The different demand calculations

When we use the maximum demand function of an energy meter, we can select different settings. What is the impact on the demand registration?

In the example below we are generating a 24 hour load-profile. It’s based on values between 30% peak and peak. (1440 samples)
Then we run a evaluation of the MD (maximum demand) for various meter settings. All fixed windows starting at midnight (00:00).

What do we learn?

  • The shorter the integration period, the higher the MD value
  • The shorter the sub-interval in the integration period, the higher the MD value (except of some strange profile constellations, you might find them)

What are the right settings?
It depends on the purpose for the demand measurement.
If you want to give a penalty to customers exceeding a defined limit, you need to follow the utility rules (e.g. 30 minutes fixed window).

If you are operating with an AMI system, you want to do a load-prediction (forecast) for a period of time. Here it is very common to use a 15 minutes integration time with 1 minute sub-intervals.

All evaluations are done with the same record-set, click on CALC

new random load profile
MD Limit kVA
Peak load kVA
Integration period 5 minutes
Integration period 15 minutes
Integration period 30 minutes
Integration period 60 minutes

one bar is equal to one minute

Pulse Calculation for Stationary Test Benches

All energy meters used for billing purpose have a test output for calibration. This can be flashing diode, a pulse output at the terminal or the mark of a rotating disk. This test output gives us information about the power consumption. 

example for meter label
example for meter label

On the meter label you can find the so called meter constant. It can be expressed in many ways. Here we only take care about the expression imp/kWh. On this example we see a meter constant of 1000i/kWh. This means, the meter diode will flash 1000 times per consumed kWh. On a stationary test bench we are testing the meter with different load points.

Each load point consists of:

  • voltage
  • current
  • power factor
  • no. of phases
  • meter constant
  • number of pulses for the test
  • frequency (not relevant for pulse calculation)

From the parameters above we can calculate the power and the duration for a pulse. 
The error evaluation at a test bench is done by comparing the meter pulses with the pulses of a reference standard. Most reference standards have meter constants based on ranges. To get resolution of 1 ppm (0.0001%) the reference standard must receive 1 million pulses for the selected load-point range.
This is only necessary for high precision measurements, e.g. when testing other reference standards or calibrators class 0.05.
Most test bench error display are showing 3 decimals (10 ppm error resolution), so making a verification with 1 ppm is not necessary.

Choosing the proper no. of pulses for each load-point individually can take a long time, especially when you have to deal with many different meter constants.
To make the meter testing faster, CLOU test benches have for this reason an algorithm inside which calculates the required no. of pulses automatically for a certain time-base. The default value is 10 seconds.
With this time based calculation we have a resolution < 10 ppm versus our reference standards for all ranges and load points.
Of coarse all settings can be overwritten manually.

Please check the pulse calculator below to get a better idea about the required pulses per load point for CLOU test benches. We are operating with a reference standard frequency of 160 kHz. The competitor standards are working with 50 kHz. This makes CLOU test benches faster and more efficient with comparable results.

Pulse Calculation
test voltage V ph-N
test current A
power factor
phases
meter constant i/kWh or i/kvar
power 1150 W
pulse frequency 0.31945 Hz
duration 3.1 seconds per pulse
Ranges based on CLOU reference standards
voltage range 240 V
current range 5 A
reference constant 160000000
reference frequency 51111.1 Hz
Time based calculation
Minimum pulses = 2
minimum time seconds
pulses 4
duration 12.4 seconds
resolution 1.6 ppm
Pulse based calculation
pulses
duration 31.0 seconds
resolution 0.6 ppm

For the specialists:
This article is technically simplified, as usual.

Thank you for reading. Comments and questions are welcome.

Calibrator RS350

RS350 calibrator with tablet

The portable reference standard and calibrator RS350 is especially designed for the needs of metering engineers for on-site testing with high precision.
The equipment offers highest functionality together with excellent menu guided operation through a 8” Tablet PC. 

It’s the perfect instrument to reduce technical- and non-technical losses.

What can I do with this instrument?

The RS350 can perform error measurement for maximum 3 meters at time. The last five individual errors are shown on the tablet together with average error and standard deviation.
The instrument can also detect the meter constant, if the meter is not proper marked.
The tablet gives full information for the testing time, remaining time and shows a progress bar. Instrument transformer ratios can be easy applied.

RS350 error measurement
RS350 error measurement

The RS350 has an internal database for all saved data. The pdf-reports are generated from the database.
Individually imported and exported for synchronisation can be:

  • customer information
  • meter types
  • site information
  • meter test workflows

All test data can be uploaded to a common PC database working under our Electric Measurement Studio platform (EMS5).

