SU920504A1 - Device for measuring linear dimensions - Google Patents

Description

(St) DEVICE FOR MEASURING LINEAR SIZES

I

The invention relates to methods of non-destructive testing and can be used in measuring the thickness of coatings on metallic surfaces, or for detecting metallic structural elements hidden under a non-metallic layer. material.

A device for measuring linear dimensions is known, comprising a sequentially connected generator, an eddy current transducer consisting of the excitation and measuring windings, a capacitor connected to the exciting winding of the eddy current transducer, a signal amplification and processing unit, and an indicator. The capacitor in this device is selected so that the temperature changes of its capacitance compensate for changes in the inductance of the windings of the eddy current transducer 11.

The closest to the invention to the technical essence is

device for measuring linear dimensions, containing an eddy current transducer, consisting of excitation and measurement windings and a ferrite core, excitation generator, a capacitor connected between the output of the excitation generator and the excitation winding of the eddy current transducer, measuring circuit connected to the measuring winding of the eddy current transducer, and indicator.

A disadvantage of the known device is the deterioration in the accuracy of control when the temperature of the eddy converter is changed and when the material of the core of the eddy current converter is aging.

The purpose of the invention is to improve the control accuracy when changing the magnetic properties of the ferrite core.

Claims (2)

The goal is achieved by the fact that the device is equipped with a resistor connected between the second output winding of the excitation winding and the generator, and the resistance (R) of the resistor and the capacitance (C) of the capacitor are chosen from the ratios / rf R 1 toLjA. With --L. f2 (oR where O) is the circular frequency of the generator; L is the inductance of the excitation winding without a core; (C is the initial magnetic permeability of the core. The drawing shows block diagrams of the proposed device. The device contains an eddy current transducer 1 with excitation and and measuring windings 2 and 3 and a ferrite core 2, generator 5, the output of which is connected to the excitation winding 2 through a capacitor 6 and a resistor 7, connected in series with the measuring circuit and the indicator 9 are connected to the output of the measuring winding 3. The device operates as follows: AC voltage From the generator 5 is supplied to When the magnetic field of the ferrite core k interacts with the metal of the object to be detected (not shown), the induced currents in the metal are recorded by measuring winding 3 of the eddy current transducer 1. The magnitude of the induced EMF depends on the distance between the detectable object and the measuring winding 3, and the magnitude of the current in the exciting winding 2. The voltage from the output of the measuring winding 3 enters the measuring circuit 8, where it is amplified, transformed and recorded by the indicator 9. Ferrite cores have a low Curie point, their magnetic properties strongly depend on temperature. Similarly, the aging of ferrites also affects magnetic permeability. The resultant changes in the inductance of the exciting winding leads to a deterioration in the measurement accuracy. When a capacitor I resistor is inserted into the device, the voltage across the measuring winding is determined from the expression It - wUKj where U) is the generator circular frequency; and - generator output voltage; K is the coupling coefficient of the field windings and measurements; ji is the initial magnetic permeability of the core; LL and Lrt are the inductances of the excitation and measurement windings without a core; R is the resistance of the resistor; С - capacitor capacitance. By analyzing the expression, it follows that changes in the magnetic permeability of the core, depending on the values of the resistance of resistor R and the capacitance of capacitor C, either increase or decrease the output voltage. In order for the magnetic permeability measurement not to affect the output voltage, it is necessary to choose the resistance of the resistor R and the capacitance of the capacitor G to choose from the conditions of the invention. A device for measuring linear dimensions containing an eddy current transducer consisting of the windings of the excitation and measurement and a ferrite core, a generator excitation capacitor connected between the output of the excitation generator and the excitation winding of the eddy current transducer, the measuring circuit connected to the measuring winding of the eddy current transducer, and the indicator, about t and h. e. so that, in order to improve the control accuracy when changing the magnetic properties of the ferrite core, it is equipped with a resistor connected between the second output winding terminal and the generator. the resistance (R) of the resistor and the capacitance (C) of the capacitor are chosen from the ratios R (GGD pr, Cr is the circular frequency of the Generator; e O) L inductance of the excitation winding without a core; initial magnetic permeability of the core. Sources of information that are taken into account in the examination of 1 USSR author's certificate 315005, cl. G 01 B 7/06, 1969. 2. Germany №,. 21 g 31/10, 1971 (prototype).