EN 1434-1:2015

SLOVENSKI STANDARD
01-januar-2016
1DGRPHãþD
SIST EN 1434-1:2007
Merilniki toplote - 1. del: Splošne zahteve
Heat meters - Part 1: General requirements
Wärmezähler - Teil 1: Allgemeine Anforderungen
Comteurs d´engine thermique - Partie 1: Prescriptions générales
Ta slovenski standard je istoveten z: EN 1434-1:2015
ICS:
17.200.10 Toplota. Kalorimetrija Heat. Calorimetry
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 1434-1
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2015
EUROPÄISCHE NORM
ICS 17.200.10 Supersedes EN 1434-1:2007
English Version
Heat meters - Part 1: General requirements
Compteurs d'énergie thermique - Partie 1: Wärmezähler - Teil 1: Allgemeine Anforderungen
Prescriptions générales
This European Standard was approved by CEN on 5 September 2015.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1434-1:2015 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Types of instruments . 11
4.1 General . 11
4.2 Complete instrument . 11
4.3 Combined instrument . 11
4.4 Hybrid instrument . 11
4.5 Sub-assemblies of a heat meter, which is a combined instrument . 11
4.5.1 General . 11
4.5.2 Flow sensor . 12
4.5.3 Temperature sensor pair . 12
4.5.4 Calculator . 12
4.6 Equipment under test (EUT) . 12
5 Rated operating conditions . 12
5.1 Limits of temperature range . 12
5.2 Limits of temperature differences . 12
5.3 Limits of flow rate . 12
5.4 Limit of thermal power . 13
5.5 Limits of working pressure (PS and P ) . 13
min
5.6 Nominal pressure (PN) . 13
5.7 Limits in ambient temperature . 13
5.8 Limits in deviations in supply voltage . 13
5.9 Maximum pressure loss . 13
5.10 Specific requirements on registration devices . 13
5.10.1 General . 13
5.10.2 Suitability . 13
5.10.3 Rated operated conditions . 14
5.10.4 Indication . 14
5.10.5 MPE . 15
6 Technical characteristics . 15
6.1 Materials and construction . 15
6.2 Requirements outside the limiting values of the flow rate . 16
6.3 Display . 16
6.4 Protection against fraud . 16
6.5 Supply voltage . 17
6.6 Qualifying immersion depth of a temperature sensor . 17
6.7 The influence on a temperature sensor pair caused by mounting in pockets . 17
6.8 Reproducibility . 17
6.9 Repeatability . 17
6.10 Software . 18
7 Specified working range . 18
7.1 General . 18
7.2 Temperature difference . 18
7.3 Flow rate . 18
8 Heat transmission formula . 18
9 Metrological characteristics (Maximum Permissible Error, MPE) . 19
9.1 General . 19
9.2 Values of maximum permissible errors . 19
9.2.1 Maximum permissible relative errors of complete heat meters . 19
9.2.2 Maximum permissible relative error of sub-assemblies . 19
9.3 Application of maximum permissible errors . 20
10 Environmental classification . 20
10.1 General . 20
10.2 Environmental class A (Domestic use, indoor installations) . 21
10.3 Environmental class B (Domestic use, outdoor installations) . 21
10.4 Environmental class C (Industrial installations) . 21
10.5 Mechanical classes M1 to M3 . 21
11 Heat meter specification . 21
11.1 General . 21
11.2 Flow sensor . 21
11.3 Temperature sensor pair . 23
11.4 Calculator. 23
11.5 Complete meters . 25
12 Information to be made available by the manufacturer or supplier . 26
12.1 Installation instructions . 26
12.2 Parameter setting instructions . 27
12.3 Adjustment instructions . 28
12.4 Maintenance instructions . 28

12.5 Hints for disposal instructions . 29
Annex A (normative) Heat coefficient equations . 30
Annex B (normative) Flow conditioner package . 32
Annex C (normative) Fast response meters . 34
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 2004/22/EC, MID . 35
Bibliography . 37

European foreword
This document (EN 1434-1:2015) has been prepared by Technical Committee CEN/TC 176 “Heat
meters”, the secretariat of which is held by SIS.
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 May 2016, and conflicting national standards shall be
withdrawn at the latest by May 2016.
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.
This document supersedes EN 1434-1:2007.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive.
For relationship with EU Directive, see informative Annex ZA, which is an integral part of this
document.
