Measurement of liquid flow in closed conduits - Method by collection of the liquid in a volumetric tank (ISO 8316:1987)

The specified measuring methods are built upon the determination of the volume of liquid collected in a volumetric tank in a known time interval. Deals in particular with the measuring apparatus, the procedure, the method for calculating the flow-rate and the assessment of uncertainties associated with the measurements.

Durchflußmessung von Flüssigkeiten in geschlossenen Leitungen - Verfahren der Volumenbestimmung mit einem Meßbehälter (ISO 8316:1987)

Diese Internationale Norm legt Verfahren zur Durchflußmessung von Flüssigkeiten in geschlossenen Leitungen fest, bei dem der Volumendurchfluß durch das Messen der Flüssigkeit in einem Volumenmeßbehälter innerhalb eines bekannten Zeitraumes bestimmt wird. Sie behandelt die Meßeinrichtung, die Durchführung, das Verfahren der Berechnung des Durchflusses und die Meßunsicherheit dieser Messungen.

Mesure de débit des liquides dans les conduites fermées - Méthode par jaugeage d'un réservoir volumétrique (ISO 8316:1987)

La présente Norme internationale spécifie la méthode de mesurage d'un débit de liquide en conduite fermée par la détermination du volume de liquide parvenant dans une capacité jaugée au cours d'un certain laps de temps. Elle traite en particulier de l'appareillage de mesure, du mode opératoire, du mode de calcul du débit et de la détermination des incertitudes sur les résultats de mesure. Telle qu'elle est décrite, la méthode peut être appliquée à tout liquide, à condition
a) que sa pression de vapeur saturante soit suffisamment faible pour que la perte de liquide par évaporation dans la capacité jaugée n'affecte pas la précision de mesure recherchée;
b) que sa viscosité soit suffisamment faible pour ne pas fausser ou retarder exagérément la mesure du niveau dans la capacité jaugée;
c) qu'il ne soit ni agressif, ni toxique.
Il n'y a pas de limite de principe à l'emploi de la présente
  méthode, mais pour des raisons pratiques, celle-ci n'est générale
  II n’y a pas de limite de principe à l’emploi de la présente
  méthode, mais pour des raisons pratiques, celle-ci n’est généralement
  utilisée que pour des débits inférieurs à 1,5 m3/s
  environ et dans des installations fixes de laboratoire. II existe cependant
  une variante de cette méthode qui utilise comme réservoir jaugé
  un bassin de retenue, naturel ou artificiel, mais cette application ne fait
  pas l’objet de la présente Norme internationale.
Du fait de la grande précision qu’elle peut atteindre, cette méthode
  est souvent utilisée comme méthode primaire pour étalonner
  d’autres méthodes ou appareils de mesure du débit-volume
  ou du débit-masse, sous réserve pour ce dernier que la masse volumique
  du liquide soit connue avec précision. Si l’installation de mesure
  par jaugeage volumétrique est utilisée pour les besoins de la
  métrologie légale, elle doit être agréée par
  les services métrologiques nationaux. De telles installations sont alors
  soumises à des inspections périodiques, à intervalles fixes.
  En l’absence de service métrologique national, une certification
  des mesures physiques do! base (longueurs, temps et températures) et
  une analyse des erreurs selon les prescriptions de la présente Norme
  internationale et de I’ISO 5168 peuvent tenir lieu d’agrément
  au regard de la métrologie légale. L’annexe A fait partie
  intégrante de la présente Norme internationale. Les annexes B
  à E ne sont données toutefois qu’à titre d’information.

