Information Guide
Details of how OIML R 46 differs from NMI M 6-1
General
Current Value Definitions


New current definitions (see Table 1).
Manufacturers can choose values provided they meet the minimum specified ratios (see Table 1 in
OIML R 46-1).
Table 1. Current value definitions.
Standard
Decreasing
current
↓
OIML R 46
Maximum Current (Imax)
[No name], but typically 10 Itr
Transitional current (Itr)
Minimum current (Imin)
Starting current (Ist)
NMI M6
Maximum Current (Imax)
Basic current (Ib) or nominal current (In)
[No name] 0.1 Ib, or 0.05 In (see NMI M 6-1, Tables 1 to 3)
[No name] Value 0.05 Ib, or 0.01 In via NMI M 6-1, Tables 1 to 3.
[No name] Corresponds to values in NMI M 6-1, Table 7.
Temperature Ranges

Manufacturer must select from a list temperature values.
Note: Australia would adopt a minimum temperature range suitable for Australian conditions.
Humidity Class

Manufacturer must specify humidity classes to match the conditions, with associated testing
depending on the class.
Accuracy Class designations



Different class designations using letters A, B, C & D are used where A is the least accurate and D is
the most accurate (see Table 2).
Class A is a lower accuracy class than class 1.5 of NMI M 6-1.
OIML R 46 recommends class B or higher where consumption exceeds 5000 kWh per year.
Table 2. Accuracy class designations.
OIML R 46 Accuracy Class
Minimum base MPE (%)
NMI M 6-1 class correspondence
A
±2.0
n/a
B
±1.0
1
C
±0.5
0.5
D
±0.2
0.2
Interval and Multi-tariff Meters


The meter must be able to measure and store data relevant for billing, with minimum storage
capabilities determined by the national authority.
Requirements for interval data and multi-tariff data to store sum correctly.
Note: the internal clock requirements are interpreted to be the same as NMI M 6-1.
Meter Markings

A recommended list of markings is specified, with mandatory markings to be determined.
Protection/Sealing



Legally relevant software must be identified by software version or similar.
Zeroing the total accumulation register is considered to be a metrological change. Protection and
sealing requirement apply.
Manufacturers may declare part(s) of the meter legally relevant – to be validated at approval.


There are requirements for storage and transmission outside of the meter. This may have applications
for Australia, but historically NMI has considered back office software and communications as outside
the scope of approval.
Requirements for software updates.
Note: OIML R 46 provides for national authorities to establish levels of authorized access. NMI is proposing to
develop a system of authorised access to address issues including battery replacement, and register zeroing
without the need for verification.
Indicating Device / Display






Characters must be at least 4 mm high.
Able to display all data relevant for billing.
Automatic sequencing displays must display each register for at least 5 s.
For multi-tariff meters, active tariff must be indicated, and each tariff register must be able to be read
locally.
Energy storage and display for 4000 h (at power P = UnomImaxn) applies to all billing relevant registers
including positive and negative flow and tariff registers.
For electronic registers, minimum retention time is 1 year for a disconnected meter. There shall also
be a display test, all segments on and off to check all segments are working.
Testability


