Page 97 - Current & voltage sensors catalog

Electronic current sensors
Instructions for mounting and wiring NCS sensors

3 - Precautions to be taken into account relative to the electromagnetic environment
Due to the continuous reduction in equipment volume and the increase in their power, internal system components are subject to strong electro-
magnetic interference. NCS sensors, based on the measure of currents by magnetic fields, (see functioning description 1SBD370024R1000) must
not be interfered by surrounding magnetic fields. They have therefore been designed in order to allow accurate measurement without interference.
Different tests carried out on NCS sensors show the rejection of the sensors to this external magnetic interference in relation to the configuration
of the predefined bar arrangement.

During type testing, the sensors were subject to 3 types of tests:
– magnetic field circuits: measure the influence of the magnetic fields generated by the primary conductor on the sensor
– interference by an external set of bars: measure the influence of the magnetic fields generated by the other conductors different from the pri-
mary conductor on the sensor
– coupling of primary bars: measure the influence of the mechanical mounting of the sensor on a primary conductor 4

During the different tests and in each configuration, the measured results (accuracy) are recorded whilst varying the following elements:
- distance between the sensor and the interfering current
- rotation of the interfering current around the sensor
- the magnitude of the interfering current
- the current form (DC or AC)
- inclination of the sensor on the primary conductor
- centricity of the sensor on the primary bar
- different primary bar configurations (rectangular simple or double, round and arrangements in "U", "S" or "L" configurations)

G0223DF G0224DF G0225DF

Primary bar in "U" Primary bar in "S" Primary bar in "L"

The tests were carried out with the primary bars in "U" configuration, the most restricting condition.
See mounting instructions ref. 1SBC146000M1704 (NCS125 & NCS165) or ref. 1SBC146010M1701 (NCS305) for further information.

3.1 Mounting for improved EMC performance (shielding)
In applications that require the sensor to be used with long cables exposed to interference, it is imperative that shielded cables are used, with the
shielding connected to ground at both ends (see figure below).
Standard NCS sensors with cable outputs are supplied in white plastic enclosures containing a ferrite core (NCS125 & NCS165). The secondary
cable passes through this white plastic enclosure to reduce the interference caused that could affect the correct functioning of the sensor.
Please contact your distributor for further information on this subject.

NCS sensor Electronic board
+ V A
+ V A
I s1
R M1
I s2 Shielded cable
R M2
V s1 0V
R M3
V s2
R M4
- V A
- V A
I p G0219DG
0V 0V
4 - Processing of the sensor's output signal
Standard codes of practice advise that, before the signal is processed, a low-pass filter adapted to the bandwidth of the sensor is used.
Moreover, in the case of digital processing of the signal, it is also recommended that the sampling frequency is adapted to the bandwidth of both
the signal to be measured and the sensor. 1SBC140068S0201
In the event of sensor failure, the processing of the output signal should take into account this deterioration in performance (e.g. absence of signal
or saturated signal) and rapidly and safely shut the system down.

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