Measurement of liquid flow in closed conduits - Method by collection of the liquid in a volumetric tank

General Information

Status
Published
Publication Date
19-Sep-1995
Current Stage
9093 - Decision to confirm - Review Enquiry
Due Date
14-Jun-2000
Completion Date
14-Jun-2000

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SLOVENSKI STANDARD
SIST EN ISO 8316:1998
01-avgust-1998

Measurement of liquid flow in closed conduits - Method by collection of the liquid

in a volumetric tank

Measurement of liquid flow in closed conduits - Method by collection of the liquid in a

volumetric tank (ISO 8316:1987)
Durchflußmessung von Flüssigkeiten in geschlossenen Leitungen - Verfahren der
Volumenbestimmung mit einem Meßbehälter (ISO 8316:1987)

Mesure de débit des liquides dans les conduites fermées - Méthode par jaugeage d'un

réservoir volumétrique (ISO 8316:1987)
Ta slovenski standard je istoveten z: EN ISO 8316:1995
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
SIST EN ISO 8316:1998 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
~ ISO
INTERNATIONAL STANDARD
8316
First edition
1987-10-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXflYHAPOflHAFI OPrAHM3A~MR n0 CTAHAAPTL43A~MM
Measurement of liquid flow in closed conduits -
Method by collection of the liquid in a volumetric tank

Mesure de d&bit des liquides dans les conduites fermees - NIethode par jaugeage d’un r&ervoir

volum4 trique
Reference number
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SIST EN ISO 8316:1998
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of

national Standards bodies (ISO member bodies). The work of preparing International

Standards is normally carried out through ISO technical committees. Esch member

body interested in a subject for which a technical committee has been established has

the right to be represented on that committee. International organizations, govern-

mental and non-governmental, in liaison with ISO, also take part in the work.

Draft International Standards adopted by the technical committees are circulated to

the member bodies for approval before their acceptance as International Standards by

the ISO Council. They are approved in accordance with ISO procedures requiring at

least 75 % approval by the member bodies voting.
International Standard ISO 8316 was prepared by Technical Committee ISO/TC 30,
Measurement of fluid flow in closed conduits.

Users should note that all International Standards undergo revision from time to time

and that any reference made herein to any other International Standard implies its

latest edition, unless otherwise stated.
International Organkation for Standardkation, 1987
Printed in Switzerland
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SIST EN ISO 8316:1998
ISO8316:1987(E)
Contents
Paqe
1 Scope and field of application ..... . . ................................ ...
2 References . . ...................................
..................... 1
3 Symbols and definitions .......... . . ...................................
4 Principle ....................... . .
................................... 2
5 Apparatus ..................... . . ....... ...........................
6 Procedure. .................... . . .
................................... 7

7 Calculation of flow-rate . . . . . . . . . . . . . . . . . . . . . . . . . . . ..................

8 Calculation of the Overall uncertainty in the flow-rate
measurement....................................... ..................
Annexes
* . . . . . . . . . . . . . . . . .
A Corrections to the measurement of filling time . . . . . . . 12
B Density of pure water at Standard atmospheric pressure
......... . . . . .
of101,325kPa........................................ 16
C Example of a volumetric flow-rate installation

using the dynamic gauging method . . . . . . . . . . . . . . . . . . . . . . ......... . . . . . 16

D Example of a volumetric flow-rate installation
......... . . . . . 17
using the standing statt and finish method . . . . . . . . . . . . . . . .

E Student’s t-distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .
Ill
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SIST EN ISO 8316:1998
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SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)
INTERNATIONAL STANDARD
Measurement of liquid flow in closed conduits -
Method by collection of the liquid in a volumetric tank

1 Scope and field of application If the installation for flow-rate measurement by the volumetric

method is used for purposes of legal metrology, it shall be cer-
This International Standard specifies methods for the measure-
tified and registered by the national metrology Service. Such in-

ment of liquid flow in closed conduits by determining the stallations are then subject to periodic inspection at stated in-

volume of liquid collected in a volumetric tank in a known time
tervals. If a national metrology Service does not exist, a certified

interval. lt deals in particular with the measuring apparatus, record of the basic measurement Standards (length, time and

the method for calculating the flow-rate
the procedure, temperature), and error analysis in accordance with this
and the assessment of uncertainties associated with the
International Standard and ISO 5168, shall also constitute
measurements.
certification for legal metrology purposes.

