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SERVILINK
SYSTEMS LIMITED
PLC SYSTEM
AND
PROGRAMMING
SERVILINK
SYSTEMS LIMITED
Part I : Conventional PLC.










History of PLC.
Conventional PLC Basic.
What is Inside PLC.
PLC Operation.
Input / Output
Steps to design PLC
system.
Hardware and Software.
Selection Criteria.
Range of Allen Bradley
PLC.
Application.
Part II : Advance
Technology in PLC.
 Short comings of
conventional PLC.
 How to over come ?
 What is Logix ?
 Advantage.
History of Control System
Before 1960
•Relay based Machine Control
• Bulky Panel, Trouble shooting difficult
• Limited life, Modification difficult
In 60s First PLC introduce.
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SYSTEMS LIMITED
10 Second Bulb
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SYSTEMS LIMITED
+ve
Timer Contact
Switch
0 – 10 Sec
Timer
Bulb
-ve
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SYSTEMS LIMITED
PROGRAMMABLE
CONTROLLER
BASICS
What is a Programmable Controller?
INPUTS
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SYSTEMS LIMITED
OUTPUTS
PROGRAMMABLE
CONTROLLER
CR
A PROGRAMMABLE CONTROLLER is a solid state control
system that monitors the status of devices connected as
inputs. Based upon a user written program, stored in
memory, it controls the status of devices connected as
outputs.
INPUT DEVICES
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SYSTEMS LIMITED
• Pushbuttons
• 120 VAC
• Selector Switches
• 24 VDC
• Limit Switches
• Level Switches
• Photoelectric Sensors
• Proximity Sensors
• Motor Starter Contacts
• Relay Contacts
• Thumbwheel Switches
OUTPUT DEVICES
• Valves
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SYSTEMS LIMITED
Relays
• Motor Starters
• 120 VAC/VDC
• Solenoids
• 240 VAC/VDC
• Control Relays
• 24 VAC/VDC
• Alarms
• Lights
Triac
• 120 VAC
• Fans
• Horns
MOSFET
• 24 VDC
Inside a PLC
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Communications
Port
I
n
p
u
t
C
i
r
c
u
i
t
s
Central
Processor
High
Voltage
Isolation
Barrier
MEMORY
data
program
Low Voltage
AC Power Supply
85-264 VAC, 50/60Hz
or
DC Power Supply
O
u
t
p
u
t
C
i
r
c
u
i
t
s
Isolation
Barrier
CR
High
Voltage
Input Wiring
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Terminal
Block
Input Devices
Isolation
Barrier
1
2
3
L1
L1
4
5
6
7
8
9
L2
10
COM
P
L
C
Output Wiring
Isolation
Barrier
CR
Terminal
Block
OUT 1
OUT 1
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SYSTEMS LIMITED
Output Devices
L1
L2
OUT 2
P
L
C
OUT 2
OUT 3
OUT 3
OUT 4
OUT 4
OUT 5
OUT 5
OUT 6
OUT 6
L1
L2
PLC Operating Cycle
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SYSTEMS LIMITED
START
Housekeeping
Input Scan
Output
Scan
Program
Scan
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SYSTEMS LIMITED
Input
Analog
Voltage ( 0-10V)
Current (4-20mA)
Digital
DC
(24V, 48V, 110V)
AC
( 24V, 48V,
110V,220V)
ANALOG INPUT DEVICES
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SYSTEMS LIMITED
Physical Devices
Range
• Temperature Transmitter
• 0- 20 mA
• Pressure Transmitter
• 4- 20 mA
• Flow Trasmitter
• 0- 5 VDC
• Level Transmitter
• 0- 10 VDC
• mV input
• -10VDC to 10VDC
• Resistor Input
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ANALOG OUTPUT DEVICES SYSTEMS
LIMITED
Physical Devices
Range
• Control Valve
• 0- 20 mA
• Damper
• 4- 20 mA
• Variable Frequency Drive
• 0- 5 VDC
• Actuator
• 0- 10 VDC
SELECTION CRITERIA
• Input / Output Number
• Voltage level
• Response time
• Memory expected
• Application
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SYSTEMS LIMITED
THUMB RULE OF MEMORY
USAGE
Type
a) Discrete I/O points
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SYSTEMS LIMITED
Quantity
a) ------------ X 10
= ---------- Instruction
words
b) Analog I/O points
b) ------------ X 25
= ---------- Instruction
words
c) Special I/O modules
c) ------------ X 100 = ---------- Instruction
words
Estimated Total Memory Required
----------- Instruction
words
Typical Control System Approach
System Layout
Design
Electrical Device
function and placement
Electrical
Design
I/O Addresses
of all Devices
Program
Development
Machine
Startup
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SYSTEMS LIMITED
Different PLCs of Allen-Bradley
•
•
•
•
•
•
•
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SYSTEMS LIMITED
PICO Controller
MicroLogix (1000, 1100, 1200, 1500)
SLC-500
PLC5
CompactLogix
FlexLogix
ControlLogix
PICO Controller
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SYSTEMS LIMITED
PICO
Controllers
PICO GFX
Controllers
MicroLogix
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1000
1500
1100
1200
MicroLogix1000
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MicroLogix1100
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MicroLogix1200
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MicroLogix1500
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SLC 500
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COMPACTLOGIX SYSTEM
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FLEXLOGIX SYSTEM
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PLC 5
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SYSTEMS LIMITED
CONTROLLOGIX SYSTEM
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SYSTEMS LIMITED
SERVILINK
CONTROLLOGIX CHASSIS SYSTEMS
LIMITED
ControlLogix chassis sizes:
• 4-slot
• 7-slot
• 10-slot
• 13-slot
• 17-slot
CONTROL LOGIX
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SYSTEMS LIMITED
Also known as ControlBus™ backplane
• Printed-circuit board at back of chassis
• Provides electrical interconnection between modules
Module
Connectors
Backplane
ControlLogix Controller
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SYSTEMS LIMITED
32-bit controller that combines logic and data in modular memory:
Locking
Tab
LEDs
Backplane
Connector
Keyswitch
Door
Battery
Labels
Battery
Label
RS-232 Serial
Port
Locking
I/O Solutions
• Native Chassis I/O
– 1771 I/O Family
• Modular I/O
–
–
–
–
1746 SLC I/O (SLC)
1793 FLEX Integra I/O
1794 FLEX I/O
1797 FLEX Ex I/O
• Packaged &
Embedded I/O
– 1791 Block I/O
– 1792 ArmorBlock I/O
SERVILINK
SYSTEMS LIMITED
CONFIGURATION DRAWING
OF CONTROL LOGIX
ENG./OP Station
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SYSTEMS LIMITED
OP. Station
Printer
CLIENT: Hindalco Industries Ltd.
