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Isolated current
and voltage transducers
Characteristics - Applications - Calculations

LEM provides multidisciplinary know-how
and solutions for power electronic
measurement in key economic segments
such as Energy, Transportation, Industry,
Automotive, R&D, Engineering, Medical,
Environmental, and Test Facilities.

The top priority of LEM is a commitment
to the quality of our products andservices.
This, together with a combination ofdesign, manufacturing, test, andcustomer service competencies, ensuresthe long-term success and satisfaction of
our customers.

2Isolated Current and Voltage Transducers
Characteristics - Applications - Calculations

1

Optimal solutions with 6 different
technologies of LEM transducers

4

2.1
2.2
2.3
2.4
2.5
2.6
2.7

Determining parameters for transducer
selection
Which parameters need to be considered ?
Understanding the LEM documentation
Additional selection criteria
Current transducers – selection check list
Voltage transducers – selection check list
Power transducers – selection check list
Type of output

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6
8
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3
3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.1.6
3.1.6.1
3.1.7
3.1.7.1
3.1.7.2
3.1.7.3
3.1.7.4
3.1.8
3.1.9
3.1.10
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.2.9
3.2.103.2.11
3.2.12
3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.5

Hall effect technologies
Open loop Hall effect current transducers
Construction and principle of operation
Advantages and limitations
Nominal and extreme currents
Output signals
Measurement accuracy
Magnetic offset considerations
Demagnetization to eliminate magnetic offset
Bandwidth and core losses
Core losses
Core loss rule-of-thumb
A core loss example
Addressing core losses
Response time, delay time, and di/dt behavior
Typical applications
Calculation of the measurement accuracy
Closed loop Hall effect current transducers
Construction and principle of operation
Advantages and limitations
Nominal and extreme currents
Output signal – Measurement resistance
Measurement accuracy
Observations regarding magnetic offset
Bandwidth and core losses
Response time and di/dt behavior
Typical applications
Transducer parameter examples
Calculation of the measurement accuracy
Unipolar power supply
Eta Technology Hall effect current transducers
Construction and principle of operation
Advantages and limitations
Nominal and extreme currents
Output signal
Measurement accuracy
Dynamic behavior
Typical applications
Closed loop Hall effect voltage transducers
Construction and principle of operation
Voltage transducer with internal resistor
Voltage transducer without internal resistor
Transducer Output
Typical applications
Other Hall effect voltage transducers

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2

4
4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.2
4.3
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5
4.4.6
4.5
4.5.1
4.5.2
4.5.3
4.5.4

Fluxgate technologies
Working principle of Fluxgate technologies„Standard“ Fluxgate – working principle
Sensing head – a current response to a voltage step
Detecting the sensing head inductance variation
Current transformer effects
Existing types of Fluxgate transduers
General performance of Fluxgate technologies„C-type“ Fluxgate transducers
Construction and principle of operation„CT-type“ current transducers„CD-type“ differential current transducers„CV-type“ voltage transducers„C-type“ transducers - typical applications
Calculation of the measurement accuracy &noise rejection„IT-type“ Fluxgate transducers
Construction and principle of operation„IT-type“ transducers – advantages & limitations„IT-type“ transducers - typical applications
Calculation of the measurement accuracy

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5
5.1
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.3
5.3.1
5.3.2
5.3.3

Air-core technologies
Basic working principle and sensitivity
LEM~flex - the flexible AC current transducer
Construction and principle of operation
Characteristics and features
Typical applications
Calculation of the measurement accuracy
PRiMETM Transducers
Construction and Principle of Operation
Characteristics and Features
Advantages and Limitations of PRiME Technology

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6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4

Other types of voltage transducer
technolo gies
OptiLEM voltage transducers„AV type“ voltage transducers
Construction and Principle of Operation
Characteristics and Features
Typical applications
Calculations & Properties

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7

Current probes

41

8
8.1
8.2
8.3
8.4
8.5

Miscellaneous
Power supply polarity inversion
Capacitive dv/dt noise
Magnetic disturbances
Typical misapplication of a transducer parameter
LEM ASIC based transducers

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9

LEM – the leader in electrical parametermeasurement

44

Glossary A-Z

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3

Optimal Solutions with 6 Different Technologies of LEM Transducers

1• Fluxgate transducers, which include „IT-types“, „C-types“,„standard types“, and „low frequency types“

Optimal solutions with 6 different technologies
of LEM transducers• Air-core transducers, which include LEM~flex(Rogowski) and PRiME™ transducers

Since 1972 LEM has been able to respond to customer
demands, creating a wide range of galvanically isolated
current and voltage transducers that have become
standards in the measurement field. Our customers areoffered a wide range of LEM transducers to meet theirneeds, based on the application requirements and transducer performance. This document is intended to provide
our customers with a technical background to allow them todetermine the best transducer to meet their needs.

• Various voltage transducers, which include Hall effect,
Fluxgate, the AV and OptiLEM™ products
The key attributes of these technologies are summarized inTable 1.
Finally, while most applications will find their best solution
with a standard transducer selected from one of thesetechnologies, LEM is fully capable of developing customized
solutions to meet customer specific requirements. A reviewof this application note will allow the customer to better
understand the critical aspects of transducer design,
determine the closest standard device for the application,and better communicate the specific requirements of acustom device to LEM.

We will begin by splitting the LEM transducer portfolio into
four main categories covering six different technologies,
discussed in detail later in this document:• Hall effect transducers, which include closed loop, open
loop, and Eta™ transducers

Table 1: Overview of the various LEM transducer technologies with their corresponding main characteristics
Hall effect technologies ①

Current
measurement

Fluxgate technologies ①

Air-core technologies ②

Closed-Loop‘Eta’ types

Open-Loop

IT-types

C-typesLowfrequency
types (CTS)

Standard
type

LEM-flex

PRiME™

25 to 150 A

0 to 10 kA

0 to 10 kA

Measuring
range

IP

0 to 15 kA

0 to 15 kA

0 to 600 A

0 to 150 A

0 to 400 A

0 to 500 A

Bandwidthf0 to 200 kHz 0 to 100 kHz 0 to 25 kHz

0 to 100 kHz

0 to 500 kHz

0 to 100 Hz

0 to 200 kHz

10 Hz to 100 kHz

Typ. response td
time (@ 90 %)< 1 µs< 1 µs< 3-7 µs

< 1 µs

< 0.4 µs

< 5 ms< 1 µs10 to 50 µs

2 to 50 µs

Typ. accuracy X
at 25 °C, in %of IPN±0.5 %±1.5 % (DC)±0.5 % (AC)±1.5 %±0.0002 %±0.1 %±0.1 %±0.2 %±1.0 % ③±0.5 % ③

Linearity-±0.1 %±0.5 % (DC)±0.1 % (AC)±0.5 %±0.0001 %±0.05 %

±0.1 %±0.1 %±0.2 %±0.2 %

Highlights-

Accuracy
Speed

Speed
Low power Best resolution High resolution Resolution
Resolution
Low power Small size Best accuracy High accuracy
Accuracy
Accuracy
Low voltage Low cost
Speed
Best speed Low frequency
Speed
(5V)
Low cost

Accuracy
Accuracy
Bandwidth
Bandwidth
Light weight Light weight
AC only
AC only① The Hall effect and Fluxgate attributes shown are based on a „solid core“ (non-opening) implementation. Split core (opening) versions are alsoavailable with reduced specifications.
② LEM~flex is a „split core“ device, implying that it can be opened to place around the conductor(s) to be measured. PRiMETM can also be
designed for split-core operation which does not affect the performances.
③ The accuracy of air-core technologies is given in percent of reading (above 10% of nominal current) rather than percent of nominal current.

Voltagemeasurement
Measuring range

Electronic Isolated
AV 100

Optically isolated
OptiLEM

VPRMS

0 to 9.5 kV

0 to 7 kV

50 V to 2 kV

100 V to 6 kV

BandwidthfSeveral kHz

0 to 2/10/800 kHz ④

0 to 13 kHz

0 to 13 kHz

Typical responsetime (@ 90%)td

10 to 100 µs

0.4µs< 30 µs< 30 µs

Typical accuracy at
25°C, in % of VPN

X

±1 %

±0.2 %±0.7 %±0.9 %

Linearity-< 0.5 %

±0.05 %

±0.1 %±0.1 %

Highlights-

Standard performanceHigh accuracy
Best speed
Low speed

Small size
Limited voltage
Low speed

Excellent EMI immunity
High common mode rejection
High isolation capability
Low speed④ Design dependent

4

Hall effect technologies Fluxgate technologies
Closed loop
C typesVoltage Transducers and Basic Working Principle

2

Determining parameters for transducer
selection

The wide variety of available LEM transducers is the direct
result of our know-how and many years of experience,
enabling us to address the many variations of customer
requirements within the greatly diversified field of powerelectronics. The application requirements create selection
criteria, guiding the user to an appropriate product.
2.1

Which parameters need to be considered?

2.2

Understanding the LEM documentation

The first step for transducer selection is a detailed understanding of the application, including parameters such ascontinuous RMS and repetitive peak measurement level,maximum possible peak or fault level, rate of change(e.g. di/dt and dv/dt) to be measured, allowable response
time, etc. One must also consider external influences thatwill impact the application, such as temperature, shock,vibration, and external fields as well as any necessary
compliance standards (EN, IEC, UL, CSA, etc.) that need tobe met.

The selection of a transducer is the result of a technical andeconomic trade-off, considering the transducer as well as
the associated sub-systems. All aspects of an applicationmust therefore be taken into account during transducer
selection and system design, with particular attention to thefollowing:

Using this information, refer to the general catalog of LEM
transducers to locate the product line(s) that have the key
characteristics to meet the requirements from the full rangeof available products. Then select the specific product(s)from those lines that meet the measurement requirements.

• electrical requirements, including power supply
requirements, peak measurement, response time, di/dt,
dv/dt, etc.

The individual datasheet (see the LEM website: http://
www.lem.com) of the selected transducer(s) will thenprovide more details to determine if the transducer(s) matchthe requirements. The checklist provided in the following
tables (§2.4 and §2.5) may help define critical concerns andassist in the transducer selection process.

• mechanical requirements, including aperture size, overall
dimensions, mass, materials, mounting, etc.
• thermal conditions, including current profile versus time,
maximum RMS measurement, thermal resistances,cooling, etc.
• environmental conditions, including vibration,
temperature, proximity of other conductors or magnetic
fields, etc.

2.3

Additional selection criteria

As previously discussed, some applications have a higher
level of complexity and combine several potentially criticalelements such as:• electromagnetic interference

The transducer development process includes a full regimenof tests that comprise the characterization report. These tests
follow the scientific method, varying individual parameters tocharacterize the transducers response to each.
During production a quality plan indicates the tests to be
carried out, on each product or batch of products, to verify
compliance with specifications. Unless otherwise specified,
performance is tested under nominal conditions of current,
voltage, temperature, etc. in the production and laboratoryenvironments.
In the actual application, several factors can act simultaneously and potentially provide unexpected results. It isessential to assess the transducer in those conditions toverify acceptable performance. Based on LEM experiences,
this assessment is typically not difficult if the working
conditions are known and defined.

• significant common mode voltage transients (dv/dt)• mechanical disturbances (vibration, shock, etc.)• special isolation or partial discharge requirements• compliance with specific standards, etc.
Obviously the best scenario is to perform tests in the specificapplication environment. If this is not reasonable or feasible,
provide LEM with a diagram of your installation and adetailed description of the transducer operating conditions(e.g. description of the environmental conditions, graph of
the waveform to be measured, nearby potentially disturbing
elements such as inductors, current carrying conductors, thepresence of magnetic materials or the desired location ofother transducers).

The operating temperature range is based on the materials
and construction of the selected transducer. The minimum
temperatures are typically -40, -25, or -10 °C while themaximums are +50, +70, +85, or +105 °C.

5Determining Parameters for Transducer Selection

2.4

Current transducers – selection check list

Electrical parameters

Selection criteria

Type of current to be measured- DC, AC or complex waveform current- Selection of the adequate technology (Table 1)

Range of current to be measured- Nominal current to be measured- Peak current to be measured- Transient current overloads to be measured- Maximum peak value and duration not measured

Required output signal- Current or voltage output- Output value at nominal or peak current- For current output transducers, selection of the necessary or desired output load
impedance

Measurement accuracy- Required accuracy at 25 °C, taking into account the DC offset and non-linearityof the output signal- Global accuracy within the operating temperature range, adding the accuracy at
25 °C, the offset drift and, if applicable, the gain drift.

Available power supply- Power supply voltage, including tolerances- Maximum allowable current consumption

Voltage- Primary working voltage- Applicable standard for isolation (design or test)- Compliance to the relevant standards- Single or reinforced insulation- Dielectric withstand voltage (e.g. 4 kVRMS, 60 Hz, 1 min.)- Pollution degree (e.g. class 2)- Over voltage category (e.g. 0V cat. 1)- Impulse withstand voltage (e.g. 8 kV with 1.2/50 µs)- Partial discharge extinction level and electric charge

Dynamic operating parameters

Selection criteria

Frequency range- Frequency range to be measured- Fundamental operating frequency- Harmonic content (e.g. drive’s switching frequency)- Current Harmonics not to be measured but likely to create transducer losses(e.g. drive’s ringing current)

di/dt- Match between the di/dt to be measured and the transducer’s response and risetimes (Figure 8)- Maximum possible di/dt overloads, to be withstood by the transducer, but not tobe measured- Maximum transducer recovery time after a di/dt overload

dv/dt- Maximum error allowed during dv/dt disturbance- Maximum transducer settling time after a dv/dt disturbance6

Determining Parameters for Transducer Selection

Environmental parameters

Selection criteria

Temperatures- Minimum and maximum working temperatures where the transducer
performance is applicable- Extreme storage temperatures

Vibration & shock- Standards and levels to be considered (when applicable)

Presence of external fields- External current identical to the one being measured- Other currents of similar or greater amplitude- Fields from transformers or inductors- Fields from magnetized materials in the area

Mechanical Interfaces

Selection criteria

Primary electrical connection- Printed wiring board (PWB/PCB) pins
- Through-hole aperture size and shape- Busbar dimensions- Other connections (e.g. screw terminals)

Secondary electrical connection- Printed wiring board pins
- Connector- Faston tabs
- Screw lugs
- Other connections (e.g. screw terminals)

External dimensions- Maximum specified dimensions- Aperture / primary location- Connector / secondary location- Required creepage / clearance distances

Package fastening- Printed circuit mount- Panel mount- Aperture (cable or busbar) mount- DIN rail mount7

Determining Parameters for Transducer Selection

2.5

Voltage transducers – selection check list

LEM produces a wide variety of galvanically isolated voltage
transducers capable of measuring up to 9.5 kV. These arebased on four different technologies, with different
performances, as outlined in Table 1.
The selection criteria for a current transducer are also
applicable to voltage transducers, especially when thevoltage measurement is based on a ‘current measurement
principle’, as described later in § 3.4. The main difference
lies in the primary parameters which affect the link between
the voltage to be measured and the current, IMES, detected by
the transducer (Figure 21), namely the effect of the series
resistance R1 and the parameters linked to the transducer
primary impedance. This leads to the following additional
selection criteria:

Electrical parameters

Selection criteria

Measurement accuracy- The transducer’s primary resistance and series resistanceR1 (built-in or external), taking into account the effect ofthe manufacturing tolerances and temperature variations

Power budget- The total power lost from the primary circuit due to power
dissipation in the primary measuring circuit- The selected series resistor, R1, shall be capable ofdissipating many times the nominal power

Dynamic operating parameters

Selection criteria

Bandwidth / response time

- Dependent on the L / R time constant of the primary circuit,the series combination of primary inductance (LP), theprimary resistance (RP), and the series resistance (R1)

2.6Power transducers – selection check list

The combination of current and voltage transducer in asingle device creates an instantaneous power transducer.
The selection criteria for this device are identical to thosepreviously listed for current and voltage transducers. There
will be a limitation on bandwidth and response time toensure proper multiplication of the signals.
2.7Type of output

The output of a LEM transducer typically represents theinstantaneous primary signal, providing both output scaling
and isolation. Transducers may also provide average, peak,sine-wave RMS, or true RMS output(s).
The secondary signal can be a current, voltage, current loop
(4-20mA), or digital output. This signal will have an offset
level, the output with no primary signal, and a range, theoutput swing with a change in primary signal. These can bematched to a specific interface, such as the A/D converter ofa DSP or microprocessor (Figure 1).
Devices can be ratiometric, implying that the offset level and/or output range are dependent on the power supply or areference input voltage. This is ideal when driving an analog
to digital converter (ADC) or other reference based
electronic processing circuitry, allowing the output to trackthe external reference, minimizing drift between thetransducer and this reference. Alternatively, the internal
8

Figure 1: Output curve of the LTS and HTS product families

reference of the transducer may be provided to act as areference source for other electronic processing circuitry,
potentially eliminating a discrete reference source.
Loop powered devices are also available. These are two
wire devices that obtain their power from a 4-20mA current
loop and provide a variable current load to represent theoutput signal. These operate with a voltage drop across thetransducer to power the internal circuitry, which must be
taken into account when supplying the loop.

Hall Effect Technologies

Conversion of a current output to a voltage is easily
accomplished by the user with the addition of a measurement resistor, RM, in series with the output. This allows theuser to easily scale a single device to the desired output
level. There is a range of acceptable RM values dependent
on the operating parameters of the application with the
maximum value limited by available voltage and a minimum
value required to limit the internal power dissipation. The
transducer datasheet provides a range of values based on
nominal parameters.

3

Hall effect technologies

Three of the LEM technologies (open loop, closed loop andEta) are based on the Hall effect, discovered in 1879 by
American physicist Edwin Herbert Hall at Johns Hopkins
University in Baltimore. The Hall effect is created by Lorentz
forces, FL = q • (V x B), which act on charges moving througha magnetic field.

3.1

Open loop Hall effect current transducers

Open loop transducers use the simplest implementation of
the Hall effect. They provide the smallest, lightest, and most
cost effective current measurement solution while also
having very low power consumption.
3.1.1 Construction and principle of operation
A current carrying conductor creates a magnetic field. This
field is concentrated by a magnetic core. The core has a gap
cut through it and a hall generator is used to sense themagnetic flux density in the gap. The control current, IC, anddifferential amplification are supplied by electronics (Fig. 3)
built into the transducer.

IP
IC
Figure 3: Conversion of the primary current into an output voltage

Figure 2: Representation of the electrical parameters of the Hall
effectA thin sheet of conducting material is traversed lengthwise
by a control current, IC (Fig. 2). The mobile charge carriers of
this current are affected as the external magnetic flux, B,
generates a Lorentz force, FL, perpendicular to the directionof current flow. The resulting deflection of current causes
more charge carriers to be located at one edge of the sheet,creating a potential difference referred to as the Hall voltage,
VH. For the arrangement described above, with the magnetic field, current, and sheet edges mutually perpendicular,
we obtain:

Within the linear region of the hysteresis loop of the material
used for the magnetic circuit (Fig. 4), the magnetic flux
density, B, is proportional to the primary current, IP, and theHall voltage, VH, is proportional to the flux density. Therefore
the output of the Hall generator is proportional to the primary
current, plus the Hall offset voltage, VOH.

VH = K / d • IC • B + VOH
where ‘K’ is the Hall constant of the conducting material, ‘d‘
is the thickness of the sheet, and ‘VOH’ is the offset voltage ofthe Hall generator in the absence of an external field. Suchan arrangement is referred to as a Hall generator and the
product ‘K / d • IC’ is generally referred to as the Hall
generator sensitivity.
The sensitivity and offset voltage of Hall generators aretemperature dependent. However, these effects can begreatly compensated by the biasing and amplificationelectronics driving and sensing the Hall generator.