The method described may be applied to any liquid provided Annex A forms an integral part of this International Standard.

that
Annexes B to E, however, are given for information only.
a) its vapour pressure is sufficiently low to ensure that any
escape of liquid by vaporization from the volumetric tank
does not affect the required measurement accuracy;
2 References
b) its viscosity is sufficiently low so as not to alter or delay
ISO 4006, Measuremen t of fluid flow in closed conduits -
unduly the measurement of the level in the volumetric tank;
Vocabulary and s ymbols.
c) it is non-toxic and non-corrosive.
ISO 4185, Measurement of liquid flow in closed conduits -
Weighing me thod.
Theoretically, there is no limit to the application of this method,
but, for practical reasons, this method of measurement is nor-
ISO 4373, Measurement of liquid flow in open channels -
mally used for flow-rates less than approximately 1,5 m3/s and
Wa ter level measuring devices.
is used on the whole in fixed laboratory installations only.
However, there is a Variation of this method which uses a
I S 0 5168, Measuremen t of fluid flow - Estimation of uncer-
natura1 or artificial storage pond as a volumetric tank, but this
tainty of a flow-rate measurement.
application is not dealt with in this International Standard.
Owing to its high potential accuracy, this method is often used
as a primary method for calibrating other methods or devices
3 Symbols and definitions
for volume flow-rate measurement or for mass flow-rate
measurement; for the latter method or device, it is necessary to
know the density of the liquid accurately.
3.1 Symbols (see also ISO 4006)
Table 1
SI unit
Symbol Quantity Dimensions
* *
Random uncertainty, in absolute terms
- -
Random uncertainty, as a percentage
* *
Systematic uncertainty, in absolute terms
- -
Systematic uncertainty, as a percentage
MT-’ kgls
Mass flow-rate
4rn
LST-” m3/s
Volume flow-rate
t Filling time of the tank T
V L3 nb
Discharged or measured volume
2 Liquid level in the tank L
ML-3 kg/m3
Density
* The dimensions and units are those of the quantities in question.
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SIST EN ISO 8316:1998
ISO 8316 : 1987 (El
3.2 Definitions One Variation of this method uses two tanks which are suc-
cessively filled (see 6.3). A further Variation, given in annex D,
uses a valve instead of a diverter mechanism to Start and stop
For the purposes of this International Standard, the definitions
the flow into a volumetric tank.
given in ISO 4006 apply. Only terms which are used with a par-
ticular meaning or the meaning of which might be usefully
a valve ins tead of a diverter that
Care shall be taken when using
restated are defined below. The definitions of some of the
the flow-rate does not Change when t he valve is operated.
terms concerned with error analysis are given in ISO 5168.
4.1.2 Dynamit gauging method
3.2.1 static gauging: A method by which the net volume of
liquid collected is deduced from measurements of liquid levels
The principle of the flow-rate measurement method by
(i.e. gauging& made respectively before and after the liquid
volumetric dynamic gauging (see figure 2 for a schematic
has been diverted for a measured time interval into the gauging
diagram of a typical installation) is
tank, to determine the volume contained in the tank.
to let liquid collect in the tank to a predetermined initial
level (and thus volume) , at w Nhich time the timer is started;
3.2.2 dynamic gauging: A method by which the net volume
of liquid collected is deduced from gaugings made while liquid
to stop the timer when a second predetermined final
flow is being delivered into the gauging tank. (A diverter is not
level (and thus volume) is reached and then to drain the
required with this method.)
liquid collected.
The flow-rate is then derived as explained in clause 7.
3.2.3 diverter: A device which diverts the flow either to the
gauging tank or to its by-pass without changing the flow-rate
during the measurement interval.
4.1.3 Comparison of instantaneous and mean flow-rates
lt should be emphasized that only the mean value of flow-rate
3.2.4 flow stabilizer: A device inserted into the measuring
for the filling period is given by the volumetric method. Instan-
System, ensuring a stable flow-rate in the conduit being sup-
taneous values of flow-rate as obtained on another instrument
plied with liquid; for example, a constant Ievel head tank, the
or meter in the flow circuit may be compared with the mean
level of liquid in which is controlled by a weir of adequate
flow-rate only if the flow is kept stable during the measurement
length.
interval, by a flow-stabilizing device, or if the instantaneous
values are properly time-averaged during the whole filling
period.
4 Principle
4.2 Accuracy of the method
4.1 Statement of the principle
uncertainty in the volumetric
4.2.1 Overall
measu rement
4.1.1 Static gauging method
The volumetric method gives a measurement of flow-rate
The principle of the flow-rate measurement method by
which, in principle, requires only level and time measurements.

