EN ISO 23581:2024

SLOVENSKI STANDARD
01-julij-2024
Naftni in sorodni proizvodi - Določanje kinematične viskoznosti - Metoda z
viskozimetrom po Stabingerju (ISO 23581:2024)
Petroleum products and related products - Determination of kinematic viscosity - Method
by Stabinger type viscometer (ISO 23581:2024)
Mineralölerzeugnisse und verwandte Produkte - Bestimmung der dynamischen
Viskosität und Berechnung der kinematischen Viskosität - Verfahren mit dem
Viskosimeter nach dem Stabinger-Prinzip (ISO 23581:2024)
Produits pétroliers et produits connexes - Détermination de la viscosité cinématique -
Méthode par viscosimètre type Stabinger (ISO 23581:2024)
Ta slovenski standard je istoveten z: EN ISO 23581:2024
ICS:
75.080 Naftni proizvodi na splošno Petroleum products in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 23581
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2024
EUROPÄISCHE NORM
ICS 75.080
English Version
Petroleum products and related products - Determination
of kinematic viscosity - Method by Stabinger type
viscometer (ISO 23581:2024)
Produits pétroliers et produits connexes - Mineralölerzeugnisse und verwandte Produkte -
Détermination de la viscosité cinématique - Méthode Bestimmung der dynamischen Viskosität und
par viscosimètre type Stabinger (ISO 23581:2024) Berechnung der kinematischen Viskosität - Verfahren
mit dem Viskosimeter nach dem Stabinger-Prinzip (ISO
23581:2024)
This European Standard was approved by CEN on 12 May 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 23581:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 23581:2024) has been prepared by Technical Committee ISO/TC 28 "Petroleum
and related products, fuels and lubricants from natural or synthetic sources" in collaboration with
Technical Committee CEN/TC 19 “Gaseous and liquid fuels, lubricants and related products of
petroleum, synthetic and biological origin” the secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by November 2024, and conflicting national standards
shall be withdrawn at the latest by November 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 23581:2024 has been approved by CEN as EN ISO 23581:2024 without any modification.

International
Standard
ISO 23581
Second edition
Petroleum products and related
2024-05
products — Determination of
kinematic viscosity — Method by
Stabinger type viscometer
Produits pétroliers et produits connexes - Détermination de
la viscosité cinématique - Méthode avec un viscosimètre type
Stabinger
Reference number
ISO 23581:2024(en) © ISO 2024
ISO 23581:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 23581:2024(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents and materials . 2
6 Apparatus . 3
7 Sampling and sample handling . 5
7.1 Sampling .5
7.2 Sample handling .5
7.2.1 General sample handling . .5
7.2.2 Conditioning of residual fuel oils .5
8 Calibration and verification . . 6
8.1 General .6
8.2 Instrument .6
9 Apparatus preparation . 7
10 Procedure . 7
10.1 Measuring procedure .7
10.2 Manual filling and cleaning using syringes .8
10.3 Manual filling using sample displacement .8
10.4 Automatic filling and cleaning by a sample changer/sample handler.9
10.5 Procedure for temperature scanning . .9
11 Calculation . 10
11.1 Kinematic viscosity, dynamic viscosity and density .10
11.2 Viscosity index .10
11.3 Density extrapolation .10
12 Expression of results .10
13 Precision .11
13.1 Repeatability, r.11
13.2 Reproducibility, R .11
13.3 Bias . 12
13.3.1 General . 12
13.3.2 Degree of agreement between results by test method ASTM D7042 and test
method ASTM D445 . 13
13.4 Interlaboratory study .14
14 Test report .15
Annex A (normative) Calculation of acceptable tolerance zone (band) for determination of
conformance with a reference material . 17
Bibliography .18

iii
ISO 23581:2024(en)
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. Each 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,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 28, Petroleum and related products, fuels and
lubricants from natural or synthetic sources, in collaboration with the European Committee for Standardization
(CEN) Technical Committee CEN/TC 19, Gaseous and liquid fuels, lubricants and related products of petroleum,
synthetic and biological origin, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 23581:2020), which has been technically
revised.
The main changes are as follows:
— base oils, formulated oils, jet fuels and residual fuel oils have been included in the scope;
— the apparatus description, sample handling procedures and determinability criteria have been updated
to accommodate the new scope.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 23581:2024(en)
Petroleum products and related products — Determination of
kinematic viscosity — Method by Stabinger type viscometer
WARNING — The use of this document can involve hazardous materials, operations and equipment.
