Plc 101

Programmable Logic
Controller 101
A tool for Automation
By: Engr. Wendell Agasen

Overview
What is a control System?
Fundamentals of PLC?
PLC hardware and basic operation
Sensor and output devices
Control program
Types of PLC programming language
Summary
Introduction to ladder diagram
PLC programming Exercises
Bonus programming (ST &SFC)
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Control System

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Human Control System

INSTRUMENTATION AND CONTROL
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Fundamentals of PLC

What is PLC?
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Hard
wiring
Soft
wiring

Hard wire circuit
using a NO switch
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Hard wired circuit using a relay

Soft wiring using a PLC
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PLC
DC

So any idea what is a PLC?
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network
digital inputs
digital outputs
analog inputs / outputs

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It is a device that is used to control an
output equipment base on the input
signal.
The PLC works by looking at its inputs,
executes a user defined program, check
for error during program execution and
then update outputs if no error
encountered.
What exactly is a PLC?

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Why use a PLC?

Consider the following design requirements
Design and build a circuit to operate
a 10 submersible pumps with its
corresponding interlocks of tank
level, discharge pressure and motor
protection sensor.
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Assuming your design required
65 relays to be installed in a
350 x 300 x 150 mm panel?
1 PLC
Over 200 possible
relay, timer,
counter, real time
clock,
combination
25 Timers
25 Switches
65
Relays
How about if you
have timers
switches?
How many PLC do you need for the
given number of relays, switches,
and timers?
1 PLC
Over 200
possible relay,
timer, counter,
real time clock,
combination
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Installation mounting, wiring, and commissioning
Troubleshooting
Configuration and reconfiguration
Remote monitoring
Networking
Major issues of conventional relay circuit
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Which is better?
RELAY CIRCUITS PLC
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VS

Comparison with other control system
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19
Major Components of a Common PLC
CPU
POWER
SUPPLY
I M
N O
P D
U U
T L
E
O M
U O
T D
P U
U L
T E
PROGRAMMING
DEVICE
From
SENSORS
Pushbuttons,
contacts,
limit switches,
Sensing devices
Proximity sensors
Light detector
To
OUTPUT
Solenoids
Contactors
motors
any electrical
devices
YOU
Memory
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20
POWER SUPPLY
Provides the voltage needed to run the primary PLC components
I/O MODULES
Receive signal from external input devices, performs signal conversion and
provide appropriate signal to external devices.
CPU
Provides intelligence to command and govern the activities of the entire PLC
systems.
PROGRAMMING DEVICE
Used to enter the desired program that will determine the sequence of operation
and control of process equipment or driven machine.
Major Components of a Common PLC
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PROGRAMMABLE LOGIC CONTROLLERS (PLC)
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Programming Terminal PC Connection
memory expansion port
communications port
TSX37-22
I/O Modules
Common PLC Hardware
Modicon
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Power Supply
I/O Modules
Siemens
Common PLC Hardware
CPU
Memory

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CPU
Allen Bradley
Common PLC Hardware
I/O Modules
Power Supply

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PLC Basic operations

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PHASE 2
Program
Execution
PHASE 3
Diagnostics/
Comm
PHASE 4
Output
Scan
PHASE 1
Read Inputs
Scan
PLC Operations
Step 1-CHECK INPUT STATUS - PLC takes a
look at each input module to determine if it is on or
off, or reads analog measurement value
Step 2-EXECUTE PROGRAM - PLC executes your
program one instruction at a time.
Step 4-UPDATE OUTPUT STATUS -PLC updates
the status of the outputs. It updates the outputs based
on which inputs were on during the first step and the
results of executing your program during the second
step. is true.
Step 3-DIAGNOSTIC AND COM – PLC preforms
diagnostic and communication task
Repeat Cycle

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Read all field input devices via the input interfaces, execute
the user program stored in application memory, then, based
on whatever control scheme has been programmed by the
user, turn the field output devices on or off, or perform
whatever control is necessary for the process application.
Scanning is the process of sequentially reading the inputs,
executing the program in memory, and updating the outputs.
Scan time (cycle time) – the time to complete one PLC
operation (step 1 to 4).
Basic Function of a Typical PLC