RS350 database
RS350 database

The RS350 can check demand registers over a defined time.

The RS350 can perform the analysis for harmonic in voltage & current circuits up to 63rd order. All harmonics are displayed simultaneously on one screen in graphical or table format.
All 6 channels can be stored together.
It’s possible to select the harmonics in percent of the fundamental wave or as total RMS value.

RS350 harmonics
RS350 harmonics

Power harmonics are displayed by phase. Shown is the active, reactive- and apparent content.
RS350 power harmonics
RS350 power harmonics

The RS350 can perform instrument transformer tests. Current transformers can be tested for ratio, phase displacement and burden.
Voltage transformers can be tested for burden.

RS350 CT error
RS350 CT error

RS350 CT burden
RS350 CT burden

RS350 PT burden
RS350 PT burden

The RS350 can record all basic measurement values in cyclic time intervals. The intervals can be set between 1 to 99 seconds. The tablet can store 36,000 records (10 hours with 1 second interval time).

RS350 long time measurement
RS350 long time measurement

RS350 long time measurement settings
RS350 long time measurement settings

The results are displayed in graphical format.
RS350 LTM graph
RS350 LTM graph

The workflow for the meter tester can be defined by the utility. It allows to create systematic meter test sequences. Once the structure is defined, all meter testers will report with the same testing content and nothing will be forgotten. The RS350 guides the user trough all test steps.
The test sequence can include:

  • recording site data
  • verification of proper sealing
  • taking of photos
  • accuracy tests
  • record of the GPS location
  • Signature of witness
  • Report generation
RS350 workflow
RS350 workflow

The RS350 real time measurement display shows all 51 electrically relevant parameters on one screen.
The instrument shows THD & Crest Factor for each phase in voltage & current. It has an easy application of Instrument transformer (IT) ratios for comparison purpose.
Supported are many measurement modes, e.g. 1Ph 2W, 3Ph 3W, 3Ph 4W, in active, reactive & apparent mode, (total & fundamental).
The Apparent power definition is switchable between arithmetical- or trigonometric calculation.

real time measurement
RS350, real time measurement

The RS350 can test energy registers.

The automatic site analysis function of the RS350 checks the essential parameters versus predefined limits and makes wiring checks for the meter tester easier.
Indicated with PASS/FAIL information are:

  • Presence of voltages & currents
  • Direction of currents
  • Balancing of phase voltages & currents
  • Phase symmetry
  • Phase sequence of voltage & current circuits
  • THD in voltage & current circuits
RS350 site analysis
RS350 site analysis

The limits can be set as per utility rules and regulations.

RS350 wiring check limits
RS350 wiring check limits

The RS350 can flexible selected display the actual voltage- and current waveforms for maximum 6 channels in parallel.
Per phase it can show the waveforms of active- and reactive power.
All waves can be saved. To capture suspicious events the RS350 has a HOLD function.

RS350 waveform analysis

The RS350 helps to debug complex wiring problems.

  • Vectorial display along with relevant electrical parameters
  • Automatic hints on the actual wiring status
  • Supports both vectorial presentations (U & I based)
  • Power quadrant display (per phase & total)
wiring check
RS350 wiring check

The calibrator RS350 has a integrated wiring simulator. The simulator can be used for analysis and for training purpose. It can either read the actual values or simulation values.
It’s written in HTML/Javascript and supports most browsers. Take a look here.

RS350 wiring simulation
RS350 wiring simulation

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Specifications

Specifications RS350

Mains and environment

Voltage:


60 V – 265 V AC

Frequency:

47 Hz – 63 Hz

Power consumption:


< 30 VA

Operating temperature:

-5 °C – 50 °C

Max. relative humidity:

≤ 85 %, not condensate

Surge voltage protection:

class C

Installation category:

III

Pollution degree:

2

Ingress protection

IP 30

Housing material

Polycarbonate

Weight:

< 3 kg

Dimensions

268 mm x 243 mm x 68 mm

Measurement parameters

Test voltages, phase-neutral

0.5 V – 576 V

Voltage ranges

60 V, 120 V, 240 V, 480 V, auto range

Test current, direct connected

1 mA – 24 A

Current ranges

20 mA, 50 mA, 100 mA, 200 mA, 500 mA,
1 A, 2 A, 5 A, 10 A, 20 A,
auto-range

Frequency range, fundamental wave

15 Hz – 70 Hz

Bandwidth

4 kHz

Voltage measurement accuracy

< 0.01 %

Voltage measurement drift

< 35 ppm/year

Current measurement accuracy < 25 mA

< 0.02 %

Current measurement accuracy ≥ 25 mA

< 0.01 %

Current measurement drift

< 65 ppm/year

Power measurement accuracy P, Q, S
(related to apparent power)