This document does not purport to address all of the safety problems associated with its use. It is
the responsibility of users of this document to take appropriate measures to ensure the safety and
health of personnel prior to application of this document and fulfil other applicable requirements for
this purpose.
1 Scope
This document specifies a procedure for the determination of kinematic viscosity, ν, by calculation from
dynamic viscosity, η, and density, ρ, of both transparent and opaque liquid petroleum products and crude
oils using the Stabinger type viscometer.
The result obtained using the procedure described in this document depends on the rheological behaviour
of the sample. This document is predominantly applicable to liquids whose shear stress and shear rate
are proportional (Newtonian flow behaviour). If the viscosity changes significantly with the shear rate,
comparison with other measuring methods is not possible except at similar shear rates.
The precision has been determined only for the materials, density ranges and temperatures described in
Clause 13. The test method can be applied to a wider range of viscosity, density, temperature and materials.
It is possible that the precision and bias are applicable for materials which are not listed in Clause 13.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content 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.
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and
calculation of dynamic viscosity
ISO 3170, Petroleum liquids — Manual sampling
ISO 3171, Petroleum liquids — Automatic pipeline sampling
ISO 12185, Crude petroleum and petroleum products — Determination of density — Oscillating U-tube method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
dynamic viscosity
η
ratio of the applied shear stress to the resulting shear rate of a liquid

ISO 23581:2024(en)
3.2
kinematic viscosity
ν
ratio of the dynamic viscosity (3.1) to the density (3.3) of a liquid at the same temperature and pressure
Note 1 to entry: The kinematic viscosity is a measure of a liquid's resistance to flow under gravity.
3.3
density
ρ
mass of a substance divided by its volume at a given temperature
3.4
determinability
d
quantitative measure of the variability associated with the same operator in a given laboratory obtaining
successive determined values using the same apparatus for a series of operations leading to a single result
Note 1 to entry: Determinability is the difference between two such single determined values that would be exceeded
about 5 % of the time (one case in 20 in the long run) in the normal and correct operation of the test method.
3.5
test specimen
portion or volume of the sample obtained from the laboratory sample, which is delivered to the measuring cells
4 Principle
A test specimen is introduced into the measuring cells, at a controlled and known temperature. The
measuring cells consist of a pair of rotating concentric cylinders and an oscillating U-tube. The dynamic
viscosity is determined from the equilibrium rotational speed of the inner cylinder under the influence of
the shear stress of the test specimen and an eddy current brake in conjunction with adjustment data. The
density is determined by the oscillation frequency of the U-tube in conjunction with adjustment data. The
kinematic viscosity is calculated by dividing the dynamic viscosity by the density.
5 Reagents and materials
5.1 Cleaning solvent, able to remove the sample from the measuring cell after the measurement and
completely miscible with all constituents of the sample. Commercially available volatile petroleum spirit or
cleaner's naphtha of technical grade or better have been proven suitable as cleaning solvents.
5.2 Drying solvent, highly volatile and miscible with the cleaning solvent, shall be filtered before use
and shall be of an appropriate purity so that no residues remain in the instrument. n-Hexane, n-heptane
(recommended due to lower toxicity) or, depending on the sample, concentrated ethanol (≥96 %) are suitable.
NOTE 1 A separate drying solvent is not needed if the cleaning solvent also meets the requirements of the drying
solvent.
NOTE 2 When measuring residual fuel, asphaltic material can be removed by pre-washing with an aromatic solvent
(e.g. toluene or xylene).
5.3 Compressed air, oil-free and filtered with a dew point lower than the lowest measuring cell
temperature at which the instrument should be dried.
The pressure should be limited to 100 kPa.
It is also possible to use inert gases, for example technical nitrogen. The requirements given for compressed
air are also valid here.
ISO 23581:2024(en)
5.4 Certified reference liquids, for kinematic viscosity and density, which shall be identical to the
reference standards for kinematic viscosity and density cited in ISO 3104 and ISO 12185, respectively.
5.5 Reference thermometer and probe, for verification of the temperature calibration.
The measuring uncertainty of the reference thermometer, including the probe, shall not exceed 0,01 °C. The
resolution shall be at least 0,001 °C.