Types of PLC
Medium PLC
Large PLC
Small
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Monolithic (one-piece) construction
Fixed casing
Fixed number of I/O (most of them binary), up to 128 I/O’s and memories
up to 2 Kbytes.
No process computer capabilities (no MMC)
Can be extended and networked by an extension (field) bus
Sometimes LAN connection
Mono-processor
Small or compact

Medium PLC
Modular design
It has up to 2048 I/O’s and memories up to 32 Kbytes

Large PLC
Modular with network of Remote IOs (RIO)
It is the most sophisticated units of the PLC family. They have up to
8192 I/O’s and memories up to 75 Kbytes.
It can control individual production processes or entire plant.

Let us consider a medium type PLC
PLC Rack
PLC
sections
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Power Supply Section
The PS output provides power to every module
in the PLC; however, it does not provide the DC
voltages to the PLC's peripheral I/O devices.
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Central Processing Unit (CPU)
The processor section makes the
decisions needed by the PLC so that it
can operate and communicate with other
modules.
Executes the programs.
It has memory section. This size tells us
how many locations are available in the
memory for storage. Additional memory
modules can be added to your PLC
system as the need arises.
Flash Memory
sometimes EEPROM
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Input Module
The input module has two functions:
– reception of an external signal
– and status display of that input
point.
The input to an input module is either a
discrete or analog signal.
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Input Module
Typical types of input modules
Analog input (4-20 mA or 0 -10 Vdc).
DC voltage (110, 220, 14, 24, 48, 15-30V)
AC voltage (110, 240, 24, 48V)
TTL (transistor-transistor logic) input (3-15VDC).
Word input (16-bit/parallel).
Thermocouple input.
Resistance temperature detector.
High current relay.
Low current relay.
Latching input (24VDC/110VAC).
Isolated input (24VDC/85-132VAC).
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Output Module
The output module transmits discrete or analog
signals to activate various devices such as hydraulic
actuators, solenoids, motor starters, and displays
the status (through the use of LEDs) of the
connected output points. Signal conditioning,
termination, and isolation are also part of the
output module's functions.
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Output Module
Some typical output modules available today include the
following:
DC voltage (24, 48,110V) or current (4-20 mA).
AC voltage (110, 240v) or current (4-20 mA).
Isolated (24VDC).
Analog output (12-bit).
Word output (16-bit/parallel).
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Sensors and Output device

Sensor
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DI CPU DOSENSOR
ACTUATORS
MOTORS
ETC
PLC
- Translates physical events to electrical signal

Sensor
I. Digital/logical sensor – detect the state of an event (either True or
False)
Mechanical switch
1. Contact (float switch, position switch etc.)
2. REED switch (electromagnetic switch)
Proximity Switch
1. Capacitive ( detect non metal object)
2. Inductive ( detect metal object)
3. Photo sensor (uses light to detect almost all types of
object)
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Sensor
II. Analog/continuous sensor
Detect variable physical events and convert it into a
corresponding proportional electrical signal. This sensors normally
requires a transmitter to amplify and condition the analog sensor
output to a level acceptable for transmission and detection of DI
module in either voltage (0 to 10Vdc) or currents (4-20 mA).
Level Sensor (ultrasonic, pressure, capacitive, mechanical)
Flow Sensor (ultrasonic, pressure , electromagnetic, etc)
Pressure Sensor ( Bourdon tube)
Temperature Sensor (RTD, Thermocouple)
Speed transmitter Sensor ( tachometer)
Force, torque, position sensor, etc.
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Output devices
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DI CPU DOSENSOR
ACTUATORS
MOTORS
ETC
PLC

