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Programmable Logic Controllers 2.3 - 1Industrial Automation 2013
2.3.1 PLCs: Definition and Market
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instruction Lists2.3.5.9 Programming environment
Programmable Logic Controllers 2.3 - 2Industrial Automation 2013
PLC = Programmable Logic Controller: Definition
Definition: “small computers, dedicated to automation tasks in an industrial environment"
cabled relay control (hence 'logic'), analog (pneumatic, hydraulic) “governors”
real-time (embedded) computer with extensive input/output
Function: Measure, Control, Protect
AP = Automates Programmables industrielsSPS = Speicherprogrammierbare Steuerungen
Formerly:
Today:
Distinguish Instrumentation
flow meter, temperature, position,…. but also actors (pump, …)Control
programmable logic controllers with digital peripherals & field bus
Visualization
Human Machine Interface (HMI) in PLCs (when it exists) is limited to service help and control of operator displays
Programmable Logic Controllers 2.3 - 3Industrial Automation 2013
Simple PLC
network digital inputs
digital outputs
analog inputs / outputs
Programmable Logic Controllers 2.3 - 4Industrial Automation 2013
PLC in a cabinet
CPU1
redundant field bus connection
CPU2
inputs/outputs
serial connections
Programmable Logic Controllers 2.3 - 5Industrial Automation 2013
example: turbine control (in the test lab)
Programmable Logic Controllers 2.3 - 6Industrial Automation 2013
PLC: functions
Measure
Control (Command and Regulation)
•
•
•Event Logging•Communication•Human interface
Protection•
(Messen, Schützen, Regeln = MSR)
PLC = PMC: Protection, Measurement and Control
Programmable Logic Controllers 2.3 - 7Industrial Automation 2013
PLC: Characteristics
• large number of peripherals: 20..100 I/O per CPU, high density of wiring, easy assembly.
• digital and analog Input/Output with standard levels
• operate under harsh conditions, require robust construction, protection against dirt, water and mechanical threats, electro-magnetic noise, vibration, extreme temperature range (-30C..85C), sometimes directly located in the field.
• programming: either very primitive with hand-help terminals on the target machine itself, or with a laptop
• network connection for programming on workstations and connection to SCADA
• primitive Human-Machine-Interface for maintenance, either through LCD-display or connection of a laptop over serial lines (RS232) or wireless.
• economical - €1000.- .. €15'000.- for a full crate.
• the value is in the application software (licenses €20'000 ..€50'000)
• field bus connection for remote I/Os
Programmable Logic Controllers 2.3 - 8Industrial Automation 2013
PLC: Location in the control architecture
Enterprise Network
directly connectedI/O
Control Bus(e.g. Ethernet)
Engineerstation
I/O I/O I/O I/OCP
U
Sensor Bus (e.g. ASI)
Field Bus
gateway
Field Stations
Control Station with Field Bus
direct I/O
I/O
Field DevicesFB
gateway
gateway
I/OI/OI/OI/OCP
U
CO
M
I/OI/OI/OCO
M
CP
U
CO
M
CO
M
CO
M
I/O
Field Bus
CP
U
CO
M 2
I/O I/O I/OCP
U
CO
M1
CO
M 2
I/OCP
U
Operatorstation
largePLCs
small PLC
PLCPLC
CO
M1
CO
M1
SupervisorStation
data concentrators,not programmable,but configurable
Programmable Logic Controllers 2.3 - 9Industrial Automation 2013
Why 24V / 48 V supply ?
… After the plant lost electric power, operators could read instruments only by plugging in temporary batteries…[IEEE Spectrum Nov 2011 about Fukushima]
Photo TEPCO
Programmable Logic Controllers 2.3 - 10Industrial Automation 2013
Global players
Total sales in 2004: 7’000 Mio €
Source: ARC Research, 2005-10
Programmable Logic Controllers 2.3 - 11Industrial Automation 2013
Kinds of PLC
Monolithic constructionMonoprocessorFieldbus connection
(1)
Modular construction (backplane)One- or multiprocessor systemFieldbus and LAN connectionSmall Micro Memory Card (MMC) function possible
(2)
Compact
Modular PLC
(3) Soft-PLCLinux or Windows NT or CE-based automation productsDirect use of CPU or co-processors
Programmable Logic Controllers 2.3 - 12Industrial Automation 2013
Compact PLC
Monolithic (one-piece) constructionFixed casingFixed number of I/O (most of them binary)No process computer capabilities (no MMC)Can be extended and networked by an extension (field) busSometimes LAN connection (Ethernet, Arcnet)Monoprocessor
Typical product: Mitsubishi MELSEC F, ABB AC31, SIMATIC S7
costs: € 2000
courtesy ABBcourtesy ABB courtesy ABB
Programmable Logic Controllers 2.3 - 13Industrial Automation 2013
Specific Controller (example: Turbine)
Thermocouple
inputs
binary I/Os,
CAN field bus
RS232 to HMI
Relays and fusesProgramming port
cost: € 1000.-
tailored for a specific application, produced in large series
courtesy Turbec
Programmable Logic Controllers 2.3 - 14Industrial Automation 2013
courtesy ABB
Modular PLC
RS232
CPU CPU Analog I/O Binary I/O
backplaneparallel bus
• housed in a 19" (42 cm) rack (height 6U ( = 233 mm) or 3U (=100mm)
• concentration of a large number of I/O
Power Supply
• high processing power (several CPUs)
• primitive or no HMI
• cost effective if the rack can be filled
• can be tailored to needs of application
• supply 115-230V~ , 24V= or 48V= (redundant)
fieldbus
LAN
• large choice of I/O boards
• interface boards to field busses
• requires marshalling of signals
fieldbus
developmentenvironment
• cost ~ €10’000 for a filled crateTypical products: SIMATIC S5-115, Hitachi H-Serie, ABB AC110
Programmable Logic Controllers 2.3 - 15Industrial Automation 2013
Small modular PLC
mounted on DIN-rail, 24V supplycheaper (€5000) not water-proof, no ventilatorextensible by a parallel bus (flat cable or rail)
courtesy ABBcourtesy Backmann
Programmable Logic Controllers 2.3 - 16Industrial Automation 2013
Compact or modular ?