The probe used for the calibration (with an adapter if necessary) shall have a shape which fits the geometry
of the viscosity cell. The probe replaces the measuring system (tube and measuring rotor).
6 Apparatus
Usual laboratory apparatus and glassware shall be used, in particular the following.
6.1 Stabinger type viscometer.
6.1.1 Viscosity measurement
The Stabinger type viscometer is a concentric rotating viscometer, containing an outer rotor and an inner
rotor (see Figure 1). The small concentric gap between these rotors is filled with the sample. The outer
rotor is driven at constant speed, which makes the inner rotor rotate due to the sample’s viscosity. The
lightweight inner rotor is centred in the heavier sample due to the centrifugal forces. The equilibrated speed
ratio depends on the driving viscous shear force and the opposing magnetic induction force (eddy current).
The dynamic viscosity is a function of the equilibrated speed ratio and adjustment constants. The kinematic
viscosity is obtained by dividing the measured dynamic viscosity by the measured density.
Key
1 outer rotor (constant speed) 3 sample fluid
2 inner rotor (measured speed) 4 magnet
Figure 1 — Viscosity cell
6.1.2 Density measurement
The Stabinger type viscometer has an integrated density measurement based on the oscillating U-tube
principle. The sample-filled U-tube is oscillated and the instrument calculates the density from the
measured natural frequency of the filled tube using adjustment factors. The viscosity-dependent error of
this procedure is corrected using the measured viscosity value.
6.1.3 Temperature control
The Stabinger type viscometer has an integrated temperature control which keeps the viscosity and density
measurement at the same temperature.

ISO 23581:2024(en)
Using Peltier elements, a highly conductive measuring cell block which surrounds the measuring cells is set
to the target temperature with a stability of ±0,005 °C over the whole temperature range at the position of
the viscosity cell.
The measurement uncertainty of the temperature calibration (k = 2; 95 % confidence level) shall be
within ±0,03 °C over the range from 15 °C to 100 °C and within ±0,05 °C outside this range.
6.2 Syringes.
Commercially available syringes with a Luer tip of at least 5 ml in volume shall be used. The user shall
ensure full chemical compatibility of the syringe construction materials with all sample and cleaning liquids
by consulting the manufacturer’s documentation.
6.3 Flow-through or pressure adapter.
A flow-through or a pressure adapter may be used as an alternative to a syringe for introduction of the
test specimen into the measuring cells. Such adapters apply either pressure or suction to the test specimen,
therefore, care shall be taken to avoid the formation of bubbles. The user shall ensure full chemical
compatibility of the flow-through or pressure adapter construction materials with all sample and cleaning
liquids by consulting the manufacturer’s documentation.
6.4 Hot filling adapter.
A hot filling adapter maintains the sample temperature during manual introduction of the test specimen
into the measuring cells. It may be added to the Stabinger type viscometer to improve the flow of the test
specimen and prevent precipitation of wax crystals while filling and cleaning the measuring cells.
6.5 Sample changer or sample handler.
The sample changer or sample handler shall be designed to ensure and maintain the integrity of the test
specimen before and during the analysis. It shall be capable of transferring a representative aliquot of the
test specimen into the measuring cells. It shall be able to mimic the procedure for sample handling described
in 7.2. The sample changer or sample handler may have heating capability, if required.
6.6 Screen.
If a screen is used, it shall have an aperture of 75 µm to remove particles from the sample.
6.7 Magnet.
If an external magnet is used, the magnet shall be strong enough to remove ferromagnetic materials from
the sample. Magnetic stirring rods may be used.
6.8 Ultrasonic bath, unheated.
To dissipate and remove air or gas bubbles from the sample, an ultrasonic bath may be used prior to analysis.
The bath should be sized to hold the container(s) placed inside, and operate at an operating frequency
between 25 kHz and 60 kHz and a typical power output of ≤100 W. Ultrasonic baths with operating
frequencies and power outputs outside this range may be used, but it is in the responsibility of the user to
confirm via a data comparison study that the results obtained after sample preparation with and without
such baths do not show significant deviations.

ISO 23581:2024(en)
7 Sampling and sample handling
7.1 Sampling
Samples shall be taken as described in ISO 3170 or ISO 3171.
NOTE National regulations can apply.
7.2 Sample handling
7.2.1 General sample handling
For samples such as viscous lube oils that are likely to contain air or gas bubbles, an ultrasonic bath (6.8)
without the heater turned on (if so equipped) may be used for typically 1 min to dissipate the bubbles.
