3. What is Relay ?
• Relays are essential for automation systems and for controlling loads.
•A relay is an electromagnetic switch operated by a relatively small electric current that can
turn
on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire
that becomes a temporary magnet when electricity flows through it).
• Also, relays are the best way for insulation between high and low voltage portions
of a circuit.
• There are hundreds of different relay types .
6. Relay Operation
• The input circuit is switched off and no
current flows through it until something
(either a sensor or a switch closing) turns it
on. The output circuit is also switched off.
• When a small current flows in the input
circuit, it activates the electromagnet , which
produces a magnetic field all around it.
• The energized electromagnet pulls the metal
bar in the output circuit toward it, closing the
switch and allowing a much bigger current to
flow through the output circuit.
• The output circuit operates a high-current
appliance such as a lamp or an electric
7.
8.
9. Excercise On Relays
1. Make a relay circuit to
switch on the lamp when
the push button is pressed
and lamp is off when push
button is released.
13. What is Contactor ?
• A contactor is also a type of relay.
Features of Contactors :
• A contactor is a relay that is used for switching power.
• They usually handle very heavy loads like an electric motor, lighting
and heating equipments and so on.
• Though their output is used for switching very high loads, they are
controlled by a circuit with very less power.
• According to the loads they handle, they vary in sizes from a small
device to as huge as a yard.
• Though they are used for switching purposes, they do not interrupt a
short-circuit current like a circuit breaker.
• They have ratings ranging from a breaking current of a few amperes
14. When a relay is used to switch a large amount of electrical power
through its contacts, it is designated by a special name: contactor.
What is Contactor ?
15. Design and Construction
Like a relay, a contactor also has
1. Coil
2. Spring
3. Armature
4. Moving contact
• The contact part of the contactor includes the power contacts as
well as the auxiliary contacts. The power contacts gains the power
for the contactor and the auxiliary contacts is used to bring a loop
with the rest of the rest of the devices it is attached to. These
contacts are connected to the contact springs.
16.
17.
18.
19. •A PLC is a digital computer used for automation of industrial processes, like controlling machinery or
factory assembly lines.
High temperature ranges,
• The main difference from other computers is that
•PLCs operate in industrial environments (dust, moisture, heat, cold,
electrical noise,vibration )
•Have multiple input/output (I/O) terminals.
•I/O terminals connect the PLC to sensors and actuators. PLCs outputs operate electric motors,
pneumatic or hydraulic cylinders, relays or solenoids, and analog outputs.
WHAT IS A PLC ?
20. History Of PLC ?
GM needed the flexibility of “solid state”; a controller that
could be programmed and maintained by plant engineers;
and was rugged enough to withstand the factory
environment and provided easy troubleshooting...
employee of Bedford
Richard E. Morley, an
Associates (Bedford, MA ) involved in the
automotive industry, proposed something called
a Modular Digital Controller (MODICON) to a
major US car manufacturer.
22. Evolution Of PLC ?
• PLCs were invented as replacements for automated systems that would use
hundreds or thousands of relays, cam timers, and drum sequencers.
•Often, a single PLC can be programmed to replace thousands of relays.
• First Programmable Logic Controllers were designed and developed
by Modicon as a relay replacer for GM .
• 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
which was designed by Michael Greenberg.
23. What is a PLC?
Inputs Outputs
The Basic Block
CPU
A PROGRAMMABLE LOGIC CONTROLLER is a solid state control system that
continuously monitors the status of devices connected as inputs. Based upon a
user written program, stored in memory, it controls the status of devices
connected as outputs.
24. 24
Major Components of a Common PLC
PROCESSOR
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,
etc.
To
OUTPUT
Solenoids,
contactors,
alarms
etc.
25. Advantages of PLCs
• Less wiring.
• Wiring between devices and relay contacts are
done in the PLC program.
• Easier and faster to make changes.
• Trouble shooting aids make programming
easier and reduce downtime.
• Reliable components make these likely to operate
for years before failure.
26.
27. Inside a PLC
The CPU contains an “Executive” program that tells the PLC
how to:
• Execute the control Instructions
• User’s Program
• Communicate with other devices
• Other PLCs, Programming devices, I/O devices, etc.