€
# I/O modules
Limit of local I/O
compact PLC (fixed number of I/Os)
modular PLC (variable number of I/Os
field busextension
Programmable Logic Controllers 2.3 - 17Industrial Automation 2013
Industry- PC
Wintel architecture (but also: Motorola, PowerPC),HMI (LCD..)Limited modularity through mezzanine boards(PC104, PC-Cards, IndustryPack)Backplane-mounted versions with PCI or Compact-PCI
Competes with modular PLCno local I/O,fieldbus connection instead,
courtesy INOVA courtesy MPI
costs: € 2000.-
Programmable Logic Controllers 2.3 - 18Industrial Automation 2013
Soft-PLC (PC as PLC)
• PC as engineering workstation• PC as human interface (Visual Basic, Intellution, Wonderware)• PC as real-time processor• PC assisted by a Co-Processor (ISA- or PC104 board)• PC as field bus gateway to a distributed I/O system
2122
33
234
I/O modules
Programmable Logic Controllers 2.3 - 19Industrial Automation 2013
Protection devices
Protection devices are highly specialized PLCs that measure the current and voltages in an electricalsubstation, along with other statuses (position of the switches,…) to detect situations that could endanger the equipment (over-current, short circuit, overheat) and trigger the circuit breaker (“trip”) to protect the substation.In addition, they record disturbances and send the reports to the substation’s SCADA. Sampling: 4.8 kHz, reaction time: < 5 ms.
Human interfacefor statusand settings
measurement transformers
Ir
Is
It
Ur
Us
UT
Programming interface
trip relay
communication to operator
costs: € 5000
substation
Programmable Logic Controllers 2.3 - 20Industrial Automation 2013
Comparison Criteria – what matters
Siemens
Number of PointsMemory
Programming Language
Programming ToolsDownload
Real estate per 250 I/O
Label surface
Network
Hitachi
64016 KB
• Ladder Diagrams• Instruction List• Logic symbols• Basic• Hand-terminal
Graphical (on PC)yes
1000 cm2
6 characters6 mm2
19.2 kbit/s
1024
• Ladder Diagrams
• Instruction List
• Logic symbols
• Hand-terminal
Graphical (on PC)no
2678 cm2
5.3 mm27 charactersper line/point
10 Mbit/s
10 KB
Mounting cabinetDIN rail
Brand
Programmable Logic Controllers 2.3 - 21Industrial Automation 2013
2.3.3 PLCs: Function and construction
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Structured Text2.3.5.5 Sequential Function Charts2.3.5.6 Ladder Diagrams2.3.5.7 Instruction Lists2.3.5.8 Programming environment
Programmable Logic Controllers 2.3 - 22Industrial Automation 2013
Implementation
• PLC operates periodically• Samples signals from sensors and converts them to digital form
with A/D converter• Computes control signal and converts it to analog form for the
actuators.
1. Wait for clock interrupt2. Read input from sensor3. Compute control signal4. Send output to the actuator5. Update controller variables7. Communication6. Repeat
Waiwera Organic Winery, Distillation Plant
Programmable Logic Controllers 2.3 - 23Industrial Automation 2013
The signal chain within a PLC
analogvariable
(e.g. 4..20mA)
filtering&
scaling
analog-digital
converter
processing
digital-analog
converter
analogvariable
e.g. -10V..10V
time
y
time
y(i)
sampling
binaryvariable(e.g. 0..24V)
filtering sampling
time
y
transistoror
relay
binaryvariable
amplifier011011001111
counter
1
non-volatilememory
0001111
time
y(i)
Programmable Logic Controllers 2.3 - 24Industrial Automation 2013
General PLC architecture
CPUReal-Time
Clockflash
EPROMROM
buffers
signal conditioning
power amplifiers
relayssignal
conditioning
serial portcontroller
Ethernet
parallel bus
ethernetcontroller
RS 232
analog-digital
converters
digital-analog
convertersDigital Output
DigitalInput
fieldbuscontroller
externalI/Os
extensionbus
field bus direct Inputs and Outputs
Programmable Logic Controllers 2.3 - 25Industrial Automation 2013
Example Architecture: Internals of a protection device
Can you find all the components from the previous slide?In addition this device uses a DSP module for complex computations.
Programmable Logic Controllers 2.3 - 26Industrial Automation 2013
2.3.5 Programming languages
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 Programming languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instruction Lists2.3.5.9 Programming environment
Programmable Logic Controllers 2.3 - 27Industrial Automation 2013
The long march to IEC 61131
Source: Dr. J. Christensen
77 78 79 8180 93 94 9570 82 83 84 85 8786 88 89 90 91 92
NEMA Programmable Controllers Committee formed (USA)GRAFCET (France)
IEC 848, Function Charts
DIN 40719, Function Charts (Germany)NEMA ICS-3-304, Programmable Controllers (USA)
IEC SC65A/WG6 formedDIN 19 239, Programmable Controller (Germany)
MIL-STD-1815 Ada (USA)
IEC SC65A(Sec)67
Type 3 report recommendation
96
IEC 65A(Sec)38, Programmable Controllers
IEC 1131-3
IEC SC65A(Sec)49, PC Languages
IEC 64A(Sec)90
IEC 61131-3name change
it took 20 years to make that standard…
PLC industry needs aggreement on •Data types (operations may only be executed on appropriate types) •Programming languages•Software structure (program organization units for modularity, encapsulation)•Discrete event system handling•Execution
Programmable Logic Controllers 2.3 - 28Industrial Automation 2013
Matching the analog and binary world
Analog WorldBinary World
AB
C
continuous processes
P2P1
I1
Regulation, controllers
discrete processes
combinatorial sequential
Relay control, pneumatic sequencer
Pneumatic and electromechanical controllers
PLC
The time constant of the control system must be at least one order
of magnitude smaller than the smallest time constant of the plant.
Described by variables of non-overlapping values. The transition from
one state to another is abrupt, it is caused by an external event.
Programmable Logic Controllers 2.3 - 29Industrial Automation 2013
"Real-Time" languages
Extend procedural languages to express time
(“introduce programming constructs to influence scheduling and control flow”)
Languages developed for cyclic
execution and real-time("application-oriented languages")
Ladder Diagrams
function block language
instruction lists
GRAFCET
SDL
etc...