Manufacturer shall declare the necessary number of pulse to ensure a standard deviation of the
measurement less than 0.1 base MPE at Imax, Itr and Imin.
Requirements for radiated signal wavelength and strength.
Pattern Approval (Type Approval)
Documentation
NMI provides information on documentation required for approval in documents and webpages separate from
NMI M 6-1. The differences listed below are not differences with NMI M 6-1, but with NMI’s broad
requirements.
Limits of Error
Class A
Class A does not correspond to a class in NMI M 6-1, so the limits of error are new. The rest of this section only
discusses differences for classes B, C and D.
Base MPEs
OIML R 46 uses the term “base maximum permissible errors” for the error limits for various current and power
factor values, but with the meter otherwise operated at reference conditions. OIML R 46 allows greater
flexibility in the selection of the current parameters. For example, for a class B (class 1) meter, with a
maximum current of 100 A, the meter must be accurate to 1% (at unity pf) down to at least 2 A. The
manufacturer may select a lower transitional current. In NMI M 6-1, the meter must be accurate to 1% (at
unity power factor) down to 1 A.
Aside from current parameterisation differences, there are the following MPE differences:
 For class B (class 1), the error limit is 1.8% at lower currents (power factor 0.5 inductive/0.8
capacitive) as opposed to 1.5%.
 Below Imin and down to Ist a formula is provided for the base MPE so that the MPE smoothly increases
at lower currents. NMI M 6-1 is silent on MPEs below the specified test current range. In practice, it is
worth noting that the actual test points specified in OIML R 46 do not extend below Imin except for the
starting current test at Ist.
Allowed Effects of Influence Quantities and Disturbances
A list of influence and disturbance tests is list in Table 3 below. Note it does not list all criteria (allowed effects)
and test procedures, but instead provides a summary of the key differences from NMI M 6-1.
Table 3. Influence and disturbance tests.
OIML R 46
Clause(s)
Influence Quantity Tests
Temperature
3.3.5:Table 3
coefficient /
6.3.2
Temperature
Dependence
Self-heating
3.3.5:Table 4
6.2.2
OIML R46 Test
Load balance
Voltage variation
Frequency
variation
Harmonics in
voltage and
current circuit
3.3.5:Table 4
6.3.3
3.3.5:Table 4
6.3.4
3.3.5:Table 4
6.3.5
3.3.5:Table 4
6.3.6
NMI M 6-1 Test
NMI M 6-1
Clause(s)
Difference?
Difference in allowed
effects
Difference in test procedure
Temperature
coefficient/Mean
Temperature
coefficient
—
5.3:Table 6
A.2.3
Similar
The limits of error are
doubled for class D
below -10 °C.
Temperature intervals must be between 15 K and
23 K. Must include the reference temperature
—
New
—
Maximum
Permissible Error
Voltage variation
4.8:Table 3
Similar
5.1:Table 4
A.2.12
5.1:Table 4
A.2.13
5.1:Table 4
A.2.21
Same
Error shift limits as
opposed to MPEs.
Same
Same
Same
Different
Error shift limits are
tighter.
—
(This new test has the meter operating
continuously at maximum current.)
Same.
(Clearer on mandatory test points.)
Same.
(Clearer on mandatory test points.)
Same.
(Clearer on mandatory test points.)
Includes up to the 13th harmonic.
5.1:Table 4
Similar
Error shift limits
provided for classes A,
B and C.
Frequency variation
Harmonic
components in
the current and
voltage
circuits
Tilt at 3° in any
direction
from the vertical
Tilt
3.3.5:Table 4
6.3.7
Severe voltage
variations
3.3.5:Table 4
6.3.8
Voltage variation
5.1:Table 4
A.2.12
Similar
Error shift limits are
tighter.
One or two
phases
interrupted
Sub-harmonics in
the AC current
circuit
3.3.5:Table 4
6.3.9
Voltage unbalance
5.1:Table 4
Same
Same
Same.
(Test remains only applicable for
electromechanical meters and other meters
influenced by working position.)
Same test, but with mandatory test points and
including either side of any distinct shut-down
voltage.
Same
3.3.5:Table 4
6.3.10
Sub-harmonics in
the AC circuit
5.1:Table 4
A.2.17
Same
Same
Same. Test point is 10 Itr instead of 0.5 Ib or 0.5 In.
OIML R46 Test
Harmonics in the
AC current circuit
Reversed phase
sequence
Continuous (DC)
magnetic
induction of
external origin
Magnetic field
(AC, power
frequency) of
external origin
Radiated, RF,
electromagnetic
fields
Conducted
disturbances ,
induced by radio
frequency fields
DC in the AC
current circuit
OIML R 46
Clause(s)
3.3.5:Table 4
6.3.11
3.3.5:Table 4
6.3.12
3.3.5:Table 4
6.3.13
3.3.5:Table 4
6.3.14
NMI M 6-1 Test
Odd harmonics in
the AC current
circuit
Reversed phase
sequence
Continuous
magnetic
induction of
external origin
Magnetic induction
of external origin
0.5 mT
NMI M 6-1
Clause(s)
5.1:Table 4
A.2.18
Same
Difference in allowed
effects
Same
Same. Test point is 10 Itr instead of 0.5 Ib or 0.5 In.
5.1:Table 4
Same
Same
Same. Test point is 10 Itr instead of 0.1 Ib or 0.1 In.
5.1:Table 4
Different
Error shift limits are
tighter.
Permanent magnet as opposed to electromagnet
