Open Magnetic Circuit Current Sensor for Parasitic Field Immunity
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Solution Overview
Problem
Existing current measurement devices are bulky, limited in dynamic range, and sensitive to parasitic fields, making them unsuitable for integration with standard electrical apparatuses like shutoff devices, which have limited space and are prone to measurement errors due to conductor proximity.
Innovation Solution
A compact current measurement device with an open magnetic circuit and wide gaps, featuring identical coils connected in series to cancel parasitic fields, made of high permeability ferromagnetic materials, allowing for high dynamic range and immunity to external fields, and designed for easy integration with electric apparatuses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current transformers or induction sensors are used, then current measurement can be achieved, but the devices are bulky and cannot be integrated with standard electrical apparatuses
Solution Approach 1:
The magnetic circuit is divided into two separate magnetic elements positioned on opposite sides of the conductor, with wide gaps between them. This segmentation allows the device to be compact while maintaining measurement capability, as the magnetic path is distributed rather than requiring a single large continuous core.
Solution Approach 2:
The patent transitions from traditional planar or toroidal magnetic circuits to a three-dimensional configuration with magnetic elements extending perpendicular to the conductor plane. This dimensional change enables compact integration within the limited space of standard electrical apparatuses while preserving measurement functionality.
2Measurement precision
If induction sensors are used to measure current, then measurement can be performed, but the sensors are susceptible to parasitic magnetic fields from nearby conductors
Solution Approach 1:
The two magnetic elements are positioned asymmetrically relative to the conductor, with specific spacing and orientation that creates an imbalance in the magnetic field distribution. This asymmetry ensures that parasitic fields from adjacent conductors do not symmetrically affect both magnetic elements, allowing the differential measurement to reject such interference.
Solution Approach 2:
The device uses a differential measurement configuration where the voltage induced in the secondary coil is measured relative to the primary coil's field. This feedback mechanism allows the system to compensate for parasitic fields by referencing the measurement against the known primary field, effectively rejecting common-mode interference.
3Measurement precision
If the section of the magnetic circuit is increased to reduce sensitivity to parasitic fields, then measurement accuracy improves, but the device size enlarges
Solution Approach 1:
Instead of increasing the overall section of the magnetic circuit, the patent concentrates the magnetic path through localized high-permeability material placement only where needed - specifically in the two magnetic elements positioned near the conductor. The rest of the magnetic path uses air or low-permeability material, maintaining compact dimensions while providing sufficient magnetic coupling for accurate measurement.
4Adaptability or versatility
If closed loop configuration with compensating winding is used, then measurement dynamic is improved, but a relatively powerful supply is required to furnish compensation current
Solution Approach 1:
The device uses the current being measured itself as the primary field source, eliminating the need for separate compensating windings or external power supplies. The measurement coil is positioned to directly sense the magnetic field generated by the primary current, creating a self-powered measurement system that requires no additional energy input beyond what is already present in the circuit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device provides high measurement dynamic range, immunity to parasitic fields, and versatility for energy metering and surge protection, enabling precise current measurement in constrained spaces without affecting the apparatus's functionality.
Implementation Method 1
at least one electric coil associated with the magnetic circuit to deliver voltage proportional to the derivative of the intensity of the current to be measured
Implementation Method 2
magnetic circuit disposed near an electric conductor traversed by a current to be measured in order to channel the magnetic field induced around the conductor by the current to be measured
Data Source
AI summary
A device for measuring the intensity of an electric current which has a simple and economical design and offers a high measurement dynamic compatible with combined measurement, protection and energy metering applications. The device (1) is insensitive to parasitic fields and to the position of the electric conductor to be measured, and that can be opened to facilitate placement thereof. The device (1) defines a closed path (C), about a conductor (2) for the circulation of the lines of magnetic field induced by the current to be measured, and the path is formed by two plates (30) having a high magnetic permeability separated by two air gaps (E) closed by two identical and opposed electric coils (4) for supplying a voltage proportional to the derivative of the intensity (I) of the current to be measured. The device (1) reduces the is compact so that it can be easily integrated into any type of electric appliance.