Technical Information
CAS / CASR / CKSR series Current Transducers
Insulated Highly Accurate Measurements
from 1.5 to 50 ARMS
CAS / CASR / CKSR series Current Transducers
Future precision.
Future performances.
Now available.
CAS / CASR / CKSR series Current Transducers
Insulated Highly Accurate Measurements from 1.5 to 50 A RMS
The Power Electronics market is in constant change and
always on the lookout for new technologies and better
performance driving our progress. To enable applications
with enhanced performance, current measurement must
always been made with the best possible performance
also allowing to the final application to differentiate itself
from all the others.
This is the human nature and allows the progress of
technology.
With the LTS / LTSR current transducers using the Closed
Loop Hall effect technology coupled with a dedicated
ASIC (Application Specific Integrated Circuit) specially
designed for these products, we thought we had reached
the optimal performance, but this was without taking the
eternal human nature into account.
The market required even better accuracy over the
temperature ranges maintaining a low price and LEM
decided to achieve this goal.
A few months later, LEM delivers the solution with the
CAS / CASR / CKSR current transducers series covering
nominal current measurements from 1,5 to 50 A RMS.
To respond to these new challenges, the Hall effect
technology was no longer the solution. Even if used
in a Closed Loop configuration and with the use of a
dedicated ASIC as done with the LTS family which allowed
a substantial performance improvement notably for the
accuracy and the size.
Fluxgate technology was selected enabling both possible
targets: the improvement in accuracy and the low price.
Without compromising the advantages of the LTS product
such as size, dynamic performances, high measuring
range, ect.
LEM has already been using multiple Fluxgate technologies
in the past and it was just a question to find the one making
the best comprise between price, size and performances.
In order for the products to be able to work in the typical
industrial applications, the insulation criteria needed to be
respected and a particular attention has then been brought
to the mechanical design of the product.
Although we were able to reduce the size even when
nobody thought it could still be done, the insulation
performances allow usage in standard industrial
applications without particular mounting with a rated
insulation voltage up to 1000 VRMS (Simple isolation
according to EN 50178 standard with following parameters:
OV 3, PD2).
The CAS / CASR / CKSR models have been specially
designed to respond to the technology advances in drives
and inverters in industrial environment requiring better
performances in areas such as:
• Common mode influence
• Thermal drift (offset and gain)
• Accuracy (in the whole temperature range)
• Response time
• Insulation
• Size
Closed Loop current transducers measure current over
wide frequency ranges, including DC. They provide
contact-free coupling to the current that needs to be
measured as well as safe galvanic isolation and high
reliability. Their output signal is an accurate, high-resolution
image of the primary current with a very short delay.
in the electronics (e.g. offset variations of the amplifiers
used) if the Open Loop sensitivity is higher.
The complexity of a Fluxgate based current transducer
is comparable to the one of a transducer based on a Hall
effect IC (integrated circuit). Like there, some AC signal
processing and synchronous rectifying is applied. In
addition, the Fluxgate detector is needed. Fortunately,
this Fluxgate is a very simple small solenoid with a tiny
soft magnetic strip used as detector core. Because of
the complexity of the signal chain, an IC is used to stay
at a competitive cost level compared to Hall effect current
transducers. A circuit in this IC forms an oscillator together
with the Fluxgate, driving it into saturation each half cycle
at a frequency of several hundred kilohertz. The effect
that is used for the detection of a residual flux in the main
transducer core is the fact that in such a configuration a
change of the duty cycle of the driving voltage will occur
when a magnetic DC flux is present in the fluxgate core.
In higher frequency ranges these transducers function
exactly the same way as (passive) current transformers,
where a relatively small induced voltage in the secondary
winding is capable to drive the secondary current through
the secondary winding and, most important, through
the burden resistor. A low induced voltage equals low
magnetic flux in the magnetic core, which is the cause
for the good accuracy (low flux means a small difference
between primary and secondary current linkage1, too).
For DC and in low-frequency ranges, the induced voltage
is too low to be able to drive the secondary current, and
the error of simple current transformers will increase with
decreasing frequency. In this domain, the magnetic flux
density in the core is measured by a sensing element and
a voltage is applied to the secondary circuit that in the
end keeps the flux density near zero, effectively creating a
closed control loop.
