METHOD FOR DETERMINING ELECTRICAL CONDUCTIVITIES IN SAMPLES BY MEANS OF AN EDDY CURRENT SENSOR

摘要

In the method for determining the electrical conductivity in samples by means of an eddy current sensor, an alternating electrical field is excited within a sample by an alternating electrical voltage applied to a transmitter coil at a known measurement frequency f, ω and an alternating electromagnetic field which is directed against the alternating electrical field is thereby formed which is detected by a receiver coil or by a suitable detector and the complex impedance Z R+jX is determined. This procedure is carried out at different measurement frequencies f, ω once in air and once with the same measurement frequencies f, ω at a calibration body with a known electrical conductivity σ. The differences of the real and imaginary portions ΔR and ΔX of the measured values in air and over the calibration body are then divided by the respective measurement frequency f, ω; wherein a product ωσ is associated with each value pair ΔR/ω and ΔX/ω=ΔL in accordance with the associated measurement frequency ω and the known conductivity σ of the calibration body and a ωσ locus is presented in a Nyquist diagram with these value pairs. With a measured impedance Z at a measurement frequency ω of a sample having an unknown conductivity σ, a value pair ΔR/ω and ΔX/ω of the values in air is formed at the measured values over the sample and a point from the ωσ locus and thus a ωσ value is associated with this value pair ΔR/ω and ΔX/ω=ΔL and the unknown electrical conductivity σ of the sample material is determined from this using the known measurement frequency f, ω. In the calibration at a calibration body and a measurement at a sample, wherein the phase angle φ=tan(ΔX/ΔR) is calculated, instead of the ωσ locus, the function of the product ωσ=f(φ) can, however, also be calculated, with a product ωσ being associated with the phase angle φ on the measurement of an un known conductivity σ of the sample material with this function and thus the electrical conductivity σ of the sample can be determined with the known measurement frequency f, ω or in the calibration at a calibration body and a measurement at a sample, the quotient q=ΔX/ΔR or its reciprocal 1/q is calculated and, instead of the ωσ locus, the function of the product ωσ=f(q) or ωσ=f(1/g) is determined and a product ωσ is associated with the quotient q or 1/g on the measurement of an unknown conductivity σ of a sample with this function f(q) or f(1/q) and thus the electrical conductivity σ of the sample material is determined.

主权项

1. A method for determining the electrical conductivity in samples by means of an eddy current sensor, in which an alternating electrical field is excited by an alternating electrical voltage applied to a transmitter coil at a known measurement frequency ω and an alternation electromagnetic field which is directed against the alternating electrical, field is thereby formed which is detected by a receiver coil or by a suitable detector and the complex impedance Z=R+jX is determined,
wherein this procedure is carried out at different measurement frequencies ω once in air and once at the same measurement frequencies at a calibration body with a known electrical conductivity σ, whereupon the differences of the real and imaginary portions ΔR and ΔX of the measured values in air and over the calibration body are divided by the respective measurement frequency ω; wherein a product ωσ is associated with each value pair ΔR/ω and ΔXω=ΔL in accordance with the associated measurement frequency ω and the known conductivity σ of the calibration body and a ωσ locus is shown in a Nyquist diagram with these value pairs; wherein a value pair ΔR/ω and ΔX/ω of the values in air is formed at the measured values over the sample at a measured impedance 7, at a measurement frequency ω of a sample with an unknown conductivity σ and a point from the ωσ locus and thus a ωσ value is associated with this value pair ΔR/ω and ΔX/ω=ΔL, and the unknown electrical conductivity σ of the sample material is determined from this using the known measurement frequency ω; or on the calibration at a calibration body and a measurement at a sample, the phase angle φ=tan(ΔX /ΔR) is calculated and the function of the product ωσ=f(φ) is determined instead of the ωσ locus, with a product ωσ being associated with the phase angle φ on the measurement of an unknown conductivity σ of the sample material with this function and thus the electrical conductivity σ of the sample being determined at the known measurement frequency ω; or on the calibration at a calibration body and a measurement at a sample, the quotient q=ΔX/ΔR or its reciprocal 1/q is calculated and, instead of the ωσ locus, the function of the product ωσ=f(q) or ωσ=f(1/q) is determined and a product ωσ is associated with the quotient q or 1/q on the measurement of an unknown conductivity σ of a sample with this function f (q) or f(1/q) and thus the electrical conductivity σ of the sample material is determined,