EN 1434, Heat meters consists of the following parts:
— Part 1: General requirements
— Part 2: Constructional requirements
1)
— Part 3: Data exchange and interfaces
— Part 4: Pattern approval tests
— Part 5: Initial verification tests
— Part 6: Installation, commissioning, operational monitoring and maintenance
In comparison to EN 1434-1:2007, the following changes have been made:
— special cases for combined cooling and heating meters are added;
— additional functionality for smart metering applications are added;
— metrological requirements for smart metering applications are added;
— definitions and requirements for the cooling meter are added;
— tariff meters are added;
— terms and definitions, requirements for registration devices and cooling meters are added;
— requirements for fast response meters are added (informative Annex C).

1)
EN 1434-3 is maintained by CEN/TC 294.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
1 Scope
This European Standard specifies the general requirements for heat meters. Heat meters are
instruments intended for measuring the energy which in a heat-exchange circuit is absorbed (cooling)
or given up (heating) by a liquid called the heat-conveying liquid. The heat meter indicates the quantity
of heat in legal units.
Electrical safety requirements are not covered by this European Standard.
Pressure safety requirements are not covered by this European Standard.
Surface mounted temperature sensors are not covered by this European Standard.
This standard covers meters for closed systems only, where the differential pressure over the thermal
load is limited.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 1434-2:2015, Heat meters — Part 2: Constructional requirements
EN 1434-4:2015, Heat meters — Part 4: Pattern approval test
EN 60751, Industrial platinum resistance thermometers and platinum temperature sensors (IEC 60751)
EN 61010-1, Safety requirements for electrical equipment for measurement, control and laboratory use —
Part 1: General requirements (IEC 61010-1)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
response time
τ
0,5
time interval between the instant when flow or temperature difference is subjected to a specified
abrupt change and the instant when the response reaches 50 % of the step value
3.2
fast response meter
meter suitable for heat exchanging circuits with rapid dynamic variations in the exchanged heat
Note 1 to entry: See also Annex C.
3.3
rated voltage
U
n
voltage of the external power supply required to operate the heat meter, conventionally the voltage of
the AC mains supply
3.4
rated operating conditions
conditions of use, giving the range of values of influence quantities, for which the metrological
characteristics of the instrument are within the specified maximum permissible errors
3.5
reference conditions
set of specified values of influence factors, fixed to ensure valid inter-comparison of results of
measurements
3.6
influence quantity
quantity, which is not the subject of the measurement, but which influences the value of the
measurement and or the indication of the measuring instrument
3.7
influence factors
influence quantity having a value within the rated operating conditions
3.8
disturbance
influence quantity having a value outside the rated operating conditions
3.9
Types of errors
3.9.1
error (of indication)
indication of the measuring instrument minus the conventional true value of the measurand
3.9.2
intrinsic error
error of a measuring instrument determined under reference conditions
3.9.3
initial intrinsic error
error of a measuring instrument as determined once prior to performance tests and durability tests
3.9.4
durability error
difference between the intrinsic error after a period of use and the initial intrinsic error
3.9.5
maximum permissible error
MPE
highest values of the error (positive or negative) permitted
3.10
Types of faults
3.10.1
fault
difference between the error of indication and the intrinsic error of the instrument
3.10.2
transitory fault
momentary variations in the indication, which cannot be interpreted, memorized or transmitted as
measurements
3.10.3
significant fault
fault greater than the absolute value of the MPE and not being a transitory fault
Note 1 to entry: If the MPE is ± 2 % then the significant fault is a fault larger than ± 2 %.
3.11
reference values of the measurand
RVM
specified value of the flow rate, the outlet temperature and the temperature difference, fixed to ensure
valid intercomparison of the results of measurements
3.12
conventional true value
quantity value attributed by agreement to a quantity for a given purpose
Note 1 to entry: A conventional true value is, in general, regarded as sufficiently close to the true value for the
difference to be insignificant for the given purpose.
EXAMPLE A true value is the heat coefficient according to Annex A.
3.13
meter model
different sizes of heat meters or sub-assemblies having a family similarity in the principles of operation,
construction and materials
3.14
electronic device
device employing electronic elements and performing a specific function
3.15
electronic element
smallest physical entity in an electronic device which uses electron hole conduction in semi-conductors,
or electron conduction in gases or in a vacuum
3.16
qualifying immersion depth of a temperature sensor
immersion depth over which the sensor measures with an accurate temperature value
Note 1 to entry: The conditions to define the qualified immersion depth are written in EN 1434-4:2015, 7.4.4.1.
