RU112430U1 - VORTEX DEVICE FOR MEASURING SPECIFIC ELECTRICAL CONDUCTIVITY - Google Patents

Abstract

A device for measuring electrical conductivity, comprising a series-connected oscillator and an eddy current converter, a phase detector, the reference voltage input of which is connected to the oscillator, and an indicator, characterized in that, in order to enable operation at large working gaps, the diameter of the receiving coil of the eddy current converter always exceeds the diameter the emitter coil and is determined either experimentally by the signal maximum, or as a result of a theoretical study on the absolute value of the maximum in the parameter (ρ) of the following formula: ! , ! where J1(x) is the 1st order Bessel function of "x"; ! λ is the integration variable, the physical meaning of which is the spatial frequency, since integration up to "∞" is impossible, in practice you can limit yourself to the value: ! , ! R is the radius, in strict mathematical terms, the radius of the turn, in practical application the average radius of the excitation coil; ! ρ - distance from the axis of the sensor; ! z is the distance along the "Z" axis of the receiving coil, the height above the test object, the gap, this value should be set; ! h is the height of the radiation coil above the test object; ! and k2=-j ω µ µ0 σ, , ! q - wave number; ! k - generalized parameter; ! j - imaginary unit; ! ω - cyclic frequency; ! µ - relative magnetic permeability; ! µ0 - vacuum magnetic permeability 4π·10-7 H/m; ! σ - electrical conductivity, ! if the thickness of the test object is known, then it is possible to calculate more accurately using a more complex formula: ! , ! where d is the thickness of the test object.

Description

The utility model relates to test equipment and can be used in various industries to control the quality of electrically conductive products by the magnitude of the electrical conductivity of their materials.

A number of eddy current devices for controlling electrical conductivity are known complete with consignment notes and screen transducers (Non-Destructive Testing and Diagnostics: Reference / edited by V.V. Klyuyev. - M.: Mechanical Engineering, 1995. - C 269-272). As a rule, all overhead and screen type converters are used to emit the original signal and receive the signal from the monitoring object coils of the same or close diameters. Sometimes the same coil is used for radiation and reception, in addition, there are converters in which the receiving coil is smaller in diameter than the radiating one. All these devices are designed to work only with small values of the working gap, as a rule, no more than 2 mm. Meanwhile, in the practice of non-destructive testing, there are often cases when it is necessary to control the structure of the material through a non-conductive coating, for example, a thermal insulation layer, while the working gap is much larger. But with relatively large values of the working clearances, for example, more than 5 mm, the maximum value of the secondary electromagnetic field appears on the circuit of a larger diameter in comparison with the emitter. It is known that the task of the receiving coil is to convert the secondary electromagnetic field into EMF, which is inefficiently implemented by the coils of these devices at large values of the working clearances.

The closest device in terms of features and adopted as a prototype is “Eddy Current Control Device” (USSR Author's Certificate No. 1310709, class G01N 27/90, 1987), which includes a series-connected oscillator, eddy current transducer and phase detector, as well as an indicator.

However, it is intended to work only with small gaps.

The technical task of this utility model is to create a device for controlling the structure of electrically conductive materials by the value of electrical conductivity, designed to operate with large values of the working clearances.

To achieve the specified technical result in a device for measuring electrical conductivity, which contains a series-connected oscillator and eddy current transducer, a phase detector, the reference voltage input of which is connected to the oscillator and an indicator, the diameter of the receiving coil of the eddy current transducer always exceeds the diameter of the emitter coil and is determined experimentally by the maximum received signal, or as a result of a theoretical study on the absolute mask maximum in the parameter (ρ) of the following formula:

,

where: J1 (x) is the 1st order Bessel function of "x";

λ is an integration variable whose physical meaning is spatial frequency, because integration to “∞” is impossible; in practice, you can limit yourself to the value:

;

R is the radius, in strict mathematical expression of the radius of the coil, in practical application, the average radius of the excitation coil;

ρ is the distance from the axis of the sensor;

z is the distance along the axis "Z" of the receiving coil, the height above the control object, the gap, this value should be set;

h is the height of the radiation coil above the control object;

and k ² = -j · ω · μ · μ 0 ^{· σ} , ,

q is the wave number;

k is the generalized parameter;

j is the imaginary unit;

ω is the cyclic frequency;

µ is the relative magnetic permeability;

µ ₀ - magnetic permeability of the vacuum 4π · 10 ^-7 GN / m;

σ is the electrical conductivity.

