Transcript Introduction-to

Programmable Logic
Controllers
PLC’s
An Overview, Use in HVAC and Web
Technologies
By Sleepy Wombat
Overview
What is a PLC ?
History
Overview of Technology
PLC Configuration and Selection
Programming PLC’s
PLC’s in HVAC
Web Technologies
What is a PLC ?
PLC (Programmable Logic Controller)
A PLC works by looking at its inputs
and depending on their state, and the
user entered program, turns on/off
outputs.
A PLC can be thought of as:
Industrial Computers with specially
designed architecture in both their
central units (the PLC itself) and their
interfacing circuitry to field devices
(input / output connections to the real
world).
History 1/4
Early control systems consisted of huge control boards
consisting of hundreds to thousands of electromechanical
relays.
An Engineer would design the system logic.
Electricians would receive a schematic outline of logic then
implement the logic with relays.
The schematic was commonly called “Ladder Schematic”
The Ladder displayed all switches, sensors, motors,
valves, relays etc in the system.
Problems: Long commissioning time, Mechanical Reliance,
Any system logic design change required the power to the
control board to be isolated stopping production.
History 2/4
General Motors was among the first to recognise a
need to replace the systems “wired control board”
Hydramatic Division of GM specified the design
criteria for the programmable controller in 1968.
Goal – Eliminate the high cost associated with
inflexible, relay controlled systems.
History 3/4
New Controller Specifications:
– Solid State System
– Computer Flexibility
– Operate in Industrial Environment (vibrations, heat,
dust etc.)
– Capability of being reprogrammed
– Easily programmed and maintained by electricians
and technicians.
History 4/4
In 1969 Gould Modicon developed the first PLC.
Strength – Programmed with Ladder Logic
Initially called Programmable Controllers PC’s
– Now - PLC’s, Programmable Logic Controllers
PLC’s have evolved from simple on/off control to
being able to communicate with other control
systems, provide production reports, schedule
production, diagnose machine and process
faults.
Overview of Technology
Basic PLC Schema
CPU
Power Supply
Memory
Input Blocks
Output Blocks
Communications
Expansion
Connections
CPU Module
The Central Processing Unit (CPU)
Module is the brain of the PLC.
Primary role to read inputs, execute
the control program, update outputs.
The CPU consists of the arithmetic
logic unit (ALU), timing/control
circuitry, accumulator, scratch pad
memory, program counter, address
stack and instruction register.
A PLC works by continually scanning
a program
Scan
Inputs
Self
Check
PLC Program
SCAN
Update
Outputs
Execute
Code
Memory
The memory includes pre-programmed ROM memory
containing the PLC’s operating system, driver
programs and application programs and the RAM
memory.
PLC manufacturer offer various types of retentive
memory to save user-programs and data while power
is removed, so that the PLC can resume execution of
the user-written control program as soon as power is
restored.
Memory cont’d
Many PLCs also offer removable memory modules,
which are plugged into the CPU module.
Memory can be classified into two basic categories:
volatile and non-volatile.
- Volatile memory is that which loses state (the
stored information) when power is removed.
- Nonvolatile memory, on the other hand, maintains
the information in memory even if the power is
interrupted.
Memory cont’d
Some types of memory used in a PLC include:
ROM (Read-Only Memory)
RAM (Random Access Memory)
PROM (Programmable Read-Only Memory)
EPROM (Erasable Programmable Read-Only Memory)
EEPROM (Electronically Erasable Programmable ReadOnly Memory)
FLASH Memory
Compact Flash – Can store complete program
information, read & write text files
I/O Modules
Input and output (I/O) modules connect
the PLC to sensors and actuators.
Provide isolation for the low-voltage, lowcurrent signals that the PLC uses
internally from the higher-power
electrical circuits required by most
sensors and actuators.
Wide range of I/O modules available
including: digital (logical) I/O modules
and analog (continuous) I/O modules.
Inputs Modules
Inputs come from sensors that translate physical or
chemical phenomena into electrical signals.
The simplest form of inputs are digital/discrete in AC/DC.
In smaller PLCs the inputs are normally built in and are
specified when purchasing the PLC.
For larger PLCs the inputs are purchased as modules, or
cards, with 8,16, 32, 64, 96 inputs of the same type on
each card.
Inputs Modules
The list below shows typical ranges for input voltages.
5 Vdc
12 Vdc
24 Vdc
48 Vdc
12 Vac
24 Vac
120 Vac
240 Vac
Example of Input Card
Outputs Modules
Output modules rarely supply any power, but instead act
as switches.
External power supplies are connected to the output
card and the card will switch the power on or off for each
output.
A common choice when purchasing output cards is
relays, transistors or triacs.
Relay are the most flexible output devices. They are
capable of switching both AC and DC outputs. But, they
are slower, cost more, and they will wear out after
millions of cycles.
Relays
The most important consideration
when selecting relays, or relay
outputs on a PLC, is the rated
current and voltage.
For transistor outputs or higher
density output cards relay terminal
blocks are available.
