ISO/TS 24155:2007

TECHNICAL ISO/TS
SPECIFICATION 24155
First edition
2007-05-01
Hydrometry — Hydrometric data
transmission systems — Specification of
system requirements
Hydrométrie — Systèmes de transmission des données
hydrométriques — Spécification des exigences des systèmes

Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Basic requirements. 1
4.1 General. 1
4.2 Objectives of use . 1
4.3 Functional requirements. 2
4.4 Geographical structures . 2
4.5 Time structures . 2
4.6 Installation conditions. 3
4.7 Considerations for designing. 3
5 Functional requirements of system. 4
5.1 General. 4
5.2 Remote telemetry stations. 4
5.3 Telemetry system. 5
5.4 Receiving center . 6
5.5 System supervision. 8
5.6 Power supply. 8
6 Operational requirement . 9
6.1 General. 9
6.2 Operating and maintenance manual. 9
6.3 Maintenance . 9
Annex A (informative) Configuration of hydrometric data transmission systems. 10
Annex B (informative) Functional block diagram of hydrometric data transmission systems. 12
Annex C (informative) Locations of remote telemetry stations. 14
Annex D (informative) Interfaces of hydrometric sensors at remote telemetry stations. 16
Annex E (informative) Data collection sequence . 17
Annex F (informative) Communication lines for data transmission . 23
Annex G (normative) Design of VHF/UHF radio link. 26
Annex H (informative) Network architecture . 28
Annex I (informative) Data repeating methods at a relay station . 32
Annex J (informative) General power supply for remote telemetry stations . 33

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
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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.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
— an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
— an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 24155 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5,
Instruments, equipment and data management.
iv © ISO 2007 – All rights reserved

Introduction
Hydrometric data transmission systems provide data for the day-to-day management of water resources and
for warning and forecasting of floods, droughts and conditions affecting water quality and public health. The
systems transmit data measured at remote telemetry stations to a receiving center for further processing.
This Technical Specification defines and standardizes the required specifications of hydrometric data
transmission systems. It does not describe the specifications of the equipment and units constituting
hydrometric data transmission systems, but does describe the functional performance that the hydrometric
data transmission systems should provide.
TECHNICAL SPECIFICATION ISO/TS 24155:2007(E)

Hydrometry — Hydrometric data transmission systems —
Specification of system requirements
1 Scope
This Technical Specification specifies the technical requirements that should be considered in designing and
operating hydrometric data transmission systems and the necessary functions of those systems.
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 772:1996, Hydrometric determinations — Vocabulary and symbols
ISO 1000:1992, SI units and recommendations for the use of their multiples and of certain other units
ISO/IEC 2382-1:1993, Information technology — Vocabulary — Part 1: Fundamental terms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 and ISO/IEC 2382-1 apply.
4 Basic requirements
4.1 General
This clause specifies the general requirements for designing a hydrometric data transmission system (HDTS).
An HDTS shall be designed to meet the basic requirements, defined hereinafter, taking into consideration
functionality, geographical structures, time structures, installation conditions, reliability, safety, maintainability
and economy. The final system specifications should be determined through the process of repetitive
discussions among technological specialists in hydrological and telecommunications fields.
The conceptual configuration of an HDTS is shown in Annex A.
4.2 Objectives of use
An HDTS shall be designed with a full understanding of the necessity and importance of hydrometric services
for appropriate water management in river basins in which this system is to be used.
4.3 Functional requirements
The functional requirements for an HDTS are classified into the following.
a) Mandatory requirements: the minimum requirements that an HDTS designer shall comply with in
designing the system. The mandatory requirements include legal requirements, for example for the site
where the system will be installed, and applicable specifications of various standards.
b) Optional requirements: the functions and methods of implementing them that an HDTS designer can
select. The optional requirements include the requirements, such as the data collection sequence and
selection of communications link as specified in Clause 5.
An HDTS should be designed to fully achieve the mandatory functional requirements, and to meet the optional
requirements in full consideration of the user's requirements and operational purposes of the system so as to
demonstrate the required system functionality.
4.4 Geographical structures
The following geographical structures shall be determined as a fundamental element of HDTS:
a) location(s) of the remote telemetry station(s);
b) location(s) of the receiving center(s); and
c) location(s) of the relay station(s), if necessary.
A remote telemetry station is located at a selected hydrometric-observation point. Therefore, remote telemetry
stations are distributed over a geographically wide area, including a river basin. Remote telemetry stations can
not always be located at optimum hydrological sites, but may be relocated from the planned sites because of
geographical problems and difficulties in data transmission.
A receiving center consists of equipment and receives data from remote telemetry stations for data processing
and display; it is located at a site where data and/or information is needed. Therefore, the receiving center will
usually be located within the facility of a user organization. In large river basins, receiving centers may be
distributed at user organizations near a hydrometric-observation point.
According to the necessity of the communication medium, a relay station shall be provided in the system.
These geographical structures should be considered not only at the time of designing but also for the future
plans.
4.5 Time structures
Usually, an HDTS is used on a real-time basis. An HDTS has two time domains: the first domain is the time
used in the natural world; the other is the time series in system operation.
The basic property of time in system operation is the time when the hydrometric observation is made at a
gauging point; the gauging intervals and the delay times are required in data presentation.
Usually, sensors at remote telemetry stations continuously measure hydrological phenomena, but the data
monitored at the receiving center are sampled in a time series. Therefore, these time characteristics and their
allowable error range should be determined for the purposes of operation. Details are shown in Annex E.
2 © ISO 2007 – All rights reserved