The signal processing stages in the IC comprise a duty
cycle demodulation, frequency response compensation,
an integrator and a bridge amplifier that provides the
secondary current. This output architecture can provide
a higher (doubled) voltage to the secondary circuit when
compared to a single output stage with the other side of the
circuit connected to a reference potential at typically 2.5 V.
The only basic difference between the CAS / CASR / CKSR
transducer series and standard Closed Loop transducers
of LEM is that the Hall element used for feedback is
replaced by a Fluxgate detector. The driving force behind
this choice is the need for a “better” feedback, which
basically means more voltage per current linkage, a
quantity that is called “Open Loop sensitivity”. Given
an equal electronic circuit, the zero output of a current
transducer (traditionally called “offset” in analogy to
operational amplifiers) will be less influenced by changes
In this configuration, the burden (or measurement) resistor
is floating, so in order to obtain an output signal referenced
to a fixed voltage, a difference amplifier is used which is
also part of the IC.
1 Current linkage is the technical term for current multiplied by turns count
Fig. 1. Closed Loop Fluxgate Technology used for the CAS / CASR / CKSR current transducers
Magnetic Core
RS
Primary conductor
I Compensation
Diff
Amp
ICOMP1
Fluxgate
Interface
IP
Filter
GND
+5V
VOUT
Driver
VREF
Int. ref
ICOMP2
Compensation
Winding
Fluxgate
CAS / CASR / CKSR Transducers Technology
CAS / CASR / CKSR Transducers Technology:
Closed Loop Fluxgate technology
CAS / CASR / CKSR Series: Main Characteristics
Mechanical and dimensions
CAS / CASR / CKSR have been designed to provide
current measurements from 6 to 50 A RMS in a very
compact size compared to the existing current
transducers based on different technologies allowing to
reach similar electrical performances.
Moreover, the same compact design is used to cover
the complete current range from 6 to 50 A RMS with 4
standard models (6 A, 15 A, 25 A and 50 A models) for
each series CAS, CASR and CKSR.
The CAS / CASR / CKSR design is 30 % smaller in
height than LTS transducer (Closed Loop Hall effect
chip technology using an ASIC): 16.5 mm height versus
24 mm. 7.5 mm won in height !
Where LTS and LTSR were limited
to 25 A RMS, with the respective
LTS 25-NP
and
LTSR 25-NP
models, as the highest nominal
current, the CAS / CASR / CKSR
models are offered with a model
expected to measure 50 A RMS as
nominal current. There has been
a requirement from the market for
years to have a 100% PCB mounted
50 A RMS current transducer with
single + 5 V power supply in such a
class accuracy.
Transducers dimensions
Fig. 2. CAS / CASR / CKSR: 30 % smaller compared to the LTS / LTSR models
The CAS and CASR construction uses three U‑shaped primary terminals integrated into the housing, providing the
designer with a great flexibility to perfectly adapt the measuring range of the current transducer to his application.
Fig. 4a shows the different connection possibilities.
Number
of primary
turns
Primary nominal
current rms
I PN [ A ]
Nominal*
output voltage
VOUT [ V ]
Primary resistance
R P [ mΩ ] ( typ. )
at +25° C
1
± 25
2.5 ± 0.625
0.24
2
± 12
2.5 ± 0.600
1.08
3
±8
2.5 ± 0.600
2.16
Recommended
connections
* Output voltage CASR 25‑NP is used with internal reference.
Fig. 4a. Different nominal current ranges possible according to the primary current circuit configuration (as example: CAS or CASR 25-NP)
Variant 1
Variant 2
When all three U-shaped terminals are connected in
parallel (variant 1 Fig. 4b) the user can measure the
maximum nominal primary current.
Expected for:
I PN (I PMAX ) = 25 A (85 A max)
Expected for:
IPN / 3 (IPMAX / 3) = 8.33 A (28.33 A max)
Fig. 4b. The 2 extreme possibilities for connecting the primary
current circuit (as example: CAS or CASR 25-NP)
The variant 2 (Fig.4b) corresponds to a series connection
of the primary terminals and leads to a reduction of the
nominal measuring range by a factor of 3, but offering a
3 times higher accuracy for low currents.