< 0.05 % (current ≥ 25 mA and λ = 1)

Power measurement drift

< 100 ppm

Phase angle

< 0.01° (current ≥ 25 mA and voltage > 30 V)

Frequency

0.005 Hz

Voltage temperature drift

< 2,5 ppm/K

Current temperature drift

< 5 ppm/K

Power temperature drift

< 7.5 ppm/K

Accessories

Standard accessories

The content of delivery for the calibrator RS350 includes:
10 pcs laboratory cable
4 pcs crocodile clips
10 pcs connector with cable lug
10 pcs adapter with 4 mm pin
10 pcs connector with pin
1 mains power supply cable
10 fuses

The calibrator RS350 has it’s own compartment inside of the transport case. The tablet is for transport safely stored in the case flap.
The actual tablet is a Lenovo TB3-850F. It has 1 GB RAM and 16 GB internal storage. Operation with battery is up to 8 hours.


RS350 case topview
RS350 case topview

The content of delivery for the calibrator RS350 includes 3 pcs. clamp-on CTs. The CLOU clamp-on CT is designed to perform measurements up to 100 A + 20 %. The CT is rated for 600 V ac circuits of Measurement Category III, Pollution Degree 2, per EN/IEC 61010-1 and EN/IEC 61010-2-032.

Specifications
The accuracy classes are related to apparent power. The given accuracy classes are including the internal RS350 error.

Range current Accuracy class
100 A 24 A ≤ 120 A 0.2
20 A 6 A < 24 A 0.2
5 A 1.2 A < 6 A 0.2
1 A 0.24 A < 1.2 A 0.3
0.2 A 0.05 A < 0.24 A 0.5

Mechanical parameters
Can be uses for wiring diameters up to ⌀ 20 mm
Max. Jaw opening 20 mm
Dimensions 53 mm x 138 mm x 28 mm
Weight 350 g
Material PC + ABS + Polycarbonate, UL94 V0

Electrical parameters
Primary current 10 mA – 120 A AC
Max. continuous input current 120 A
Ratio 1200 : 1
Load capacity ≤ 4 Ω
Over voltage category CAT III 600 V
Frequency range 40 Hz – 3800 Hz
Dielectric strength 3 kV 50 Hz / 60 Hz for 1 minute
Temperature range -20 °C – +55 °C
Output 2.0 meter cable with connector for RS350
Max. voltage not insulated conductors 600 V
Compliant with Standards EN/IEC 61010-1, EN/IEC 61010-2-032, IEC60044-1

The documentation for the calibrator RS350 includes:

  • user manual
  • calibration certificate
  • warranty card

This cable adapter is used for accuracy verification of the RS350 against a higher accurate standard (e.g. our reference standard CL3115)

pulse cable
pulse cable

A wired scanning head belongs to the standard scope of delivery for the RS350. It can detect rotor marks for electromechanical meters and pulse diodes for electronic meters. LEDs with a wave-length of 400 – 1100 nm and with pulse frequencies up to 3 kHz can be detected.
The scanning head is delivered with a fixing device. The clamping width is 10 mm to 180 mm.

Scanning Head TP-17C
Scanning Head TP-17C

Bag for scanning head and small parts
Bag for scanning head and small parts

Scanning head specifications

parameter

value

Wave-length

400 – 1100 nm

max. frequency, unmodulated

> 3 kHz

max. frequency, modulated

> 9 kHz

dark to light change

max. 15 µs

light to dark change

max. 15 µs

uncertainty of switching edge detection

±1 µs

pulse width

min. 0.2 ms

operating voltage

3.3 V – 24 V DC

operating current

≤ 50 mA

scanning distance

0 – 50 mm

output signal, high

≥ 3.0 V

output signal, low

≤ 0.3 V

Housing

Polycarbonate

Color

blue-grey

dimensions

30 mm x 46 mm x 22 mm

weight incl. cable

< 80 g

cable length

2 m

ingress protection

IP 54

operating temperature

-40 °C – +85 °C

relative humidity

> 85 %

The equipment is delivered in a trolley with wheels and handle for easy transportation. The trolley is designed in such way that you can leave the RS350 inside and only make the connections to the meter. The cables can remain connected to the RS350 during transport. This saves time and increases the efficiency of use. The suitcase dimensions are 483.5 mm x 474 mm x 237 mm. The weight with standard accessories is less than 12 kg.