volumetric static gauging (see figure 1 for a schematic diagram After the weighing method, the static gauging method in a

of a typical installation) is
volumetric tank may be considered as one of the most accurate
of all flow-rate measuring methods, particularly if the precau-
tions given in 4.2.2 are taken. For this reason, it is often used as
- to determine the i nitial volume of liquid contained in the
a Standard or calibration method. When the installation is
tank;
carefully constructed, maintained and used, an uncertainty of
k 0,l % to + 0,2 % (with 95 % confidence limits) may be
to divert the flow into the volumetric tank, until it is
achieved.
considered to contain a sufficient quantity to attain the
desired accuracy, by Operation of a diverter which actuates
4.2.2 Requirements for accurate measurements
a timer to measure the filling time;
The volu metric method gives an accurate measurement of
to determine the final volume of liquid contained in the
flow-rate provid ed that
tank. The volume contained at the initial and at the final
times is obtained by reading the liquid levels in the tank and
a) there is no leak in the flow ci rcuit and there is no
by reference to a preliminary calibration which gives the
un measured leakage flow across the diver
ter ;
level-volume relationship.
b) the conduit is running full at the measuring section and
iquid col-
The fl ow-rate is then derived from the volume of I
there is no vapour or air-leck between the measuring sec-
lected and the filling time as explain ed in clause 7.
tion and the volumetric tank;
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SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)
f) the level measuring devices and the means for starting
c) there is no accumulation (or depletion) of liquid in a part
and stopping the timer achieve the required accuracies;
of the circuit by thermal contraction (or expansion) and
there is no accumulation (or depletion) by Change in vapour

or gas volume contained unknowingly in the flow circuit; g) the time required by the diverter (for the static gauging

method) for traversing is short with respect to the filling

care has been taken to avoid any leakage from or un- time, the timer being started and stopped while the diverter

is crossing the hydraulic centreline (this Position shall be
wanted flow into the tank, absorption of liquid by the Walls

or their coatings, deformation of the Walls etc.; checked and adjusted, if necessary, using the methods

described in annex AI;
e) the level-volume relationship in the tank has been
h) the temperature of the liquid flowing through the
established by transferring known volumes, or by calcula-
flowmeter under test is either the same as that collected in
tion from dimensional measurements of the tank, as
the volumetric tank or it is corrected accordingly.
specified in 5.5;
Constant level
head tank
Flowmeter under
calibration Flow control valve
Alk
- _
Stilling weil
* --
Volumetric tank

Figure 1 - Schematic diagram of a volumetric flow-rate installation using the static gauging method

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SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)
Timer
Compressed
air supply
Displacement
devices
Flow stabil i zer
Measuring
chamber
Volumetric tank
Leve I sei nsing
element
Storage tank
Pump
Control valve
Flowmeter

Figure 2 - Schematic diagram of a volumetric flow-rate installation using the dynamic gauging method

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SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)
an electrical or pneu matic actuator. The diverter shall in no way
Apparatus
influence the in the circuit during any
flow p hase of the
measurement procedure.
5.1 Diverter
However, for large flow-rates, which could involve excessive
The diverter is a moving device used to direct flow alternately
mechanical Stresses, a diverter with a proportionately langer
along its normal course or towards the volumetric tank. lt tan
travel time (1 to 2 s, for example) may be used provided that
be made up of a moving conduit or gutter, or by a baffle plate
the operating iaw is constant and any Variation in flow-rate
pivoting around a horizontal or vertical axis (see figure 3).
distribution as a function of diverter stroke is approximately
linear and is in any case known and tan be verified. Any