The CAS / CASR models are 100% compatible
with the LTS and LTSR models in regards to
the footprint mounting and also with all the
other models that are available on the market
with the same footprint as the LTS / LTSR.
Fig. 3. CAS and CASR transducers can be mounted at the
exact place of the LTS and LTSR transducers
CAS / CASR / CKSR Series: Main Characteristics
Multifunctional primary circuit
CAS / CASR / CKSR Series: Mechanical differences
CAS / CASR / CKSR Mechanical differences
Ref IN/OUT*
Nb
on a
primary
secondary
pins
pin
Nominal
current
range
Nb
secondary
pins
CAS 6-NP
6
3
NO
CAS 15-NP
15
3
CAS 25-NP
25
CAS 50-NP
3D
drawing
Footprint
drawing
Compatibility
with
LTS and LTSR
footprints
Creepage
distance
Clearance
distance
3
7.7 mm
7.7 mm
LTS 6-NP
NO
3
7.7 mm
7.7 mm
LTS 15-NP
3
NO
3
7.7 mm
7.7 mm
LTS 25-NP
50
3
NO
3
7.7 mm
7.7 mm
LTS
CASR 6-NP
6
4
YES
3
7.5 mm
7.5 mm
LTSR 6-NP
CASR 15-NP
15
4
YES
3
7.5 mm
7.5 mm
LTSR 15-NP
CASR 25-NP
25
4
YES
3
7.5 mm
7.5 mm
LTSR 25-NP
CASR 50-NP
50
4
YES
3
7.5 mm
7.5 mm
LTSR
CKSR 6-NP
6
4
YES
4
8.2 mm
8.2 mm
/
CKSR 15-NP
15
4
YES
4
8.2 mm
8.2 mm
/
CKSR 25-NP
25
4
YES
4
8.2 mm
8.2 mm
/
CKSR 50-NP
50
4
YES
4
8.2 mm
8.2 mm
/
Model
CAS Series
CASR Series
CKSR Series
* The internal reference voltage is provided on a secondary pin or can be forced by an external reference voltage
The CKSR has one more primary pin (4 primary pins in
total) than the CAS and CASR models (3 primary pins in
total) making it incompatible with the footprint of these last
8 models. It is possible to measure not less than 1.5 ARMS
nominal (using a CKSR 6-NP model set up in one of the 4
possible primary pins layout: Layout with 4 turns. Fig. 5) with
the performances mentioned in the CKSR 6-NP data sheet.
Using this layout configuration, the current measured by
the transducer is still 6 ARMS (its designed nominal current)
as when connected in series the primary pins have 4 loops
(instead of 1 when connected in parallel) through the aperture
of the transducer.
Then 4 loops, carrying 1.5 A each, results into a total current of
6 A.t (Amps.turn). Finally, the transducer “sees” a 6 A current.
Number
of primary
turns
Primary nominal
current rms
I PN [ A ]
Nominal*
output voltage
VOUT [ V ]
Primary resistance
R P [ mΩ ] ( typ. )
at +25° C
1
±6
2.5 ± 0.625
0.18
2
±3
2.5 ± 0.625
0.72
3
±2
2.5 ± 0.625
1.8
4
± 1.5
2.5 ± 0.625
2.88
Recommended
connections
* Output voltage CKSR 6‑NP is used with internal reference.
Fig. 5. Different nominal current ranges possible according to the primary current circuit configuration – CKSR 6-NP model as example
allows nominal current measurement from 1.5 to 6 A RMS
With that value, and PD2 and CTI of 600 V (group I), this leads to
a possible rated insulation voltage of 800 VRMS.
The CKSR primary pin footprint is different to the CAS and
CASR models.
In conclusion, the possible reinforced rated insulation voltage, in
these conditions of use, is of 450 VRMS (interpolation) or 300 VRMS
(without interpolation)(the lowest value given by the both results
from the creepage and clearance distances).
Thanks to this different primary footprint, higher creepage and
clearance distances are achieved.
This can be of interest when higher insulation is required for
applications under higher working voltages than normal.
Creepage and clearance distances for CKSR models are
8.2 mm (internal distances).