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Optional accessories

The basic set of the calibrator RS350 includes one scanning head. Sometimes it’s useful to check the accuracy of two or three energy meters in parallel. The hardware is supporting maximum 3 scanning heads.

Scanning head with fixing device
Scanning head with fixing device

The additional scanning heads are delivered with fixing devices.
Please note that the extension box is needed when using more than one scanning head.
The specifications are the same like the original delivered head.

The RS350 can measure the current in Neutral together with the phase currents.
For Neutral current measurement an additional current clamp is needed.
The specifications are the same like for the 100 A clamps.

The CLOU clamp-on CT is designed to expand the measurement capabilities of CLOU calibrators like RS350 in industrial and power environments to measurements up to 1000 A + 20 %. The CT is rated for 600 V ac circuits of Measurement Category III, Pollution Degree 2, per EN/IEC 61010-1 and EN/IEC 61010-2-032.

clamp-on CT 1000 A
clamp-on CT 1000 A

Specifications
The accuracy classes are related to apparent power. The given accuracy classes are including the internal RS350 error.

Range

current

Accuracy class

1000 A

between 1200 A and 100 A

0.2

100 A

between 100 A and 10 A

0.1

100 A

Between 10 A and 500 mA

0.2


Mechanical parameters

Can be uses for wiring diameters

up to ⌀ 50 mm

Max. Jaw opening

50 mm

Dimensions

103 mm x 220 mm x 28 mm

Weight

550 g

Material

PC + ABS + Polycarbonate, UL94 V0


Electrical parameters

Primary current

0 – 1000 A AC

Max. continuous input current

1200 A

Ratio

2000 : 1

load capacity

≤ 4 Ω

Over voltage category

CAT III 600 V

Frequency range

40 Hz – 3800 Hz

Dielectric strength

3 kV 50 Hz / 60 Hz for 1 minute

Temperature range

-20 °C – +55 °C

Output

2 m cable with connector for RS350

Max. voltage not insulated conductors

600 V

Compliant with Standards

EN/IEC 61010-1, EN/IEC 61010-2-032, IEC60044-1

The CLOU clamp-on CT is designed to expand the measurement capabilities of CLOU calibrators like RS350 in industrial and power environments to measurements up to 2000 A + 20 %. The CT is rated for 600 V ac circuits of Measurement Category III, Pollution Degree 2, per EN/IEC 61010-1 and EN/IEC 61010-2-032.

clamp-on CT 2000 A
clamp-on CT 2000 A

Specifications

The accuracy classes are related to apparent power. The given accuracy classes are including the internal RS350 error.

Range current Accuracy class
2000 A between 2400 A and 600 A 0.1
500 A between 600 A and 120 A 0.2
100 A Between 120 A and 24 A 0.3
20 A Between 24 A and 2 A 0.5
Mechanical parameters
Can be uses for wiring diameters up to ⌀ 50 mm
Max. Jaw opening 75 mm
Dimensions 116 mm x 327 mm x 35 mm
Weight 550 g
Material PC + ABS + Polycarbonate, UL94 V0
Electrical parameters
Primary current 0 – 2400 A AC
Max. continuous input current 2400 A
Ratio 4000 : 1
load capacity ≤ 4 Ω
Over voltage category CAT III 600 V
Frequency range 40 Hz – 3800 Hz
Dielectric strength 3 kV 50 Hz / 60 Hz for 1 minute
Temperature range -20 °C – +55 °C
Output 2 m cable with connector for RS350
Max. voltage not insulated conductors 600 V
Compliant with Standards EN/IEC 61010-1, EN/IEC 61010-2-032, IEC60044-1

The CLOU clamp-on CT is designed to perform measurements up to 5 A + 20 %. The CT is rated for 600 V ac circuits of Measurement Category III, Pollution Degree 2, per EN/IEC 61010-1 and EN/IEC 61010-2-032.

clamp-on CT 5 A
clamp-on CT 5 A

Specifications

The accuracy classes are related to apparent power. The given accuracy classes are including the internal RS350 error.

