Bryan L. Programmable controllers. Theory and implementation
Подождите немного. Документ загружается.
369
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
Figure 9-122. Get node functional block operation.
9-15 BOOLEAN MNEMONICS
As discussed in Section 9-2, Boolean mnemonics is a PLC language based
primarily on the Boolean operators AND, OR, and NOT. A complete Boolean
instruction set consists of the Boolean operators and other mnemonic instruc-
tions, which implement all of the functions of the basic ladder diagram
instruction set. A mnemonic instruction is written in an abbreviated form,
using three or four letters that imply the operation of the instruction. Table 9-
12 lists a typical set of Boolean instructions and their equivalent ladder
diagram symbols. The Boolean language is used to enter logic into a PLC’s
memory. However, a PLC may display the entered Boolean information as a
ladder diagram on the programming terminal.
Enhanced Boolean output operators, which perform additional control func-
tions, are a result of further enhancements to the Boolean instruction set.
Figure 9-123 shows a short Boolean program and its equivalent ladder
diagram representation. Chapter 3 discusses the principles of Boolean alge-
bra, which are applied in the Boolean language. The next chapter illustrates
other forms of Boolean programming utilizing the IEC 1131-3 instruction
list language.
node instruction. The first output is energized when the instruction is
completed; the second output is energized if a communication error occurs
during network transmission.
PLC #1 PLC #2
GET Node
100
Enable/Done
10
Node 05
Reg 400
Length 02
101
Error
The contents of registers
400 and 401 in the sending
node 05 are retrieved and
stored by the receiving
node (node 10) in registers
1000 and 1001.
Reg 400
401
(length = 2)
Reg 1000
1001
Node 05 Node 10
Dest
Reg 1000
370
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
cinomenMnoitcnuFnoitpircseDtnelaviuqEreddaL
RTS/DLtrats/daoLtcatnocONahtiwecneuqescigolastratS
TONRTS/RLtontrats/daoLtcatnocCNahtiwecneuqescigolastratS
DNAtniopdnAnoitcennocseirestcatnocONasekaM
TONDNAtnioptondnAnoitcennocseirestcatnocCNasekaM
ROtnioprOnoitcennoclellaraptcatnocONasekaM
TONROtnioptonrOnoitcennoclellaraptcatnocCNasekaM
TUOliocezigrenE lioctuptuonahtiwecneuqesasetanimreT
TONTUOliocezigrene-eD lioctuptuoTONahtiwecneuqesasetanimreT
RCTUOlioclanretniezigrenE tuptuolanretninahtiwecneuqesasetanimreT
LTUOlioctuptuohctaL tuptuohctalahtiwecneuqesasetanimreT
UTUOlioctuptuohctalnU tuptuohctalnunahtiwecneuqesasetanimreT
RMTremiTremitahtiwecneuqesasetanimreT
UTCretnuocpU retnuocpunahtiwecneuqesasetanimreT
DDAnoitiddA noitcnufnoitiddanahtiwecneuqesasetanimreT
BUSnoitcartbuS noitcnufnoitcartbusahtiwecneuqesasetanimreT
LUMnoitacilpitluM noitcnufnoitacilpitlumahtiwecneuqesasetanimreT
VIDnoisiviD noitcnufnoisividahtiwecneuqesasetanimreT
PMC)>,<,=(erapmoC noitcnuferapmocahtiwecneuqesasetanimreT
PMJpmuJ noitcnufpmujahtiwecneuqesasetanimreT
RCMyalerlortnocretsaM tuptuoRCMnahtiwecneuqesasetanimreT
DNEmargorpro,pmuj,RCMdnE noitcnufwolflortnocfodnenahtiwecneuqesasetanimreT
TNEretsigerrofeulavretnEsretsigerfoseulavteserpretneotdesU deriuqertoN
Table 9-12. Boolean instructions and their ladder diagram equivalents.
