CASR-6-NP Datasheet, PDF (11/24 Pages) LEM – CAS / CASR / CKSR series Current Transducers

Fig. 9. CASR 50‑NP ‑ Frequency response
Common mode behaviour
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 I_PN during the dv / dt
when measurement V_OUT is referenced to 0 V. Note the
very short duration of the disturbance of less than 250 ns,
which can be easily filtered. When V_OUT is referenced to
V_REF to do the output measurement, then the disturbance
during dv/dt seen on the output is equal to the difference
between the disturbance on V_OUT and the disturbance on
V_REF (Fig. 10b). In these conditions, we can notice on the
output signal (V_OUT ‑ V_REF) an interference of about 55 %
of I_PN during the dv/dt and 24 % of I_PN after the dv/dt, the
signal coming back to its normal state only 350 ns after
the end of the dv/dt.
Standards
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.
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).
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.
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