Range

current

Accuracy class

5 A

2.4 A ≤ 6 A

0.2

2 A

1.2 A < 2.4 A

0.2

1 A

0.6 A < 1.2 A

0.2

0.5A

0.24 A < 0.6 A

0.2

0.2 A

0.12 A < 0.24 A

0.3

0.1 A

0.05 A < 0.12 A

0.3


Mechanical parameters

Can be uses for wiring diameters

up to ⌀ 8 mm

Max. Jaw opening

10 mm

Dimensions

53 mm x 136 mm x 28 mm

Weight

350 g

Material

PC + ABS + Polycarbonate, UL94 V0


Electrical parameters

Primary current

10 mA – 6 A AC

Max. continuous input current

6 A

Ratio

1000 : 1

Load capacity

≤ 4 Ω

Over voltage category

CAT III 600 V

Frequency range

40 Hz – 3800 Hz

Dielectric strength

3 kV 50 Hz / 60 Hz for 1 minute

Temperature range

-20 °C – +55 °C

Output

2.0 meter cable with connector for RS350

Max. voltage not insulated conductors

600 V

Compliant with Standards

EN/IEC 61010-1, EN/IEC 61010-2-032, IEC60044-1

The functionality of the RS350 hardware can be extended to use 3 scanning heads in parallel. For this purpose we have an extension box together with a connection cable to the RS350.

This switch is connected to the pulse input socket of the RS350. It is used to test electromechanical meters under low load conditions.
A scanning head needs about 2 full rotations of the meter disk for adjustment. With the Start-Stop switch you can monitor the mark on the disk. When it is in front, you press the button for starting the measurement. Once the mark arrives again at the front, press the button and see the error result.

start - stop switch
start – stop switch

wireless scanning head
wireless scanning head

The RS350 can work together with one or more wireless scanning heads TP17. This accessory is helpful to test energy meters in parallel without need of extension cables.
See the detailed description here.

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FAQ

Our manual can give only guidance how to use the RS350-Application. For general information of this Android tablet please refer to the original Lenovo instructions.

This is only a short reference for most common meters. Make sure that you have read the RS350 operation manual with more examples.
Always follow your company safety guidelines. In addition it’s no mistake to take a look at our safety regulations.

Single phase 2 wire, DIN terminal
Singlephase two wire meter, DIN terminal
Singlephase two wire meter, DIN terminal
Single phase 2 wire, BS- or ANSI bottom connected terminal
single phase 2 wire, BS terminal
single phase 2 wire, BS terminal

Threephase 3 wire, DIN terminal
DIN threephase 3 wire
DIN threephase 3 wire
Threephase 4 wire, DIN terminal
DIN threephase 4 wire, direct connected
DIN threephase 4 wire, direct connected
Threephase 4 wire CT, DIN terminal
DIN threephase 4 wire CT
DIN threephase 4 wire CT
Threephase 4 wire CT/PT, DIN terminal
DIN threephase 4 wire CT/PT
DIN threephase 4 wire CT/PT

The calibrator RS350 communicates with the Android device (usually the delivered tablet) via Bluetooth. If it’s necessary to pair this two devices new, go to SETTINGS (RS350 application) and select Bluetooth.

RS350 Bluetooth
RS350 Bluetooth

Click on Refresh and select RS350-xxxxxx
The number xxxxxx is matching with the last 6 digits of the RS350 serial no. indicated on the type-label.
The device will show Connected and device battery status as soon as the communication is established.

The calibrators RS350 are leaving our factory with a traceable calibration certificate.
All metrological instruments need to be recalibrated regular. The recalibration period depends on country regulations. In most countries portable calibrators have a recalibration period of one year.
The recalibration can be done in any for this purpose accredited laboratory.
The general principle is to compare the calibrator pulses with the reference standard pulses. Connect the P-OUT to the pulse input and GND to the ground, calculate the meter constant for the actual load and verify the RS350 accuracy with the higher accurate standard.

RS350 meter constants
RS350 meter constants

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Contact Us

Would you like to receive a quotation or to talk to our wonderful sales team? Please enter your email, so we can follow up with you.

Downloads

Specifications in Word-Format

can be used for comparison or tender purpose

Size: 1.2 MB, doc-file
Brochure RS350

Highlights of the portable calibrator RS350.

Size: 12 MB, pdf-file

Training

We are also offering theoretical- and practical training, either in our headquarter in Shenzhen or at customer site.

Universal Quick Connectors for Meter Test Benches

Electrical energy meters have various sizes, shapes and terminal connections. Is it possible to have a universal quick connector for connection of all kind of meters? 

meter types
overview for energy meter types

energy meter terminal, bottom viewBefore electronic meters came to the market the meter connections had much less variants. Each terminal was made from brass with two screws to fix the conductor. The picture shows the view from the meter terminal bottom. Depending on the pin-design the quick connector touches either the screw or the screw and the inside of the brass terminal with a certain force (about 30 N for a maximum current of 60 A). The DIN 43857 gives a hole diameter of 6.5 mm for 60 A meters.

