Inductive Coil Calibration for Accurate EMI Field Ratio Measurement
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Solution Overview
Problem
Existing electromagnetic induction methods for determining physical parameters of electrically conductive media face errors in calculating the calibration factor due to complex and potentially inaccurate geometrical analyses, and require a compact measuring arrangement.
Innovation Solution
An indirect calibration method that metrologically determines the calibration factor by measuring mutual inductance between the receiving and calibration coils, using a strong inductive coupling to eliminate spatial distance errors, and involves a two-stage process for precise calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the calibration factor is calculated from coil geometries using complex mathematical formulas, then the calibration process can be performed, but significant errors occur due to the cubing of distance measurements and weak inductive coupling
Solution Approach 1:
The patent replaces the mechanical/geometrical calculation method with an electrical measurement method. Instead of calculating the calibration factor from coil geometries and distances, the system measures the electrical voltage ratio between the calibration coil and receiving coil, which directly reflects the magnetic field ratio. This substitution of measurement approach eliminates the complex mathematical calculations and their associated errors.
Solution Approach 2:
The patent introduces a calibration coil as an intermediary element that generates a known calibration magnetic field. This calibration coil serves as a mediator between the transmitting coil and receiving coil, allowing the system to establish a known reference ratio that can be used to calibrate the measurement system without requiring complex geometric calculations.
2Productivity
If the transmitting and receiving coils are positioned far apart (approximately one meter), then the measurement setup works, but the primary field is several orders of magnitude stronger than the secondary field, requiring amplification and compensation
Solution Approach 1:
The patent applies preliminary action by introducing a compensation coil that is activated before the actual measurement to cancel out the primary field's effect on the receiving coil. This preliminary compensation ensures that when the secondary field measurement is taken, the receiving coil is not saturated by the strong primary field, allowing for accurate measurement of the weak secondary field signal.
Solution Approach 2:
The compensation coil acts as a counterweight to the primary field's unwanted influence. By generating an opposing magnetic field that equalizes the primary field's effect at the receiving coil location, the system can accurately measure the secondary field without the overwhelming presence of the primary field.
3Measurement precision
If a calibration coil is installed coplanarly between transmitting and receiving coils, then calibration can be performed, but the inductive coupling is very weak and not directly measurable due to the considerable distance required
Solution Approach 1:
The patent inverts the traditional calibration approach by having the calibration coil generate a field that is measured by the receiving coil, rather than having the transmitting coil's field induce a response in the calibration coil. This inversion allows for direct measurement of the inductive coupling between the calibration coil and receiving coil, making the calibration process simpler and more accurate.
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 method significantly reduces errors in determining the calibration factor, allows for a more accurate and compact measuring arrangement, and accounts for time-dependent environmental influences.
Implementation Method 1
The electromagnetic induction method utilizes the effect that strong alternating magnetic fields induce eddy currents in a conductive medium
Implementation Method 2
A receiving coil is positioned at a distance of approximately one meter from the transmitting coil. This receiving coil detects the secondary field emitted by the medium at the substrate and converts it into a voltage
Implementation Method 3
The calibration coil generates a calibration field as a secondary field (also called a calibration signal or calibration pulse) with a precisely known amplitude and phase at the time of calibration
Data Source
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AI summary
Elecromagnetic induction methods are also used in geophysics on conductive substrates (09) by evaluating the ratio of generated magnetic primary and secondary fields (HP, HS), for example in order to determine sea ice thickness. The required calibration is carried out by means of a calibration coil (10). In order to improve the accuracy and to simplify the measuring assembly (01), according to the invention the calibration coil (10) and the receiving coil (08) are permanently inductively coupled to one another, whereby a calibration field (HCX) is generated at the calibration coil (08) by a calibration pulse and thereby a magnetic flux is induced in the receiving coil (08). Furthermore, the calibration method is designed in two stages. In the first stage (S1), a calibration factor (HCX/HP) is determined in a purely metrological manner depending on the generated mutual inductance (MRC) (electrical generation of the calibration pulse by a calibration signal generator (12) when the transmitting coil (02) is inactive), and, in the second stage (S2), the actual calibration of the measuring assembly (01) is carried out (inductive generation of the calibration pulse by the transmitting signal generator (03) when the transmitting coil (02) is active). The measured received voltage (URx) is calibrated via the secondary field (HS= HCX) known from the measured calibration factor (HCX/HP). A measuring assembly (01) preferably has two switches (14, 15) for carrying out the two stages (S1, S2).