IEC 60534-9:2007

Industrial-process control valves - Part 9: Test procedure for response measurements from step inputs

It defines the testing and reporting of the step response of control valves that are used in throttling closed-loop control applications. A control valve consists of the complete, ready-to-use assembly of the control valve body, the actuator, and any required accessories. The most probable accessory is a valve positioner. It defines how to test, measure, and report control valve response characteristics in an open-loop environment. This information can be used for process control applications to determine how well and how fast the control valve responds to the control valve input signal. The contents of the corrigendum of June 2008 have been included in this copy.

Vannes de régulation des processus industriels - Partie 9: Procédure d'essai pour la mesure de la réponse des vannes de régulation à des signaux d'entrée échelonnés

Elle définit les essais et les rapports d'essai relatifs à la réponse à un échelon des vannes de régulation utilisées dans les applications de commande en boucle de régulation fermée. Une vanne de régulation consiste en un assemblage complet, prêt à l'emploi, d'un corps de vanne de régulation, d'un actionneur et de tout autre accessoire requis. L'accessoire le plus fréquent est un positionneur de vanne. Elle définit également comment réaliser les essais, les mesures et le rapport relatifs aux caractéristiques de la réponse des vannes de régulation dans un environnement en boucle ouverte. Cette information peut être utilisée pour des applications de commande de processus afin de déterminer comment et avec quelle rapidité la vanne de régulation répond au signal d'entrée de commande de la vanne. Le contenu du corrigendum de juin 2008 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 09-Sep-2007
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 23.060.40 - Pressure regulators
• ICS: 25.040.40 - Industrial process measurement and control
• Technical Committee: SC 65B - Measurement and control devices
• Drafting Committee: WG 9 - TC 65/SC 65B/WG 9
• Current Stage: PPUB - Publication issued
• Start Date: 10-Sep-2007
• Completion Date: 30-Sep-2007

Relations

• Corrected By: IEC 60534-9:2007/COR1:2008 - Corrigendum 1 - Industrial-process control valves - Part 9: Test procedure for response measurements from step inputs
• Effective Date: 05-Sep-2023

Overview

IEC 60534-9:2007 is an international standard published by the International Electrotechnical Commission (IEC) that details test procedures for measuring the response of industrial-process control valves to step input signals. This standard is part 9 of the IEC 60534 series, which addresses various aspects of control valves used in industrial process automation. Specifically, IEC 60534-9 focuses on testing the dynamic response characteristics of control valves in throttling closed-loop control applications.

A control valve, per this standard, is a complete assembly including the valve body, actuator, and any necessary accessories, typically a valve positioner. The goal is to provide a consistent methodology to evaluate how quickly and accurately a control valve responds to changes in input signals, measured in an open-loop testing environment. This ensures that process control systems can be better designed and tuned to maintain optimal performance.

Key Topics

• Scope and Objective
  Defines how to conduct and report valve step response tests relevant to process control feedback loops, without restricting valve selection or performance criteria. Focuses on throttling valves and excludes on-off control valves.

• Testing Conditions and Setup
  Includes requirements for test valve conditions, system setup, measurement instruments, and nominal test positions. It covers bench tests, laboratory tests, and in-process tests under different operational environments.

• Step Response Measurements
  Provides detailed procedures for baseline tests, small-step tests, and response-time tests. Measurements include valve dead band, resolution, dead time, dynamic response time, and response gain ratios.

• Terminology and Definitions
  Clearly explains essential concepts such as closed-loop time constant, dead band, dead time, dynamic response, gain ratio, input step size, limit cycle, and nonlinear systems-crucial for understanding valve behavior.

• Test Data Presentation
  Guidance on how to document and present test results professionally, including sample signal sequences, plots, and calculated parameters.

• Applicability and Limitations
  The standard explicitly states that the tests may not suffice for all valve applications and that parties can agree to variants for acceptance testing. It focuses primarily on the measurement process, not on defining acceptable performance levels.

Applications

IEC 60534-9:2007 is invaluable for:

• Valve Manufacturers
  Ensuring consistent quality and verifying valve dynamic response under standardized conditions, helping with product development and certification.