For higher currents you can find terminals with diameters of 8.5 mm or 10.5 mm. For CT- and CT/PT connected meters you have diameters around 4 mm.
So, to cover direct connected meters and transformer operated meters with one quick connector is not possible. The connector pin diameter must match with the maximum current. Otherwise the heat (coming from the resistance) will destroy either the terminal block or the quick connector.
For this reason a test bench used to have:

  • a set of quick connectors with 6 mm pins to cover 60 A long duration or 100 A for short duration (< 2 minutes, 20 % duty cycle)
  • a set of quick connectors with 4 mm pins for transformer operated meters
  • a set of wires for direct connected meters > 60 A

cagelift terminal Since electronic energy meters are in the market, we have also to deal with cage lifting terminals. The photo shows the view from the meter bottom. 
Cage lifting terminals have neither a screw to touch, nor conducting material at the bottom. Therefor a round pin has no touching point to connect the current.


For all kind of ANSI socket type meters are also different adapters or quick connectors required.

What about universal quick connectors for voltage?

If the voltage is supplied via the secondary side of Insulated Current Transformers there is no need for a separate voltage quick connector. This applies for direct connected polyphase meters. For direct connected singlephase meters with Multi Secondary Voltage Transformers is also no need for a voltage quick connector.
For CT- and CT/PT meters a universal quick connector would require pins which can be moved and fixed in all 3 axes.

Conclusion

We can do all kind of quick connectors, including voltage, auxiliary circuits, pulse outputs and communication. But we can’t combine everything in one quick connector.
We would really like to solve your meter testing problems, especially for huge meter quantities. With our high degree of automation or with manual operated test benches we can cover the real needs.
Please ask us for more information or let us know your comments.

Terminal Wiring for Electrical Energy Meters

There are two standards for the wiring of bottom-connected
energy meters.

  • DIN 43857
  • BS 5685

In meter- or test bench descriptions you can find various expressions, all with the same meaning.
 

DIN 43857 refers also to:
– DIN terminal
– asymmetrical connection
– sequential wiring
– LLLLLLNN (for 3 phase 4 wire meters)
– LLNN (for singlephase meters)
– AABBCCNN (for 3 phase 4 wire meters)

The DIN wiring looks always similar to this.

   

BS 5685 refers also to:
– BS terminal
– symmetrical connection
– LLLNNLLL (for 3 phase 4 wire meters)
– LNNL (for singlephase meters)
– ABCNNCBA (for 3 phase 4 wire meters)

The BS wiring always looks similar to this.

Simulation of faulty energy meter wiring

This simulation shows the impact of wrong wiring or meter tamper on energy meters.
The RS-Button works only together with a connected RS350 on a tablet. The simulation is equal to the delivered one with our calibrator RS350. It’s copied on this page for educational purpose.
All grey circles are interactive. Just try and have fun here or in full-screen mode, recommended for touch-screen devices.

The interesting part is the financial loss due to irregular wiring at the right bottom.

Security for Optical Ports on Energy Meters

Optical ports provide local access for service engineers during installation or maintenance of energy meters.

Households have physical access to their energy meter and might try to get access to the meter software.

ir-port
The optical interface for smart meters from almost every manufacturer is specified in the IEC 62056-21. (The US-American ANSI C12.18 is not covered by this article.)

Main functions that can be accessed using optical communication

  • Billing data readout
  • TOU (Time of Use) readout and modification
  • Billing period reset
  • Register and profile resets
  • Parameter readout and modification
  • Communication input settings
  • Analysis and diagnostic functions

Note: During the production process electronic meters need to be adjusted. This is done by writing correction values in a dedicated memory inside the meter. This correction values are protected against external access and can not be overwritten once the meter has left the manufacturing site. There are different protection solutions. Some manufacturers are using the optical port for adjustment and lock later this memory section. CLOU meters are using a special port on the PCB for adjustment, which has no physical connection with the infrared port in compliance with the Measuring Instruments Directive (MID).

Protection of the Optical Port

The IEC specification defines the following communication modes:

  • Mode A
  • supports bidirectional data exchange at 300 baud without baud rate switching. This protocol mode permits data readout and programming with optional password protection.