3.17
self-heating effect
increase in temperature signal that is obtained by subjecting each temperature sensor of a pair to a
continuous power dissipation of 5 mW when immersed to the qualifying immersion depth in a water
bath, having a mean water velocity of 0,1 m/s
3.18
heat meter
instrument intended for measuring the energy which in a heat-exchange circuit is absorbed (cooling) or
given up (heating) by a liquid called the heat-conveying liquid
3.19
meters other than for heating
3.19.1
cooling meter
heat meter designed for cooling applications at low temperatures, normally covering the temperature
range 2 °C to 30 °C and ΔΘ up to 20 K
3.19.2
bifunctional meters for change-over systems between heating and cooling
instrument measuring heating and cooling energy in two separate registers
Note 1 to entry: In other directives and requirements, bifunctional meters are called combined meters.

Key
No energy recording
Heating
Cooling
Figure 1 — Example for function of heating and cooling register
3.20
flow direction
direction of the liquid going through the system from inlet to outlet
Note 1 to entry: The inlet is for the heating case the hot side and for the cooling case the cold side.
Note 2 to entry: In the literature the word “flow” is also being used for “inlet”, and the word “return” is also
being used for “outlet”.
Note 3 to entry: Different temperature values for θ for heating and cooling applications may also occur.
hc
3.21
electrical pulse
electrical signal (voltage, current or change in resistance), that departs from an initial level for a limited
duration of time and ultimately returns to the original level
3.22
pulse output and input devices
3.22.1
pulse output device
functional part of flow sensor, calculator or auxiliary devices
EXAMPLE Remote displays or input devices of control systems.
3.22.2
pulse input device
functional part of flow sensor, calculator or auxiliary devices
EXAMPLE Remote displays or input devices of control systems.
3.23
maximum admissible temperature
maximum temperature of the heat conveying liquid the meter can withstand in combination with the
maximum admissible working pressure and the permanent flow rate for short periods of time (< 1 h /
day; < 200 h / year) without a significant fault after the exposure to this maximum admissible
temperature
3.24
durability
characteristic of a measuring instrument to keep the metrological characteristics over time (e.g. to fulfil
the double of MPE), provided that it is properly installed, maintained and used within the permissible
environmental conditions
3.25
long life flow sensor
flow sensor designed to have a longer lifetime than a normal flow sensor, which typically has a
durability of 5 years under the specified operating conditions
3.26
user interface
interface forming part of the instrument that enables information to be passed between a human user
and the measuring instrument or its components (e.g. display)
3.27
communication interface
electronic, optical, radio or other technical interface that enables information via correct transceiving of
at least thermal energy to be passed between measuring instruments, sub-assemblies or external
devices
3.28
meter for smart metering
heat meter or cooling meter with the capability of data communication and support of smart metering
functionalities
Note 1 to entry: Data could be transmitted via user interface and/ or communication interface in fixed time
intervals and/or on request.
Note 2 to entry: For more information on smart meters, see standard series EN 13757 and
CEN/CLC/ETSI/TR 50572.
3.29
registration device
an optional additional device fitted to the meter as an integral part or separate device, in order to
register the amount of thermal energy accumulated in additional registers during periods, depending
on conditions, e. g. flow rate, inlet or outlet temperatures, temperature differences or time points
3.30
register
component of a registration device which contains accumulated or actual values e. g. thermal energy,
volume, maximum flow rate, power or temperature
3.31
interval register
register which contains frequently accumulated or copied values used for registration of billing
purposes and/ or for controlling processes
Note 1 to entry: During consecutive time intervals values could be achieved by copying from an accumulating
main register which contains actual values of e.g. thermal energy or volume.
Note 2 to entry: During consecutive time intervals the measured process values of flow rate and/or
temperature could be additionally stored.
3.32
maximum flow
highest rate of flow which is expected at operating conditions
Note 1 to entry: For the limits of flow rates, see 5.3.
4 Types of instruments
4.1 General
For the purposes of this European Standard, heat meters are defined either as complete instruments or
as combined instruments.
4.2 Complete instrument
A heat meter, which does not have separable sub-assemblies as defined in 4.5.
4.3 Combined instrument
A heat meter, which has separable sub-assemblies as defined in 4.5.
4.4 Hybrid instrument
A heat meter, which for the purpose of pattern approval and verification can be treated as a combined
instrument as defined in 4.3 or combinations between sub-assemblies. However, after verification, its
sub-assemblies shall be treated as inseparable.