OUR OFFER REF NO.: SSE-V:229-R1:08:MM
1000 TPD Copper Slag Beneficiation Plant
Redundant Controllogix Controllers
Ethernet
Switch
Ethernet Way
Redundant Controlnet Way
Flex I/Os
BY : Servilink Systems Ltd, Vadodara.
Language for Programming
SERVILINK
SYSTEMS LIMITED
SERVILINK
SYSTEMS LIMITED
IDENTIFYING SYSTEM
COMPONENTS
Logix5000 System
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Logix5000 control engine available in several
platforms/physical formats:
• ControlLogix® - High-performance, multi-controller modular
chassis
ControlLogix
System
SoftLogix System
DriveLogix System
Compact Logix
System
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Logix5000 System
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Logix5000 control engine available in several platforms/physical
formats:
• CompactLogix™ - Small modular stand-alone to medium sized
• DriveLogix™ - Distributed drive control
• SoftLogix™ - Combines control, information, visualization on an
open-control system
– (e.g., control engine housed in computer/other terminal.)
ControlLogix
System
DriveLogix
System
7/7/2015
SoftLogix System
CompactLogix System
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Logix5000 Control Disciplines
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SYSTEMS LIMITED
Control disciplines supported:
• Sequential Control: Sequence process units through series of
discrete states
– (e.g., conveyor systems).
• Motion Control: Direct movement by controlling current,
acceleration, position, speed
– (e.g., labeling, packaging, picking and placing).
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Logix5000 Control Disciplines
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SYSTEMS LIMITED
Control disciplines supported:
• Drive Control: Manage speed, torque, horsepower, direction of
motor
– (e.g., mixing, winding).
• Process Control: Operate machine or manufacturing environment
on regulated parameters
– (e.g., batching, filling).
• Safety Control: To monitor safety circuitry and safety devices
– (e.g., light curtains, to minimize risks).
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Example: Bottling Line
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Various tasks in bottling line controlled using Logix5000
system:
• Sequential control - high speed counting
• Motion control - capping and labeling .
• Process control - batching and filling
• Drive control - conveyor motor
• Safety control – operator safety
High Speed Bottling Line
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Platform and Components
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SYSTEMS LIMITED
• High-performance
• Multi-controller system
• Modular chassis format
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Platform and Components
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SYSTEMS LIMITED
• Easy integration with any existing systems (i.e., PLC-5®, SLC™)
• Capable of high-speed communications and data transfers
• Allow multiple controllers, I/O modules, and communications modules in
any order/location within chassis
Chassis
Power
Supply
I/O and Communication
Modules
7/7/2015
Controllers
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Chassis
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SYSTEMS LIMITED
Chassis: Hardware assembly houses devices:
• Controllers
• I/O
• Communications modules
Chassis
Tip: Slots are the openings in a chassis that hold individual modules.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Chassis
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SYSTEMS LIMITED
ControlLogix chassis sizes:
•
•
•
•
•
4-slot
7-slot
10-slot
13-slot
17-slot
0
1
2
3
4
5
6
7
8
9
Slots
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Chassis
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SYSTEMS LIMITED
Slots numbered from left to right starting with 0:
0
1
2
3
4
5
6
7
8
9
Slots
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Chassis
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SYSTEMS LIMITED
1756 (ControlLogix) modules
are not slot dependent (i.e.,
any 1756 module can be
placed in any slot in the
chassis).
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Backplane
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SYSTEMS LIMITED
Also known as ControlBus™ backplane
• Printed circuit board at back of chassis
• Provides electrical interconnection between modules
Module
Connectors
Backplane
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Backplane
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SYSTEMS LIMITED
The backplane allows
data to be multicast (i.e.,
an input module sends
data once that is
received by multiple
controllers
simultaneously).
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Controller
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SYSTEMS LIMITED
32-bit controller that combines logic and data in modular
Locking Tab
memory:
LEDs
Backplane
Connector
Keyswitch
Door
Battery
Labels
Battery Label
RS-232 Serial Port
7/7/2015
Locking Tab
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Controller
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SYSTEMS LIMITED
Controllers have two main internal components:
• Central Processing Unit (CPU): The decision making component
that executes the program stored in memory.
• Memory: A group of circuit elements where programs and data
Tip:
battery will maintain controller memory when power is turned off.
areA stored.
There are also controllers that support nonvolatile memory.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix I/O Modules
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SYSTEMS LIMITED
1756-I/O modules provide input/output capability to many
applications.
I/O modules offer the following capabilities:
• Easy configuration using a wizard
• Electronic keying
• Scaling of analog values
• Diagnostics (depending on the module)
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix I/O Modules
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SYSTEMS LIMITED
Wiring from process/machine connected to I/O modules
through one of the following special devices:
• RTB (Removable Terminal Block): field wiring connector for I/O
modules.
– Connected to RTB rather than directly to terminal block
• IFM (Prewired Interface Module): field wiring arm that uses
prewired/factory-wired cable to connect to I/O module.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix I/O Modules
SERVILINK
SYSTEMS LIMITED
Tip: RTBs and IFMs allow for easy replacement or interchanging of I/O
modules without rewiring them.
RTBs and IFMs are not
included with I/O
modules. They must be
purchased separately.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Communications Modules
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SYSTEMS LIMITED
Communications Modules: Used for creating communications
between controller and network:
Network
EtherNet/IP™
Required
Communications Module
1756-ENBT
ControlNet™
1756-CNB, 1756-CNBR,
1756-CN2, 1756-CN2R
DeviceNet™
1756-DNB
Data Highway Plus™
(DH+™) or Universal
Remote I/O
1756-DHRIO
Tip: For serial communications, the computer connects directly to the
controller.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
ControlLogix Platform Modularity
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SYSTEMS LIMITED
Modular format allows users to design, build, and modify
flexible systems:
• Select the number of controllers and appropriate
memory size
• Select the number and type of I/O modules
• Select the number and type of communications
modules
Tip: Modularity allows for easy reconfiguration and repair by replacing
individual units.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
SERVILINK
ControlLogix Platform Modularity SYSTEMS
LIMITED
System can range in complexity:
• Simple stand-alone controller and I/O modules in a
single chassis
• Complex system with multiple controllers, chassis,
and networks in different locations
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Example: Platform Modularity
ControlLogix
Chassis
DeviceNet Network
EtherNet/IP
Network
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SYSTEMS LIMITED
ControlLogix
Chassis
ControlNet
Network
CompactBlock
I/O
PLC-5® System
PanelView™ Plus
Terminal
RediSTATION™
Flex I/O™ System
1336 FORCE™ Drive
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
Example: Platform Modularity
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SYSTEMS LIMITED
Tip: The ControlLogix system is ideal for network bridging, or sharing
information between different networks.