  • Mode B
  • offers the same functionality as protocol mode A, but with additional support for baud rate switching.

  • Mode C
  • offers the same functionality as protocol mode B with enhanced security and manufacturer-specific modes.

  • Mode D
  • supports unidirectional data exchange at a fixed baud rate of 2400 baud and permits data readout only.

  • Mode E
  • allows the use of other protocols.

For the password command, the following command type identifiers are defined:

– 0 data is operand for secure algorithm

– 1 data is operand for comparison with internally held password

– 2 data is result of secure algorithm (manufacturer-specific)

These defined command type identifiers allow static passwords (1) or a manufacturer-specific challenge-response algorithm (0 and 2). Furthermore operation mode C supports manufacturer-specific enhanced security, which is out of the scope of the IEC standard.

Besides this password protection, the IEC standard defines a set of security levels for use in combination with mode C.

  • Access level 1
  • only requires knowledge of the protocol to gain access.

  • Access level 2
  • requires a password to be correctly entered.

  • Access level 3
  • requires operation of a sealable button or manipulation of certain data with a secret algorithm to gain access.

  • Access level 4
  • requires physical entry into the case of the meter and effecting a physical change, such as making/breaking a link or operation of a switch, before further communications access is allowed.

Practical security implementation

The safest method for optical port protection is a authentication by a challenge-response algorithm. This requires that each meter has a unique key. The complex key administration is a back-draw for optical port communication because each handheld- or PC need to keep the meter specific key, while each meter needs to keep the PC specific key. For remote access (AMI systems) this procedure is recommended.

The CLOU risk analysis shows that the most suitable approach is to use a password for read-only operations, together with a manufacturer specific data encryption. For writing operations the terminal cover must be open.

Once the terminal cover is opened unauthorized the meter is recording a tamper event. Depending on the meter type the relay trips and in case of a AMI system the tamper event is forwarded to the centre.

A sealing of the optical port itself does not provide additional security.

When do I need Isolation Current Transformers?

This question comes always up together with stationary meter testing in laboratories. Isolation Current Transformers (ICT) are needed to test more than one direct connected energy meter on a test bench with multiple positions, assuming that the I-P links can not be opened.
terminal blockIf you can’t find the links (red arrows) on the meter terminal block you need to use ICTs for testing.
And why?
All electronic meters have a power supply, linked between phases and neutral. This power supplies have a consumption (see e.g. IEC62053-21, #7.7.1). According to the Kirchhoff’s Circuit Laws a fraction of the test current will be used by the power supply. This leads to a current-drop on the next test position and to an increasing error from position to position.
The smaller the test current, the higher is the impact on error measurement.
And how does an ICT overcome this problem?
An ICT is principally a transformer with a 1:1 ratio. You have a primary side (where the source is injecting the current) and a secondary side with the connections to the meter. The test voltage is individually provided to each meter on the secondary side of the ICT. So all meters get the same test current. See for example our ICT CL2030 with advanced additional features like protection and remote access by PC-software.
What about single phase meters?
Closed link single phase meters can be tested with ICTs. For single-phase test benches a Multi Secondary Voltage Transformer (MSVT) can be used. With a MSVT the test voltage is made galvanic free, while an ICT makes the currents galvanic free.
Conclusion
To test single-phase meters with closed links you need to have a testbench with MSVTs.
To test three-phase meters with closed links you need to have a testbench with ICTs.
For testing of transformer operated meters (CT, CT/VT) we recommend a direct connection to the test bench. This meters have the current- and voltage circuits separated internally.

Why do I need a vector diagram?

Modern reference standards and calibration devices have usually a graphical function to show the relationship between the voltages and the currents. Most equipment manufacturers call this function vector diagram or vectorial diagram.
In fact it is a phasor diagram. It represents a the phase relations of a sinusoidal rotating system at a certain time.
The system rotation (everything inside the circle) is anti-clockwise. The graph is shown either with

  • current phase L1 in zero degrees position
  • voltage phase L1 in 90° position

Actually the vector diagrams in test equipments are showing only the angles and not the amplitude of the phases. The reason behind is that you won’t see very small current vectors with the given resolution. Anyway, we can nicely read all amplitude values from the instrument. Common practice is to show the voltages with higher amplitude than the currents (voltages are on the outer circle).

Main use for vector diagrams is to check the proper connection of the instrument before you make error measurements.
If you see e.g. that the current of a phase is in opposite to the voltage, it is likely possible that the current clamp is connected in the wrong direction.