•
•
•
•
•
wide-spread in the control industry.Now standardized as IEC 61131
ADA
Real-Time Java
MARS (TU Wien) Forth
“C” with real-time features
etc…
could not impose themselves
•
•
•
•
•
•
Programmable Logic Controllers 2.3 - 30Industrial Automation 2013
The five IEC 61131-3 Programming languages
Structured Text (ST)
VAR CONSTANT X : REAL := 53.8 ;Z : REAL; END_VARVAR aFB, bFB : FB_type; END_VAR
bFB(A:=1, B:=‘OK’);Z := X - INT_TO_REAL (bFB.OUT1);IF Z>57.0 THEN aFB(A:=0, B:=“ERR”);ELSE aFB(A:=1, B:=“Z is OK”);END_IF
Ladder Diagram (LD)
OUT
PUMP
http://www.isagraf.com
Function Block Diagram (FBD)
PUMP
AUTO
MAN_ON
ACT
DO
V
Instruction List (IL)A: LD %IX1 (* PUSH BUTTON *) ANDN %MX5 (* NOT INHIBITED *) ST %QX2 (* FAN ON *)
Sequential Flow Chart (SFC)
START STEP
T1
T2
D1_READY
D2_READY
STEP A ACTION D1N
D ACTION D2
STEP B D3_READY
D4_READY
ACTION D3N
D ACTION D4T3
CALC1
CALC
IN1
IN2
OUT >=1
graphical languages
textual languages
AUTO
MAN_ON
ACT
CALC1
CALC
IN1
IN2
OUT
Programmable Logic Controllers 2.3 - 31Industrial Automation 2013
61131 Elementary Data Types
1 BOOL Boolean 12 SINT Short integer 83 INT Integer 164 DINT Double integer 325 LINT Long integer 646 USINT Unsigned short integer 87 UINT Unsigned integer 168 UDINT Unsigned double integer 329 ULINT Unsigned long integer 6410 REAL Real numbers 3211 LREAL Long reals 6412 TIME Duration variable13 DATE Date (only) variable14 TIME_OF_DAY or TOD Time of day (only) variable15 DATE_AND_TIME or DT Date and time of day variable16 STRING Character string variable17 BYTE Bit string of length 8 818 WORD Bit string of length 16 1619 DWORD Bit string of length 32 3220 LWORD Bit string of length 64 64
No. Keyword Data Type Bits
Programmable Logic Controllers 2.3 - 32Industrial Automation 2013
Importance of IEC 61131
IEC 61131-3 is the most important automation language in industry.
80% of all PLCs support it, all new developments are based on it.
Depending on the country, some languages are more popular than others.
More information:http://www.plcopen.org/pages/tc1_standards/downloads/plcopen_iec61131-3_feb2014.pptxhttp://www.plcopen.org/pages/pc2_training/downloads/index.htm
Programmable Logic Controllers 2.3 - 33Industrial Automation 2013
2.3.5.2 Input and Output
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Input & Output2.3.5.3 Function blocks2.3.5.4 Program Execution2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instruction Lists2.3.5.9 Programming environment
Programmable Logic Controllers 2.3 - 34Industrial Automation 2013
Connecting to Input/Output, Method 1: dedicated I/O blocks
The Inputs and Outputs of the PLC must be connected to (typed) variables
OUT_1
The I/O blocks are configured to be attached to the corresponding I/O groups.
IN_1
Programmable Logic Controllers 2.3 - 35Industrial Automation 2013
Connecting to Input / Output, Method 2: Variables configuration
All program variables must be declared with name and type, initial value and volatility.A variable may be connected to an input or an output, giving it an I/O address.Several properties can be set: default value, fall-back value, store at power fail,…These variables may not be connected as input, resp. output to a function block.
predefined addresses
Programmable Logic Controllers 2.3 - 36Industrial Automation 2013
2.4.2.3 Function Blocks Language
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Input / Output2.3.5.3 Function blocks language2.3.5.4 Program Execution2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instruction Lists2.3.5.9 Programming environment
Programmable Logic Controllers 2.3 - 37Industrial Automation 2013
Function Block Languages
The function block languages express "combinatorial" programs in a way similar to electronic circuits.
They draw on a large variety of predefined and custom functions
This language is similar to the Matlab / Simulink language used for simulations
(Funktionsblocksprache, langage de blocs de fonctions)(Also called "Function Chart" or "Function Plan" - FuPla)
Programmable Logic Controllers 2.3 - 38Industrial Automation 2013
Function Block Examples
&AB C
Trigger Tempo &
Running
Reset
S
R
Spin
Graphical programming language, similar to electrical and block diagrams. Mostly expresses combinatorial logic, but blocks may have memory (e.g. RS-flip-flops)
Example 1:
Example 2:external inputs external outputs
Q
Programmable Logic Controllers 2.3 - 39Industrial Automation 2013
Function Block Elements
"continuously" executing block, independent, no side effects
set point
measurement
command
parameters
The block is defined by its: • Data flow interface (number and type of input/output signals) • Black-Box-Behavior (functional semantic, e.g. in textual form).
Typed connections that carry a pseudo-continuous data flow.Connects the function blocks.
Signals
Function block
(set point)
(set point)
set point
Example
Example
PID
input signals output signals
overflow
Programmable Logic Controllers 2.3 - 40Industrial Automation 2013
Function Block Example
Programmable Logic Controllers 2.3 - 41Industrial Automation 2013
Function Block Rules
There exist exactly two rules for connecting function blocks by signals (this is the actual programming):
Each signal is connected to exactly one source. This source can be the output of a function block or a plant signal. The type of the output pin, the type of the input pin and the signal type must be identical.
•
•
The function plan should be drawn so the signals flow from left to right and from top to bottom. Some editors impose additional rules.
Retroactions are an exception to this rule. In this case, the signal direction is identified by an arrow (forbidden in some editors – use global variables instead).
ab
y
x
z
c
Programmable Logic Controllers 2.3 - 42Industrial Automation 2013
Types of Programming Organisation Units (POUs)
1) “Functions”- are part of the base library.- have no memory. Examples: and gate, adder, multiplier, selector,....
2) “Elementary Function Blocks” (EFB)- are part of the base library- have a memory ("static" data).- may access global variables (side-effects !)Examples: counter, filter, integrator,.....
3) “Programs” (Compound blocks)- user-defined or application-specific blocks- may have a memory- may be configurable (control flow not visible in the FBDExamples: PID controller, Overcurrent protection, Motor sequence(a library of compound blocks may be found in IEC 61804-1)
Programmable Logic Controllers 2.3 - 43Industrial Automation 2013
Function Block library
The programmer chooses the blocks in a block library, similarly to the hardware engineer who chooses integrated circuits in a catalogue.
The library describes the pinning of each block, its semantics and theexecution time.
The programmer may extend the library by defining function block macroscomposed of library elements.
If some blocks are used often, they will be programmed in an external language (e.g. “C”, micro-code) following strict rules.