Let’s take an example to see the advance this brings.
Conditions of use:
• Creepage distance: 8.2 mm
• Clearance distance: 8.2 mm
• CTI: 600 V (group I)
• Overvoltage category: III
• Pollution Degree: 2
Basic or Single insulation:
According to EN 50178 and IEC 61010-1standards:
With clearance distance of 8.2 mm and PD2 and OV III, the rated
insulation voltage is of 1000 VRMS.
With a creepage distance of 8.2 mm and PD2 and CTI of 600 V
(group I), this leads to a possible rated insulation voltage of
1600 VRMS.
In conclusion, the possible rated insulation voltage, in these
conditions of use, is 1000 VRMS (the lowest value given by the
both results from the creepage and clearance distances).
Reinforced insulation:
Let’s look at the reinforced insulation for the same creepage and
clearance distances as previously defined:
Using only the EN 50178 standard as a reference for industrial
applications, the possible reinforced rated insulation voltage in
these conditions of use is of 600 VRMS.
With CASR models, not using the special primary pins footprint,
the clearance and creepage distances are each of 7.5 mm.
In the same conditions of use as for the CKSR example here
before, the result would be the following:
According to EN 50178 and IEC 61010-1 standards:
Basic or Single insulation ➔ Rated insulation voltage: 600 VRMS.
Reinforced insulation ➔ Rated insulation voltage: 404 VRMS
(interpolation) or 300 VRMS (without interpolation).
With CAS models, not using the special primary pins footprint,
the clearance and creepage distances are each of 7.7 mm
(distances are higher compared to the CASR models as there
are only 3 secondary pins versus 4 on the CASR models).
In the same conditions of use as for the CKSR example here
before, the result would be the following:
According to EN 50178 and IEC 61010-1 standards:
Basic or Single insulation ➔ Rated insulation voltage: 600 VRMS.
Reinforced insulation ➔ Rated insulation voltage: 417 VRMS
(interpolation) or 300 VRMS (without interpolation).
(Note: all these calculations are done with creepage and
clearance distances taken on the transducer itself not mounted
on a PCB).
When looking at dimensioning reinforced insulation, from the
clearance distance point of view, with OV III and according
to EN 50178 and IEC 61010-1 standards, the rated insulation
voltage is given whatever the pollution degree at 450 VRMS
(interpolation) or 300 VRMS (without interpolation).
From the creepage distance point of view, when dimensioning
reinforced insulation, the creepage distance taken into account
has to be the real creepage distance divided by 2, that is to say
8.2 / 2 = 4.1 mm.
The measurement of differential currents
is also possible with special versions of
CAS, CASR and CKSR (Fig. 6). These
models are possible on request. The
current measured is the difference
of the currents I1 - I2. For insulation
reasons (creepage and clearance
distances), these models are designed
in order to have enough space between
the 2 primary conductors carrying the 2
opposite currents (due to the possible
potential difference between the two
phases).
Fig. 6: Differential current measurement (I = I1 – I2), many possibilities
CAS / CASR / CKSR Series: Mechanical & Insulation features
Higher insulation provided with the CKSR models thanks to their
mechanical design
CAS / CASR / CKSR Series: Electrical performances
Electrical data
CAS / CASR / CKSR current transducers series have been
designed to work with a single + 5 V power supply to cover
nominal current measurements from 6 to 50 ARMS.
This is a common power supply used in the power electronics
word to make working the various µprocessors, or DSPs or
ADCs (Analog Digital Converters) ect.
The models provide an analogue voltage output referenced
around a reference voltage.
By default, this reference voltage is the internal reference
voltage used inside the transducer: 2.5 V + a certain tolerance
(please see adequate data sheet according to the model).
voltage at the Ref pin + an offset depending to the model
used (between the voltage output and the Ref pin).
The voltage provided at the Ref pin (Typically 2.5 V) stays
stable although the primary current changes.
The second mode is called “Ref in mode”. In this mode, you
can apply an external voltage to the Ref pin to overdrive the
internal voltage reference. The minimum external voltage is
0 V and maximum 4 V. However, this mode defines different
measuring ranges according to the level of the external
voltage reference used (0 to 4 V) and according to the model
used (6, 15, 25 or 50 A model).