The test specimen shall be obtained as follows:
a) The laboratory sample shall be mixed if it is not homogeneous. The mixing should be carried out in a
closed, pressurized container or at sub-ambient temperatures to avoid the loss of volatile material.
b) The test specimen may be drawn with an appropriate syringe from a properly mixed laboratory sample.
Alternatively, the sample may be delivered from the mixing container directly to the measuring cells by
means of a flow-through or pressure adapter or sample changer or sample handler, provided that the
proper attachments and connecting tubes are used. For waxy or other samples with high pour point,
before drawing the test specimen, heat the sample to the desired temperature, which shall be high
enough to dissolve the wax crystals.
c) Samples that are prone to contain particles, such as used oils or crude oils, shall be passed through
a 75 µm screen prior to measurement. If these particles are ferromagnetic in nature, a magnet (6.7)
should be used instead.
7.2.2 Conditioning of residual fuel oils
7.2.2.1 Place the required number of disposable syringes or sample vials for batch analysis in a sample
preheat apparatus (e.g. oven, heating block or bath) held between 60 °C and 65 °C. When manually filling the
measuring cells, the Stabinger type viscometer shall be equipped with a hot filling adapter and the injection
adapters shall be pre-warmed together with the syringes.
7.2.2.2 Heat the sample in its tightly closed original container in the sample preheat apparatus, held
between 60 °C and 65 °C, for 1 h. After heating, the sample shall be sufficiently fluid for easy shaking and
stirring.
7.2.2.3 For samples of a very waxy nature or oils of high kinematic viscosity, it may be necessary to
increase the heating temperature above 60 °C to achieve proper mixing. The sample should be sufficiently
fluid after heating for ease of stirring and shaking.
7.2.2.4 Thoroughly stir the sample with a suitable rod of sufficient length to reach the bottom of the
container. Continue stirring until the sample is entirely homogeneous and there is no sludge or wax adhering
to the rod.
7.2.2.5 Recap the container tightly and shake vigorously for 1 min to complete the mixing.
7.2.2.6 Immediately thereafter, pour a sufficient amount of the sample into a glass flask to fill the
apparatus’ sampler system and loosely stopper the flask.

ISO 23581:2024(en)
7.2.2.7 Immerse the flask in a heated liquid bath or another equipment which will maintain the sample
between 100 °C and 105 °C for 30 min.
Care shall be taken at this step, as vigorous boil-over can occur when opaque liquids which contain high
levels of water are heated to high temperatures. Appropriate personal protective equipment should be worn
when handling hot materials.
7.2.2.8 Remove the flask from the bath (or other equipment), stopper tightly and shake for 1 min.
7.2.2.9 If the sample is manually introduced into the viscometer, fill the sample into a preheated syringe
by using a preheated injection adapter and measure immediately.
7.2.2.10 If a heated sample changer is used, set the vial magazine temperature to be held between 60 °C and
80 °C. Load each sample into a preheated sample vial and insert the vials into the vial magazine. Wait for
10 min to 15 min before starting the measurement.
7.2.2.11 If a heated sample handler is used, load the preheated sample vial or syringe (depending on the
model) with the first sample to be tested in the batch and place the sample vial or syringe in the sample
handler that is held between 60 °C and 80 °C. Set the temperature of the sample preheat apparatus to
between 60 °C and 80 °C and place the other containers in it.
7.2.2.12 Measurement of samples shall be completed within 1 h from completion of the step specified in
7.2.2.8.
8 Calibration and verification
8.1 General
The calibration shall be verified periodically using certified reference liquids (5.4).
Due to the measuring range of the viscosity and temperature, more than one certified reference liquid can
be required. If a reference liquid gives no reference value or if the given reference value is not sufficiently
precise for one of the two parameters (viscosity or density), (e.g. a density standard without viscosity
values), the affected parameter shall be verified with another suitable reference liquid.
Verify the calibration of the temperature measurement periodically by using a reference thermometer (5.5).
The recommended interval to verify viscosity and density calibration is once a month; for temperature
control, once a year.
8.2 Instrument
Ensure that the instrument is leak tight and the measuring cells have been cleaned and dried before
verification of the calibration is undertaken.
The verification of the calibration (calibration check measurement) should be carried out according to the
instrument manufacturer's instructions.