Programmable Logic Controllers 2.3 - 44Industrial Automation 2013
Library functions for discrete and continuous plants
logical operations(AND, OR, …)Flip-flopSelector m-out-of-nMultiplexer m-to-nTimerCounterMemorySequencing
Basic blocks
Display
Manual input, touch-screen
Safety blocks (interlocking)
Logging
Compound blocks
Alarm signaling
Basic blocksSummator / SubtractorMultiplier / DividerIntegrator / DifferentiatorFilter Minimal value, Maximum valueRadixFunction generator
Regulation Functions
P, PI, PID, PDT2 controllerFixed set-pointRatio and multi-component regulationParameter variation / setting2-point regulation3-point regulationOutput value limitationRamp generatorAdaptive regulationDrive Control
Programmable Logic Controllers 2.3 - 45Industrial Automation 2013
Function Block library for specialized applications
MoveAbsolute
AXIS_REFAxis Axis
AXIS_REF
BOOL Execute Done BOOL
REAL Position BOOLREAL Velocity
CommandAborted
WORDREAL AccelerationBOOL
REAL Deceleration
REAL Jerk
MC_Direction Direction
ErrorErrorID
standardized blocks are defined in libraries, e.g. Motion Control or Robotics
Programmable Logic Controllers 2.3 - 46Industrial Automation 2013
Specifying the behaviour of Function Block
Time Diagram: 0 T
T
x
y
yx
S
R
x1
0
0
1
1
x2
0
1
0
1
y
previous state
0
1
1
Truth Table:
Mathematical Formula:
x1
x2
Textual Description:
yx
t
idp xdKdt
dxKxK
0
Calculates the root mean square of the input with a filtering constantdefined in parameter „FilterDelay“
Programmable Logic Controllers 2.3 - 47Industrial Automation 2013
Function Block specification in Structured Text
Programmable Logic Controllers 2.3 - 48Industrial Automation 2013
IEC 61131-3 library (extract)
CU – input (rising edges count up) R – reset counter (CV:=0) PV – preset value Q – 1 if CV >= PV CV – current value
dominant resetQ:=!R1&(Q|S)
rising edgedetector
dominant setQ:=S1|(Q&!R)
ADD
SUB
MUL
DIV
adder
subtractor
multiplier
divider
INT
PV
Integrator
In
Reset(if reset) Out := PV, else Out:= Δt *In + Out
More details http://calc1.kss.ia.polsl.pl/content/dydaktyka/PC/PLC_IEC61131-3.pdf
Boolean Functions
Select one of N inputs depending on input K
Binary selection
Arithmetic Functions
Flip-flop
Trigger
Up counter
Selector
Programmable Logic Controllers 2.3 - 49Industrial Automation 2013
CTUCURESETPV
QCV
https://docs.google.com/forms/d/1ynmoXf3JTcRn2yv2_4bKhcK0HJNDYpiTnQQm13lDSso/viewform
1.
DIV
INT
PVIn
Reset = 0
Out
In1
(2) (initially 0)
2.(1024)
In2
3. t1 t2 t3 t4 t5 t6 t7 t8
CU Reset = 0, PV = 3, CV = #up Q = (CV >= PV) ?
Remember: INT If (Reset) : Out := PV, Else: Out := Δt *In + Out
Exercise: What do the following blocks do ? (Δt = 1)
4.S
R
Q
Flipflop: dominant set or reset?
SRS
QR1
dominant resetQ:=!R1&(Q|S)
S1SR
QR
dominant setQ:=S1|(Q&!R)
http://tinyurl.com/IAFunctionBlock
ADD OutIn(10)
(initially 2)
What are the values of Out?What happens if out is initially 1024?
What are the values of Out?
Programmable Logic Controllers 2.3 - 50Industrial Automation 2013
https://docs.google.com/forms/d/1ynmoXf3JTcRn2yv2_4bKhcK0HJNDYpiTnQQm13lDSso/viewform
3.CV = 1, 1, 2, 2, 3, 3, 4, 4 Q = 0, 0, 0, 0, 1, 1, 1, 1
4.S
R
Q
ftp://advantechdownloads.com/Training/KW%20training/
S1SR
QR
dominant setQ:=S1|(Q&!R)
Exercise: What do the following blocks do ?
1.
2, 12, 22, 32, 42
2.
If out is initially 0: 0, 0, 0, 0, 0If out is initially 1024: 1024, 1024, 1024,
Programmable Logic Controllers 2.3 - 51Industrial Automation 2013
Exercise: Asymmetric Sawtooth Wave
Build an asymmetric sawtooth wave generator withIEC 61131 function blocks
75
0
-25
5s 12s
Programmable Logic Controllers 2.3 - 52Industrial Automation 2013
Exercise: Asymmetric Sawtooth Wave
Build an asymmetric sawtooth wave generator withIEC 61131 function blocks
75
0
-25
5s 12s
Hints:- Compute the slopes- Use integrators, comparators, flip-flops and selectors
Programmable Logic Controllers 2.3 - 53Industrial Automation 2013
Exercise: Saw-tooth FBD
+ 8.3-20.0
0
75.0
-25.0
Other solutions exists.
Out
Programmable Logic Controllers 2.3 - 54Industrial Automation 2013
Function Block decomposition
A function block describes a data flow interface.Its body can be implemented differently:
The body is implemented in an external language(micro-code, assembler, IEC 61131 ST):
Elementary block
The body is realized as a function block programEach input (output) pin of the interface is implemented asexactly one input (output) of the function block. All signals must appear at the interface to guaranteefreedom from side effects.
. Compound block
procedure xy (a,b:BOOLEAN; VAR b,c: BOOLEAN);begin ...... ....end xy;
=
=
Programmable Logic Controllers 2.3 - 55Industrial Automation 2013
Function Block segmentation
An application program (task) is decomposed into segments ("Programs")for easier reading, each segment being represented on one (A4) printed page.
• Within a segment, the connections are represented graphically.• Between the segments, the connections are expressed by signal names.
Segment A
Segment B
X1
M2 M1
Y1
Y2
M2
X2
M1
X3
Programmable Logic Controllers 2.3 - 56Industrial Automation 2013
2.3.5.3 Program execution
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instruction Lists2.3.5.9 Programming environment
Programmable Logic Controllers 2.3 - 57Industrial Automation 2013
Execution of Function Blocks
F1ABX01F2X01XF3BCX02F4XX02Y
Machine Code:functioninput1input2output
AF1 F2
BF4
Y
X01
X02F3
C
XSegment or POU(program organization unit)
The function blocks aretranslated to machine language(intermediate code, IL),that is either interpreted orcompiled to assembly language
Blocks are executed in sequence, normally from upper left to lower right
The sequence is repeated every t ms.
