The terminology used in this glossary conforms to the International Vocabulary of Basic and General Terms in Metrology and the International Vocabulary of Legal Metrology. In addition, for CLOU documentation purpose, the following definitions shall apply

Test condition acc. to IEC 62053-21 for protective class II:
a) Apply 4 kV for 1 minute to the meter terminals while all terminals with 40 V or less are pulled to ground.
b) Apply 2 kV for 1 minute between circuits not intended to be connected together in service
No discharging or sparking is allowed.

active power integrated over time

Note: Active energy is usually expressed in kWh or MWh

rate at which energy is transported

Note: In an electrical system active power is measured as the time mean of the instantaneous power, which is calculated at each instant as the product of voltage and current

At sinusoidal conditions active power is the product of the r.m.s. values of current and voltage and the cosine of the phase angle between them, calculated for each phase. It is usually expressed in kW.

powerP ≙ active power in W
U ≙ voltage
I ≙ current
cosφ ≙ power factor

Active Power Calculation
test voltage V
test current A
power factor
power1.150 kW

This is the power calculated from a certain energy over a time.
average power = recorded energy divided by duration time for the record

COmpanion Specification for Energy Metering
sets the rules, based on existing standards, for data exchange with energy meters
used together with DLMS

value of the electrical current flowing through the meter
Note: The term “current” indicates r.m.s. (root mean square) values unless otherwise specified

internal connections of the meter and part of the measuring element through which flows the current of the circuit to which the meter is connected

The principle of electrical energy measurement is to detect the actual current, the actual voltage and the phase shift (power factor). This values are giving us the instantaneous power . The power multiplied by the time is the consumed energy.
Let’s take a look at a terminal block for a direct connected threephase 4 wire meter.
terminal blockThe red arrows are indicating the so-called “I-P links”, one for each phase. By unfastening the two screws the link can be moved to the right side. So there will be no connection between the current- and voltage measurement circuits. This links are only for meter testing purpose with a test bench, as here the voltages and currents are provided individually. (The voltages are connected to the screw on the right side of the link.)
A meter in the field must have all links closed.

meter intended for use by direct connection to the circuit(s) being measured, without the use of external device(s) such as instrument transformer(s)

part of the meter that displays the measurement results either continuously or on demand

ratio of the r.m.s. value of the harmonic content to the r.m.s. value of the fundamental term

Note 1: The harmonic content is obtained e.g. by subtracting from a non-sinusoidal alternating quantity its fundamental term.

Note 2: The distortion factor is usually expressed as a percentage. It is equivalent to THD, total harmonic distortion

Device Language Message specification
a generalised concept for abstract modelling of communication entities
Official website

instrument intended to measure electrical energy continuously by integrating power with respect to time and to store the result

DIN EN BS 50470-3, VDE 0418-0-3
Electricity metering equipment (a.c.)
– Part 3: Particular requirements
– Static meters for active energy (class indexes A, B and C)

Laboratory meter test equipment should operate under the following climatic conditions.

Nominal temperature23 °C ±2 °C
Operating temperature range+5 °C … 45 °C
Limit range for storage and transport

(max. 6 h at the extremes of this temperature range)

-25 °C … 60 °C
Max. relative humidity≤ 85 %, not condensate

The environment should be dust free.

The European Accreditation Association has per country one member. This members are allowed to approve test laboratories for e.g. calibration according to according to ISO / IEC 17025. The approved test laboratories are so-called Notified Bodies.
The members of the Association will never issue a type-test certificate by themselves, but they guarantee that the certificates issued by their notified bodies are in compliance with the relevant standards.

Example: Type Test Certificate, issued by KEMA, Netherlands
The responsible member of the European Accreditation Association is the Dutch Accreditation Council (RvA). The RvA has issued under the registration no. K006 and K009 the approval for DNV GL Netherlands B.V. to issue calibration certificates.
KEMA is operating under the umbrella of DNV GL Netherlands B.V. For recognition purpose still the old name “KEMA” is in use.
So a KEMA certificate is traceable to the European Accreditation Association.