Output devices
I. Digital/Logical controlled output devices
Digital controlled actuators
Convert command signal from DO module into mechanical
motion, which will either directly or indirectly control a
process.
Solenoid – electrical current to a limited linear motion
Solenoid valve – redirect flow of gas or fluids
Hydraulic controlled actuators – to control large and rigid
load at lower speed.
Pneumatic controlled actuators – to control small and not
stiff load at higher speed. Use combination of solenoid valve
and cylinders
Electrical (motor) controlled actuators
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Output devices
Digital controlled Motors
Receive command signal from PLC to start and stop. Low
current motors can be directly connected to PLC DO
module. However large and high current rated motor
requires a relay, contactor or motor control devices.
Below are some motor control devices typically use in
industry
DOL (Direct on line)
Soft starter
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Output devices
II. Continuous control output devices
Continuous controlled actuators
Allows the system output to be adjusted to pre determine
range of values.
Hydraulic controlled actuators with a positioner – to control
large and rigid load at lower speed.
Pneumatic controlled actuators with a positioner – to
control small and not stiff load at higher speed. Use
combination of solenoid valve and cylinders
Electrical (motor) controlled actuators with a positioner
Cylinder with a position feedback.
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Output devices
Continuous controlled motor
The motor can be controlled using additional motor
control devices such as VFD
VFD – Variable Frequency Drives, rotor speed will
vary in proportion to input signal from AO module.
Normally, AO output signal is 4 – 20 mA.
Configuration and parameterization are done in
VFD and SCADA. Settings in VFD and SCADA should
match to avoid any have a proper control.
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Interfacing of external device to
IO modules

Selection of Sensor
Voltage
Direct current (12-24, 10
-60 Vdc)
AC (24 Vac, 100-240Vac)
Direct current (5 Vdc)
Sensor
Relay type (Dc rating)
Relay type (Ac rating)
or mechanical switch
Transistor (TTL)
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Basic circuit of Digital Input
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Sinking and Sourcing
Sinking – if Active, the output will allow the current
to flow to a common reference voltage (-). This is
best selected when different voltage are supplied
Sourcing – if Active, the output will allow the
current from common source (+) through the
input/output devices and to the ground. This
method is best used when all devices uses single
supply voltage.
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Sourcing sensor and Sinking DI
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Sinking DI module
Sensor
Output
Circuit
Source (+)
PNP or Sourcing sensor
Provide a pathway to a Source (+)
To PLC Input

Sinking sensor and Sourcing DI
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Sourcing DI module
Sensor
Output
Circuit
From PLC Input
Common (-)
NPN or Sinking input sensor
Provide pathway to a common (-)

Interface b/n Sensor & DI module
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Conclusion (sensor/DI interconnection)
Sensor (transistor)
Sinking (NPN)
Sourcing(PNP)
Digital Input module
Sourcing (Common +)
Sinking (Common -)
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Sink/Source input
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Same concept is applicable to DO module
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Discrete Analog Inputs
Rectifier circuit is added to opto-
coupler circuit
AC input module requires longer
recognition time than DC input
module.
However AC signal are more
immune to noise than DC.
Suitable for long distances and
noisy environments.
Common
Input 0
Input 1
AC
Switch
Switch
P
L
C
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Analog Modulating Inputs
• For transmitter it can be,
– Analog Current (0/4 to
20 ma)
– Analog Voltage (0-
10VDC)
• You need power source to
power up the transmitters.
Common
Input 0
Input 1
24
VDC
P
L
C
Transmitter(+) (-)
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Discrete - Relay Outputs
A relay is non-polarized and typically it can
switch either AC or DC.
Here the common is connected to one
end of our power supply and the other
end of the supply is connected to the
load. The other half of our load gets
connected to the actual plc output you
have designated within your ladder
program.
When the program like ladder tells the
output to turn on, the plc will internally
apply a voltage to the relay coil. This
voltage will allow the proper contact to
close. When the contact closes, an
external current is allowed to flow
through our external circuit. When the
ladder tells the plc to turn off the output,
it will simply remove the voltage from the
internal circuit thereby enabling the
output contact to release.
Internal Circuit
Coil Coil Coil
Contact Contact Contact
COM COM0100 0101 0102
Etc,
Note:
0100, 0101, 0102 are output relay
designated in the program.
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Discrete -Transistor Outputs
• Transistor can only switch a dc
current. For this reason it cannot
be used with an AC voltage.
• Transistor are solid-state switch. A
small current applied to the
transistors "base" lets us switch a
much larger current through its
output.
• Transistor is fast, switches a small
current, has a long lifetime and
works with dc only.
Internal Circuit
Photo coupler
COM 0100
Etc.
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Analog Modulating Outputs
• For transmitter it can be,
– Analog Current (0/4 to
20 ma)
– Analog Voltage (0-
10VDC)
Common
Input 0
Input 1
P
L
C
Field
Devices
(+)
( - )
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How to set up your PLC
Choose a chassis.
Count the number of input (digital
or analog)
Count the number of output (digital
or analog)
From the number of I/O compute
for the power consumption and
select the correct power supply.
InputInputInput Output OutputChoose your processor
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Control Program