– Advantage of individual standard
replaceable relays
Outputs
Typical output voltages are listed below,
5 Vdc
12 Vdc
24 Vdc
48 Vdc
24 Vac
120 Vac
240 Vac
WARNING: Always check rated voltages and currents for
PLCs and never exceed.
Example of Output Card
Analogue Cards
Typical Analogue Input
signals are:
– Flow sensors
– Humidity sensors
– Load Cells
– Potentiometers
Analogue Output signals
control:
–
–
–
–
–
Analogue Valves
Actuators
Chart Resorders
Variable Speed Drives
Analogue Meters
– Pressure sensors
– Temperature sensors
– Vibration
Typical Analogue Signal
Levels
–
–
–
–
4-20mA
1-5 Vdc
0-10 Vdc
-10 – 10Vdc
Analogue Inputs/Outputs
Analogue input cards convert continuous signals via a
A/D converter into discrete values for the PLC
Analogue output cards convert digital values in then PLC
to continuous signals via a D/A converter.
Resolution can be important in choosing an applicable
card
Example, for a temperature input of 0 to 100 degrees C
– For 8 bit resolution the value in the PLC is 0 to 255
– For 12 bit resolution the value in the PLC is 0 to 4095
– For 12.5 bit resolution the value in the PLC is 0 to 6000
– For 13 bit resolution the value in the PLC is 0 to 8192
– For 16 bit resolution the value in the PLC is 0 to 32768
Special Modules
RF ID
Voice
Gas Flow Calculation
Weigh Cell
Hydraulic Servo
ASCII
Fuzzy Logic
Temperature Sensor
Temperature Control
Heat/Cool Control
Field Bus Cards
– DeviceNet, Profibus etc
– Lonworks, BACNet
Fast Response (Interrupt)
PID
Loop Controller
BASIC Cards
RS232 Comm’s
Modbus ASCII/RTU
Ethernet Comm’s
High Speed Counters
Position Control Cards
Per to Per Comm’s
– Controller Link
– DH+
– Modbus Plus
Available Instructions
Sequence
– Input
– Output
– Control
Logic
Timer and Counters
Comparison
Range Comparison
Data Movement
Data Shift
Step / Step Next
Serial Communications
Text String Processing
File Manipulation
Increment/Decrement
Conversion
– ASCII
– Number Systems
Math
Floating Point Math
Statistics
Scaling
PID
PID with Auto tune
Clock / Date
Block Processing
– IF,THEN,ELSE,LOOP
Table Processing
– LIFO, FIFO
Networks
ASI
Devicenet
Interbus-S
Profibus
Interbus
Fieldbus
Ethernet I/P
Smart Distributed System
(SDS)
Seriplex
CANopen
Lonworks
BACNet
Gateways enable communications between
different network topologies
PLC Configuration
RACK
SHOE BOX
MINI
MICRO
The Configuration of PLC
The configuration of PLC refers to the packaging of the
components.
Typical configurations are listed below from largest to
smallest.
– Rack Type : A rack can often be as large as 18” by 30” by 10”
– Mini: These are similar in function to PLC racks, but about the
half size. Dedicated Backplanes can be used to support the
cards OR DIN rail mountable with incorporated I/O bus in
module.
– Shoebox: A compact, all-in-one unit that has limited expansion
capabilities. Lower cost and compactness make these ideal for
small applications. DIN rail mountable.
– Micro: These units can be as small as a deck of cards. They tend
to have fixed quantities of I/O and limited abilities, but costs will
be lowest. DIN rail mountable.
Sizing of PLC
Micro PLCs: I/O up to 32 points
Small PLC: I/O up to 128 points
Medium PLC: I/O up to 1024 points
Large PLC: I/O up to 4096 points
Very Large: I/O up to 8192 points
Selecting a PLC
Criteria
Number of logical inputs and outputs
Memory
Number of special I/O modules
Expansion Capabilities
Scan Time
Communication
Software
Support
Dollars
Selecting a PLC
Example of PLC Specifications
Example of PLC Specifications
Manufactures
Major Brands
OMRON
Allen Bradley
Schneider (Modicon, Telemecanique, Square D)
GE Fanuc
Siemens
Keyence
Automation Direct (Koyo)
Festo
Toshiba
Eberle
Texas Instruments
Mitsubishi
April
Hitachi
Programming PLC’s
Programming PLC’s
Ladder Logic remains the most common
technique for programming PLC’s
PLC Standardization
Open Controller
IEC 61131
– Based on IEC 1131 (1992) standard, developed to be
a common and open framework for PLC architecture.
IEC 61131-1 Overview
IEC 61131-2 Requirements & Test Procedures
IEC 61131-3 Data Types & Programming
IEC 61131-4 User Guidelines
IEC 61131-5 Communications
IEC 61131-7 Fuzzy Control
IEC 61131-7 Guidelines for the application and
implementation of programming languages
IEC 61131-3
IL (Instruction List) – mnemonic programming
LD (Ladder Diagram) – Relay logic
ST (Structured Text) – A BASIC like programming
language
FDB (Functional Block Diagram) – Graphical dataflow
programming language
SFC (Sequential Flow Chart) – Graphical method for
structured programs
IEC 61131-3 Examples
Ladder
Instruction List
Structured Text
Function Block
Sequential Flow Chart
PLC’s in HVAC control
PLC’s in HVAC control
Despite the versatility of today’s PLC’s,
many controls professionals are skeptical of
applying PLC’s to new applications such as
HVAC control.