• Process Control Engineers
  Selecting appropriate control valves by understanding valve responsiveness characteristics to optimize closed-loop control performance in industries such as chemical processing, oil and gas, power generation, and water treatment.

• Test Laboratories
  Conducting objective and repeatable valve performance tests that comply with international best practices, enabling fair comparison across different valve models and manufacturers.

• Automation System Integrators
  Tuning control loops by leveraging accurate valve response data to reduce control loop settling time, minimize oscillations, and improve process stability.

• Research and Development
  Analyzing valve dynamic behaviors to innovate new valve designs or positioner technologies with improved responsiveness and reliability.

Related Standards

To fully utilize IEC 60534-9, it is beneficial to reference related standards from the IEC 60534 series and other pertinent documents:

• IEC 60534-1: Industrial-process control valves – Part 1: Control valve terminology and general consideration
  Provides essential definitions and general concepts applicable across the control valve domain.

• IEC 60534-4: Industrial-process control valves – Part 4: Inspection and routine testing
  Covers standard inspection and testing methods aside from dynamic response.

• ANSI/ISA-TR75.25.02
  Offers background and extended technical guidance on control valve static and dynamic response characteristics to aid interpretation of test data.

• IEC 60050-351: International Electrotechnical Vocabulary – Control technology
  Clarifies control system terminology that overlaps with valve testing.

• Other IEC control valve parts and technical reports
  For comprehensive understanding of valve design, application, and testing.

---

By adhering to IEC 60534-9:2007, organizations achieve improved control valve evaluation consistency and enhanced process automation system reliability. Incorporating this standard supports effective control valve selection based on scientifically measured response times and behaviors, ultimately leading to optimized process performance and efficiency.

Standards Content (Sample)

IEC 60534-9
Edition 1.0 2007-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial-process control valves –
Part 9: Test procedure for response measurements from step inputs

Vannes de régulation des processus industriels –
Partie 9: Procédure d’essai pour la mesure de la réponse des vannes de
régulation à des signaux d’entrée échelonnés

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IEC 60534-9
Edition 1.0 2007-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial-process control valves –
Part 9: Test procedure for response measurements from step inputs

Vannes de régulation des processus industriels –
Partie 9: Procédure d’essai pour la mesure de la réponse des vannes de
régulation à des signaux d’entrée échelonnés

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
U
CODE PRIX
ICS 23.060; 25.040.40 ISBN 2-8318-9280-5

– 2 – 60534-9 © IEC:2007
CONTENTS
FOREWORD.3

1 Scope and object.5
2 Normative references .5
3 Terms and definitions.5
4 Symbols .10
5 General test procedures .11
5.1 Test valve conditions.11
5.2 Test system.11
5.3 Measuring instruments .11
5.4 Process variable.12
5.5 Nominal test position.13
6 Examples of step response.13
7 Tests specified for each of three test environments .15
7.1 Bench tests .15
7.2 Laboratory tests .16
7.3 In-process tests.16
8 Detailed test procedures.17
8.1 Baseline test .17
8.2 Small-step test .18
8.3 Response-time tests.19
9 Presentation of test results.21
9.1 General information.21
9.2 Test results .22
9.2.1 Baseline test.22
9.2.2 Small-step test .22
9.2.3 Response-time tests.22

Annex A (informative) Sliding friction measurement .24

Bibliography.26

Figure 1 – Dead band and resolution .6
Figure 2 – Typical step change and response without overshoot.14
Figure 3 – Step response with some overshoot.15
Figure 4 – Example step and response during baseline test.18
Figure 5 – Signal sequence for small-step test.19
Figure 6 – Sample signal step sequence for response time tests .20
Figure 7 – Sample data from small-step test (Δs = 0,13 %) performed in a process loop .23
Figure 8 – Sample plot showing step response, t , versus step size for four different
valves .23

60534-9 © IEC:2007 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
INDUSTRIAL-PROCESS CONTROL VALVES –

Part 9: Test procedure for response measurements from step inputs

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
International Standard IEC 60534-9 has been prepared by subcommittee 65B: Devices, of IEC
technical committee 65: Industrial-process measurement and control.
The text of this standard is based on the following documents:
FDIS Report on voting
65B/632/FDIS 65B/639/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – 60534-9 © IEC:2007
The list of all the parts of the IEC 60634 series, under the general title Industrial-process
control valves, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of June 2008 have been included in this copy.