PLC program
The PLC hardware requires a PLC
program.
There are many types available in
building a program. Typical are as
follows,
– Ladder Logic
– Structured text
– Function block diagram
– SFC (Sequential Function Charts).
– Instruction list
Regardless of which method is chosen,
it will be executed by the PLC's CPU
module. The software can be written
and executed with the processor in an
online state or in the off-line state
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Sample Application
Here, we want the fill motor to pump
the fluid into the tank until the high
level sensor turns on. At that point we
want to turn off the motor until the
level falls below the low level sensor.
Then we should turn on the fill motor
and repeat the process.
Input (High Level)
Input
(Low Level)
Output (Motor)
Level
Controller
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Ladder program
Low
Level
High
Level Internal PLC Coil
Motor Contact
Internal PLC Relay
Internal PLC Relay
END
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Types of programming language

IEC 61131
IEC 61131 -1 Overview
IEC 61131 -2 Requirements and Test
procedures
IEC 61131 -3 Data Types and Programming
IEC 61131 -4 User Guidelines
IEC 61131 -5 Communications
IEC 61131 -7 Fuzzy Control
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IEC 61131 – 3 Programming Languages
Five standard programming languages
Ladder Logic (LD)
Structured text (ST)
Function block diagram (FBD)
Sequential Function Charts (SFC )
Instruction list (IL)
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Ladder Logic (LD)
Most widely used
Initially invented to replace hardwired relay
circuit
Graphical representation of control circuit
with a series of control inputs needing to
made true to activate one or more output.
Ideal for simple control circuit, but difficult to
implement for advance and complex control
system such as PID, mathematical calculation
and data analysis.
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Ladder Logic (LD)
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Functional Block Diagram
Second widely used programming language
Interconnection of functional block to
represent a graphical representation of the
control circuit.
Easier to follow process flow. Just follow the
path!
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Functional Block Diagram
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Structured Text (ST)
Similar to a high level computer programming
such as “C”.
Mobility from non-PLC programs
Highest rate of adoption
Ideal for more complex control circuit
requirements such as mathematical
calculations, data analysis, decision loops,
Faster execution time than LD,FBD and SFC.
Not maintenance friendly
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Structured Text (ST)
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Sequential Function charts (SFC)
Similar to computer flow charts
Consist of Step and transition
Starting point is the initial action box
Step or Action Box (equipment status
represented by a variable or a
code of any language)
Transition (input variables or conditions)
Easiest to implement
Maintenance friendly/Easy to trouble shoot
Slowest execution time
Not applicable to all applications
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Sequential Function charts (SFC)
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Instruction List (IL)
Text based non graphical
A low level language similar to assembler
language use microprocessor programming
Very step by step in layout and format
Can be move easily between hardware
platforms
Fastest execution time
Not maintenance friendly.
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Instruction List (IL)
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Sensor
PLC
Hardware – I/Os(DI, AI, DO, AO), CPU, Memory, PS
Operation – Scan input, execute program,self diagnostic and Scan
output
Control programs – As per IEC 611313 – 3 ( LD, FBD, ST, SFC and
IL)
Output devices
Interfacing of external devices
Source and sinking.
Sensor (sink) – DI (source), Sensor (Source) – DI (Sink)
Sensor (Either sink or source) – DI (sink and source)
Configuration in DO is the same if the output devices is transistorized
Internal switching component of IO module
Relay – for AC/DC
Transistor – for low rating DC and AC (with rectifier circuit0
TRIAC– higher rating AC DC
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Summary