LinearRegionFigure 4: Magnetization curve

The measurement signal is then compensated to remove theoffset component and address temperature effects andamplified to supply the user with the desired output.
In the case of low current measurement (< 50 A) multiple
turns are recommended or implemented internally toachieve 50 Ampere-turns nominal providing reasonable flux
density levels for measurement.
9

Hall Effect Technologies

3.1.2 Advantages and limitations• gain error (current source, hall generator, core gap)
• linearity (core material, hall generator, electronics)

Open loop transducers measure DC, AC and complex current
waveforms while providing galvanic isolation. As mentioned
earlier, the advantages include low cost, small size, lightweight, and low power consumption and are especiallyadvantageous when measuring high (> 300 A) currents. As
with most magnetic based measurement techniques,insertion losses are very low. Primary current overloads canbe easily handled although it may result in somemagnetization of the core creating an offset shift, calledremanence or magnetic offset (§ 3.1.6).
Compared to other technologies the limitations of open looptransducers are moderate bandwidth and response time, alarger gain drift with temperature, and a limitation on thecurrent frequency product (power bandwidth).
In many applications the advantages outweigh the limitations
and an open loop solution is advised.
3.1.3 Nominal and extreme currents
LEM open loop transducers are made for nominal currents,
IPN, from several amperes to 10 kA, with a peak current rating
up to 30 kA. This wide range of products addresses virtually
all of the industrial requirements.
The maximum current an open loop transducer can measure
is dependent on the design and material used for the magnetic circuit and on the design of the processing electronics.
In general, LEM open loop transducers are designed suchthat the maximum measurable current is 200 % to 300 % of
the nominal RMS current rating.
Even so, open loop transducers can withstand current
overloads significantly beyond the maximum measurable
value, for example 10 times the nominal current. However, as
described earlier, this can create a magnetic offset resulting
in an additional measurement error, to be removed byapplying a dedicated demagnetization procedure.
3.1.4 Output signals• output noise floor (hall generator, electronics)• bandwidth limitation (attenuation, phase shift,current frequency)
Temperature changes also create drift in:• DC offset• gain
LEM transducers are factory calibrated at nominal temperature and nominal current, leading to the „accuracy at 25 °C“given in the LEM datasheets. The datasheet also provides
the temperature drift specifications.
The location of the primary conductor through the aperture
as well as the positioning of the return conductor can affectdynamic performance of the transducer. LEM generally
recommends an optimal routing / position for the primaryand return conductors. In addition, high frequency
disturbances can affect the transducer output due tocapacitive coupling, so the routing and layout of the transducer output must be considered (e.g. twisted and shieldedcables, appropriate routing of the output PWB tracks).
3.1.6 Magnetic offset considerations
Depending on the type of transducer and the magnetic
material used, the residual flux (BR or remanence) of themagnetic core induces an additional measurement offset
referred to as ‘magnetic offset’. The value depends on theprevious core magnetization and is at a maximum after themagnetic circuit has been saturated. This might occur after ahigh overload current.
As an example, measurements carried out on the HAL and
HTA types of open loop transducers give the following
results: after a cycle of current varying from 0 to 300 % of IPN
and then back to zero, the magnetic offset is 2.5 mV for HAL
transducers and 3 mV for HTA transducers, less than 0.1 %of the nominal output, VSN.

The output of an open loop transducer is generally a voltage
directly proportional to the measured current. This voltage istypically equal to 0V without primary current and 4V at thenominal current, IPN. Variations are possible, including
different offset, and/or nominal values or a current output.

In the case of a higher current overload (e.g. 1000 % of IPN),a larger magnetic offset error may occur. Recovering fromthis condition requires demagnetization, either byappropriate reversal of the primary current or a dedicateddegauss cycle. This process will return the transducer to theinitial, pre-overload, performance.

3.1.5 Measurement accuracy

3.1.6.1 Demagnetization to eliminate magnetic offset

The typical open loop transducer has an overall accuracy of afew percent. There are a number of error terms that combine
to create this error, at nominal temperature (25°C) and acrossthe temperature range.

The elimination of magnetic offset requires demagnetization.
A degauss cycle requires driving the core through the entire
B-H loop with a low frequency AC source, then gradually
decreasing the excitation returning the B-H operating point
to the origin (Fig. 5). As a minimum, provide 5 cycles at full
amplitude and then decrease the excitation smoothly nofaster than 4 % per cycle, requiring 30 cycles or 500 ms at
60 Hz. For closed-loop devices, additional care must be
taken to be sure the compensation coil does not negate thedemagnetization effort (see § 3.2.6).

The accuracy is limited by the combination of:• DC offset at zero current (hall generator, electronics)• DC magnetic offset (remanent magnetization of corematerial)
10Hall Effect Technologies

Demagnetization current> 5 cycles

>3
0c
ycl
es

Figure 5: Degauss cycle current

Alternatively, a partial demagnetization of the core is possible
by providing an appropriate signal in the opposite polarity ofthe magnetization. The difficulty is determining the exact
amplitude and duration to obtain a satisfactory result. With awell-defined application it may be feasible to determine therequired value empirically and apply this correction asnecessary.
3.1.7 Bandwidth and core losses
The bandwidth limitation of open loop transducers is mainly
due to two factors:• limitations of the processing electronics• magnetic core heating due to core losses, a combination ofeddy current and hysteresis losses
3.1.7.1 Core losses
The magnetic material and core design as well as the current
amplitude versus frequency spectra define the level of corelosses:• eddy current losses are proportional to the square of threedifferent parameters: the peak flux density in the core, thefrequency of induction and the lamination sheet thicknessof the core
• hysteresis losses are proportional to frequency, core
volume and the square of peak flux density
For LEM transducers, this leads to the following conclusions:• core losses become significant at high frequencies and it
is essential to limit the current amplitude at thesefrequencies to acceptable levels (dependent on ambientand maximum transducer temperatures); this implies not
only limiting the maximum frequency of the fundamental
current, but also harmonic content, since even a low
amplitude signal may create unacceptable losses at highfrequencies.
3.1.7.2 Core loss rule-of-thumbs
Iron losses calculation are complex and, as a „rule-of-thumb“
judgment, it is possible to consider that the iron losses areminimized if the product "N • I • f" is kept as small as
possible, where:
N = number of internal or external primary turns
I = primary current or amplitude of a current harmonicf = frequency of the primary current or current harmonic
As a result, when one of the three factors is increased (i.e.
the current), the iron losses are increased unless at least
one of the two other factor is decreased (i.e. the frequency ofthe measured current and/or the number of primary turns).
While this formula implies that the core losses will increase
with an increase of any of these parameters, it is notintended to say that acceptable core losses are realized if
the product of the three parameters is kept constant. For
example, it is wrong to say that one can operate at twice thefrequency if the Ampere-turns are cut in half.
At a given frequency, it is nevertheless correct to assume
that keeping constant the "N • I" product implies similar ironlosses, even the probable change on the primary conductor
magnetic coupling may affect the iron losses value.
To conclude, trouble-free operation of a current transducer
requires limiting the temperature rise to avoid overheating
the internal components. Parameters affecting temperaturerise go beyond core losses and include the primary busbar
resistive losses, the losses of the electronics and the various
thermal resistances. In particular, to keep losses constantrequires to decrease the transducer primary current while
the working frequency increases.
3.1.7.3 A core loss example
Considering the LEM open loop HY 10-P transducer, where
the primary is integrated into the transducer and the numberof primary turns cannot be changed, tests show the following
maximum working conditions:• these losses are directly proportional to the square of theflux density, which is directly related to the primary ampereturns, implying core losses are theoretically proportional to
the square of primary ampere-turns if no magnetic
saturation occurs. When increasing sensitivity by using
multiple primary turns, core losses are increased by thesquare of the turns

11Hall Effect Technologies

At an ambient temperature of 25 °C
IP

fmax

N•I•f

10 A
6A
2A

13 kHz33 kHz340 kHz

130,000
198,000
680,000

At an ambient temperature of 70 °C
IP

fmax

N•I•f

10 A
6A
2A

6 kHz
12 kHz90 kHz59,00072,000180,000

Obviously these values are far from constant, but they can beconsidered as limits for acceptable operation. Even so, thistransducer cannot operate above 50 kHz as limited by the
maximum bandwidth (3dB) of the electronics.
3.1.7.4 Addressing core losses
Often the adverse effects of core losses are not considered orcannot be predicted accurately during the initial design
stages. Therefore many designers find themselves in adifficult situation when a design, or a specific application ofthat design, causes overheating of the transducer due to corelosses. There are solutions to this problem, but a carefulanalysis of the tradeoff between reducing core losses andmaintaining acceptable response time of the transducer isrequired.
Although the insertion loss of a transducer is extremely low
this impedance is, in fact, a combination of the resistance andinductance of the primary. Placing a series resistor-capacitor
in parallel with the primary (Fig. 6) diverts the high frequency
components of the current around the primary, significantly
reducing core losses. This also removes these frequencies
from the measurement path increasing the response time. An
example is shown in Fig. 7 where the VOUT response of the
HX 15-NP transducer is given, with and without parallel
resistor R (C = 0).

Figure 7: HX 15-NP transducer response

response, also called di/dt following (the transducers ability
to follow a fast change in primary current).
LEM defines the response time tr as the delay between the
primary current reaching 90 % of its final value and thetransducer reaching 90 % of its final amplitude (Fig. 8). The
primary current shall appoximately behave as a current step,with an amplitude close the nominal current value.
This is actually the combination of three effects: the input risetime (from 10 % input to 90 % input, also called di/dt), the

I[A]
IN

90 % of IN
IPIS
IP: primary reference
current
Responsetime tr

10 % of IN

IS: secondary currentof the LEM

Rise time
Reaction time trat [µs]

Figure 8: Definition of the transient response parameters3.1.8 Response time, delay time, and di/dt behavior
Three different criteria are used to characterize the dynamic
behavior of a transducer: bandwidth, response time, and step

reaction time tra (from 10 % input to 10 % output), and theoutput rise time (from 10 % output to 90 % output, also called
slew rate).
Open loop transducer response is dependent on the transducer design and the magnetic coupling of the signal to bemeasured, as well as those not to be measured. The latter
places some responsibility on the user to investigate thecoupling effects and determine the appropriate placement of
the primary and other conductors to optimize the response of
the transducer in the application. Careful consideration of thecabling in and around the transducer usually resolves
response time and di/dt performance problems.
Fig. 9 shows the response of a HAL 600-S transducer, wherea slight difference between the input and output currents canbe noticed at the corners. In this case, the response time isless than 3 µs with a di/dt of 50 A/µs.

Figure 6: Schematic of high frequency bypass

12

Hall Effect Technologies

600 A-50 A/µs

0Figure 9: Dynamic behavior of an HAL 600-S transducer at 600 A

3.1.9 Typical applications
Open loop current transducers are used in numerous
industrial applications as the key element of a regulation loop
(e.g. current, torque, force, speed, position) or simply to drive
a current display.

two values are independent because the accuracy (40 mV)
is confirmed with an AC signal while the offset (10 mV) is a
DC measurement. Therefore, when measuring a 200A DC
current at 25 °C the output could be in error by as much as
50 mV, which is 1.25 % of the 4 V output.
Operating at a different temperature causes both offset andgain drift. The maximum offset drift is specified as 1 mV/K
and the maximum gain drift is 0.05 %/K. When we operate
the transducer at 85 °C there can be an additional 1 mV/K • (85 – 25) °C = 60 mV of offset voltage and 0.05%/K •4 V • (85 – 25) °C = 120 mV of gain drift. The total error fromall of these effects is 230 mV, or 5.75 % of the nominal 4 V
output.
3.2

Closed loop Hall effect current transducers

Typical applications include:

Compared to the open loop transducer just discussed, Hall
effect closed loop transducers (also called Hall effect‘compensated’ or ‘zero flux’ transducers) have acompensation circuit that dramatically improves
performance.

• frequency inverters and 3-phase drives, for the control of
the output phase and DC bus currents

3.2.1 Construction and principle of operation• power factor correction converters, for monitoring of themains current(s)• electric welding equipment, for the control of the welding
current• uninterruptible power supply (UPS) or other battery
operated equipment, for the control of charge and discharge
currents• electric vehicles, for motor drives and battery current control

While open loop current transducers amplify the Hall
generator voltage to provide an output voltage, closed looptransducers use the Hall generator voltage to create acompensation current (Fig. 10) in a secondary coil to create
a total flux, as measured by the Hall generator, equal tozero. In other words, the secondary current, IS, creates a flux
equal in amplitude, but opposite in direction, to the flux
created by the primary current.

• electric traction systems, trackside circuit breaker andrectifier protection, rolling stock traction converters andauxiliaries

IS• energy management systems, switching power supplies,
electrolysis equipment, and other applications
3.1.10 Calculation of the measurement accuracy
As indicated previously, the accuracy indicated in thedatasheets applies at the nominal current at an ambient
temperature of 25 °C. The total error at any specific current
includes the effects of offset, gain, non-linearity, temperatureeffects and possibly remanence. The LEM datasheet provides
the worst-case value of each of these factors individually.
The theoretical maximum total error corresponds to the
combination of the individual worst-case errors, but in practicethis will never occur.

I PP
IC

IISS
Figure 10: Operating principle of the closed loop transducer

Example: Current transducer HAL 200-S (see datasheet)
In this example it is assumed the power supplies are accurate
and stabilized and magnetic offset is negligible. A current of
200A is measured at an ambient temperature of 85 °C.

Operating the Hall generator in a zero flux condition
eliminates the drift of gain with temperature. An additional
advantage to this configuration is that the secondary winding
will act as a current transformer at higher frequencies,
significantly extending the bandwidth and reducing the
response time of the transducer.

The datasheet indicates the output voltage is 4 V at the
200 A nominal current. The worst-case accuracy at IPN, 25 °C
and with ±15 V supplies is 1 %, or 40 mV. In addition there isa maximum offset voltage at Ip = 0 and 25 °C of 10 mV. These

When the magnetic flux is fully compensated (zero), themagnetic potential (ampere-turns) of the two coils are
identical. Hence:
NP • IP = NS • IS which can also be written as IS = IP • NP / NS
13

Hall Effect Technologies

Consequently, the secondary current, IS, is the exact imageof the primary current, IP, being measured. Inserting a„measurement resistor“, RM, in series with the secondary coil(Fig. 10) creates an output voltage that is an exact image ofthe measured current.
To give an order of magnitude, the typical number of
secondary turns is NS = 1000…5000 and the secondary
current is usually between IS = 25…300 mA, although it
could be as high as 2 A. For higher output currents an
output power stage is needed to produce the transducer
output current.
At low frequencies the transducer operates using the Hall
generator. At higher frequencies the secondary coil operates
as a current transformer, providing a secondary output
current again defined by the turns ratio and converted to a
voltage by the measuring resistor. These effects areillustrated in Fig. 11.
Frequency limitof the electronics

Currenttransformer area

V

Figure 11: Bandwidth of the „Hall generator“ and „current
transformer“

The unique design of closed loop transducers provides an
excellent bandwidth, typically from DC to 200 kHz. The
challenge is to ensure a flat frequency response across theentire range, especially where the two response curves cross,to provide excellent dynamic response and accuracy for all
possible signals.
Finally, while closed loop transducers work theoretically atzero flux, various magnetic imperfections (leakage flux, nonperfect coupling) imply a residual flux into the core which
results in iron losses at high frequencies. Consequently, theheating phenomena described in § 3.1.7 for open-looptransducer also applied in this case, even if much lesssignificantly.
3.2.2 Advantages and limitations
Closed loop transducers are capable of measuring DC, AC
and complex current waveforms while ensuring galvanic
isolation. The advantages of this design include very good
accuracy and linearity, low gain drift, wide bandwidth, andfast response time. Another advantage is the output current
signal that is easily scalable and well suited to high noise
environments; nevertheless, closed loop transducers areavailable in voltage output configurations. Again, as with mostmagnetic based measurement techniques, insertion losses
are very low.
14

The main limitations of the closed loop technology are thehigh current consumption from the secondary supply (whichmust provide the compensation as well as bias current), thelarger dimensions (more noticeable on high current
transducers), a more expensive construction compared withthe simpler open loop designs and a limited output voltage
due to the internal voltage drops across the output stage andsecondary coil resistance.
Again, depending on the application requirements, theadvantages often outweigh the limitations and the accuracy
and response of a closed loop solution is desirable over otheralternatives.
3.2.3 Nominal and extreme currents
LEM closed loop current transducers are available in models
with nominal currents from 2 A to more than 20 kA. Specificdesigns even allow current measurements up to 500 kA.
With closed loop technology the maximum measurable peakcurrent is typically 150 to 300 % of the nominal current rating.
For a given closed loop transducer, the maximum peakcurrent which can be measured can be defined in threedifferent ways:• from DC to mid-frequencies (in the closed loop
compensation mode, § 3.2.1), the maximum measurable
current is limited by the ability of the electronics to drivecompensation current, IS, in the secondary coil; this limit isbased on the available supply voltage, internal voltage
drops, and current through the total series resistance andexceeding this limit at low frequency will result in „electronic
saturation“• also, each transducer is designed for a specific measurable
current range and exceeding the transducer ratings will
result in non nominal magnetic effects (excessive fringing)that does not allow the electronics to properly compensate
the loop resulting in „magnetic saturation“• for transient currents at higher frequencies the transducer
operates as a current transformer and the current can reachhigher values, limited by magnetic (pulse duration inampere seconds) and thermal (core losses related toampere-hertz) constraints; the transducer user should
consult LEM when considering working in the transformer
mode, beyond the limits set in LEM datasheets.
In some specific LEM transducer types (e.g. the LTS family),primary currents exceeding the peak measuring range cancreate abnormal, though non-destructive, results due to theunique electronic configurations.
In case of current overload, a too long overload duration (e.g.
> 1 ms) may in some case start to overheat the snubber which
protects the transducer against short time overloads.
3.2.4 Output signal – Measurement resistance
The majority of closed loop transducers have a current output
that can be easily converted to a voltage for measurement byadding a measurement resistor in series with the output.
Refer to § 2.7 for more details.

Hall Effect Technologies

3.2.5 Measurement accuracy
Due to the closed loop working principle, operating at nearlyzero flux (some flux remains due to system loop gain andmagnetic leakage phenomena), LEM closed loop current
transducers have excellent linearity and minimal gain drift
over a wide measuring and temperature range, with total
accuracy typically remaining below 1 %.
At ambient temperature, the accuracy is given by the
combination of:• if one or both of the secondary supply voltages are missing,disabling the electronic compensation process, there will nolonger be zero flux compensation• when an external conductor creates localized core
saturation, not totally detected by the Hall generator andcompensated by the electronics, the total flux in different
areas of the core will be non-zero
If any of these conditions occur the result could be magnetic
offset, resulting in an additional measurement error. This canbe corrected with demagnetization (§ 3.1.6.1).