Then, at the output, these 2.5 V provided at no primary
current can be considered as a virtual “0” V.
For more information on these 2 modes, please refer to the
chapter “Application advice”.
The gain is defined in order to get 0.625 V at IPN whatever the
model used (CAS or CASR or CKSR, 6 or 15 or 25 or 50 ARMS
models).
With zero primary current, the consumption is max 20 mA.
With more than zero primary current, the transducer
consumes 20 mA max + (the primary current divided by the
number of turns used by the transducer: IP / Ns).
Accuracy
Using a Closed Loop Fluxgate technology allows reaching
accuracy that was impossible with traditional Closed Loop
Hall effect based technology (even with a dedicated ASIC).
Some applications required higher accuracy especially for
lower offset and gain drifts in temperature ranges.
CAS / CASR / CKSR models achieve an accuracy of 0.8 %
of IPN at +25°C regardless of the model and the following
accuracy at +85°C:
CAS: 2.5 to 3 % of IPN
The output voltage range is limited to between 0.375 V for the
negative current range and 4.625 V for the positive current
range centred around 2.5 V when external reference voltage
is not used.
The positive and negative voltage variation spans are each
of 2.125 V and fluctuate around the internal voltage reference
fixed at 2.5 V.
To define the measuring range, just divide the possible max
voltage variation span (positive or negative) by the gain
defined by the concerned model.
In general, the measuring range provided for each model is
more than 3 times the nominal current.
For the 50 A models (CAS 50-NP, CASR 50-NP and CKSR
50-NP), the current measuring range is limited to +/- 150 A
(nevertheless 3 times the nominal current) (due to some
current limitations inside the transducer) meaning only
1.875 V as positive and negative variation spans, resulting
in a minimum output voltage of 0.625 V for –150 A and in a
maximum output voltage of 4.375 V for +150 A.
However, for these 50 A models, the limits for output voltage
rails remain +0.375 V and +4.625 V.
With the CASR and CKSR models, the internal voltage
reference is provided on a separate secondary additional pin
called VREF what is not the case with the CAS models.
This pin is a direct access to the voltage reference used
inside set around 2.5 V.
The Ref pin has two basic functional modes:
The first mode is called “Ref out mode”. In this mode, for a
primary current of 0 A, the output voltage is equal to the
CASR: 1.2 to 1.8 % of IPN
CKSR: 1.2 to 1.8 % of IPN
As you can see, the accuracy of the CAS is less good as the
CASR and CKSR models.
This is explained as follows: The CAS models do not provide
the internal voltage reference outside and then the voltage
output integrating the voltage reference inaccuracy.
What is not the case with the CASR and CKSR models
providing their internal voltage reference outside or being
able to feed their internal voltage reference with an external
voltage reference. When using both these last models (CASR
and CKSR), the output (VOUT) is usually measured referenced
to the voltage available on the voltage reference pin (which
one is used as reference for the whole electronic of the
application).
The voltage reference value available on this pin being well
known and under control (used and usually controlled by
the microcontroller or DSP), the microcontroller can easily
remove the initial offset at +25°C at no primary current.
The use of the Closed Loop Fluxgate technology allowed achieving significantly better performances for the following
parameters:
• Initial offset at +25°C
• Offset drift
• Gain drift
as expressed per the following charts (Fig. 7: Comparison between CAS and LTS ; CASR and LTSR models).
CAS 6-NP LTS 6-NP CAS 15-NP LTS 15-NP CAS 25-NP LTS 25-NP
Nominal current, I PN
A
6
15
25
Measuring range
A
20
19.2
51
48
85
80
Response time
us
< 0.3
0.4
< 0.3
0.4
< 0.3
0.4
Bandwidth (±1 dB)
kHz
200
200
200
200
200
200
mVpp
2.4
10
1.0
4.2
0.6
Output voltage noise, 100 Hz..10 kHz (typ.)