Programming Language
IL – Mnemonic programming
ST – C or BASIC like programming
LD – Relay logic diagram based
FBD – Graphical data flow
programming method
SFC – Graphical method of
structuring programs
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Summary

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II - Introduction to
Ladder programming

Ladder Diagrams
Ladder Diagrams is the oldest programming language for PLC
based on relay intuition of electricians.
widely in use outside Europe.
not recommended for large new projects.
Consist of rung and rail
Rung 0
Rung 1
Rung 2
Input (contact) Output (Coils)
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Ladder Diagrams
The main Ladder Diagrams symbols represent the elements:
NO contact (input), %I
NC contact (input), %I
Coil (output), %Q
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Control Elements
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Operate block & Compare block
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Ladder Diagrams

Network by network based on the object links
from above and below.
Execution between networks shall be from top
to bottom except if it is influence by control
element.
Processing of network is ended before
processing begins on another network
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Execution sequence of Networks

Signal flow for Boolean link is:
Left to right for horizontal link
Top to Bottom for vertical link
Rung is one line from left rail (power) to right
rail (neutral).
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Signal flow within a Network

Link – Highest priority
Network by network
Rung by rung – Lowest priority
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Signal flow within a Network

Ladder Diagrams
01 02
50
01
02
03 50
03
relay coil
(bobine)
break contact
(contact repos)
make contact
(contact travail)
corresponding
ladder diagram
origin:
electrical
circuit
50 05
44
rung
"coil" 50 is used to move
other contact(s)
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Ladder Diagrams
Binary combinations are expressed by series and parallel relay contact:
+ 01 02
50
Coil 50 is active (current flows) when 01 is active and 02 is not.
01
02 50
Series
+ 01
40
02
Coil 40 is active (current flows) when 01 is active or 02 is not.
Parallel
Ladder Diagrams representation “logic" equivalent
01
02 40
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Ladder Diagrams
Ladder Diagrams diagram for a batch process: ﬁlling a container with a liquid,
mixing the liquid, and draining the container. The sequence of events is as follows:
1. ﬁll valve opens and lets the liquid into the container until it is full.
2. liquid in the container is mixed for 3 minutes.
3. a drain valve opens and drains the tank.
O = output
I = input
Address of variable
(module number,
port number)
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Ladder Diagrams (PLC termination)
Consider a PLC with one input module and one output module. Two external switches
(SW-0 & SW-1) are connected via terminal IN-0 and In-1 of input module. Two
terminals of the output module (OUT-0 & OUT-1) drive two indicator lamps (Lamp-0 &
Lamp-1).
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III - PLC programming
exercises using LD

Application # 1 – Detection of fallen bottle
Control philosophy Illustration
WGA_01312016 105
Condition: Fallen bottle will be
push to outside the conveyor
Input sensor: Capacitive sensor
“X0” & “X1”
Output device: Pneumatic
pushing pole “Y0”

Application # 2 – two location control
t 106
Input: S1 & S2
Output: L1
Condition_1: Lamp L1 will switch on
and off if either of switch S1 is
activated
Condition_2: Switch S1 and S2 are
replace with Push button switch.
L1
S2
S1

Application # 3 – Car entry/exit control
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Input: Sensor I1 and I2
Output: “GO signal light” Q1 ,
“STOP signal light” Q2 and stopper
Q3
Condition_1: Initially stop is active.
Stop light is off, Go light is on and
Stopper will go up if I1 is active
Condition_2: Stop light is on, Go
light will off and stopper will move
down if I1 and I2 is not active.

Application # 4 – Latching circuit
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Input: Push button I1(start), I2(stop)
and I3(test)
Output: Ceiling fan Q1
Condition: Push Start button to
activate ceiling fan, and push stop
button to stop. Push test button to
test temporary activate fan.