• output offset at zero primary current (IP = 0)
• non-linearity of the Hall generator, electronics, andmagnetics• gain tolerance (tolerance of the number of secondary coilturns)• tolerance of the measuring resistor, RM (internal or external)
And temperature changes imply:• offset drift (or with respect to the reference voltage, if
appropriate)• drift of the measuring resistor value, RM
While those factors may be simple to assess for DC current,
AC signals and complex waveforms may have their total
accuracy affected by transducer bandwidth limitations(Fig. 11), possibly introducing frequency attenuations andphase shifts.
To make the best use of the transducer, the mounting
conditions must be such that it optimizes the primary to
secondary magnetic coupling, specifically for AC signals
where the transducer works as a current transformer. The
designer must consider both the primary conductor (wire orbusbar being measured) and other conductors in close
proximity, such as the return conductor or the conductors ofother phases.
Additionally, the routing of the transducer output wires, orpaths of the PWB tracks, at the transducer output should limit
high frequency disturbances created by external conductors.
The output wiring should have minimal loop area, to minimize
di/dt effects, and long runs parallel to power wires must be
avoided, to limit capacitive coupling and minimize dv/dt
effects.
3.2.6 Observations regarding magnetic offset
In standard working conditions, a closed loop transducer isalways working near zero flux, either when the low frequency
Hall based closed loop is effective or when the highfrequency current transformer is working (§ 3.2.1). However,this does not imply that closed loop transducers are not at riskof having a permanent magnetic offset. As discussed for open
loop transducers:• if a low or medium frequency primary current exceeds themeasuring range (based on supply voltage, transducer
parameters, and measuring resistor value) the electronics
can no longer drive sufficient secondary coil current tomaintain the zero flux condition

With compensated devices care must be taken to ensure thecompensation does not negate the demagnetization effort.
Ideally the output can be disconnected to open thecompensation loop. If this is not possible, disabling the power
supplies accomplishes the same goal if a low frequency isused for excitation, to avoid the current transformer effect.
3.2.7 Bandwidth and core losses
Closed loop transducers demonstrate excellent bandwidthcharacteristics. Typically the bandwidth is from DC to 200 kHz,
while a LEM patented design (the LB family) achieves a
bandwidth better than DC to 300 kHz.
Nominal current can not be considered over the full frequency
range. To keep constant the transducer losses, current value
shall be decreased while working frequency increases.
While the current transformer effect of closed loop transducers
provides excellent high frequency performance they are still
subject to core losses due to hysteresis and eddy current
losses. As with open loop transducers (§ 3.1.7), care must be
used when attempting long term measurement of highcurrents at high frequencies.
3.2.8 Response time and di/dt behavior
The response time of a transducer characterizes how it will
respond to a step current with a controlled rate of change,
called di/dt following. It is defined by several parameters suchas the delay time, rise time and reaction time (§ 3.1.8, Fig. 8).
Closed loop transducers show fast reaction times, typically
better than 1 µs.
The correct following of di/dt depends on the intrinsic
construction of each product and, as mentioned in § 3.2.5, themounting conditions of the transducer within the circuit to bemeasured.
Dependent on the closed loop transducer model, it is possible
to measure a di/dt of 50 to 400 A/µs or more. This makes themwell suited for the short-circuit protection of semiconductors in
power equipment.
3.2.9 Typical applications
Closed loop transducers are particularly well suited forindustrial applications that require high accuracy, wide
bandwidth and fast response time. They are often used as the
key element of a regulation loop for the control of current,
15

Hall Effect Technologies

torque, force, speed and/or position as well as for theprotection of semiconductor devices.
Applications are identical to those for open loop transducers,
except higher performance results can be expected:• frequency inverters and 3-phase drives, for the control of
the output phase and DC bus currents as well asprotection of the power semiconductors from fault
conditions such as output short-circuits• converters for servo-motors frequently used in robotics, forhigh performance speed and position control• special wide bandwidth power supplies for special
equipment, such as radar
Other applications include energy management systems,
switching power supplies, electrolysis equipment, lasers,
rectifiers for electrolysis and, finally, many applications forlaboratories or test and control benches.
In the specific case of the LTS family, with a through-holeand several U-shaped primary conductors, series-parallel
connections combined with wire sensing offers a multitude
of possibilities, such as the measurement of differential
currents or performing phase current mathematic calculation(Iu – Iv or Iu + Iv + Iw) with a single device.
3.2.10 Transducer parameter examples
The following examples are intended to help the user
estimate the limits of the operating values for a closed loop
current transducer based on operating parameters and themeasurement resistor. Two approaches can be used todetermine the appropriate measuring resistance; based on
the range provided on the datasheet or based on acceptable
operating values outside those listed on the datasheet. In
some cases it is also possible to measure beyond the
maximum current given on the datasheet and two examples
are provided for this case.
Example 1: LA 55-P operating within nominal datasheet
parameters (see datasheet)a) What maximum measuring voltage can be obtained withthe following parameters ?
IP = 70 A, TA = 70 °C, VC = ±15 V
The number of secondary turns, 1000, determines thesecondary current, IS = IP • NP / NS = 70 mA
The LEM datasheet indicates RMmax = 90 Ω for these
conditions leading to a maximum measuring voltage of:
VM = RM • IS = 90 Ω • 70 mA = 6.3 Vb) Using the following parameters, which measurement
resistance must be selected to achieve a measuring
voltage of 3.3 V at the nominal primary current?
IPN = 50 A, TA = 85 °C, VC = ±12 V, and ISN = IPN • NP/
NS = 50 mA
We have RM = VM/IS = 3.3 V / 50 mA = 66 Ω and, for the
given parameters, the datasheet recommends ameasuring resistance between RMmin = 60 Ω andRMmax = 95 Ω; therefore a 66 Ω resistor can be used.
16c) For the same parameters, is it possible to have a 6 V
measuring voltage?
RM = VM/IS = 6 V/50 mA = 120 Ω
The 50 A current will not be measured with this resistancesince it exceeds the specified RMmax value of 95 Ω. The
maximum measuring voltage is obtained with the RMmax
resistance and is equal to 50 mA • 95 Ω = 4.75 V.
If a 120 Ω resistor is used, the measurement will only becorrect for primary currents less than 50 A (actually up to
43.9 A and 5.25 V). In this case the calculation of the
maximum current value is not straightforward and is
described in the following paragraphs.
Example 2: LA 55-P operating outside of nominal
datasheet parameters
When operating at lower measurement currents it is possible
to get more output voltage by selecting a larger measurement resistor than specified on the datasheet. Alternatively,
when operating at power supply voltages other than thosespecified on the datasheet the measurement range may belimited.
a) What is the maximum voltage available at the amplifier
output?
Fig. 12 shows the schematic diagram of the output of atypical closed loop current transducer. The output
voltage is limited by the voltage drops across each of thecircuit elements: the maximum output stage driving
voltage (VA), the transistor drop (VCE), the secondary coilresistance (RS), and the measuring resistance (RM).
Knowing the maximum possible value of the voltage at
the output of the amplifier stage (VA) will allow thedetermination of the measurable current range. The
worst-case situation will be considered, with the
maximum temperature and the minimum supply voltage,
but other situations can be evaluated with this same
method.
Using datasheet values for peak current (70 A), coilresistance (80 Ω @ 70 °C), and maximum measurement
resistance (90 Ω @ 70 °C with ±15 V supplies) we have:
VA = IS • (RS + RM) = 0.07 A • (80 Ω + 90 Ω) = 11.9 Vb) What is the maximum output voltage with IP = 60 A,
TA = 70 °C, and VC = ±15 V ± 5 %, IS = 60 mA?
Using the results from a) above, the maximum level for
VA under similar circumstances with a min 14.25 V
supply is 11.9 V. We can determine the maximum valueof VM and then RM.
VM = VA - ∆VC - RS • IS = 11.9 V - 80 Ω • 60 mA = 7.1 V
RMmax = VM/IS = 7.1 V/60 mA = 118 Ω

Hall Effect Technologiesb) The datasheet allows an RMmin value equal to zero.
VCmin = 14,25 V

VCE(sat) = ?

RS = 80 Ω

RM = 90 Ω

VS

VM

VA
ÎS

Figure 12: Diagram for calculation of the available voltage, VA, atthe output stage

VCmin = 14,25 V

VCE(sat) = 2,35 V

RS = 80 Ω

RM = ?

VS

VM

VA
ÎS

Figure 13: Equivalent diagram to calculate the measuringresistance, RM

Example 3: Measuring current higher than the maximum
value given in the datasheet
LEM datasheets indicate the transducer operating conditions,with a measuring range that is generally limited to 150 to200 % of the nominal current (IPN). However, it is possible tomeasure currents exceeding this range if the following two
parameters are considered:• the measurement resistance must not be smaller than the
RMmin value given in the datasheet; this minimum value isrequired to limit the power dissipated in the transducer
output stage; depending on the selected transducer RMmin
can be very small, in some cases equal to zero
• the primary conductor temperature must not exceed thevalue specified in the datasheet (e.g. 90 °C), to keep thetransducer within acceptable operating temperature levels
The following examples demonstrate the calculation of the
maximum measurable current. Various scenarios are
examined to address different types of LEM transducers.
a) The datasheet requires an RMmin value greater than zero.
For example, the following parameters are defined for the
LA 55-P transducer: VC = 15 V ± 5 %, TA = 70 °C, RS =80 Ω, RMmin = 50 Ω, VA = 11.9 V (as calculated in example
2a). The maximum value of the measurable secondary
current is:
IS = VA / (RS + RMmin) = 11.9 V / (80 + 50)Ω = 91.5 mA
The corresponding maximum measurable primary current
is 91.5 A.

For example, the following parameters are defined for an
LA 305-S transducer: VC = 15 V ± 5 %, TA = 70 °C, IP = 300
A, RS = 35 Ω (at 70 °C), RMmin = 0 Ω, NP:NS = 1:2500. The
minimum measurement resistance RM can be zero and it is
up to the user to select the most suitable value. The
smaller the value the larger the maximum measurable
current, but the smaller the available output voltage signal.
The available voltage at the amplifier output (VA) is
determined as follows:
RMmax = 75 Ω at 300 A for VC = 15 V, IS = 300 A/2500 = 120 mA
So:
VA = (RS + RMmax) • IS = (35 + 75)Ω • 0.12 A = 13.2 V
The maximum value of the measurable secondary current
depends on the selected measurement resistance.
For example, with RM = 5 Ω, we have:
IS = (VA-∆VC)/(RS + RM) = (13.2 V) / (35 + 5)Ω = 330 mA
The maximum measurable primary current is consequently equal to 330 mA • 2500 = 825 A, corresponding to
2.75 • IPN. The voltage measured on the measurement
resistance is VM = 330 mA • 5 Ω = 1.65 V.
With RM = 2 Ω, we have IS = 357 mA, a maximum
measurable primary current of 3 • IPN (892 A) with a smaller
output voltage of 0.71 V.
If a zero ohm measurement resistor is considered, thetransducer can provide IS = 377 mA, which represents
3.14 • IPN (943 A). This arrangement provides no output
voltage, so a virtual ground referenced current to voltage
converter will be required to obtain a usable output signal.
It is up to the user to decide exactly what is needed.
Under these higher current conditions it is especially
important to keep the temperature of the primary conductor
below the maximum allowable temperature to avoid
permanent damage.
Example 4: Measuring transient current higher than the
maximum value given in the datasheet
In some cases higher currents can be measured using thecurrent transformer effect, provided the frequency and/or the
di/dt are high enough. This can be useful for short circuit
detection, as this is typically a high di/dt event, but care must
be exercised when attempting to use this capability forstandard or continuous measurement. See § 3.2.3 for moredetails.
It is important to note that some transducers (e.g. LTS) havean internal measurement resistor value that cannot be
adjusted and, in these circumstances, the measuring range
cannot be adjusted.

17

Hall Effect Technologies

Example 5: Periodic transient current overload

400

IPt1 = 100 A
DT = 0.07

360

The following measurement sequence is considered,illustrated for the LTS 25-NP transducer:

320

IPt1 = 75 A
DT = 0.105

280
240
200

• The transducer is measuring the nominal current of 25 A

IPt1 = 50 A
DT = 0.26• During the time t1 a current overload occurs (IPt1), exceeding
the 25 A nominal value• During the time t2 the current returns to the initial value (IPt2)
of 25 A, allowing the transducer to cool after the overload

t2 (s)

160
120
80

IPt1 = 34 A
DT = 140
00• In the worst-case, the sequence is continuously repeatedFig. 14 shows DC current levels, but these can also represent
the RMS value of the primary current over time. The following
examples use DC values, but total RMS (using AC and DC
values) has an equivalent effect.

2

4

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
t1 (s)

Fig. 16 Overload diagram of the LTS 25-NP for a rest current of
25 Arms, linear zone

Duty cycle = DT = t1 / (t1 + t2)
Giving:t2 = (1 – DT) • t1 / DT

IPt2

Examplet1

t2

t1

Figure 14: Periodic overload with a standby current of 25 A at 85 °C

The maximum environmental temperature of 85 °C is
considered and, in this specific example of an LTS 25-NP
transducer, the three configurable primary terminals must beconnected in parallel to allow the long-term measurement of
25 A.
What is the acceptable limit for t1 and t2 based on themagnitude of IPt1?
For given overload duration (t1) and amplitude (IPt1), Fig. 15
and Fig. 16 give the minimum time (t2) required for thetransducer to cool when the continuous current, IPt2, is thenominal 25 A value with a maximum ambient temperature of
85 °C. Fig. 16 is a close-up view of the linear zone shown in
the lower left corner of Fig. 15 for short overload duration. In
this case the curves are linearized, allowing to define a
simple duty cycle relation:
IPt1 = 75 [A]t2 (min.)

IPt1 = 100 [A]
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0

IPt1 = 50 [A]Considered aslinear zone

IPt1 = 34 [A](permanently)

For a current overload of 50ARMS applied during t1 = 14 s, therecovery time shall be at least t2 = 40 s. This value can either
be taken from Fig. 15 or Fig. 16, or calculated according to theduty cycle relation, considering a 26 % duty cycle in this case:t2 = (1 - 0.26) • 14 / 0.26 = 40 s.
At 85 °C, 34A can be measured continuously by the LTS 25NP transducer. In this condition the various parts of thetransducer (the ASIC, coil, and primary pins) remain at or
below their maximum critical temperatures.
Unfortunately the failure rate of a transducer increases
significantly as the temperature increases. Therefore theseoverload conditions will reduce the transducer reliability. Thisoverload capability is considered a key element of the safety
factor inherent in all LEM designs and, while temporary
excursions are anticipated, long term operation at levels
beyond those specified in the datasheet must not be allowed.
Important! The maximum operating temperature defined in
the transducer datasheet must always be observed. If not,abnormal and possibly destructive behavior may result.
Always consult LEM when actual operating or storage
conditions fall outside of those specified on the datasheet.
To conclude, Fig. 17 and Fig. 18 give the maximum overload
conditions for a rest current of IPt2 = 0A.
3.2.11 Calculation of the measurement accuracy

0

10

20

30

40

50

60

70

80

90

100 110120130 140 150

t1 (s)

Figure 15: Overload diagram of the LTS 25-NP with a standby
current of 25 A

For closed loop transducers, examples of the maximum error
calculations are provided below. It is important to note that
there are four regions of operation that exist:• the region at or near zero primary input, which ischaracterized by the offset specification

18

Hall Effect Technologies

34
32
30

IP =
100 A

28
26
24
22

IP = 50 A

20
18
16
14

t2 [min]±0.65 %
±1.20 %

Worst-case error (+85 °C)±1.85 %IP = 75 A

The worst-case error when measuring a 50 A current isconsequently equal to ±1.85 % • 50 A = ±0.93 A.

IP = 40 A

When a 40 A current is measured the output current is 40 mA
and the errors are:

12
10
8
6
4
2
0

IP = 34 A
0

30

60

90

120

150

180

210

240

270

300

330

360

390

420

450

t1 [sec]

Figure 17: Overload diagram of the LTS 25-NP for a standby
current of 0A

170

150

IP = 75 A

140
130
120

IP = 50 A

110
100
90
80
70

IP = 40 A

60±0.81 %
±1.50 %

Worst-case error (+85 °C)±2.31 %The errors when measuring lower currents are larger as apercentage of reading due to the offset currents becoming
significantly larger with respect to the output signal current.
The initial offset current, IO, of ±0.2 mA and the residual
current, IOM, (magnetic offset) of ±0.3 mA after a current
overload, are also given in the data sheet. It shall be read as
follows: When measuring a 0 A current the output can be±0.2 mA, or ±0.4 % of IPN = ±0.2 A. In addition, after
experiencing an accidental 300 % overload (150 A) there
can be an additional ±0.3 mA of offset for a total of ±0.5 mA,or 1.0 % of IPN = ±0.5 A.

IP =
100 A

160

Accuracy at 25 °C±0.65 % of IPN
Offset drift with temperature ±0.6 mA / 40 mA

The worst-case error when measuring a 40 A current isconsequently equal to ±2.31 % • 40 A = ±0.93 A.

180

t2 [sec]

Accuracy at 25 °C±0.65 % of IPN
Offset drift with temperature ±0.6 mA / 50 mA

50
40
30

IP = 34 A

20

Current transducer LTS 25-NP (see datasheet)

10
0
0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

t1 [sec]

Fig. 18 Overload diagram of the LTS 25-NP for a rest current of
0 A, linear zone

For the LTS 25-NP transducer, the accuracy at 25 °C is given
as ±0.7 % of IPN. This breaks down as follows:• the region at or near the nominal primary level, which ischaracterized by the accuracy specification

Number of secondary turns ±0.1 % of IPN
Non-linearity±0.1 % of IPN
Tolerance on RIM±0.5 % of IPN• the region between these two, characterized by the linearity
specification

Worst-case error• and the region near the limit of the measuring range, where
saturation effects may begin

The internal measurement resistance, RIM, has a value of
50 Ω and a thermal drift specified as 50 ppm/K. Considering a-10…85 °C temperature range, the maximum variation is±0.15 Ω and the corresponding error due to the RM drift isequal to 50 ppm/K • (85 - 25)°C = ±0.3 % of IPN.

Maximum error takes all factors into account using the worstcase parameters. Because of the statistical distribution of eachparameter it is highly unlikely that all will be at worst-casevalues in a single device. Nonetheless, this is the basis ofworst-case design analysis.
Current transducer LA 55-P (see datasheet)
In this example, a DC current is measured with the LA 55-P
current transducer with a ±15 V supply.
The datasheet provides the following information: IPN = 50 A,
ISN = 50 mA, accuracy (@ 25 °C and ±15 V) is 0.65 % of IPN.
The accuracy is breakdown in several parameters, including
linearity < 0.15 %, offset error IO = 0.2 mA, and offset drift
IOT = 0.6 mA for 25…85 °C.
When a 50 A current is measured (one primary turn) the
output current is 50 mA and the errors are:±0.7 % of IPN

In addition, the voltage output of the LTS 25-NP transducer
uses a 2.5V ‘reference voltage’ corresponding to a zeroprimary current (Fig. 1). The offset on this reference voltage(given in the datasheet) is ±25 mV at 25 °C. Considering a-10…85 °C temperature range, the worst-case offset value
goes up an additional 100 ppm/K • (85 - 25)°C = 0.6 % to a
total of ±40 mV at 85 °C, corresponding to 1 % initial offset
plus 0.6 % drift.
Because a primary nominal current (IPN) generates an output
voltage of 625 mV at 25 °C, the error introduced by the offset
on the reference voltage is:• error due to the standard offset ±25 / 625 = ±4.0 % of IPN• maximum error due to the drift±15 / 625 = ±2.4 % of IPN
19

Hall Effect Technologies

The worst-case measurement error throughout thetemperature range is: 0.7 + 0.3 + 2.4 = ±3.4 % of IPN
The error due to the standard offset (4%) is not taken into
account because it represents a constant deviation which
can easily be eliminated by an adequate electronic design.
3.2.12 Unipolar power supply
The vast majority of LEM closed loop transducers are specified for use with bipolar supply voltages (e.g. ±15 V). Evenso, most transducers can also be operated from a single,
unipolar, supply for the measurement of unidirectional
currents. In these cases the following must be taken into
account:• the supply voltage should be equal to the sum of thepositive and negative voltages indicated in the datasheet(e.g. a ±15 V product should be powered with +30 V)• selection of the measurement resistance and the
maximum current must not imply excessive power
dissipation in the transducer output stage; assessment of
the worst-case condition is not straightforward

3.3.1 Construction and principle of operation
Hall effect Eta transducers are similar in construction toclosed loop transducers (Figure 20), with the same magnetic
circuit geometry, a Hall generator and secondary winding.
Differences lie in the details of the magnetic core andprocessing electronics designs, leading to the Eta specificfeatures. A Hall effect Eta transducer is a mix of open loop
and current transformer technologies providing the following
characteristics:• it works as an open loop transducer at low frequencies (upto 2…10 kHz depending on the specific transducer
design), with the Hall generator providing a signal proportional to the primary current to be measured (§ 3.1.1)• it works as a current transformer at higher frequencies,
where the output current is proportional to the AC primary
current (§ 3.2.1)
Both the Hall effect and transformer signals areelectronically added to form a common output signal.

