Specifications for diagrams for process industry — Part 2: Measurement and control
0.1 General
The ISO 15519 series consist s of st andards for specif icat ion of diagrams for process indust r y, published
under the general title: Specification for diagrams for process industry.
This International Standard specifies preparation of different t ypes of diagrams and use of graphical
symbols, let ter codes, and reference designation in diagrams. This International Standard addresses
all process industry fields for example chemical, petrochemical, power, pharmaceutical, foodstuff,
pulp, and paper.
This part of ISO 15519 deals with representation of measurement, actuation, and control in process
diagrams which in this context covers process f low diagrams (PFD), process and instrument diagrams
(PID), process control diagrams (PCD), and t ypical diagrams (TYD).
0.4 Letter codes
ISO 14617-6, 7.3.1 have been moved to this part of ISO 15519 and the description has been changed to
“Let ter codes for Process Control Information (PCI)”.
0.6 Reference designation
In this part of ISO 15519, IEC 81346-1, IEC 81346-2, and ISO/TS 81346-3 are used to illustrate the
application of reference designation in diagrams.
1 Scope
BS ISO 15519-2:2015
INTERNATIONAL STANDARD ISO 15519-2:2015(E)
This part of ISO 15519 provides rules and guidelines for representation of measurement, control, and
actuation in diagrams for process industry.
General rules and guidelines for preparation of diagrams for process industry, for example t ypes
and descriptions of diagrams, layout of diagrams, graphical symbols, lines and connection, reference
designation, are given in ISO 15519-1.
Rules and guidelines for preparation of electrotechnical diagrams are given in IEC 61082-1.
3.2 Document types
3. 2.1
process f low diagram
PFD
diagram representing the configuration of a process plant or a process system by means of graphical symbols
process and instrumentation diagram
PID
diagram representing the technical realization of a process system by means of graphical symbols for
equipment, connections, process measurement, and manipulating objects
3.2.3
process control diagram
PCD
diagram representing the configuration of measuring, control, and actuating functions of a process
system, by means of graphical symbols for measuring, control, and manipulating functions
3.2.4
typical diagram
TYD
diagram representing the detailed configuration of a definite measuring or actuating system which can
be referred to in an associated diagram by a graphical symbol and document reference
4.2 Diagram types, structures, and life cycle aspects
Diagrams are used for visual representation of process functions. Objects and connections, represented
by graphical symbols, serve as carrier of technical information either represented direct in the diagram
or in associated lists or databases.
Depending on the task of the diagram and the stage in the live cycle matrix described in Figure 3,
diagrams can represent process functions on high and generic level or on detailed and specific level.
Life cycle stage principles are described in ISO 15226 and ISO/IEC 15288
Measuring, control, and actuation are illustrated in diagrams with variable degree of detailing
depending of needs for the actual life cycle stage. In the start of a project the representation in process
f low diagrams (PFD) is pure functional. Later in the project course, when more detailed diagrams are
developed, for example: process control diagram and process and instrumentation diagrams (PID), the
amount of information is increased and the representation is extended to also to include products like
sensors built in the process system also.
Letter codes for process variables and control functions, see 5.2, shall be placed in the upper part of the
symbol and reference designation in the lower part of the symbol, see Figure 7.
nformation placed outside the PCI symbol shall be placed in the four quadrants around the symbol as
illustrated in Figure 8. This allows for horizontal and vertical connections to the symbol.
a) Reference to t ypical diagram, safet y information, e.g. SIL or SIF identifiers;
b) Specification of t ype of measured variable when using let ter code U (multivariable), e.g. pH, µS,
MJ/s, etc.;
c) Information of high output/input functions, e.g. alarm or switching;
d) Information of low output/input function, e.g. alarm or switching.
Representation of high and low output/input function for measurement and actuation are given in 5.2.5.
5.2 Letter codes
Figure 8 — Placement of information outside the PCI symbol
5.2.1 General
Let ter codes are used for identification of process variables and control f unctions.
Process variables are measured quantity, quality, or condition of process media or process objects, e.g.
pressure, t emperat ure, or c alculated var iables, e. g. energ y f low based on di rec t measurement s of volume
f low, pressure, a nd t emper at ure u si ng bui l t i n mat hemat ic f unc t ions a nd medi a proper t y t ables or out put
variables f rom an analyser. Process variable are also human observations based on human sensory.
Control functions are manipulating functions which via the final controlling element of process media
or process objects in order to bring the media or object into a condition or state defined by the process
control system on basis of measured process variables and pre-defined values. Control functions are
also display and registration of process variables.
Letter codes shall be represented with upper-case letters.