Programmable Logic Controllers 2.3 - 58Industrial Automation 2013
Input-Output of Function Blocks
execute individual period
I OX I OX I OX
read inputs
writeoutputs
Run-time:
The function blocks are executed cyclically.• all inputs are read from memory or from the plant (possibly cached)• the segment is executed• the results are written into memory or to the plant (possibly to a cache)
The order of execution of the blocks generally does not matter. To speed up algorithms and avoid cascading, it is helpful to impose an execution order to the blocks.
The different segments may be assigned a different individual period.
time
Programmable Logic Controllers 2.3 - 59Industrial Automation 2013
Program configuration
The programmer divides the program into tasks (sometimes called pages or segments), which may be executed each with a different period.
The programmer assigns each task (each page) an execution period. Since the execution time of each block in a task is fixed, the execution time is fixed.
Event-driven operations are encapsulated into blocks, e.g. for transmitting messages.
If the execution time of these operations take more than one period, they are executed in background.
The periodic execution always has the highest priority.
Programmable Logic Controllers 2.3 - 60Industrial Automation 2013
IEC 61131 - Execution engine
configuration
resource
task task
program program
FB FB
task
execution control pathvariable access paths
FB function block
variable
represented variables
communication function
Legend:
program
FB FB
resource
task
program
global and directly
access paths
Programmable Logic Controllers 2.3 - 61Industrial Automation 2013
Parallel execution
Function blocks are particularly well suited for true multiprocessing (parallel processors).
The performance limit is given by the needed exchange of signals by shared memory.
Semaphores are not used since they could block an execution and make the concerned processes non-deterministic.
processor1
processor2
processor3
shared memory
shared memory
shared memory
shared memory
input/output
Programmable Logic Controllers 2.3 - 62Industrial Automation 2013
2.3.5.5 Structured Text
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Programming environment
Programmable Logic Controllers 2.3 - 63Industrial Automation 2013
Structured Text
(Strukturierte Textsprache, langage littéral structuré)
Structured Text is an imperative language similar to Pascal (If, While, etc..)
The variables defined in ST can be used in other languages
ST is used to do complex data manipulation and write blocks
Caution: writing programs in structured text can breach the real-time rules !
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Data Types
binary types: analog types:
•Derived Types are user-defined and must be declared in Structured Textsubrange,enumerated,arrays,structured types(e.g. AntivalentBoolean2)
Variables can receive initial values and be declared as non-volatile (RETAIN), so after restart they contain the last value before power-down or reset.
BOOLBYTEWORDDWORD
181632
REAL (Real32)LREAL (Real64)
Function Blocks are typed: the types of connection, input and output must match.
•Elementary Types are defined either in Structured Text or in the FB configuration.
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Example of Derived Types
TYPE ANALOG_CHANNEL_CONFIGURATION STRUCT RANGE: ANALOG_SIGNAL_RANGE; MIN_SCALE : ANALOG_DATA ; MAX_SCALE : ANALOG_DATA ; END_STRUCT; ANALOG_16_INPUT_CONFIGURATION : STRUCT SIGNAL_TYPE : ANALOG_SIGNAL_TYPE; FILTER_CHARACTERISTIC : SINT (0.99) CHANNEL: ARRAY [1..16] OF ANALOG_CHANNEL_CONFIGURATION; END_STRUCT ;END_TYPE
Programmable Logic Controllers 2.3 - 66Industrial Automation 2013
Structured Text Examples
IF tank.temp > 200 THEN pump.fast :=1;pump.slow :=0; pump.off :=0;
ELSIF tank.temp > 100 THENpump.fast :=0; pump.slow :=1; pump.off :=0;
ELSE pump.fast :=0; pump.slow :=0; pump.off :=1;
END_IF;
pos := 0; WHILE((pos < 100) & s_arr[pos].value <> target)) DO
pos := pos + 2; String_tag.DATA[pos] :=
SINT_array[pos]; END_WHILE;
[http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm007_-en-p.pdf]
Predefined functions, e.g.:SIZE(SINT_array, 0, SINT_array_size); Count the number of elements in SINT_array (array that contains inputs) and store result in SINT_array_size (DINT tag).
IF( Switch_0 AND Switch_1 ) THEN Start_Motor := 1; Start_Count := Start_Count + 1;
END_IF;
Programmable Logic Controllers 2.3 - 67Industrial Automation 2013
Structured Text Example
Move ASCII characters from a SINT array into a string tag. (In a SINT array, each element holds one character.) Stop when you reach the carriage return.
element_num := 0; SIZE(SINT_array, 0, SINT_array_size);
WHILE SINT_array[element_num] <> 13 DO String_tag.DATA[element_num] := SINT_array[element_num]; element_num := element_num + 1; String_tag.LEN := element_num; IF element_num = SINT_array_size then
exit; END_IF; END_WHILE;
[http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm007_-en-p.pdf]
Explanations:1.Initialize element_num to 0. 2.Count the number of elements in SINT_array (array that contains the ASCII characters) and store the result in SINT_array_size (DINT tag).3.If the character at SINT_array[element_num] = 13 (carriage return), then stop. 4.Set String_tag[element_num] = the character at SINT_array[element_num]. 5.Add 1 to element_num. This lets the controller check the next character in SINT_array. 6.Set the Length member of String_tag = element_num. (This records the number of characters in String_tag so far.) 7.If element_num = SINT_array_size, then stop. (You are at the end of the array and it does not contain a carriage return.) 8.Go to 3.
Programmable Logic Controllers 2.3 - 68Industrial Automation 2013
Structured Text Exercise
A user-defined data type (structure) stores information about an item in an Inventory array: • Inventory[i].ID: Barcode ID of the item (string data type) • Inventory[i].Qty: Quantity in stock of the item (DINT data type)An array of the above structure contains an element for each different item in your inventory. You want to search the array for a specific product (by its barcode) and determine the quantity in stock.Pseudocode:1.Get size (number of items) of Inventory array and store result in Inventory_Items (DINT tag). 2.Loop over positions in array. 3.If Barcode matches the ID of an item in the array, then:a. Set the Quantity tag = Inventory[position].Qtyb. Stop.
