Industrial Automation
Content
Report on “Industrial Automation”
Submitted in partial fulfillment of the Requirement for the
degree of
Bachelor of Technology
in
Electronics and Communication Engineering
Submitted By:
Siddharth Garg
(ECE,7th Sem,3147)
Session 2009-2013
Department of Electronics and Communication Engineering
Delhi Institute of Technology and Management, Sonepat
Affiliated to Deenbandhu Chhotu Ram University of
Science and Technology, Murthal (Haryana).
Table of Content
1
S.No
Particulars
Page No.
1.
Introduction
4
2.
SCADA
9
3.
Programmable logic controller PLC
18
4.
Drives
24
5.
Conclusion
35
2
CHAPTER – 1
INTRODUCTION
Industrial automation or numerical control is the use of control systems such as
computers to control industrial machinery and processes, reducing the need for human
intervention. In the scope of industrialization, automation is a step beyond
mechanization. Whereas mechanization provided human operators with machinery to
assist them with the physical requirements of work, automation greatly reduces the
need for human sensory and mental requirements as well. Processes and systems can
also be automated.
Automation plays an increasingly important role in the global economy and in daily
experience. Engineers strive to combine automated devices with mathematical and
organizational tools to create complex systems for a rapidly expanding range of
applications and human activities.Many roles for humans in industrial processes
presently lie beyond the scope of automation. Human-level pattern recognition,
language recognition, and language production ability are well beyond the capabilities
of modern mechanical and computer systems. Tasks requiring subjective assessment or
synthesis of complex sensory data, such as scents and sounds, as well as high-level tasks
such as strategic planning, currently require human expertise. In many cases, the use of
humans is more cost-effective than mechanical approaches even where automation of
industrial tasks is possible.
1.1
For the purpose of AUTOMATION Specialised hardened computers, referred to as
programmable logic controllers (PLCs), are frequently used to synchronize the flow of
3
inputs from (physical) sensors and events with the flow of outputs to actuators and
events. This leads to precisely controlled actions that permit a tight control of almost
any industrial process. Human-machine interfaces (HMI) or computer human interfaces
(CHI), formerly known as man-machine interface, are usually employed to
communicate with PLCs and other computers, such as entering and monitoring
temperatures or pressures for further automated control or emergency response. Service
personnel who monitor and control these interfaces are often referred to as stationary
engineers.
1.2
Automation has had a notable impact in a wide range of highly visible industries
beyond manufacturing. Once-ubiquitous telephone operators have been replaced largely
by automated telephone switchboards and answering machines. Medical processes such
as primary screening in electrocardiography or radiography and laboratory analysis of
human genes, sera, cells, and tissues are carried out at much greater speed and accuracy
by automated systems. Automated teller machines have reduced the need for bank visits
to obtain cash and carry out transactions. In general, automation has been responsible
for the shift in the world economy from agrarian to industrial in the 19th century and
from industrial to services in the 20th century.
1.3 The widespread impact of industrial automation raises social issues, among them its
impact on employment. Historical concerns about the effects of automation date back to
the beginning of the industrial revolution, when a social movement of English textile
machine operators in the early 1800s known as the Luddites protested against Jacquard's
automated weaving looms— often by destroying such textile machines— that they felt
threatened their jobs. One author made the following case. When automation was first
4
introduced, it caused widespread fear. It was thought that the displacement of human
operators by computerized systems would lead to severe unemployment.
1.4 Currently, for manufacturing companies, the purpose of automation has shifted
from increasing productivity and reducing costs, to broader issues, such as increasing
quality and flexibility in the manufacturing process.The old focus on using automation
simply to increase productivity and reduce costs was seen to be short-sighted, because it
is also necessary to provide a skilled workforce who can make repairs and manage the
machinery. Moreover, the initial costs of automation were high and often could not be
recovered by the time entirely new manufacturing processes replaced the old. (Japan's
"robot junkyards" were once world famous in the manufacturing industry.)
1.5 Automation is now often applied primarily to increase quality in the manufacturing
process, where automation can increase quality substantially. For example, automobile
and truck pistons used to be installed into engines manually. This is rapidly being
transitioned to automated machine installation, because the error rate for manual
installment was around 1-1.5%, but has been reduced to 0.00001% with automation.
Hazardous operations, such as oil refining, the manufacturing of industrial chemicals,
and all forms of metal working, were always early contenders for automation.
1.6
Another major shift in automation is the increased emphasis on flexibility and
convertibility in the manufacturing process. Manufacturers are increasingly demanding
the ability to easily switch from manufacturing Product A to manufacturing Product B
without having to completely rebuild the production lines. Flexibility and distributed
processes have led to the introduction of Automated Guided Vehicles with Natural
Features Navigation.
5
1.7 The widespread impact of industrial automation raises social issues, among them
its impact on employment. Historical concerns about the effects of automation date back
to the beginning of the industrial revolution, when a social movement of English textile
machine operators in the early 1800s known as the Luddites protested against Jacquard's
automated weaving looms often by destroying such textile machines— that they felt
threatened their jobs. One author made the following case. When automation was first
introduced, it caused widespread fear. It was thought that the displacement of human
operators by computerized systems would lead to severe unemployment.
1.8
At first glance, automation might appear to devalue labor through its replacement
with less-expensive machines; however, the overall effect of this on the workforce as a
whole remains unclear. Today automation of the workforce is quite advanced, and
continues to advance increasingly more rapidly throughout the world and is encroaching
on ever more skilled jobs, yet during the same period the general well-being and quality
of life of most people in the world (where political factors have not muddied the picture)
have improved dramatically. What role automation has played in these changes has not
been well studied. Currently, for manufacturing companies, the purpose of automation
has shifted from increasing productivity and reducing costs, to broader issues, such as
increasing quality and flexibility in the manufacturing process. Different types of
automation tools exist
6
Block Diagram Of Industrial Automation
SCADA System
with HMI
Screens
Programmable
Logic Controller
Field Equipments
and Machineries
AC OR DC
Drives
Sensors
Auxiliaries
MAIN BODY OF AUTOMATION
SCADA - Supervisory Control and Data Acquisition
PLC - Programmable Logic Controller
DRIVES - Variable Speed Drives
SENSORS – Transducers, Feedback equipments.
AUXILIARIES – Converters, Power Supplies, Different Communication
mediums etc.
7
CHAPTER – 2
SCADA
SCADA stands for “Supervisory Control And Data Acquisition.” It generally refers to
an industrial control system: a computer system monitoring and controlling a process.
The process can be industrial, infrastructure or facility based as described
below:Industrial processes include those of manufacturing, production, power
generation, fabrication, and refining, and may run in continuous, batch, repetitive, or
discrete modes. Infrastructure processes may be public or private, and include water
treatment and distribution, wastewater collection and treatment, oil and gas pipelines,
electrical power transmission and distribution, and large communication systems.
Facility processes occur both in public facilities and private ones, including buildings,
airports, ships, and space stations. They monitor and control HVAC, access, and energy
consumption.
2.1 A SCADA System usually consists of the following subsystems:
a) A Human-Machine Interface or HMI is the apparatus which presents process data
to a human operator, and through this, the human operator, monitors and controls the
process.
b) A supervisory (computer) system, gathering (acquiring) data on the process and
sending commands (control) to the process.
8
c) Remote Terminal Units (RTUs) connecting to sensors in the process, converting
sensor signals to digital data and sending digital data to the supervisory system.
d) Programmable Logic Controller (PLCs) used as field devices because they are
more economical, versatile, flexible, and configurable than special-purpose RTUs.
e) Communication infrastructure connecting the supervisory system to the Remote
Terminal Units
There is, in several industries, considerable confusion over the differences between
SCADA systems and Distributed control systems (DCS). Generally speaking, a SCADA
system usually refers to a system that coordinates, but does not control processes in
real time. The discussion on real-time control is muddied somewhat by newer
telecommunications
technology,
enabling
reliable,
low
latency,
high
speed
communications over wide areas. Most differences between SCADA and Distributed
control system DCS are culturally determined and can usually be ignored. As
communication infrastructures with higher capacity become available, the difference
between SCADA and DCS will fade.
The term SCADA usually refers to centralized systems which monitor and control entire
sites, or complexes of systems spread out over large areas (anything between an
industrial plant and a country). Most control actions are performed automatically by
remote terminal units ("RTUs") or by programmable logic controllers ("PLCs"). Host
control functions are usually restricted to basic overriding or supervisory level
intervention. For example, a PLC may control the flow of cooling water through part of
an industrial process, but the SCADA system may allow operators to change the set
points for the flow, and enable alarm conditions, such as loss of flow and high
temperature, to be displayed and recorded. The feedback control loop passes through the
RTU or PLC, while the SCADA system monitors the overall performance of the loop.