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
SERVILINK
FlexLogix Platform and Components SYSTEMS
LIMITED
System characteristics:
• Reduced size for smaller spaces
• Can be mounted on a DIN rail or panels
• Can be mounted vertically or horizontally
• Modular
7/7/2015
(Confidential – For Internal Use Only) Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
SERVILINK
SYSTEMS LIMITED
CONTROL
LOGIX !!!
Logix Architecture
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SYSTEMS LIMITED
One Controller Platform To Do It All
RSLogix 5000
programming
software provides
all of the tools to
control any Logixbased application
in your plant
Sequential
control
Motion
control
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SYSTEMS LIMITED
Safety control
Process
control
Drive
control
ControlLogix55xx Controllers
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SYSTEMS LIMITED
• Multiple processors for the ControlLogix platform
– Expandable network communications via separate modules
– Built-In RS232 ASCII Serial, DF1, and DH485 protocol Support
– Varying memory capacity and nonvolatile (NVS) memory backup
• Multiple controllers in one small package
– The ControlLogix55xx’s integrated motion capability saves you
money by eliminating separate motion controllers and software
– Function Blocks for process and drive systems
– SIL 3 Safety controller
• Fully scalable solution allows you to purchase exactly what you need
– Memory options for any size application
– Modular networks provides the right communications mix for your
application
– I/O capacity sufficient to meet large applications
• TÜV SIL 2 certified
– Standard off-the-shelf components
– Hardware, firmware and wiring restrictions apply
ControlLogix55xx Controllers
Logix5555 1756-L55
• 250 I/O Connections
• 0K Base Version
• 750K, 1.5M, 3.5M, and
7.5MByte RAM Memory
cards
• 750K, 1.5M, 3.5M RAM /
Flash Non-volatile
storage Combo Memory
Cards
• Local / Remote Battery
Backup (1756-BATM)
• 30% Increase in motion
and FBD performance
over Logix5550
• Forced LED
• Hardware changes to
support Redundancy
(hot backup)
• Real Time Clock (RTC)
chip
• SIL 2 certified
Logix5561 1756L61(S)*
• 250 I/O
Connections
• 2Mb Fixed RAM
Memory
• Local / Remote
Battery Backup
(1756-BATM)
• CompactFlash card
socket for program
storage, logging or
firmware updating
• Built In Floating
Point Math Coprocessor
• Four to five times
faster on motion
and FBD than
Logix5550
• SIL 2 certified
• Integrated SIL3
safety control w/
safety partner
(1756-LSP)
Logix5562 1756L62(S)*
• 250 I/O
Connections
• 4Mb Fixed RAM
Memory
• Local / Remote
Battery Backup
(1756-BATM)
• CompactFlash card
socket for program
storage, logging or
firmware updating
• Built In Floating
Point Math Coprocessor
• Four to five times
faster on motion
and FBD than
Logix5550
• SIL 2 certified
• Integrated SIL3
safety control w/
safety partner
(1756-LSP)
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SYSTEMS LIMITED
Logix5563 1756L63*
• 250 I/O
Connections
• 8Mb Fixed RAM
Memory
• Local / Remote
Battery Backup
(1756-BATM)
• CompactFlash card
socket for program
storage, logging or
firmware updating
• Built In Floating
Point Math Coprocessor
• Four to five times
faster on motion
and FBD than
Logix5550
• SIL 2 certified
Logix5555 Memory Options
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SYSTEMS LIMITED
• The Logix5555 processor provides scalable memory
– Purchase the right amount of memory for the
applications
– A single memory expansion card may be installed
• Base processor has no user RAM memory
– Flash based non-volatile (NV) combination cards
also available
• Combined RAM / non-volatile flash memory built
in
• Backup storage for program and data
• Avoids battery dependence
RAM Cards
Processor
with RAM
NV memory
only
Processor with
NV Memory
750KByte
1756-M12
1756-L55M12
1756-M22
1756-L55M22
1.5Mbyte
1756-M13
1756-L55M13
1756-M23
1756-L55M23
3.5Mbyte
1756-M14
1756-L55M14
1756-M24
1756-L55M24
7.5Mbyte
1756-M16
1756-L55M16
N/A
N/A
Logix556x Nonvolatile Memory Storage
•
The ControlLogix5563 processor supports
nonvolatile memory storage (NVS)
– Provides long-term memory storage without
a battery
– Same functionality as with the
ControlLogix5555 processor
– Removable CompactFlash memory card
• Industrial environment grade rated
– CompactFlash memory card needs to be
ordered separately:
• 1784-CF64 Memory card 64MB
– RSLogix 5000 provides tools to store
controller configuration, firmware,
application program, and data
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SYSTEMS LIMITED
SERVILINK
SYSTEMS LIMITED
ControlLogix Communications
Backplane and Network Communications
• ControlLogix provides fully scalable
network communications that lets you
purchase only what you need
– ControlLogix chassis based network
modules purchased separately to
meet application needs
– Any mix DH+/RIO/ControlNet
/DeviceNet /EtherNet/IP/Serial
– De-couples network and controller
development
• Flexible networking
– Bridging and routing between
messaging networks across
backplane without any code in the
controller
• Supports I/O sharing
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SYSTEMS LIMITED
Ethernet
ControlNet
ControlNet
RIO, DH+
DeviceNet
ControlLogix Communications
•
•
•
Networks
– EtherNet/IP
– ControlNet
– DeviceNet
– DH+/RIO
– DH485
– Foundation FieldBus (ControlNet to FB
converter or Ethernet to FB)
– HART
– 3rd Party (SST or Prosoft)
• Profibus DP
• Interbus-S
• Modbus/Modbus Plus via the 1756-MVI
card
Mix and Match networks as needed
Bridge NetLinx networks without a controller
(Gateway)
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SYSTEMS LIMITED
Ethernet
ControlNet
ControlNet
RIO, DH+
DeviceNet
SERVILINK
ControlLogix Network Products - EthernetSYSTEMS
LIMITED
1756-ENET
1756-ENBT
1756-EWEB
1756-EN2T/EN2F
•10Mbit Ethernet bridge
module
•10/100MBit
Ethernet/IP
•Half/Full-Duplex
Communication
•RJ45 Twisted Pair
connector
•4 Character Diagnostic
Display
•High speed
Interlocking between
ControlLogix
processors via
EtherNet/IP
•Web-Enabled for
remote management
activity
•EtherNet/IP I/O
•10/100MBit
Ethernet/IP
•Half/Full-Duplex
Communication
•RJ45 Twisted Pair
connector
•4 Character Diagnostic
Display
•Functions as customer
data monitor, bridge for
controller and custom
web server
•6M of memory for web
server and email
support
•Can output Data in
XML format
•Ethernet I/P driver
supported
•No EtherNet/IP I/O
•10/100MBit
Ethernet/IP
•Half/Full-Duplex
Communication
•RJ45 Twisted Pair
connector (EN2T)
•Fiber optic media
(EN2F)
•4 Character Diagnostic
Display
•High speed
Interlocking between
ControlLogix
processors via
EtherNet/IP
•Web-Enabled for
remote management
activity
•EtherNet/IP I/O
•Type B USB 1.1 PNP
port for programming
and configuration
•RJ45 Twisted Pair
connector
•Using AUI interface,
Thick or Thin coax or
Fiber can be used
•Built in Web page
provides access to
chassis diagnostics