[http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm007_-en-p.pdf]
Programmable Logic Controllers 2.3 - 69Industrial Automation 2013
Structured Text Exercise Solution
A user-defined data type (structure) stores information about an item in an Inventory array: • Inventory[i].ID: Barcode ID of the item (string data type) • Inventory[i].Qty: Quantity in stock of the item (DINT data type)An array of the above structure contains an element for each different item in your inventory. You want to search the array for a specific product (by its barcode) and determine the quantity in stock.Pseudocode:1.Get size (number of items) of Inventory array and store result in Inventory_Items (DINT tag). 2.Loop over positions in array. 3.If Barcode matches the ID of an item in the array, then:a. Set the Quantity tag = Inventory[position].Qtyb. Stop.
[http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm007_-en-p.pdf]
Solution:SIZE(Inventory,0,Inventory_Items);FOR position:=0 to Inventory_Items - 1 DO
IF Barcode = Inventory[position].ID THENQuantity := Inventory[position].Qty; EXIT;
END_IF; END_FOR;
Programmable Logic Controllers 2.3 - 70Industrial Automation 2013
2.3.5.6 Sequential Function Charts
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.3 PLCs: Functions and construction2.3.5 PLC Programming Languages
2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Programming environment
Programmable Logic Controllers 2.3 - 71Industrial Automation 2013
SFC (Sequential Flow Chart)
(Ablaufdiagramme, diagrammes de flux en séquence )
• Describes sequences of operations and interactions between parallel processes.• Derived from Grafcet and SDL (Specification and Description Language, used for
communication protocols), mathematical foundation lies in Petri Nets.
START STEP
ACTION D1N D1_READY
D ACTION D2 D2_READY
T1
T2
STEP BSTEP A
Programmable Logic Controllers 2.3 - 72Industrial Automation 2013
SFC: Elements
The sequential program consists of states connected by transitions. A state is activated by the presence of a token (the corresponding variable becomes TRUE).The token leaves the state when the transition condition (event) on the state output is true.Only one transition takes place at a time, the execution period is a configuration parameter(task to which this program is attached)
Ec = ((varX & varY) | varZ)
token
Sa
Sb
"1"
Ea
Sc
Eb
transitions
states
event condition("1" = always true)
example transition condition
S0
Rule: there is always a transition between two states, there is always a state between two transitions
Programmable Logic Controllers 2.3 - 73Industrial Automation 2013
SFC: Initial state
State which come into existence with a token are called initial states.
All initial states receive exactly one token, the other states receive none.
Initialization takes place explicitly at start-up.
In some systems, initialization may be triggered in a user program(initialization pin in a function block).
Programmable Logic Controllers 2.3 - 74Industrial Automation 2013
SFC: Switch and parallel execution
Sa
Sb
"1"
Se
token switch : the token crosses the first active
transition (at random if both Ea and Eb are true)Note: transitions are after the alternance
token forking : when the transition Ee is true, the token
is replicated to all connected statesNote: transition is before the fork
Ed
token join : when all connected states have tokensand transition Eg is true, one single token is forwarded.Note: transition is after the join
Ee
Sc
Sd
SfSg
Eg
E0
Ea Eb
Ec
Ef
Programmable Logic Controllers 2.3 - 75Industrial Automation 2013
SFC: P1, N and P0 actions
P1 State1_P1: do at enter
N State1_N: do while
P0 State1_P0: do at leaving
State1
P1 (pulse raise) action is executed once when the state is enteredP0 (pulse fall) action is executed once when the state is leftN (non-stored) action is executed continuously while the token is in the state
P1 and P0 actions could be replaced by additional states.
The actions are described by a code block written e.g. in Structured Text.
Programmable Logic Controllers 2.3 - 76Industrial Automation 2013
Special action: the timer
rather than define a P0 action “ reset timer….”, there is an implicit variable defined as<state name>.t that express the time spent in that state.
Sf
S.t > t#5s
S
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SFC: graphic rules
The input and output flow of a state are always in the same vertical line (simplifies structure)
Alternative paths are drawn such that no path is placed in the vertical flow (otherwise would mean this is a preferential path)
intentional displacement to
avoid optical preference of a
path.
Priority:• The alternative path most to the left has the
highest priority, priority decreases towards the right.
• Loop: exit has a higher priority than loopback.
Programmable Logic Controllers 2.3 - 78Industrial Automation 2013
SFC: Exercise
Speed = 5 cm/s from I1 to I0 and from I2 to I3, faster otherwise. Initially: move vehicle at reduced speed until it touches I0 and open the trap for 5s(empty the vehicle).
1 - Let the vehicle move from I0 to I32 - Stop the vehicle when it reaches I3.3 - Open the tank during 5s.
4 - Go back to I05 - Open the trap and wait 5s.
repeat above steps indefinitely
I2 I3Inputs generate “1” as long as the tag of the vehicle (1cm) is over the sensor.
Register = {0: closed; 1: open}
I0 I1
trap+speed
Speed = {+20: +1 m/s; +1: +5 cm/s; 0: 0m/s}
negative values: opposite direction
VariablesInput: I0, I1, I2, I3 (boolean);Output:Trap = {0: closed; 1: open}
Register = {0: closed; 1: open}
Programmable Logic Controllers 2.3 - 79Industrial Automation 2013
Exercise SFC Example Solution
Programmable Logic Controllers 2.3 - 81Industrial Automation 2013
SFC: Structuring
Every flow chart without a token generator may be redrawn as astructured flow chart (by possibly duplicating program parts)
A
B
C
a
b
d
c
Not structured
A
B
C
a
b
a
bB'
A'
d
c
d
structured
Programmable Logic Controllers 2.3 - 82Industrial Automation 2013
SFC: Complex structures
Problems with general networks:Deadlocks, uncontrolled token multiplication
These general rules serve to build networks, termed by DIN and IEC as flow charts
Solution:assistance through the flow chart editor.
Programmable Logic Controllers 2.3 - 83Industrial Automation 2013
Function Blocks And Flow Chart
Function Blocks:
Continuous (time) control
Sequential Flow Charts:
Discrete (time) Control
Many PLC applications mix continuous and discrete control.
A PLC may execute alternatively function blocks and flow charts.
Communication between these program parts must be possible.
Principle:
A flow chart taken as a whole can be considered a function block with binary inputs (transitions) and binary outputs (states).
Programmable Logic Controllers 2.3 - 84Industrial Automation 2013
Executing Flow Charts As blocks
A function block may be implemented in different ways:
procedure xy(...);begin ...end xy;
extern (ST/IL) function blocks flow chart
Function blocks and flow chart communicate over binary signals.