L
U
TON
CTU
+
–
CMP
JMP
END
÷
MCR
×
371
CHAPTER
9
Programming
Languages
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
Figure 9-123. Boolean program and its ladder diagram representation.
KEY
TERMS
10010 11
12
10223 24
25
101
END 210
20
21
T 20013 14
40116 17
MCR 21015
CTU 22022
PR: 10
TB: 1 Sec
PR: 5
STR of LD
OR
AND NOT
OUT
Boolean
10
12
11
100
STR of LD NOT
AND
TMR
ENT
13
14
200
10
STR of LD
MCR
15
210
END 210
STR of LD
AND
OUT
16
17
401
STR of LD
OR NOT
OUT
20
21
101
STR of LD
CTU
ENT
22
220
5
STR of LD
AND NOT
OR
OUT
23
24
25
102
arithmetic instructions
Boolean language
coil
contact
counter instructions
data manipulation instructions
data transfer instructions
double-precision arithmetic
enhanced ladder language
Grafcet
ladder language
ladder relay instructions
ladder rung matrix
372
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
9
Programming
Languages
network communications instructions
program/flow control instructions
single-precision arithmetic
special function instructions
timer instructions
network communications instructions
program/flow control instructions
single-precision arithmetic
special function instructions
timer instructions
THE IEC 1131 STANDARD AND
PROGRAMMING LANGUAGE
CHAPTER
TEN
Thought is the blossom; language the opening
bud; action the fruit behind it.
—Henry Ward Beecher
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
374
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
10
The IEC 1131 Standard and
Programming Language
As we have discussed in the previous chapters, programming a PLC can be
a difficult task due to increased interlocking requirements in the control
program as it becomes larger and more complicated. Additionally, each PLC
manufacturer offers a different set of instructions within its PLC family.
Many of these instruction sets are not applicable to other PLCs, and there is
no easy way to translate an already written PLC program to another brand of
PLC’s programming format.
In this chapter, we will introduce you to the IEC 1131 standard, which
attempts to simplify and standardize PLC programming. We will explain the
languages used with the IEC standard, as well as discuss how these languages
are implemented in the control program using sequential function charts to
ease interlocking. Moreover, we will explain how some manufacturers use
the IEC standard to implement a PLC-like environment without a program-
mable controller.
CHAPTER
HIGHLIGHTS
10-1 INTRODUCTION TO THE IEC 1131
The International Electrotechnical Commission (IEC) SC65B-WG7
committee developed the IEC 1131 standard in an effort to standardize
programmable controllers. One of the committee’s objectives was to create
a common set of PLC instructions that could be used in all PLCs. Although
the IEC 1131 standard reached the status of international standard in August
1992, the effort to create a global PLC standard has been a very difficult task
to accomplish due to the diversity of PLC manufacturers and the problem of
program incompatibility among PLC brands. However, the inroads that have
been made so far have had a tremendous impact on the way PLCs will be
programmed in the future.
The IEC 1131 standard for programmable controllers consists of five parts:
• general information
• equipment and test requirements
• programming languages
• user guidelines
• messaging services (communications)
Although there are five parts in the IEC 1131 standard, the third part—
programming languages—provides all of the information about instructions
and programming standards. The other four sections describe the different
guidelines to be used for the testing and communication of language instruc-
tions, as well as the methodology that must be employed by the programmable
controller user.
375
CHAPTER
10
The IEC 1131 Standard and
Programming Language
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
The IEC 1131 programming language standard is referred to as the IEC
1131-3 programming standard, since part 3 of the standard deals with
programming languages—hence the dash three (-3). In this chapter, we will
refer to the actual programming language as the IEC 1131-3 standard and
to the overall standard as the IEC 1131.
LANGUAGES AND INSTRUCTIONS
The IEC 1131-3 standard defines two graphical languages and two text-
based languages for use in PLC programming. The graphical languages use
symbols to program control instructions, while the text-based languages use
character strings to program instructions.
