RU2371672C2 - Method to control properties of entity made from electrically conducting materials - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: self-oscillator frequency is measured. Self-oscillator oscillatory circuit comprises Eddy-current transformer wired to reference and controlled entities. Frequencies of reference and controlled entity self-oscillators are compared. Note that frequencies are measured for several magnitudes of self-oscillator oscillatory circuit components, at least one of which being controlled component. Properties of entity are set in compliance with plurality of variations in frequencies on which measurements have been made. Number of aforesaid frequencies may not be less than that of controlled parametres.

EFFECT: tuning out from effects of uncontrolled properties.

4 cl, 3 dwg

Description

1. The technical field

The invention relates to non-destructive testing by the method of eddy currents and can be used to control the properties of objects from electrically conductive materials, in particular the thickness of the coating and the conductivity of the base.

2. The level of technology

A known two-frequency method for controlling the properties of an object (US Pat. RF No. 2184931, IPC G01B 7/06, 2000), in which the property of an object of electrically conductive materials is determined.

The disadvantage of this method is the low accuracy of measurements caused by inevitable errors in measuring the amplitude and phase of an alternating voltage.

Also known, adopted by the applicant for the closest analogue (prototype), is a method of controlling the properties of an object on an electrically conductive base (invention certificate No. 99127414/28, IPC G01B 7/06, publ. 10.10.2001), including the operation of measuring the frequency of the oscillator, the oscillatory circuit of which includes an eddy current transducer installed sequentially on the reference and controlled objects, comparing the frequencies of the oscillator of the reference and controlled object and establishing the property of the object by the magnitude of the frequency change.

The disadvantage of this method is the low accuracy of the measurement, due to its one-parameter, not allowing, for example, to detune from the influence of the conductivity of the substrate on the measurement results of the coating thickness.

3. The invention

3.1. A task

The technical task is to increase the accuracy of control.

The technical result is the detuning from the influence of the uncontrolled properties of the object on the measurement results of the controlled parameters due to the transition to multi-parameter control.

3.2. List of drawings

Figure 1 shows an example 1 implementation of a device for multi-parameter control of the properties of an object of electrically conductive materials, figure 2 shows the nature of the family of dependences of the increment of two frequencies - the upper (Δfв) and lower (Δfн) on the thickness of the dielectric coating (h) for different values of specific dielectric conductivity of the base (σ), figure 3 is an example 2 of the implementation of a device for multi-parameter control of the properties of an object of electrically conductive material, where 1 is an oscillator, 2 is an eddy current transducer block with an inductance L1, 3 is bl managed to condenser 4 - analog converter (DAC), 5 - microprocessor 6 - display device 7 - a set of analog switches.

The essence of the proposed method is as follows.

3.3. Features

In contrast to the known method, including the operation of measuring the frequency of the oscillator, in the oscillatory circuit of which is included an eddy current transducer installed sequentially on the reference and controlled objects, comparing the frequencies of the oscillator of the reference and controlled object and establishing the property of the object by the magnitude of the frequency change, in the method of controlling the properties of the object from conductive materials measure the frequencies at several values of the elements that make up the oscillatory circuit oscillator, at least one of the elements which is made controllable, and is set according to properties of the object the plurality of frequency change on which the measurements were made, the number of frequencies at which measurements are made is chosen not less than the number of monitored parameters. When monitoring the coating thickness and base conductivity, a family of reference dependencies of the frequency increment on the gap and base conductivity is removed, the frequency increment is measured on the controlled object, compared with the family of reference dependencies and the base conductivity of the monitored object is determined by the ratio of the frequency increment, and the coating thickness by the approximated dependence increments of the upper frequency from the gap for the set value of the conductivity of the base.

3.4. Method description

The technical result is the detuning from the influence of the uncontrolled properties of the object on the measurement results of controlled parameters due to the transition to multi-parameter control by introducing additional frequencies. Moreover, the elements of the oscillatory circuit of the oscillator (at least one) must be controlled, the resonance frequency of the oscillator circuit is measured sequentially at several (two or more) values of these elements, and the change in the properties of the control object is judged by the totality of frequency changes.

Improving the accuracy of control, compared with other multi-frequency multi-parameter control methods, is achieved by measuring the resonant frequency of the oscillatory circuit of the oscillator with an eddy current transducer included in it, and not by using the amplitude-phase characteristics of the eddy current transducer signal.

4. Information confirming the possibility of carrying out the invention

Figure 1 presents an example implementation of the device for the case when the controlled capacitor is made of the oscillatory circuit of the oscillator.

The oscillator 1, made according to the scheme of a capacitive three-point circuit, on the transistor T1, is taken as the basis. Capacitors C1-C3 and resistors R1-R3 provide a self-excitation mode and a constant current mode of the transistor T1. L1 - the inductance of the winding of the eddy current transducer 2, forms with the controlled capacitor 3 an oscillatory circuit of the oscillator. As a controlled capacitor, a varicap D1 (KB 105A) and a digital-to-analog converter of type 4 code-voltage (AD7390 from Analog Device) are used. Capacitor C4 is a separator and serves to maintain the DC transistor mode when the control voltage on the varicap D1 changes. The resistor R4 allows you to avoid shunting the oscillator circuit with a low output resistance of the DAC 4 and maintain a high quality factor of the circuit. The information input of the DAC 4 is connected to the output of the microprocessor 5 (ATmega 64 manufactured by ATMEL). The output of the oscillator is connected to the input of the microprocessor 5, which provides the necessary modes of measurement, control of the DAC 4, processing the results and presenting the results of the monitoring on the indicating device 6 (MT-6464A from MELT).