European Accreditation Association
Dutch Accreditation Council

International Electrotechnical Commission
official website

IEC 62053-41
Electricity Metering Equipment (DC)
– Particular Requirements
– Part 41: Static meters for direct current energy (classes 0,2, 0,5 and 1) (IEC 13/1592/CD:2014)

DIN 62053-41:2015-05;
VDE 0418-3-41:2015-05

IEC 62055-41
Electricity metering
– Payment systems – Part 41:
Standard transfer specification (STS)
– Application layer protocol for one-way token carrier systems

Electricity metering data exchange
– The DLMS/COSEM suite –
Part 6-1: Object Identification System (OBIS) (IEC 62056-6-1)

This standard replaces the IEC 62056-61.

Test of the insulation performance of the EUT.
Applicable standard
IEC 62052-11, part 7.3 Insulation

Energy meters have typically protection class II. The rated impulse voltage is 4 kV for meters < 150 V ph-earth or 6 kV for meters with ph-earth voltage between 150 V and 300 V. For each test the impulse voltage is conducted ten times with one polarity and ten times with reversed polarity. The minimum time between the impulses shall be 3 s. Impulse waveform is 1.2/50 μs.

part of the meter that displays the measurement results either continuously or on demand

Phase current is measured and presented in corresponded DLMS/COSEM objects for each phase separately. Internally currents are always measured in mA.

Instantaneous current is measured in the meter every second.

OBIS identifiers





Instantaneous current





The STS Key management centre is operated for the STS association by the national electricity utility company Eskom in South Africa. Their services are as follows:

  • The registration of Supply Group Codes (SGCs) on the KMC
  • The registration of all security modules on the KMC
  • The initialisation of all security modules on the KMC
  • The generation of all STS vending keys for the relevant Supply Group Codes
  • The loading / coding of the relevant STS vending keys into security modules, for use by the appointed vending equipment manufacturer/s. This will include security modules that are new, repaired or that need to be re-coded. The physical coding needs to take place in Eskom’s KMC in Midrand
  • The loading of a key file onto a disk to accompany the security module (for loading onto the vending equipment). The disks will be supplied by Eskom
  • The loading of STS vending keys on key cards, for use by the appointed meter manufacturer/s. The physical loading of the key cards needs to take place in Eskom’s KMC in Midrand.

A latching relay keeps its contact position indefinitely without power applied to the coil. The advantage is that the coil consumes power only for an instant moment while the relay is being switched, and the relay contacts retain this setting across a power outage.

Usually in electricity meters the load switch is a latching relay.
It is located between the supply input and load output terminals of the energy meter.
The relay is able to make, carry and break all values of currents between the minimum switched current rating to the rated breaking current for all values of the rated operating voltage range and the specified operating temperature range of the meter.
For prepayment meters (see also IEC 62055-31)
The rated breaking current (Ic) shall be equal to Imax of the payment meter.
The minimum switched current shall be equal to the nominal starting current of the payment
The rated breaking voltage (Uc) shall be equal to the upper limit of the extended operating voltage range of the payment meter.
The load switches have different categories for utilization. (UC = Utilization Category)
The payment meter load switching utilization category is subject to the purchase agreement between the payment meter supplier and the purchaser and shall be marked on the label of the payment meter as UC1, UC2, UC3, or UC4.
Category UC1 is applicable to payment meters rated at maximum currents up to 100 A. There is no requirement for the load switch to also switch the neutral circuit. The short time overcurrent is acc. to IEC 62053-21 for meters for direct connection (30* Imax for half cycle).

