DRAFT UGANDA STANDARD  
  DUS 2160  
First Edition  
yyyy -mm-dd 
 
 
 Reference number  
DUS 2160 : 2019  
© UNBS yyyy   
  
Measurement of fluid flow — Methods of specifying flowmeter 
performance  
 DUS 2160 : 2019  
ii © UNBS yyyy  – All rights reserved  
 Compliance with this standard does not, of itself confer immunity from legal obligations  
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS yyyy  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, including photocopying and microfilm,  without prior written 
permission from UNBS.  
Requests for permission to reproduce this document should be addressed to  
The Executive Director  
Uganda National Bureau of Standards  
P.O. Box 6329  
Kampala  
Uganda  
Tel: +256 41 4 333 2 50/1/2/3  
Fax: +256 41 4 286 123  
E-mail: info@unbs.go.ug  
Web: www.unbs.go.ug  DUS nnnn -n: 2019  
© UNBS yyyy  – All rights reserved  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................... iv 
1 Scope  ................................ ................................ ................................ ................................ ................ 2 
2 Normative references  ................................ ................................ ................................ ....................... 2 
3 Terms and definitions  ................................ ................................ ................................ ...................... 2 
4 General requirements  ................................ ................................ ................................ ...................... 4 
5 Traceability  ................................ ................................ ................................ ................................ .......5 
6 Uncertainty of flow measurement  ................................ ................................ ................................ ....5 
7 Conditions of use  ................................ ................................ ................................ ............................. 5 
7.1 Measuring range  ................................ ................................ ................................ ............................... 5 
7.1 Uncertainty over measuring range  ................................ ................................ ................................ ..5 
8 Traceability group  ................................ ................................ ................................ ............................ 6 
8.1 General  ................................ ................................ ................................ ................................ ............. 6 
8.2 Traceability Group A: calibrated in an Accredited Calibra tion Laboratory  ................................ ...6 
8.3 Traceability Group B: calibrated against a traceable standard in a non -accredited 
laboratory  ................................ ................................ ................................ ................................ ......... 6 
8.4 Traceabilit y Group C: calibrated against a non -traceable standard  ................................ .............. 6 
8.5 Traceability Group D: manufactured in accordance with an International Standard  .................... 7 
8.6 Traceability Group E: type -tested  ................................ ................................ ................................ ....7 
8.7 Traceability Group F: uncalibrated  ................................ ................................ ................................ ..7 
Annex  A (normative)  Repeatability  ................................ ................................ ................................ ............. 8 
A.1 Calculation of repeatability  ................................ ................................ ................................ .............. 8 
A.2 Presentation of results  ................................ ................................ ................................ ..................... 9 
Annex  B (informative)  Illustrations of linearity  ................................ ................................ .........................  10 
Bibliography  ................................ ................................ ................................ ................................ .................. 3 
. DUS 2160 : 2019  
iv © UNBS yyyy  – All rights reserved  
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  UNBS is mandated to co -
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex Alimentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT  Agreement  of the World Trade Organisation (WTO).  
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is establishe d to deliberate on standards in a given field or area and consists of key stakeholders 
including government, academia, consumer groups, private sector and other interested parties.  
Draft Uganda Standards adopted by the Technical Committee are widely circu lated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
The committee responsible for this doc ument is Technical Committee UNBS /TC 16, Petroleum , Subcommittee 
SC 2, Drilling, Development and production equipment and materials . 
 
 
 
 
 