9
Data acquisition begins at the RTU or PLC level and includes meter readings and
equipment status reports that are communicated to SCADA as required. Data is then
compiled and formatted in such a way that a control room operator using the HMI can
make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may
also be fed to a Historian, often built on a commodity Database Management System, to
allow trending and other analytical auditing.
2.1.1 Human Machine Interface:
A Human-Machine Interface or HMI is the apparatus which presents process data to a
human operator, and through which the human operator controls the process.
An HMI is usually linked to the SCADA system's databases and software programs, to
provide trending, diagnostic data, and management information such as scheduled
maintenance procedures, logistic information, detailed schematics for a particular sensor
or machine, and expert-system troubleshooting guides.
The HMI system usually presents the information to the operating personnel
graphically, in the form of a mimic diagram. This means that the operator can see a
schematic representation of the plant being controlled. For example, a picture of a pump
connected to a pipe can show the operator that the pump is running and how much fluid
it is pumping through the pipe at the moment. The operator can then switch the pump
off. The HMI software will show the flow rate of the fluid in the pipe decrease in real
time. Mimic diagrams may consist of line graphics and schematic symbols to represent
process elements, or may consist of digital photographs of the process equipment
overlain with animated symbols.
10
The HMI package for the SCADA system typically includes a drawing program that the
operators or system maintenance personnel use to change the way these points are
represented in the interface. These representations can be as simple as an on-screen
traffic light, which represents the state of an actual traffic light in the field, or as
complex as a multi-projector display representing the position of all of the elevators in a
skyscraper or all of the trains on a railway.
An important part of most SCADA implementations are alarms. An alarm is a digital
status point that has either the value NORMAL or ALARM. Alarms can be created in
such a way that when their requirements are met, they are activated. An example of an
alarm is the "fuel tank empty" light in a car. The SCADA operator's attention is drawn to
the part of the system requiring attention by the alarm. Emails and text messages are
often sent along with an alarm activation alerting managers along with the SCADA
operator.
2.1.2 Hardware solutions:
SCADA solutions often have Distributed Control System (DCS) components. Use of
"smart" RTUs or PLCs, which are capable of autonomously executing simple logic
processes without involving the master computer, is increasing. A functional block
programming language, IEC 61131-3 (Ladder Logic), is frequently used to create
programs which run on these RTUs and PLCs. Unlike a procedural language such as the
C programming language or FORTRAN, IEC 61131-3 has minimal training
requirements by virtue of resembling historic physical control arrays. This allows
SCADA system engineers to perform both the design and implementation of a program
to be executed on an RTU or PLC. Since about 1998, virtually all major PLC
manufacturers have offered integrated HMI/SCADA systems, many of them using open
11
and non-proprietary communications protocols. Numerous specialized third-party
HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also
entered the market, allowing mechanical engineers, electrical engineers and technicians
to configure HMIs themselves, without the need for a custom-made program written by
a software developer.
2.2 Around the world, SCADA systems control:
Electric power generation, transmission and distribution: Electric utilities use
SCADA systems to detect current flow and line voltage, to monitor the operation of
circuit breakers, and to take sections of the power grid online or offline.
Water and sewage: State and municipal water utilities use SCADA to monitor and
regulate water flow, reservoir levels, pipe pressure and other factors.
Buildings, facilities and environments: Facility managers use SCADA to control
HVAC, refrigeration units, lighting and entry systems.
Manufacturing: SCADA systems manage parts inventories for just-in-time
manufacturing, regulate industrial automation and robots, and monitor process and
quality control.
Mass transit: Transit authorities use SCADA to regulate electricity to subways,
trams and trolley buses; to automate traffic signals for rail systems; to track and locate
trains and buses; and to control railroad crossing gates.
Traffic signals: SCADA regulates traffic lights, controls traffic flow and detects out-
of-order signals.
12
2.3 Importance of SCADA:
Maybe you work in one of the fields I listed; maybe you don’t. But think about your
operations and all the parameters that affect your bottom-line results:
Does your equipment need an uninterrupted power supply and/or a controlled
temperature and humidity environment?
Do you need to know — in real time — the status of many different components and
devices in a large complex system?
Do you need to measure how changing inputs affect the output of your operations?
What equipment do you need to control, in real time, from a distance?
Where are you lacking accurate, real-time data about key processes that affect your
operations?
Real-Time Monitoring and Control Increases Efficiency and Maximizes
Profitability
2.4 A SCADA system performs four functions:
1.
Data acquisition
2.
Networked data communication
3.
Data presentation
4.
Control
2.4.1 Data Acquisition:
13
First, the systems you need to monitor are much more complex than just one machine
with one output. So a real-life SCADA system needs to monitor hundreds or thousands
of sensors. Some sensors measure inputs into the system (for example, water flowing
into a reservoir), and some sensors measure outputs (like valve pressure as water is
released from the reservoir).
Some of those sensors measure simple events that can be detected by a straightforward
on/off switch, called a discrete input (or digital input). For example, in our simple model
of the widget fabricator, the switch that turns on the light would be a discrete input. In
real life, discrete inputs are used to measure simple states, like whether equipment is on
or off, or tripwire alarms, like a power failure at a critical facility.
Some sensors measure more complex situations where exact measurement is important.
These are analog sensors, which can detect continuous changes in a voltage or current
input. Analog sensors are used to track fluid levels in tanks, voltage levels in batteries,
temperature and other factors that can be measured in a continuous range of input.
For most analog factors, there is a normal range defined by a bottom and top level. For
example, you may want the temperature in a server room to stay between 60 and 85
degrees Fahrenheit. If the temperature goes above or below this range, it will trigger a
threshold alarm. In more advanced systems, there are four threshold alarms for analog
sensors, defining Major Under, Minor Under, Minor Over and Major Over alarms.
2.4.2 Data Communication:
In our simple model of the widget fabricator, the “network” is just the wire leading from
the switch to the panel light. In real life, you want to be able to monitor multiple
14
systems from a central location, so you need a communications network to transport all
the data collected from your sensors.
Early SCADA networks communicated over radio, modem or dedicated serial lines.
Today the trend is to put SCADA data on Ethernet and IP over SONET. For security
reasons, SCADA data should be kept on closed LAN/WANs without exposing sensitive
data to the open Internet.
Real SCADA systems don’t communicate with just simple electrical signals, either.
SCADA data is encoded in protocol format. Older SCADA systems depended on closed
proprietary protocols, but today the trend is to open, standard protocols and protocol
mediation.
Sensors and control relays are very simple electric devices that can’t generate or
interpret protocol communication on their own. Therefore the remote telemetry unit
(RTU) is needed to provide an interface between the sensors and the SCADA network.
The RTU encodes sensor inputs into protocol format and forwards them to the SCADA
master; in turn, the RTU receives control commands in protocol format from the master
and transmits electrical signals to the appropriate control relays.
2.4.3 Data Presentation:
The only display element in our model SCADA system is the light that comes on when
the switch is activated. This obviously won’t do on a large scale — you can’t track a
light board of a thousand separate lights, and you don’t want to pay someone simply to
watch a light board, either.
15
A real SCADA system reports to human operators over a specialized computer that is
variously called a master station, an HMI (Human-Machine Interface) or an HCI
(Human-Computer Interface).
The SCADA master station has several different functions. The master continuously
monitors all sensors and alerts the operator when there is an “alarm” — that is, when a
control factor is operating outside what is defined as its normal operation. The master
presents a comprehensive view of the entire managed system, and presents more detail
in response to user requests. The master also performs data processing on information
gathered from sensors — it maintains report logs and summarizes historical trends.
An advanced SCADA master can add a great deal of intelligence and automation to
your systems management, making your job much easier.
2.4.4 Control:
Unfortunately, our miniature SCADA system monitoring the widget fabricator doesn’t
include any control elements. So let’s add one. Let’s say the human operator also has a
button on his control panel. When he presses the button, it activates a switch on the
widget fabricator that brings more widget parts into the fabricator.
Now let’s add the full computerized control of a SCADA master unit that controls the
entire factory. You now have a control system that responds to inputs elsewhere in the
system. If the machines that make widget parts break down, you can slow down or stop
the widget fabricator. If the part fabricators are running efficiently, you can speed up the
widget fabricator.
16
If you have a sufficiently sophisticated master unit, these controls can run completely
automatically, without the need for human intervention. Of course, you can still
manually override the automatic controls from the master station.