60534-9 © IEC:2007 – 5 –
INDUSTRIAL-PROCESS CONTROL VALVES –

Part 9: Test procedure for response measurements from step inputs

1 Scope and object
This part of IEC 60534 defines the testing and reporting of the step response of control valves
that are used in throttling closed-loop control applications. A control valve consists of the
complete, ready-to-use assembly of the control valve body, the actuator, and any required
accessories. The most probable accessory is a valve positioner.
NOTE For background, refer to technical report ANSI/ISA-TR75.25.02 [6] .
The object of this standard is to define how to test, measure, and report control valve
response characteristics in an open-loop environment. This information can be used for
process control applications to determine how well and how fast the control valve responds to
the control valve input signal.
This standard does not define the acceptable control valve performance for process control
nor does it restrict the selection of control valves for any application. If this standard is used
for evaluation or acceptance testing, the parties may agree to documented variations from
these requirements.
The information using the defined test methods is specifically applicable to closed-loop
feedback control but may have some application to open-loop control applications. It does not
address valves used in on-off control service.
Tests specified in this standard may not be sufficient to measure the performance required for
all applications. Not all control valve applications will require this testing.
2 Normative references
The following 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.
IEC 60534-1, Industrial-process control valves – Part 1: Control valve terminology and
general consideration
IEC 60534-4, Industrial-process control valves – Part 4: Inspection and routine testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions, as well as those given
in IEC 60534-1 and other parts of IEC 60534, apply.
NOTE 1 In the specific area of non-linear dynamics, it was determined that some terms defined in IEC 60050-351
or in [5] lacked the precision desired for these documents. Others were inconsistent with the terminology used in
the non-linear control literature.
—————————
Figures in square brackets refer to the Bibliography.

– 6 – 60534-9 © IEC:2007
NOTE 2 Reference [6] explains applicable terms and explores control valve static and dynamic response
characteristics important for process control. That information will aid correct interpretation and application of the
test results obtained from the tests defined in this standard.

Output
b
a c
d
a < resolution ≤ b
Input
c < dead band ≤ d
Time
Dynamics are not shown
IEC  1630/07
Figure 1 – Dead band and resolution
3.1
closed-loop time constant
time constant of the closed-loop response of a control loop, used in tuning methods such as
Internal Model Control (IMC) and Lambda Tuning and is a measure of the performance of a
control loop
3.2
dead band
finite range of values within reversal of the input variable does not produce any noticeable
change in the output variable
[IEC 60534-4, 3.2]
3.3
dead time
time interval between the instant when a variation of an input variable is produced and the
instant when the consequent variation of the output variable starts
3.4
dynamic response
time-dependent output signal change resulting from a defined time-dependent input signal
change
NOTE Commonly used input signal changes include impulse, pulse, step, ramp, and sinusoid [4]. Dynamic means
that the control valve is moving. Dynamic response can be measured without process loading in bench-top tests,
with simulated or active loading in a flow laboratory or under normal process operating conditions.
Amplitude
60534-9 © IEC:2007 – 7 –
3.5
gain ratio
G
R
response gain G divided by the response gain G determined from the multi-step test
Z Z02
performed with a step size of 2 %. The ideal gain ratio equals 1,0 for tests about any nominal
position
G = G /G
R Z Z02
NOTE Measuring the gain ratio may not be possible if a digital positioner with pulse-modulated output is involved
in the system since, on such positioners, the gain measurement may give infinite values.
3.6
input step size
Δs
difference between the beginning and ending signal in a step change expressed as a per cent
of the signal span
3.7
limit cycle
oscillation caused by the non-linear behaviour of a feedback system
NOTE 1 These oscillations are of fixed amplitude and frequency and can be sustained in a feedback loop even if
the system input change is zero. In linear systems, an unstable oscillation grows theoretically to infinite amplitude,
but non-linear effects limit this growth [3].
NOTE 2 The occurrence of the limit cycle may be dependent on current valve position.
3.8
non-linear system
system whose response depends on the amplitude and the nature of the input signal, as well
as the initial conditions of the system. As an example, a non-linear system can change from
being stable to unstable by changing the size of the input signal
NOTE When a non-linear system is driven towards a set point by feedback control action, it is likely to develop a
limit cycle. The amplitude and frequency of such limit cycles are a function of the nature of the non-linearities
which are present, and the effective gain of the feedback control action. As the gain of the feedback is increased,
the frequency of the limit cycle is likely to increase. More aggressive gain increases may produce behaviour such
as bifurcation, frequency doubling and eventually chaotic behaviour.
3.9
overshoot
for a step response, the maximum transient deviation from the final steady-state value of the
output variable, expressed as a percentage of the difference between the final and the initial
steady-state values
3.10
relative travel
h
ratio of the travel at a given opening to the rated travel
[IEC 60534-1, 4.5.4]
3.11
resolution
smallest step increment of input signal in one direction for which movement of the output is
observed, expressed as a percentage of the input span
NOTE The term “valve resolution” in this standard means the tendency of a control valve to move in finite steps in
responding to step changes in the input signal applied in the same direction. This happens when the control valve
sticks in place, having stopped moving after the previous step change.