Calculate an acceptable verification limit in accordance with Annex A. If, despite the correct condition of
the instrument, the measured viscosity or density does not lie within the acceptable verification limit 19
out of 20 times, then the viscosity or density cell or both shall be adjusted according to the instrument
manufacturer's instructions. Perform a calibration check measurement for verification after the adjustment.
NOTE Measurement values of viscosity and density that do not correspond to the certified values within the
limits given are typically attributable to deposits in the measuring cells which are not removed by a routine flushing
procedure. Refer to 10.2.7 and the manufacturer’s instructions for more thorough cleaning methods.

ISO 23581:2024(en)
If the measured temperature does not correspond to the certified value in acceptable deviation, i.e. ±0,03 °C
over the range from 15 °C to 100 °C or ±0,05 °C outside this range, then the instrument shall be adjusted
according to the instrument manufacturer's instructions.
9 Apparatus preparation
Ensure that the measuring cells are clean and dry before filling the sample. The displayed density value of
air can be used as an indicator.
Set the desired measuring temperature. The Stabinger type viscometer automatically ensures temperature
control and temperature equilibration of the sample.
When the test temperature is below the dew point of the ambient air, a suitable air-drying apparatus shall
be connected to the air pump inlet of the instrument. When using external compressed air or inert gases,
ensure that the dew point is lower than the lowest test temperature which can be expected.
Set the determinability and stability criteria according to the values stated in Table 1.
NOTE RDV (repeat deviation viscosity), RDD (repeat deviation density), temperature stability, viscosity stability,
density stability and time settings can be summarized under the term “precision class”. Refer to the manufacturer’s
instructions for details.
Table 1 — Determinability and stability settings
RDV (Deter-
RDD Tempera- Viscos- Equili-
minability, Density Sta-
b
(Determinability, ture stabil- ity sta- Time bration
Re-
dynamic bility
c
density) ity bility time
peats
s
viscosity) 3
g/cm
g/cm °C % s
mPa·s
For all
materials at
all tempera-
tures unless 0,001 X 0,000 2 ±0,005 ±0,07 0,000 03 60 3 0
specifically
listed in this
a
table
Residual fuel
oils at 50 °C 0,003 5 X 0,000 3 ±0,010 ±0,10 0,000 05 40 3 30
a
and 100 °C
Jet fuel at
–20 °C and
–40 °C, 0,001 188 9 X 0,000 113 ±0,005 ±0,07 0,000 1 60 0 0
Scanning
a
procedure
X  final determination.
a [12]
Reprinted from ASTM D7042-21a .
b
Minimum time during which temperature, viscosity and density shall be within the specified stability criteria.
c
Maximum number of allowed repeat measurements to reach the stated determinability criteria.
10 Procedure
10.1 Measuring procedure
There are three different procedures for determination, that include filling and cleaning, which may be used;
details are given in 10.2, 10.3 and 10.4. The fourth procedure for determination, temperature scanning (see
10.5), can be applied with either filling and cleaning procedure specified in 10.2, 10.3 or 10.4.

ISO 23581:2024(en)
10.2 Manual filling and cleaning using syringes
10.2.1 Load a sufficient amount of the sample into a syringe and remove any air bubbles. Ensure that for
the first filling enough sample (at least 2 ml) is used to fill all measuring cells. If a sufficient amount of the
sample is available, it is recommended to fill until the sample is visible in the drain hose. Leave the syringe
connected to the instrument during the whole measurement procedure. Typically, a 5 ml syringe entirely
filled with sample is enough for a measurement with the viscometer.
10.2.2 Switch on the motor for a short time (5 s to 10 s) to ensure that the measuring cells are pre-wetted. In
this way any residues are also absorbed into the sample. By subsequently filling at least a further 0,25 ml of
the sample, the sample in the measuring cell is replaced by fresh sample. If there is enough sample available,
it is recommended to refill with a further 1 ml. Alternatively, the instrument may be set to perform the pre-
wetting automatically before the measurement is started.
10.2.3 Start the first determination of viscosity and density. The instrument should automatically and
continuously check the stability of the measured values until the set criteria are met (see Clause 9). Then
refill at least 0,25 ml, but preferably 1 ml of sample for the next determination. The procedure is the same as
for pre-wetting the cells (see 10.2.2).