5.2.2 Representation of letter codes for process variables
Letter codes for process variables shall initiate the letter code string placed in the upper part of the PCI
symbols.
The letter codes shall be taken from Table 2 and supplemented with modif ying let ter code from Table 3.
Examples of letter code strings are given in Figure 9.
Table 2 — Letter codes for process variables and control functions
5.3 Reference designation
Reference designation shall comply with IEC 81346-1, IEC 81346-2, and ISO/TS 81346-3. Rules for
application of reference designation in diagrams are given in ISO 15519-1.
Reference designation, shall be placed in the lower part of the PCI symbol.
The technical realization of signal transmission e.g. electronic, hard wired, bus system, etc., should not
be represented diagrams.
6.3.2 Instruments with integrated display
6.3.3 Multifunction instruments
Instruments with two or more functions in common housing/envelope shall be represented with PCI
symbols for each function. The PCI symbols shall be placed “side by side” as illustrated in Figure 14
showing a local pressure gauge with integrated switch.
6.3.5 Differentiating of representation
The same function can be represented in different t ypes of diagrams with different graphical appearance,
see Figure 16.
7 Representation in diagrams
7.1 Introduction
Clause 7 specifies rules for representation of measurement, control, and actuation. General rules for
preparation of process diagrams can be found in e.g. ISO 15519-1.
© ISO 2015 – All rights reserved 15
BS ISO 15519-2:2015
ISO 15519-2:2015(E)
Clause 7 deals with following t ypes of diagrams:
— Process f low diagram, PFD;
— Process and instrumentation diagram, PID;
— Process control diagram, PCD;
— Typical diagram, TYD.
NOTE The Block Diagram (BLD) is not dealt with in this part of the standard, as it normally not includes
representation of measurement and control.
Each diagram t ype is specifies, in tables, basic and additional information concerning measurement,
control, and actuation. The basic information is mandatory in an early stage of the diagram. In a final
stage of the diagram, the additional information should be added.
Examples of above mentioned process diagrams are given in Annex C.
7.2.1 Description
A process f low diagram represents the configuration of a process plant or a process system by means of
graphical symbols.
DCC: FB
7.2.2 Application
The diagram is used for project planning and coordination especially in the basic engineering phase and
form basis for the preparation of process and instrumentation diagrams and process control diagrams.
Functional groups such as redundant pumps shall only be represented by one symbol, with remark of
the redundancy e.g. 2 × 100 %.
7.3.1 Description
A process and instrumentation diagram represents the technical realization of a process system by
means of graphical symbols for equipment, process f low paths and process measurement, actuation,
and control functions.
DCC: FB
7.3.2 Application
The diagram is based on the relevant process f low diagram and is used for detailed engineering of
process systems like piping, conveyance systems, instrument ation to coordinate mechanical, electrical,
and instrumentation engineering.
In operation and maintenance, the process and instrumentation diagram is the “master” document
for references to documentation, operation manuals, fault-finding, securing of systems for repair, and
maintenance works.
7.3.4.3 Reference to typical diagram
The reference to a t ypical diagram for an object in a process diagram, e.g. a pneumatic control valves,
shall be placed as illustrated in Figure 19.
7.4.1 Description
The process control diagram represents the configuration of measurement, control, and actuation
objects for a complete process system or part of a process system in order to understand the function
of the process.
7.4.2 Application
PCDs are used in the engineering phase to communicate process control requirements and form basis
for development of function and logical diagrams.
PCDs are based on process f low diagrams and process and instrumentation diagrams.
DCC: FB
7.4.4.2 Layout of PCD
PCD shall be drawn with horizontal layers with following structure from top to bottom:
— Process control symbols for operator interface
— Process control symbols
— PCI symbols inclusive of let ter codes and reference designation
— Graphical symbols representing the primary process objects.
7.5.1 Description
Typical diagrams are detailed diagrams which represent standardized detailed configuration of definite
measuring systems e.g. a transmitter including instrument valves or a definite actuating system, e.g. a
pneumatic control valve with actuator, valve positioner, etc.
Objects of identical technical configuration but different signal interfaces with the control system shall
be represented in separate typical diagrams.
DCC: FB
7.5.2 Application
Typical diagrams contribute to limitation of the technical documentation, as several objects in process
diagram can refer to same t ypical diagram and to the communication bet ween the engineering disciplines.
Each TYP is allocated a unique document identit y, which is used as reference in PID, see Figure 19.
7.5.4.2 Reference designation
The objects in the t ypical diagram are designated with a product oriented reference designations which
can be linked to the reference designation of the main object for example a pneumatic on-off valve fail
to close, see Figure 20.