EN ISO 4373:2008

SLOVENSKI STANDARD
01-januar-2009
Hidrometrija - Naprave za merjenje višine gladine vode (ISO 4373:2008)
Hydrometry - Water level measuring devices (ISO 4373:2008)
Hydrometrie - Geräte zur Wasserstandsmessung (ISO 4373:2008)
Hydrométrie - Appareils de mesure du niveau de l'eau (ISO 4373:2008)
Ta slovenski standard je istoveten z: EN ISO 4373:2008
ICS:
17.120.20 Pretok v odprtih kanalih Flow in open channels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 4373
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2008
ICS 17.120.20
English Version
Hydrometry - Water level measuring devices (ISO 4373:2008)
Hydrométrie - Appareils de mesure du niveau de l'eau (ISO Hydrometrie - Geräte zur Wasserstandsmessung (ISO
4373:2008) 4373:2008)
This European Standard was approved by CEN on 4 October 2008.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4373:2008: E
worldwide for CEN national Members.

Contents Page
Foreword.3

Foreword
This document (EN ISO 4373:2008) has been prepared by Technical Committee ISO/TC 113 "Hydrometric
determinations" in collaboration with Technical Committee CEN/TC 318 “Hydrometry” the secretariat of which
is held by BSI.
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 April 2009, and conflicting national standards shall be withdrawn at the
latest by April 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 4373:2008 has been approved by CEN as a EN ISO 4373:2008 without any modification.

INTERNATIONAL ISO
STANDARD 4373
Third edition
2008-10-15
Hydrometry — Water level measuring
devices
Hydrométrie — Appareils de mesure du niveau de l'eau

Reference number
ISO 4373:2008(E)
©
ISO 2008
ISO 4373:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 4373:2008(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Instrument specification . 1
4.1 Performance classifications . 1
4.2 General. 1
4.3 Maximum rate of change. 2
4.4 Environment . 2
4.5 Timing . 3
5 Recording . 3
5.1 Chart recorders . 3
5.2 Data loggers . 3
6 Enclosure. 3
7 Installation . 3
8 Estimation of measurement uncertainty . 4
8.1 General. 4
8.2 Type-A estimation. 4
8.3 Type-B estimation. 4
8.4 Level measurement datum . 4
8.5 Combining primary measurement uncertainties. 4
Annex A (informative) Types of water level measuring devices . 5
A.1 Reference gauges. 5
A.2 Peak level gauges. 9
A.3 Mechanical float and counterweight gauges . 10
A.4 Air reaction gauges . 11
A.5 Electrical pressure transducers . 14
A.6 Echo-location, acoustic instruments. 15
A.7 Echo-location, radar instruments . 16
A.8 Systems using electrical properties . 17
A.9 Recording devices. 18
Bibliography . 20

ISO 4373:2008(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 4373 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5, Instruments,
equipment and data management.
This third edition cancels and replaces the second edition (ISO 4373:1995), which has been technically
revised.
iv © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 4373:2008(E)