CHAPTER – 3
PROGRAMMABLE LOGIC CONTROLLERS
Programmable Logic Controllers (PLCs), also referred to as programmable controllers,
are in the computer family. They are used in commercial and industrial applications. A
PLC monitors inputs, makes decisions based on its program, and controls outputs to
automate a process or machine. This course is meant to supply you with basic
information on the functions and configurations of PLCs.
Drive
Motors
Photo
Sensor
s
Pumps
Other
equipments
PLC
Start
Push
Button
s
Lights
17
3.1 Basic PLC Operation :
PLCs consist of input modules or points, a Central Processing Unit (CPU), and output
modules or points. An input accepts a variety of digital or analog signals from various
field devices (sensors) and converts them into a logic signal that can be used by the
CPU. The CPU makes decisions and executes control instructions based on program
instructions in memory. Output modules convert control instructions from the CPU into
a digital or analog signal that can be used to control various field devices (actuators). A
programming device is used to input the desired instructions. These instructions
determine what the PLC will do for a specific input. An operator interface device allows
process information to be displayed and new control parameters to be entered.
Input
Module
CPU
Central
processing unit
Programming
Device
Output
Module
Operator
Interface
Pushbuttons (sensors), in this simple example, connected to PLC inputs, can be used to
start and stop a motor connected to a PLC through a motor starter (actuator). Prior to
PLCs, many of these control tasks were solved with contactor or relay controls. This is
often referred to as hardwired control. Circuit diagrams had to be designed, electrical
18
components specified and installed, and wiring lists created. Electricians would then
wire the components necessary to perform a specific task. If an error was made, the
wires had to be reconnected correctly. A change in function or system expansion
required extensive component changes and rewiring.
3.2 Advantages of PLCs :
The same, as well as more complex tasks, can be done with a PLC. Wiring between
devices and relay contacts is done in the PLC program. Hard-wiring, though still
required to connect field devices, is less intensive. Modifying the application and
correcting errors are easier to handle. It is easier to create and change a program in a
PLC than it is to wire and re-wire a circuit.
Following are just a few of the advantages of PLCs:
• Smaller physical size than hard-wire solutions.
• Easier and faster to make changes.
• PLCs have integrated diagnostics and override functions.
• Diagnostics are centrally available.
• Applications can be immediately documented.
3.3 Logic 0, Logic 1:
Programmable controllers can only understand a signal that is On or Off (present or not
present). The binary system is a system in which there are only two numbers, 1 and 0.
Binary 1 indicates that a signal is present, or the switch is On. Binary 0 indicates that the
signal is not present, or the switch is Off.
The language of PLCs consists of a commonly used set of terms; many of which are
unique to PLCs.
19
3.4 In order to understand the ideas and concepts of PLCs, an understanding of these
terms is necessary.
3.4.1 Sensor :A sensor is a device that converts a physical condition into an electrical
signal for use by the PLC. Sensors are connected to the input of a PLC. A pushbutton is
one example of a sensor that is connected to the PLC input. An electrical signal is sent
from the pushbutton to the PLC indicating the condition (open/ closed) of the
pushbutton contacts.
3.4.2 Actuators: Actuators convert an electrical signal from the PLC into a physical
condition. Actuators are connected to the PLC output. A motor starter is one example of
an actuator that is connected to the PLC output. Depending on the output PLC signal the
motor starter will either start or stop the motor.
3.4.3 Discrete Input: A discrete input, also referred to as a digital input, is an input
that is either in an ON or OFF condition. Pushbuttons, toggle switches, limit switches,
proximity switches, and contact closures are examples of discrete sensors which are
connected to the PLCs discrete or digital inputs. In the ON condition a discrete input
may be referred to as a logic 1 or a logic high. In the OFF condition a discrete input may
be referred to as a logic 0 or a logic low.
A Normally Open (NO) pushbutton is used in the following example. One side of the
pushbutton is connected to the first PLC input. The other side of the pushbutton is
connected to an internal 24 VDC power supply. Many PLCs require a separate power
supply to power the inputs. In the open state, no voltage is present at the PLC input.
This is the OFF condition. When the pushbutton is depressed, 24 VDC is applied to the
PLC input.
20
3.4.4 Analog Inputs : An analog input is a continuous, variable signal. Typical
analog inputs may vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts. In
the following example, a level transmitter monitors the level of liquid in a tank.
Depending on the level transmitter, the signal to the PLC can either increase or decrease
as the level increases or decreases.
3.4.5 Discrete Outputs:A discrete output is an output that is either in an ON or OFF
condition. Solenoids, contactor coils, and lamps are examples of actuator devices
connected to discrete outputs. Discrete
outputs may also be referred to as digital outputs. In the following example, a lamp can
be turned on or off by the PLC output it is connected to.
3.4.6 Analog Outputs : An analog output is a continuous, variable signal. The output
may be as simple as a 0-10 VDC level that drives an analog meter. Examples of analog
meter outputs are speed, weight,
and temperature. The output signal may also be used on more complex applications such
as a current-to-pneumatic transducer that controls an air-operated flow-control valve.
3.4.7 CPU : The central processor unit (CPU) is a microprocessor system that contains
the system memory and is the PLC decision making unit. The CPU monitors the inputs
and makes decisions based on instructions held in the program memory. The CPU
performs relay, counting, timing, data comparison, and sequential operations.
3.5 Programming :
21
A program consists of one or more instructions that accomplish a task. Programming a
PLC is simply constructing a set of instructions. There are several ways to look at a
program such as ladder logic, statement lists, or function block diagrams.
3.5.1 Ladder Logic: Ladder logic (LAD) is one programming language used with
PLCs. Ladder logic uses components that resemble elements used in a line diagram
format to describe hard-wired control. The left vertical line of a ladder logic diagram
represents the power or energized conductor. The output element or instruction
represents the neutral or return path of the circuit. The right vertical line, which
represents the return path on a hard-wired control line diagram, is omitted. Ladder logic
diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as
networks. A network may have several control elements,
but only one output coil.
22
CHAPTER – 4
DRIVES
4.1 AC DRIVES
AC MOTORS BASICS
In an induction motors, when the 3-phase stator windings, are fed by 3– phase AC
supply then, a magnetic flux of constant magnitude, but rotating at synchronous speed,
is set up. The flux passes through the air gap; sweeps past the rotor surface and so cuts
the rotor conductors, which as yet, are stationary. Due to the relative speed between the
rotating flux and the stationary conductors, an E.M.F. is induced in the letter according
to Faraday’s law of Electro–Magnetic induction. The frequency of the induced E.M.F. is
the same as the supply frequency. Its magnitude is proportional to the relative velocity
between the flux and the conductors and Fleming’s Right
Hand Rule gives its
directions.The Synchronous Speed (Ns) of an induction motor is given by,
23
Ns = (120*f) / P
Where,
‘F’= frequency
‘P’= no’s of Pole.
In an induction motor, the motors run at a speed, which is always less than the speed of
the stator field. The difference in speeds depends upon the load on the motor. The
difference between the synchronous speed Ns & the actual speed N of the rotor is
known as Slip.
Therefore, Slip (S) = (Ns - N) / Ns
Where, N is the rotor speed.
Therefore, Actual speed of shaft
(N) = Ns * (1- S).
The torque equation of an AC motor is given as:
Torque (T) = Ia *
Where,
‘Ia’ = stator current.
‘’= Air gap flux.
24
4.2 VOLTAGE/FREQUENCY CONCEPT:
The V/F concept is mainly used in AC drives. Therefore AC drives are also known as
“V/F DRIVES”.
In drives it is necessary for a motor to deliver rated torque at set speed. In order to
change the speed of AC motor stator frequency is to be changed. Since torque delivered
by motor is proportional to the product of the stator current and flux, it is essential that
motor flux be to be kept constant. This means at any speed, motor can deliver torque
(maximum up to rated torque) demanded by load and is roughly proportional to the
product of stator current and motor flux. So we have,
Torque = Ia *
Where, Ia = Armature current which varies with load
= Motor flux which remains constant
25
VOLTAGE / FREQUENCY CURVE:
The EMF generated is proportional to the rate at which conductors cut the flux. So we
have,
EMF = Rate of change of flux = V / F
i.e.
V = d / dt
d = V * dt
=V*T
i e.
=V/F
Therefore, in order to maintain constant flux in motor, the ratio of voltage to frequency is
always maintained constant so that motor can deliver rated torque through out the speed
range.
4.3 BASIC THEORY OF INVERTER:
26
Inverter is what industry sees as an ultimate and supreme controller of AC drives
system. With micro controller based logical controls, the inverter is very fast, efficient
safe and easily operable device. The range of application of inverter is enhancing day by
day, so it is imperative to study inverter.
