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CHAPTER 2
TYPES OF CONTROLLER
BY:
Salsabila Ahmad
DIGITAL LOGIC CONTROLLER
INTRODUCTION
 Lowest level controller
 Not flexible
 Many limitations
 Digital Signals have two basic states:
1 (logic “high”, or H, or “on”)
0 (logic “low”, or L, or “off”)



Digital values are in a binary format.
 Binary means 2 states.
A good example of binary is a light (only on
or off)
Need 2 inputs to produce 4 states
BINARY AS A VOLTAGE
Voltages are used to represent logic
values:
 A voltage present (called Vcc or Vdd) =
1
 Zero Volts or ground (called gnd or Vss)
=0
Basic Digital logic is based on 3 primary
functions (the basic gates):
 AND, where all inputs must be high for a
high output
 OR, where any input must be high for an
output high
 NOT, where the output is the opposite
(compliment) of the input
FUZZY LOGIC CONTROLLER
WHAT IS FUZZY LOGIC?
 is a control method that attempts to make
decisions as a human being would
 It attempts to mimic human decisions
making (not only uses fixed
mathematical formula, but can weight
each rule as to its importance).

A logic based on the two truth values
True and False is sometimes inadequate
when describing human reasoning
 Fuzzy logic uses the whole interval
between 0 (False) and 1 (True) to
describe human reasoning
 As a result, fuzzy logic is being applied
in rule based automatic controllers
EXAMPLE IN TODAY’S
APPLICATION


Video recorders with fuzzy logic can
differentiate wanted movement of the
camera from unwanted movement thus
stabilize the picture.
Many industrial applications are appropriate
for fuzzy logic
AS FOR EXAMPLE:


A fuzzy controller, in a cement plant for
example, aims to mimic the operator’s
terms by means of fuzzy logic.
To illustrate, consider the tank in Fig. 1
 which is for feeding a cement mill such
that the feed flow is more or less
constant.
Figure consists of
 a tank
 two level sensors
 a magnetic valve.
The objective
 to control the valve VL i.e.
 refilled when the level is
as low as LL
 stop the refilling when the
level is as high as LH
Note:
 VL=1 (valve open)
 VL=0 (valve close)
 LL=1 (level above mark)
 LL=0 (level below mark)
 LH=1 (level above mark)
 LH=0 (level below mark)
An operator responsible to
open and close the valve
would describe the control
strategy as:


if the level is LOW then
open VL
if the level is HIGH then
close VL
(1)
But in Boolean/Digital
logic controller, it can
be described as:


if LL switches from1
to 0
 Then VL=1
if LH switches from 0
to 1
 Then VL=0
(2)
PROGRAMMABLE LOGIC
CONTROLLER
INTRODUCTION TO PLC
 user friendly electronic computer
 used to control functions of many types
and levels of complexity.


A substitution for hardwired relay which is
 not economical
 Not reliable
 Hard to rewire when to be modified
Easy to understood by plant engineers
and maintenance electricians/technicians
 for its simple relay logic and ladder
diagrams
THE PLC SYSTEM
Programming
device
Memory
Input
interface
Processor
Power supply
Output
interface
MAJOR PARTS OF PLC
1.
2.
A CPU (processor) = serves as the
“brain” of the system
A programmer/monitor unit = enter PLC
programs to be stored in CPU = to
monitor the status of the running system
The input/output (I/O) modules = sends
signals to devices being controlled =
receives signals from the sensors on the
factory floor