Multi Secondary Voltage Transformer (MSVT)

Single phase meters with closed I-P links require galvanic isolation for testing.This galvanic isolation is done by a Multi Secondary Voltage Transformer (MSVT). The MSVT has one secondary taping for each meter under test.

The CLOU CL6202-xx can be configured for various secondary tappings. For requests please indicate the no. of meter positions.

item value
No. of windings max. 48
Primary voltage 220 V  –  240 V
Primary frequency 50 Hz  –  60 Hz
Secondary voltage 220 V  –  240 V
Range of secondary burden 4 VA – 15 VA
Accuracy Error prim/sec ≤ ± 0,1%
Phase Error prim/sec ≤ ± 2 min
Accuracy Error sec/sec (within burden range) ≤ ± 0,01%
Phase Error sec/sec (within burden range) ≤ ± 1 min
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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
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
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.

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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.


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.

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Isolating Current Transformer CL2030-D


If a meter has no possibility to open the internal link between voltage and current, the test must be performed with an Isolated Current Transformer (ICT) at each measurement position.
The CL2030-D has a built-in electronic compensation. The ICTs can be remote controlled by PC. A safety protection by controller is built in. This assures that the secondary side is closed in case of high burden or open circuit. Each ICT will be delivered with a company calibration certificate. A certificate issued by an ILAC accredited laboratory is optional available.

ce mark


Specifications ICT CL2030-D

Nominal Current100 A, max. load 120 %
Ratio1 : 1
Ratio error±0.01 % (0.2 A … 120 A)
±0.03 % (0.05 A < 0.2 A)
±0.05 % (0.01 A < 0.05 A)
Phase displacement±0.3’ (0.2 A … 120 A)
± 3’ (0.05 A < 0.2 A)
± 8’ (0.01 A < 0.05 A)
Max. rated secondary voltage 0.7 V
Max. rated burden for 10 mA ≤ I < 2 A200 mΩ
Max. rated burden for I ≥ 2 A0.7 V / I
Frequency range45 Hz … 65 Hz
Weight:15 kg


CLOU control box CL2030-3D-CB The ICTs can operate stand-alone or together with a remote/control by PC. For remote control with 3rd party equipment a control box CL2030-3D-CB is needed. A interface-description is available on request.

This links are uses to interconnect the primary side of ICTs. The copper links are galvanized. This links are designed to connect ICTs with a center to center distance of min 297 mm and max 317 mm.

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If you are test equipment manufacturer you can get the ICT2030-D with your company-logo and without any CLOU indication from outside visible.

Principally yes, there must be enough space behind the quick connectors and the source must be powerful enough. Please sent us more information, then we can do a proper integration.

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Wireless Scanning Head for Pulse Detection TP-17

wireless scanning head
wireless scanning head

This scanning head can be used for detection of metrological LED pulse outputs for static electronic meters together with CLOU portable meter test equipment.
The TP-17 Wireless scanning head is based on the Nordic nRF24L01+, highly integrated, ultra low power (ULP) 2 Mbps RF transceiver for the 2.4 GHz ISM (Industrial, Scientific and Medical) band. It includes the Enhanced ShockBurst™ hardware protocol accelerator for a high-speed SPI interface. The no. of TP-17 Wireless scanning heads working in parallel is not limited.


Specifications scanning head TP-17 Wireless
wavelength 400 …1100 nm
max. sampling frequency 3 kHz
uncertainty of switching edge detection ± 1 μs
pulse width ≥ 0.2 ms
operating voltage 3.3 V DC
scanning distance 10 … 100 mm
housing hard plastic
color blue-grey
dimensions 55 mm x 30 mm x 38 mm
weight < 90 g
transmission power 0 dBm ≙ 1 mW
transmission range, outdoor max. 40 m
transmission range, indoor, industrial environment 25 m (one wall)
battery capacity 800 mAh
permanent operation, battery full charged 72 h
battery charging USB adapter cable
ingress protection IP 54
operating temperature: -40 °C…+85 °C
relative humidity: > 85 %


Specifications receiver for scanning head TP-17 Wireless
operating voltage 3.3 V … 5 V DC
operating current ≤ 30 mA
output signal, high ≥ 4.5 V
output signal, low ≤ 0.3 V


The scanning system consists of

  • Scanning head TP-17 wireless 2.4 GHz transmitter, fixed at the energy meter
  • Fixing device TP-GS 2
    – fastening to meter by two side-plates, can be moved up and down along the meter
    – can be used for rectangle- or round meters
    – adjustable width from 35 to 180 mm
    – provides magnetic adhesion to scanning probes
    – provides mechanical adhesion to scanning probes
    – probes can be moved left/right freely
    – made of insulation material, which ensures safety and portability
  • Receiver TP-17 wireless
  • USB charging cable for scanning head
  • Pairing cable
  • Transport bag


ce mark
Yes, the scanning head TP17-wireless is designed and manufactured in conformity with health, safety, and environmental protection standards for products sold within the European Economic Area (EEA). The compliance was verified by MicroTest (external type test laboratory).