The motion of the diverter shall be sufficiently fast (less than hysteresis between the two directions of diverter travel shall

0,l s, for example) to reduce the possibility of a significant also be controlled.

error occurring in the measurement of the filling time. This is
In the design of the mechanical Parts of the diverter and its
achieved by ensuring, first, that the diverter travel across the
movement device, care shall be taken to ensure that no leakage
flow is rapid and, second, that the flow is in the form of a thin
or splashing of liquid occurs when liquid is either removed from
stream, which is produced by passing it through a nozzle slot.

Generally, this liquid stream has a length 15 to 50 times its the volumetric tank or allowed to flow from one diverter

channel to the other. This condition shall be checked frequently
width in the direction of diverter travel. The pressure drop
across the nozzle slot shall not exceed about 20 kPa to avoid during Service.
splashing, air entrainmentl) and flow across the diverter and
Alternatives to a thin flat liquid stream entering the diverter are
turbulente in the volumetric tank. The movement of the

diverter may be generated by an electrical, mechanical or acceptable provided that corrections to the diversion time, as

indicated in annex A, are applied.
electro-mechanical device, e.g. by a spring or torsion bar, or by
I nf low
- Nozzle
N ozzle
Diverter
lk-
Splitter plate -
\\’
Pivot Point
Pivot
\ /
////,
Flow to volumetric tank
Flow to storage tank
Figure 3 - Examples of diverter design

1) In certain designs of nozzle slot, however, special vents to allow air ingress to the fluid jet may be necessary to ensure stable fiow within the test

circuit.
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SIST EN ISO 8316:1998
ISO 8316 : 1987 (EI
leak-proof lining. Attention shall be paid to the construction
5.2 Time measuring apparatus
materials and protective coatings and to the dimensions so that
the bottom and Walls sf the tank are perfectly Ieak-proof and
The time of discharge into the volumetric tank is normally
rigid enough to retain their shape. lf the tank is buried in the
measured by using an accurate electronie timer, e.g. a quartz
ground, it is advisable to provide a clear space around the tank
crystal timer. The diversion period may thus be read to within
so as to avoid any risk of distortion due to the effect of soil
0,Ol s or better. The error arising from this Source may be
pressure and to make any possible Ieakage obvious. The Walls
regarded as negligible provided that the resolution of the timer
of the tank shall be smooth in Order to avoid water retention
display is sufficiently high and the equipment is checked
and to ensure complete drainage of the tank.
periodically against a national time Standard, e.g. the frequency
Signals transmitted by certain radio stations.
The tank shall be large enough to ensure that any errors in tim-
ing and in level measurements are negligible; moreover, it is
The timer shall be actuated by the motion of the diverter itself
necessary for the ratio of cylinder height to diameter to be large
through an Optical, magnetic or other suitable switch fitted on
enough to provide acceptable accuracy in determining the fill-
the diverter. The time measurement shall be started (or stop-
ing volume on the one hand and to limit the oscillations in the
ped) at the instant when the hatched areas shown in figure 4,
level of the free liquid surface on the other hand. With account
which represent the diverted flow variations with time, are
taken of the requirements of 5.1 and 5.2, the minimum Change
equal. In practice, however, it is generally accepted that this
in level shall be about 1 m and the tank filling time, at maximum
Point corresponds to the mid-travel Position of the diverter in
flow-rate, shall be at least 30 s. However, these values may be
the fluid stream. The error will generally be negligible provided
reduced provided that it is possible to verify experimentally that
that the time of passage of the diverter through the stream is
the required accuracies have been achieved.
very short in comparison with the period of diversion to the
tank.
The flow into the tank, particularly if the tank is large, shall be
provided with a guiding device for reducing the transmission of
If, however, the error in the filling time measurement arising
air into the tank and limiting the liquid oscillations.
from the Operation of the diverter and the starting and stopping
of the timer is not negligible, a correction should be made in
The tank may be drained by various means as follows:
accordance with the directions given in annex A.
- by a stop-valve at the base, the leak-proof quality of
which shall be capable of being verified, such as by a free
discharge or a transparent section of Pipe;
5.3 Volumetric tank
- by a Siphon fitted with an efficient and checkable
The tank into which the liquid flows during each measuring
Siphon break;
Stage is generally but not necessarily cylindrical in form, with