 DUS 2160 : 2019  
2 © UNBS yyyy – All rights reserved  
 
 Measurement of fluid flow  — Methods of specifying flowmeter 
performance  
1 Scope  
This Draft Uganda  Standard specifies  methods of describing the performance of any flowmeter, for use in 
either closed conduits or open channels. It indicates how flowmeters may be classified according to their 
traceability group, and specifies how manufacturer's statements on traceability, q uality assurance and 
conditions of use should be expressed, although further statements may be required for other conditions of 
use. 
2 Normative references  
The following referenced documents referred to in the text in such a way that some or all of their c ontent 
constitutes requirements 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.  
DUS  ISO 5168, Measurement of fluid flow — Estimation of uncertainty of a flowrate measurement . 
3 Terms and definitions   
For the purposes of this document, the following terms and definitions apply. :  
3.1 
accuracy (deprecated)  
ability of a flowmeter to give responses close to a true value  
3.2 
calibrat ion 
set of operations which establish, under specified conditions, the relationship between values of quantities 
indicated by a flowmeter and the corresponding values indicated by a standard of reference  
NOTE 1  The result of a calibration permits either th e assignment of values of measurands to the indications or the 
determination of correctio ns with respect to indications.  
NOTE 2  A calibration may also determine other metrological properties, such as the effect of influence quantities.  
NOTE 3  The result of  a calibration may be recorded in a document, sometimes called a calibration certi ficate or a 
calibration report.  
NOTE 4  The result of a calibration is often expressed as a calibration factor, or as a series of calibration factors, or as a 
calibration curv e. 
NOTE 5  Calibrati on does not include adjustment.  
3.3 
linearity  
specific, but often used, case of conformity in which the specified curve is a straight line  
NOTE  Illustrations of linearity are given in annex A.  DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  3 
 
 3.4 
deadband  
maximum interval through which a stimulus can be changed in both directions without producing a change in 
response of the flowmeter  
NOTE  Some flowmeters (turbines for example) may have a “deadband” from zero flow to some flowrate but 
thereafter have a small di scrimination threshold; ie.  they have a minimum starting flow.  
3.5 
error  
result of a measurement minu s a true value of the measurand  
NOTE 1  Since a true value cannot be determined, in practice a conventional true value is used.  
NOTE 2  When it is necessary to distinguish “error” fro m “relative error”, the former is sometimes called “absolute error 
of measurement”. This should not be confused with “absolute value of error”, which is the modulus of the error.  
3.6 
experimental standard deviations  
quantity characterizing the dispersion o f the results of a series of n measurements of the same measurand  
3.7                                                                                                                                                            
flowmeter  
flow-measuring device  which indicates the measured flowrate  
 
3.8 
hysteresis  
property of a flowmeter whereby its response to a given stimulus depends on the sequence of the preceding 
stimuli  
NOTE 1  Hysteresis may be expressed quantitatively as the maximum difference between the  value of the measurand 
when the stimulus is increasing and the value of the measurand when the stimulus is decreasing  
NOTE 2  Hysteresis may be quoted in terms of the measurand or, more usually, as a percentage given by the equation  
3.9 
K-factor  
output sig nal of a flowmeter, expressed in number of pulses per unit quantity  
NOTE  Where required, this term may carry a subscript to show the unit quantity (e.g. Km -factor for pulses per unit 
mass, Kv -factor for pulses per unit volume).  
3.10 
measuring range / worki ng range  
set of values of a measurand for which the performance of a flowmeter is intended to lie within specified limits  
3.11 
repeatability  
value below which the absolute difference between two single successive test results obtained with the same 
flowmet er on the same fluid under the same conditions (same operator, same test facility, and a short interval 
of time, but without disconnecting or dismounting the flowmeter) can be expected to lie with a probability of 95 
% 
NOTE  The method for calculating r epea tability is given in annex A. DUS 2160 : 2019  
4 © UNBS yyyy – All rights reserved  
 