4.6 Installation conditions
The environmental conditions of the remote telemetry stations may be more severe than those of
telecommunication equipment installed indoors. Therefore, the following conditions should be considered:
a) temperature range and rate of change;
b) relative humidity range with no condensation;
c) wind velocity;
d) seismic resistance;
e) damage due to sea wind, dust, and/or toxic gases;
f) available power supply conditions (including impact of surge currents due to lightning);
g) equipment damage and access during flooding.
The environmental conditions of the telecommunications and information equipment to be installed at a
receiving center should also be considered for items a), b), d) and f) above. Details are shown in Annex C.
4.7 Considerations for designing
4.7.1 Reliability
An HDTS is basically designed for continuous operation for its original purpose of use, particularly in the case
of heavy rains and floods. Designers shall consider the reliability of equipment and the entire system. For the
important functions of the system, alternative means or a redundancy of the system should be provided.
For example, duplicate communication lines can be installed to connect important remote telemetry stations in
a gauging area to a receiving center. A hot-standby system can also be used for the equipment having
important functions. The hydrological data measured by important remote telemetry stations can be input to
site recorder and the storage term(s) and period should meet the user’s requirements.
4.7.2 Safety
An HDTS shall be designed as a safe (fail-safe) system that can always secure safe system operation in the
case of a malfunction of equipment, faulty operation by a user, or a system failure due to any external factor.
The fail-safe should prevent such problems from spreading over the entire system.
If the malfunction or failure in part of the system or faulty operation by a user is non-critical, the principal
functions of the system should continuously operate because of the importance of hydrometric observation.
4.7.3 Data permanence
The permanence of hydrometric data should be assured, since these are stored and used for water resources
management over a long period.
The permanence of the data shall be assured even if peripheral unit(s) are replaced. In addition, interface
specifications shall be defined for the data transmission system, format and transfer timing between the
sensors to be installed in the pre-stage of an HDTS and the information processing system to be installed in
the post-stage of an HDTS. Data received at the receiving center should be saved on reliable media.
4.7.4 Maintainability
The HDTS equipment shall be designed to have a composition that is easy to maintain and repair.
The HDTS equipment should be designed so that it is easy to check and replace parts, and so that
inspections and adjustments can be conducted (easily or) conveniently.
Software shall be designed with future maintainability taken into consideration, i.e. for future modifications
and/or future improvements. Documentation shall be provided in order to easily carry out necessary
procedures for the cases when modifications are required.
4.7.5 Operability
Each piece of the equipment shall be designed to allow for simple operation and to avoid erroneous operation,
such as authority limits and wrong operation refuse. An HDTS should be designed to enable the receiving
center to supervise the operational status of the entire system, identify problems and control necessary
operations.
4.7.6 Economy
An HDTS should be designed to have a good cost performance in terms of required functions and reliability.
The economy of the system should be evaluated considering the entire life cycle cost including the initial cost
and operational cost. An HDTS should allow future updating or expansion.
5 Functional requirements of system
5.1 General
The functional block diagram of an HDTS is shown in Annex B. The hydrometric data measured at remote
telemetry stations are encoded into a format adequate for transmission at the remote telemetry stations.
Communications are made between the remote telemetry stations and the receiving center according to a
prescribed collection sequence, transmitting the encoded data from the remote telemetry stations to the
receiving center. The receiving center decodes the received data and performs data verification and
processing to disseminate it to users as hydrometric information. An information processing system may be
provided in the stage following this system.
5.2 Remote telemetry stations
5.2.1 General
The principal function of a remote telemetry station is to measure hydrometric data using sensors. This is a
process for collecting data to be input to the system and for monitoring hydrological phenomena that change
with time.
5.2.2 Locations
The locations of remote telemetry stations shall be determined in considering the distances from the receiving
center and the topography of the sites of the stations. The possibility of using the sites, the availability of
existing communication lines and radio links, the radio propagation conditions (if radio links are chosen), the
lead-in conditions from power sources and the access roads should also be considered as important factors
for determining the locations. The items that should be investigated in selecting the sites of remote telemetry
stations from the viewpoint of data transmissions are shown in Annex C.
4 © ISO 2007 – All rights reserved