Output
Sensitivity
Voltage
mV/A
Voltage
104.2
Sensitivity error (max)
% of I PN
0.7
Offset drift (25°C .. 85°C) (max)
% of I PN
1.92
Sensitivity drift (25°C .. 85°C) (max)
% of I PN
0.24
2.5
Voltage
41.7
0.6
25.0
0.7
0.6
0.7
0.6
4.8
1.68
2.9
1.44
2.4
0.3
0.24
0.3
0.24
0.3
Linearity (max)
% of I PN
0.1
0.1
0.1
0.1
0.1
0.1
Accuracy at +25 °C (max)
% of IPN
0.80
0.70
0.80
0.70
0.80
0.70
Accuracy at +85 °C (max)
% of IPN
3.0
5.80
2.7
3.58
2.5
3.40
Offset (max)
mV
10.4
25
7.1
25
6.3
25
Operating temperature range
°C
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
CASR 6-NP LTSR 6-NP CASR 15-NP LTSR 15-NP CASR 25-NP LTSR 25-NP
Nominal current, I PN
A
6
15
25
Measuring range
A
20
19.2
51
48
85
80
Response time
us
< 0.3
0.4
< 0.3
0.4
< 0.3
0.4
kHz
200
200
200
200
200
200
mVpp
1.7
10
0.7
4.2
0.4
2.5
Bandwidth (±1 dB)
Output voltage noise, 100 Hz..10 kHz (typ.)
Output
Sensitivity
Voltage
mV/A
Sensitivity error (max)
% of I PN
Offset drift (25°C .. 85°C) (max)
Sensitivity drift (25°C .. 85°C) (max)
Voltage
104.2
Voltage
41.7
0.7
0.6
0.7
% of I PN
0.72
3.6
% of I PN
0.24
0.3
25.0
0.6
0.7
0.6
0.48
1.5
0.24
0.9
0.24
0.3
0.24
0.3
Linearity (max)
% of I PN
0.1
0.1
0.1
0.1
0.1
0.1
Accuracy at +25 °C (max)
% of IPN
0.8
0.70
0.8
0.70
0.8
0.70
Accuracy at +85 °C (max)
% of IPN
1.8
4.60
1.5
2.54
1.3
1.90
Offset max
mV
5.3
25
2.2
25
1.4
25
Operating temperature range
°C
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
-40 .. 85
Fig. 7. Comparison between CAS and LTS ; CASR and LTSR models – Electrical performances
CAS / CASR / CKSR Series: Accuracy
It is also possible to cancel the offset drift of the reference voltage when working over the defined temperature range by
using the same method.
CAS / CASR / CKSR Series: Dynamic performances & Common mode behaviour
Dynamic performances
CAS / CASR / CKSR transducers max response
times (Response time defined at 90 % of IPN)
against a current step at IPN will have a delay of
Max 0.3 µs (Fig. 8).
As a result of the fast response time,
a large bandwidth has been verified at
300 kHz @ + / - 3 dB (Fig. 9).
Fig. 8. CASR 50‑NP Response time to a current step of 50 A
Fig. 10a. Typical common mode behaviour
(1200 V of voltage variation applied with dv / dt = 20 kV /µs)
Fig. 10b. CASR 50-NP ; Typical common mode behaviour ; VOUT ‑ VREF ;
(1200 V of voltage variation applied with dV/dt = 20 kV/µs)
10
The CAS / CASR / CKSR models have been designed
and tested according to latest recognized worldwide
standards for industrial applications:
The EN 50178 standard dedicated to “Electronic
Equipment for use in power installations” in industrial
applications is our standard of reference for electrical,
environmental and mechanical parameters.
It guarantees the overall performances of our products
in industrial environments.
Fig. 9. CASR 50‑NP ‑ Frequency response
Common mode behaviour
CAS / CASR / CKSR products are CE marked as
a guarantee of the products compliance to the
European EMC directive 89/336/EEC and low voltage
directive. They also comply with the derived local EMC
regulations (EMC: Electro-Magnetic Compatibility).
Common mode noises (dv/dt) are often encountered in
applications using fast switching components like IGBTs. It
is not surprising to encounter switching frequencies up to
and even higher than 20 kHz for highly efficient inverters.
The result of a dv/dt between the primary conductor and
the electronic circuit of a current transducer is a capacitive
current perturbating the various electronic components
that are sensitive to that.