Graphical languages
• ladder diagrams (LD)
• function block diagram (FBD)
Text-based languages
• instruction list (IL)
• structured text (ST)
Additionally, the IEC 1131-3 standard includes an object-oriented program-
ming framework called sequential function charts (SFCs). SFC is
sometimes categorized as an IEC 1131-3 language, but it is actually an
organizational structure that coordinates the standard’s four true program-
ming languages (i.e., LD, FBD, IL, and ST). The SFC structure is much like
a flowchart-type of programming framework, utilizing different languages
for different control tasks and also routing control program actions. The SFC
structure has its roots in the early French standard of Grafcet (IEC 848).
The IEC 1131-3 standard is a graphic/object-oriented block programming
method, which increases the programming and troubleshooting flexibility of
its programmable controllers. It allows sections of a program to be individu-
ally grouped as tasks, which can then be easily interlocked with the rest of the
program. Thus, a complete IEC 1131-3 program may be formed by many
small task programs represented inside SFC graphic blocks. The combination
of languages available in the IEC 1131-3 standard also enhances PLC
programming and troubleshooting by providing not only a better program-
ming language, but also a better method for implementing control solutions.
The IEC 1131-3 uses a wide variety of standard data functions and function
blocks, which operate on a large number of data variable types. Table 10-1
shows some examples of these data types and functions, as well as some
typical function blocks. Data variable type refers to the kind of data received
by the controller (e.g., binary, real numbers, time data, etc.), while data
functions are the operations performed on the data (e.g., comparison, invert,
376
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
10
The IEC 1131 Standard and
Programming Language
addition, etc.). Function blocks are sets of data function instructions that
work on blocks of data. Moreover, variable scope refers to the extent that a
variable can be used in an application. For example, global variables can be
used by any program in an application, while local variables can only be used
by one particular program. Note that, in addition to the standard types of
variables, functions, and blocks, the IEC 1131-3 allows for other types of
vendor- and user-defined PLC programming elements. Thus, the IEC 1131-3
does not specify a set number of programming features, but rather establishes
the groundwork for standard and additional functions.
Table 10-1. Data variable types, functions, and blocks.
The IEC 1131 standard’s data type and function flexibility allows
programmable controller manufacturers to provide instructions they
consider necessary, but that are not defined within the standard. Such
instructions may include specific application instructions, such as a servo
positioning instruction used with a particular vendor’s intelligent servo
control module. While this instruction may fall within the programmability
parameters of the standard, it may not be available in other PLCs that comply
with the standard. Thus, the IEC 1131 standard lets vendors enhance their
IEC 1131-3 instruction sets by adding more powerful, customized
instructions. It also allows users to create their own instructions, in block
form, to perform a specific task.
selbairaVnoitpircseD
sepytelbairavataD)drow,etyb,tibronaelooB(sgnirtsdesab-tiB•
)dengisnudnadengis(sregetnI•
laeR•
)yaD_fO_emiT,.g.e—etad,emit(emiT•
sgnirtsretcarahcIICSA•
)syarradnaelgnis(denifed-resudna-rodneV•
snoitcnufataD).cte,TON,RO,DNA:naelooB(desab-tiB•
,RQS,VID,LUM,BUS,DDA(citemhtira/laciremuN•
).cte,NAT,SOC,NIS,NL,GOL
snoisrevnocnoitcnufataD•
).cte,NIM,XAM,TIMIL(snoitcnuftceleS•
)><,<=,=>,=,<,>(snosirapmoC•
,THGIR,TFEL,htgNEL(snoitcnufgnirtsIICSA•
).cte,ETELED,ECALPER,TRESNI
snoitcnufdenifed-resudna-rodneV•