NOTE Hybrid instruments are often called “compact instruments”.
4.5 Sub-assemblies of a heat meter, which is a combined instrument
4.5.1 General
The flow sensor, the temperature sensor pair and the calculator or a combination of these.
4.5.2 Flow sensor
A sub-assembly through which the heat-conveying liquid flows, at either the inlet or outlet of a heat-
exchange circuit, and which emits a signal, which is a function of the volume or the mass or the
volumetric or mass flow rate.
4.5.3 Temperature sensor pair
A sub-assembly (for mounting with or without pockets), which senses the temperatures of the heat-
conveying liquid at the inlet and outlet of a heat-exchange circuit.
4.5.4 Calculator
A sub-assembly, which receives signals from the flow sensor, and the temperature sensors and
calculates and indicates the quantity of heat exchanged.
4.6 Equipment under test (EUT)
A sub-assembly, a combined sub-assembly or a complete meter subject to a test.
5 Rated operating conditions
5.1 Limits of temperature range
5.1.1 The upper limit of the temperature range, θ , is the highest temperature of the heat conveying
max
liquid, at which the heat meter shall function without the maximum permissible errors being exceeded.
5.1.2 The lower limit of the temperature range, θ , is the lowest temperature of the heat-conveying
min
liquid, at which the heat meter shall function without the maximum permissible errors being exceeded.
5.1.3 The optional switching over temperature, θ , is for switching over between heating and cooling
hc
in bifunctional meters.
5.2 Limits of temperature differences
5.2.1 The temperature difference, ΔΘ, is the absolute value of the difference between the
temperatures of the heat-conveying liquid at the inlet and outlet of the heat-exchange circuit.
5.2.2 The upper limit of the temperature difference, ΔΘ , is the highest temperature difference, at
max
which the heat meter shall function within the upper limit of thermal power, without the maximum
permissible errors being exceeded.
5.2.3 The lower limit of the temperature difference, ΔΘ , is the lowest temperature difference, above
min
which the heat meter shall function, without the maximum permissible errors being exceeded.
5.2.4 The value ΔΘ for switching over between heating and cooling energy and reversed is the
hc
threshold in bifunctional meters for change-over systems between heating and cooling.
5.3 Limits of flow rate
5.3.1 The upper limit of the flow rate, q , is the highest flow rate, at which the heat meter shall
s
function for short periods (<1 h / day; < 200 h / year), without the maximum permissible errors being
exceeded.
5.3.2 The permanent flow rate, q , is the highest flow rate, at which the heat meter shall function
p
continuously without the maximum permissible errors being exceeded.
5.3.3 The lower limit of the flow rate, q, is the lowest flow rate, above which the heat meter shall
i
function without the maximum permissible errors being exceeded.
5.4 Limit of thermal power
The upper limit of the thermal power is the highest power at which the heat meter shall function
without the maximum permissible errors being exceeded.
5.5 Limits of working pressure (PS and P )
min
PS is the maximum positive internal pressure that the heat meter can withstand permanently at the
upper limit of the temperature range, expressed in bar. P is the lowest pressure permitted in order to
min
avoid deterioration of its metrological performance, e.g. cavitation.
NOTE P is depending on flow rate and temperature.
min
5.6 Nominal pressure (PN)
A numerical designation, which is a convenient rounded number for reference purposes.
All equipment of the same nominal size (DN) designated by the same PN number shall have compatible
mating dimensions.
5.7 Limits in ambient temperature
The ambient temperature range in which the heat meter shall function without the maximum
permissible errors being exceeded.
5.8 Limits in deviations in supply voltage
The supply voltage range in which the heat meter shall function without the maximum permissible
errors being exceeded.
5.9 Maximum pressure loss
The loss of pressure in the heat conveying liquid passing through the flow sensor, when the flow sensor
is operating at the permanent flow rate q .
p
5.10 Specific requirements on registration devices
5.10.1 General
A registration device is an additional functionality of smart meters outside of the requirements of the
MID. For a registration device, the essential requirements for meters shall apply, if applicable. In
addition, the requirements 5.10.2 to 5.10.5 shall apply.