 3.12 
span  
modulus of the difference between the two limits of a nominal range of a flowmeter  
EXAMPLE  Nominal range —10 l/s to +10 l/s; span 20 l/s.  
3.13 
stability  
ability of a flowmeter to maintain constant its metrological c haracteristics  
NOTE  It is usual to consider stability with respect to time. Where stability with respect to a nother quantity is 
considered, this should be stated explicitly.  
3.14 
traceability  
property of the result of a measurement or the value of a standa rd whereby it can be related to stated 
references, usually national or International Standards, through an unbroken chain of comparisons, all having 
stated uncertainties  
NOTE See clause 5  
3.15 
uncertainty of measurement  
estimate characterizing the range of  values within which the true value of the measurand lies  
NOTE Uncertainty of measurement comprises, in g eneral, many components.  Some of these components may  be  
estimated on the basis of the statistical distribution of the results of series of measure ments and can be characterized by 
experimental standard deviations. Estimates of other components can only be based on experience or other information.  
ISO and IEC maintain terminological databases for use in standardization at the following addresses:  
— ISO Online browsing platform: available at http://www.iso.org/obp  
4 General requirements  
The flowmeter specification shall enable the potential user to predict the flowmeter's performance at any 
flowrate and environmental condition within the limits of the  specification. In this context, environment includes 
not only climatic conditions but any other operating conditions or disturbances which influence performance, 
e.g. pressure of the fluid, configuration of the conduit, presence of impurities in the fluid . 
The term "flowmeter" refers to the total flowmeter package which may comprise a primary and a secondary 
device, specified by the manufacturer. The technical specifications shall give a clear description of the 
"flowmeter" to which the performance specifi cations refer, together with a reference or order number by which 
they can be related to a particular flowmeter or model of flowmeter. Compliance with relevant International 
Standards should be indicated and these may refer to the flowmeter as defined in t he technical specification 
or to individual components.  
The traceability group of the flowmeter shall always be given (see clause 8). Only terms defined in this 
national Standard shall be used in the performance specification and they shall be accompa nied by 
statements of traceability and conditions of use. If it is essential for any other new or trade terms to be 
employed, they shall be carefully defined in order to make their meaning absolutely clear.  
In the calibration of a flowmeter, it is essentia l that the terms “dry calibration” and “wet calibration” NOT be 
used. If the performance of a flowmeter is theoretically predicted, then this fact should be stated together with 
the method of prediction.  DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  5 
 
 Repeatability shall be calculated in accordance with  annex B.  
5 Traceability  
Any performance specification produced by the manufacturer shall be accompanied by a statement of how the 
specification was produced, with reference being made to relevant national or International Standards.  
A statement of the “tr aceability group” of the flowmeter (see clause 8) should include additional information on 
the test sample size, any quality assurance standard used and the traceability (e.g. to national or International 
Standards) of the measurements taken in determining  the calibration.  
6 Uncertainty of flow measurement  
Statements of the uncertainty of measurement of a flowmeter shall be accompanied by a record of the 
condition limits at which the uncertainty was derived. If the device is used outside these limits, the u ncertainty 
does not strictly apply.  
The uncertainty shall be calc ulated in accordance with DUS ISO 5168.  
EXAMPLE Uncertainty: ±1 % of measured flowrate (calc ulated in accordance with ISO  5168 using the root -sum-square 
method to give 95 % coverage)  
Calibrat ion: 50 m3/h to 1000 m3/h at 500 kPa, 20 °C on air (in accordance with  DUS 2160 :2019 , traceability group A1).  
7 Conditions of use  
7.1 Measuring range  
The range of properties over which the manufacturer has designed the flowmeter to operate such that the 
performance is within the specified limits shall be clearly stated. This shall include relevant environ - 
mental/operational conditions such as ambient temperature, fluid type and pressure, etc.  
EXAMPLE  Fluid   Natural gas  
Measuring range 20 m3/h to 1000 m3/h  
Maximum working pressure 1500 kPa  
Fluid temperature range —15 °C to +20°C  
Permissible ambient temperature —15 °C to +60°C.  
7.1 Uncertainty over measuring range  
The specification shall enable the user of a flowmeter to predict the uncertainty of the flow measurement at 
any flow within the measuring range. Use of a flowmeter outside the measuring range will undoubtedly give 
rise to an increase in uncertainty.  
The environmental/operational conditions in which the flowmeter operates may also affect the uncert ainty of 
the measurement. Therefore a table of flows, environmental conditions and consequent uncertainty values 
may be required. The table should be drawn up so that the uncertainty of measurement can be easily 
established for any combination of the flow and environmental conditions within the specified limits.  DUS 2160 : 2019  
6 © UNBS yyyy – All rights reserved  
 