•Series A – messaging
only
Series B –
messaging and
EtherNet/IP I/O
ControlLogix Network Products –
ControlNet and DeviceNet
1756-CNB/R
•5Mbit ControlNet
bridge module
•Available in single
or redundant media
•Built-in Network
Access Port (NAP)
provides
programming
terminal access
•Supports up to 64
simultaneous I/O or
peer to peer
connections
•4 Character
diagnostic display
•SIL 2 certified
(series E)
1756-DNB
•DeviceNet
Scanner/ Bridge
•Supports
125K,250K, &
500Kbaud
•Supports up to 64
simultaneous
devices
•Up to 500bytes of
input and 496bytes
of output data to
Logix processor
•All I/O owned by a
single Logix
processor
•4 Character
diagnostic display
•Configured using
RSNetWorx for
DeviceNet
SERVILINK
SYSTEMS LIMITED
ControlLogix Network Products –
Legacy Networks
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SYSTEMS LIMITED
1756-DHRIO
1757-ABRIO
1756-DH485
•2 ports configurable
as DH+ or a RIO
Scanner
•56K, 115K,
230Kbaud
•DH+ routing table
permits devices on
DH+ to
communicate to
other networks
•DH+ default CPU
Slot routing forwards
messages to a Logix
controller
•RIO Scanner
supports up 64
logical racks (32 per
port)
•Block Transfer to
intelligent I/O
•Specifically
designed for
process applications
with 1771 Analog
I/O
•Supports 1771 IFE, OFE, IR, IXE,
IL, NOC, NOV, NIV,
NR, 1770-HT1 (Hart
Module)
•Simplifies analog
I/O configuration
•2 RS232 ports
•DH485 routing
table permits
devices on DH485
to communicate to
other networks
•DH485 default CPU
Slot routing forwards
messages to a Logix
controller
Logix Serial Communications
•
Software configurable ControlLogix RS232
interface port acts as your portal into the
system
– 9-pin D shell port
– Provides full bridging through the
controller onto the backplane so you can
access other modules or processors,
distributed in the system
• Eliminate the need for computer
cards
• Provides remote diagnostic support
– Supports DF1 protocol for programming
terminals and other intelligent devices to
access data and upload/download
programs (up to 38.4kbaud)
• DF1 Master/Slave and Point-to-Point
modes for SCADA applications
– ASCII Read/Write
– DH485 Protocol
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Ethernet
ControlNet
ControlNet
RIO, DH+
DeviceNet
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ControlLogix I/O
ControlLogix I/O is the
integral I/O platform for the
ControlLogix series of
programmable controllers
ControlLogix I/O Overview
• Wide Selection of 52 I/O modules
– Digital
– Analog
– Motion Modules
– High Speed Counter
– Programmable Limit Switch
– Configurable Flow Meter
– Hydraulics Module
• Options in termination
– Screw-style
– Spring-style
– Bulletin 1492 pre-wired
• Includes a variety of chassis sizes
• AC / DC Power Supply choices, both
Standard and Redundant
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ControlLogix I/O Functional Overview
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Features Common to All 1756 I/O Modules
• Producer/Consumer model
• Module-Level fault reporting
• RIUP (Removal and Insertion Under Power)
– for both field and backplane sides
• Fully software configurable
• Software retrievable module I.D. information
• Isolated versions of digital and analog modules
• Electronic backplane keying
• System clock access for various time-stamping functions
• Field FLASH firmware upgradeable
• Class 1 Division 2 certified
• Certifications approved: UL, CE, CSA, Marine & FM
Standard Digital Input Features
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• Wide variety of voltage selections:
– 79-132 VAC, 159-265 VAC and 10-30 VAC
– 10-31 VDC, 30-60 VDC, 90-146 VDC and TTLLevel
• Isolated and Non-Isolated choices
• Current Sink / Source options for DC
• 8, 16, and 32-point densities
• Software configurable noise filtering
• Two multi-cast methods of sending input status
– Change of State
• sends data only when it changes
• saves backplane and controller bandwidth
– Cyclic
• sends data on user selected time basis
79
Standard Digital Output Features
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• Wide variety of voltage selections:
– 74-132 VAC, 74-265 VAC and 10-30 VAC
– 10-31 VDC, 30-60 VDC, 90-146 VDC and TTL-Level
• Isolated and non-isolated choices
• Current Sink / Source options for DC
• 8, 16, and 32-point densities
• 2 Amp Outputs available for AC and DC
• Electronic fusing on select modules
– designated by “E” in catalog number
• Output data echo broadcast to system
– validates the receipt of controller commands
• Time-stamped blown fuse reporting
• Output scheduling based on system clock
• Configurable Output point definitions for program mode and
communication failure (Hold, Reset or Energize)
Diagnostic Digital I/O Features
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All Standard Digital I/O features plus . . .
Diagnostics
Open-wire detection
No-load detection
Field-side output verification
Point-level electronic fusing
Output pulse test
Diagnostic time stamping
Point-level fault reporting
Latching of intermittent fault
data
8-pt AC and 16-pt DC
densities
Input
Modules
Y
Output
Modules
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Analog Input Module Features
• All ControlLogix analog input modules feature
powerful on-board functionality...
– Up to 16-bit resolution over a selected input
range
– Two data formatting selections:
• Floating point
• Integer
– Channel Update Rates:
• Temperature: 50 mS (Float)
• Isolated Analog:
25 mS (Float) / 10
mS (Integer)
• Non-Isolated: 18 mS (Float) / 5 mS
(Integer)
• Hi-Speed Combo: Input - 400uS (Float) /
Out 1mS (Float)
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Analog Input Module Features
• On-board scaling to engineering units
• On-board alarming:
– High, High-High, Low, Low-Low
alarms
– Latching option for intermittent
alarms
– Deadband option for controllable
sensitivity
• Over / Under-range and open sensor
detection
• Real time sampling of channel data
• Calibration data and date stored in
non-volatile memory
• Digital filtering & notch filter selections
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Analog Output Module Features
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Analog Output Module Features
•
•
•
•
•
•
•
•
Isolated and non-isolated module types
13 to 16 bit resolution - range dependent
Two data formatting selections:
– Floating point (scalable)
– Integer (scalable)
Rate of change limiting
Configurable program mode and fault states on a per
point basis:
– Hold last state
– Set to user specified value
Output clamping at specified low - high value
Output hold for initialization feature for PID
applications
Specialty I/O
– Thermocouple
– RTD
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Table of Contents:
0. PLC Systems
1. PLC Programming
2. Architecture
PLC21010
Basics of Sequential Control Systems
This course is designed to give you an overview on basics of
sequential control system.