4.3.1 DEFINITION:
The DC to AC power converter is known as INVERTER. In other words, an
inverter is a circuit, which converts a fixed dc power in to an ac power at desired output
voltage and frequency.
4.3.2 INVERTER SCHEMATIC DIAGRAM:
Since the inverter is dc to ac converter it has to have a constant dc source. Normally the
power available in industry is ac, so to derive dc power, we need to rectify available ac power.
The rectifier produces pulsating dc output voltage from ac power. The filter reduces the
pulsation or the ripples contents in the rectified output and gives reasonably constant dc
output. Then true inverter function occurs i.e. Variable Voltage Variable Frequency control.
The main role is performed by the switching element which is invariably a semiconductor
device.i.e.BJTs, IGBTs.
27
TESTING PROCEDURE
During testing of the AC Drive following tests are carried out:
1.Visual checks
2.Electrical checks
Visual checks
Carry out visual inspection as per Inspection Report for AC drives.
Output and Input supply terminals of panels should be distinctly identified and output
terminals of inverter are connected to the motor.
Check correctness and firmness of wires, cables and earth of the panel.
Electrical checks :
Give the power supply to the panel according to the scheme.
Check logic circuit as per scheme.
Check phase sequence of auxiliary supplies.
Verify that the direction of airflow of panel +fan is upward.
Put the inverter ON.
Set the parameters
28
Check flash ID.
Set control circuit's terminals according the scheme.
Connect test motor at parameter outgoing terminals of panel and check RUN, SPEED
RAISE, SPEED LOWER, STOP commands in all possible selections according to the
scheme.
Check Forward and Reverse RUN commands
Check the operation by varying the reference (4-20 mA or 0-10V) in Remote mode.
Check correctness and firmness of wires, cables and earth of the panel.
4.4 DC MOTOR
DC MOTOR BASICS
An electrical motor is a machine, which converts electrical energy into mechanical
energy. The basic principle is that when a current carrying conductor is placed in a
magnetic field it experiences a mechanical force whose direction is given by Fleming’s
left hand rule. There is no basic difference between the construction of a dc generator
and dc motor; the same machine can be used as a generator or a motor.
In case of a dc motor the field electromagnet and armature conductors are supplied with
the current from mains supply and mechanical force is obtained by rotation of armature.
In case of dc motor, the e.m.f (E) is less than the applied voltage (V) and the direction of
the current (Ia) is the reverse of that when the machine is used as a generator.
E = V – IaRa
OR
V = E + IaRa
29
As the e.m.f. generated in the armature of a motor is in opposition to the applied
voltage, it is also referred as ‘Back emf.’
4.5 WHY WE USE A DC DRIVE?
Basically, DC drive is used due to following things: DC drive has precise control on speed & torque.
DC drive is a soft starter means it has ramp input. It is useful in order to minimize the
maintenance of the DC motor.
DC drive has good efficiency, which is an around 80 % to 95 % giving good result
during running condition of DC motor.
DC drive gives good speed regulation means it can sense load variation (from no-load to
full-load) in proper manner & maintain the same speed.
DC drive has speed controlling range from 0% to 100%, so it can control speed from 0
rpm to rated rpm of the motor.
DC drive has 0.01% accuracy which means motor can run at 0.01% of its rated rpm
speed.
DC drive gives various types of protection over the motor control like Feedback loss,
Integrated Overload, Phase sequence failure, Under Voltage, Over Voltage, Over
Current, Over Speed, Over temperature etc.
4.6 CLASSIFICATION OF DC DRIVES :
There are two types of converter used in DC Drives. These are following: DC Thyristor converter drives
DC Transistor converter drives.
4.6.1 DC Thyristor Converter Drives:
30
These drives are available in rating from a few hundred watts up to several megawatts
and have a great variety of applications in industries. But these drives have certain
advantages & disadvantages:
Advantages:
1.These are simple and highly efficient than their transistor equivalents.
2.Thyristors are available with very high current and voltage ratings.
Disadvantages:
1.Because of delay in thyristor operation (3.3ms), the current control loop bandwidth of
the thyristor converter is limited to approximately 25Hz, which is too low for many
servo drive applications.
2.Thyristor phase control rectifiers have poor input power factor, particularly at low
output voltages.
3.Electronic short circuit protection is not possible with thyristorised converters. Fuses
normally accomplish protection.
4.6.2 DC Transistor Converter Drives:
These drives are usually of low power rating and are typically used in rather specialist
applications. The main advantage of DC transistor drives is that, they can be battery
supplied or mains supplied.
Advantages:
1.Due to ability of transistor to interrupt current, it operate from battery or DC supply.
31
2.Transistor phase control rectifiers have high input power factor, particularly at low
output voltages.Electronic short circuit protection is possible with transistorized
converters.
3.Fuses normally accomplish protection.
Disadvantage:
1.These are more complex and less efficient than their thyristor equivalents.
2.Transistors are not available with very high current and voltage ratings.
4.7 SPEED CONTROL OF DC MOTOR USING DC DRIVES:
The speed control of DC motor is given by
N = (Va – IaRa) /
From the above equation we can say that, the speed of separately excited DC motor can
be varied in two ways:
1 .Field current is kept constant while the armature voltage is varied from zero to rated
value.
2. Armature voltage is kept constant at the rated value and field current is varied from
maximum to minimum.
These two speed control result in speed-torque characteristics, which are different from
each other.
Armature voltage control gives constant torque and variable power
characteristics while variable field flux gives constant power and variable torque
characteristics.
32
4.7.1 Armature Voltage Control:
This method is used for controlling speed up to base speed of the motor. Base speed is
the speed at which the motor delivers the rated power and torque at rated armature and
field current. Since the field flux is kept constant, the torque is entirely dependent on
the value of armature current. Once the value of starting torque i.e. starting current is
determined, the armature voltage can be varied smoothly up-to base speed, keeping the
armature current within the fixed limit. As the motor speeds up, Eb increases and the
current tends to lower but since the voltage is also increasing, the current level can be
maintained. As the current and the flux are kept constant the motor has a constant
torque characteristics and power of the machine rises.
By varying the armature voltage below the nominal rated voltage, motor can be made to
operate at various speeds in a wider range delivering full torque and reduce power
output.
It is not possible to operate the motor at higher than the base speed by
increasing the armature voltage above nominal rated voltage. This method of speed
control is used in cranes, rolling mills etc. Thus up to base speed the motor can be
controlled easily by controlling the armature voltage, called as ‘constant torque
application’.
4.7.2 Field current control:
Upto the base speed, the motor is controlled by armature voltage control. Now if the
speed required is more than the base speed and the armature voltage is not be increased
beyond the rated voltage, the choice is to decrease the field flux. To achieve this, the
field current is to be decreased. This is called ‘constant power application’ since
power remains constant. This is also termed as field weaking of the system.
33
4.8 DRIVES ADVANTAGES AND DISADVANTAGES:
Advantages
Disadvantages
1.Potentially lower installed cost above
Brush Maintenance.
50 HP.
2.Good energy efficiency & regeneration
Higher Repair Costs.
of power can possible by 4-Quadrant
method.
3.Speed control of DC Drive is better
Limited Dynamic Response due to line
than AC Drive.
commutation restrictions, coupled with
higher mass moments of inertia imposed
by the wound field armature.
34
4.DC motor tuning is good in DC Drive
Limited range to 5,000-hp, due to
means current autotuning is done in
commutation restrictions.
proper manner & also all gains are set by
auto tuning.
5.Few distance limitations.
Potential
for
rapid
acceleration
to
destructive velocities upon loss of the
stationary field.
CHAPTER – 6
CONCLUSION
5.1 Automation plays an increasingly important role in the global economy and in daily
experience. Engineers strive to combine automated devices with mathematical and
organizational tools to create complex systems for a rapidly expanding range of
applications and human activities.
5.2 Automation provides 100% accuracy alltime. So the failures and mismatch in
production completely eliminates. It makes the system’s effeciency higher than manual
35
as well as It controls wastages.. So the overall savings increses. It provides safety to
human being. By that industry can achieves the safety majors and ISO and OHSAS
reputation. It makes the operation faster than manual which causes higher production
and proper utilization of utilities. It increases the production by which the cost of each
product decreses and industry profit increases . It provides smooth control on system
response. It provides repeatability, so that the same kind of products are easier to
manufacture at different stages without wasting time. It provides quality control, so that
the products become reliable which improves industrial reputation in market.
It
provides integration with business systems. It can reduce labor costs, so the final profit
increases.