 Where the uncertainty of measurement is not significantly affected by environmental conditions, a table 
relating flow to uncertainty is acceptable. In many cases only two values are required, viz.:  
a) uncertainty as a percentage of flow, for flow within a specified range, and  
b) uncertainty as a numerical value, for flows below a specified value.  
If it is necessary to express uncertainty as a percentage of full -scale flow, this full -scale flow shall be sta ted. 
8 Traceability group  
8.1 General  
In order to specify uncertainty of measurement (see clause 6), the systematic uncertainty must be estimated. 
This can only be done if either a calibration has been undertaken or a large amount of calibration data exist s 
for the type of flowmeter concerned.  
If the flowmeter performance specification specifies the uncertainty of measurement, then the traceability 
group into which the flowmeter falls shall be stated as shown.  
8.2 Traceability Group A: calibrated in an Accr edited Calibration Laboratory  
Flowmeters in this group are calibrated in an Accredited Laboratory by comparison with another flowmeter, or 
by some other means of calibration, traceable to national standards.  
NOTE  The criteria to be satisfied by an Accredit ed Laboratory are given in ISO/IEC Guide 25.  
This traceability group is subdivided thus:  
a) Traceability Group A1 : every flowmeter calibrated  
Every flowmeter in this group is calibrated as de scribed above. Each flowmeter shall be  supplied with a 
calibration c ertificate or report stating the associated uncertainty of calibration.  
b) Traceability Group A2 : a sample of flowmeters calibrated  
Flowmeters in this group are calibrated using a recognized batch testing or Quality Assurance procedure. The 
method or procedur e used shall be stated. Flowmeters tested by an ad hoc batch testing method are not 
included in this group  
8.3 Traceability Group B: calibrated against a traceable standard in a non -accredited 
laboratory  
Flowmeters in this group are calibrated in a non -accredited laboratory by comparison with another flowmeter 
which itself has a calibration traceable to national standards, or by some other means of calibration using 
equipment which has a calibration that is traceable to national standards.  
This group is sub divided into tracea bility groups B.1 and B.2 as described for traceability groups A.1 and A.2  
8.4 Traceability Group C: calibrated against a non -traceable standard  
Flowmeters in this group are calibrated as for traceability group B, but by reference to the  manufacturer’s or 
other body's standards. Traceability to national standards cannot be quoted, but a calibration certificate which 
indicates the calibration source and the associated uncertainty may be issued.  DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  7 
 
 This group is subdivided into traceability gr oups C1 and C2 as described for traceability groups A1 and A2 . 
8.5 Traceability Group D: manufactured in accordance with an International Standard  
Flowmeters in this group are not calibrated as described in traceability groups A or B, but are manufactured in 
accordance with a relevant International Standard which specifies the associated uncertainty. The 
International Standard used shall be stated (e.g. ISO 5167 -1). 
8.6 Traceability Group E: type -tested  
An early or pre -production batch of flowmeters in this  group are calibrated to establish a typical uncertainty. 
The flowmeter specification may then quote a typical uncertainty . 
8.7 Traceability Group F: uncalibrated  
Flowmeters in this group are not calibrated or built to a standard which allows the estimatio n of uncertainty. As 
such, no statement of the uncertainty of measurement can be ascribed to them  DUS 2160 : 2019  
8 © UNBS yyyy – All rights reserved  
 
 Annex  A 
(normative)  
 
Repeatability  
A.1 Calculation of repeatability  
To determine repeatability the following steps shall be followed.  
The test conditions shal l be kept constant throughout the test period. Failure to do so will result in an apparent 
increase in repeatability.  
Set the flowrate so that the maximum value of repeatability over the specified measuring range is obtained; 
this is generally just below t he maximum or just above the minimum flowrate of the specified measuring range.  
a) Obtain a set of consecutive flowrate readings preferably containing a minimum of 30 values (for less 
than 30 readings, repeatability generally increases with decreasing number of readings).  
(For integrating flowmeters, flowrate may be obtained by noting the volume or mass passed in a suitable time 
period.)  
Calculate the experimental standard deviation, s, of these values using the equation:  
112