The course is organized into sections as listed on the left. For
the first time viewer, we suggest following the presentation
order by mouse click to advance each slide. To jump to a
specific topic, you can click on any topic links on the left. At
any time, you may return to this Main menu by clicking the
HOME button on the bottom left corner.
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PLC Systems
Automation Control Systems
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This training module addresses automation control systems. These
control systems are used in manufacturing plants of all types, and some
other applications that you may not have considered.
The control systems are built around special devices, designed to
operate industrial machines, and processes. We call these devices
Programmable Logic Controllers (PLC) and Programmable Automation
Controllers (PAC).
PLC and PAC Systems
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PLCs were introduced in the early 1970s. The term “PAC”, was
developed to differentiate those older systems from today’s much more
powerful, and flexible devices.
An analogy can be made between the VHS video tape, and a DVD.
Both systems allow viewers to record TV programs for viewing at a latter
time, but the DVD also can also be used to record music, data, and
more.
PLCs were designed to control machinery. PACs can be used for
machine control, process, motion control, and other applications.
PLC and PAC Systems
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In this module, we will use the term PLC generically to refer to both
PLCs, and PACs.
This section will explore the various components that comprise a PLC
system.
Basic Components of a PLC System
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There are five basic components in a PLC system:
•
•
•
•
•
The PLC processor, or controller
I/O (Input /Output) modules
Chassis or backplane
Power supply
Programming software that runs in a PC
In addition to these 5, most PLCs also have:
• A network interface
Let’s look at each in more detail..
Basic Components of a PLC System
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Processor, Controller, or CPU
•
•
•
•
Stores the control program and data in its memory
Reads the status of connected input devices
Executes the control program
Commands connected outputs to change state based on program
execution
– For example: Turn a light on, start a fan, adjust a speed, or
temperature
• Comes in various physical forms
Processor that fits in a
chassis
Stand alone PLC
Basic Components of a PLC System
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I/O Modules
• Physically connect to field devices
• Input modules convert electrical signals coming in from input field
devices such as pushbuttons, to electrical signals that the PLC can
understand.
• Output modules take information coming from the PLC and convert it
to electrical signals the output field devices can understand, such as
a motor starter, or a hydraulic solenoid valve.
• I/O comes in various forms
I/O that fits in a chassis with
the PLC
I/O that is remotely located
from the PLC requires a
network connection back to
the PLC
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Input Modules
• Input modules interface directly to devices such as switches and
temperature sensors.
• Input modules convert many different types of electrical signals
such as 120VAC, 24VDC, or 4-20mA, to signals which the
controller can understand.
24 Volt DC
System
Field device - this is
showing a simple
switch
+ 24 Volts
- 24 Volts
1
2
3
4
5
6
7
8
9
10
COM
A/D conversion
Terminal block - this is
where wires from the
field devices are
connected
Input Module
To PLC
Input Modules
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• Input modules convert real world voltage and currents to
signals the PLC can understand. Since there are different
types of input devices, there is a wide variety of input
modules available, including both digital and analog
modules.
Switch
24V DC
Pressure
4-20 mA
Temperature
0-10V DC
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Discrete vs. Analog Modules
• Discrete modules use only a single bit to represent the state of the
device. For example, a switch is either open or closed. Therefore,
the bit is either a 0 (switch is open) or a 1 (switch is closed). Discrete
modules are also known as Digital modules.
• Analog modules use words to represent the state of a device. An
analog signal represents a value.. For example, the temperature
could be 5, 9, 20, 100, etc degrees. Analog modules use a value,
such as 52, rather than a 0 or 1 to represent the state of the device.
The switch is either on or off.
Therefore it is a digital
device and will interface to a
digital, or discrete input
module.
The temperature could have
many states or values.
Therefore it is an analog
device and will interface to
an analog input module.
DC Input
Analog Input
Discrete vs. Analog Modules
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Discrete Modules
• Devices that are either on or off, such as a
pushbutton, get wired to discrete modules.
Discrete modules come in a variety of types, such as
24VDC or 120VAC. You can buy discrete modules
that allow you to typically connect anywhere from 2 to
32 devices, with the most popular being 16 devices.
• Since it takes only 1 bit to represent the state of a
device, a 16 point discrete module only requires 16
bits of memory in the controller to store the states of
all the points on the module.
.
Discrete vs. Analog Modules
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Analog Modules
• Devices that have a number associated with them,
such as a temperature sensor, get wired to analog
modules. Analog modules come in a variety of types,
such as 4 to 20 mA or 0 to 10 VDC. You can buy
analog modules that allow you to connect anywhere
from 2 to 16 devices.
• Since it takes 1 word to represent a number, a 16
point analog module requires 16 words of memory in
the controller to store the value of all the numbers on
the module. Each word in a PLC takes 16 or 32 bits
(depending on the PLC), therefore it takes 16 or 32
times the amount of PLC memory to store analog
points vs. digital points.
Output Modules
D/A Conversion
• Output modules interface
directly to devices such as
motor starters and lights
• Output modules take digital
signals from the PLC and
convert them to electrical
signals such as 24VDC and 4
mA that field devices can
1
understand
2
Output Module
3
4
5
From PLC
6
7
8
9
10
COM
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Terminal block - this is
where wires from the
field devices are
connected
Field device -Motor
starter, controlling
an AC motor.
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Output Modules
• Output modules take a signal from a PLC and convert it to
a signal that a field device needs to operate. Since there
are different types of output devices, there is a wide
variety of output cards available, including both digital and
analog cards.
Valve
0-10V DC
Fan
120V AC
Light
24V DC
Basic Components of a PLC System
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Chassis/Backplane
All PLCs need some method of communicating between the controller,
I/O and communications modules. Here are three ways used to
accomplish this communications between the various components that
make up the PLC system.
• Modules are installed in the same chassis as the PLC
and communicate over the chassis backplane
• Modules are designed to “plug” into each other. The
interconnecting plugs form a backplane. There is no
chassis
• Modules are built into the PLC. The modules come
together in one physical block. The backplane in this
case is transparent to the user.
Basic Components of a PLC System
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Below is an example of a backplane in a chassis based system. You
can see the backplane in the area where the modules are not inserted.