5.3 Industrial automation is very compulsory need of industries in today’s scenario to
meet market competition.
36
Submitted in partial fulfillment of the Requirement for the
degree of
Bachelor of Technology
in
Electronics and Communication Engineering
Submitted By:
Siddharth Garg
(ECE,7th Sem,3147)
Session 2009-2013
Department of Electronics and Communication Engineering
Delhi Institute of Technology and Management, Sonepat
Affiliated to Deenbandhu Chhotu Ram University of
Science and Technology, Murthal (Haryana).
Table of Content
1
S.No
Particulars
Page No.
1.
Introduction
4
2.
SCADA
9
3.
Programmable logic controller PLC
18
4.
Drives
24
5.
Conclusion
35
2
CHAPTER – 1
INTRODUCTION
Industrial automation or numerical control is the use of control systems such as
computers to control industrial machinery and processes, reducing the need for human
intervention. In the scope of industrialization, automation is a step beyond
mechanization. Whereas mechanization provided human operators with machinery to
assist them with the physical requirements of work, automation greatly reduces the
need for human sensory and mental requirements as well. Processes and systems can
also be automated.
Automation plays an increasingly important role in the global economy and in daily
experience. Engineers strive to combine automated devices with mathematical and
organizational tools to create complex systems for a rapidly expanding range of
applications and human activities.Many roles for humans in industrial processes
presently lie beyond the scope of automation. Human-level pattern recognition,
language recognition, and language production ability are well beyond the capabilities
of modern mechanical and computer systems. Tasks requiring subjective assessment or
synthesis of complex sensory data, such as scents and sounds, as well as high-level tasks
such as strategic planning, currently require human expertise. In many cases, the use of
humans is more cost-effective than mechanical approaches even where automation of
industrial tasks is possible.
1.1
For the purpose of AUTOMATION Specialised hardened computers, referred to as
programmable logic controllers (PLCs), are frequently used to synchronize the flow of
3
inputs from (physical) sensors and events with the flow of outputs to actuators and
events. This leads to precisely controlled actions that permit a tight control of almost
any industrial process. Human-machine interfaces (HMI) or computer human interfaces
(CHI), formerly known as man-machine interface, are usually employed to
communicate with PLCs and other computers, such as entering and monitoring
temperatures or pressures for further automated control or emergency response. Service
personnel who monitor and control these interfaces are often referred to as stationary
engineers.
1.2
Automation has had a notable impact in a wide range of highly visible industries
beyond manufacturing. Once-ubiquitous telephone operators have been replaced largely
by automated telephone switchboards and answering machines. Medical processes such
as primary screening in electrocardiography or radiography and laboratory analysis of
human genes, sera, cells, and tissues are carried out at much greater speed and accuracy
by automated systems. Automated teller machines have reduced the need for bank visits
to obtain cash and carry out transactions. In general, automation has been responsible
for the shift in the world economy from agrarian to industrial in the 19th century and
from industrial to services in the 20th century.
1.3 The widespread impact of industrial automation raises social issues, among them its
impact on employment. Historical concerns about the effects of automation date back to
the beginning of the industrial revolution, when a social movement of English textile
machine operators in the early 1800s known as the Luddites protested against Jacquard's
automated weaving looms— often by destroying such textile machines— that they felt
threatened their jobs. One author made the following case. When automation was first
4
introduced, it caused widespread fear. It was thought that the displacement of human
operators by computerized systems would lead to severe unemployment.
1.4 Currently, for manufacturing companies, the purpose of automation has shifted
from increasing productivity and reducing costs, to broader issues, such as increasing
quality and flexibility in the manufacturing process.The old focus on using automation
simply to increase productivity and reduce costs was seen to be short-sighted, because it
is also necessary to provide a skilled workforce who can make repairs and manage the
machinery. Moreover, the initial costs of automation were high and often could not be
recovered by the time entirely new manufacturing processes replaced the old. (Japan's
"robot junkyards" were once world famous in the manufacturing industry.)
1.5 Automation is now often applied primarily to increase quality in the manufacturing
process, where automation can increase quality substantially. For example, automobile
and truck pistons used to be installed into engines manually. This is rapidly being
transitioned to automated machine installation, because the error rate for manual
installment was around 1-1.5%, but has been reduced to 0.00001% with automation.
Hazardous operations, such as oil refining, the manufacturing of industrial chemicals,
and all forms of metal working, were always early contenders for automation.
1.6
Another major shift in automation is the increased emphasis on flexibility and
convertibility in the manufacturing process. Manufacturers are increasingly demanding
the ability to easily switch from manufacturing Product A to manufacturing Product B
without having to completely rebuild the production lines. Flexibility and distributed
processes have led to the introduction of Automated Guided Vehicles with Natural
Features Navigation.
5
1.7 The widespread impact of industrial automation raises social issues, among them
its impact on employment. Historical concerns about the effects of automation date back
to the beginning of the industrial revolution, when a social movement of English textile
machine operators in the early 1800s known as the Luddites protested against Jacquard's
automated weaving looms often by destroying such textile machines— that they felt
threatened their jobs. One author made the following case. When automation was first
introduced, it caused widespread fear. It was thought that the displacement of human
operators by computerized systems would lead to severe unemployment.
1.8
At first glance, automation might appear to devalue labor through its replacement
with less-expensive machines; however, the overall effect of this on the workforce as a
whole remains unclear. Today automation of the workforce is quite advanced, and
continues to advance increasingly more rapidly throughout the world and is encroaching
on ever more skilled jobs, yet during the same period the general well-being and quality
of life of most people in the world (where political factors have not muddied the picture)
have improved dramatically. What role automation has played in these changes has not
been well studied. Currently, for manufacturing companies, the purpose of automation
has shifted from increasing productivity and reducing costs, to broader issues, such as
increasing quality and flexibility in the manufacturing process. Different types of
automation tools exist
6
Block Diagram Of Industrial Automation
SCADA System
with HMI
Screens
Programmable
Logic Controller
Field Equipments
and Machineries
AC OR DC
Drives
Sensors
Auxiliaries
MAIN BODY OF AUTOMATION
SCADA - Supervisory Control and Data Acquisition
PLC - Programmable Logic Controller
DRIVES - Variable Speed Drives
SENSORS – Transducers, Feedback equipments.
AUXILIARIES – Converters, Power Supplies, Different Communication
mediums etc.
7
CHAPTER – 2
SCADA
SCADA stands for “Supervisory Control And Data Acquisition.” It generally refers to
an industrial control system: a computer system monitoring and controlling a process.
The process can be industrial, infrastructure or facility based as described
below:Industrial processes include those of manufacturing, production, power
generation, fabrication, and refining, and may run in continuous, batch, repetitive, or
discrete modes. Infrastructure processes may be public or private, and include water
treatment and distribution, wastewater collection and treatment, oil and gas pipelines,
electrical power transmission and distribution, and large communication systems.
Facility processes occur both in public facilities and private ones, including buildings,
airports, ships, and space stations. They monitor and control HVAC, access, and energy
consumption.
2.1 A SCADA System usually consists of the following subsystems:
a) A Human-Machine Interface or HMI is the apparatus which presents process data
to a human operator, and through this, the human operator, monitors and controls the
process.
b) A supervisory (computer) system, gathering (acquiring) data on the process and
sending commands (control) to the process.
8
c) Remote Terminal Units (RTUs) connecting to sensors in the process, converting
sensor signals to digital data and sending digital data to the supervisory system.
d) Programmable Logic Controller (PLCs) used as field devices because they are
more economical, versatile, flexible, and configurable than special-purpose RTUs.
e) Communication infrastructure connecting the supervisory system to the Remote
Terminal Units
There is, in several industries, considerable confusion over the differences between
SCADA systems and Distributed control systems (DCS). Generally speaking, a SCADA
system usually refers to a system that coordinates, but does not control processes in
real time. The discussion on real-time control is muddied somewhat by newer
telecommunications
technology,
enabling
reliable,
low
latency,
high
speed
communications over wide areas. Most differences between SCADA and Distributed
control system DCS are culturally determined and can usually be ignored. As
communication infrastructures with higher capacity become available, the difference
between SCADA and DCS will fade.
The term SCADA usually refers to centralized systems which monitor and control entire
sites, or complexes of systems spread out over large areas (anything between an
industrial plant and a country). Most control actions are performed automatically by
remote terminal units ("RTUs") or by programmable logic controllers ("PLCs"). Host
control functions are usually restricted to basic overriding or supervisory level
intervention. For example, a PLC may control the flow of cooling water through part of
an industrial process, but the SCADA system may allow operators to change the set
points for the flow, and enable alarm conditions, such as loss of flow and high
temperature, to be displayed and recorded. The feedback control loop passes through the
RTU or PLC, while the SCADA system monitors the overall performance of the loop.