5.10.2 Suitability
a) The registration device shall register energy in different registers activated by:
1) signals of an internal time switch;
2) signals of an internal quantity dependent threshold indication;
3) remote control signals at peripheral interface terminals; and/or
4) signal of an result or measurement or an internal register.
b) A registration device shall be designed to provide:
1) one or several non-resettable registers counting, e.g. the thermal energy and volume after
activation, starting with the value registered at the last deactivation; and/or
2) a set of interval registers for controlling processes.
c) A registration device shall be able to provide the time and date at which an interval value and/ or
the related error status have been registered.
d) The number of interval registers shall be sufficient to cover sufficient time intervals. If a new
interval value is memorized, the oldest value shall be deleted.
e) Thermal power shall be determined on basis of discrete interval values. Peak values shall be
determined for separate periods, e.g. as a day, or a week, or a month or a year and stored in
particular registers.
f) In addition to the interval values, a registration device can determine and register average values of
quantities, if measured by the meter.
5.10.3 Rated operated conditions
Taking into account the internal resolution of the thermal energy meter and the properties of the used
interface, the manufacturer shall specify the rated operating conditions, in particular the minimum
length of measuring intervals, in order to avoid inadmissible errors for the intended measurement task.
5.10.4 Indication
The registration device shall provide on a legally controlled display
— the information which register(s) is (are) currently activated;
— the information which register(s) is (are) intended for billing purposes;
— values of registers and / or interval registers;
— the unit of values, which are assigned to the displayed values;
and, if applicable
— information identifying the direction of thermal energy flow belonging to the values for delivered
and absorbed energy;
— date and time;
— lifetime of internal battery supply;
— list of registers and their definitions;
— the threshold values used for activating registers; and
— parameters and information important for the correct working of the registration device and the
inability of changing legally parameters in use.
The description of the main identifiers shall be on the nameplate or in the documentation
accompanying the instrument.
The registration device itself or an appropriate associated software for use by the consumer shall allow
to verify the correct assignment of single interval values or sums of interval values to rates (like the
maximum consumption or the sum of consumption during daily periods), if such processed values serve
as basis for the price to pay.
And if applicable other registers can also be displayed.
5.10.5 MPE
5.10.5.1 Clock
If applicable for the instrument:
For frequent time based tariff switches between registers (e.g. for day and night tariff) within a billing
period, the deviation from legal time shall be one of the following three options.
Option 1: deviation less than 1 h/year
Option 2: deviation less than 6 min from legal time
Option 3: deviation less than 7 s from legal time
NOTE The above chosen maximum time deviations are derived from the physical inertia (thermal capacity to
be heated or cooled) of the heat conveying liquid, within the heat and cooling circuits.
For periodic interval registers for a billing period (e.g. hourly, daily, weekly or monthly registers), the
time deviation shall not be more than 1 % of the length of this period. In this case the deviation of the
internal clock from legal time is the accumulated deviation of all measurement periods.
5.10.5.2 MPE of tolerance quantities used for threshold activation of additional energy
accumulations
for temperature measurement in case of a complete meter (calculator with single temperature
1,0 K
sensor); up to 100 °C
0,7 K for temperature measurement in case of a combined meter (single temperature sensor); up to
100 °C
NOTE In applications of smart metering, one or both single sensors of the pair are used as additional single
sensor. In case of Platinum (Pt) sensors, according to EN 60751, at least class B with 4 wire connections is
recommended.
6 Technical characteristics
6.1 Materials and construction
6.1.1 All the constituent elements of heat meters shall be solidly constructed of materials having
appropriate qualities to resist the various forms of corrosion and wear which occur under rated
operating conditions, especially those due to impurities in the heat conveying liquid. Correctly installed
meters shall also be able to withstand normal external influences. Meters shall, in all circumstances,
withstand the maximum admissible pressure and the temperatures for which they are designed,
without malfunction.
6.1.2 The manufacturer of the heat meter shall declare any limitations with regard to installation of
the heat meter and its orientation, with respect to the vertical.
6.1.3 The casing of a heat meter shall protect the interior parts against water and dust ingress. The
minimum forms of enclosure protection shall be IP54 for heating applications and IP65 for cooling
applications for equipment that is to be installed into pipe work and IP52 for other enclosures, all in
accordance with EN 61010-1.
6.1.4 Heat meters may be fitted with interfaces allowing the connection of supplementary devices.
Such connections shall not modify the metrological qualities of the heat meter.
6.1.5 The maximum pressure loss at q shall not exceed 0,25 bar.
p
6.2 Requirements outside the limiting values of the flow rate
When the true value of the flow rate is less than a threshold value declared by the manufacturer, no
registration is allowed.
The flow rate through a “nominally” closed valve or the movement of liquid in the pipe behind a closed
valve caused by thermal expansion and contraction should not be recorded.