The modules have connectors that plug into the black connectors on
the backplane. All of the connectors on the backplane are connected
together electrically.
Backplane
connector
Chassis and Backplane Examples
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Example of a modular based
PLC. The PLC slides into the
chassis along with other
modules
Slide modules into
available slots
Example of a PLC that plugs
into adjacent modules to form
a backplane with no chassis
required
Example of a PLC with the
modules built in. Comes as
one block
Each module plugs
into the one to the left
Connections for the
built in I/O
Benefits of the Different Forms
• Great flexibility in choice of
modules. Modules can be
easily installed or removed
without affecting other
modules
• Great flexibility in choice of
modules. In some cases
modules cannot be removed
without “breaking the chain”
and affecting all modules
downstream. No chassis cost.
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Slide modules into
available slots
Each module plugs
into the one to the left
Connections for the
built in I/O
Basic Components of a PLC System
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Power Supply
A power supply is needed to provide power to the PLC and any other
modules. Power supplies come in various forms:
• Power supply modules that fit into one of the slots in
a chassis
• External power supplies that mount to the outside of
a chassis
• Stand alone power supplies that connect to the PLC
or I/O through a power cable
• Embedded power supplies that come as part of the
PLC block.
Power supply
mounted to the
side of the
chassis
Power supply
that fits in a
slot of the
chassis
Basic Components of a PLC System
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Programming Software
Software that runs on a PC is required to configure and program PLCs.
• Different products may require different programming
software
• Software allows programs to be written in several
different languages
Basic Components of a PLC System
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Network Interface
Most PLCs have the ability to communicate with other devices. These
devices include computers running programming software, or
collecting data about the manufacturing process, a terminal that lets an
operator enter commands into the PLC, or I/O that is located in a
remote location from the PLC. The PLC will communicate to the other
devices through a network interface.
PLC
Network
interface
module
Network connecting other devices
Network Interface
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Modular systems allow the user to
add network interface modules to
the chassis. The controller
communicates to the network
interface over the backplane.
In some cases the
network interface is built
directly into the PLC and
will appear as a plug on
the front of the PLC
Network interface
Controller
PLC Control Panel
Typically, PLCs are installed
in enclosures, on a “panel”
Power supply
mounted to the side
of the chassis
PLC
controller
I/O modules
Network interface
modules
Wiring to field
devices
Backplane of chassis
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PLCs are part of a Control System
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The PLC system is the center of a control system, but it is not the entire
control system. There are several other key pieces that must be added
to a PLC system to make a complete control system. Examples are:
• Operator terminals
• Networks
• Distributed I/O devices (I/O that is in a different
location then the PLC)
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REDUNDANCY
FEATURES !!!
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Controllogix Controllers
Overview
The Controllogix controller provides a scalable controller solution that is capable of addressing a large amount
of I/O points.
The controller can be placed into any slot of a ControlLogix I/O chassis and multiple controllers can be
installed in the same chassis. Multiple controllers in the same chassis communicate with each other over
the backplane (just as controllers can communicate over networks) but operate independently
ControlLogix controllers can monitor and control I/O across the Controllogix backplane, as well as over I/O
links. ControlLogix controllers can communicate over EtherNet/IP, Control Net, Device Net, DH+, Remote I/O,
and RS-232-C (DF1/DH-485 protocol) networks and many third party process and device networks. To provide
communication for a ControlLogix controller, install the appropriate communication interface module into the
chassis.
The Controllogix controller is part of the Logix5000 family of controllers. A ControlLogix system includes:
the Controllogix controller, available in different combinations of user memory.
RSLogix 5000 programming software.
1756 Controllogix I/O modules that reside in a 1756 chassis.
separate communication modules for network communications
a built-in serial port on every Controllogix controller.
Features:
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Feature
1756-L61
Controller tasks
• 32 tasks
• 100 programs/task
• Event tasks: all event triggers
Built-in communication ports
1 port RS-232 serial
Communication options
• EtherNet/IP
• ControlNet
• DeviceNet
• Data Highway Plus
• Remote I/O
• SynchLink
• Third-party process and
device networks
Serial port communications
• ASCII
• DF1 full/half-duplex
• DF1 radio modem
• DH-485
• Modbus via logic
Controller connections
supported, max
250
Network connections, per
network module
• 100 ControlNet
(1756-CN2/A)
• 40 ControlNet (1756CNB)
Controller redundancy
Full support
Integrated motion
SERCOS interface
Analog options:
• Encoder input
• LDT input
• SSI input
Programming languages
• Relay ladder
• Structured text
• Function block
• SFC
• 256 EtherNet/IP; 128 TCP
(1756-EN2x)
• 128 EtherNet/IP; 64 TCP
(1756-ENBT)
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CONTROLLOGIX CONTROLLERS
Cat.
No.
1756L5561
Memory
Available User
Memory
(Kbytes)
I/O
Meme
ryT
Nonvolatil
e Memory
2048 K bytes
478 K
bytes
64 Mbytes
Compact
flash
Power
Dissipation
, Max.
Thermal
Dissipation,
Max.
Backplane
Current (mA) at
5V
Backplane
Current (mA) at
24V
3.5 W
11.9 BTU/hr
1200 mA
14 mA
Control net Communication Modules: 1756 – CN2R
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Cat. No.
Communic
ation Rate
Connectio
ns
Cable
Power
Dissipation
, Max.
Backplane
Current
(mA) at 5V
Backplane Current (mA) at
24V
1756-CN2R
5 Mbps

Standalon
e
controller
systems
only

Redundant
media
100 (any
combinati
on of
scheduled
and
unschedul
ed)
1786RG6F
(quad
shield
high flex
coax
cable)
1786-XT
terminatio
n resistor
5.14 W
970 mA
1.7 mA
Controllogix Hardware Redundancy Features
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Switch Over Time
20ms, No special Configuration
is required
Configuration and Online Edits
Automatically Copied to
Secondary System
Yes, It has been taken care by
Redundancy module
automatically
High Speed Fiber Optic Link For Yes
Data Synchronization
Data Synchronization
Automatically by
Redundancy Module, No
special code is require to
synchronize data
IO Communication True
Redundant?
Yes
Specialize Programming
Required/Care to Take While
Program The Logic
No Specialize Programming is
Required
Any Engineering is Involved to
Configure REDUNDUNCY.
No Special configuration is
Required
Forces are Updated in Both
CPU?
Yes, Do not require to force in
SECONDARY Processor.
IO Bus Redundancy and Speed
100% Speed is 5Mbps.
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PLC Programming
Programming a PLC
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Every PLC has associated programming software that
allows the user to enter a program into the PLC.
• Software used today is Windows based, and can
be run on any PC.