Programmable Logic Controllers 2.3 - 85Industrial Automation 2013
Flow Charts or Function Blocks ?
A task can sometimes be written indifferently as function blocs or as flow chart.The application may decide which representation is more appropriate:
c
d
"1"
b
a
a
b c
d
Flow Chart Function Block
NOT
S
R
Programmable Logic Controllers 2.3 - 86Industrial Automation 2013
Flow Charts Or Blocks ? (2)
In this example, a flow chart seems to be more appropriate:
A
B
C
"1"
a
b
c
S
R
≥
&
S
R&
S
R&
init
a
b
c
A
B
C
Flow Chart Function Blocks
Programmable Logic Controllers 2.3 - 87Industrial Automation 2013
Exercise: write the SFC for this task
L1
T
V1 V2
open V1 until tank’s L1 indicates upper level open V2 during 25 secondsopen V3 until the tank’s L1 indicates it reached the lower levelwhile stirring. heat mixture during 50 minutes while stirring empty the reactor while the drying bed is movingrepeat
MSV3
MD
temperature(sensor)
H1
upperlower
V4
heater(actor)
Programmable Logic Controllers 2.3 - 88Industrial Automation 2013
2.3.5.7 Ladder Diagrams
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.2 PLCs: Kinds2.3.3 PLCs: Functions and construction
2.3.5 PLC Programming Languages2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Programming environment
Programmable Logic Controllers 2.3 - 89Industrial Automation 2013
Ladder Diagrams (1)
Ladder Diagrams is the oldest programming language for PLC- based on relay intuition of electricians.- widely in use outside Europe.- not recommended for large new projects.
(Kontaktplansprache, langage à contacts)
Rung 0
Rung 1
Rung 2
Input instructions (conditions) Output (actions)
Programmable Logic Controllers 2.3 - 90Industrial Automation 2013
Ladder Diagrams (2)
The contact plan or "ladder diagram" language allows an easy transition from the traditional relay logic diagrams to the programming of binary functions.
It is well suited to express combinational logic
It is not suited for process control programming (there are no analog elements).
The main Ladder Diagrams symbols represent the elements:
make contact
break contact
relay coil
contact travail
contact repos
bobine
Arbeitskontakt
Ruhekontakt
Spule
Programmable Logic Controllers 2.3 - 91Industrial Automation 2013
Ladder Diagrams Example (3)
01 02
50
0102
03 50
03
relay coil(bobine)
break contact(contact repos)
make contact(contact travail)
correspondingladder diagram
origin:electrical
circuit
50 0544
rung
"coil" 50 is used to move other contact(s)
Programmable Logic Controllers 2.3 - 92Industrial Automation 2013
Ladder Diagrams (4)
Binary combinations are expressed by series and parallel relay contact:
+ 01 02
50
Coil 50 is active (current flows) when 01 is active and 02 is not.
01
02 50
Series
+ 01
40
02
Coil 40 is active (current flows) when 01 is active or 02 is not.
Parallel
Ladder Diagrams representation “logic" equivalent
01
02 40
Programmable Logic Controllers 2.3 - 93Industrial Automation 2013
Ladder Diagrams (5)
The Ladder Diagrams is more intuitive for complex binary expressions than literal languages
501 2 3 4
5 6
! 1 & 2 & ( 3 & ! 4 | ! 5 & 6 ) = 50
Or
N1 & 2 STR 3 & N4 STR N5 & 6/ STR & STR = 50
500 1 4 5
6 72 3
10 11
12
N0 & 1 STR 2 & 3 / STR STR 4 & 5 STR N 6 & 7
/ STR & STR STR 10 & 11 / STR & 12 = 50
textual expression
Programmable Logic Controllers 2.3 - 94Industrial Automation 2013
Ladder Diagrams (6)
Ladder Diagrams stems from the time of the relay technology. As PLCs replaced relays, their new possibilities could not be expressed any more in relay terms. The contact plan language was extended to express functions:
literal expression: !00 & 01 FUN 02 = 200
200FUN 02
0100
The intuition of contacts and coil gets lost.
The introduction of «functions» that influence the control flow itself, is problematic.
The contact plan is - mathematically - a functional representation.
The introduction of a more or less hidden control of the flow destroys thefreedom of side effects and makes programs difficult to read.
Programmable Logic Controllers 2.3 - 95Industrial Automation 2013
Ladder Diagrams Example
Source: http://teacher.buet.ac.bd/zahurul/ME6401/ME6401_PLC.pdf
Ladder Diagrams diagram for a batch process: filling a container with a liquid,mixing the liquid, and draining the container. The sequence of events is as follows: 1. fill valve opens and lets the liquid into the container until it is full.2. liquid in the container is mixed for 3 minutes.3. a drain valve opens and drains the tank.
O = output I = input
Address of variable(module number, port number)
Programmable Logic Controllers 2.3 - 96Industrial Automation 2013
Ladder Diagrams Exercise
Source: http://teacher.buet.ac.bd/zahurul/ME6401/ME6401_PLC.pdf
Consider a PLC with one input module and one output module. Two external switches (SW-0 & SW-1) are connected via terminal IN-0 and In-1 of input module. Two terminals of the output module (OUT-0 & OUT-1) drive two indicator lamps (Lamp-0 & Lamp-1).
Which lamps are lit with the current switch positions? What happens if you change the position of Switch SW-1?
Programmable Logic Controllers 2.3 - 97Industrial Automation 2013
Ladder Diagrams Exercise Solution
Source: http://teacher.buet.ac.bd/zahurul/ME6401/ME6401_PLC.pdf
The top rung will light Lamp-0 if both SW-0 and SW-1 are closed. The bottom rung will lightLamp-1 if either SW-0 or OUT-0 are closed.
In the current position LAMP-1 is lit.If we change the position of Switch SW-1 then LAMP 0 will be lit too.
Programmable Logic Controllers 2.3 - 98Industrial Automation 2013
Ladder Diagrams (7)
Ladder Diagrams provides neither:• sub-programs (blocks), nor • data encapsulation nor • structured data types.
It is not suited to make reusable modules.
IEC 61131 does not prescribe the minimum requirements for a compiler / interpreter such as number of rungs per page nor does it specifies the minimum subset to be implemented.