with different specifications.
5.1:Table 4
Similar
Error shift limits are
tighter.
Similar test with new reference to IEC 61000-4-8.
The limits of error are
wider for class C (class
0.5)
The limits of error are
wider for class C (class
0.5)
Frequency range extends up to 6000 MHz as
opposed to 2400 MHz.
Limits of error
introduced for class C
and D.
—
Same
Difference?
3.3.5:Table 4
6.3.15.1
Electromagnetic RF
fields
5.1:Table 4
A.2.9
Different
3.3.5:Table 4
6.3.15.2
Conducted RF
Fields
5.1:Table 4
A.2.10
Similar
3.3.5:Table 4
6.3.16
DC component in
the AC circuit
5.1:Table 4
Similar
Difference in test procedure
Same
High-order
3.3.5:Table 4
—
—
New
—
harmonics
6.3.16
(New test: 15fnom to 40fnom)
Disturbance Tests
The allowed effects generally include “no significant fault” where changes in the registers and pulses of the test output are less that the critical change value.
Magnetic field
3.3.6.2:Table 5
—
—
New
—
—
(AC, power
6.4.2
(This new test is at 1000 A/m, 3 s, and references
frequency) of
IEC 61000-4-8)
external origin
Electrostatic
3.3.6.2:Table 5
Electrostatic
A.2.11
Same
Same
Same
discharges
6.4.3
discharge test
OIML R46 Test
Fast transients
Voltage dips
Voltage
interruptions
OIML R 46
Clause(s)
3.3.6.2:Table 5
6.4.4
3.3.6.2:Table 5
6.4.5
3.3.6.2:Table 5
6.4.5
NMI M 6-1
Clause(s)
5.1:Table 4
A.2.15
A.2.14
Similar
Difference in allowed
effects
Same
Different
Same
A.2.14
Different
Same
Radiated
Electromagnetic
(EM)
Radiofrequency
(RF) Fields
—
A.2.9
Different
No significant fault
(critical change value)
instead of “not
perturbed”
—
New
—
—
(New test)
3.3.6.2:Table 5
6.4.8
—
—
New
—
—
(New test)
Same, but only with tests A (30 Imax for directconnected) and B (20 Imax for transformeroperated). In particular, the 7000 A test is not
present in OIML R 46.
Same procedure, but with different parameters,
typically 10 kV and 10 J at standard rated system
voltage of 230/240 V.
NMI M 6-1 Test
Fast transient
bursts
Voltage Dips and
interruptions
Voltage Dips and
interruptions
Difference?
Radiated, RF,
electromagnetic
fields
3.3.6.2:Table 5
6.4.6
Surges on AC
mains power
lines
Damped
oscillatory waves
immunity test
Short-time
overcurrent
3.3.6.2:Table 5
6.4.7
3.3.6.2:Table 5
6.4.9
Short-time
Overcurrents
5.1:Table 4
A.2.16
Similar
Same
Impulse voltage
3.3.6.2:Table 5
6.4.10
Impulse voltage
Test
A.2.19
Similar
Earth fault
3.3.6.2:Table 5
6.4.11
3.3.6.2:Table 5
6.4.12
3.3.6.2:Table 5
6.4.13.1
—
—
New
No significant fault
(critical change value)
instead of error shift
not greater than
uncertainty of
measurement.
—
Operation of
accessories
Vibration
(Sinusoidal) Test
5.1:Table 4
Similar
A.2.7
Different
Operation of
ancillary devices
Vibration
Error shift limits are
different
Error shift limits after
the test
Difference in test procedure
Same, but with references to IEC 61000-4-1 and
IEC 61000-4 -4.
Three different voltage dip tests. References to
IEC 61000-4-11, IEC 61000-6-1 and IEC 61000-6-2.
One different voltage interruption test.
References to IEC 61000-4-11, IEC 61000-6-1 and
IEC 61000-6-2.
Frequency range extends up to 6000 MHz as
opposed to 2400 MHz.
—
(New test)
Same test, but test points are Itr and Imax instead
of other values such as 0.05 Ib.
The vibration test references IEC 60068-2-47 and
IEC 60068-2-64.
OIML R46 Test
Shock
Protection
against solar
radiation
OIML R 46
Clause(s)
3.3.6.2:Table 5
6.4.13.2
3.3.6.2:Table 5
6.4.14
NMI M 6-1 Test
Shock / Mechanical
shock Test
Solar Radiation Test
NMI M 6-1
Clause(s)
5.1:Table 4
A.2.8
5.5
A.2.5
Difference?
Similar
Different
Difference in allowed
effects
Error shift limits after
the test
Same but with specific
mention of
metrological properties
and sealing added.
Same
Protection
against ingress of
dust
Dry Heat
3.3.6.2:Table 5
6.4.15
Dust Test
5.6
A.2.6
Same
3.3.6.2:Table 5
6.4.16.1
Dry Heat
A.2.1
Similar
Cold
3.3.6.2:Table 5
6.4.16.2
Cold
A.2.2
Similar
Damp Heat
3.3.6.2:Table 5
6.4.16.3
6.4.16.4
Damp Heat Cyclic
Test
A.2.4
Different
Water
3.3.6.2:Table 5
6.4.16.5
6.4.17
—
—
New
Error shift limits after
the test instead of
MPEs. No high
temperature accuracy
testing.
Error shift limits after
the test instead of
MPEs. No low
temperature accuracy
testing.
Error shift limits after
the test instead of
MPEs. No significant
fault during the test.
No insulation testing
afterwards.
—
—
—
New
—
Durability
Difference in test procedure
Same as per mechanical shock test in NMI M 6
(A.2.8).
A different 66 days test in a cycling rig with
reference to ISO 4892-3.
Same
Same test but conducted at one standard step
higher than the upper temperature limit specified
for the meter.
Same test but conducted at one standard step
lower than the lower temperature limit specified
for the meter.
There are two separate Damp Heat tests selected
by the humidity class of the meter: Steady State
(IEC 60068-2-78, IEC 60068-3-4) for H1 meters,
and cyclic IEC 60068-2-30, IEC 60068-3-4) for H2
and H3 meters.
—
(New test)
—
(New test)