5.2.3 Data measurements
The measuring conditions for data to be acquired shall be specified based on operational purposes.
The items to be specified are
a) data type and number of measuring points,
b) range of measurement, effective digits and measuring accuracy and resolution,
c) timing of measurement,
d) input interface (typical interfaces are shown in Annex D),
e) threshold values for detecting alarms, and
f) other necessary items.
Specifications of sensors and converters are outside the scope of this Technical Specification. However, the
SI Units (International System of Units) specified in ISO 1000 shall be used for measurement.
5.2.4 Data processing
In general, the results of data measurements should be transmitted as momentary data without being
processed. However, such input data may be processed for conversion into a form that can be transmitted at
the interfaces with the sensors. For some data and under certain measuring conditions, it may be effective to
calculate the moving average; maximum and minimum values of the data measured at successive time points
at remote telemetry stations and transmit the calculated results. Judgement, marking and deletion of abnormal
data should be considered.
In recording and displaying the data measured at remote telemetry stations, the following items should be
considered and decided:
a) storage of multiple data for batch transmission;
b) protection against data loss due to system troubles;
c) securing the convenience for system maintenance.
5.3 Telemetry system
5.3.1 General
The telemetry system is the core of this HDTS, and its principal function is to transmit the data measured by
sensors at remote telemetry stations to the data processing system at the receiving center.
5.3.2 Amount and intervals of data transmission
The total amount of data and intervals of data transmission shall be provided for each data transmission link.
The necessary capacity (speed) of a communication line is determined by adding the allowable transmission
delay time to these parameters and also depends on the selected data communication channel.
5.3.3 Data collection sequence
The data collection sequence that is the fundamental function of the telemetry system shall be determined.
There are various data collection and transmission sequences, such as continuous data transmission with
time, data transmission in certain intervals, and data transmission when the data reaches certain threshold
values.
The method in which the receiving center polls the remote telemetry stations one after another and receives
the data measured at each polling time may cause time differences in measurement as restricted by the
polling order. On the other hand, the method in which remote telemetry stations measure data at regular times,
temporarily record the data and transmit the data to the receiving center asynchronously with the
measurements can minimize the delay time in measurements.
The typical methods are shown in Annex E.
5.3.4 Communication lines
There are various types of communication links and communication methods such as wired lines, radio links,
public telecommunication lines, mobile telephone network and satellite communication links. The type of
communication link and communication method shall be decided by taking into consideration the
communication environment and conditions of use including the amount of information to be transmitted,
transmission speed, reliability of transmission, operating environment, feasibility and economy, and allowable
delay time.
The communication lines available for data transmission and their technical outlines are shown in Annex F.
Communication lines should be decided through comprehensive evaluation of the following items:
a) types and functions of communication lines that are provided by the telecommunication company in the
area where HDTS is to be installed;
b) possibility (including technical and legal restrictions) of constructing dedicated communication lines for the
telemetry system other than those provided by telecommunication company;
c) required transmission speed calculated from the amount of data that the telemetry system transmits
(amount of data transmissions), sampling intervals and allowable delay time;
d) required reliability and economy of communication lines. Reliability should be considered in event of
disasters and floods, and economy should be considered for the initial cost and life cycle cost.
Usually, exclusive radio communication links are used. In such cases, the frequencies and output powers are
provided by international standards and national laws. Radio communications are usually available over
distances of several tens of kilometres. Relay stations may be needed for longer distances and/or steep
terrain. Since the quality of radio communication depends on the peripheral conditions, propagation tests
should be made after designing the communication links. A general process of designing simplex radio links is
shown in Annex G.
5.3.5 Network architecture
Networks for interconnecting remote telemetry stations and receiving centers may be configured as various
architectures depending on the locations of the remote telemetry stations and the receiving centers, the types
of communication lines to be used, presence of relay stations, etc. Appropriate network architecture shall be
determined with a full understanding of the advantages and disadvantages of various architectures, such as
economy, reliability and adaptability. Some network architectures for the telemetry system are shown in
Annex H. Data repeating methods at a relay station are shown in Annex I.
5.4 Receiving center
5.4.1 General
The principal functions of the receiving center are data collection through telemetry, data verification and
processing, and dissemination of the results to users. The process of data processing and the subsequent
process may be conducted by providing a separate information processing system. In such a case, the details
are outside the scope of this Technical Specification.
6 © ISO 2007 – All rights reserved

