1. Industrial Electronic Control
EET 425
Industrial Electronic Control
Introduction to PLC
Syafruddin Hasan

2. Industrial Motor Control Circuits
Complex industrial machines require sophisticated control systems
These control systems schematics are referred to as motor control circuits even though other types of systems may actually be controlled, such as hydraulic, pneumatic or mechanical systems

3. Relay Ladder Logic Circuits
Electrical control circuits are referred to as relay ladder logic diagrams
Ladder refers to the manner in which the diagrams are constructed
Logic refers to the decision-making function of the circuit

4. Elements of a Wiring Diagram
The ladder circuit consists of four elements:
A power source
An input control device
A load device
Interconnecting wires

5. Components Used as Input Devices
Manual switches
Momentary switches
Normally open push buttons
Normally-closed push buttons
Multiple-pole push button
Palm operated
Foot switches
Maintained Switches
Selector Switches
Mechanical limit switches
Proximity limit switches
Pressure switches
Flow switches
Level switches
Temperature switches

6. Components Used as Output Devices
Direct Devices
Motors
Pilot lights
Indirect Devices
Relays
Time delay relay
Contactor
solenoid

7. Relay ladder Logic Circuits
Relay ladder logic circuits perform several logical functions
AND OR
NOT
NAND
NOR

8. Building a Ladder Diagram
Using the water pumping system as a guide, the following diagram illustrates how various elements are constructed to build a ladder diagram

9. Modified Ladder Logic Circuit

10. Labeling Components in a Ladder Circuit
Labeling is important for troubleshooting, diagnosis, and analysis purposes
The example below is a properly labeled circuit

11. Motor Control Starter Circuits
Three-phase motor control circuits are common in industrial applications

12. Definition
A Programmable Logic Controller (PLC) is defined by Capiel (1982) as: (based on National Electrical Manufacturers Association (NEMA) standard ICS Part ICS3-304):
“A digitally operating electronic system designed for use in an industrial environment, which uses a programmable memory for the internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through analog or digital input/output modules, various types of machines or processes”.
What Is A PLC?
A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.

14. The first Programmable Logic Controllers were designed and
History of PLCs
The first Programmable Logic Controllers were designed and
developed by Modicon as a relay re-placer for GM and
Landis.
These controllers eliminated the need for rewiring and adding
additional hardware for each new configuration of logic.
The new system drastically increased the functionality of the
controls while reducing the cabinet space that housed the
logic.
The first PLC, model 084, was invented by Dick Morley in
1969
The first commercial successful PLC, the 184, was introduced
in 1973 and was designed by Michael Greenberg.

15. Initial specification was provided:
The controller must be:
Easily programmed and reprogrammed, preferably in-plant, to alter its sequence of operations.
Easily maintained and repaired—preferably using plug-in modules.
More reliable in a plant environment.
Smaller than its relay equivalent.
Cost competitive, with solid-state and relay panels then in use.

16. Basic Stop/Start Circuit
The most basic of all industrial control circuits
Demonstrates two important functions of a ladder diagram: stopping and interlocking

17. Rugged, noise immune equipment
Although PLCs are similar to ‘conventional‘ computers in terms of hardware technology, they have specific features suited to industrial control:
Rugged, noise immune equipment
Modular plug-in construction, allowing easy
replacement/addition of units
(e.g. input/output).
Standard input/output connections and signal
levels.
Easily understood programming language (e.g.
ladder diagram or function chart)
Ease of programming and reprogramming in-
plant.

18. PLC Advantages: Flexibility. Security.
Implementing Changes and Correcting Errors.
Large Quantities of Contacts.
Ease of Changes by Reprogramming.
Lower Cost
Pilot Running.
Visual Observation.
Speed of Operation.
Ladder or Boolean Programming Method.
Reliability and Maintainability.
Simplicity of Ordering Control System Components.
Documentation.

19. PLC Disadvantages: Newer Technology. Fixed Program Applications.
Environmental Considerations.
Fail-Save Operation.
Fixed-Circuit Operation.

