER RESPONSE TIME
PLCs operate in real-time which means that an event taking place in the field will result in an operation or output taking place.
Machines that process thousands of items per second and objects that spend only a fraction of a second in front of a sensor require the PLC’s quick response capability.

27. EASIER TO TROUBLESHOOT
PLCs have resident diagnostic and override functions that allows users to easily trace and correct software and hardware problems.
The control program can be watched in real-time as it executes to find and fix problems

28. PLCs VERSUS PERSONAL COMPUTERS
Same basic architecture
PLC
operates in the industrial environment
is programmed in relay
ladder logic
has no keyboard, CD drive, monitor, or disk drive
has communications ports, and terminals for input and output devices PC
-capable of executing several programs simultaneously, in any order
some manufacturers have software and interface cards available so that a PC can do the work of a PLC

29. PC BASED CONTROL SYSTEMS
Advantages
lower initial cost
less proprietary hardware
and software required
straightforward data exchange with other systems
speedy information processing easy customization

30. PLC SIZE CLASSIFICATION
Criteria
number of inputs and outputs (I/O count)
cost
physical size
Nano PLC ≤ 16 I/O points
smallest sized PLC
Micro PLC ≤ 32 I/O points

31. Small PLC <256 I/O points
Medium PLC < 1024 I/O points
Large PLC ≥ 1024 I/O points

32. Example given on a PLC Mixer Process Control
PLC APPLICATIONS
Example given on a PLC Mixer Process Control

33. PLC Mixer Process Control Problem
Mixer motor to automatically stir the liquid in the vat when the temperature and pressure reach preset values.
Alternate manual pushbutton control of the motor to be provided.
The temperature and pressure sensor switches close their respective contacts when conditions reach their preset values.

34. Process Control Relay Ladder Diagram
Motor starter coil is energized when both the pressure and temperature switches are closed or when the manual pushbutton is pressed.

35. PLC Input Module Connections
The same input field devices are used.
These devices are wired to the input module according to the manufacturer’s labeling scheme.

36. PLC Output Module Connections
Same output field
device is used and
wired to the output
module.
Triac switches motor
ON and OFF in accordance
with the control signal from the processor.

37. PLC Ladder Logic Program
The numbers represent addresses
The symbols represent instructions
The format used is similar to that of the hard-wired relay circuit.
I/O address format will differ, depending on the PLC manufacturer. You give each input and output device an address. This lets the PLC know where they are physically connected.

38. Entering And Running The PLC Program
To enter the program into the PLC, place
the processor in the PROGRAM mode and
enter the instructions one-by-one using
the programming device.
To operate the program, the controller
is placed in the RUN mode, or
operating cycle.

39. Modifying A PLC Program
The change requires that the manual pushbutton control should be permitted to operate at any pressure but not unless the specified temperature setting has been reached.
Relay ladder diagram for
modified process.
If a relay system were used, it would require some rewiring of the system, as shown, to achieve the desired change.

40. PLC ladder logic diagram for modified process.
Modifying A PLC Program
PLC ladder logic diagram for
modified process.
If a PLC is used, no rewiring is necessary!
The inputs and outputs are still the same.
All that is required is to change the PLC program