5.4.2 Data verification
Data shall be verified to ensure the quality of collected data.
The data verification can be classified into two processes.
⎯ The first is to detect errors in data transmission. This can be performed using parity bit, Cyclic
Redundancy Check (CRC) error detection codes or other methods. These methods may be included in
the communication control procedure.
⎯ The other process is to examine the properties of hydrometric data, which can be performed using
measured range of sensors, the upper and lower limits of data values, and limits of changing rate of
measured data. Since most of the threshold values of these items vary depending on types of systems
and/or application forms, the system should be designed to enable threshold values to be set as
parameters that can be specified individually. These data verification processes may be handled in the
data processing system.
The system will generate a report that identifies potentially spurious data.
5.4.3 Data processing
Data processing in the HDTS is the process that generates meaningful hydrological information from the data
measured at remote telemetry stations.
Users generally make their decisions based on operational information instead of basic hydrometric data.
Therefore, necessary conversion functions should be incorporated in the real-time environment if the system
is not provided with an information processing system in the post-stage of the HDTS.
Parameters for processing, such as the stage-discharge relation, may be modified afterwards. Therefore, the
real-time information that is necessary for decision-making and the information that is stored as hydrometric
records for a long time should be separated within the HDTS.
5.4.4 Data storage
The HDTS shall have a function to store data and information in a memory media on the system.
The data storage in the HDTS should be intended for
⎯ buffering measured data until it is transmitted to an information processing system after the HDTS,
⎯ real-time generation of information by combining data at multiple time points, and
⎯ temporary storage of real-time information necessary for decision-making.
Information that will be stored for a long time and used as standards should be stored as a database in an
separate information-processing system from the HDTS.
5.4.5 Data display and printing
The system shall have the functions of displaying and printing out data and information in tables and graphs.
For these functions, there are methods for displaying and printing data immediately after each timing of data
collection, and methods for outputting a batch of data collected at multiple sampling times (such as daily) and
for outputting information on a timing as requested by a user.
5.5 System supervision
5.5.1 General
An HDTS shall be able to record its operational status, to provide a report of this record in order to check its
operational status and to quickly notify users of problems, so that users can identify and remove the causes of
problems, and quickly and appropriately restore the system.
5.5.2 Supervision of operational status
The system should always be supervised to promptly detect any problems.
The remote telemetry stations are to be installed geographically distributed and operated unmanned.
Therefore, the operational status of the entire system including the remote telemetry stations should be
supervised, and any problems should be detected remotely from the receiving center.
The remote telemetry stations should be designed to report the status of telemetry equipment, sensors and
power supplies to the receiving center. The receiving center should check the contents of status reports from
remote telemetry stations inspect for any equipment malfunctions in the receiving center and provide
notification of potential problems.
5.5.3 Alarming
The contents of status reports and the affected ranges shall be defined to record and report the extent of
malfunctions and related problems. The necessity of troubleshooting should be ranked into two levels.
⎯ “Warning” is used for an alarm that needs a countermeasure.
⎯ “Caution” is used for an alarm that signals a warning level and/or a temporary problem that can
automatically be recovered.
5.6 Power supply
Power supply shall be designed with thorough consideration for stable operation of the system. Especially, the
power supply to remote telemetry stations shall be carefully designed because external power supply may not
be available or stable depending on the installation environment. Typical concepts of power supply are given
below.
a) During ordinary times, an external power supply such as a commercial power line is used to run the
system. In the case of external power failure, batteries and other backup power sources are used. The
systems that need a high power capacity and important systems may be equipped with generators. The
guaranteed backup hours should be determined based on the importance of the system (usually, several
hours to several days).
b) Instead of using an external power supply, photovoltaic and/or wind power generation is used. Backup
batteries should also be used if there is a possibility that there may be periods during which power cannot
be generated because the photovoltaic or wind power supply is affected by weather conditions. The
guaranteed backup duration should be determined based on the prevailing weather conditions at the area
where the system will be installed and the importance of the system (usually, one week to a month).
Details are given in Annex J.
The scale of backup power supply is determined by the electric power required at the load side and the
guaranteed backup duration. The load electric power should be calculated by investigating the necessity of a
backup power supply for each equipment and screening the equipment that really needs backup. The
guaranteed duration should be calculated by considering weather conditions, such as annual sunshine hours
and wind conditions, the voltage and frequency fluctuation ranges of commercial power sources, estimated
frequency of power failures, and other possible external factors as well as the importance and economy of the
equipment.
8 © ISO 2007 – All rights reserved