20. Introduction to PLC Components
All PLC systems are comprised of the same basic building blocks
Rack assembly
Power supply
Programming unit
Input/Output Section
Processor unit

21. Execute the Control Instructions contained in the User's
What Is Inside A PLC?
The Central Processing Unit, the CPU, contains an internal program that tells the PLC how to perform the following functions:
Execute the Control Instructions contained in the User's
Programs. This program is stored in "nonvolatile" memory,
meaning that the program will not be lost if power is removed
Communicate with other devices, which can include I/O
Devices, Programming Devices, Networks, and even other PLCs.
Perform Housekeeping activities such as Communications,
Internal Diagnostics, etc.

23. Rack Assembly
The rack assembly contains the power supply, I/O modules, processor unit and is built upon a back plane which provides the various connections

24. Power Supply
The power supply provides the voltages necessary to operate the circuitry

25. PLC Programming Units
Several types of programming units are available for PLCs
Handheld programmers
Dedicated terminals
Microcomputers

26. Input/Output Sections
The purpose of the I/O section is to provide an interface for the internal circuitry to the outside world
Input/Output modules serve four functions:
Termination
Signal conditioning
Isolation
Indication

27. Input Modules Input modules receive signals from switching devices
The input module provides the necessary conversion to logic voltages
Three common types of input signals are:
120 VAC
Low-level DC
High-level DC

28. The input module performs 4 tasks electronically:
It senses the presence or absence of an input signal at each of its input terminal.
The input signal tells what switch, sensor, or other signal is on or off in the process
being controlled
It converts the input signal for on, or high, to a dc level usable by the module’s
electronic circuit. For a low, or off, input signal, no signal is converted, indicating off. .
The input module carries out electronic isolation by electronically isolating the
input module output from its input.
Its electronic circuit must produce an output to be sensed by the PLC CPU.

29. A typical input module has 4, 6, 8, 12, 16 or 32 terminals plus common and safety ground terminals

30. Output Modules
Outgoing discrete signals are transmitted to field devices using output modules
Typical output modules are:
120 VAC
Low-level DC
High-level DC

31. The output module operates in the opposite manner from the input module.

32. PLC I/O module

33. Processor Unit
The processor unit coordinates and controls the operation of the PLC
The PLC processor is composed of three main sections
The central processing unit
The arithmetic logic unit
Memory

35. How Does A PLC Operate?
There are four basic steps in the operation of all PLCs; Input Scan, Program Scan, Output Scan, and Housekeeping. These steps continually take place in a repeating loop.
Four Steps in the PLC Operations
1.) Input Scan
Detects the state of all input devices that are connected to the PLC
2.) Program Scan
Executes the user created program logic

36. These steps are continually processed in a loop.
3.) Output Scan
Energizes or de-energize all output devices that are connected to the PLC.
4.) Housekeeping
This step includes communications with programming terminals, internal diagnostics, etc...
These steps are continually processed in a loop.

37. Processor Files
The processor contains several types of files to support the program and logic being used
In an Allen-Bradley system there are four types of program files and 11 types of data files

38. The type of delimiter specifies the kind of information that follows:
Addressing
To address data files, alphanumeric characters separated by delimiters are used
The type of delimiter specifies the kind of information that follows:
A number that follows a colon represents which element will be used
A number that follows a slash represents the bit is used in a file
A number that follows a period represents which bit is used within a word

39. Address Identifiers

40. Word Address T4:7.ACC File Number File Type Word Word delimiter
Element Delimiter

41. Element Address
File
Number
File Type
Element
N7:12
Element Delimiter

42. Input Output Address Input addresses are formatted as: I:e/b
I = identifier as Input
: = slot delimiter
e = slot number of module
/ = bit or terminal delimiter
b = terminal number of the module
Output addresses are formatted as: O:e/b
O = identifier as Input
: = slot delimiter
e = slot number of module
/ = bit or terminal delimiter
b = terminal number of the module

43. Relationship of Data File Addresses to I/O Modules

44. What Do I Need To Consider When Choosing A PLC?
There are many PLC systems on the market today. Other than cost, you must consider the following when deciding which one will best suit the needs of your application.
Will the system be powered by AC or DC voltage?
Does the PLC have enough memory to run my user program?
Does the system run fast enough to meet my application’s
requirements?
What type of software is used to program the PLC?
Will the PLC be able to manage the number of inputs and outputs
that my application requires?
If required by your application, can the PLC handle analog inputs
and outputs, or maybe a combination of both analog and discrete
inputs and outputs?
How am I going to communicate with my PLC?
Do I need network connectivity and can it be added to my PLC?
Will the system be located in one place or spread out over a large
area?