The device operates as follows.

The microprocessor 5 before each cycle of measuring the frequency of the oscillator 1 transmits to the DAC 4 of the controlled capacitor 3 a digital code that provides the output voltage of the DAC 4, in which the varicap D1 connected in series and the capacitor C4 with the inductance L1 of the ECP 2 form an oscillatory circuit tuned to one of the selected frequencies. After the transition process in the oscillator 1, caused by a change in the value of the controlled capacitor 3, the microprocessor 5 measures the current frequency value. After completion of the measurement process, the cycle repeats again, but for a different frequency.

After enumerating all the selected frequencies, the results are processed and displayed on indicator 6. After that, the entire measurement cycle can be repeated again.

As an example of constructing the algorithm of microprocessor 5, we consider the problem of separately controlling the thickness of the dielectric coating and the electrical conductivity of a base made of non-magnetic material.

Initially, a family of dependences of the frequency increment on the thickness of the dielectric coating h and the conductivity of the base σ is constructed using two frequencies f _H and f _B.

The nature of these dependencies is shown in Fig.2.

Such a mutual arrangement of the graphs and their relative value correspond to the conditions: f _B > f _H and σ ₁ <σ ₂ <σ ₃ <σ ₄ .

The conductivity of the base σ is determined, for example, by the ratio Δf _H / Δf _B (in the case of straight lines). From the found value of conductivity, one should select the corresponding curve (or calculate a new one using the neighboring ones), and then from the selected curve, using the dependence h (Δf _B ), determine the desired value of h.

The choice of the number and magnitude of frequencies at which measurements are made is determined by the control conditions. If the problem of measuring the thickness of an electrically conductive non-magnetic coating on an electrically conductive non-magnetic substrate (the thickness of aluminum cladding on duralumin sheets) is solved, the influence of changes in the conductivity of the substrate will be an obstacle when measuring the thickness of a coating with constant conductivity. In this case, it is sufficient to carry out measurements at two values of the controlled capacitor, which should be chosen so that the depth of penetration of the electromagnetic field at the first resonant frequency is approximately equal to the thickness of the cladding layer, and at the second it is much higher, but still less than the sheet thickness, which carried out by well-known calculations (see, for example, “Physical Encyclopedic Dictionary.” Soviet Encyclopedia. M: 1984, p. 690, ref. “Skin Effect”).

In this case, changes in the first resonant frequency will be mainly associated with a change in the thickness of the cladding layer, and the second with a change in the conductivity of the base.

Having removed these dependencies and entered them into the microprocessor memory, it is possible to determine the deviation of the parameters of the controlled product from the nominal value by the totality of changes in these frequencies.

In the case when it is also necessary to control the sheet thickness, it is necessary to enter a third value of the capacitance of the capacitor corresponding to the resonant frequency of the oscillator, at which the penetration depth of the electromagnetic field is greater than the thickness of the sheet and the changes of which will strongly depend on the sheet thickness and weaker on the base conductivity and coating thickness.

If the conductivity is also found as a quantity affecting the accuracy of measuring the thickness of the coating, then one more value of the capacitance of the oscillator circuit capacitor will be required, corresponding to the frequency at which the penetration depth of the electromagnetic field is less than the thickness of the cladding and will depend, under other conditions, on conductivity of this layer.

Figure 3 presents an example implementation of the device for the case when the controlled coil is made inductance of the oscillatory circuit of the oscillator.

In this case, the winding of the ECP 2, which plays the role of an inductor L1 of the oscillatory circuit of the oscillator 1, is made up of two parts, and using a set of analog switches 7 (for example, ADG719 from Analog Device), either only part of it can be included in the oscillatory circuit, or the whole coil. The keys are controlled by the signal of the microprocessor 5, and the ratio of the frequencies at which the measurement is made is determined through the ratio of the inductance of the parts of the coil winding L1.

Capacitor C4 is the second element of the circuit and the value of its capacitance, together with the magnitude of the inductance of the coil L1, determines the resonant frequency of the oscillatory circuit of the oscillator 1. In this case, the set of keys 7 allows you to use only two values of the resonant frequency, and therefore, the device can be used to solve only two-parameter problems . By increasing the number of keys 7 and sections of the inductor L1, you can increase the number of operating frequencies, and therefore the number of measured parameters of the control object.

Claims (3)

1. A method of controlling the properties of an object made of electrically conductive materials, including the steps of measuring the frequency of the oscillator, the oscillatory circuit of which includes an eddy current transducer installed sequentially on the reference and controlled objects, comparing the frequencies of the oscillator of the reference and controlled object and establishing the property of the object by the magnitude of the frequency change, characterized in that make measurements of frequencies at several values of the elements that make up the oscillatory circuit torus, at least one of the elements which is made controllable, and is set according to properties of the object changes the plurality of frequency at which the measurements were made. 2. The method according to claim 1, characterized in that the number of frequencies at which measurements are made, at least the number of controlled parameters is selected. 3. The method according to claim 1, characterized in that when controlling the thickness of the coating and the conductivity of the base, remove the family of standard dependencies of the frequency increment on the size of the gap and conductivity of the base, measure the frequency increment on the controlled object, compare with the family of standard dependencies and establish the value of the conductivity of the base of the controlled object according to the ratio of the increment of frequencies, and the thickness of the coating by the approximated dependence of the increment of the upper frequency on the value of the gap for the set value pr base conductivity.

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