6 Operational requirement
6.1 General
For stable operation of the HDTS, specialists in hydrology and telecommunications technology should prepare
various manuals and standards concerning the management of the system, including its operation and
maintenance.
6.2 Operating and maintenance manual
The data management system should be determined for the whole system, including methods for long-term
data storage and for recovery of data loss as well as ordinary operations. Methods for maintaining the system,
hardware countermeasures against data errors and system failures, and methods for keeping and handling
consumables and spare parts in stock should also be determined.
6.3 Maintenance
For stable data acquisition over a long period, the system should have a preventive maintenance schedule.
Preventive maintenance consists of daily inspection, periodical inspection and exchange of parts. Daily
inspection is to check whether the entire system is normally operating by referring to the printouts from the
printer or displays at the receiving center. Periodical inspection consists of checking the system through visual
checks and using testing instruments for preventive maintenance; inspection items differ depending on the
inspection periods. If there are parts that have predefined life cycles, these parts are changed during
periodical inspections.
Remote telemetry stations are usually operated unmanned. It is difficult to inspect such remote telemetry
stations at their sites on a daily basis; these stations should be subject to periodical inspection. The intervals
of periodical inspection (and the parts changed) vary depending on the equipment to be installed and the
climatic conditions at the sites, but are usually several months, or are before and after the flood season.
Annex A
(informative)
Configuration of hydrometric data transmission systems
Figure A.1 shows the concept of HDTS configuration.
The HDTS is configured by remote telemetry stations and a receiving center. The remote telemetry stations
are installed at hydrometric points and the receiving center is installed at a point needing hydrometric data and
information.
A remote telemetry station basically consists of telemetry equipment and communications equipment, to which
power is supplied from power supply equipment. The telemetry equipment is connected to sensors to
measure hydrometric data and it communicates with the receiving center in accordance with a preset data
acquisition sequence. The communications equipment is available in types corresponding to line types and
provides communication functions between the telemetry equipment and the monitoring equipment at the
receiving center.
The remote telemetry stations are connected to the receiving station via communication lines, which are radio
links in many cases, but may be wired lines. If radio links are used, relay stations are deployed as needed.
The receiving station basically consists of communications equipment and monitoring equipment to which an
operating console and a printer are installed as peripheral equipment. The operating console is used for
various operations to the monitoring equipment and may display data. The monitoring equipment collects the
hydrometric data from remote telemetry stations in a preset collection sequence and performs data processing,
on-line storage, data display and printing and recording. An information processing system may be installed in
the stage after this system, but this system is out of the scope of the HDTS.
10 © ISO 2007 – All rights reserved

Figure A.1 — Configuration of hydrometric data transmission systems
Annex B
(informative)
Functional block diagram of hydrometric data transmission systems
Figure B.1 shows the functional block diagram of HDTS. The equipment configuration corresponding to that
shown in Annex A is indicated on both sides of the figure.
A remote telemetry station measures the data via interfaces with sensors and encodes the data in accordance
with control logic, and communicates with the sensors on a collection sequence under communication control.
If the remote telemetry station is required for data display, storage and processing, the control logic performs it.
The encoded data from each remote telemetry station is transmitted via a communication interface on a
communication link to the receiving center.
The receiving center performs communications on a collection sequence under communication control and
collects the data from remote telemetry stations via communication interface. The system control is the core
function of HDTS, which performs centralized control of the system operations such as collection sequence.
The received data is decoded and verified. Then, the data is displayed, stored or further processed.
12 © ISO 2007 – All rights reserved