– 8 – 60534-9 © IEC:2007
3.12
step response
time history of a variable after a step change in the input. In this standard, the step response
can be stem position, flow, or another process variable
3.13
response flow coefficient
C
R
apparent flow coefficient as determined by testing in an operating type environment. The data
available in the operating environment may differ from the laboratory data required by valve
sizing standards
NOTE 1 Flow coefficients in current use are K and C depending upon the system of units. For further
v v
information, refer to IEC 60534-1.
NOTE 2 It will be noted that the dimensions and units on each of the following defined flow coefficients are
different. However, it is possible to relate these flow coefficients numerically. This relationship is as follows:
K
v
= 0,865
C
v
3.14
response gain
G
Z
ratio of the steady-state magnitude of the process change, ΔZ, divided by the signal step, Δs,
that caused the change. One special reference response gain is defined as that calculated
from the 2 % step size response time test which is designated as G
Z02
G = ΔZ/Δs
Z
G = ΔZ /Δs
Z02 02 02
3.15
sampling interval
Δt
s
time increment between sampled data points which is the inverse of the sampling rate,
f
Δt = 1/f
S
NOTE As used in this standard, since more than one variable is being sampled, it is the time between the sets of
sampled data. Ideally, all variables in one set are sampled at the same time. If data is recorded using analogue
equipment, the time constant for the recording equipment should be less than, or equal to, the maximum allowed
Δt .
s
3.16
sampling rate
f
rate at which data samples are taken or the number of samples per unit time (see 3.15)
3.17
sliding friction
F or T
R R
force or torque required to maintain motion in either direction at a prescribed input signal
ramp rate
60534-9 © IEC:2007 – 9 –
3.18
static
means without motion or change [4]; readings are recorded after the device has come to rest.
Static performance can be measured either without process loading (bench-top tests), with
simulated or active loading, or under process operating conditions
NOTE This kind of test is sometimes called a dynamic test [4] which may cause confusion. The static behaviour
characteristics identified as important to the control valve performance are the dead band, the resolution, and the
valve travel gain.
3.19
steady state
state of a system which is maintained after all transient effects have subsided as long as all
input variables remain constant
3.20
step change
nearly instantaneous step change made to an input signal of a dynamic system with the
intention of stimulating a step response of the dynamic system. Such a test is used to
characterize the step response of the dynamic system
3.21
step change time
Δt
sc
time between the start of a signal input step and attainment of its maximum value
3.22
step test
application of a step change to an input signal in order to test the step response dynamics
3.23
step response time
t
interval of time between initiation of an input signal step change and the moment that the
response of a dynamic reaches 86,5 % of its full steady-state value. The step response time
includes the dead time before the dynamic response
3.24
stiction (static friction)
resistance to the start of motion, usually measured as the difference between the driving
values required to overcome static friction upscale and downscale [5]
3.25
time constant
τ
time required to complete 63,2% (i.e. 1-1/e) of the total change of the output of a first-order
linear system produced by a step-wise variation of the input variable
NOTE The term is used in this standard to describe the dynamic characteristics of the analogue measuring
instruments.
3.26
valve travel gain
change in closure member position divided by the change in input signal, both expressed in
percentage of full span
G = ΔX/Δs
X
– 10 – 60534-9 © IEC:2007
3.27
valve system approximate time constant
τ'
time constant of a first-order response without dead time, which may fit the actual control
valve step response reasonably well. The approximate time constant is defined to provide a
basis for comparison of the valve with other time constants, such as the closed-loop time
constant for the control loop
NOTE 1 A first-order system reaches 86,5 % of its final step response value in two time constants; the
approximate time constant is considered to be one-half of the step response time, t .
NOTE 2 The use of the approximate time constant in no way implies that the response of the control valve is first-
order. The step response of the control valve is typically complex, having dead time initially, followed by potentially