• Perform Housekeeping activities
• Diagnostics, etc
This program is stored in “nonvolatile” memory
• Meaning that the program will not be lost if power is removed
28. 2
8
I/O Module
•The I/O interface section of a PLC connects it to external field
devices.
•The main purpose of the I/O interface is to condition the various
signals received from or sent to the external input and output
devices.
•Input modules converts signals from discrete or analog input
devices to logic levels acceptable to PLC’s processor.
•Output modules converts signal from the processor to levels
capable of driving the connected discrete or analog
output devices.
29. 29
I/O Circuits
Discrete Inputs
Circuits of this type are used to sense the status of limit switches, push buttons, and
other discrete sensors. Noise suppression is of great importance in preventing false
indication of inputs turning on or off because of noise.
Analog I/O
Circuits of this type sense or drive analog signals.
Analog inputs come from devices, such as thermocouples, strain gages, or pressure
sensors, that provide a signal voltage or current that is derived from the process variable.
Standard Analog Input signals: 4-20mA; 0-10V
Analog outputs can be used to drive devices such as voltmeters, X-Y recorders,
servomotor drives, and valves through the use of transducers.
Standard Analog Output signals: 4-20mA; 0-5V; 0-10V
30. 30
Discrete Input
A discrete input also referred as digital input is an input that is either ON or OFF are
connected to the PLC digital input. In the ON condition it is referred to as logic 1 or a
logic high and in the OFF condition maybe referred to as logic o or logic low.
Normally Open
Pushbutton
Normally Closed
Pushbutton
Normally Open switch
Normally Closed switch
Normally Open contact
Normally closed contact
32. 32
OUT
PLC
Lamp
Digital
Output
Module
A discrete output is either in an ON or OFF condition. Solenoids,
contactors coils, lamps are example of devices connected to the
Discrete or digital outputs. Below, the lamp can be turned ON or OFF
by the PLC output it is connected to.
Digital Output
33. 33
IN
PLC
Analog
Input
Module
Tank
Level Transmitter
An analog input is an input signal that has a continuous signal. Typical
inputs may vary from 0 to 20mA, 4 to 20mA or 0 to10V. Below, a level
transmitter monitors the level of liquid in the tank. Depending on the
level Tx, the signal to the PLC can either increase or decrease as the
level increases or decreases.
Analog Input
34. 34
An analog output is an output signal that has a
continuous signal. Typical outputs may vary from 0 to
20mA, 4 to 20mA or 0 to10V.
Analog Output
PLC
Analog
Output
Module
E
P
Pneumatic control valve
Supply air
Electric to pneumatic transducer
OUT
0 to 10V
36. 36
I/O Module
DC INPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
Prevent voltage
transients from
damaging the
processor.
Helps reduce the
effects of electrical
noise
Current
Limiting
Resistor
FROM INPUT
DEVICE
USE TO DROP
THE VOLTAGE
TO LOGIC LEVEL
Buffer, Filter,
hysteresis
Circuits TO
PROCESSOR
38. What is the difference between PNP and NPN when describing 3 wire
connection of a sensor?
• Most industrial proximity sensors (inductive, capacitive, ultrasonic and photo
electric) are solid state.
• The term solid state refers to the type of components used within the sensor.
Solid state electronic components such as transistors are used to switch the
output of the sensor upon detection of an object.
• Two specific types of 3 wire sensors are available; PNP and NPN. The difference
is a result of the internal circuit design and type of transistors used.
• A key point to observe is that PNP and NPN has nothing to do with whether the
sensor is normally open (N/O) or normally closed (N/C), i.e. a PNP sensor may be
either N/O or N/C as can an NPN be either N/O or N/C.
39. Why two types?
• The selection of a PNP sensor verses an NPN sensor is determined by the nature
of the circuit the device is to be used in.
• When used in a traditional relay type control circuit, it is normally possible to use
either the PNP or the NPN type of sensor as shown below.
• PNP sensors tend to be more commonly used.