• Different products may require different software:
PLC5, SLC, and ControlLogix each require their
own programming software.
Example of PLC programming software
Programming a PLC
Before a PLC can perform
any control task, it must be
programmed to do so. The
most popular language
used to program a PLC is
ladder logic.
Example of a ladder logic program
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Programming a PLC
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Ladder logic
program in PLC
In a conveyor system, we have several “requirements” to accomplish; for
example, timing and counting parts on the conveyor. Each of these
requirements must be programmed into the PLC so that it knows how to
respond to different events.
Programming a PLC
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Ladder logic
program in PLC
The programmer develops the program, and connects their personal
computer to the PLC through a network or cable and then downloads the
program to the PLC.
Ladder Logic Example
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Here, we can see an example of ladder logic. Each line of code is known
as a “rung”. In this example there are 4 rungs, numbered 0, 1 and 2, and
the end rung marking the end of the program.
The PLC executes the program 1 rung at a time, starting with the first rung
and then working down.
Ladder Logic Example
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Ladder logic rungs are basically IF-THEN statements. Each individual
rung is executed from the left to the right. The outputs at the right side of
each rung is set to a condition that reflects the status of the permissive
contacts in a particular rung.
Ladder Logic Example
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This is a very simple rung of logic, from a PLC program:
Start Button
Motor
The rung is read as:
If the Start Button is on, turn the Motor on.
If the Start Button is off, then turn the Motor off.
Let’s take a look at this simple program in detail…
Ladder Logic Example
Start Button
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Motor
The first instruction is as an “eXamine If Closed”, or “XIC” instruction.
Start Button
In this example, if the actual Start Button is on, then the value of all the
XICs named Start Button, in the program will be true (also known as a
‘one”, or “closed”).
If the start button is off (not on) then the value of the Start Button XICs
will be false (also known as a “zero”, or “open”).
Ladder Logic Example
Start Button
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Motor
The second instruction is known as an Output Energize, or “OTE”. This
is an output instruction.
This instruction turns on if the logic to the left of the OTE is true. If the
logic is false, then the output will be turned off. The OTE commands a
physical output located on a output module to turn either on or off.
Ladder Logic Example
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If there are multiple XIC’s on the rung, then all would have to be on for
the rung to be true.
All the inputs have to be on for the rung to be true
Ladder Logic Example
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If there are multiple OTE’s on the rung, then all would be turned on or off
based on the rung condition (true or false).
All the outputs
will turn on if the
rung is true
Ladder Logic Example
Start Button
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Motor
The text above the XIC and OTE is the address associated with the
instruction. PLC addresses may appear in many different ways
depending on the PLC being used.
• Start_Button
• Local:2:I.Data[0].1
• I:020/2
The address is used by the PLC to tell exactly which input to read or
which output to command.
I/O Addressing
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Since a PLC will be controlling real devices down on a plant floor, it has to
have some way of communicating to the correct device. All PLCs use
some sort of method of I/O Addressing to perform this function.
• I/O addresses are a means to tie a physical I/O
point to a location in PLC memory
• An input address will represent the state of an
input device, i.e. the switch is on or off.
• An output address will represent the commanded
Example
of for a device. i.e., turn the motor on or off.
Example of
state
input address
output address
representing an
actual input
representing an
actual output
Local:5:I.Data[0].1
Local:7:O.Data[6].11
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I/O Addressing
Often, a descriptive name of the device connected to the I/O point is used
in addition to, or in place of the base I/O address which describes the
physical location of the module in the rack.
Example of
symbolic input
address
Start Button
Local:5:I.Data[0].1
Motor
Local:7:O.Data[6].11
Example of
base Input
address
I/O Addressing vs. Data Addressing
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I/O addresses are a means to tie a physical I/O point to a location in PLC
memory. There are other addresses that do not connect to physical I/O,
but are used to hold a value.
Data addresses store a value used for functions like timers, counters,
or calculations.
Example of
I/O address
Part_detected
Local:5:I.Data[0].1
Counter
part_count
Example of
data address
I/O Addressing vs. Data Addressing
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In this example, parts on a conveyor are counted.
The input, “Part_detected” looks at the I/O address of the actual sensor
counting the parts.
The counter references a data address, and accumulates the counts in that
location in memory.
Each time the “Part_detected” switch closes, the counter adds one more
count to the area of memory called “part_count”
Example of
I/O address
Part_detected
Local:5:I.Data[0].1
Counter
part_count
Example of
data address
Ladder Logic Example
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Next, we will take a look at an actual segment of ladder logic code. The
code will be the code used to control our conveyor from the first lesson.
Before we do that, let’s take a look at a few more ladder logic instructions:
L
U
Timer On Delay
timer
preset
accum
OTL - Output Latch - turns on the output and
keeps it even if the rung goes false
OTU - Output Unlatch - turns off the output
when the rung is true
TON - Timer On Delay - when the rung is true
TON
the timer will run. It will store the elapsed time
timer1
in the “Accum” field (accumulator). As long as
100
the rung remains true it will count until it
0
reaches the preset value. If the preset value is
hit the DN bit will go on (Done bit). When the
rung goes false the timer will be reset.
Programming a PLC - Conveyor example
Photoeye 2
Light 1
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Photoeye 1
Motor 1
Now let’s take a look at a simple program for a conveyor application.
When a box is placed on the conveyor in front of Photoeye 1, Light 1,and
Motor 1 will turn on, causing the box to move down the conveyor to the left.
When the box passes in front of Photoeye 2, Motor 1 and Light 1 will turn
off, stopping the conveyor.
Relay Ladder Logic Example
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Here’s the program for the conveyor: The first line of code turns on the
motor and the light when a box is detected by photoeye1. Likewise, the
motor and light are turned off when photoeye2 detects the box in the
second line of code.
Relay Ladder Logic Example
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The third line begins a timer when the box passes by photoeye1, and if the
box does not pass by photoeye2 in 30 seconds (the timer counts in
milliseconds), the motor and light are shut off by line 4. This is the
indication of a jam condition.
PLC Addressing Examples
•
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Logix Controller sample addresses:
– Motor_start - Binary Tag
– Tank_temp - Integer Tag
– Local:5:I.Data.0 - Input Tag (Local - same chassis
as processor, in slot 5, is an input, data bit 0)
• PLC-5 sample addresses:
– B3:0/2 - Binary File
– N7:0 - Integer File
– I:012/3 - Input file (Describes: Rack#, Group, Bit)
• SLC sample addresses:
– B3:0/2 - Binary File
– N7:0 - Integer File
– I:3.0/2 - Input file (Describes: Slot.word/bit)
Other Programming Languages
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While ladder logic is the oldest and most popular language
used in PLCs today, many other languages are gaining in
popularity and are in wide use. Examples are:
• Sequential Function Chart (SFC)
• Function Block
• Structured Text
If Water_Valve=0 and Mixer
speed = 60 then EOT
• Higher level languages such as C.
if (!hostto) {
sprintf(hostbuf, "unknown (%s)",
inet_ntoa(ip->ip_src));
hostto = hostbuf;
}
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Architecture
Control System Architectures
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A complete control system is made up of a combination of PLCs, networks,
I/O, terminals and software. All the components work together to form a
complete control system.