the axis vertical, made of steel or reinforced concrete with a - by a self-priming or submersible pump.

100
Operating law of diverter
Figure 4 -
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SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)
tly high that test runs may
The ra te of drainin g shall be sufficien 6 Procedure
follow each other at sho rt intervals.
6.1 Static gauging method
In Order to take account of any residual liquid likely to have
5.4 Level measuring apparatus
remained in the bottom of the tank or on the Walls, first
discharge into the tank (or leave at the end of draining after the
The liquid level may be measured by a Point or hook gauge
preceding measurement) a sufficient quantity of liquid to resch
(possibly with electrical contact), by a float gauge or by any
the operational threshold of the gauge. Record this initial level,
other device providing equivalent accuracy (for the specifica-
zo, for which there is a corresponding initial volume, Vol accor-
tions of these apparatus, see ISO 4373).
ding to the rating table, while the diverter directs the flow to the
storage tank and the flow-rate is being stabilized. After the test
For large discharges, because of the relatively large variations in
flow-rate has been achieved, operate the diverter to direct the
the liquid surface, and in Order to dampen the oscillations of the
liquid into the volumetric tank, thereby automatically starting
liquid in the tank, these devices should preferably be installed in
the timer.
a stilling weil, having either a transparent side or a gauge glass
with a fixed graduated scale. The stilling weil should be con-
After an appropriate quantity of liquid has been collected, the
nected with the tank by means of a number of tappings spaced
diverter operates in the opposite direction to return the liquid to
over the entire height. lt shall be of a constant Cross-section,
storage, which automatically Stops the timer and thus deter-
large enough to make the effect of capillarity negligible.
mines the filling time, t. When the oscillations in the tank have
subsided, record the apparent final level, zl, for which there is a
corresponding final volume, VI, according to the rating table.
Care shall be taken to eliminate errors due both to temperature

differentes between the tank and the stilling well and to incor- Then drain the tank, unless the total volume of the tank is suffi-