9
Data acquisition begins at the RTU or PLC level and includes meter readings and
equipment status reports that are communicated to SCADA as required. Data is then
compiled and formatted in such a way that a control room operator using the HMI can
make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may
also be fed to a Historian, often built on a commodity Database Management System, to
allow trending and other analytical auditing.
2.1.1 Human Machine Interface:
A Human-Machine Interface or HMI is the apparatus which presents process data to a
human operator, and through which the human operator controls the process.
An HMI is usually linked to the SCADA system's databases and software programs, to
provide trending, diagnostic data, and management information such as scheduled
maintenance procedures, logistic information, detailed schematics for a particular sensor
or machine, and expert-system troubleshooting guides.
The HMI system usually presents the information to the operating personnel
graphically, in the form of a mimic diagram. This means that the operator can see a
schematic representation of the plant being controlled. For example, a picture of a pump
connected to a pipe can show the operator that the pump is running and how much fluid
it is pumping through the pipe at the moment. The operator can then switch the pump
off. The HMI software will show the flow rate of the fluid in the pipe decrease in real
time. Mimic diagrams may consist of line graphics and schematic symbols to represent
process elements, or may consist of digital photographs of the process equipment
overlain with animated symbols.
10
The HMI package for the SCADA system typically includes a drawing program that the
operators or system maintenance personnel use to change the way these points are
represented in the interface. These representations can be as simple as an on-screen
traffic light, which represents the state of an actual traffic light in the field, or as
complex as a multi-projector display representing the position of all of the elevators in a
skyscraper or all of the trains on a railway.
An important part of most SCADA implementations are alarms. An alarm is a digital
status point that has either the value NORMAL or ALARM. Alarms can be created in
such a way that when their requirements are met, they are activated. An example of an
alarm is the "fuel tank empty" light in a car. The SCADA operator's attention is drawn to
the part of the system requiring attention by the alarm. Emails and text messages are
often sent along with an alarm activation alerting managers along with the SCADA
operator.
2.1.2 Hardware solutions:
SCADA solutions often have Distributed Control System (DCS) components. Use of
"smart" RTUs or PLCs, which are capable of autonomously executing simple logic
processes without involving the master computer, is increasing. A functional block
programming language, IEC 61131-3 (Ladder Logic), is frequently used to create
programs which run on these RTUs and PLCs. Unlike a procedural language such as the
C programming language or FORTRAN, IEC 61131-3 has minimal training
requirements by virtue of resembling historic physical control arrays. This allows
SCADA system engineers to perform both the design and implementation of a program
to be executed on an RTU or PLC. Since about 1998, virtually all major PLC
manufacturers have offered integrated HMI/SCADA systems, many of them using open
11
and non-proprietary communications protocols. Numerous specialized third-party
HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also
entered the market, allowing mechanical engineers, electrical engineers and technicians
to configure HMIs themselves, without the need for a custom-made program written by
a software developer.
2.2 Around the world, SCADA systems control:
Electric power generation, transmission and distribution: Electric utilities use
SCADA systems to detect current flow and line voltage, to monitor the operation of
circuit breakers, and to take sections of the power grid online or offline.
Water and sewage: State and municipal water utilities use SCADA to monitor and
regulate water flow, reservoir levels, pipe pressure and other factors.
Buildings, facilities and environments: Facility managers use SCADA to control
HVAC, refrigeration units, lighting and entry systems.
Manufacturing: SCADA systems manage parts inventories for just-in-time
manufacturing, regulate industrial automation and robots, and monitor process and
quality control.
Mass transit: Transit authorities use SCADA to regulate electricity to subways,
trams and trolley buses; to automate traffic signals for rail systems; to track and locate
trains and buses; and to control railroad crossing gates.
Traffic signals: SCADA regulates traffic lights, controls traffic flow and detects out-
of-order signals.
12
2.3 Importance of SCADA:
Maybe you work in one of the fields I listed; maybe you don’t. But think about your
operations and all the parameters that affect your bottom-line results:
Does your equipment need an uninterrupted power supply and/or a controlled
temperature and humidity environment?
Do you need to know — in real time — the status of many different components and
devices in a large complex system?
Do you need to measure how changing inputs affect the output of your operations?
What equipment do you need to control, in real time, from a distance?
Where are you lacking accurate, real-time data about key processes that affect your
operations?
Real-Time Monitoring and Control Increases Efficiency and Maximizes
Profitability
2.4 A SCADA system performs four functions:
1.
Data acquisition
2.
Networked data communication
3.
Data presentation
4.
Control
2.4.1 Data Acquisition:
13
First, the systems you need to monitor are much more complex than just one machine
with one output. So a real-life SCADA system needs to monitor hundreds or thousands
of sensors. Some sensors measure inputs into the system (for example, water flowing
into a reservoir), and some sensors measure outputs (like valve pressure as water is
released from the reservoir).
Some of those sensors measure simple events that can be detected by a straightforward
on/off switch, called a discrete input (or digital input). For example, in our simple model
of the widget fabricator, the switch that turns on the light would be a discrete input. In
real life, discrete inputs are used to measure simple states, like whether equipment is on
or off, or tripwire alarms, like a power failure at a critical facility.
Some sensors measure more complex situations where exact measurement is important.
These are analog sensors, which can detect continuous changes in a voltage or current
input. Analog sensors are used to track fluid levels in tanks, voltage levels in batteries,
temperature and other factors that can be measured in a continuous range of input.
For most analog factors, there is a normal range defined by a bottom and top level. For
example, you may want the temperature in a server room to stay between 60 and 85
degrees Fahrenheit. If the temperature goes above or below this range, it will trigger a
threshold alarm. In more advanced systems, there are four threshold alarms for analog
sensors, defining Major Under, Minor Under, Minor Over and Major Over alarms.
2.4.2 Data Communication:
In our simple model of the widget fabricator, the “network” is just the wire leading from
the switch to the panel light. In real life, you want to be able to monitor multiple
14
systems from a central location, so you need a communications network to transport all
the data collected from your sensors.
Early SCADA networks communicated over radio, modem or dedicated serial lines.
Today the trend is to put SCADA data on Ethernet and IP over SONET. For security
reasons, SCADA data should be kept on closed LAN/WANs without exposing sensitive
data to the open Internet.
Real SCADA systems don’t communicate with just simple electrical signals, either.
SCADA data is encoded in protocol format. Older SCADA systems depended on closed
proprietary protocols, but today the trend is to open, standard protocols and protocol
mediation.
Sensors and control relays are very simple electric devices that can’t generate or
interpret protocol communication on their own. Therefore the remote telemetry unit
(RTU) is needed to provide an interface between the sensors and the SCADA network.
The RTU encodes sensor inputs into protocol format and forwards them to the SCADA
master; in turn, the RTU receives control commands in protocol format from the master
and transmits electrical signals to the appropriate control relays.
2.4.3 Data Presentation:
The only display element in our model SCADA system is the light that comes on when
the switch is activated. This obviously won’t do on a large scale — you can’t track a
light board of a thousand separate lights, and you don’t want to pay someone simply to
watch a light board, either.
15
A real SCADA system reports to human operators over a specialized computer that is
variously called a master station, an HMI (Human-Machine Interface) or an HCI
(Human-Computer Interface).
The SCADA master station has several different functions. The master continuously
monitors all sensors and alerts the operator when there is an “alarm” — that is, when a
control factor is operating outside what is defined as its normal operation. The master
presents a comprehensive view of the entire managed system, and presents more detail
in response to user requests. The master also performs data processing on information
gathered from sensors — it maintains report logs and summarizes historical trends.
An advanced SCADA master can add a great deal of intelligence and automation to
your systems management, making your job much easier.
2.4.4 Control:
Unfortunately, our miniature SCADA system monitoring the widget fabricator doesn’t
include any control elements. So let’s add one. Let’s say the human operator also has a
button on his control panel. When he presses the button, it activates a switch on the
widget fabricator that brings more widget parts into the fabricator.
Now let’s add the full computerized control of a SCADA master unit that controls the
entire factory. You now have a control system that responds to inputs elsewhere in the
system. If the machines that make widget parts break down, you can slow down or stop
the widget fabricator. If the part fabricators are running efficiently, you can speed up the
widget fabricator.
16
If you have a sufficiently sophisticated master unit, these controls can run completely
automatically, without the need for human intervention. Of course, you can still
manually override the automatic controls from the master station.