skcolbnoitcnuFhctalnu/hctal—elbatsib—teser/teS•
(noitcetedreggirtegdE•π,≠,↓)
)nwod/pu,nwod,pu(sretnuoC•
)FOT,NOT(sremiT•
skcolbdenifed-resudna-rodneV•
epocselbairaVlabolG•
lacoL•
(=, , )
377
CHAPTER
10
The IEC 1131 Standard and
Programming Language
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
SECTION
3
PLC
Programming
DECLARING VARIABLES
During the implementation of a control system, the user must name, or
declare, the variables used. This variable declaration is nothing more than the
mapping of I/O addresses, indicating which field devices are wired to which
I/O modules (see Chapter 5). Figure 10-1a shows a limit switch (LS1)
implemented in a standard programmable controller environment. In this
configuration, the device is declared (or named) in the control program as its
address—10. In an IEC 1131-3 environment, however, a device can be
described by any alphanumeric name. This name can include underscores
(_). Hence, the limit switch can be declared as a variable named
Limit_Switch_1, Clamp_Limit_Switch, or another appropriate name (see
Figure 10-1b). From the moment a variable is declared, it will be known by
that name throughout the control program, regardless of the IEC 1131-3
programming language used. The name assigned to a variable is not case
sensitive; that is, it can be declared in uppercase, lowercase, or a combination
of the two. Therefore, the user may choose the appropriate name represen-
tations for the purposes of program appearance (e.g., the use of uppercase for
a main variable name and lowercase for a secondary variable name).
Figure 10-1. Limit switch addressed in (a) a standard PLC environment and (b) an IEC
1131-3 environment.
(a)
(b)
0
1
2
3
C
10
11
12
13
L1 Rack 0
Slot 1
L2
LS1
Address
10
PLC
Address 10
Limit_Switch_1
Input variable address
Limit_Switch_1
assigned to PLC address
LD Language
ST Language
IF Limit_Switch_1 THEN Motor=True
Limit_Switch_1 0 1 0
VAR_NAME
Type: Boolean
Name: Limit_Switch_1
Address: 010
Rack Slot Terminal
Location
Variable Definition
378
SECTION
3
PLC
Programming
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
CHAPTER
10
The IEC 1131 Standard and
Programming Language
When declaring a variable, the user must specify the variable type in addition
to the variable name. This allows the PLC to know what type of data the
device corresponding to the variable transmits. The IEC 1131-3 supports
many different local and global data variable types (see Table 10-2); however,
the three most common are:
• Boolean
• integer
• real
Table 10-2. Data variable types.
Boolean variables are single-bit variables, meaning that the data transmit-
ted and received is in the form of 1s and 0s. Discrete I/O variables fall under
this category; therefore, they must be specified as “Bool” (short for Boolean)
variables in the control program. Many nondiscrete variables, such as analog
input signals that are read through an analog input card, are integer
variables, because they transmit data in the form of whole numbers (e.g.,
2042, –127, etc.). Thus, they must be specified in the control program as
integer variables. Internal variables that transmit fractional and floating-
point data (i.e., a number multiplied by an exponential expression—2.7 ×
10
2
) are real variables and, again, must be classified as such.
ssalCepyTelbairaVnoitpircseDelpmaxE
etercsiDnaelooB)0(ESLAF/)1(EURT,rotom,hctiwstimiL
nottubhsup
golanAregetnI4673+ro821–,tupniSWT,eulavremiT
noitaluclacregetni
gnitaolf(laeR
)tniop
ro375.43–
53.1+×01
3
lareneg,O/IgolanA
noitatupmoc
gnirtsIICSAegasseM
sgnirts
=:”erutarepmeT“
raV_eulaV_pmeT
anonoitamrofniyalpsiD
retnirprorotinom
metsySlanretnI)looB(syalerlortnoCremit,sliocyalerlanretnI
stuptuo
laerdnaregetnI
selbairav
citemhtiralanretnI
snoitatupmoc
tupnIdetcennocselbairaV
secafretnitupniot
,stupnigolana/etercsiD
golana,stupniSWT
secafretni
tuptuOdetcennocselbairaV
secafretnituptuoot
,stuptuogolana/etercsiD
,syalpsidDELotstuptuo
secafretnigolana