nx x
sn
ii
 
Where; 
xi is th e i-th flowrate value, and  
x is the arithmetic mean of the n values considered.  
b) When 30 or more values have been used to estimate the standard deviation, calculate the 
repeatability, r, using the equation:  
r = 2,83 s  
c) When less than 30 values have been u sed to estimate the standard deviation, calculate the 
repeatability, r,using the equation:  
r =  t95 √2.s 
where t 95 is Student's t for 95 % coverage and can be found from statistical tables for n-1 degrees of freedom 
or from Table B.1.  
c) If it is suspected that the set of flowrate readings contains spurious values (outliers), these may only 
be removed from the set of readings if they have been identified using a standard statistical outlier test 
as detailed in ISO 5168  DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  9 
 
 A.2 Presentation of results  
Repeatability may be presented in absolute terms or as a percentage of the flowrate:  
Repeatability: r = 0.15 kg/h  
(calculated in accordance with  DUS 2160 :2160 ) 
 
OR 
Repeatability: r = 0. 06 % of reading  
(calculated in accordance with  DUS 2160 :2019 ) 
Table B.1 — Student's t values ( t95) 
Degrees of 
freedom  
(n-1)  
t95 Degrees of 
freedom  
(n-1)  
t95 
1 12,706  16 2,120  
2 4,303  17 2,110  
3 3,182  18 2,101  
4 2,776  19 2,093  
5 2,571  20 2,086  
6 2,447  21 2,080  
7 2,365  22 2,074  
8 2,306  23 2,069  
9 2,262  24 2,064  
10 2,228  25 2,060  
11 2,201  26 2,056  
12 2,179  27 2,052  
13 2,160  28 2,048  
14 2,145  29 2,045  
15 2,131  • 1,96 
 DUS 2160 : 2019  
10 © UNBS yyyy – All rights reserved  
 
 Annex  B 
(informative)  
 
Illustrations of linearity  
The forms of the graphs in Figure B .1 a), b) and c) are generalized to illustrate the three different expression 
of linearity  
 
 
a) Independent linearity   
b) Terminal -based linearity  
 
 
c) Zero-based linearity  
Key 
1 Response (% span)  
2 Stimulus (% span)  
3 Straight line  
4 Maximum deviation  
5 Actual result  
Figure B .1 — Different expressi ons of linearity  
DUS 2160 : 2019  
2 © UNBS yyyy – All rights reserved  
 
  
Figure B .2 shows a typical turbine meter characteristic as an example of how linearity might be used in 
practice. This illustrates independent linearity in which the straight line has been positioned so as to minimize 
the deviation over a  range and to give a constant K -factor  
 
Key 
1 K-factor (pulses/unit volume)  
2 Flowrate, Q (% span)  
3 Maximum deviation  
Figure B .2 — Typical application of independent linearity  
 
DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  3 
 
 Bibliography  
[1] ISO 3534 -1, Statistics — Vocabula ry and symbols — Part 1: Probability and general statistical terms.  
[2] ISO 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols.  
[3] ISO/TR 7066 -1, Assessment of uncertainty in the calibration and use of flow measurement devices — 
Part 1: Linear calibration relationships.  
[4] ISO 7066 -2, Assessment of uncertainty in the calibration and use of flow measurement devices — Part 
2: Non - linear calibration relationships.  
[5] ISO Guide 25, General requirements for the competence of calibrat ion and testing laboratories.  
[6] IEC 60770, Methods of evaluating the performance of transmitters for use in industrial -process control 
systems.  
[7] International Vocabulary of Basic and General Terms in Metrology (VIM), BIPM/IEC/ISO/OIML, 1993  
 DUS  2160 : 2019  
© UNBS yyyy – All rights reserved  5 
 
 Certific ation marking  
Products that conform to Uganda standards may be marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is governed by the Standards Act, and the Regulation s made 
thereunder. This mark can be used only by those licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relat ion to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and testing in accordance with the 
certification mark scheme of the Uganda National Bureau of Standards. UNBS marked produc ts are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 
 DUS 2160 : 2019    
 
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