CHAPTER – 3
PROGRAMMABLE LOGIC CONTROLLERS
Programmable Logic Controllers (PLCs), also referred to as programmable controllers,
are in the computer family. They are used in commercial and industrial applications. A
PLC monitors inputs, makes decisions based on its program, and controls outputs to
automate a process or machine. This course is meant to supply you with basic
information on the functions and configurations of PLCs.
Drive
Motors
Photo
Sensor
s
Pumps
Other
equipments
PLC
Start
Push
Button
s
Lights
17
3.1 Basic PLC Operation :
PLCs consist of input modules or points, a Central Processing Unit (CPU), and output
modules or points. An input accepts a variety of digital or analog signals from various
field devices (sensors) and converts them into a logic signal that can be used by the
CPU. The CPU makes decisions and executes control instructions based on program
instructions in memory. Output modules convert control instructions from the CPU into
a digital or analog signal that can be used to control various field devices (actuators). A
programming device is used to input the desired instructions. These instructions
determine what the PLC will do for a specific input. An operator interface device allows
process information to be displayed and new control parameters to be entered.
Input
Module
CPU
Central
processing unit
Programming
Device
Output
Module
Operator
Interface
Pushbuttons (sensors), in this simple example, connected to PLC inputs, can be used to
start and stop a motor connected to a PLC through a motor starter (actuator). Prior to
PLCs, many of these control tasks were solved with contactor or relay controls. This is
often referred to as hardwired control. Circuit diagrams had to be designed, electrical
18
components specified and installed, and wiring lists created. Electricians would then
wire the components necessary to perform a specific task. If an error was made, the
wires had to be reconnected correctly. A change in function or system expansion
required extensive component changes and rewiring.
3.2 Advantages of PLCs :
The same, as well as more complex tasks, can be done with a PLC. Wiring between
devices and relay contacts is done in the PLC program. Hard-wiring, though still
required to connect field devices, is less intensive. Modifying the application and
correcting errors are easier to handle. It is easier to create and change a program in a
PLC than it is to wire and re-wire a circuit.
Following are just a few of the advantages of PLCs:
• Smaller physical size than hard-wire solutions.
• Easier and faster to make changes.
• PLCs have integrated diagnostics and override functions.
• Diagnostics are centrally available.
• Applications can be immediately documented.
3.3 Logic 0, Logic 1:
Programmable controllers can only understand a signal that is On or Off (present or not
present). The binary system is a system in which there are only two numbers, 1 and 0.
Binary 1 indicates that a signal is present, or the switch is On. Binary 0 indicates that the
signal is not present, or the switch is Off.
The language of PLCs consists of a commonly used set of terms; many of which are
unique to PLCs.
19
3.4 In order to understand the ideas and concepts of PLCs, an understanding of these
terms is necessary.
3.4.1 Sensor :A sensor is a device that converts a physical condition into an electrical
signal for use by the PLC. Sensors are connected to the input of a PLC. A pushbutton is
one example of a sensor that is connected to the PLC input. An electrical signal is sent
from the pushbutton to the PLC indicating the condition (open/ closed) of the
pushbutton contacts.
3.4.2 Actuators: Actuators convert an electrical signal from the PLC into a physical
condition. Actuators are connected to the PLC output. A motor starter is one example of
an actuator that is connected to the PLC output. Depending on the output PLC signal the
motor starter will either start or stop the motor.
3.4.3 Discrete Input: A discrete input, also referred to as a digital input, is an input
that is either in an ON or OFF condition. Pushbuttons, toggle switches, limit switches,
proximity switches, and contact closures are examples of discrete sensors which are
connected to the PLCs discrete or digital inputs. In the ON condition a discrete input
may be referred to as a logic 1 or a logic high. In the OFF condition a discrete input may
be referred to as a logic 0 or a logic low.
A Normally Open (NO) pushbutton is used in the following example. One side of the
pushbutton is connected to the first PLC input. The other side of the pushbutton is
connected to an internal 24 VDC power supply. Many PLCs require a separate power
supply to power the inputs. In the open state, no voltage is present at the PLC input.
This is the OFF condition. When the pushbutton is depressed, 24 VDC is applied to the
PLC input.
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3.4.4 Analog Inputs : An analog input is a continuous, variable signal. Typical
analog inputs may vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts. In
the following example, a level transmitter monitors the level of liquid in a tank.
Depending on the level transmitter, the signal to the PLC can either increase or decrease
as the level increases or decreases.
3.4.5 Discrete Outputs:A discrete output is an output that is either in an ON or OFF
condition. Solenoids, contactor coils, and lamps are examples of actuator devices
connected to discrete outputs. Discrete
outputs may also be referred to as digital outputs. In the following example, a lamp can
be turned on or off by the PLC output it is connected to.
3.4.6 Analog Outputs : An analog output is a continuous, variable signal. The output
may be as simple as a 0-10 VDC level that drives an analog meter. Examples of analog
meter outputs are speed, weight,
and temperature. The output signal may also be used on more complex applications such
as a current-to-pneumatic transducer that controls an air-operated flow-control valve.
3.4.7 CPU : The central processor unit (CPU) is a microprocessor system that contains
the system memory and is the PLC decision making unit. The CPU monitors the inputs
and makes decisions based on instructions held in the program memory. The CPU
performs relay, counting, timing, data comparison, and sequential operations.
3.5 Programming :
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A program consists of one or more instructions that accomplish a task. Programming a
PLC is simply constructing a set of instructions. There are several ways to look at a
program such as ladder logic, statement lists, or function block diagrams.
3.5.1 Ladder Logic: Ladder logic (LAD) is one programming language used with
PLCs. Ladder logic uses components that resemble elements used in a line diagram
format to describe hard-wired control. The left vertical line of a ladder logic diagram
represents the power or energized conductor. The output element or instruction
represents the neutral or return path of the circuit. The right vertical line, which
represents the return path on a hard-wired control line diagram, is omitted. Ladder logic
diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as
networks. A network may have several control elements,
but only one output coil.
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CHAPTER – 4
DRIVES
4.1 AC DRIVES
AC MOTORS BASICS
In an induction motors, when the 3-phase stator windings, are fed by 3– phase AC
supply then, a magnetic flux of constant magnitude, but rotating at synchronous speed,
is set up. The flux passes through the air gap; sweeps past the rotor surface and so cuts
the rotor conductors, which as yet, are stationary. Due to the relative speed between the
rotating flux and the stationary conductors, an E.M.F. is induced in the letter according
to Faraday’s law of Electro–Magnetic induction. The frequency of the induced E.M.F. is
the same as the supply frequency. Its magnitude is proportional to the relative velocity
between the flux and the conductors and Fleming’s Right
Hand Rule gives its
directions.The Synchronous Speed (Ns) of an induction motor is given by,
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Ns = (120*f) / P
Where,
‘F’= frequency
‘P’= no’s of Pole.
In an induction motor, the motors run at a speed, which is always less than the speed of
the stator field. The difference in speeds depends upon the load on the motor. The
difference between the synchronous speed Ns & the actual speed N of the rotor is
known as Slip.
Therefore, Slip (S) = (Ns - N) / Ns
Where, N is the rotor speed.
Therefore, Actual speed of shaft
(N) = Ns * (1- S).
The torque equation of an AC motor is given as:
Torque (T) = Ia *
Where,
‘Ia’ = stator current.
‘’= Air gap flux.
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4.2 VOLTAGE/FREQUENCY CONCEPT:
The V/F concept is mainly used in AC drives. Therefore AC drives are also known as
“V/F DRIVES”.
In drives it is necessary for a motor to deliver rated torque at set speed. In order to
change the speed of AC motor stator frequency is to be changed. Since torque delivered
by motor is proportional to the product of the stator current and flux, it is essential that
motor flux be to be kept constant. This means at any speed, motor can deliver torque
(maximum up to rated torque) demanded by load and is roughly proportional to the
product of stator current and motor flux. So we have,
Torque = Ia *
Where, Ia = Armature current which varies with load
= Motor flux which remains constant
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VOLTAGE / FREQUENCY CURVE:
The EMF generated is proportional to the rate at which conductors cut the flux. So we
have,
EMF = Rate of change of flux = V / F
i.e.
V = d / dt
d = V * dt
=V*T
i e.
=V/F
Therefore, in order to maintain constant flux in motor, the ratio of voltage to frequency is
always maintained constant so that motor can deliver rated torque through out the speed
range.
4.3 BASIC THEORY OF INVERTER:
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Inverter is what industry sees as an ultimate and supreme controller of AC drives
system. With micro controller based logical controls, the inverter is very fast, efficient
safe and easily operable device. The range of application of inverter is enhancing day by
day, so it is imperative to study inverter.