Therefore, it should not be used for large programs made by groups of people
It is very limited when considering analog values (it has only counters)
→ used mostly in manufacturing, not in process control
Programmable Logic Controllers 2.3 - 99Industrial Automation 2013
2.3.6 Instruction Lists
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.2 PLCs: Kinds2.3.3 PLCs: Functions and construction
2.3.5 PLC Programming Languages2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instructions Lists2.3.5.9 Programming environment
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Instruction Lists (1)
Instruction lists is the machine language of PLC programmingIt has 21 instructions (see table)
Three modifiers are defined:"N" negates the result"C" makes it conditional and "(" delays it.
All operations relate to one result register (RR) or accumulator.
(Instruktionsliste, liste d'instructions)
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Instruction Lists (2)
Accumulator-based pogramming:•First, values are loaded into the accumulator (LD instruction)•Then, operations are executed with first parameter taken out of accumulator and second parameter of operand. •Result put in the accumulator, from where it can be stored (ST instruction)
Conditional executions or loops are supported by comparing operators like EQ, GT, LT, GE, LE, NE and jumps (JMP, JMPC, JMPCN, for the last two the accumulators value is checked on TRUE or FALSE)
Syntax:-each instruction begins on a new line and contains an operator and, depending on the type of operation, one or more operands separated by commas-before an instruction there can be a label, followed by a colon (:), as target for jumps-use brackets to define order of execution-comments must be placed last-empty lines are allowed.
(Instruktionsliste, liste d'instructions)
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Instruction Lists Example (3)
Instructions Lists is the most efficient way to write code, but only for specialists.
Otherwise, IL should not be used, because this language: • provides no code structuring• has weak semantics• is machine-dependent
End: ST speed3 (* result *)
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Instruction Lists Examples (4)
LabelsLD TRUE (*load TRUE into the accumulator*) ANDN BOOL1 (*execute AND with the negated value of the BOOL1 variable*) JMPC mark (*if the result was TRUE, then jump to the label "mark"*) LDN BOOL2 (*load the negated value of BOOL2 into the accumulator*) ST RES (*store the content of the accumulator in RES*) JMP continue (*jump to label “continue"*)
mark: LD BOOL2 (*save the value of *) ST RES (*BOOL2 in RES*)
continue:…
Brackets (without) (with)LD 2 LD 2MUL 2 MUL(2ADD 3 ADD 3
)ST RES (*7 is stored in RES*) ST RES (* 10 is stored in RES*)
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Instruction Lists Exercise(3)
What is the resulting speed3 for the following input?
End: ST speed3 (* result *)
a) Temp1 = 10Temp2 = 15Speed1 = 50Speed2 = 100
b) Temp1 = 10Temp2 = 5Speed1 = 50Speed2 = 100
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Exercise IEC 61131 Languages
http://tinyurl.com/IA61131https://docs.google.com/forms/d/1lGkFXQrlwlnoKc8gUg-_ESAdtVy-RgIOLnFbkIOGNa8/viewform
Instruction List
? ?
? ?
? ?
Function Block Diagram
A C
B
?
C:= ?
Structured Text
A B C
-| |--|/|----------------( )
Ladder Diagram
?
?
Programmable Logic Controllers 2.3 - 106Industrial Automation 2013
Exercise IEC 61131 Languages
http://tinyurl.com/IA61131https://docs.google.com/forms/d/1lGkFXQrlwlnoKc8gUg-_ESAdtVy-RgIOLnFbkIOGNa8/viewform
Instruction List
LD A
ANDN B
ST C
Function Block Diagram
A C
B
AND
C:= A AND NOT B
Structured Text
A B C
-| |--|/|----------------( )
Ladder Diagram
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2.3.5.9 Programming environment
2.1 Instrumentation2.2 Control2.3 Programmable Logic Controllers
2.3.1 PLCs: Definition and Market2.3.2 PLCs: Kinds2.3.3 PLCs: Functions and construction
2.3.5 PLC Programming Languages2.3.5.1 IEC 61131 Languages2.3.5.2 Function blocks2.3.5.3 Program Execution2.3.5.4 Input / Output2.3.5.5 Structured Text2.3.5.6 Sequential Function Charts2.3.5.7 Ladder Diagrams2.3.5.8 Instructions Lists2.3.5.9 Programming environment
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Programming environment capabilities
A PLC programming environment (e.g. ABB ControlBuilder, Siemens Step 7, CoDeSys,...) allows the programmer to
- program in one of the IEC 61131 languages
- define the variables (name and type)
- bind the variables to the input/output (binary, analog)
- run simulations
- download programs and firmware to the PLC
- upload from the PLC (if provided, rare)
- monitor the PLC
- document and print
Programmable Logic Controllers 2.3 - 109Industrial Automation 2013
61131 Programming environment
workstation
download
symbols
code
variable monitoring
andforcing
for debugging
firmware
network
configuration, editor, compiler, library
PLC
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Program maintenance
The source of the PLC program is generally on the laptop of the technician.
This copy is frequently modified, it is difficult to track the original in a process database, especially if several people work on the same machine.
Therefore, it would be convenient to be able to reconstruct the source programs out of the PLC's memory (called back-tracking, Rückdokumentation, reconstitution).
This supposes that the instruction lists in the PLC can be mapped directly to graphic representations -> set of rules how to display the information.
Names of variables, blocks and comments must be kept in clear text, otherwise the code, although correct, would not be readable.
For cost reasons, this is rarely implemented.
Programmable Logic Controllers 2.3 - 111Industrial Automation 2013
Is IEC 61131 FB an object-oriented language ?
Not really: it does not support inheritance.
Blocks are not recursive.
But it supports interface definition (typed signals), instantiation, encapsulation, some form of polymorphism.
Some programming environments offer “control modules” for better object-orientation
Programmable Logic Controllers 2.3 - 112Industrial Automation 2013
Limitations of IEC 61131
- No support to distribute execution of programs over several devices
- No support for event-driven. Blocks may be triggered by a Boolean variable (intentionally, for good reasons).
- If structured text increases in importance, better constructs are required (object-orientation)
Programmable Logic Controllers 2.3 - 113Industrial Automation 2013
Assessment
Which are programming languages defined in IEC 61131 and for what are they used ?
In a function block language, which are the two elements of programming ?
How is a PLC program executed and why is it that way ?
Draw a ladder diagram and the corresponding function block chart.
Draw a sequential chart implementing a 2-bit counter
Program a saw tooth waveform generator with function blocks
How are inputs and outputs to the process treated in a function block language ?
Write a program for a simple chewing-gum coin machine
Program a ramp generator for a ventilator speed control (soft start and stop in 5s)