Any electrical component with a galvanic isolation
between the primary and the secondary circuit has a
capacitive coupling between the isolated potentials.
This capacitive current results in an additional error on the
transducer output during a short time.
The error caused by these dv/dt has to be as low as
possible in order to avoid any unwanted activation of a
possible protection circuit, which could lead to a shut
down of the application.
This additional noise caused by the dv/dt can be filtered,
but the best way is to have it at the lowest possible value
and during the shortest time avoiding then any additional
filter to be installed.
For example, a voltage change of 10 kV/µs in combination
with a 10 pF coupling capacity generates a parasitic
output current of 100 mA. For the CAS 25‑NP for example,
this would represent seven times the nominal current.
Fig. 10a shows the behaviour at a voltage change of
20 kV/µs and an applied voltage of + 600 V (total voltage
variation of 1200 V from –600 V to + 600 V) with a
CASR 50‑NP.
Due to CAS – CASR – CKSR low parasitic capacitance,
the effect of dynamic common mode is reduced. We can
notice an interference of about 74 % of IPN during the dv / dt
when measurement VOUT is referenced to 0 V. Note the
very short duration of the disturbance of less than 250 ns,
which can be easily filtered. When VOUT is referenced to
VREF to do the output measurement, then the disturbance
during dv/dt seen on the output is equal to the difference
between the disturbance on VOUT and the disturbance on
VREF (Fig. 10b). In these conditions, we can notice on the
output signal (VOUT ‑ VREF) an interference of about 55 %
of IPN during the dv/dt and 24 % of IPN after the dv/dt, the
signal coming back to its normal state only 350 ns after
the end of the dv/dt.
Insulation and safety
The EN 50178 and IEC 61010-1 standards (“Safety
requirements for electrical equipment for measurement,
control, and laboratory use”) are used as references to
design the creepage and clearance distances versus
the needed insulation levels (rated insulation voltage)
and the conditions of use (as previously seen page 7).
The rated insulation voltage level for transducers in
“industrial” applications, is defined according to several
criteria listed under the both standards EN 50178
and IEC 61010-1. Some criteria are dependent on
the transducer itself when the others are linked to the
application.
The products comply with UL 508C for UR marking.
Reliability and Quality
Of course, reliability and lifetime are guaranteed
by the quality in design and process. Accelerated
tests have been performed to estimate failure rate
(temperature cycle and/or humidity test and complete
characterization of the product according to standards).
Beside, the CAS / CASR / CKSR models have been
designed to pass the + 85°C + 85 % relative humidity
test during 1000 hours (transducers power supplied
during the test).
The CAS / CASR / CKSR models are manufactured in
one of the LEM production center that is ISO/TS 16949,
ISO 14001, ISO 9001:2000 and IRIS certified and where
quality tools such as DPT FMEA, Control Plan, Cpk,
R&R, QOS-8D, IPQ, ect are used in addition to the Six
Sigma methodology.
11
CAS / CASR / CKSR Series: Standards & Quality & Reliability
Standards
CAS / CASR / CKSR Series: Application advice
Filtering Vout
The output Vout has a very low output impedance of
typically 2 Ω; it can drive 100 pF directly and shows
50 % overshoot with approximately 1 nF capacitance.
Adding Rf allows much larger capacitive loads. Note
that with Rf of only 20 Ω, the load capacitor should be
either smaller than 1 nF or larger than 33 nF to avoid
overshoot; with Rf of 50 Ω this transient area is avoided.
Empirical evaluation may be necessary to obtain
optimum results.
Example: Filtering the typical 450 kHz frequency of the
detector:
To have an attenuation of 20 dB at 450 kHz, the cutting
frequency of the 1st order filter is chosen at Fc = 45 kHz.
When the Ref pin is connected to a load, due to the
leakage current and internal resistance (680 Ω),
VREF OUT (internal reference) can change and reduce
the measuring range. To guarantee the measuring
range:
• The leakage current from the Ref pin (source)
must be lower than 350 µA when the load is
connected to a voltage > 2.5 V.
• The leakage current from the Ref pin (sink) must
be lower than 4.4 µA when the load is connected
to a voltage
工商网监
湘ICP备2023018690号