complex dynamics before the steady state is achieved. t includes the dead time in the initial part of the response,
as well as the possibility of slower settling in the last portion of the response. Some valve positioner designs
attempt to achieve a slow-down in the final part of the response in order to limit overshoot. τ' attempts to produce a
simple linear time constant approximation of the control-valve dynamic response, which can be compared to the
closed-loop time constant of the control loop on the same basis in time-constant units. It should be noted that as
the portion of t that is dead time increases, this approximation becomes less ideal.
3.28
wait time
Δt
w
time spent after a step input change waiting for the response to come to the new steady-state
value
3.29
X-Y plot
plot of the output excursions plotted against input excursions. Input-output plots are useful for
defining the steady-state characteristics of non-linearities
4 Symbols
Symbol Description Unit
C Response flow coefficient (K or C ) Various
R v v
(see IEC 60534-1)
Δs Input step size % of input range
Reference input step size of 2 % % of input range
Δs02
Sample interval s
Δt
s
Δt Step change time s
sc
Δt Wait time s
W
Change of closure member position % rated travel
ΔX
ΔZ Process variable change % of process output
ΔZ Process variable change at 2 % input change % of process output
f Sampling rate 1/s
F Friction force N
R
G
R Gain ratio 1
G Valve travel gain 1
X
G Response gain 1
Z
G Response gain at 2 % step input 1
z02
n
down Number of steps (falling signal) in a response time test sequence 1
n Number of steps (rising signal) in a response time test sequence 1
up
h Relative travel %
τ Time constant s
60534-9 © IEC:2007 – 11 –
Symbol Description Unit
T Friction torque Nm
R
t Step response time s
t
86B Base response time s
t Step response time (increasing signal) s
t Step response time (decreasing signal) s
t Dead time s
d
5 General test procedures
5.1 Test valve conditions
The test valve shall be set to its desired test configuration. This includes configuring the valve
assembly with the desired packing type and condition, the positioner if applicable, and the
actuator configuration. The positioner configuration shall include any applicable adjustments
or parameters (at digital positioners). In some cases, preliminary tests may be performed
such as testing to assure there is no excessive overshoot. (Excessive overshoot is not
defined here and the amount allowed may vary according to the application but shall be
reported.) All applicable characteristics of the valve configuration that would affect test
results shall be reported (see 7.1)
5.2 Test system
Testing to determine the response of a control valve requires a signal generator or source and
instruments to measure the input signal, the position of the closure member and, for
laboratory testing or in-process testing, the desired response variable. The response variable
could be derived from other variables that may need to be measured as well.
The tests can be performed manually with appropriate instrumentation but computers are
recommended for all, or at least part, of the testing and analyses.
When measuring response time, data shall be collected fast enough to give good time
resolution using the requirements for the sampling interval, Δt , given in equation (1).
s
Measurement of static behaviour (dead band, gain, and resolution) generally does not depend
on sample interval and can be performed using existing field instrumentation, with the sample
interval reported.
For a control valve with a pneumatic input signal, the input signal shall be measured as close
as possible to the device input port to avoid input distortion caused by the piping. The total
time for the complete input signal step change, Δt , shall meet the requirements given in
sc
equation (2).
The valve position should be measured as close as possible to the closure member or at least
at a location that closely approximates the closure member position within the resolution limits
given in 5.3. Care should be taken to avoid measurement errors due to excessive elastic
deformation, clearances, linkages, etc. In all cases, the location of measurement points shall
be reported.
5.3 Measuring instruments
The measurement of each output variable, which includes the combined effects of
transducers, any signal conditioning equipment, and recording equipment shall meet the
following minimum requirements.
t
Δt ≤ or 0,5 s, whichever is less (1)
s
– 12 – 60534-9 © IEC:2007
t
Δt ≤ (2)
sc
t
Time constant τ ≤
Instrumentation used to measure the static parameters dead band, gain, and resolution need
not meet these requirements but time constants, Δt and Δt , shall be reported.
s sc