4.3.1 DEFINITION:
The DC to AC power converter is known as INVERTER. In other words, an
inverter is a circuit, which converts a fixed dc power in to an ac power at desired output
voltage and frequency.
4.3.2 INVERTER SCHEMATIC DIAGRAM:
Since the inverter is dc to ac converter it has to have a constant dc source. Normally the
power available in industry is ac, so to derive dc power, we need to rectify available ac power.
The rectifier produces pulsating dc output voltage from ac power. The filter reduces the
pulsation or the ripples contents in the rectified output and gives reasonably constant dc
output. Then true inverter function occurs i.e. Variable Voltage Variable Frequency control.
The main role is performed by the switching element which is invariably a semiconductor
device.i.e.BJTs, IGBTs.
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TESTING PROCEDURE
During testing of the AC Drive following tests are carried out:
1.Visual checks
2.Electrical checks
Visual checks
Carry out visual inspection as per Inspection Report for AC drives.
Output and Input supply terminals of panels should be distinctly identified and output
terminals of inverter are connected to the motor.
Check correctness and firmness of wires, cables and earth of the panel.
Electrical checks :
Give the power supply to the panel according to the scheme.
Check logic circuit as per scheme.
Check phase sequence of auxiliary supplies.
Verify that the direction of airflow of panel +fan is upward.
Put the inverter ON.
Set the parameters
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Check flash ID.
Set control circuit's terminals according the scheme.
Connect test motor at parameter outgoing terminals of panel and check RUN, SPEED
RAISE, SPEED LOWER, STOP commands in all possible selections according to the
scheme.
Check Forward and Reverse RUN commands
Check the operation by varying the reference (4-20 mA or 0-10V) in Remote mode.
Check correctness and firmness of wires, cables and earth of the panel.
4.4 DC MOTOR
DC MOTOR BASICS
An electrical motor is a machine, which converts electrical energy into mechanical
energy. The basic principle is that when a current carrying conductor is placed in a
magnetic field it experiences a mechanical force whose direction is given by Fleming’s
left hand rule. There is no basic difference between the construction of a dc generator
and dc motor; the same machine can be used as a generator or a motor.
In case of a dc motor the field electromagnet and armature conductors are supplied with
the current from mains supply and mechanical force is obtained by rotation of armature.
In case of dc motor, the e.m.f (E) is less than the applied voltage (V) and the direction of
the current (Ia) is the reverse of that when the machine is used as a generator.
E = V – IaRa
OR
V = E + IaRa
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As the e.m.f. generated in the armature of a motor is in opposition to the applied
voltage, it is also referred as ‘Back emf.’
4.5 WHY WE USE A DC DRIVE?
Basically, DC drive is used due to following things: DC drive has precise control on speed & torque.
DC drive is a soft starter means it has ramp input. It is useful in order to minimize the
maintenance of the DC motor.
DC drive has good efficiency, which is an around 80 % to 95 % giving good result
during running condition of DC motor.
DC drive gives good speed regulation means it can sense load variation (from no-load to
full-load) in proper manner & maintain the same speed.
DC drive has speed controlling range from 0% to 100%, so it can control speed from 0
rpm to rated rpm of the motor.
DC drive has 0.01% accuracy which means motor can run at 0.01% of its rated rpm
speed.
DC drive gives various types of protection over the motor control like Feedback loss,
Integrated Overload, Phase sequence failure, Under Voltage, Over Voltage, Over
Current, Over Speed, Over temperature etc.
4.6 CLASSIFICATION OF DC DRIVES :
There are two types of converter used in DC Drives. These are following: DC Thyristor converter drives
DC Transistor converter drives.
4.6.1 DC Thyristor Converter Drives:
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These drives are available in rating from a few hundred watts up to several megawatts
and have a great variety of applications in industries. But these drives have certain
advantages & disadvantages:
Advantages:
1.These are simple and highly efficient than their transistor equivalents.
2.Thyristors are available with very high current and voltage ratings.
Disadvantages:
1.Because of delay in thyristor operation (3.3ms), the current control loop bandwidth of
the thyristor converter is limited to approximately 25Hz, which is too low for many
servo drive applications.
2.Thyristor phase control rectifiers have poor input power factor, particularly at low
output voltages.
3.Electronic short circuit protection is not possible with thyristorised converters. Fuses
normally accomplish protection.
4.6.2 DC Transistor Converter Drives:
These drives are usually of low power rating and are typically used in rather specialist
applications. The main advantage of DC transistor drives is that, they can be battery
supplied or mains supplied.
Advantages:
1.Due to ability of transistor to interrupt current, it operate from battery or DC supply.
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2.Transistor phase control rectifiers have high input power factor, particularly at low
output voltages.Electronic short circuit protection is possible with transistorized
converters.
3.Fuses normally accomplish protection.
Disadvantage:
1.These are more complex and less efficient than their thyristor equivalents.
2.Transistors are not available with very high current and voltage ratings.
4.7 SPEED CONTROL OF DC MOTOR USING DC DRIVES:
The speed control of DC motor is given by
N = (Va – IaRa) /
From the above equation we can say that, the speed of separately excited DC motor can
be varied in two ways:
1 .Field current is kept constant while the armature voltage is varied from zero to rated
value.
2. Armature voltage is kept constant at the rated value and field current is varied from
maximum to minimum.
These two speed control result in speed-torque characteristics, which are different from
each other.
Armature voltage control gives constant torque and variable power
characteristics while variable field flux gives constant power and variable torque
characteristics.
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4.7.1 Armature Voltage Control:
This method is used for controlling speed up to base speed of the motor. Base speed is
the speed at which the motor delivers the rated power and torque at rated armature and
field current. Since the field flux is kept constant, the torque is entirely dependent on
the value of armature current. Once the value of starting torque i.e. starting current is
determined, the armature voltage can be varied smoothly up-to base speed, keeping the
armature current within the fixed limit. As the motor speeds up, Eb increases and the
current tends to lower but since the voltage is also increasing, the current level can be
maintained. As the current and the flux are kept constant the motor has a constant
torque characteristics and power of the machine rises.
By varying the armature voltage below the nominal rated voltage, motor can be made to
operate at various speeds in a wider range delivering full torque and reduce power
output.
It is not possible to operate the motor at higher than the base speed by
increasing the armature voltage above nominal rated voltage. This method of speed
control is used in cranes, rolling mills etc. Thus up to base speed the motor can be
controlled easily by controlling the armature voltage, called as ‘constant torque
application’.
4.7.2 Field current control:
Upto the base speed, the motor is controlled by armature voltage control. Now if the
speed required is more than the base speed and the armature voltage is not be increased
beyond the rated voltage, the choice is to decrease the field flux. To achieve this, the
field current is to be decreased. This is called ‘constant power application’ since
power remains constant. This is also termed as field weaking of the system.
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4.8 DRIVES ADVANTAGES AND DISADVANTAGES:
Advantages
Disadvantages
1.Potentially lower installed cost above
Brush Maintenance.
50 HP.
2.Good energy efficiency & regeneration
Higher Repair Costs.
of power can possible by 4-Quadrant
method.
3.Speed control of DC Drive is better
Limited Dynamic Response due to line
than AC Drive.
commutation restrictions, coupled with
higher mass moments of inertia imposed
by the wound field armature.
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4.DC motor tuning is good in DC Drive
Limited range to 5,000-hp, due to
means current autotuning is done in
commutation restrictions.
proper manner & also all gains are set by
auto tuning.
5.Few distance limitations.
Potential
for
rapid
acceleration
to
destructive velocities upon loss of the
stationary field.
CHAPTER – 6
CONCLUSION
5.1 Automation plays an increasingly important role in the global economy and in daily
experience. Engineers strive to combine automated devices with mathematical and
organizational tools to create complex systems for a rapidly expanding range of
applications and human activities.
5.2 Automation provides 100% accuracy alltime. So the failures and mismatch in
production completely eliminates. It makes the system’s effeciency higher than manual
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as well as It controls wastages.. So the overall savings increses. It provides safety to
human being. By that industry can achieves the safety majors and ISO and OHSAS
reputation. It makes the operation faster than manual which causes higher production
and proper utilization of utilities. It increases the production by which the cost of each
product decreses and industry profit increases . It provides smooth control on system
response. It provides repeatability, so that the same kind of products are easier to
manufacture at different stages without wasting time. It provides quality control, so that
the products become reliable which improves industrial reputation in market.
It
provides integration with business systems. It can reduce labor costs, so the final profit
increases.
5.3 Industrial automation is very compulsory need of industries in today’s scenario to
meet market competition.
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