• the output stage is designed for use with a bipolar power
supply and diodes must be inserted in series with theoutput (Fig. 19) to allow a minimum output bias voltage
without creating a measurement offset
The LEM portfolio also includes standard transducers
dedicated to unipolar operation and use of these is advisedas the electronic design and specifications are based
directly on expected operating conditions.
Applications that only require a second supply voltage forthe transducers, with the associated cost, complexity, spaceand reliability concerns of this additional circuitry, would
justify the use of a unipolar transducer.

+
TransducerM

Eta technology is better suited than others when thefollowing performance is expected:

+
RM

-

Figure 19: Addition of series diode(s) when operating with aunipolar power supply

3.3

Eta Technology Hall effect current transducers

Eta is the name of the Greek symbol ‘η‘, representing
efficiency. This product family has been given this namebecause of its very low secondary power requirements while
also providing exceptional performance. In terms of
performance, Eta falls between open loop and closed loop
technologies. Because the construction is similar to closed
loop, this technology offers no price advantage.
20

Figure 20: Hall effect Eta principle• wide bandwidth – DC to 100 kHz or more
• low power consumption• use of a low voltage secondary supply (e.g. +5 V)
Power consumption is minimal because the power supply is
not required to drive the secondary coil with compensation
current, which also makes them suitable for use with a low
voltage secondary supply, as they do not require the voltage‘headroom’ of a closed loop device (§ 3.2.1).
Indeed, it is very difficult to design closed loop transducers
that will operate from low voltage secondary supplies (lessthan or equal to 5 V) with primary currents exceeding 25 A.
This design issue is due to the fact that there is very limited
voltage ‘headroom’ to drive a suitable secondary coil andmeasuring resistance. It is this combination of requirementsthat are best address with Eta technology.

Hall Effect Technologies

3.3.2 Advantages and limitations

3.3.5 Measurement accuracy

Eta transducers are capable of measuring DC, AC andcomplex current waveforms while ensuring galvanic isolation and low insertion loss. Their significant advantages
are the low power consumption and suitability for small
secondary supply voltages, such as a unipolar 5 V supply,as with open loop transducers along with the highbandwidth and fast response time of a current transformer.

The accuracy of an Eta transducer is dependent on theworking frequency:

These characteristics also lead to the limitations of an open
loop transducer at low frequencies; offset and gain drift withtemperature and moderate accuracy. With higher
frequencies (> 2…10 kHz) the current transformer effectprovides very good accuracy and negligible temperaturedrift. In addition, the flux canceling nature of a current
transformer reduces the concern of core losses with highfrequency currents.

Refer to the related open loop Hall effect (§ 3.1.5 and§ 3.1.10) and closed loop (§ 3.2.5 and § 3.2.10) sections formore details on the factors affecting the accuracy and toreview calculation examples.

With Eta technology the major inconveniences are the sizeof the magnetic circuit, with a large core sized for low
frequencies as with open loop transducers, and the need fora large secondary coil for detecting high frequencies, ascompared to closed loop transducers. This typically results
in a more expensive construction than is required for asimilarly rated closed loop transducer.
3.3.3 Nominal and extreme currents
The LEM Eta transducer range is made for nominal currents
IPN from 25 to 150 A. This rather narrow range is not limited
by technical issues, but rather by the market itself: forcurrents less than or equal to 25 A it is possible to work withthe higher performance closed loop technology, while forcurrents greater than 150 A secondary voltage supplies witha greater amplitude (e.g. ±15 V) are generally available,
again allowing the use of closed loop transducers. The
reduced secondary power consumption of the Eta
technology is often not a sufficient asset to promote Eta
technology beyond this current range, although there arealways exceptions.

• for low frequencies (< 2…10 kHz), the overall accuracy is afew percent, as with open loop designs• for higher frequencies, the overall accuracy is typicallybelow one percent

3.3.6 Dynamic behavior
The bandwidth, response time and di/dt behavior of Eta transducers is very close to those of the closed loop technology(§ 3.2.7 and § 3.2.8), although slight performance reductions
may come from the use of a less efficient magnetic circuit(material, design) for high frequency operations.
Measurements carried out on Eta transducers show a typicalbandwidth range of DC to 100 kHz or more.
The response to a current step demonstrates the ability tocorrectly reproduce a transient. It is defined by several
parameters such as the delay time, rise time, reaction time(§ 3.1.8) with a particular waveform. Eta transducers show
fast reaction time, better than 1 µs, similar to closed loop
designs.
The correct following of di/dt depends on the intrinsic
construction of each product and, as mentioned previously,
the mounting conditions of the transducer in the circuit to bemeasured. Depending on the selected Eta transducer model,
it is possible to measure di/dt from approximately 50 A/µs to
400 A/µs or more. This feature makes them well suited for theprotection of semiconductor devices.
3.3.7 Typical applications

For a given Eta transducer, the maximum current which canbe measured depends on the limitations set by the open
loop (§ 3.1.3) or current transformer (§ 3.2.3) behavior, at
low and high frequencies respectively. This leads to a
maximum measurable current of typically 150 to 200 % of
the nominal current at low frequencies, and a capability
going significantly beyond that at higher frequencies.

Eta current transducers are used in numerous industrial
applications, generally as an important element of aregulation loop (for current, torque, force, speed, position
feedback), but also for current monitoring and display.
Examples of applications are similar to the ones of open loop(§ 3.1.9) and closed loop (§ 3.2.9) transducers.

The risk of magnetic offset after an unexpected current
overload is similar to that of open loop and closed looptransducers (§ 3.1.6 and § 3.2.6), again at the expected
frequency of disturbance.

3.4

3.3.4 Output signal
By design an Eta transducer has a voltage output, although
the internal design could be modified or voltage signal postprocessed to provide other output types. Refer to § 2.7 formore details.

Closed loop Hall effect voltage transducers

Previous sections address the measurement of current with
galvanic isolation, but it is also possible to measure a primaryvoltage with galvanic isolation using the same LEM
technology. These voltage transducers are based on the
more sensitive and accurate current measurement
technologies, such as closed loop Hall effect designs.
The main difference from a current transducer is the additionof an internal primary winding with a large number of turns,
21

Hall Effect Technologies

allowing the transducer to create the necessary ampere•turns
to measure the small primary current.

R1

IP

3.4.1 Construction and principle of operation

RP

The operating principle of closed loop Hall effect voltage
transducers is to measure a small current that is directly
proportional to the voltage of interest. Dividing the voltage tobe measured by a large resistance, R1, creates a small
current, Imes, that can be measured by an ‘optimized’ transducer (Fig. 21), enabling it to accurately measure the small Imes
current, while also having controlled insertion impedance tomaintain suitable accuracy and measurement bandwidth.
The R1 resistance is added in series with the transducer
primary coil to obtain the optimal Imes current value for thenominal voltage level. This resistance is often split into two
resistors, placed on both sides of the primary coil, to improvecommon mode rejection.
V+

R1 / 2Imes

Sensitive
Currenttransducer

or

Sensitive
Currenttransducer

R1 / 2

Imes
V-

Figure 22: Equivalent diagram for the R1 primary series resistancecalculation

3.4.3 Voltage transducer without internal resistor

V+
R1

LP

VP

V-

Figure 21: A basic principle for voltage measurement

Two situations exist with the LEM voltage transducer
portfolio:• the series resistance, R1, is built into the LEM voltage
transducer providing optimal performance when used at ornear the product ratings, as with the LEM LV 100-100• the series resistance, R1, is external, allowing thecustomer to tune the transducer working voltage range
and/or response time, as with the LEM LV 100 and LV 200
The equivalent electric diagram of a voltage transducer
primary part is show on Fig. 22, including the serial
resistance R1, the primary coil resistance RP and the primarycoil inductance LP. The latter generally creates a negligeable
insertion reactance (ωLP), in most cases neglected.

Example 1: LV 100 closed loop voltage transducer withexternal R1 resistor (see datasheet)a) What external resistance, R1, is required to measure anominal voltage of VPN = 230 VAC?
The LV 100 datasheet provides the following information:
nominal current, IPN = 10 mA, measuring range, IP = 20 mA,primary coil resistance, RP = 1900 Ω at TA = 70 °C. We
have:
R1 = VPN / IPN - RP = (230 / 0.01) - 1900 = 21.1 kΩ
We select the nearest standard resistance value of 21.0 kΩ
The total resistance of the primary circuit is consequently
equal to 22.9 kΩ at 70 °C.
The nominal power PN dissipated in R1 is:
2

VPN

PN = IPN2 • R1 =( R + R ) • R = 0.012 • 21000 = 2.1 W
1P

1In order to avoid excessive thermal drift of the resistor, andto improve reliability, the user would preferably select a
resistor with a power rating of 300 to 400 % of thecalculated nominal power. In this example, a 21.0 kΩ, 8 W
resistor should be considered.
b) With this resistor, can we measure a maximum voltage
of 500 V ?

3.4.2 Voltage transducer with internal resistor

The measurement of a voltage higher than the nominal
value is possible during transient operation, depending on
the following two conditions:

For the „LV 100-[voltage]“ transducers (e.g. LV 100-100) theseries resistance, R1, is built into the transducer and cannot
be changed by the user. This design has a 10 W input power
at nominal voltage. The internal series resistor allows factory
calibration of the transducer at the specified nominal
voltage, implying better accuracy.

• the RMS value of the primary voltage shall be such thatit keeps the transducer current below nominal value(10 mA for the LV 100); in our example, if this rule is not
fulfilled at 500 V with the selected 21.0 kΩ resistance, ahigher resistance value must be considered

The measuring range is limited to 150 % of the nominal
value, except for transient measurements where the RMS
transducer input power remains below the specified 10 W.
22• the primary current at the higher voltage should normally
be lower than the transducer specified ‘measuring
range’, 20 mA for the LV 100; we have: IP = (VP/RPtot) =500/22900 = 21.8 mA and are therefore beyond theHall Effect Technologies

specified measuring range; a check on the transducer
secondary side is required to see if this transient
measurement is nevertheless possible
For the latter point, as discussed in § 3.2.10 – example 2,
it is sometimes possible to measure a current beyond thatspecified in the transducer datasheet, more precisely
when the measurement resistor is not exceeding amaximum RMmax value. In this example, we have:• the conversion ratio of the transducer is 10000 / 2000,
giving a secondary current of IS = 5 • 21.8 = 109 mA• the voltage available at the amplifier output is (Fig. 12)
VA = (RS + RMmax) • IS = (60 + 150)Ω • 50 mA = 10.5 V

For the resistance R1, typical values for the temperaturedrift and tolerance are 50ppm/°C and ± 0.5% respectively.
The minimum value becomes:
R1 = 21’000 • (1 - 50 • 50 • 10-6) • (1 – 0.005) = 20’942 Ω
The primary resistance RP is made of copper and exhibitsa resistance change with temperature as follows:
RP20 (1 + α • ∆T) where
RPF =RPF : resistance at Final temperature (e.g. +70 °C)
RP20 : resistance at +20 °C
α : copper temperature coefficient = 0.004 K-1∆T : change in temperature (Final – 20 °C), positive
when above +20 °C• the maximum measurement value is
RMmax = (VA / IS) -RS = (10.5 / 0.109) – 60 = 36.3Ω

Note that the temperature of the RP copper is likely to behigher than the maximum ambient temperature due tointernal transducer heatings.

In conclusion, measuring a 500 V transient is possible if ameasurement resistance lower than 36.1 Ω is used.

In our case:c) Measurement accuracy: influence of the serial resistanceR1 and primary resistance RP
The measurement principle discussed in § 3.4.1 is basedon the measurement of a current Imes (Fig. 21) proportional
to the voltage to be measured. The two main factors
affecting the measurement accuracy are:
• The accuracy of the measurement of the collectedcurrent Imes
• Unexpected changes of the ratio between the collected
Imes current and the voltage to be measured.
Thus, changes of the resistances R1 and RP will affect themeasurement accuracy, since it will change the value ofthe Imes current.
The example below calculates the impact on accuracy ofa change in resistances, due to both resistance tolerances
and temperature effects. A LV 100 voltage transducer isconsidered, with a +20°C to +70°C worst case working
temperatures.
Reference case
The reference value of the current to be measured, Imes, isdefined as the value obtained at +70°C when bothresistors R1 and RP have their nominal value. These
values are R1 = 21.0 kΩ (as calculated in point a), at+70°C) and RP = 1.9 kΩ (data-sheet, measured value).
The collected Imes current is then equal to 230 V / (21 +1.9) kΩ = 10 mA
Maximum error
The value of the resistances are smaller at +20 °C whencompared to +70 °C. The worst case shall additionallyconsider the tolerance on the resistances' value when attheir minimum.

RP20 = 1’900 / (1 + 0.004 • 50) = 1’538 ΩCollected current become equal to Imes = 230 V / (20’942 +1’538) = 10.21 mA, corresponding to a +2.1 % error
compared to the reference value.
The measurement accuracy of the Imes current has still tobe added to this 2.1 % error.
d) What is the accuracy of the transducer, converting the
primary current into an isolated output signal ?
In this case, we assume that the resistor R1 has been
selected in order to have a 10 mA primary current IPN.
According to the LV 100 datasheet, the accuracy of thecurrent measurement at 25 °C is ±0.7 % of IPN. The
thermal drift of the offset current is ±0.3 mA max. With aconversion ratio of 10000:2000, the input current of
10 mA generates an output current of 50 mA. The valuesof the errors are:Accuracy at 25 °C±0.7 % of IPN
Temperature offset drift ±0.3 mA/50 mA±0.7 %±0.6 %

Maximum error of the current measurement: ±1.3 %e) What is the total measurement error?
The effects listed in c) and d) above provide the total
measurement error of the output current of the transducer.
Typical applications include a measuring resistance, RM,
to convert this output into a voltage for measurement.
Assuming typical parameters for RM, we have an intial
tolerance of ±0.5 % and a 50 ppm/K temperature drift,
giving a 0.225 % variation for a 20 °C to 70 °C
temperature range. The total RM error becomes 0.5 +0.225 = 0.725 %.
For the LV 100 transducer, the total measurement error atthe 230 V nominal, considering a temperature range of
20 to 70°C, is the combination of the effects in c) and d)
and RM above:
total measurement error =2.1 % + 1.30 % + 0.725 % = 4.125 %23

Hall Effect Technologies

Example 2: Design for continuous measurement of1000 V nominal
Select the value of the external primary resistance R1 tocontinuously measure a voltage of VPN = 1000 V nominal
and determine the corresponding measurement accuracy.
a) Calculation of the primary resistance
Again using the LV 100 datasheet values: nominal
current, IPN = 10 mA, measuring range, IP = 20 mA,primary coil resistance, RP = 1900 Ω at 70 °C or RP =1615 Ω at 25 °C. We have: R1 = (VPN/IPN) -RP = (1000/0.01) - 1615 = 98 385 Ω.
The nominal power, P1N, dissipated in R1 is:P1N = IPN2 • R1 = 0.012 • 98385 = 9.8 W and, as alreadydiscussed, it is suggested to use a resistor with 300 to
400 % of this power rating: a 40 W resistor.
The total resistance, RPtot, of the primary circuit is:
RPtot = RP + R1 = 100.3 kΩb) Voltage measurement accuracy: effects of the series
resistance, R1, and coil resistance, RP
Following the same methodology as in example 1c
above, we have a maximum R1 value of:
R1max = 98 385 Ω • 1.005 • 1.00225 = 99 099 ΩConclusions based on these two examples
The use of the LV 100 transducer for the measurement of a
230 V or a 1000 V nominal voltage leads to a worst-casemeasurement accuracy of 3.84 % or 2.97 %, respectively.
The measurement accuracy is significantly better for larger
voltages because the variation of the primary coil resistanceis less significant in comparison to the primary total
resistance (R1 + RP) due to the larger series resistor value.
To obtain better accuracies when measuring low voltages
one must select transducers with a larger conversion ratio.
This will, however, require higher power dissipation in the
primary circuit and thus increase the power taken from thesource being measured. A second benefit of considering alarger conversion ratio (smaller number of primary turns) is
the resulting larger bandwidth (reduced inductance value L
in R / L time constant limitation).
Finally, if needed, the calibration of the output signal of a
voltage transducer can be made by either tuning theexternal resistor value, R1, or, as with current transducers, by
adjusting the measuring resistor, RM.
3.4.4 Transducer Output
The output of a closed loop voltage transducer is identical tothat of a closed loop current transducer. Therefore, themethodology previously described in § 3.2.4 and § 2.7 forthe selection of the transducer measuring resistor and output
voltage also applies to these devices.

and a minimum value of:R1min = 97.6 kΩ • 0.995 • 0.99875 = 97 771 Ω

3.4.5 Typical applications

The maximum value of RP at 70 °C is 1.9 kΩ while theminimum value, at 20 °C, is equal to:
RP70 °C
RPmin =
1583 Ω(1 + 0.004 • 50)

Closed loop Hall effect voltage transducers are used inmany industrial applications to detect, monitor and regulate
voltages. A typical application is the monitoring of input,
output and DC filter voltages of frequency inverters, whereaccuracy and isolation are of primary importance.

The primary resistance calculations are the same so thevalue of the total resistance, RTOT, is between
97 771 + 1583 = 99 354 Ω and99 099 + 1900 = 100 999 Ω
The range of primary current collected at nominal voltage
is:1000 V / 100 999 Ω = 9.90 mA to1000 V / 993 54 Ω = 10.07 mA
This can be interpreted as a value of 9.985 mA ± 0.085
mA, corresponding to a ± 0.85 % tolerance.
c) The current measurement accuracy is identical to thecalculation in example 1d before, namely 1.3 %.
d) For the LV 100 transducer, the total measurement error
for a 1000 V nominal voltage over the temperature range
20 to 70 °C, making the same RM assumptions as inexample 1e is 0.85 % + 1.3 % + 0.725 % = 2.875 %.

24

3.5

Other Hall effect voltage transducers

Actually, most current transducers technologies can be
modified into a voltage transducer by ensuring the small
measurement current (proportional to primary voltage) is
applied to a large number of primary turns to create theAmpere-turns necessary for measurement. This is commonly
made with Fluxgate technologies (§4.4.4) but less typicalwith open loop and Eta Hall based transducers.

Fluxgate Technologies

4

Fluxgate technologies

The Fluxgate technologies discussed in this chapter cover
several types of isolated current and voltage transducers
based on the same basic measurement principle: themagnetic field created by the primary current to bemeasured is detected by a specific sensing element. The
latter is driven through its B-H loop by a dedicated electronic
and the resulting magnetic effects are used for primary
current detection. There are a wide variety of methods forconcentrating the field, driving the magnetic core, andsensing the field intensity, but in all cases the underlying
working principle is the same.
4.1

Working principle of Fluxgate technologies

To start, the ‘standard’ Fluxgate design will be investigatedas this has a construction similar to the closed loop Hall
effect current transducer already described (§ 3.2.1). After
this the Fluxgate principle should be understood and other
topologies can be covered, highlighting their specificcharacteristics and performances.
4.1.1 „Standard“ Fluxgate – working principle
An isolated Fluxgate current transducer (Fig. 23) can be
designed in the same manner as a Hall effect based closed
loop transducer (§ 3.2.1), using the same magnetic circuit
including a gap and secondary winding. The secondary
winding is driven to provide zero flux in the gap as sensed
by the Fluxgate element, rather than a Hall generator.