Hydrometry — Water level measuring devices
1 Scope
This International Standard specifies the functional requirements of instrumentation for measuring the level of
water surface (stage), primarily for the purpose of determining flow rates. This International Standard is
supplemented by an annex providing guidance on the types of water level measurement devices currently
available and the measurement uncertainty associated with them (see Annex A).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60079-10, Electrical apparatus for explosive gas atmospheres — Part 10: Classification of hazardous
areas
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 772 apply.
4 Instrument specification
4.1 Performance classifications
The parameters of performance of a water level measuring device shall be described by the classification
categories of uncertainty, temperature range and relative humidity so that the overall performance of the
equipment may be summarized in three digits.
4.2 General
Water level measuring devices shall be classified in accordance with the performance classes given in
Table 1 that account for the resolution to be achieved and the limits of uncertainty required over specified
ranges.
It should be made clear whether these levels of attainment can only be achieved by the use of special works,
for example installation within stilling wells. It is also important to remember that in the measurement of stage,
uncertainty expressed as a percentage of range gives rise to worst case uncertainty in the determination of
stage at low values of stage. This is highly significant for the measurement of low flows and should be taken
into account in the design of equipment for this purpose.
ISO 4373:2008(E)
The manufacturer has to state the physical principle of the measuring device in order to allow the user to
judge the device's suitability for the proposed environment.
Table 1 — Performance classes of water level measuring devices
Class Resolution Range Nominal uncertainty
Performance class 1 1 mm 1,0 m u ±0,1 % of range
2 mm 5,0 m
10 mm 20 m
Performance class 2 2 mm 1,0 m u ±0,3 % of range
5 mm 5,0 m
20 mm 20 m
Performance class 3 10 mm 1,0 m u ±1 % of range
50 mm 5,0 m
200 mm 20 m
4.3 Maximum rate of change
As water levels may rise and fall rapidly in some applications, in order to provide guidance on suitability, the
manufacturer shall state on the equipment specification sheet and in the instruction manual:
a) the maximum rate of change which the instrument can follow without damage;
b) the maximum rate of change which the instrument can tolerate without suffering a change in calibration;
c) the response time of the instrument.
4.4 Environment
4.4.1 General
Water level measuring devices shall operate within the ranges of temperature in 4.4.2 and the ranges of
relative humidity in 4.4.3.
4.4.2 Temperature
Water level measuring devices shall operate within the following temperature classes:
Temperature class 1: −30 °C to +55 °C;
Temperature class 2: −10 °C to +50 °C;
Temperature class 3: 0 °C to +50 °C.
4.4.3 Relative humidity
Water level measuring devices shall operate within the following relative humidity classes:
Relative humidity class 1: 5 % to 95 % including condensation;
Relative humidity class 2: 10 % to 90 % including condensation;
Relative humidity class 3: 20 % to 80 % excluding condensation.
2 © ISO 2008 – All rights reserved

ISO 4373:2008(E)
4.5 Timing
4.5.1 General
Where timing, either analogue or digital, is part of the instrument specification, the timing method used shall
be clearly stated on the instrument and in the instruction manual.
NOTE It is recognized that digital timing is inherently more accurate than analogue timing.
4.5.2 Digital
The uncertainty of digital timing devices used in water level measuring devices shall be within ±150 s at the
end of a period of 30 days, within the range of environmental conditions defined in 4.4.
4.5.3 Analogue
The uncertainty of analogue timing devices used in water level measuring devices shall be within ±15 min at
the end of a period of 30 days, within the range of environmental conditions defined in 4.4.
5 Recording
5.1 Chart recorders
Where a chart recorder is to be used as the primary source of data, the resolution and uncertainty parameters
shall take account of changes in the dimensions of the recording medium due to atmospheric variables.
NOTE Chart recorders have been superseded to a large extent by data logging devices. However, they are still used
as back-up units or to provide rapid visual assessment of flow changes on site.
5.2 Data loggers
A data logger shall be able to store at least the equivalent of four digits per reading. Where a data logger
includes the interface electronics, the resolution and uncertainty shall relate to the stored value.
6 Enclosure
The performance of the enclosure shall be stated in terms of the IP classification system in accordance with
IEC 60529. It shall be stated whether or not any parts in contact with water are suitable for contact with
potable water. It shall be stated whether or not the equipment may be used in a potentially explosive
environment in accordance with IEC 60079-10.
7 Installation
The manufacturer shall provide clear instructions for the installation of water level measuring devices.
ISO 4373:2008(E)
8 Estimation of measurement uncertainty
8.1 General
The uncertainty of a value derived from primary measurements may be due to
a) unsteadiness of the value being measured (waves on the water surface), or
b) resolution of the measurement process (the eye’s resolution of submillimetre distance).
Two methods of estimation, Type A and Type B, are described in the Guide to the expression of uncertainty in
measurement for relating the dispersion of values to the probability of “closeness” to mean value.
8.2 Type-A estimation
A Type-A estimation is determined directly from the standard deviation of a large number of measurements.
(Note that the distribution of these results need not be Gaussian.) Type-A estimations can be readily
computed from continuous measurements when the dispersion is not masked by hysteresis of the
measurement process. Of course, the dispersion must exceed by a significant margin the resolution of the
measurement process.
8.3 Type-B estimation
A Type-B estimation is assigned to a measurement process for which large numbers of measurements are not
available or to a measurement with defined limits of resolution. To define a Type-B uncertainty, the upper and
lower limits of the dispersion or the upper and lower limits of resolution are used to define the limits of a
probability diagram whose shape is selected to represent the dispersion, i.e. uniform dispersions would have a
rectangular distribution; dispersions with most measurements congregated about the mean value would have
a triangular distribution.
Allocation of probability distributions is described in Annex A.
The relationship between the uncertainty of primary measurements and the value of the uncertainty of the
result is derived from the formula defining the relationship between the value and its primary measurements.
Sensitivities are the partial derivatives of the value with respect to each primary measurement.
In the case of level, its relationship to primary measurement is generally linear. Sensitivity coefficients would
then be equal to 1.
8.4 Level measurement datum
Level measurement is not absolute measurement; it is always relative to a datum, for example a local
benchmark or the elevation of a weir crest. The uncertainty associated with the datum should be combined
with the uncertainty of the derived value.
8.5 Combining primary measurement uncertainties
To determine the uncertainty of the derived value, U, it is necessary to combine the uncertainties of all primary
measurements, u, thus,
Uulevel=+level datumu level measurement
() ( ) ( )
This illustrates the method when combining the uncertainty of a reference level datum value. Other
components of measurement uncertainty are added by inclusion of their squared value within the brackets.
4 © ISO 2008 – All rights reserved