cient to allow several successive measurements without drain-
rect damping of oscillations by the stilling weil.
ing it in between.
5.5 Calibration of the volumetric tank, 6.2 Dynamit gauging method
If the incoming flow is such that no significant disturbance of
The greatest care shall be taken in establishing the capacity of
the liquid level occurs, it is possible to proceed as follows.
the tank and this shall be regularly checked. lt is important that
Close the tank valve and Start the timer when the liquid level
the dimensions and shape of the tank do not Change, as
reaches a predetermined value, zo, corresponding to an initial
specified in 5.3.
volume, Vol according to the rating table. Stop the timer
(preferably automatically) when the level reaches a second
The most accurate method is, in the case of small movable
predetermined value, zl, corresponding to a final volume, V,,
tanks, to weigh the liquid contained in the tank, or, for large
according to the rating table. Record the filling time, t, after
fixed tanks, to add together the successive volumes introduced
which the tank may be drained.
by means of a graduated delivery vessel. This may take the
form of a calibrated pipe so that the volume contained in it may
Depending on the type of level measuring device used, this pro-
be determined accurately by the filling level, or its contents may
cedure may be carried out either by positioning the gauge (or
be weighed.
level Sensors) successively at levels zo and z1 or by recording
continuously the motion of the gauge.
The volume-level relationship may also be determined by
measuring accurately the geometric dimensions of the tank. In
6.3 Twin tanks method
this case, it is necessary to take a large number of measure-
ments to take account of any irregularities in the shape.
This method tan reduce the error due to the time required to
switch the flow and it enables the discharge to be measured
If variations in operating temperature are sufficient to introduce
over a long time period. Two similar tanks, having approx-
significant errors, then calibrations should be carried out at
imately the same capacity, may be used, measurements being
several temperatures over the operating range.
made on the one tank while the other is being filled. The re-
duced timing error means that the total error depends mainly
lt is necessary to take into account any liquid that sticks to the
on the accuracy of measuring the volumes.
Walls of the graduated delivery vessel when empty. The volume
of this residual liquid varies according to the draining time and,
The two tanks are usually connected at the top by a sharp angle
to a lesser extent, the temperature, owing to viscosity and sur-
Splitter weir. Check valves or quick-acting valves are located at
face tension effects. lt is essential to wait for a sufficient length
the bottom of each tank. A movable tipping channel diverts the
of time, usually approximately 30 s, until as much liquid as
liquid into one or other of these tanks (see figure 5).
possible has drained down the Walls of the tank.
Measurements are made in the following manner. At the Start
Whatever the method used, a rating curve or preferably a rating
of the run, operate the switching device to divert the liquid
table should be established which Shows the volume against
towards one of the empty tanks whose shut-off valve is closed.
liquid level at intervals sufficiently close together that any linear
Proceed with the filling until the liquid overflows into the
interpolation will not introduce a significant error.
second tank and the flow is then switched to the second tank.
---------------------- Page: 17 ----------------------
SIST EN ISO 8316:1998
ISO 8316 : 1987 (EI
/Baff Ie
Tank Tank
Drain (quick-acting valve)
Twin tanks method
Figure 5 -

While filling the latter, let the liquid level of the first tank tank filled up to the levels z1 and z. respectively, these volumes

become stable and then empty it rapidly (the stabilizing time of being obtained from the rating tables of the tank applicable at

the liquid level may be shortened by reducing the cross-
the test temperature.
sectional areas at the tops of the tanks). At the end of the run,
before the filling tank is full, divert the flow towards the empty
The mean volume flow-rate, qv, during the filling time is thus
tank. The total volume discharged is thus equal to the product
of the number of total fillings and the volume of the tanks, plus
b - Vo
the volume of liquid in the partially filled tank at the end of the 4v = ~
run.
where t is the filling time which should be corrected in accor-
6.4 Common provisions
dance with annex A to take account of any timing error.
lt is recommended that at least two successive measurements
be carried out for each of a series of flow-rate measurements
7.2 Calculation of mass flow-rate
if a subsequent analysis of random errors is to be carried out.
The mean mass flow-rate during the filling time may be derived
The various quantities to be measured may be noted manually
from the volume flow-rate, calculated as stated in 7.1, and from
by an Operator or transmitted by an automatic data acquisition
the density of the liquid at the temperature in the volumetric
System to be recorded in numerical form on a Printer or to be
tank, this density being obtained from Standard tables?
fed directly into a Computer.
NOTE - For unusual liquids or when the best possible accuracy is
required, the density should be measured directly.
7 Calculation of flow-rate
The mean mass flow-rate, q,,,, is thus equal to
7.1 Calculation of volume flow-rate
@( 1/, - &))
The volume discharged during the filling time is equal to the dif-
4m =
eqv = ---
ference in the volumes VI and VO contained in the volumetric

1) A table of water densities for the range of ambient temperatures is given in annex B.

---------------------- Page: 18 ----------------------
SIST EN ISO 8316:1998
ISO 8316 : 1987 (E)

8 Calculation of the Overall uncertainty in the lt is important that the resolution of the timing device be ade-

quate. Instruments with a digital display will give a reading
flow-rate measurement
which is in error by up to one last-order digit, the sign of the
error depending on whether the digit is advanced at the end or
The calculation of the uncertainty in the flow-rate measurement
beginning of the corresponding time interval. In Order to render
shall be carried out in accordance with ISO 5168. For con-
this effect negligible, the resolution of any timing device used
venience, the m
...

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