Application # 5 – Latching circuit (set/reset function)
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Input: Push button I1(start), I2(stop)
and I3(test)
Output: Ceiling fan Q1
Condition: Use set reset function

Application # 6 - Forward/reverse motor control
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Application # 6 - Forward/reverse motor control
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Input: Push buttons FWD,REV,STOP
Output: Forward contactor M1,
Reverse contactor M2. Safety
interlock “overload protection” OL
Condition: Press PB_Fwd to operate
motor Forward,PB_Rev for Reverse.
PB_Stop to stop. Motor stop if OL
circuit is activated.

Application # 7 – Sequential start
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Providing lube for the gear box
the lathe spindle starts to run. Oil
pump starts first before main
pump can be starts

Application # 8 – Level and pressure control
Control philosophy
Inputs: 1 pressure switch
3 level sensor
Output: Pump “M1” and
Solenoid valve “K”
Condition 1: Pump will run according
discharge pressure set point in the
pressure tank. Incorporate a delay 20
sec prior to stopping
Condition 2: Refilling through
solenoid valve “K” will be controlled
by float switch “S2” and “ S3”
Condition 2: Pump “M1” will stop
when a level is near the pipe suction
elevation. (Dry run protection).
Illustration
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Application # 9 – Entry/exit control for underground
car park (for attendees)
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Application # 11 – Participant request
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Basics of Structured
Programming

IF function (Logical branching)
Syntax
If ….. End_if
If ….. Else….. End_if
If ….. Elseif ….. End_if
Flow chart
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TIMER:=%S6; (* System bit, time base, 1 sec*)
COUNTER := 0;
IF TIMER THEN
IF COUNTER = 0 THEN
COUNTER_SEC:=COUNTER_SEC+1;
END_IF;
COUNTER:= COUNTER + 1;
ELSE
COUNTER:=0;
END_IF;
IF COUNTER_SEC >= 61 THEN
COUNTER_MIN:= COUNTER_MIN+1;
COUNTER_SEC:=1;
END_IF;
IF COUNTER_MIN >= 60 THEN
COUNTER_HOUR:= COUNTER_HOUR+1;
COUNTER_MIN:=0;
END_IF;
IF COUNTER_HOUR >23 THEN
COUNTER_HOUR:=0;
END_IF;

Syntax
Case ….. Of
Else …… End_Case
CASE SELECT OF
1: C := B + A;
2,3: C := B - A;
5..10: C := C;
ELSE
• C:= B*A;
END_CASE;
Flow chart
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Case function (multiple Branching)

While Function (Looping)
Syntax
WHILE ….. DO
END_WHILE;
PEOPLE:= 0
WHILE PEOPLE<1 DO
COUNTER:=COUNTER+1;
END_WHILE;
Note: test condition then
execute
Flow chart
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Syntax
REPEAT
UNTIL ……
END_REPEAT;
G:=1;
REPEAT
G:=G+1;
UNTIL G>100
END_REPEAT ;
Note: execute then test
condition
Flow chart
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Repeat function (Looping)

For function (Looping)
Syntax
FOR A TO B BY C DO
END_FOR;
FOR I:= 2 TO 3 BY 1 DO
D:=D+1;
END_FOR;
Flow chart
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Basic of Sequential
function Chart

Simple Sequence
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Divergence of a Selective Sequence
WGA_PLC_02092016
ONLY ONE PATH
IS ALLOWED

Convergence of a Selective Sequence
WGA_PLC_02092016
ONLY ONE PATH
IS ALLOWED

Divergence of a Simultaneous Sequence
WGA_PLC_02092016
BOTH STEP WILL BE
ACTIVATED

Convergence of a Simultaneous Sequence
WGA_PLC_02092016
BOTH STEP SHOULD
BE ACTIVE

Application # 12 – SFC
WGA_PLC_02092016

Control Parameters
Control Inputs
Sample detection
sensor
Automatic PB
Stop PB
Reset PB
Lower limit switch
Upper limit switch
Output
Solenoid valve for Piston up
Solenoid valve for
Piston down
Auto mode indicator LED
Sample part holder
WGA_PLC_02092016

Salamat sa Pagdalo!
WGA_PLC_02092016

Plc 101

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Plc 101