ISO 4373:2008(E)
Annex A
(informative)
Types of water level measuring devices
A.1 Reference gauges
A.1.1 Staff and ramp gauges
A.1.1.1 Description
A staff gauge (see Figure A.1) comprises a scale marked on, or securely attached to, a suitable vertical.
Where the range of water levels exceeds the capacity of a single vertical gauge, other gauges may be
installed in the line of a cross-section normal to the direction of flow. The scales on such a series of stepped
staff gauges should overlap by not less than 15 cm.
Dimensions in millimetres
Key
A detachable plate for metre numeral, coloured red
B 10 mm divisions
Figure A.1 —Staff gauge
A ramp gauge (see Figure A.2) consists of a scale marked on, or securely attached to, a suitable inclined
surface, which conforms closely to the contour of the riverbank. Throughout its length, the ramp gauge may lie
on one continuous slope or may be a compound of two or more slopes. The ramp gauge should lie on the line
of a cross-section normal to the direction of flow.
ISO 4373:2008(E)
Figure A.2 — Ramp gauge installed in parallel sections
A.1.1.2 Materials
A staff or ramp gauge is constructed of durable material, able to cope with alternating wet and dry conditions.
It resists the accretion of both vegetable and mineral matter. The markings should be resistant to wear or
fading.
A.1.1.3 Strengths
A staff or ramp gauge is an inexpensive, simple, robust and absolute method of determining water level. It can
be utilized by relatively unskilled staff. A ramp gauge provides, in addition, the opportunity to achieve a higher
resolution.
A.1.1.4 Weaknesses
A staff gauge can only be used for spot measurements. It is difficult to obtain readings in the field with a true
resolution higher than ±5 mm. Most staff gauge locations are such that the gauges require regular cleaning.
Ramp gauges amplify surges and ripples. Whilst a stilling box may reduce this, it may also introduce a bias
due to flow across the gauge.
A.1.1.5 Uncertainty
A triangular distribution applies to the uncertainty, u, associated with reading a staff or ramp gauge, x, so that
xx−
1()
max min
ux = (A.1)
()
mean
16 2
where
x is the discernible upper limit;
max
x is the discernible lower limit.
min
EXAMPLE If, from inspection, the discernible upper limit is 0,150 and the discernible lower limit is 0,145, then the
best estimate is 0,147 5 with an uncertainty of 0,001.
A.1.2 Wire or tape weight gauge
A.1.2.1 Description
A wire or tape weight gauge consists of a weight that is manually lowered
...