NOTE 1 Since t is dependent on the step size, measuring equipment with a shorter time constant, τ, may be
required on smaller step sizes.
t
NOTE 2 For in-process tests, the flow-meter time constant should not be τ , unless it is used to measure
≤
t .
If installed in-process instrumentation used to measure t does not meet these requirements, an external position
transducer and recording equipment which meet the above requirements are recommended.
valve resolution ⎡ valve resolution ⎤
⎛ ⎞ ⎛ ⎞
Instrument resolution ≤⎜ ⎟ , preferably ≤⎜ ⎟
⎢ ⎥
3 10
⎝ ⎠ ⎝ ⎠
⎣ ⎦
Inaccuracy ≤5 % of full-scale value, preferably ≤2 % of full-scale value.
NOTE 3 The full-scale value is the range of the measured variable known or estimated as the control valve goes
from 0 % to 100 % open.
5.4 Process variable
For laboratory and in-process dead-band and resolution testing, a process variable shall be
measured, if possible, in addition to the input signal and the position. Reference [6] provides
guidance for choosing the best process variable out of those that may be available at a
specific plant or laboratory.
The response flow coefficient, C , shown below, is a simplified flow coefficient recommended
R
for use as the process variable, if measurement of the variables necessary to calculate it is
possible. It is used here because an accurate determination of C is outside the scope of this
standard and may not be feasible in many plant and in some laboratory environments.
Measurements of dead band and resolution using C would equal those using C since
R
changes would be equal within the typical change of input signal. This assumes the flow
through the control valve is fully turbulent and not choked. This response flow coefficient is
calculated according to equations (3) or (4).
For incompressible flow
Q ρ ρ
1 0
C = (3)
R
N Δp
where
Q is the liquid flow rate;
ρ /ρ is the relative density (ρ /ρ = 1,0 for water at 15 °C);
1 o 1 o
Δp is the pressure drop across the valve;
N = 1, if C is expressed as K in m³/h, Q in m³/h and ΔP in bar;
1 R v
N = 0,865, if C is expressed as C in gpm, Q in m³/h and ΔP in bar;
1 R v
60534-9 © IEC:2007 – 13 –
Or, for compressible fluid flow,
W
C = (4)
R
N Y x p ρ
6 1 1
where
W is the mass flow rate;
p is the upstream absolute pressure in bar;
Δp
x =
x is the pressure drop ratio where Δp is the pressure drop;
p
x
Υ = 1− , where Fγ X can be assumed to be 0,7;
T
3F x
γ T
N = 31,6, if C is expressed as K in m³/h, W in kg/h and ΔP in bar;
6 R v
N = 27,3, if C is expressed as C in gpm, Q in kg/h and ΔP in bar
6 R v
NOTE If the flow through the control valve is not fully turbulent, or choked, such as may occur during “in-process
testing”, the actual C could be calculated using the normal flow equations for control valve sizing (IEC 60534-2-1).
To calculate the percentage change of the process variable when using the response-flow
coefficient, defined by equations (3) or (4), the maximum value of C (at 100 % valve
R
opening) shall be measured, estimated, or determined from manufacturer-supplied data. The
value of C at 100 % valve opening used shall be stated in the test results.
R
The measured process variable will often fluctuate significantly during the course of the
testing because of normal fluctuations due to disturbances, etc., in the process itself or
because of electrical noise in a plant environment or because of measurement noise. Curve
fitting or averaging routines can therefore be applied to the data around key points such as
the point where t occurs and where the total magnitude of the step change is measured. If
the tests are performed manually, this may have to be done visually from a plot. In all cases,
the raw data shall be plotted and if curve-fitting procedures are applied, the curve-fit data
should be plotted along with the raw data. This could be used later or by others to verify
calculations as required.
5.5 Nominal test position
The tests shall typically be performed at 50 % valve opening and at other positions that may
be specified in lieu of, or in addition to, this position. Testing at additional, or other, positions
may be desirable for valve types known to have anomalies at openings other than 50 %. In-
process testing may require testing only at the current operating position plus and minus
allowed step sizes. All nominal positions at which tests are performed shall be recorded.
6 Examples of step response
Figure 2 and Figure 3 show examples of responses due to input step changes. The response
shown in Figure 2 has no overshoot while the one in Figure 3 does. In these figures, there is
some measurement noise superimposed on the signal. The input signal is shown along with
the response which could be the valve position or a process variable.