Figure B.1 — Functional block diagram of hydrometric data transmission systems
Annex C
(informative)
Locations of remote telemetry stations
C.1 Conditions for selecting locations of remote telemetry stations
Examples of the conditions for selecting the locations of remote telemetry stations are given below.
⎯ The land area shall be sufficiently large.
⎯ It shall be possible to obtain the permission of the landowner to use the land or to purchase the land.
⎯ The weather conditions shall not be very different from those of the surrounding areas.
⎯ The sites shall be safe against floods, landslides, etc.
⎯ If solar batteries are used, the annual average sunshine duration shall be sufficient and the conditions of
obstacles, such as trees, buildings and mountains, shall not be fatal to solar batteries.
⎯ If wind power generation is used, a sufficient wind velocity shall be available throughout a year.
⎯ The access to the sites shall be easily available for installation and maintenance.
⎯ If there are possible noise sources (such as factories, high-voltage transmission lines, heavy traffic road
sections) near the sites, they shall not affect data transmissions.
⎯ There shall be no adverse effects of vibrations, dusts, toxic gases, etc.
⎯ The routes for transporting equipment shall be available.
⎯ The sites shall be appropriate for the layout and installation of the equipment in terms of the dimensions
and weight, and selected after investigation of those factors.
⎯ The frequency of lightning should be known so that adequate countermeasures can be taken.
C.2 Locations for installing radio communications equipment
Examples of the conditions for selecting the locations for installing the radio communications equipment when
very high frequency (VHF)/ultra high frequency (UHF) radio communication links are used are given below.
⎯ The degree of interference from the said radio station or from other radio stations shall be low enough for
communications.
⎯ If two or more antennas are installed within very close quarters in a same site, the degree of mutual
interference should be sufficiently low. If there is mutual interference, the degree of interference should be
minimized by separating the antennas, inserting filters, etc.
⎯ Radio communication stations for point-to-point communication should be located at elevations as low as
possible through comprehensive evaluation of the radio paths, communication links, terrain profiles, and
conditions of the locations, and should never been located at high points, such as the tops of mountains
except for relay station.
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⎯ The equipment composition and radio link design should be appropriate in terms of frequency,
transmission method, radio paths and terrain profiles.
⎯ It shall be possible to set an antenna post having a height that is estimated from the results of radio
propagation tests.
Annex D
(informative)
Interfaces of hydrometric sensors at remote telemetry stations
The interfaces between hydrometric sensors and data transmission systems (telemetry equipment) should be
determined through comprehensive consideration of the properties of measured data, detection methods of
sensors, distances between the sensors and the data transmission system, costs, affinity with the data
transmission system, and universality.
Usually, sensors are determined first, because of using existing sensors or the limited types of sensor that are
physically restricted by the hydrometric data to be measured and the observation sites. In such cases,
interfaces are chosen from the available interfaces for the sensors in considering the above factors.
General and typical interfaces are
⎯ Analogue: 0-1V, 1-5V, 4-20 mA, etc.,
⎯ Digital: bit parallel input such as Binary Coded Decimal (BCD), Gray code, etc.,
⎯ Pulse: AC pulse, no-voltage contact pulse, etc.,
⎯ Serial: RS-232, RS-422, RS-485, SDI-12, HART, etc.
16 © ISO 2007 – All rights reserved

Annex E
(informative)
Data collection sequence
E.1 General
Typical data collection and transmission sequences are shown in this annex. There are three (3) categories of
working modes of HTDS: interrogation, self-reporting, and a combination of interrogation and self-reporting.
The interrogation mode includes E.2, E.3 and E.4. The self-reporting mode includes E.5, E.6 and E.7. In the
combination mode, a system normally operates in the interrogation mode; it operates under both modes when
a threshold value is exceeded or upon the demand of the receiving center.
It also is advisable for remote telemetry stations to have the capability for field operators to enter supplemental
data such as field-measured parameters (for example, suspended sediment concentration).
E.2 Cyclic polling
Cyclic polling is used on the condition that various remote telemetry stations can jointly use a single
communication line. Remote telemetry stations are polled one after another, and after polling of the last
remote telemetry station, the first station is polled again, making a cyclic polling.
In general, the entire system should be polled at intervals
...