Payment meters with load switching category UC2, UC3 or UC4 shall have the following properties:
a) capable of making and breaking negligible currents of specified values
b) capable of making, breaking and carrying rated currents of specified values
c) capable of making into fault currents with specified value and under specified conditions
d) capable of carrying short-circuit currents of specified value for a specified time period and under specified conditions
e) not required to provide safety isolation properties in the open contact position. These are requirements for the installation mains isolation switch
f) not required to break overload currents or short-circuit currents. These are requirements for fuses and circuit breakers that are normally used to protect the installation.

Summary of test currents for UC2, UC3 and UC4
Test UC2 UC3 UC4
Fault current making capacity, C.5 2.5 kA 3 kA 4.5 kA
Short-circuit current, C.6 test 1 4,5 kA 6 kA 10 kA
Short-circuit current,

C.6 test 2

2.5 kA 3 kA 4,5 kA

For detailed information refer to IEC 62055-31, annex C.

maximum current (Imax)

highest value of current at which the meter is specified by the manufacturer to meet the accuracy requirements

Maximum demand registers are storing the highest actual average value measured in each period. At the end of each period the actual average value from 1.0.x.4.0 registers are compared with the maximum demand value. If the actual average demand value is higher than the maximum demand value, it replaces the value stored in the maximum demand register.

Maximum demand values are set to zero value at the end of each billing period.

Maximum demand can be calculated for:

– active energy in both directions

-reactive energy per quadrant and as sum of two quadrants

– apparent energy in both flow directions

The tariff 1…8 is indicated by i.

OBIS identifiers


extreme value of measurement error, with respect to a known reference quantity value, permitted by specifications or regulations for a given measurement, measuring instrument or measuring system

Note: Usually, the term “maximum permissible errors” or “limits of errors” is used where there are two extreme values

part of the meter that transforms a current and a voltage into a signal proportional to the power and or energy

minimum current (Imin)

lowest value of current at which the meter is specified by the manufacturer to meet the accuracy requirements

nominal frequency (fnom)

frequency of the voltage (and current) specified by the manufacturer for normal operation of the meter

nominal voltage (Unom)

voltage specified by the manufacturer for normal operation of the meter

Note: Meters designed for operation across a range of voltages may have several nominal voltage values.

OBIS stands for OBject Identification System

Each COSEM object is identified by its logical name given by OBIS. A complete list of standard OBIS codes can be downloaded here.

Personal Safety

  • Avoid contact with energized electrical circuits
  • Treat all electrical devices as if they are live or energized
  • Disconnect the power source before servicing or repairing electrical equipment.
  • Use only tools and equipment with non-conducting handles when working on electrical devices.
  • Never use metallic pencils or rulers, or wear rings or metal watchbands when working with electrical equipment.
  • When it is necessary to handle equipment that is plugged in, be sure hands are dry and, when possible, wear nonconductive gloves, protective clothes and shoes with insulated soles.
  • If it is safe to do so, work with only one hand, keeping the other hand at your side or in your pocket, away from all conductive material.
  • Never touch another person’s equipment or electrical control devices unless instructed to do so.
  • Enclose all electric contacts and conductors so that no one can accidentally come into contact with them.
  • Never handle electrical equipment when hands, feet, or body are wet or perspiring, or when standing on a wet floor.
  • When it is necessary to touch electrical equipment (for example, when checking for overheated motors), use the back of the hand. Thus, if accidental shock were to cause muscular contraction, you would not “freeze” to the conductor.
  • Be aware that interlocks on equipment disconnect the high voltage source when a cabinet door is open but power for control circuits may remain on.
  • De-energize open experimental circuits and equipment to be left unattended.

This typetest is also called burden measurement. Applicable standards IEC62053-21, IEC62053-22

The active and apparent power consumption in each circuit of a meter at reference voltage, reference temperature and reference frequency shall not exceed the values shown below.

Cl. 0.2 SCl. 0.5 SCl. 1Cl. 2
Voltage circuits2 W, 10 VA2 W, 10 VA2 W, 10 VA2 W, 10 VA
Current circuits1 VA1 VA4.0 VA2.5 VA

ratio of the active power to the apparent power

Note: At sinusoidal and either one-phase or symmetrical three-phase conditions, the power factor = cos Φ = the cosine of the phase difference Φ between voltage U and current I.