Control System Architectures
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Within a control system architecture there are many subsystems and
terms used to describe them. This section will go over some of the
popularly used terms to describe parts of control systems.
•
•
•
•
•
•
•
•
Local I/O
Distributed I/O
Centralized I/O
Centralized Control
Distributed Control
Control System
Data Acquisition System
Safety System
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I/O Systems
I/O systems are often referred to as local or distributed.
• Local refers to the I/O being attached directly to the
Controller or on the same backplane as the Controller
• Distributed refers to I/O which is not on the same
backplane as the Controller. Distributed I/O is connected
using a network.
Local I/O
I/O adapter
PLC
I/O network
Input module - distributed
I/O
Switch-input
The distributed input module sends the inputs across the backplane to the
adapter.
The adapter sends them over the I/O network to the PLC (Controller).
I/O Architectures
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I/O architectures are made up of I/O systems. The architectures
are referred to as Centralized and Distributed
• Centralized refers to the I/O being located near or in the
same cabinet as the processor. Wires from field devices are
brought back to the I/O, and can be quite long.
• Distributed refers to I/O that is located near the field devices.
The wires from the field devices are short. The network cable
is run out to the Distributed I/O instead of running the field
wires back to the I/O.
Centralized I/O
I/O network
Distributed I/O
field wiring
Switch-input
Processor cabinet
Systems Vs. Architectures
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• I/O systems are part of an I/O architecture.
– If all the I/O is located near or in the same
cabinet as the processor, it is a centralized
architecture. Within the centralized architecture
could be either local or distributed I/O, or both.
I/O network
Centralized architecture made
up of both local I/O and
distributed I/O
Processor cabinet
Local I/O - I/O that is attached
to or in the same chassis as
the PLC
Distributed I/O - I/O that is
connected to the PLC over a
network.
Systems vs. Architectures
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• I/O systems are part of an I/O architecture.
– If some of the I/O is located remotely from the
processor it is a distributed architecture. Within
the distributed architecture is distributed I/O, or
both local and distributed I/O.
I/O network
Distributed I/O
Distributed I/O
Local I/O
Processor cabinet
Distributed architecture made
up of both local I/O and
distributed I/O
Distributed I/O
Local vs. Distributed I/O System
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Why use Local I/O?
• Faster than distributed I/O
• Easy to install - add a module to the chassis
• In some cases the I/O is already attached to the processor
• Less expensive than adding distributed
• Use the I/O on the processor or simply add a module to the backplane.
Don’t need to add a chassis, power supply, etc.
Why use Distributed I/O?
• Field devices distributed around the machine - too much wiring to take back to
one chassis
• Out of local I/O
• local I/O limited by number of slots in the backplane or fixed I/O attached
to the processor
• Local I/O does not meet your needs
• module type, current capability, etc
Centralized vs. Distributed I/O Architecture
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Why use a Centralized Architecture?
• If using local only, then it is faster than distributed I/O
• If the only centralized I/O is local I/O, then you don’t have to buy additional
chassis, power supply, etc.
• The field devices are near the cabinet or processor so there is no wiring cost
savings of going distributed
Why use a Distributed Architecture?
• Field devices distributed around the machine - too much wiring to take back to
one chassis
• I/O mounted to machine - becomes a part of it instead of in a central cabinet.
* * * Many systems will combine both * * *
Centralized Control
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Centralized control refers to a control system where a single (usually
large) PLC controls all of the I/O and performs all the control for the
system
A single PLC controls
the local I/O and all the
networked I/O
Centralized Control
Advantages and disadvantages of centralized control
• Advantages
– The control program is all in one
place
– Easier to troubleshoot system
problems
– I/O performance throughout entire
system
• Disadvantages
– Programs can get quite large
– related I/O performance slower
compared to distributed control
– Single PLC failure shuts down
entire system
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Distributed Control
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Distributed control refers to a control system where multiple PLC
controllers share the responsibility of controlling the system. The PLC’s
usually communicate frequently with each other.
ALLEN-BRADLEY
ALLEN-BRADLEY
ALLEN-BRADLEY
Multiple PLCs share control of
the networked I/O. The
sections are often broken up
into logical systems. For
example, one controller might
control the conveyor bringing
ingredients to the ovens while
the other 2 are controlling the
ovens.
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Distributed Control
Advantages and disadvantages of distributed control
• Advantages
– Segmented programs to specific
tasks
– Easier to troubleshoot local
problems
– Performance on local network
• Disadvantages
– System problems harder to
troubleshoot
– Performance from I/O across
PLC’s
– Cost
– Maintain multiple programs
ALLEN-BRADLEY
ALLEN-BRADLEY
ALLEN-BRADLEY
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The Control System
The control system is the system that is responsible for the control of the
process. This is the system that includes the PLC, all of the I/O and any
Human Machine Interfaces (HMI).
HMI
PLC
I/O
Data Acquisition System
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The Data Acquisition system is generally responsible for collecting data
about the control system, and storing it on master computers or servers, or
displaying it on terminals. The data is often used later for reporting or
charting purposes.
Data Acquisition System
gateway
computers
Control System
File server
Made up of devices and networks which are responsible for
acquiring data about the process. Not responsible for direct
control of the process.
Data Acquisition System
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The network used for data acquisition is often Ethernet. While data
acquisition devices can exist directly on the control network, a gateway is
often used to separate network traffic between the data acquisition system
and the control system.
Data Acquisition System
gateway
computers
File server
Control System
Safety System
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• The Function of a Safety System is to monitor and control conditions
on a machine or process that are hazardous in themselves or, if no
action were taken, may give rise to hazardous situations
• The Safety System runs in parallel with the Control System
The Control System and Safety System may share components
– Focus of Control System is Throughput
– Focus of Safety System is Protection
• A Safety system is designed to protect
– People
– Environment
– Machinery
Safety System
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• The safety system is often referred to as “safety control”
while the PLC system controlling the devices that produce
the end product is often referred to as the “standard
control”
The PLC performing standard
control would control the robot
while it performs tasks related to
producing the desired product
The safety control would monitor the light curtain to make
sure that the operator never moved into the robot area
while the robot was moving. If the operator broke the light
curtain, the safety system would remove power to the robot
so that it could not move and injure the operator
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