IEC PAS 60027-6:2004

PUBLICLY
IEC
AVAILABLE
PAS 60027-6
SPECIFICATION
First edition
2004-09
Letter symbols to be used
in electrical technology –
Control technology
Reference number
IEC/PAS 60027-6:2004(E)
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PUBLICLY
IEC
AVAILABLE
PAS 60027-6
SPECIFICATION
First edition
2004-09
Letter symbols to be used
in electrical technology –
Control technology
© IEC 2004 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
K
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

– 2 – PAS 60027-6 © IEC:2004 (E)

CONTENTS
FOREWORD. 3

1 Scope .4

2 Normative references .4

3 Principles.5

4 General quantities and functions.6

5 Characteristic quantities of the step response .7
6 Parameters of transfer elements and control loops.7
7 Variable quantities of the control loop .8
8 Mapping functions and their variable quantities .9
9 Functional diagrams. 10

PAS 60027-6 © IEC:2004 (E) – 3 –

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
LETTER SYMBOLS TO BE USED IN ELECTRICAL TECHNOLOGY –

CONTROL TECHNOLOGY
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
A PAS is a technical specification not fulfilling the requirements for a standard but made
available to the public.
IEC-PAS 60027-6 has been processed by IEC technical committee 25: Quantities and units, and
their letter symbols.
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
25/271/NP 25/283/RVN
Following publication of this PAS, the technical committee or subcommittee concerned will
investigate the possibility of transforming it into an International Standard.

– 4 – PAS 60027-6 © IEC:2004 (E)

LETTER SYMBOLS TO BE USED IN ELECTRICAL TECHNOLOGY –

CONTROL TECHNOLOGY
Introductory note
This Publicly Available Specification (PAS) is intended to replace section 11 of

IEC 60027-2:2000.
In comparison to section 11 of IEC 60027-2:2000 the following has been altered.
– The number of physical quantities and of their symbols listed in this PAS has been
increased significantly. New sections for general quantities and functions, for characteristic
quantities of the step response, for parameters of transfer elements and control loops, and
for mapping functions and their quantities have been included.
– The hitherto existing series of reserve symbols has been deleted. Four symbols out of this
series have been used as new symbols for main quantities.
– The presentation of the denotation of some mathematical concepts specific to the field
formerly given in 11.4 has been removed to the column “remarks” of the relevant tables.
1 Scope
This PAS is applicable to control technology. It gives names and symbols for quantities,
signals and functions, and their units.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
lEC 60027-1:1992, Letter symbols to be used in electrical technology - Part 1: General.
IEC 60027-2:2000, Letter symbols to be used in electrical technology – Part 2:
Telecommunications and electronics
IEC 60050-101:1998, International Electrotechnical Vocabulary – Part 101: Mathematics
IEC 60050-351:1998, International Electrotechnical Vocabulary – Part 351: Automatic control

ISO 31-2:1992, Quantities and units – Part 2: Periodic and related phenomena
ISO 31-5:1992, Quantities and units – Part 5: Electricity and magnetism.

PAS 60027-6 © IEC:2004 (E) – 5 –

3 Principles
3.1 This PAS presents a coherent body of letter symbols for the most important physical

quantities and functions used in control technology science and technology, particularly for

important variable quantities and (without distinction) the signals representing them.

3.2 Signals and quantities may have any physical form; it is the control engineering design

function which characterizes them. Therefore, for most of the quantities and functions listed in

this PAS, it is not possible to appoint a special unit to them. For those quantities and
functions for which this is possible (1.04 to 1.16, 2.01 to 2.05, 3.04 to 3.15, 5.01, 5.02, and
5.06) any user of this PAS knows the inherent unit.

3.3 The names of quantities, functions and signals, their definitions, their 7-digit reference
numbers and the names of functional blocks within the functional diagrams are based on IEC
60050-351.
3.4 In IEC 60050-101 and IEC 60050-351, letter symbols are just used but not
standardized. International standardization of letter symbols and units is to be found in the
different parts of ISO 31 and IEC 60027 only.
3.5 Any of the basic symbols listed in sections 1 to 5 may be supplemented by the signs
and subscripts to be found in IEC 60027-1.
3.6 Symbols for time-dependent quantities are covered by IEC 60027-1.
3.7 Some entries in the column “remarks” give the notation of some mathematical concepts
specific to the field.
3.8 Vector quantities are represented by the same symbols as the corresponding scalar
quantities, but by bold type letters.
3.9 The list of recommended letter symbols in sections 1 to 5 is followed in section 6 by
functional block diagrams intended to show typical applications.

– 6 – PAS 60027-6 © IEC:2004 (E)

4 General quantities and functions

Table 1
Item
Entry Item
Item number Name of quantity
number number in Symbol Remarks
number in or function
1)
in IEV IEC 60027-1
ISO 31
u
4.01 351-21-06  input variable

2)
v
4.02 351-21-07  output variable
Arabic numeral
subscripts for
x
4.03 351-21-08  state variable
j
components
j = 1, 2, 3, ., n
f
4.04 101-14-08 18 2-3.1 frequency
τ , T
4.05 351-24-24 24 2-2 time constant
angular frequency;
ω ω= 2π f
4.06 101-14-36 13 2-4
pulsatance
characteristic
ω
4.07 351-28-14
o
angular frequency
4.08 351-24-18  damping ratio ϑ
eigen angular
frequency;
ω
4.09 351-24-18  angular frequency
d ω=−ωϑ1
do
of damped
oscillation
damping
δ=ϑω
4.10 101-14-20 26 2-11 δ
o
coefficient
rotational
f
4.11 19 2-3.2
r
frequency
ϕ
4.12 351-24-37 103 5-43 phase angle
Dirac function;
δ()t
4.13 101-13-06 953 unit pulse;
unit impulse (US)
unit-step function;
ε()t
4.14 101-13-02 952
Heaviside function
ht()
4.15 351-24-21  unit-step response
unit-pulse
response;
g()t
4.16 351-24-19  unit-impulse
response (US);
weighting function
1)
As far as the entry number starts with 351, this is the term number in edition 3 of IEC
60050-351 (to be published).
2)
The symbol v is a Latin “vee”, not a Greek “nu”.

PAS 60027-6 © IEC:2004 (E) – 7 –

5 Characteristic quantities of the step response

Table 2
Item Entry number
3)
Name of quantity Symbol
number in IEV
T
5.01 351-24-27 equivalent time constant
b
T
5.02 351-24-26 equivalent dead-time
e
T
5.03 351-24-28 step response time
sr
T
5.04 351-24-29 settling time
s
4)
v
5.05 351-24-30 overshoot
m
6 Parameters of transfer elements and control loops
Table 3
Item Entry number
5) Name of quantity Symbol Remarks
number in IEV
proportional action
K
6.01 351-28-17
P
coefficient
Equation of an ideal PID
control element:
integral action
t
K
6.02 351-28-20
I
coefficient
&
yt()=+K u()t K u(ττ)d+K ut( )
PI D
∫
derivative action
K
6.03 351-28-25
D
coefficient
T TK= /K
6.04 351-28-23 reset time
i iP I
T TK= /K
6.05 351-28-28 rate time
d dD P
T
6.06 351-28-41 dead-ti
...