ISO 6358-2:2019/FDAmd 1

FINAL DRAFT
Amendment
ISO 6358-2:2019/
FDAM 1
ISO/TC 131/SC 5
Pneumatic fluid power —
Secretariat: AFNOR
Determination of flow-rate
Voting begins on:
characteristics of components using
2026-01-26
compressible fluids —
Voting terminates on:
2026-03-23
Part 2:
Alternative test methods
AMENDMENT 1: Evaluation of
measurement uncertainty
Transmissions pneumatiques — Détermination des
caractéristiques de débit des composants traversés par un fluide
compressible —
Partie 2: Méthodes d'essai alternatives
AMENDEMENT 1: Évaluation de l'incertitude de mesure
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Reference number
ISO 6358-2:2019/FDAM 1:2026(en) © ISO 2026

FINAL DRAFT
ISO 6358-2:2019/FDAM 1:2026(en)
Amendment
ISO 6358-2:2019/
FDAM 1
ISO/TC 131/SC 5
Pneumatic fluid power —
Secretariat: AFNOR
Determination of flow-rate
Voting begins on:
characteristics of components using
compressible fluids —
Voting terminates on:
Part 2:
Alternative test methods
AMENDMENT 1: Evaluation of
measurement uncertainty
Transmissions pneumatiques — Détermination des
caractéristiques de débit des composants traversés par un fluide
compressible —
Partie 2: Méthodes d'essai alternatives
AMENDEMENT 1: Évaluation de l'incertitude de mesure
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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Published in Switzerland Reference number
ISO 6358-2:2019/FDAM 1:2026(en) © ISO 2026

ii
ISO 6358-2:2019/FDAM 1:2026(en)
Foreword
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This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 5,
Control products and components.
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iii
ISO 6358-2:2019/FDAM 1:2026(en)
Pneumatic fluid power — Determination of flow-rate
characteristics of components using compressible fluids —
Part 2:
Alternative test methods
AMENDMENT 1: Evaluation of measurement uncertainty

Annex A
Replace Annex A with the following to update the method of calculation of the measurement uncertainty of
the sonic conductance.
ISO 6358-2:2019/FDAM 1:2026(en)
Annex A
(informative)
Evaluation of measurement uncertainty
A.1 General
The ISO Guide on uncertainty in measurement [ISO/IEC Guide 98-3:2008 (GUM:1995)] provides the
current international consensus method for estimating measurement uncertainty. There are different
ways to estimate measurement uncertainty; the strict mathematical way is described most extensively in
ISO/IEC Guide 98-3, but the other pragmatic methods that are compliant with ISO/IEC Guide 98-3 can be
used. The main rule appears as follows: effort and expenditure for determination of uncertainties are clearly
guided by the principle “fit for purpose”, i.e. effort and expenditure for determination of uncertainties are up
to standards to meet the requirements set by the user of the measurement data, but it is not over qualitative
in light of the application. This annex uses this principle.
ISO/IEC Guide 98-3 groups uncertainty components into Type A and Type B according to the way data were
obtained. Type A components are calculated by statistical means from repeated measurements, while Type
B components are taken from other sources, e.g. reference material, calibration certificates, accepted values
of constants, resolution, instability, environmental conditions.
In practice, however, a combined approach is most of the time considered as the most suitable. This combined
approach will apply very often, as each uncertainty cannot be estimated individually. In this case, Type B will
be used with reference materials and quality control materials to avoid any systematic measuring error. The
single uncertainties are combined applying the law of propagation of uncertainty. The Type A uncertainty
estimate is an estimate derived from the statistical analysis of experimental data. This type of uncertainty
evaluation is preferred when the value of a measurand will be the average of several test results or is in
relation with non-independent variables.
A.2 Measurement uncertainties
The measurement uncertainty of the instruments used to determine the flow characteristic parameters do
not exceed the values given in Table 7.
A.3 Evaluation of measurement uncertainty of the sonic conductance, C
A.3.1 Calculation of the sonic conductance, C
This document specifies that the most important flow-rate characteristic parameter of a pneumatic
component is the sonic conductance, C, which is determined in three steps according to 6.3.1.
— Calculation to smooth the raw pressure data in the tank from a 21-point moving average using Formula (4),
in 6.3.1.1:
1 ij10

pj  pi (A.1)
 

ij10
where
pi is the pressure in the tank, in Pa, (i = 1, 2, ···, n);


pj is the pressure in the tank after moving average processing, in Pa, (j = 11, 12, ···, n-10);

n is the number of pressure data points measured during the discharge test or the charge test.

ISO 6358-2:2019/FDAM 1:2026(en)
— Calculation of the conductance, Cj , for each value of j over the measured region for the discharge

e
test, or for the charge test:
— for discharge test:
Vp  jp10   j10 
 
 
Cj  (A.2)

e
20pj Rt  TT

10 03
— for charge test:
Vp  jp10   j10 
 
 33 
Cj  (A.3)

e
20pj Rt  TT

10 03
where j is each data points from 21 to n−20 .
— Calculation of the sonic conductance, C ,in the choked flow region by averaging the saturated region of
the conductance C as shown in Figures 7 or 8, according to Formula (A.4):
e
im
C  Ci (A.4)


e
i1
m
where i is each data points from 1 to m in the choked flow region.
A.3.2 Combined standard uncertainty
Combined standard uncertainty is calculated according to Formulae (A.2) and (A.3):
2 2 2
 
 C   C   C  C
2 2 2
ee e e
 

...