For flow rates greater than q , the behaviour of the meter, e.g. by producing spurious or zero signals
s
shall be declared by the manufacturer. Flow rates greater than q until declared maximum flow shall not
s
result in an error greater than 10 % of the actual flow rate.
6.3 Display
6.3.1 The quantity of heat shall be indicated in Joules, Watt-hours or in decimal multiples of those
units. The name or symbol of the unit, in which the quantity of heat is given, shall be indicated adjacent
to the figures of the display.
6.3.2 Heat meters shall be designed that in the event of a failure or interruption of the external power
supply (mains or external DC) the meter indication of energy remains accessible for a minimum of one
year (totally). The manufacturer shall specify how the indication of energy is handled in case of a failure
or interruption in the external power supply (mains or external DC).
NOTE The energy indication can either be stored in a permanent way (memory) at certain intervals, or it can
be stored through a controlled shut-down process (powered from an internal source).
6.3.3 The reading of the indication shall be sure, easy and unambiguous.
6.3.4 The real or apparent height of the figures on the display for energy shall not be less than 4 mm.
6.3.5 The figures indicating decimal fractions of a unit shall be separated from the others, either by a
comma or by a point. In addition, the figures indicating decimal fractions of energy shall be clearly
distinguishable from the others.
6.3.6 Where the display is of the roller-type, the advance of a figure of a particular significance shall
be completed during the time, when the figure of next lower significance changes from 9 to 0. The roller
carrying the figures of lowest significance may have a continuous movement, of which the visible
displacement shall then be from bottom to top.
6.3.7 The display indicating the quantity of heat shall be able to register, without overflow, a quantity
of heat at least equal to the transfer of energy, which corresponds to a continuous operation for 3 000 h
at the upper limit of the thermal power of the heat meter.
The quantity of heat, measured by a heat meter, operating at the upper limit of the thermal power for
1 h shall correspond to at least one digit of lowest significance of the display.
6.4 Protection against fraud
Heat meters shall have protective devices which can be sealed in such a way, that after sealing, both
before and after the heat meter has been correctly installed, there is no possibility of dismantling,
removing, or altering the heat meter or its adjustment devices without evident damage to the device(s)
or seal(s).
Means shall also be provided for meters with external power supply, either to give protection against
the meter being disconnected from the power supply, or to make it evident, that this has taken place.
This requirement does not apply to meters with external power supply with automatic switchover to
internal battery supply.
NOTE Embodiment of an hour's run counter in the meter casing will make it evident if the power supply has
been disconnected.
6.5 Supply voltage
6.5.1 AC mains operated heat meters or subassemblies shall have a rated voltage, 196 V < U < 253 V.
n
6.5.2 Remote DC or AC operated heat meters or subassemblies shall have a rated voltage U of 24 V.
n
The tolerance for DC shall be 12 V to 42 V and for AC 12 V to 36 V.
If the remote supply lines are also used for data transmission (e.g. M-bus, see EN 1434-3) these values
shall be maintained during any data transmission.
6.5.3 Local external DC operated meters or subassemblies shall preferably have a rated voltage U of
n
6 V, 3,6 V or 3 V, in accordance with Table 1.
Table 1 — Standardized levels for external powering
Nominal voltage 6 V 3,6 V 3 V
Max. average current 100 mA 10/20/50/100/200 μA 10/20/50/100/200 μA
Tolerance at average
5,4 V to 6,6 V 3,4 V to 3,8 V 2,8 V to 3,3 V
current
Peak current 100 mA 10 mA 5 mA
Min. voltage at peak
5,4 V 3,2 V 2,7 V
current
6.6 Qualifying immersion depth of a temperature sensor
By immersion beyond the qualifying immersion depth the resistance shall not change by more than
what correspond to 0,1 K.
6.7 The influence on a temperature sensor pair caused by mounting in pockets
The difference in measuring result with and without specified pockets shall be within 1/2 of the MPE.
6.8 Reproducibility
The application of the same meter (or sub-assembly) in a different location or by a different user, all
other conditions being the same, shall result in the close agreement of successive measurements. The
difference between the measurement results shall be small when compared with the maximum
permissible error.
6.9 Repeatability
The application of the same meter (or sub-assembly) under the same conditions of measurement shall
result in the close agreement of successive measurements. The difference between the measurement
results shall be small when compared with the maximum permissible error.
6.10 Software
Software that is critical for metrological characteristics shall be identified as such and shall b
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