Reasons included :
– Lack of knowledge of these systems
– Requirement for programming
– Lack of initial capability of technology
– Premium first up cost
Advantages
PLC’s remain a predominate piece of equipment
on the factory floor and will probably remain so for
some time to come.
The advantages they offer are:
– Cost effective for controlling complex systems
– Flexible and can be reapplied to control other systems
quickly and easily
– Computational abilities allow more sophisticated control
– Trouble shooting aids make programming easier and
reduce downtime
– Reliable components (high MTBF) ensure operation for
years
Advantages continued….
– Variety of I/O interfaces
– Small size
– Growing with technology, faster scan times, capability
etc
– Quick I/O disconnects that aids in field servicing
– Modularity in hardware architecture
– Modularity in software design (programmer
dependant)
– Software Timers/Counter, Relays
– Clean failure mode
– On-line programming
– Self inspecting for operation code during execution
– Availability of programmers/trouble
shooters/integrators
– Availability of replacement parts
Benefits
The benefits achieved with programmable
controllers will grow with the individual using
them:
“The more you learn about PLC’s, the more you
will be able to solve other control problems.”
Examples
Southgate – Melbourne
Millennium Dome – London
Woolworths – Britain
ST Microelectronics – France
Einstein III Building - Munich
Web Technologies
Web Enabled Automation...?
Is it just more Internet hype or is there
some benefit behind the idea.
Is it possible to connect all of these
systems by their PLC’s to the Internet ?
Is it practical ?
Is it profitable ?
Short Answers……
Internet access can provide compelling
competitive advantages linking customers,
suppliers, subcontractors, front line management.
– Improve fault reporting and response time
– Enhance flexibility
– Optimise process control
Proven affordable technologies are readily
available to connect any PLC, Process Controller
or I/O to the Internet and Intranet.
Process to Internet access has the potential to
become a standard utility.
What is Web Enabling
Web enabling gives real time access to data and
control, virtually anytime, anywhere.
It uses communication with any manufactures
PLC or I/O to send information via the Internet to
anywhere in the world.
Web enabled automation drives real-time
accessibility “Vertically Down” to the control
device level.
What can we do with it ?
Check real time process data without waiting for
end of shift reports
Track equipment run time and initiate
maintenance requests
Automatically notify a technician via email or
GSM phone etc of faults and allow rectification
Collect process data on a server PC and
analyse with statistics and control (SPC)
Use HTML help files including graphics
Monitor and control remote operations reducing
field staffing and unnecessary travel
What pieces and parts are required ?
Interface
Web Server
Data Service
Browser
Interface
An interface to the equipment to be monitored
and controlled via the web (network) connection
–
–
–
–
Ethernet Line
Modem / Phone line
ISDN
Wireless Modem (eg 802.11b Ethernet)
Type of connection is typically determined by the
thin server and the existing network
infrastructure – or lack thereof
Web Server
Web Server (or “thin server” data service) to
enable the remote browser to view the desired
displays and web pages.
– Typical installation requires a connection to an
existing PLC or proprietary controller.
– Most PLC’s support at least a serial connection using
the vendor supplied protocol to communicate.
– Use an Open network controller (interface)
– Some PLC’s have Web Servers built into their
Ethernet Units.
Data Service
A data service or interface to handle exchanging
data between the local equipment/ process
(server) and the remote system (client)
– A common “language”, protocol is required..
– XML (Extended Markup Language)
– Benefit of XML is its independence from senders and
receivers hardware, OS, and application.
Browser Interface
Use the thin servers assigned IP address to
access the remote system.
Simple browsing requires standard browser
interface found on a desktop computer, PDA,
WAP, or “Thin Client”
For application information sharing (SPC,
Enterprise Software), if the thin server and
remote application software support a common
interface such as OPC, setting up the data
exchange can be accomplished in a couple of
minutes
New term … OPC
OLE for Process Control
Object Linking and Embedding
One of industries most popular standards
Maintained by OPC foundation
OPC standard is non proprietary technical
specification based on Microsoft's
OLE/DCOM technology.
www.opc.org
Web Servers
Computer Based Displays
SCADA – Supervisory Control and Data Acquisition
Citect, Wonderware, Fix, Iconics, Genius
– Ethernet, Serial, OPC (OLE for Process Control), Dedicated
Computer Boards for Propriety Buses
Dedicated Packages for BMS
– Citect SCADA Facilities
Embedded Web Servers
Open Network Controller Interface – Gateway
Embedded Web Servers in PLC’s Ethernet cards
New Dedicated HMI Screens – some have embedded Web
Servers
Example of Web Technology visit www.WebHMI.com
Thank you….
Questions ?