U(t)

I

P

Isi

Magnetic core

Fluxgate Sensing head

Bext

coil

L = f(Bext; Isi)

0.5 mmBsi

Figure 24: Fluxgate magnetic sensing head (saturable inductor)

As with any inductor, the value of inductance of the „saturable
inductor“ depends on the magnetic permeability of the core.
When the flux density is high, the core is saturated, itspermeability low, and the inductance high. At low fielddensity, the inductance is high.
The „saturable inductor“ is purposely designed so that any
change in the external field, BEXT (Fig. 24), affects its saturtionlevel, changing its core’s permeability and consequently its
inductance. Thus, the presence of an external field change
the inductance value of the field sensing element. Thischange can be very pronounced if the saturable inductor isadequately designed. The second factor affecting thisinductance is the current, ISI, injected into the coil of thesaturable inductor (Fig. 24). This current produces a flux,
channeled into the magnetic core, resulting in an additional
magnetic field components, BSI. The saturable inductor isgenerally designed in a way that BEXT and BSI have the sameorder of magnitude, both affecting the inductance value.
With the „standard Fluxgate“ design (Fig. 25), the primary
current creates an airgap flux, ΦP (corresponding to BEXT),
added to the flux ΦSI created by the saturable inductor current
ISI. The addition of these two flux creates an over saturation of
the saturable inductor’s core and its inductance drops. Whenthe polarity of the ISI current is reversed, the flux ΦP and ΦSI
are substracted, giving a lower total flux when ΦSI is smaller
than Φp, a zero total flux when ΦP and ΦSI are equals, or areverse total flux when ΦSI is larger. The latter case lead to astrong core saturation when ΦSI is much larger than ΦP. The
design of the saturable inductor shall provide high inductancenear zero total flux and low inductance under saturation.
Isi (positive)

Figure 23: Structure of the „standard Fluxgate“

The main difference between the closed loop Hall
technology and the Fluxgate is on the way the airgap field is
detected: by a Hall cell in the first case, and by a so-called„saturable inductor“ (Fig. 24) in the second. This implies adrastic change of the transducer electronics, to drive thesensing element and to process the resulting signal.
The Fluxgate sensing element is intentionally a „saturable
inductor“ (Fig. 24) made of a small, thin magnetic core with acoil wound around it. It is generally made of discrete pieces
of material (lamination sheet & copper wires), but various
designs can be considered, including advanced concepts
based on MEMS technologies (not yet commercially viable).

Φ
IP

Φ

P

Φ si

Figure 25: Standard Fluxgate - gap flux distribution – additive flux

In conclusion, changes in the magnetic saturation of theFluxgate sensing head leads to inductance variations to be
detected by the processing electronics (Fig. 26). The closed
loop principle is then used, where variations in inductance25

Fluxgate Technologies

IS

Small inductancecurrent iSI (t)created by the primary current, IP, can be detected andcompensated using the closed loop principle, feeding acurrent into the transducer’s secondary coil, IS, to return the
gap field to zero and thus inductance back to a referencecase. The relation between primary and secondary current isthen simply given by the primary to secondary turns ratio(§ 3.2.1). The next paragraphs details the methodology
followed to detect inductance variations.

nce
cta
u
d
in
ge
Lar

IP

time

ΦP

No

L = L (IP = 0)?

lS = IP /NS

Yes

Figure 28: Current response to a voltage step – constant inductance

Figure 29 again shows the current response to a voltage
step, but in this case with a saturable inductor, where the ISI
current increase lead to an increase or decrease of theinductance value, depending if the field BSI (created by thesame ISI current) is added or substracted from the external
BEXT airgap field. When those fields are for example added,
an ISI current increase leads to an increase of the saturationlevel, implying a decrease of the inductance value and thus
a faster current variation.

Adjusts IS

Figure 26: Principle of the „standard Fluxgate“

4.1.2 Sensing head – a current response to a voltage
step

The electric diagram of the saturable inductor is given in
Fig. 27. The resistance represents the copper resistance of
the inductor coil, constant at a given temperature, while theinductance is variable, depending on both the external field
applied on the saturable inductor and the injected i(t) current
.

R

L

u(t)
i(t)

current iSI (t)Since the Fluxgate working principle is based on thedetection of an inductance change, it is necessary to firsthave a good understanding of the electric behavior of thesaturable inductor. Thus, before analyzing the way
inductance changes are detected (§ 4.1.3), lets first see whatis the current response of the saturable inductor when avoltage step is applied.

ec
L-d

reas

nc
L-i

e

reas

e

time
Figure 29: Current response to a voltage step – saturable inductanceIn practice, Fluxgate sensing heads are designed so that thecurrent response to a voltage step is very „sharp“, as shownin Figure 30 (BEXT = 0), where the current behaves in threedifferent stages: (1a) For small current values, the current
variation is slow, the saturable inductor being designed witha very high inductance when non-saturated; (2a) When thecurrent exceeds a pre-defined level, its variation becomesvery fast due to a sudden drop of the inductance value (useof magnetic materials with a sharp magnetic characteristic);(3a) The current reaches the asymptotic level defined by the
excitation voltage and coil resistance.

Figure 27: Electric diagram of the sensing head inductor

If the inductance of the sensing head were constant, thecurrent response to a voltage step would be as shown in
Fig. 28, given for three different inductance values: small,medium and large. The initial slope is defined by di/dt = V / L
for t=0, giving lower slopes, or slower current responses,
with higher inductances, while the final value is always thesame and is defined by i = V / R.
26

This sharp profile is desired because it acts as a „closed“ or„open“ gate for the current, restraining or allowing thecurrent flow depending on the saturation level of the core.
This behavior, of the core flux controlling the current „gate“,is the origin of the name Fluxgate.

current iSI (t)Fluxgate Technologies

nce
ducta
n
i
t
n
ta
Cons
(1b)

BEXT = 0(1a)

BEXT = 0

(3)
(2b)

(2a)

(Ob)

time

Assuming the loop is not closed, and compensating secondary
current is not available, Fig. 32 shows the current behavior
when a primary current (or external field BEXT) is present, as
described in Fig. 30. The current almost immediately goes to a
non-zero positive value, then stays relatively stable until thecore saturates in the other direction. Again, the voltage polarity
changes prior to reaching the asymptotic current level.
Compared to the Figure 31 current, the main differences areon the peaks amplitude (comparing the peaks above andbelow the DC value of the signal) and the appearanceof a DC current component.

Figure 30: Current response to a voltage step – Fluxgate sensing
head (BEXT set at a parameter)

In the case where the external field BEXT is non-zero, thecurrent response appears as in Fig. 30, where the current
behaves in four different ways: (0b) For small ISI current
values, the external field BEXT is pre-dominant and drives thecore into saturation, leading to a low inductance and a fastcurrent change; (1b) As the inductor current ISI reaches alevel where it creates a BSI field equal and opposite to the
BEXT field (total core flux equal to zero), the saturation level islow, the inductance high and the resulting current variation
slow; (2b) As the inductor ISI current continues to grow, the
BSI field becomes pre-dominant and drives again the
inductor core into opposite saturation, resulting in an
inductance drop and a fast current variation; (3) the current
reaches the asymptotic level defined by the excitation
voltage and coil resistance.
4.1.3 Detecting the sensing head inductance variation
As mentioned before (Fig. 26), the Fluxgate working
principle is based on the detection of an inductance change.
This change can be detected in different ways, the mostcommon being described here.
Looking at Fig. 31, the saturable inductor is driven with asquare wave voltage, u(t), leading to the sensing headcurrent, i(t), when no primary current IP (or no external field
BEXT) is applied. This current shape is directly related to the
behavior shown in Figure 30, with the applied voltagechanging polarity prior to reaching the asymptotic current
level.

u(t)

i(t)

i(t)
time
u(t)

Figure 32: Voltage steps and current response (IP = 0)

The polarity of the applied voltage can be triggered tochange by different parameters (e.g. when the current
reaches pre-defined trigger levels) or by having a fixed
frequency.
Different techniques are then used to sense the change of
inductance (Fig. 26), leading to various complexities andperformances. The most common are (1) to measure the DC
current component of Fig. 32; (2) to perform a spectral
analysis of the Fig. 32 current and measure the amplitude ofa selected current harmonic, the one which is the mostsensitive to current shapes changes (generally the second
harmonic order), or (3) to measure the duty-cycle of theFig. 32 voltage. Once the changes of these signals aredetected, the closed loop principle of Fig. 26 is used tocompensate the flux in the gap.
4.1.4 Current transformer effects
As with a closed loop Hall effect transducer (§ 3.2.1), thesecondary coil of Fig. 26 acts as a current transformer tomeasure high frequency currents. Depending on the type of
Fluxgate considered, this is not always possible and, in
those cases, the result is a reduced bandwidth and limited
response time.

time

Figure 31: Voltage steps and current response (IP = 0)27

Fluxgate Technologies

Existing types of Fluxgate transducers• A large dynamic range, allowing measurement of both
small and large currents with the same transducer

The main types of Fluxgate transducers are shown in
Figure 33 and briefly described here:• Very high resolution, provided by the low offset. See
comment on the noise hereunder.

(1) The „standard“ Fluxgate (§ 4.1), similar to a closed loop
Hall effect design• Large temperature range, the low offset drift make
Fluxgate technologies suitable for broader operating
temperature ranges (still limited by the transducer
materials and component limits)

4.2(2) The „C-type“ Fluxgate (§ 4.4), where the performance issignificantly improved by:• Making the field sensing element with the entire
toroidal core, without a gap• Ensuring high frequency performance by using aseparate core for the transformer effect(3) The „IT-type“ Fluxgate (§ 4.5), where the performance isimproved a step further by:• Duplicating the field sensing element, using two
toroidal cores with opposing excitation coils• Improving the design of the high frequency current
transformer and processing electronics(4) the „Low frequency“ Fluxgate, using only the low
frequency part of the „C-type“ Fluxgate transducer, notconsidering the current transformer, to have a costeffective and efficient transducer for low frequencies• High bandwidth – fast response time, provided by thecurrent transformer effect (when relevant) which is further
enhanced on C-type and IT-type Fluxgates.
The technology has in general the following limitations:• Limited bandwidth for the simpler designs• A large noise level at the excitation frequency, present at
the output and possibly coupled into the primary• Voltage noise injection into the primary lines (acceptable
for the vast majority of applications)• Relatively high secondary power consumption, similar tothat of closed loop Hall effect transducers• More efficient designs are more complex and thus more
expensive to produce

(1)

(2)

(3)

(4)

• The design of Fluxgate transducers is relatively complex
and makes for more difficult customization
More details are given in the following sections outlining thedetails of specific Fluxgate designs.

Figure 33: Main types of Fluxgate transducers - field sensing
element in dark color

4.3

General performance of Fluxgate technologies

In general, Fluxgate technologies offer the following
advantages:• Low offset & offset drift, because the magnetic core iscycled throughout its B-H loop suppressing any magnetic
offset in the Fluxgate core (not avoiding offset or offset
drift of the processing electronics or, for the „standard“
Fluxgate, the magnetic offset created by the main toroid).

4.4„C-type“ Fluxgate transducers„C-type“ closed loop Fluxgate transducers are a significant
part of the LEM current and voltage product portfolio. This
technology was developed in co-operation with the
University of Auckland - New Zealand (Prof. Dan Otto) andprovides very high performance in terms of accuracy,
temperature drift, bandwidth and response time. This highperformance is the result of a patented design used for thecompensation of Ampere-turns.
4.4.1 Construction and principle of operation• Excellent accuracy due to the quasi absence of offset.
Compared Hall based technologies, this advantage ismore noticeable for small currents measurements, where
the relative effect of the offset is more significant

The basic working principle and performance of a „standard“
Fluxgate has been discussed in § 4.2 and § 4.1. An understanding of this device is the foundation for a complete
description of „C-type“ operation, provided here.

• Excellent over-current recovery, again because any
permanent magnetization of the field sensing element isreset with subsequent B-H cycles (and again, notaffecting the main toroid of the „standard“ Fluxgate)A „C-type“ Fluxgate transducer (Fig. 34) is made with two
identical magnetic cores (T1 and T2), each wound with anequal number of secondary turns, NS. The primary winding,NP, is common to both cores. The two secondary windings
are connected in series and the shared center point is also
connected to the electronics.

• Much higher sensitivity than other technologies, allowing
the measurement of very low Ampere-turns (determinedby design and dependent on the required magnitudes of
BEXT and BSI)28

One core, T1, uses the Fluxgate principle to measure thelower frequencies (T1 being the so called Fluxgate sensinghead), while the other, T2, acts as a current transformer forFluxgate Technologies

higher frequencies. Both secondary windings of T1 and T2
also acts as the zero flux compensation winding, ensuring thetransducer works in a closed loop mode.
This design has the ability to supply a single coil (secondary ofT1) with the „Fluxgate“ current (Fig. 32 and Iµ in Fig. 34) as wellas the secondary current (IS in Fig. 34) required for flux
compensation. The processing electronics then removes theFluxgate current in a „filter“ (ref. 2 in Fig. 34) to prevent noiseat the transducer output. The output current (point C of
Figure 34) is then equal to IS = IP • NP/NS. Finally, for a wide
operating temperature range, the electronics are designed toautomatically compensate the electronic offsets and voltage
drops, eliminating the need for adjustments.
„C-type“ transducers internally control the loading of thesecondary current and therefore have a voltage output.

• Very high isolation levels and excellent resistance topartial discharge (e.g. CT 5-T/SP3 transducers have
50 kVrms isolation with a partial discharge extinction levelof 14.5 kV with < 20 pC)
The limitation of the CT transducer is the injection of arectangular voltage ripple on the primary line. This is causedby the Fluxgate excitation voltage, typically at a frequency of
500 Hz, and is a function of the primary to secondary turns
ratio. This primary voltage ripple induces a current noise,with an amplitude dependent on the primary circuit
impedance; the lower the impedance the higher the current
noise (see calculation examples in § 4.4.6b). While thiscurrent noise is generally not a problem, it is measured by
the transducer and will be seen as an additional
measurement error.
4.4.3

IP
NP
T2

T1
①
Generator

B

NS
A

NS

C

IS

IS +Iµ④
I/V
Transducer

Iµ
③

②

⑤

Trigger

FilterControl Loop

VM

„CD-type“ differential current transducers

A LEM „CD“ transducer is designed to measure differential
currents, the difference between two primary currents
flowing in opposite directions. This application takes
advantage of the very high sensitivity of this topology,
allowing measurement of a differential current that is only
0.1 % of the main current flowing in each primary conductor.
For example, a differential current of 1 A can be measured
with a main current of 1000 A, or 0.1 A with a main current of
100A. The measurement accuracy is about 5 to 10 % within
the specified operating temperature range.
The main advantages are:
• Very good differential resolution (able to measure low
differential currents with high main currents)

Figure 34: Block diagram of the C-type Fluxgate transducers

4.4.2 „CT-type“ current transducers

Please note that „CT“ is a LEM product designation and is not
used as an abbreviation for current transformer.
The LEM „CT“ current transducers measure currents up to a
maximum of 150 A. They typically have an accuracy of 0.1 %and a remarkable 0 to 500 kHz bandwidth.
The main advantages are:• Possibility to have an external adjustment by the user ofthe level of the differential current to be measured (aspecial design provides external terminals in the housing,where an adjustment resistor is connected)• Special designs allow the adjustment of the time constantof the measured differential current, which is convenientwhen the output signal of the transducer is used as a
trigger in a safety system• Options to define several levels of differential currents tobe measured (the transducer is then designed with aseparate individual output for each current level)• Protection against primary current overloads• Excellent accuracy across the entire operating temperature
range

The main limitations are:• Wide bandwidth• Limited frequency bandwidth, typically DC to 2kHz

• Extremely short response time

• A differential current measurement should theoretically be
independent of the main current value, but the maincurrent must never exceed the transducer rated value to
avoid permanent local saturation affects, due to bothinternal and external magnetic effects, which will reduce
the accuracy of the transducer• Excellent immunity to surrounding magnetic fields• High overload current capability (e.g. a CT 1-S transducer,
with a 1 A nominal current, can withstand a overload above
15 kA for 150 ms)• Output short circuit protection29

Fluxgate Technologies

4.4.4 „CV-type“ voltage transducers
The „CV“ family of transducers measure voltages up to 7 kV.
The typical accuracy is 0.2 % and 1 % for the CV3 and CV4series respectively. The bandwidth is from DC to a maximum
frequency ranged between 10 kHz and 800 kHz, dependingon the selected transducer reference. CV voltage transducers
generally include the primary resistor as this value is tuned
for optimum performance. Because of the high sensitivity ofthe „C-type“ design the required primary ampere-turns issmall, leading to a lower primary inductance and resistance,
improving accuracy, bandwidth, and response time.
Their main advantages are:• Excellent accuracy over a broad operating temperature
range• Measurement of the heating current in the cathode of a
KLYSTRON accelerator.
CD differential current transducers• Measurement and detection of earth leakage currents.
• Replacement of the classic differential relays, with a better
accuracy and the detection of much smaller currents.
• Measurement of differential currents, as a safety function
in electric traction equipment.
CV voltage transducers• Measurement of AC voltages in high power industrial
inverters.
• Voltage measurement in electric traction converters (DCand AC).

• Low primary power consumption• Wide frequency bandwidth and fast response time

• Voltage measurement between phases of power cycloconverters.

• Excellent fast dv/dt measurement capability• Calibration benches for power converters and motors.

• Very good immunity against surrounding magnetic fields• Voltage measurement in photovoltaic plants (precise
measurement of the maximum power point).

• Very good immunity against common mode voltage
variations
The limitation of most of the CV transducers is the dielectricwithstand voltage of 6 kVRMS, with a partial discharge
extinction level of 2 kVRMS with < 10 pC. The CV4 transducer
has been designed with an extended isolation capability.
4.4.5 „C-type“ transducers - typical applications„C-type“ transducers are used in industrial applications
requiring very high accuracy, for example calibration units,diagnosis systems, test platforms and laboratory equipment.
It is also appropriate when the application needs an absoluterobustness of performance with temperature changes.
CT current transducers• Current measurement in transmitters.
• Measuring the magnetizing current and DC current in
power transformers, avoiding unexpected magnetic
saturation (industrial equipment and electric traction).
• Current measurement in induction heating systems.
• Measurement of charge and discharge currents for battery
testers.

• Laboratory measurement instruments: isolated voltage
measurement, power measurement for inverters, as aninterface with a power analyzer, etc.
4.4.6 Calculation of the measurement accuracy & noise
rejection
The following examples show the high performance of the„C-type“ transducers.
Example 1: Accuracy of the CT 100-S current transducer(see datasheet)
In this example a 100 A DC current is measured and,according to the transducer datasheet, the output voltage
will be 5 V. Using this part within its operating temperature
range of 25 to 70 °C the indicated accuracy is ±0.15 %,including an initial offset of maximum ±0.4 mV, and thetemperature drift of the offset voltage can be ±0.6 mV.
Accuracy
Offset drift with temperature±0.15 % of IPN±0.6 mV/5 V

Worst-case error±0.15 %
±0.012 %±0.162 %This worst-case error is expressed as a percentage of thenominal value• Calibration benches for power converters and motors.
• Current measurement in the electric energy distribution
simulators and substations.

Example 2: Ripple rejection and the CT 5-T current
transducer (see datasheet)• Current measurement in photovoltaic plants (precise
measurement of the maximum power point).