– 14 – 60534-9 © IEC:2007
51,2
Δt
w
Δt
sc
51,0
Input signal
50,8
Response
Δs
50,6
ΔZ
0,865ΔZ
50,4
50,2
50,0
t
49,8
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
Time
IEC  1631/07
Figure 2 – Typical step change and response without overshoot
When the valve input signal suddenly changes, the valve begins to respond (if the input signal
change is large enough) after some delay or dead time, t . The response then begins moving
d
toward its final value like that shown, often exponentially. The signal is held constant after the
step for a specified amount of time, Δt , to allow the response to reach its final new steady-
w
state value. The response time, t , is defined as the time it takes for the response to reach
86,5 % of its final value from the initiation of the step.
Percent of span
60534-9 © IEC:2007 – 15 –
51,2
51,0
50,8
Overshoot
Input signal
50,6
Response
ΔZ
50,4
50,2
50,0
49,8
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8
Time
IEC  1632/07
Figure 3 – Step response with some overshoot
7 Tests specified for each of three test environments
Detailed test procedures required for each of the three test environments are listed in the
following subclauses along with special recommendations and precautions.
7.1 Bench tests
Bench tests are usually the simplest to perform and often provide much useful information.
The results, however, can be significantly different from results from laboratory or in-process
tests because there is no flow [6]. The following requirements shall apply.
a) Valve configuration
Complete valve with packing configuration that would be specified for intended service. The
valve may or may not be pressurized, but packing should be tightened as it normally would be
for typical, or specially defined, conditions. The procedure used for tightening the packing
shall follow the manufacturer’s instructions meeting the requirements given in IEC 60534-4
and shall be documented. The positioner configuration (if applicable) shall include all relevant
adjustments or parameters.
The nominal valve position shall be set at 50 % unless otherwise specified.
Actuator assemblies can also be tested separately (not attached to the valve body assembly)
when permitted by the user and preconditioned to all applicable points. Actuator assemblies
shall also be installed in a test fixture that includes a normal control valve packing box unless
the manufacturer and the user agree to alternative procedures. The packing shall be
tightened according to the manufacturer’s specifications. The test report shall clearly identify
the actuator tested, the test fixture used, the stem friction measured or estimated as
available, the procedure used to tighten the packing, and the operating temperatures and
pressures.
Percent of span
– 16 – 60534-9 © IEC:2007
If a valve is tested in a condition other than that described above, that condition shall be
described.
b) Special considerations
Tapping or vibrating the valve under test is not allowed unless required and specified in the
test report.
With the valve under test pressure (if applicable), the cycle valve shall be opened then closed
10 times. Then the total friction shall be measured (see Annex A).
c) Measured variables
Input signal and relative travel.
d) Applicable test procedures
Baseline test (see 8.1), small-step tests (see 8.2), and response-time tests (see 8.3)
7.2 Laboratory tests
Laboratory tests are performed in a laboratory with flow. The flow shall be fully turbulent and
not choked unless otherwise specified and noted. These tests represent in-process tests more
closely than bench tests. The following requirements shall apply.
a) Valve configuration
Complete valve mounted in flow line with packing tightened as it normally would be for typical
conditions unless specified otherwise.
The nominal valve position shall be set at 50 % unless otherwise specified.
With the valve running under flow with test fluid, the cycle valve shall be opened then closed
10 times while measuring pressure drops and flows. Then total friction shall be measured
(see Annex A).
b) Special considerations
No tapping or extra vibration is permitted. However, there will be some vibration with the flow,
which may be measured, especially if it appears to influence the test results.
c) Measured variables
Input signal, relative travel and process variable
d) Applicable procedures
Baseline test (see 8.1), small-step test (see 8.2), and response-time test (see 8.3).
7.3 In-process tests
In-process tests give valve response in actual, or close-to-actual, process conditions. The
range of test conditions may be more limited than that possible in laboratory testing, however.
It may also be more difficult to get good measurements. Valve input and measurements of
some process variables can sometimes be taken direct from existing plant instrumentation if it