Traditional relay type control circuit
40. Using PNP / NPN Sensors with PLC
When selecting a sensor to be used with a PLC, it is very important that the sensor
matches the type of PLC input card to be used.
•
• Two types of input cards exist, those that 'sink' current (also known as positive
logic) and those that 'source' current (also known as negative logic).
• It is therefore important to identify the type of sensor to be used with the PLC card
based on the PLC manufacturer's documentation and / or wiring diagrams.
41. • “Sinking (NPN) provides a path to 0 VDC (-DC)
“Sourcing (PNP) provides a path to +24 VDC (+DC)
42. 42
I/O Module
AC INPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
Prevent voltage
transients from
damaging the
processor.
Helps reduce the
effects of electrical
noise
Rectifier,
Resistor
Network
FROMINPUT
DEVICE
CONVERTS THE AC INPUT
TO DC AND DROPS THE
VOLTAGE TO LOGIC LEVEL
Buffer,
Filter,
Hysteresis
Circuits
TO
PROCESSOR
43. What are Inputs?
DIGITAL :
•Switches and Pushbuttons
• Sensing Devices
• Limit Switches
• Photoelectric Sensors
• Proximity Sensors
• Condition Sensors
• Pressure Switches
• Level Switches
• Temperature Switches
•Encoders
ANALOG:
• RTDs
•Thermo couple
45. Output MoT
d
er
u
mi
ln
e
al
s
block -
From
PLC
this is where wires
from the field
devices are
connected
Field device
-Motor starter,
controlling an
AC motor.
2
3
4
5
6
7
8
9
10
COM
D/A
Conversion
Output
Module
1
46. OUTPUT MODULES ARE OF THREE TYPE
(1)Relay Type (AC or DC load)
(2)DC Type or Transistor Type or Mosfet Type
(3)Triac Type (only ac load)
47. 47
I/O Module
DC / AC OUTPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
Prevent voltage
transients from
damaging the
processor.
Helps reduce the
effects of electrical
noise
FROM
PROCESSOR
TTL
Circuits
Amplifier
RELAY
TRIAC
X’SISTOR
TO
OUTPUT
DEVICE
50. What are Outputs?
• Valves
• Motor Starters
• Solenoids
• Actuators
• Control Relays
• Horns & Alarms
• Stack Lights
• Fans
• Counter/Totalizer
• Pumps
• Printers
51. MODULAR & STAND ALONE PLCs
MODULAR PLC :
CPU , Inputs , Outputs , Network
Adapters are available as
separate modules that fits into
the chassis slots.
Stand Alone PLC :
CPU , Inputs & Outputs points
are available in a single package.
Has fixed no. of I/Os
52. The backplane provides a communication path between the I/O
modules and either the processor module or the I/O adapter module.
53. Each module plugs
into the one to the
left
Connections for the
built in I/O
Slide modules into
available slots
Example of a modular
based PLC. The PLC slides
into the chassis along with
other modules
Example of a PLC that plugs
into adjacent modules to
form a backplane with no
chassis required
Example of a PLC with the
modules built in. Comes as
one block
55. 5
5
PLC Size
1. SMALL -it covers units with up to 128 I/O’s and
memories up to 2 Kbytes.
- these PLC’s are capable of providing simple to
advance levels or machine controls.
2. MEDIUM - have up to 2048 I/O’s and memories up
to 32 Kbytes.
3. LARGE - the most sophisticated units of the PLC family.
They have up to 8192 I/O’s and memories up to
750 Kbytes.
- can control individual production processes or
entire plant.
56. Allen Bradley USA
Siemens Germany
Modicon
Mitshubishi
France
Japan
GE Fanuc USA
Omron Japan
Various Brands of PLCs
57. Selecting a PLC
Criteria
• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Software
61. PLC APPLICATIONS
• Packaging
• Bottling & Canning
• Material Handling
• Machining
• Power Generation
• HVAC/ Building Automation
• Security Systems
• Automated Assembly
• Paint Lines
• Water treatment
Plastics
INDUSTRY
Cement
Metals
Automobile
Paper
Chemicals
F&B
…. Any application in any industry that requires electrical control