This example demonstrates the ripple rejection in the
primary circuit of a CT 5-T transducer. We have:• Laboratory instruments: isolated current measurement for
use with an oscilloscope or a digital multi-meter; power
measurement for inverters, as an interface with a power
analyzer, etc…

• The internal square-wave generator (Fig. 34 - ref. 1)
provides a voltage of USW = ± 6.8 V

30• Number of primary turns is NP = 10

Fluxgate Technologies• Number of secondary turns is NS = 1000

4.5.1 Construction and principle of operation• I / V converter resistance (Fig. 34 - ref. 4) is RC = 100 Ω
If the primary circuit impedance is ZP = 100 Ω, the induced
primary current becomes:
IPind = VSW • NP / (NS • ZP) = 6.8 • 10 / (1000 • 100) = 0.68 mA
The voltage induced in the secondary by this parasitic
current is:
VSind = IPind • (NP/NS) • RC = 0.68 mA • (10/1000) • 100 = 0.68 mV
For a primary current giving a 5 V output signal, thecorresponding measurement error is 0.68 mV/5 V = 0.014 %.

The „IT-type“ transducer consists of a current measuring
head made of three magnetic cores, C1, C2, and C3, withprimary (wP1) and secondary (wS1 to wS4) windings as shownin Fig. 35. Closed loop compensation is obtained by asecondary current, IC, fed into one of the secondary coils(wS2). The latter coil, magnetic coupled to the three magnetic
cores, is connected in series with the measuring resistor to
obtain an output voltage of typically 1 V with secondary
currents of 200 or 400 mA.
Compensation
AmplifierLow frequency
correction

V+

SecondHarmonic
Detector++If, on the other hand, the primary impedance is small, forexample ZP = 1 Ω the measurement error becomes much
more significant, 1.4 % in this case.

-–
V–

High frequency
correction

Iµ-

Ic

WS1

φµ

Example 3: CV voltage transducer – Accuracy
calculationTA+25 °CTA max+70 °C

WS3

Ic

φµ

WS4

IP & wP1

Square wave
generator

φP

C1

WS2

Iµ+

C2

WS2

Zero flux
current

φP

C3

Rm

WS2

Output voltage

Typical accuracy of the primary
resistances

0.05 %

0.05 %

Variation with temperature(typical coefficient 20 ppm/°C)-0.10 %

Figure 35: Principle of the IT transducer

For the upper frequency range, the secondary current resultsfrom a transformer effect in two secondary coils (w 1 and w 2).
For lower frequencies, including DC, the design functions asa closed loop Fluxgate transducer (§ 4.1), with the winding
wS3 and wS4 being the Fluxgate sensing coils. These features
are described in details hereunder.
S

Typical resistance accuracyof the converter

0.05 %

0.05 %

Variation with temperature(typical coefficient 20 ppm/°C)-0.10 %

Secondary offset voltage:- nominal is 5 mV- Maximum with temperature
is 10 mV
Maximum total error

4.5.1.1 Transformer effect – high frequencies
0.10 %--

0.20 %

0.20 %

0.5 %Example 4: Accuracy of the CV 1-1500 voltage
transducer (see datasheet)
The CV 1-1500 voltage transducer is designed to measure a
1500V peak voltage. According to the transducer datasheet,the output voltage will then be 10 V peak. Using this partwithin its operating temperature range of 25 to 70 °C theindicated accuracy is ±3. 0% including an initial offset of max±100 mV. This worst-case error is expressed as apercentage of the peak value.
4.5

S„IT-type“ Fluxgate transducers

LEM „IT-type“ closed loop Fluxgate transducers allow AC
and DC current measurement with very high accuracy,
linearity and stability, while eliminating the injection of noise
into the primary.

The current transformer is made with a primary (wP1) and two
secondary coils (wS1 and wS2), wound around the samemagnetic core (C1). The secondary coils are connected to acompensation amplifier in order to improve the overall
performances. This system works as follow:• The coils wP1 and wS2 work as a classical current
transformer, where a current IC is induced into thesecondary coil, proportional to the primary current to bemeasured, leading theoretically to a zero total flux into themagnetic core.
• In practice, a residual flux remains, reflecting the imperfectcoupling between the primary (wP1) and secondary (wS2)
coils as well as the transformer burden. For a current
transformer, this residual flux is an image of themeasurement imperfections.
• The coil wS1, connected on a high impedance, collects a
non zero voltage when an AC residual flux occurs: a signal
is then sent into the correction amplifier, adjusting thesecondary current IS until the total flux is equal to zero.
The resulting current transformer performances are
remarkable.
31Fluxgate Technologies

wWS4
I
I µ+

W
w
S3
S3

S4

IµIµ-

µ+

iµ+ (t)Second harmonic detectortime
iµ- (t)Low frequency
correction

Masse

GND
2f2f

Masse
GND

Figure 37: Iµ+ and Iµ- currents

IT transducer working principle
Figure 36: Block diagram of the symmetrical zero flux detector

4.5.1.2 Fluxgate detector – low frequencies
The Fluxgate sensor (Fig. 35) is made of two magneticallysymmetric parts (two saturable inductors), each of themmade with one magnetic core (C2 or C3), one primarywinding (wP1), one compensation winding (ws2) and one
secondary winding (wS3 or wS4).
Close-loop not active
At low frequency, assuming in first instance that the zero flux
compensation created by wS2 is inactive, the flux ΦP createdby the primary current is identical in both C2 and C3 cores(Fig. 35), with the same magnetic polarity.
The secondary windings are connected to a square-wave
generator that supplies the Iµ currents (Fig. 36), bringing thecore C2 and C3 into saturation. The resulting Iµ currents
have a shape as shown on Fig. 31 and Fig. 32.
Due to the magnetic construction and electric connections of
wS3 or wS4 windings, the fluxes created by the Iµ currents into
the C2 and C3 cores have an opposite magnetic polarity(±Φµ). The total flux in the C2 and C3 core are consequently
different, since at a given time the flux Φµ and ΦP are
additive in C3 and subtractive in C2 (Fig. 35). The level ofsaturation in the two cores being different, the shape of theIµ+ and Iµ- currents will be at any time different, including
differences on the DC value and when the current ‘peaks’(or saturation) occur. Assuming a frequency of the Iµ currents
significantly larger than the primary current frequency, the Iµ+
and Iµ- currents have typically the shape shown on Fig. 37.
In term of noise, the fact that the switched currents (Iµ+ and Iµ-)create fluxes with an opposite polarity (± Φµ) explains why
the conducted noise created by the IT transducer is very
limited.

32

In normal working conditions, the close-loop coil wS2 isactive and the principle can be further described as follow :When there is no primary current, the system is magneticallysymmetric and the Iµ currents are identical, with a shapelooking like that shown in Fig. 31.
An increase of the primary current has the following
consequences (Fig. 37):
• It creates a DC current component on the Iµ+ and Iµcurrents, positive or negative respectively.
• The „AC“ behavior of the two Iµ currents different, withpeaks with large and small amplitudes not occurring at
the same time.
The IT transducer only monitors the differences in the Iµ
currents shapes, reflecting a change in the primary current.
When a change is noticed, the compensating Is current in thesecondary coil wS2 is adjusted in order to be back to theinitial magnetic stage. This is identical to the general closed
loop principle described before.
The shape change is detected by a „second harmonic
detector“ (Fig. 36), described hereunder, which detects
changes in the harmonic content of the Iµ current waveform.
The second harmonic order is selected because it is themost sensitive.
Due to the targeted very high resolution and accuracy,
preference is given to this harmonic detection principle
rather than a monitoring of the changes in the Iµ current’s
DC offset. Indeed, while the latter principle is regularly
considered for less efficient Fluxgate designs, it suffers from
offset errors introduced by the processing electronic.
A key element of this detector is the center-tapped
transformer, which naturally sort out the second harmonics
of its Iµ primary currents. The transformer primary coil ismade in two parts, connected in a way that the Iµ+ and Iµcurrents create flux with an opposite polarity:

Fluxgate Technologies• When the two Iµ currents are identical (IP = 0), the flux
cancellation is such that there is no signal induced into
the secondary of the center-tapped transformer• When the two Iµ currents are different (IP different fromzero), only their AC differences create a signal. In thiscase, where the Iµ currents have the Fig. 37 shapes, all
the Iµ currents uneven harmonics (1, 3, 5…) create a zero
total flux, while the even harmonics (2, 4…) create an AC
flux and thus a signal into the secondary winding of thecenter-tapped transformer.
Finally, among the harmonic content of the transformer
output signal, only the second harmonic is detected by the
dedicated processing electronics (Fig. 36), using an analog
switch driven at twice the excitation frequency, ensuring„synchronous rectification“ of the second harmonic signal.
The output of the synchronous rectifier is then filtered using
a low-pass filter, before controlling the amplifier that drives
flux compensation coil, wS2 (Fig. 35).
This WS2 coil is consequently compensating both the low
frequencies, using the Fluxgate principle, and the highfrequencies, through current transformer effects.
4.5.2 „IT-type“ transducers – advantages & limitations
The main advantages are:
• Very high accuracy and stability

4.5.4 Calculation of the measurement accuracy
Set an IT 600-S transducer to measure nominal current andcheck accuracy at 100 % and 10 % of this level.
Example 1: Accuracy of the IT 600-S at 600A (seedatasheet)
When measuring a 600 A DC current, an IT 600-S can only
provide a 1 V output. With a current transfer ratio of 1500:1,
the secondary current is 400 mA and therefore themeasurement resistance must be 2.5 Ω. We will assume theworst-case rated operating temperature of 50 °C for the
analysis. This amounts to a 25 °C deviation which creates a
0.1 µA/°C • 25 °C = 2.5 µA offset drift. The error is given inboth mA and ppm of reading.
At 25 °C ambient
DC offset on secondary current
at IP = 0

< 4 mA

10 ppmNon-linearity: <1 ppm of full scale < 0.4 mA

1 ppm

Measuring ratio stability of< 2ppm of reading< 0.8 mA

2 ppm

Total error at 25 °C< 5.2 mA

13 ppmDrift with temperature (from 25 °C to 50 °C)
DC offset drift: 0.1 mA/K

2.5 mA

6.25 ppm• Excellent linearity (< 1 ppm)

Measuring ratio stability of
0.3 ppm of reading/K

3 mA

7.5 ppm• Very good temperature stability (< 0.3 ppm/K)

Maximum global error at 50 °C< 10.7 mA• Very low initial offset and drift with temperature• Large bandwidth (DC to 100 kHz)26.75 ppm

Example 2: Accuracy of the IT 600-S at 60 A

• Very low distortion for AC current measurement• Very low noise on the output signal
The limitations are:• Operating temperature presently limited to laboratory or
clean environment usage (basically 10 °C to 50 °C)

With the same configuration, capable of measuring 600 A,
the IT 600-S will only give 40 mA and 0.1 V at 60 A. The
error is given in both mA and ppm of reading.
At 25 °C ambient• High power supply current consumption

DC offset on secondary current
at IP = 0

• Relatively large dimensions

Non-linearity : <1 ppm of full scale < 0.4 mA

4.5.3 „IT-type“ transducers - typical applications

Measuring ratio stability of< 2ppm of reading< 0.08 mA

2ppm• Feedback measurement in precision current regulated
power supplies.

Total error at 25°C

< 4.48 mA

112ppm• Precision current control in gradient amplifiers for medical
imaging.

Drift with temperature (from 25 °C to 50 °C)• Current measurement for power analysis.
• Calibration device for test benches.
• Battery charging equipment requiring high-resolution
measurement.

< 4 mA

100 ppm
10 ppmDC offset drift: 0.1 mA/K

2.5 mA

62.5 ppm

Measuring ratio stability of
0.3 ppm of reading/K

0.3 mA

7.5 ppm

Maximum global error at 50°C

< 7.28 mA

182 ppm• Laboratory/metrology equipment requiring high accuracy
measurement.
33

Air-Core Technologies

5

Air-core technologies

The performance of current and voltage transducers are often
limited by the characteristics of the magnetic core material
itself (e.g. remanence, hysteresis, non-linearity, losses,
saturation) so the design of an air-core, or coreless,transducer is often considered.
In this case the following issues have to be taken into
account:• the measurement of DC current requires the use of a fieldsensing element; due to the absence of a field focusedarea (e.g. gap), a highly sensitive field sensing device
must be considered (e.g. GMR, Hall cell) ideally in an arrayaround the conductor.
• when available, a magnetic circuit can be used as a shield
to external magnetic field disturbances (e.g. earth’s field,
external conductors); with air-core technologies thesensitivity to external disturbances must be managed in adifferent way, for example an array of field sensors insteadof a single sensor or, when coils are considered, special
design execution such as the Rogowski method of routing
the return wire; the ability to accurately measure thedesired current while also rejecting external fields is asignificant challenge for air-core technologies.

the waveform of the measured current requires theintegration of the induced voltage. Therefore, the current
transducer includes an integration function in the processing
electronics.
In the LEM~flex and PRiME™ transducer datasheets thevalue of sensitivity (S12) is provided, linking the amplitude ofa sinusoidal current to the amplitude of the transducer output
voltage at a specific frequency. The same sensitivity parameter can also be used to link the RMS values of a sine
wave primary current and the corresponding sine wave
output voltage, namely:
EPEAK = S12 • f • IPEAK and ERMS = S12 • f • IRMS
To give an order of magnitude, the typical sensitivity is:• LEM~flex probe

S12 = 2.0 [µVs/A]• PRiME™

S12 = 1.0 [µVs/A]

5.2

LEM~flex - the flexible AC current transducer

LEM~flex is a transducer based on the Rogowski coilprinciple (Fig. 38), providing a flexible air-core sensor thatcan be opened, allowing it to be installed on a primaryconductor without interrupting the circuit.

Two efficient air-core transducer technologies are presented
in this chapter, both related to AC measurements: theLEM~flex and PRiME™(1) technologies.
(1) patented and licensed to LEM by Suparule Ltd.

5.1

Basic working principle and sensitivity

LEM~flex and PRiME™ technologies both work on the same
basic principle; a pick-up coil is magnetically coupled withthe flux created by the current to be measured. A voltage is
induced on the pick-up coil proportional to the derivative offlux and thus proportional to the derivative of the current to bemeasured. Because the derivative of DC is zero thesetechnologies are only useful for the measurement of AC or
pulsed currents.
The instantaneous voltage induced in the pick-up coil istypically:
EOUT(t) = L12 • di(t)/dt[V]

For a sinusoidal current, we have:[A]

Hence:EOUT (t) = L12 • IPEAK • 2 • π • f • cos(2 • π • f • t)
= EPEAK • cos (2 • π • f • t)

[V]

As shown in this example, where a sinusoidal current i(t)creates a phase delayed (cosine) voltage EOUT(t), reproducing
34

Figure 38: Rogowski AC current measurement

5.2.1 Construction and principle of operation

where i(t) is the primary current [A] and L12 is the mutual
inductance [H] between the primary and pick-up coil.

i(t) = IPEAK • sin(2 • π • f • t)

IP

The key element of the LEM~flex transducer is the flexible
measuring head (Figure 39), which is a coil uniformly woundaround a flexible former of insulating material. The end of
the coil wire is returned to the same end as the start by
returning it co-axially through the coil former (Fig. 38). This
construction technique minimizes the sensitivity to external
field disturbances.
To make a measurement, it is not necessary to have theLEM~flex transducer formed as a circle or to have theprimary conductor(s) centered within the perimeter. In
practice, the flexible measuring head is wrapped around the
conductor(s) carrying the current to be measured and thetwo ends are brought together and mechanically connectedby a coupling latch (Fig. 40) to form a closed path.

Air-Core Technologies

sectional area. Note that changing the length of a Rogowski
coil does not affect the sensitivity.
5.2.2 Characteristics and features
The LEM~flex family of transducers has been designed toconveniently measure single and 3-phase AC currents, aswell as pulsed DC currents. Standard ranges include 30/300/
3 kARMS and 60/600/6 kARMS, but scaling is easily designed forother currents. Theoretically the size of the measuring head
and/or measurement range is unlimited.
The standard LEM~flex current transducer provides asensitivity of 50 or 100 mV/A at 50 Hz and at the output of theprocessing electronic. The analog output voltage, galvanicallyisolated from the measured current, is 0 to 3 VRMS, or to beprecise 4.25 VPEAK.
Fig. 39 LEM-flex transducers

Due to the flexibility of the measuring heads, it is possible toposition them around one or more irregularly shaped ordifficult to access conductors or busbars. The transducer canbe quickly and easily installed as well as removed. Installationand measurement is performed without mechanical orelectrical interruption of the current carrying conductor, while
also ensuring galvanic isolation. LEM~flex transducers arealso very lightweight.
In terms of bandwidth, the performance of the LEM~flex
transducer is similar in concept to a band-pass circuit,exhibiting both high and low cut-off frequencies. As theintegrator gain can be very high, shielding and appropriate
filtering prior to the integrator must be used to minimize theinfluences from low frequency influences. For high frequency
performance, the upper cut-off frequency is determined by thecoil inductance and capacitance. It should also be noted thatthe integrator includes compensation circuits that limit thethermal drift. The typical bandwidth targeted by the LEM~flex
portfolio is 10 to 100 kHz, with possible extension to 1 MHz.
As the LEM~flex measuring head is fundamentally an air-core
coil, there is no magnetic hysteresis, no saturation
phenomena or non-linearity, as is present with magnetic
cores. The main factors that affect the accuracy of thistechnology are:4

1.30
Phase Degree

The sensitivity (§ 5.1) of a LEM~flex transducer can bedetailed as follows:
S12 = 8 • 10-7 • π2 • N • A
where N is the density of the coil turns made around theflexible insulating cylinder [turns/m] and A is the crosssectional area of the coil [m2].

2
0

1.20

Phase Degree ( ° )Fig. 40 Typical LEM-flex use, surrounding conductor(s) and latched.

Relative Amplitude

1.25

-2

1.15

-4

1.10

-6
-8

1.05

Output

-10

1.00

-12
-14

0.95
8 10

40

100

400

1k

4k

10k

40k

100k

Frequency (Hz)Figure 41: Integrator circuit & bandwidth

To design a Rogowski coil with a high sensitivity requires
either a large number of turns per meter or a large cross35

Air-Core Technologies• the manufacturing tolerances of the wound coil (consistentturns/m and m2)• the fact this is a mechanically open structure, leading to aslight gap in the coil perimeter where the two ends arebrought together• the error introduced by the processing electronics, such as
the integrator circuit phase angle error and relative
amplitude as shown in Fig. 41.
These factors lead to slight errors based on the position of thecurrent conductor inside the LEM~flex and sensitivity to fields
from conductors just outside the perimeter of the LEM~flex.
These errors are typically below 1 %, with a maximum of 2 %,and can be avoided entirely by proper positioning of the
LEM~flex.
5.2.3 Typical applications
LEM~flex is a lightweight measuring head combined withremote electronics (distance between head and electronics
can be as great as 4 meters, or 12 feet). This, along with all of
the previous described attributes, lead to a device suitable foruse in a wide range of applications.
• Measuring currents in busbar sets, in particular in induction
heating equipment.
• Frequency converters, variable speed drives andgenerators.
• Control of power semiconductors.
• Analysis of the current distribution in mains networks.
• Analysis of harmonics, power measurements,
measurement of the peak load in the mains, and in UPS.

Linearity error±0.2 % of reading
Accuracy at 25 °C ±1 % of range
Accuracy drift±0.08 %/K • 25°C • 280
Position error±2.0 % of reading±0.56 A
±3 A
±5.6 A±5.6 A

Worst-case error±14.76 A ⇔±5.3 % of reading

Care must be exercised in properly identifying errors basedon reading and those based on range.