The simulation below is kept very simple. You can set the phase angles between I and U, the phase sequence and the reference for the system. The power values are calculated based on your settings.

phase L1 phase L2 phase L3
Voltage
Current
I-U
reference sequence



With a right-click on desktop PCs you can save your drawing(s).

What is the meaning of the different current subscripts?

Together with tender documents and meter specifications you will find various subscripts related to current.

  • current I without subscript
    This is the actual current flowing trough the energy meter.
  • starting current Ist
    This is the lowest value of current at which the meter should register electrical energy at unity power factor and, for poly-phase meters, with balanced load.
  • minimum current Imin
    This is the lowest value of current at which the meter is specified to meet the accuracy requirements.
  • transitional current Itr
    At this value of current and above the meter must to lie within the smallest maximum permissible error corresponding to the accuracy class of the meter.
  • basic current Ib
    This term is used in IEC standards for direct connected meters. All accuracy values  are related to Ib
  • nominal current In
    This is the same like Ib but for transformer operated meters
  • reference current Iref
    The term is only used in EN 50470-1. It is the reference current (for direct connected meters Iref = 10 x Itr = Ib according to EN 62052-11, 3.5.1.2; for CT-connected meters Iref = 20 x Itr = In
  • maximum current Imax
    This is the highest value of current at which the meter is specified to meet the accuracy requirements.

Now let’s look more in detail:

Starting current Ist according to IEC
The starting current is a fraction of the basic current or nominal current. See the multiplication factors below:

IEC 62053-11 direct connectedclass 1: 0.004 Ib
class 2: 0.005 Ib
IEC 62053-11 transformer connectedclass 0.5: 0.002 In
class 1: 0.002 In
class 2: 0.003 In
IEC 62053-21 direct connectedclass 1: 0.004 Ib
class 2: 0.005 Ib
IEC 62053-21 transformer connectedclass 0.2S: 0.001 In
class 0.5S: 0.001 In
IEC 62053-23 direct connectedclass 2: 0.005 Ib
class 3: 0.01 Ib
IEC 62053-23 transformer connectedclass 2: 0.003 In
class 3: 0.005 In

PASS/FAIL criteria:
The meter has to start and continue recording energy. Means, we need to receive at least two pulses from the meter within a certain period of time.

How to calculate the time?
We have the nominal voltage, the number of elements, the starting current and the meter constant. Now we can calculate:

pulse duration

This is the duration for one pulse for a meter with zero error. So, first we double the time because we need to receive two pulses. Then, the IEC does not specify any accuracy for starting test. So we need to consider the meter error. Best practice is to add 20 % to your calculated time for two pulses. This will be in most cases sufficient.
If the meter fails with this time-out calculation you are allowed to extend it. The standard setting of CLOU test benches is 120 %.
From the formula you can see that a higher meter constant is preferable because it saves testing time.

Minimum Required Time for Starting Test
nominal voltage V
nominal current A
elements
meter constant i/kWh
IEC62053-11 DC class 1
IEC62053-11 DC class 2
IEC62053-11 CT/PT class 0.5
IEC62053-11 CT/PT class 1
IEC62053-21 DC class 1
IEC62053-21 DC class 2
IEC62053-22 CT/PT class 0.2S
IEC62053-22 CT/PT class 0.5S
IEC62053-23 DC class 2
IEC62053-23 DC class 3
IEC62053-23 CT/PT class 2
IEC62053-23 CT/PT class 3

Starting current Ist according to EN
As usual we have to deal with more standards. For MID the relevant standards are EN 50470-1 and EN 50470-3 .
Here is the starting current a fraction of Itr
Itr is directly liked to Iref (see above). So, if we have a direct connected meter Itr is 10 % of Ib. For CT meters Itr is 5 % of In
The PASS/FAIL criteria are exactly the same as described in #1: starting current Ist according to IEC

Starting current Ist according to OIML R46
OIML stands for ORGANISATION INTERNATIONALE DE MÉTROLOGIE LÉGALE, in English: International Organization of Legal Metrology. The OIML has published the recommendation R46 (please download the actual version from the OIML website). This description is based on the document r46-p-e12.pdf.
PASS/FAIL criteria:
The R46 requires an error measurement for starting current. This means, we set our test equipment to error measurement mode. Best practice is to make the error measurement for two pulses. During production and knowing the behavior of the meter you can also test with one pulse (leads to a higher error deviation).
The maximum permissible error needs to be calculated.

Note: The 2010 edition had a more restrict calculation formula for the allowed error. Please make sure that you work with the actual document.