If the thickness of the control object is known, then it is possible to calculate more precisely using a more complex formula:

,

where d is the thickness of the object of control.

Distinctive features of the proposed device is the choice of the ratio between the diameters of the emitting and receiving coils, it is calculated by a special proposed method.

The proposed device is illustrated by drawings, presented in figures 1-3.

Figure 1 shows the structural diagram of the device.

Figure 2 - circuit of eddy currents excited by a coil located above the half-space.

Figure 3 - in addition to the circuit of the eddy currents presents the configuration of the electromagnetic field initiated by these eddy currents.

The eddy current device for measuring electrical conductivity contains an oscillator (1) that generates a sinusoidal current to power the eddy current transducer; eddy current transducer (2) that converts an electric current into an electromagnetic field and receives a secondary electromagnetic field generated by the control object; a phase detector (3), which selects the necessary information, and an indicator (4), which converts the information to a form convenient for the consumer.

The eddy current device is as follows.

The self-oscillator (1) generates an electric current of a sinusoidal shape supplied to the exciting coil of the eddy current transducer (2). The receiving coil of the converter receives the total field, which is the sum of the electromagnetic field generated by the excitation coil and the secondary field created by eddy currents. From the receiving coil, the signal is supplied to the phase detector (3), and then to the indicator (4). A feature of the proposed device is the design and relative position of the exciting and receiving coils in the eddy current transducer. This is due to the peculiarity of the topography of the secondary electromagnetic field with large working gaps. The drawing shown in Figure 2 shows that the eddy current circuit is significantly expanded in the radial direction relative to the radius of the coil. The expansion effect is even clearer in Figure 3, showing the topography of the secondary electromagnetic field. The contour of maximum values is expanded more than 3 times relative to the radius of the turn. For clarity, an extreme case is taken here; the distance between the transducer and the excitation (gap) object is 20 mm. In the practice of non-destructive testing, such situations are also not excluded when it is impossible to control with lower values of the working gap, however, as a rule, the distance between the emitter and the test object is much smaller. But, as calculations show, even with a gap of 5 mm, the effect of the expansion of the secondary field is noticeable. This leads to a completely obvious conclusion: for large values of the working gap, the receiving coil should be of a larger diameter relative to the radiating one.

Claims (1)

A device for measuring electrical conductivity, comprising a series-connected oscillator and eddy current transducer, a phase detector, the reference voltage input of which is connected to the oscillator, and an indicator, characterized in that to ensure the possibility of operation at high values of the working gap, the diameter of the receiving coil of the eddy current transducer always exceeds the diameter emitter coils and is determined either experimentally by the maximum signal, or as a result of theoretical studies on the absolute value of the maximum in parameter (ρ) of the following formula:

, where J1 (x) is the 1st order Bessel function of "x"; λ is an integration variable whose physical meaning is spatial frequency, because integration to “∞” is impossible; in practice, you can limit yourself to the value:

, R is the radius, in strict mathematical expression of the radius of the coil, in practical application, the average radius of the excitation coil; ρ is the distance from the axis of the sensor; z is the distance along the axis "Z" of the receiving coil, the height above the control object, the gap, this value should be set; h is the height of the radiation coil above the control object;

and k ² = -j · ω · μ · μ ₀ · σ,

, q is the wave number; k is the generalized parameter; j is the imaginary unit; ω is the cyclic frequency; µ is the relative magnetic permeability; µ ₀ - magnetic permeability of the vacuum 4π · 10 ^-7 GN / m; σ is the electrical conductivity, if the thickness of the test object is known, then it is possible to calculate more precisely using a more complex formula:

, where d is the thickness of the object of control.