5.3

PRiMETM Transducers

PRiMETM has been developed to measure AC and pulsed DC
currents with minimal effect from external sources, achievedby the application of a novel compensation technique.
PRiMETM is an air-core technology based on planar magnetic
sensors, constructed using no ferromagnetic material. It issimilar to the LEM~flex technique, but uses discrete coils at
regular intervals around a fixed perimeter rather than acontinuous uniform coil. A specific coils arrangement gives
the robustness to external field perturbations.
5.3.1 Construction and Principle of Operation
The transducer head comprises two parts, a number of
sensor printed wiring boards (PWBs), and a base-PWB (Fig.
42). The sensor PWB consists of two separate coils
constructed on a multi-layer PWB (Fig. 43). Several sensors
are mounted onto the base-PWB, at right angles to it, andconnected in series to form two concentric inner and outer
loops (Fig. 44). A larger number of sensor PWBs provides
higher accuracy, lower sensitivity to conductor position andimproved external field rejection performance.

• Switched mode power supplies.
• Low or medium voltage distribution installations.
• Power electronics installations.
• Sensing devices for watt meters and network analyzers
installed by electric power distribution companies.
• Electrical maintenance, repair and machine installation andstart-up applications.

To make measurements, the current carrying conductor
needs to be positioned within the aperture of the transducer
head, within both loops (Fig. 42). This creates an AC
magnetic flux, which is coupled into the sensors and induces
a voltage proportional to the rate of change of the current (di/dt) in both the inner and outer loops (Fig. 44). As a result, a• Connection to most measuring instruments including
multimeters, oscilloscopes, recording devices, data loggers,
etc.

Conductor to bemeasured
Sensor PWB

5.2.4 Calculation of the measurement accuracy
An example of a total error calculation is given for the
LEM~flex RR 3020, (see datasheet) having threeselectionable working ranges of 30/300/3000 A nominal
current. Considering a 280 ARMS current giving a 2.8 VRMS
output signal (10 mV/A), what is the measurement accuracy at
an ambient temperature of 50 °C? According to thedatasheet, the error values are:36

Base PWB

IP
Figure 42: PRiMETM current transducer

Air-Core Technologies

measured. The integrator circuit (Fig. 45) is kept as close
to the transducer head as possible to reduce stray inductive
pickup that would give rise to errors.
Finally, the comments made previously (§ 5.1) regarding the
instantaneous voltage collected by the coils of an air-coretechnology are again applicable.
5.3.2 Characteristics and Features
Figure 43: PRiMETM sensor multi-layers printed wiring board

Figure 44: PRiMETM – two coils concentric loops

constant DC current will not produce a voltage andtherefore cannot be measured. However, as with LEM~flex,
it will respond to pulsed currents.
The output signal VTOTAL (Fig. 45), used for the current
measurement is:
VTOTAL = VINNER – VOUTER / λ = VINNER • [1 - (VOUTER / VINNER)/ λ]For an external current source, the essence of thetechnology is that the ratio of the induced voltage in eachloop of sensor PWBs (VOUTER / VINNER) is almost constant,irrespective of the magnitude or position of this externalsource. As a result, the external field effects are cancelled if
the correct proportion of the voltage induced in the outer
loop (VOUTER) is substracted from that in the inner loop
(VINNER). Making λ = VOUTER / VINNER will force VTOTAL = 0 or, inother words, an external current source will not produce any
signal at the output.
To measure the current from the conductor placed within theaperture, an optimized transducer design leads to a typical
VOUTER / VINNER ratio of λ / 2, again irrespective of the
conductor position. As a result, the usable signal for themeasurement is close to VTOTAL = VINNER / 2, meaning thatapproximately half of the signal collected by the innerconcentric chain of sensing PWB coils is used for themeasurement.
In short, this novel arrangement provides one-half of the total
possible signal for measurement while effectively cancelingthe unwanted influence of signals from external current
sources.
As with the LEM~flex, the collected signal is proportional tothe derivative of the current and it is necessary to integrate
the voltage induced in the transducer head to obtain both
amplitude and phase information for the current being

Since PRiMETM utilizes an air-core coil as the sensing
element, there is no magnetic hysteresis, saturation, or nonlinearity, as is present in a current transformer with amagnetic core.
There is no theoretical maximum limit to the measuring
range, but the typical dynamic range is 1000:1,
corresponding to the ratio of the maximum to minimum
measurable current with a given transducer. The accuracy is
typically specified as a percentage of reading, above 10 %of the nominal rated current, leading to a highly accurate
solution when the current is only a fraction of the nominal
current. The accuracy is generally better than 0.8 % ofreading and the gain variation due to temperature is low,
typically 0.01 %/K.
The output voltage is directly proportional to the measured
current and provides accurate phase information. The levelof sensitivity depends on the required measuring range andsupply voltage.
The aperture sizes for existing transducers range from20 mm to 160 mm in diameter, in both ring and split format.
There is no theoretical limit to the size of the aperture. With
split versions, installation and measurement can be
performed without mechanical or electrical interruption of thecurrent carrying conductor, while also ensuring galvanic
isolation.
The bandwidth of PRiMETM has both a high frequency and a
low frequency cut off. The high frequency limit is dependent
on the resonant frequency of the sensors while the low
frequency limit is a function of the integrator design.
Products are designed for a given bandwidth, typically 5 to
100 kHz, but an upper limit in the MHz range appears to befeasible.

Vinner-Cf

R1
VouterR1λVtotal+Figure 45: PRiMETM – processing of the coil signals

37

Air-Core Technologies

3

30

2

20

1

10

0

0

-1

-10

-2

-20
-30

-3
○

○

○

Attenuation (dB)
Phase shift (°)

Figure 46: PRiMETM – typical bandwidth 5 to 100 kHz

5.3.3 Advantages and Limitations of PRiMETM Technology• Capable of measuring AC and pulsed DC currents.
• Wide current measuring range, capable of withstanding
high overload.
• Accuracy given in percent of reading; high accuracy over awide measuring range.
• Large bandwidth, not including DC.
• Lightweight in comparison with current transformers ortransducers.
• On-board electronics that can potentially be merged withthe users electronics.
• Provides an isolated output signal (e.g. 4-20 mA, 0-10 V)
usable with PLCs without conditioning.
• Requires a power supply, but has low current consumption
requirements.
This makes them suitable for portable applications and power
quality monitoring where weight and battery life are aconcern. This performance also make them suitablereplacements for current transformers.

38

Other Types of Voltage Transducers Technologies

6and transmitted to the secondary side through an opticallink. The same is done with the required datasynchronization signals.

Other types of voltage transducer technologies

Two additional voltage measurement technologies have beendeveloped by LEM to achieve differentiated measurement
performance compared to Hall (§ 3.4) or Fluxgate (§ 4.4.4)
based voltage transducers. The first technology, OptiLEM,
uses fiber optics for the transmission of the voltage
measurement information, providing a high level of dielectricisolation. The second technology is the AV-type of voltage
transducer based on electronic isolation circuitry that also
provides galvanic isolation, but at the component level rather
than using discrete fiber optics.
6.1

On the secondary side the data stream is converted backinto an analog signal and converted into an output current
for high noise immunity and easy scaling. A very critical
function of the transducer is to provide a low voltage supply
for the components on the primary side, requiring a very
high level of voltage isolation and very low capacitive
coupling from primary to secondary. A sine wave signal isused to minimize noise levels.

OptiLEM voltage transducers

The OptiLEM voltage transducer has been developed toprovide an optimal solution for higher isolation voltages. The
result is an interesting product containing numerous patented
concepts.
The following key attributes are reached with the first voltage
transducer model:• isolated voltage measurements up to 12 kVRMS• 100 V to 6 kV measuring range• overall accuracy better than 1.5 %• bandwidth from DC to 12 kHz• low stray capacitance between primary and secondary(less than 10 pF)

Figure 48: OptiLEM voltage transducer• low partial discharge extinction level of 5 kV with < 10 pC
The working principle of the OptiLEM voltage transducers isshown in Fig. 47. The primary voltage is directly applied to thetransducer primary connections, ±U. An internal resistor
divider network and differential amplifier measure the primaryvoltage signal. This output is converted to a serial data string
12 bits A/D
converterU+

SERIAL DATAADIFFERENTIALAMPLIFIER

D

M

U

D

OPTIC FIBERAIUOPTIC FIBERSYNCHRONIZATION+V+
OSCILLATORVOLTAGE REGULATOR

supply-V-

PRIMARY SUPPLY+0-RECTIFIER/ FILTERPRIMARY SIDEHIGH INSULATIONVOLTAGE
TRANSFORMER

SINEOSCILLATORSECONDARY SIDE

Figure 47: OptiLEM working principle

39

Other Types of Voltage Transducers Technologies

6.2

voltage value. Any kind of signal can be measured: DC, AC,or complex waveforms. The output current is always a true
image of the primary voltage.

„AV type“ voltage transducers

6.2.1 Construction and Principle of Operation
The working principle of the AV-type voltage transducers isshown in Fig. 49. The primary voltage (VPN) is applied
directly to the transducer primary connections (±HT). An
internal resistor network and amplifier perform the voltage
measurement and drive an isolation amplifier. The latterensures an accurate and isolated transfer of the measured
information from the primary to the secondary side of thetransducer, based on a capacitive isolation principle.
Another important function of the transducer is to provide alow voltage supply for the components on the primary side,which requires the use of an efficient, well isolated, voltage
transformer capable of withstanding the specified primary to
secondary insulation levels.
At the output, the transmitted signal is recovered and thenconditioned to supply a current at the transducer output thatis an exact representation of the primary voltage. While theAV-type transducer is a new LEM product, it utilizes only
well-known electronic components and techniques toensure quality and reliability.
6.2.2 Characteristics and Features

The measurement bandwidth ranges from DC to 13 kHz.
The delay time is less than 13 µs while the response time isless than 33 µs. Compared to magnetically isolated voltage
transducers, the frequency bandwidth is not linked to themodel chosen, as there is no appreciable primary
inductance to create an L / R rolloff.
The linearity errors are within 0.1 % while the overall
accuracy is 1.7 % of VPN between –40 and 85 °C.
The main advantage of the AV technology is the small sizeand lightweight, with a common compact design for eachmodel from 50 V to 1.5 k VRMS nominal. Compared to Hall
based voltage transducers, the large heat sink often used for
power dissipation of the integrated primary resistors is notneeded. This is a significant space and weight reduction. As
a comparison, the AV 100 family has approximately one-halfthe volume (3 • 10-4m3) of the LV 100 family. The limitations
are a lower accuracy and limited insulation capability
compared to some of the other available voltage
transducers.
The AV 100 family delivers an output current of 50 mA at VPN.

The AV-type is a galvanically isolated voltage transducer
made for measurements from 50 V to 1.5 kVRMS. The peakvoltage measurement capability is 150 % of the nominal

Power Supply +VC
Primary+HT

Operational
AmplifierSecondary

Isolating
Amplifier

U/I
Secondarycurrent
outputVPN
PrimaryIS
Voltage-HT-VC

RectifierFigure 49: AV type voltage transducers

40

Transformer

Oscillator

Other Types of Voltage Transducers Technologies

6.2.3 Typical applications+ HT

Presently, the main market for the AV 100 is in traction
inverters, but they can also be used in or adapted for any
industrial application.

+ HT• Auxiliary and main converters (input voltage, DC link,
output phase voltages).

- HT

+ Vc

+

RM
M
0V

• Chopper and power factor correction circuits.
• Battery chargers.
• Sub-Stations and others.

- HT

Figure 50: Electric connection – AV 100 with positive unipolar
power supply

6.2.4 Calculations & Properties
Calculation of the measuring resistor RM
The AV 100 family provides a current output. This current
can be transformed into a voltage with the addition of ameasuring resistor, RM, at the output which cannot exceed adefined RMmax value, based on the available voltage at thetransducer supply and the maximum voltage measured. For
the AV 100 family, RMmax can be easily calculated using thefollowing formula:

Negative unipolar power supply
In this case, the zener diode must be inserted as shown in
Figure 51 and the zener voltage, VZ, must be greater than
5.1 volts. The maximum measuring resistance becomes:
RMmax = [(abs(VCmin) - 2.0 - VZ) • VPN / (VPmax • ISN) - 31] • 0.9
with abs (VCmin) corresponding to the absolute value of the
VCmin voltage.
+ HT

R Mmax= ((VCmin - 5.1) • VPN / (VPmax • ISN) - 31) • 0.9 [Ω]

With:
VCmin

= Minimum value of the secondary power supply [V]5.1= Internal voltage drop of the electronics [V]VPN= Nominal measurable primary voltage [V]V Pmax= Maximum measurable primary voltage [V]ISN= Secondary output current at VPN [A]31= Secondary internal resistance [Ω]0.9= Safety factor [-]

+ HT

+

0 V
RM

M
- HT

-

- Vc

- HT
Figure 51: Electric connection – AV 100 with negative unipolar
power supply

The RMmax values indicated in the datasheets are the values
calculated using VPmax.
Unipolar Power Supply
For unipolar voltage measurements the AV 100 family canoperate from a unipolar secondary supply. A positive supply
allows positive voltage measurements while a negative
supply allows negative voltage measurements.
Positive unipolar power supply
In this case, a zener diode must be inserted as shown in
Figure 50 and the zener voltage, VZ, must be greater than
2.0 V. The maximum measuring resistance becomes:
RM max = [(VCmin - 5.1 - VZ) • VPN / (VPmax • ISN) - 31] • 0.9

41

Current Probes

7

Current probes

A comprehensive range of LEM clamp-on current probes(Figure 52) allows current measurements from 5mA to 6kA.
The technologies used for the probes have been presented
before, including Hall effect, Fluxgate and air-coretechnologies. Probe performance depends on the selected
sensing technology with bandwidths from DC up to 50MHz
and accuracies as low as 0.1% - 1%.

Compared to current transducers, additional issues need tobe considered when specifying a probe, linked to the way an
end-user handles a probe. For example, the effect of theposition of the conductors in the head, the manner in which
the jaw opens, the need for the head to fit into tight areas,and safety concerns, such as „tactile barrier“ (indicating asafe working distance from the operator’s hand to the live
conductor) and a reinforced or double-isolated output cablewith safety connectors.
In term of applications, clamp-on current probes open many
opportunities: in maintenance, repair-shops, and for the
installation and commissioning of industrial machines andequipment. Applications include automobile diagnostics inthe factory and in garages, electroplating plants, telecommunication and computer equipment, drives controlled byfrequency inverters, industrial controllers and electricalvehicles. In Hi-Fi amplifiers, the different loudspeakercurrents can be easily measured. Earth-leakage measurements in single or 3-phase AC networks are also possible,
by inserting two or three conductors in a single probe head.
Finally, current probes are also frequently used in processcontrol applications, for measuring the status of 4 to 20mA
current loops.

Figure 52: Clamp-on current probes

42

Miscellaneous

8

Miscellaneous

Here are additional concerns when using the types ofmeasurement devices described in this document.
8.1

Power supply polarity inversion

A LEM transducer may be damaged by an inversion of thepower supply voltage or connection of supply voltages to the
output or common pins. If this is a concern, LEM advises theuser to insert a diode on each power supply line, both
positive and negative, or to look for a specific LEM transducer that incorporates these protection diodes.
8.2

Capacitive dv/dt noise

Any electrical component with galvanic isolation has
capacitive coupling between the isolated potentials.
Applications with fast switching speeds, and consequently
fast voltage changes (dv/dt), across this capacitanceexperience some coupling of the primary transient to thesecondary side creating undesirable interferences.
For example, a voltage change of 10 kV/µs in combination
with a 10 pF coupling capacitance generates a parasitic
current of i = C • dv/dt = 100mA. This represents an error of
two times the nominal output current for a transducer with a
50 mA nominal output.
This issue typically occurs with power converters where a
power component, such as a MOSFET (Metal Oxide
Semiconductor Field Effect Transistor) or IGBT (Insulated
Gate Bipolar Transistor), switch the voltage at frequencies in
the 10 kHz to 1 MHz range, generating dv/dt values in the
5 to 50 kV/µs range.

Figure 53: dv/dt disturbance and transducer signal

The following points can be highlighted:• when long cables are used for the secondary connectionsof the transducer, it is advisable to use a shielded cableconnecting the shield to a driven common at themeasurement end of the cable• when possible, it is recommended to desynchronize themeasurement from the dv/dt occurrence, never performinga measurement during the dv/dt disturbance and settlingtime• it is possible to attenuate the dv/dt disturbances using a
low pass filter; while this is detrimental to the transducer
bandwidth, in many cases it is a reasonable and desirable
solution- CH2 is the output of an LAS 50-TP representing a primary
current of 16 A/div;• during printed wiring board (PWB) layout it is important tokeep secondary traces and primary traces, wires, or bus
bars separated and avoid long parallel runs to minimize
capacitive coupling; the best scenario has the secondary
traces running perpendicular to the primary providing
immediate separation; it is also advantageous to include ascreening trace or plane, connected to a star ground point,
between the primary and secondary to shunt the
disturbance to the screen rather than the secondary- CH3 is the output of an LAH 50-P representing a primary
current of 4 A/div.

8.3

Figure 53 is an example of a primary dv/dt and the resulting
output noise:- the time scale is 200 ns/div;- CH1 is the primary voltage of 250 V/div, a 1 kV excursion
creating a 6 kV/µs transient (800 V in 133 ns);

For these two transducers, the settling time is close to 800 ns
and the peak disturbance is 50% and 7% of the nominal
current, for the LAS 50-TP and LAH 50-P respectively.
dv/dt disturbances can be minimized at two different levels:• at the transducer level the design is optimized to limit the
primary-secondary capacitive coupling and to minimize
the settling time after a dv/dt disturbance• at the user level care must be taken in the application of
the transducer into the system
For the latter, good EMI control practices must be observed.

Magnetic disturbances

Because the majority of transducers use magnetic coupling,
it is important to be concerned with external magnetic fields
likely to disturb a measurement. Potential sources include
transformers, inductors, wires, busbars, as well as othertransducers. Typical power electronics equipment has
multiple conductors, oftentimes in close proximity to eachother. A transducer may be disturbed by the magnetic fields
from adjacent conductors, with the disturbance being thelargest with short distances and high currents. A key
parameter in this case is the relative position between thefield sensing element (e.g. Hall or Fluxgate cell) and the
conductor creating the disturbance.
43

Miscellaneous

To minimize the disturbance please try:
• to increase the distance between the transducer and theexternal conductor as much as possible• to modify the transducer and/or conductor layout to
optimize the conductor position with regard to the fieldsensing element of the transducer• to twist, layer or parallel, if possible, the source and returnconductors to minimize the external field• to divide the external conductors into equal parts andplace them symmetrically on each side of the transducer,
canceling or minimizing the external magnetic influence• to magnetically shield the transducer
Typically, tests are performed by LEM to record external field
influences. The results of these tests and further advise areavailable on request.
8.4

Typical misapplication of a transducer parameter

The incorrect use of a transducer may impact the performance or reliability of the design. Here are a few classicalcases of misapplication, although an analysis at a specificoperating condition may lead to these results.
Measurement resistance
Risk of overheating (current output) or- RM < RMmin
measurement range reduction (voltage
output)- RM > RMmax
Measurement range reduction andelectronic saturation (current output)
Current- IN > I P- IN < IPN

Magnetic saturation and permanent offset
Reduced accuracy

Secondary supply voltage- VC < VCmin
Reduced accuracy and/or limited output
signal range- VC > VCmax
Risk of overheating or permanent damage
Temperature range- Excessive measurement error- Mechanical damage to components

44

8.5

LEM ASIC based transducers

One of LEM’s answers to the market need for size and cost
reduction, along with accuracy and reliability improvement,
has been the move toward Application Specific Integrated
Circuits (ASICs) which replace all the discrete circuitry in atransducer with an „all in one“ chip solution.
While the impact of an ASIC in terms of size reduction is
obvious, the challenge is to make the best use of ASIC
capabilities to improve accuracy. LEM uses state-of-the-art
techniques to minimize offset and other parameters affecting
the transducer accuracy. The transducer environment is also
taken into account, in particular the presence of very high di/
dt and dv/dt, which could impact measurement quality if not
appropriately considered.
LEM today employs ASIC technology in a number of
products including Hall effect based open loop, closed loop
and Eta transducers as well as various Fluxgate
technologies. This puts LEM in the position to produce awide range of ASIC based transducers and to better address
customer specific requirements, providing a continuous
improvement path into the future.