Duration of time between two off-on edges of the test output device

Pulse Calculation
test voltage V ph-N
test current A
power factor
meter constant i/kWh or i/kvar
power1150 W
pulse frequency 0.31945 Hz
duration 3.1 seconds per pulse
Ranges based on CLOU reference standards
voltage range240 V
current range5 A
reference constant160000000
reference frequency51111.1 Hz
Time based calculation
Minimum pulses = 2
minimum time seconds
duration12.4 seconds
resolution1.6 ppm
Pulse based calculation
duration31.0 seconds
resolution0.6 ppm

part of the meter that stores the measured values

Indication minus reference quantity value, divided by the reference quantity value

Note: The relative error is usually expressed as a percentage of the reference quantity value.

In CLOU teminology the short form “error” is used for relative error.

relative error

IEC 62052-11, #7.2
Short-time overcurrent test shall not damage the meter. The meter shall perform correctly when back to its initial working condition.

Conditions for direct connected meters:
Test current: 30 Imax, duration one half cycle at nominal frequency

Conditions for meters connected trough current transformers:
Test current: 20 Imax, duration 0.5 s

A sine wave or sinusoid is a mathematical curve that describes a smooth repetitive oscillation. A sine wave is a continuous wave.

The Standard Transfer Specification (STS) has become recognised as the only globally accepted open standard for prepayment systems, ensuring inter-operability between system components from different manufacturers of prepayment systems.
The application of the technology is licensed through the STS Association, thus ensuring that the appropriate encryption key management practices are applied to protect the security of the prepayment transactions of utilities operating to protect the security of the prepayment transactions of utilities operating STS systems.
It has become established as a worldwide standard for the transfer of electricity prepayment tokens since its introduction in South Africa in 1993 and subsequent publication by the International Electrotechnical Commission as the IEC62055 series of specifications.

Shenzhen CLOU is member of the STS association. See a member list here.

starting current (Ist)

lowest value of current specified by the manufacturer at which the meter should register electrical energy at unity power factor and, for poly-phase meters, with balanced load

meter in which current and voltage act on solid state (electronic) elements to produce an output proportional to the energy to be measured

Security issues are of prime importance to the utility supplier and the consumer. The use of the STS standard prevents:

  • Fraudulent generation of tokens from hit and miss attempts at entering the correct number
  • Fraudulent generation of tokens from a stolen vending station
  • Fraudulent generation of tokens from legitimate vending stations outside of the utility’s area
  • Fraudulent use of tokens which have already been used
  • Tampering of legitimate tokens e.g. to change the value

STS provides the facility of generating (e.g. credit transfer) tokens which can only be used by the intended meter, and furthermore in the case of credit tokens, can only be used once in that meter.
In order to achieve the above security, the standard defines the following:

  • the use of advanced encryption techniques, which are at all times hidden from the consumer
  • the use of very secure key management procedures, including the manner in which keys are generated and transported
  • Required functionality at both the vending station and the meter

The Supply Group Code (SGC) is usually assigned to a meter by the manufacture for a specific utility and location (usually a large distribution area). The meter SGC must match with the vending system SGC. If it does not match, it is not possible to run STS token operations.
Supply Group Codes are currently managed by the Eskom Key Management Centre, physically located at Eskom Midrand.

transitional current (Itr)

value of current at and above which the meter is specified by the manufacturer to lie within the smallest maximum permissible error corresponding to the accuracy class of the meter

Note: If not otherwise specified the Itr is 10 % of nominal- or basic current

value of the electrical voltage supplied to the meter

Note: The term “voltage” indicates r.m.s. (root mean square) values unless otherwise specified

internal connections of the meter, part of the measuring element and, in the case of static meters, part of the power supply, supplied with the voltage of the circuit to which the meter is connected

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