10.2.4 If the difference between the determinations is within the set determinability limits (see Clause 9),
then the value of the last determination shall be reported as valid measured result.
10.2.5 For products not described in Clause 13, it is the responsibility of the user to establish reasonable
determinability limits by a series of tests.
10.2.6 If the syringe is empty before a valid determination can be obtained, rinse and dry the measuring
cells as described in 10.2.7 and repeat from step 10.2.1.
10.2.7 Cleaning of the measuring cells
Fill the measuring cells with at least 3 ml of the cleaning solvent (5.1). Check if the density cell is filled
completely by examining the displayed density value. Run the motor for at least 10 s. For poorly soluble
samples, extend this time and repeat the procedure. Then rinse the measuring cells with the drying solvent
(5.2) and pass through a stream of dry air or nitrogen (5.3) until the last trace of solvent is removed. Make
sure that the measuring cells are clean and dry by checking if the air density value is lower than 0,002 0 g/
cm . If the value exceeds this limit, repeat the procedure or parts of it.
If more thorough cleaning is necessary, the viscosity measuring cell can additionally be cleaned by manually
wiping and brushing the measuring rotors with an appropriate sample solvent. The density oscillator can be
cleaned with a suitable cleaning agent. Follow the instructions provided by the instrument manufacturer.
10.3 Manual filling using sample displacement
10.3.1 This procedure should only be used if the samples are mutually soluble. The user shall determine if
this procedure is applicable to the class of samples to be measured.
10.3.2 Ensure the sample volume is sufficient for complete displacement of the previous sample. Load the
sample into the syringe (typically 25 ml) and remove any air bubbles.
10.3.3 Inject at least 3 ml of the test specimen slowly into the measuring cells to prevent merging of the
new and the old sample. Leave the syringe connected to the instrument during the whole measurement
procedure.
10.3.4 Switch on the motor for a short time (5 s to 10 s) to ensure that the measuring cells are pre-wetted. In
this way, any residues are also absorbed into the sample. Fill the cell with a further 1 ml of sample to replace

ISO 23581:2024(en)
the sample in the measuring cell by fresh sample. Alternatively, the instrument may be set to perform the
pre-wetting automatically before the measurement is started.
10.3.5 Start the first determination of viscosity and density. The instrument should automatically and
continuously check the stability of the measured values until the set criteria are met (see Clause 9). Then
refill at least 2 ml of sample for the next determination. The procedure is the same as for pre-wetting the
cells (see 10.3.4).
10.3.6 If the difference between the determinations is within the set determinability limits (see Clause 9),
then the value of the last determination shall be reported as valid measured result.
10.3.7 For products not described in Clause 13, it is the responsibility of the user to establish reasonable
determinability limits by a series of tests.
10.3.8 If the syringe is empty before a valid determination can be obtained, rinse and dry the measuring
cells as described in 10.2.7 and repeat from step 10.3.2.
10.3.9 After completing the last determination in a series of measurements, clean the measuring cells using
the steps described in 10.2.7.
10.4 Automatic filling and cleaning by a sample changer/sample handler
10.4.1 Before starting the measuring procedure, set appropriate filling, cleaning and drying parameters in
line with the manufacturer’s instructions.
10.4.2 Fill sufficient sample volume into a suitable container for the sample changer or sample handler and
place the container into the magazine or holder (depending on the model). If the sample changer, the sample
handler or the sample requires it, close the containers with appropriate covers.
10.4.3 Before starting the analysis, ensure there is sufficient cleaning solvent (5.1) and drying solvent (5.2)
and enough space in the waste vessel for collection of the sample and solvent.
10.4.4 After starting the analysis, the measuring cells are automatically filled and pre-wetted and the first
determination of viscosity and density is carried out. The instrument should automatically and continuously
check the stability of the measured values until the set criteria are met (see Clause 9). Then the sample
changer or sample handler should refill the sample for the next determination.
10.4.5 If the difference between the determinations is within the set determinability limits (see Clause 9),
then the value of the last determination are given as valid measured result.
10.4.6 For products not described in Clause 13, it is the responsibility of the user to establish reasonable
determinability limits by a series of tests.
10.4.7 After the analysis, ensure the cells are clean and dried (typically fully automatically).
10.4.8 If after the automatic cleaning and drying sequence, the air density value still exceeds 0,002 0 g/
cm , perform a manual or automated cleaning of the
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