LEM – the Leader in Electrical Parameter Measurement

9

LEM – the leader in electrical parametermeasurement

With over 30 years of research, design, development, andproduction, LEM is your source for electrical parametermeasurement components. LEM commitment to quality andits customers has made it the leader in its market for over
20 years in a row. We work towards continuous
improvement of our products and processes.
Let us show you our wide array of products, developed
specifically for customers like you. If you can’t find the
product you are looking for, we have R&D resources inevery area of the world to address your needs.
Please take this opportunity to contact the LEM regional
office nearest you to learn more about how LEM can help
you solve your problems and improve your products, making
you more competitive.
It is the objective of all LEM employees to adhere to the LEM
Quality Policy:
The key to success for our company is the customer’ssatisfaction regarding respect for their demands as well as
their expectations.
In a continuous effort to fulfill the LEM Mission Statement:
To Help optimize the Utilization of World Energy and Natural
Resources, LEM contributes to the Mastery of Electricity byproviding innovative and cost effective Components, Instruments, Systems and Services.

45

Glossary A-Z

10Glossary A-Z

Ampere-turns
The ability of a coil to generate a magnetic field. This is given by the
product of the coil current and the number of coil turns.
Bandwidth, small signal
The range of low level sine-wave frequencies that can be
reproduced with a specified reduction in signal amplitude, typically 1 or -3dB. Typically, the bandwidth of most transducers given in thedata sheet are assuming a current derating with frequency
increase.
Bandwidth, power
The range of nominal amplitude sine-wave frequencies that can be
reproduced, typically limited by internal heating.
Closed loop current transducer
A current transducer in which the magnetic field created by the
primary (measured) current is cancelled by a magnetic field with an
opposite direction, created by a secondary (output) current. The
secondary current is a true image of the primary current scaled
based on the primary to secondary turns ratio.(§3.2; §3.5)
C-type transducer (§ 4.4)
Highly accurate Fluxgate transducers operating on the closed loop
principle. Very good frequency behavior. Sensitivity to temperaturechanges is minimized. C-type transducer portfolio includes CT(current: § 4.4.2), CD (differential: § 4.4.3) and CV (voltage: § 4.4.4)
transducers.
Current transformer
A transformer used to measure AC current while also providing
isolation. Current is scaled based on primary to secondary turns
ratio.
Degauss cycle
Applying a decaying AC field to return a magnetic material to a zeroremanence (BR) condition (§ 3.1.6.1). See also Demagnetization,
Magnetic offset and Remanence.
Demagnetization
Returning a magnetic material to a zero remanence (BR) condition(§ 3.1.6.1). See also Degauss cycle, Magnetic offset andRemanence.
di/dt following
The ability of a transducer to accurately reproduce a step inprimary current with a controlled rate of change (di/dt).
Differential current transducer
A transducer used to measure the difference between two opposing
currents. These are often used to measure leakage current.
EMC
Electro-Magnetic Compatibility, implying conformance with defined
standards.
Eta
Eta technology is a combination of open loop and current
transformer technologies. In general, Eta transducers have open
loop performance at low frequencies and current transformer
performance at high frequencies (§ 3.3).
Fluxgate
Fluxgate technology implies driving a magnetic core material
through its complete B-H loop. The field from a primary current
causes a shift in this behavior that is measurable. See also C-type,IT-type, Low frequency Fluxgate, Standard Fluxgate and § 4.

46

Global error
The worst-case error considering all possible factors. This is notnecessarily the addition of all error factors as some factors are
multiplicative while others cannot be simultaneously in their worstcase conditions. This is an absolute limit used in worst-case design
scenarios. In practice errors should be considered statistically, withthe probability and distribution of deviations leading to a muchsmaller actual total error.
Hall effect / Hall generator
The Hall effect is the force applied to charge carriers in a magnetic
field causing an imbalance in voltage.
The device referred as Hall generators or Hall cells are designed totake advantage of the Hall effect by providing a usable output formeasurement of magnetic fields.
Hysteresis
The hystereses curve of a magnetic material described his overallmagnetic performances, advantages and drawbacks included(Figure 4).
Because a Hall generator measures the magnetic field, transducer
Hysteresis has typically an impact on the transducer accuracy(magnetic offset), gain (possible saturation effects in open loop),
behavior after a current overload (eventual need of demagnetization), heating at high frequency (hysteresis losses), influence of
external magnetic field (local saturation).
IT-type transducer
One of the most accurate transducer technologies available, basedon a closed loop Fluxgate principle (§ 4.5). See also C-type,
Fluxgate, Low frequency Fluxgate, Standard Fluxgate and § 4.
Low-frequency Fluxgate
A low cost product from the Fluxgate transducer portfolio with alimited bandwidth. See also C-type, IT-type, Fluxgate, Standard
Fluxgate and § 4.
Magnetic offset
The output offset resulting from the remanence of the magnetic
material being used. See also Degauss cycle, Demagnetization
and Remanence.
Measurement resistor
When a device provides an output current a resistor is typicallyused to convert the output current into a voltage for measurement.
This „measurement resistor“ is also commonly referred to as a„burden“ or „load“ resistor.
Measurement voltage
The voltage created across a „measurement resistor“ is referred toas the „measurement voltage“.
Nominal (current or voltage)
The maximum rated continuous RMS value of input signal.
Sometimes called „continuous“ or „rated“ current or voltage.
Offset drift
The drift of offset current or voltage versus temperature at thetransducer output, specified in mA/K or mV/K.
Offset error / voltage
Output signal of the transducer when subject to no primary
excitation (e.g. IP = 0). It is mostly due to electrical parameters but
also depends on magnetic influences.

Glossary A-Z

Open loop current transducers (§ 3.1)
Current transducers where the output signal is an image of themagnetic field created by the primary current to be measured. It
generally uses a magnetic circuit which focuses the field on a fieldsensing element, e.g. made of a Hall generator. The output signal isa direct amplification of the Hall signal, giving a true image of themeasured current if the system is designed for a linear behavior.
Primary
The input, driving or measured side of a circuit and the components
related to that side of the circuit. Galvanic isolation is provided
between the primary and the secondary side. For example, theprimary winding carries the primary current. See also Secondary.
PWB (printed wiring board)
Often referred to as a „PCB“ or printed circuit, or PWB dependingon the geographic location.
Ratiometric
The output (offset and/or transfer function) is directly proportional to
the supply or a reference voltage. See also Offset and Transfer
function.
Reaction time
The delay between the measured signal reaching 10% of final value
and the output signal reaching 10% of final value. See also
Response time, and Rise time (Figure 8).
Recovery time
The time required to ‘recover’ and resume normal operation after an
event that interrupts operation, such as saturation. Not to be
confused with Settling time.

Secondary
The output, driven or measurement side of an isolated circuit andthe components related to that side of the circuit. Isolation isprovided between primary and secondary side components. For
example, the secondary supply provides secondary compensation
current. See also Primary.
Settling time
The amount of time required to ‘settle’ to within a defined tolerance
after a disturbance, such as dv/dt. Not to be confused with
Recovery time.
Standard Fluxgate
A LEM definition, Standard Fluxgate transducers operate on theclosed loop principle and provide the most „standard“ performancein term of accuracy or bandwidth. Non-standard Fluxgate
transducers include the more efficient IT or C-types, or the lessdynamic „low frequency“ Fluxgates. See also C-type, IT-type,
Fluxgate, Low frequency Fluxgate and § 4.
Transfer function
The ratio of output signal to input signal. For example, if a 100A
input creates a 1V output the transfer function is 1V / 100A or 1mV /100mA. The output of a ratiometric device is dependent on the
supply voltage, so VS will be part of the transfer function.
Turns ratio
The ratio of primary turns to secondary turns in a transformer. With
closed loop current transducers, the turns ratio typically assumes asingle primary turn. For example, 1:1000 implies 1000 secondary
turns and a secondary current of 1mA with a single primary turn
carrying 1A.

Remanence
After traversing a hysteresis loop the output will not return to zero
when the input is at zero. The amount remaining at the output is theremanence and, in essence, creates an additional output offset.
See also Magnetic offset and Hysteresis.
It is minimized by design in LEM transducers and is often resulting
from a non-expected primary current overload. The magnetic offset
defines the offset on the transducer output signal, positive or
negative depending on the direction of the current overload.
Response time
The time difference between the driving signal reaching 90% of its
final value and the measured signal reaching 90% of its final value.
This is a combination of delay time, driving signal rise time, andmeasured signal rise time. See also Reaction time and Rise time
(Figure 8).
Rise time
The time difference between a signal reaching 10% and 90% of its
final value. See also Delay time, Reaction time, and Response timedifference (Figure 8).
Saturable inductor
An inductor designed to operate into its saturation region. The
inductance value varies from a high value at low currents (based on
the permeability of the core) to a low value at high currents (thecore permeability becomes unity when saturated). (Figure 25).

47

LEM International Sales Representatives
Austria
LEM NORMA GmbH
Liebermannstrasse F01
A-2345 Brunn am Gebirge
Tel. +43 2236 69 15 01
Fax +43 2236 69 14 00
e-mail: lna@lem.com

Asia • Pacific

Africa, America

Europe • Middle East

BeNeLux
LEM BE SA
Avenue Newton 8
B-1300 Wavre
Tel. +32 10 22 67 16
Fax +32 10 22 69 98
e-mail: lbe@lem.com
Croatia
Proteus ElectricVia di Noghere 94/1
I-34147 Muggia-Aquilinia
Tel. +39 040 23 21 88
Fax +39 040 23 24 40
e-mail:dino.fabiani@proteuselectric.it
Czech Republic
PE & ED Spol. S.R.O.
Koblovska 101/23
CZ-71100 Ostrava/Koblov
Tel. +420 59 6239256
Fax +420 59 6239531
e-mail: peedova@peed.cz

Field Applications Engineer
Dominique Roggo
Tel. +358 40 564 22 91
e-mail: dro@lem.com
FranceLEM France Sarl
La Ferme de Courtaboeuf
19 avenue des Indes
F-91969 Courtaboeuf Cedex
Tel. +33 1 69 18 17 50
Fax +33 1 69 28 24 29
e-mail: lfr@lem.com

IsraelOfer Levin Technological Application
PO Box 18247
IL- Tel Aviv 611 81
Tel.+972 3 5586279
Fax +972 3 5586282
e-mail: ol_teap@netvision.net.il

TVELEM
Leningradski Avenue, d. 80
Korp. 32, 3d floor, room 19.
125190 Moscow
Tel. +7 095 363 07 67
Fax +7 095 363 07 67
e-mail: tvelem@lem.com

Switzerland
SIMPEX Electronic AG
Binzackerstrasse 33
CH-8622 Wetzikon
Tel. +41 1 931 10 10
Fax +41 1 931 10 11
e-mail: contact@simpex.ch

NorwayHolst & Fleischer A/SStanseveien 6B
N-0975 OsloTel. +47 2333 8500
Fax +47 2333 8501
e-mail: knut@hf-elektro.no

TVELEM
V.O., 2 linia, 19, Liter „A“
199053 S. Petersburg
Tel. +7 812 323 83 83
Fax +7 812 323 83 83
e-mail: tvelem@lem.com

LEM SA
8, Chemin des Aulx
CH-1228 Plan-les-Ouates
Tel. +41 22 706 11 11
Fax +41 22 794 94 78
e-mail: lsa@lem.com

Slovenia
Proteus ElectricVia di Noghere 94/1
I-34147 Muggia-Aquilinia
Tel. +39 040 23 21 88
Fax +39 040 23 24 40
e-mail: dino.fabiani@proteuselectric.it

TurkeyÖzdisan Electronik Pazarlama
Galata Kulesi Sokak N° 34
TR-80020 Kuledibi / Istanbul
Tel. +90 212 2499806
Fax +90 212 2436946
e-mail: oabdi@ozdisan.com

Spain
LEM Components
Stefan Lüscher
Mobile +34 64 756 0903
Fax +34 938 866 087
e-mail: slu@lem.com

United Kingdom and Eire
LEM UK Sales
Geneva Court, 1Penketh Place, West Pimbo
Skelmersdale
Lancashire WN8 9QX
Tel. +44 1 695 72 07 77
Fax +44 1 695 5 07 04
e-mail: luk@lem.com

Germany
Central Office:
LEM Deutschland GmbH
Frankfurter Strasse 74
D-64521 Gross-Gerau
Tel. +49 6152 9301 0
Fax +49 6152 8 46 61
e-mail: postoffice.lde@lem.com

PolandDACPOL Sp. z o.o.
Ul. Pulawska 34
PL-05-500 Piaseczno K. Warszawy
Tel. +48 22 7500868
Fax +48 22 7035101
e-mail: dacpol@dacpol.com.pl

Hauber & Graf Electronics GmbH
Bavaria / Baden Württemberg
Wahlwiesenstr. 3
D-71711 Steinheim
Tel: +49 7144 28 15 03/04
Fax: +49 7144 28 15 05
e-mail: electronics@hauber-graf.de

Portugal
QEnergia, Lda
Praceta Cesário Verde - 10 S/CaveP-2745-740 MassamáTel. +351 214 309320
Fax +351 214 309299
e-mail: qenergia@qenergia.pt
Romania
SYSCOM -18 Srl.
Protopopescu 10, bl. 4. ap 2 Sector 1
R-011728 Bucharest
Tel. +40 21 310 26 78
Fax +40 21 310 26 79
e-mail: georgeb@syscom.ro

AVANZELCOMPONENTES, S.L.
Madrid region
Avda. Sancho Rosa 66
E-28708 San Sebastián de los Reyes
Tel. +34 91 6236828
Fax +34 91 6236702
e-mail: ventas@avanzel.com

Denmark
Deltron-Conelec A/S
Banemarksvej 50 B
2605 Broendby
Tel. +45 43 434342
Fax +45 43 293700
e-mail: sales@conelec.dk

Hungary
Orszaczky Trading LTD.
Korányi Sandor U, 28
H-1089 Budapest
Tel. +36 1 314 4225
Fax +36 1 324 8757
e-mail: orszaczky@axelero.hu

FinlandEtra-Dielectric Oy
Lampputie 2
SF-00741 Helsinki
Tel. +358 207 65 160
Fax +358 207 65 23 11
e-mail: markku.soittila@etra.fi

Italy
LEM Italia Srl
via V. Bellini, 7I-35030 Selvazzano Dentro, PD
Tel. +39 049 805 60 60
Fax +39 049 805 60 59
e-mail: lit@lem.com

BrazilIntech Engenharia Ltd
5 Andar CJ 52
Av. Adolfo Pinheiro1010
BR-04734-002 Sao Paulo
Tel. +55 11 5548 1433
Fax +55 11 5548 1433
e-mail: intech@intechengenharia.com.br

CanadaOptimum Components Inc.
7750 Birchmount Road Unit 5
CAN-Markham ON L3R 0B4
Tel. +1 905 477 9393
Fax +1 905 477 6197
e-mail:mikep@optimumcomponents.com

South Africa
Denver Technical Products Ltd.
P.O. Box 75810
SA-2047 Garden View
Tel. +27 11 626 20 23
Fax +27 11 626 20 09
e-mail: denvertech@pixie.co.za

LEM U.S.A., Inc
999, Pennsylvania Ave.
USA-Columbus, OH 43201
Tel. +1 614 298 84 34
Fax +1 614 540 74 36
Mobile +1 614 306 73 02
e-mail: afg@lem.com

Chile
ELECTROCHILE
Freire 979 of. 303-304
QuilpueTel. +56 32 92 32 22
Fax +56 32 92 32 22
e-mail: elechile@entchile.net

U.S.A
Central Office:LEM U.S.A., Inc.
6643 West Mill Road
USA Milwaukee, Wi 53218
Tel. +1 414 353 07 11
Toll free: 800 236 53 66
Fax +1 414 353 07 33
e-mail: lus@lem.com

LEM U.S.A., Inc.
27 Rt 191A
PO Box 1207
USA-Amherst, NH 03031
Tel. +1 603 672 71 57
Fax. +1 603 672 71 59
e-mail: gap@lem.com

Australia and New Zealand
Fastron Technologies Pty Ltd.
25 Kingsley Close
Rowville - Melbourne Victoria 3178
Tel. +61 39 763 51 55
Fax +61 39 763 51 66
e-mail: sales@fastron.com.au

India
Globetek
122/49, 27th Cross
7th Block, Jayanagar
IN-Bangalore-560082
Tel. +91 80 2 663 57 76
Fax +91 80 2 653 40 20
e-mail: globetek@vsnl.com

Korea
Youngwoo Ind. Co.
C.P.O. Box 10265
K-SeoulTel. +82 2 312 66 88 58
Fax +82 2 312 66 88 57
e-mail: c.k.park@ygwoo.co.kr

Singapore
Overseas Trade Center Ltd.
03 - 168 Bukit Merah L. 1
BLK 125/Alexandra Vil
RS-150125 Singapore
Tel. +65 6 272 60 77
Fax +65 6 278 21 34
e-mail: octpl@signet.com.sg

China
Beijing LEM Electronics Co. Ltd
No. 1 Standard Factory
Building B
Airport Industria Area
CN-Beijing 101300
Tel. +86 10 80 49 04 70
Fax +86 10 80 49 04 73
e-mail: hzh@lem.com

Japan
NANALEM K.K.
2-1-2 Nakamachi
J-194-0021Tokyo
Tel. +81 42 725 8151
Fax +81 42 728 8119
e-mail: nle@lem.com

Malaysia
Acei Systems SDN BHD
No. 3, SB Jaya 7
Taman Industri SB Jaya
47000 Sungai Buloh
Selangor, Malaysia
Tel. +60 36157 85 08/55 08
Fax +60 3615715 18
e-mail: ssbhullar@aceisys.com.my

TaiwanTope Co., Ltd.
P.O. Box 101-356
3F, No. 344, Fu Shing Road
ROC-10483 Taipei
Tel. +886 2 509 54 80
Fax +886 2 504 31 61
e-mail: tope@ms1.hinet.net

SwedenBeving Elektronik A.B.
Jägerhorns väg 8
S-14105 Huddinge
Tel. +46 8 6801199
Fax +46 8 6801188
e-mail: information@bevingelektronik.se

RussiaCentral Office:
TVELEM
Marshall Budionny Str.11
170023 Tver / Russia
Tel. +7 822 44 40 53
Fax +7 822 44 40 53
e-mail: tvelem@lem.com

LEM U.S.A., Inc.
7985 Vance Drive
USA Arvada, CO 80003
Tel. +1 303 403 17 69
Fax. +1 303 403 15 89
e-mail: dlw@lem.com

LECTRON Co., Ltd..
9F, No 171, SEC. 2
Tatung, RD, Hsichih City
Taipei Hsien 221
Taiwan, R.O.C.
Tel. +886 2 8692 6023
Fax +886 2 8692 6098
e-mail: silas@lectron.com.tw

BAC/E, 05.04

Distributor

LEM Components
8, Chemin des Aulx, CH-1228 Plan-les-Ouates
Tel. +41/22/7 06 11 11, Fax +41/22/7 94 94 78
e-mail: Isa@lem.com; www.lem.com
Publication CH 24101 E/US (05.04 • 15/8 • CDH)