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Three Phase Reference Standard CL3115

reference standard CL3115-HW

This reference standard has accuracy class 0.02 related to apparent power
It can be used for

  • voltage measurement
  • current measurement
  • phase angle measurement
  • frequency measurement
  • harmonics analysis up to the 63th
  • power measurement, active-, reactive-, apparent
  • self consumption measurements
  • accuracy error calculations [note]stand-alone with one pulse input socket, or together with error calculators in stationary test benches[/note]
  • register tests


Specifications Reference Standard CL3115-HW, Mains connection




85 V … 265 V AC


45 Hz … 65 Hz

Power consumption

< 30 VA

Preheating time

15 minutes

Operating temperature

5 °C … 45 °C

Max. relative humidity

≤ 85 %, not condensate

Surge voltage protection

class C

Installation category


Pollution degree



approx. 13 kg


19” 3 units,
H x W x D: 132,5 mm x 483 mm x 405 mm

Specifications Reference Standard CL3115-HW, measurement values



Test voltage, phase-neutral

30 V … 576 V

Voltage ranges

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

Test current

1 mA … 120 A

Current ranges

10 mA, 20 mA, 50 mA, 0.1 A, 0.2 A, 0.5 A, 1 A, 2 A,
5 A, 10 A, 20 A, 50 A, 100 A, auto range

Frequency range, fundamental wave

40 Hz … 70 Hz


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

< 0.02 % (current ≥ 25 mA and λ = 1)

Power measurement drift

< 100 ppm / year

Phase angle

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


0.005 Hz

Voltage temperature drift

< 2,5 ppm / K

Current temperature drift

< 5 ppm / K

Power temperature drift

< 7.5 ppm / K

Errors are independent of measurement mode and when using auto range. The reference standard provides a power proportional frequency output (160 kHz nominal).


The equipment can be operated manually with menu keys or via RS485 remote control. A interface description for integration into 3rd party meter test equipment is available on request. Below are some screen-shots

Power indication in 3 phase 4 wire mode

voltage, current, phase angle

Power indication in 3 phase 4 wire mode

power indication in 3ph 3 wire mode

accuracy measurement


scanning head
transport case


The recalibration period is defined by national rules or by company policy. Typically it’s one or two years. The reference standard can be calibrated by any recognized body or metrological institute. Please note that there is a difference between recalibration and readjustment. An adjustment becomes necessary once the reference standard accuracy is out of the specified class. The adjustment can be done locally. There is no need to sent the instrument back to us.

The reference standard CL3115 is by default delivered with a company calibration certificate. It can also be delivered with a calibration certificate issued by an ILAC accredited laboratory on additional cost.

Following measurement modes are supported by the reference standard CL3115:

  • Three-phase four-wire system, active/ reactive true/apparent
  • Three-phase three-wire system, active/ reactive true/ apparent
  • Single-phase system, active/ reactive true/ apparent
  • Three elements cross connected 90° (Q390)
  • Two elements cross connected 90° (Q290)
  • Two elements cross connected 60° (Q260)

A frequency proportional to the total power is generated by a signal processor, which applies to the pulse output fOUT of the CL3115. The energy output pulse constant can be set to automatic mode or manual mode. Setting range is: 1…2,000,000,000 i/kWh. The pulse output frequency is 160 kHz for End of range in voltage and current. The energy pulse is on TTL/CMOS level, burden capacity >20 mA. The range can be selected in Auto-mode or direct assigned.
Calculation formula for the output frequency


Calculation formula for the meter constant

UR and IR are the ranges, the frequency is 160 kHz


CL3115 meter constants
3 wire and 4 wire mode
60V 120V 240V 480V












0.01A 2.0×109 2.0×109 2.0×109 2.0×109
0.02A 2.0×109 2.0×109 2.0×109 2.0×109
0.05A 2.0×109 2.0×109 2.0×109 2.0×109
0.1A 2.0×109 2.0×109 2.0×109 2.0×109
0.2A 2.0×109 2.0×109 2.0×109 2.0×109
0.5A 2.0×109 2.0×109 1.6×109 8.0×108
1A 2.0×109 1.6×109 8.0×108 4.0×108
2A 1.6×109 8.0×108 4.0×108 2.0×108
5A 6.4×108 3.2×108 1.6×108 8.0×107
10A 3.2×108 1.6×108 8.0×107 4.0×107
20A 1.6×108 8.0×107 4.0×107 2.0×107
50A 6.4×107 3.2×107 1.6×107 8.0×106
100A 3.2×107 1.6×107 8.0×106 4.0×106

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