60534-9 © IEC:2007 – 17 –
has the required time constant, sampling rate, resolution, and accuracy. The following
requirements shall apply.
a) Valve configuration
Complete valve running at designated process conditions. Total friction shall be measured or
estimated, giving the method of estimation. Tests shall be performed at the required positions
and conditions. Sometimes, only operation close to the existing operating conditions may be
permitted.
b) Special considerations
Limitations in plant operation procedures or safety requirements may not allow the complete
test as defined here.
c) Measured variables
Input signal, relative travel, and process.
d) Applicable procedures
Baseline test (see 8.1), small-step test (see 8.2), and response-time test (see 8.3).
8 Detailed test procedures
8.1 Baseline test
The baseline test is normally conducted first but is an optional test. It is used to evaluate
measurement noise, the presence of limit cycling of the valve or other similar behaviour, and
to determine the baseline response time, t . Figure 4 shows the input signal and an
86B
example of the position and the response during the test. The following steps are included in
this test.
− Set the control signal to the desired base value and allow the valve to come to its steady-
state condition. When performing in-process tests, the control signal will normally already
be at the desired setting and the controller will be put on manual.
t
− Monitor variables for 3 min using a sample interval, Δt , no longer than 0,5 s or ,
s
whichever is shorter.
− Step input up 2 % and continue monitoring variables for another 1 min or longer.
− Repeat stepping in 2 % increments up until there is movement, then step one more time to
get the full response.
− Step input down by 2 % and continue monitoring variables for 1 min.
− Repeat stepping down 2 % increments until the valve position returns to approximately its
starting position.
− Evaluate the data for evidence of limit cycling. If there is any, estimate the peak-to-peak
magnitude and period of the limit cycling.
− For the last 1 min segment in the up direction, determine the response time, t . If there
is overshoot, measure its magnitude and the elapsed time from the step initiation until
reaching the final position.
− For the last 1 min segment, after stepping down, determine the response time, t . If
there is overshoot, measure its magnitude and the elapsed time from the step initiation
until reaching the final position.

– 18 – 60534-9 © IEC:2007
− Determine the base response time t as the greater of t or t (see Figure 4).
86B 861 862
If there was any overshoot, determine the overshoot and the overshoot time from the largest
overshoot for the increasing or decreasing input signal steps.
ΔY
Input signal z
0,865ΔY
z
52 Relative travel
t
t
Process variable
0 60 120 180 240 300 360 420
Time  (s)
IEC  1633/07
Figure 4 – Example step and response during baseline test
8.2 Small-step test
The small-step test is performed to determine dead band and resolution. This test may be
omitted by agreement if the response-time test provides the required information to the
required accuracy. Figure 5 shows the signal versus time for a t
...