FEATURE SENSORS & SENSING SYSTEMS Swift current measurements
HARTING has introduced a range of current sensors that have been specially developed to offer a high level of interference resistance in addition to highly accurate measurements
or power electronic systems such as frequency converters, switch mode power supplies, UPS systems and welding systems, swift and precise current measurements are needed for their exact regulation. Current sensors are electromechanical
F
components that supply a precise mapping of the input and output currents in real time. These measurement signals are used for precision monitoring and control of power semiconductors and other components in power electronics systems. The sensors described in this article have been developed in close cooperation with key users in sectors such as railways and renewable energy, and represent a solution that fulfils the requirements of modern power electronics. The new current sensor product family
is based on the proven Hall effect, which measures, in an electrically isolated manner, the current via its magnetic field. Two measurement principles are
utilised here: l
Compensation current sensing (closed loop technology) for demanding
measurement tasks. l
Direct mapping current sensing (open
loop technology) for applications where the requirements in terms of precision are less stringent.
OPEN AND CLOSED LOOP SENSORS For open loop sensors, the primary current’s magnetic field is concentrated in a magnetically soft toroid. A Hall element that generates a voltage proportional to the magnetic field or to the current is positioned in the toroid’s air gap. The Hall voltage is amplified and delivers a mapping of the primary current as an output signal. One advantage of these sensors is the simple design. However, the temperature dependency of the Hall element and the amplification (offset and gain drift) influence the precision. Closed loop sensors have a design
similar to that of direct mapping sensors. The Hall voltage, however, is not used directly as the measurement signal - instead, it is used to regulate a secondary current. The secondary current flows through a coil with N windings and generates a magnetic compensation field in the toroid. If the secondary current multiplied by N is
36 NOVEMBER 2014 | ELECTRICAL ENGINEERING
resistance to interference from external magnetic fields. A further advantage for developers is that the sensors are easy to integrate into existing applications, as they have standard footprints and installation dimensions. The termination technology and pre assembled signal lines allow economical and reliable assembly. Separate purchasing processes for mating connectors and cabling are eliminated, and the variety of parts is reduced. The latest addition to
HARTING’s range of Hall effect current sensors offers a current range
exactly the same as the primary current, the two magnetic fields cancel each other out in the toroid. The Hall element always regulates the
magnetic flux to zero. The secondary current is simultaneously the sensor’s output signal. These sensors consume more current, but work very precisely (with an accuracy better than one percent) throughout the entire temperature range (-40°C to 85°C). These sensors can measure direct or
alternating currents, including signals with complex waveforms, over a frequency range from 0 to 50kHz. Because the devices use proven Hall effect technology to sense the magnetic field created by the current flowing in a conductor, they provide non-contact, galvanically isolated measurements with high immunity to interference from the magnetic fields of external current carrying conductors. The wide temperature range of -25° to 85°C allows use in thermally critical applications. The housing material and potting mass have a flammability rating to UL94 V0, and the devices meet the requirements of EN Standard 50 178: Electronic equipment for use in power installations. They also conform to the EN 50155 standard for rail applications.
SUMMARY In addition to the robust design developed for use in harsh environments, as found in the rail and renewable energy markets, the new current sensors also offer a high level of
Above: HARTING’s new range of current sensors that have been specially developed for these environments and offer a very high level of interference resistance in addition to highly accurate measurements
from 100A to 800A. The HCSE (Hall effect current sensors Eco) family consists of four models, all based on the open loop measurement principle.
HARTING
www.harting.co.uk T: 01604 827 500
Enter 219
Top: open loop sensors
Above: closed loop sensors
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