FR2566894A1 - Wire dia. measurement using capacitive electrodes - Google Patents

Abstract

A wire (8) is placed symmetrically between two identical electrically connected electrodes (1,2) of a transducer to form a capacitor which forms a bridge arm with the secondary coil of a transformer(s). The bridge is first balanced using a wire (7) of known dia. between the electrodes. With the measurement wire in position the bridge is again balanced by displacing one or more electrodes. The dia. of the wire is evaluated from the separation of the electrodes.

Description

METHOD FOR MEASURING THE DIAMETER OF A WIRE
The present invention applies to methods of measuring various geometric parameters of long products, and more particularly to a method of measuring the diameter of a wire.

 The invention can be used in the laboratory, to control the diameter of a wire and, industrially, for example in metallurgy, in radioelectricity, in the electronic industries, to measure the diameter of a conductive wire during its manufacturing.

 At present, the measurement of the diameter of a wire from a diameter of a few microns is carried out by a method consisting in weighing a segment of wire of determined length on a torsion balance and then determining its diameter a from the specific density of the constituent material.

 From 300 µm and beyond, the diameter of a wire is determined by a contact process using micro-indicators and micrometers.

 Determining the diameter of a wire by weighing requires precise knowledge of the specific density of the material, which is currently only determined in the ingot structure, which does not correspond to the density of the material actually constituting the wire.

 The contact measurement process can be performed with an error of about 0.05 µm, but it leads to deformation of the wire to be measured which is practically impossible to determine.

 There is a method for capacitive measurement of the humidity of a sheet or sheet material from its dielectric permeability consisting in measuring the capacity of a transducer produced in the form of a flat capacitor between the electrodes of which is placed the sheet or sheet sample to be studied, then remove the sample and gradually approach one of the transducer electrodes to the other until the initial capacity is equal to the capacity of the transducer in the presence of the sample, the humidity of the material then being evaluated as a function of the distance of the electrodes (cf. Measurement of humidity "by Berliner MA, Moscow, Editions" Energia ", 1973, p.86).

 This method can also be used for measuring the diameter of a wire, but this measurement has the drawback of generating considerable errors due to the high initial capacity of the transducer, increased by the non-linearity of its characteristic to be measured, d 'where it follows an insufficient precision of the measurement of the diameter of a wire.

There is also a method of measuring the diameter of laminated products consisting in comparing the partial capacities of the material of a laminated product placed between the electrodes of a transducer with the primary capacity of the latter (cf. patent of the Democratic Republic
German no. 32032).

 This method can also be used for measuring the diameter of a wire. However, in this case, the measurements are subject to significant errors due to the need to measure the capacity of the transducer and to the non-linearity of the characteristic to be measured of the transducer, responsible for the poor accuracy of measurement of the diameter of a wire.

There is also a method of measuring the diameter of a wire which consists of placing it between the two identical electrodes, connected to each other, of a transducer so that it is arranged symmetrically with respect to these electrodes with which it forms. a capacitor coming in turn to constitute, with the secondary of a transformer, one of the branches of the bridge and to determine by one of the parameters of the bridge the diameter of the wire (cf. collection "Measurements, controls, automation", Moscow, 1978, n "3, pp. 19 to 24," Modern means for measuring the transverse dimensions of current-conducting filaments "by
Grokholsky AL, Gorbov MM, Strunsky MG, Fedotov VK).

 This method, in addition to the fact that it causes considerable errors in measuring the diameter of a wire caused by the measurement of the capacity of the transducer, reveals a non-linearity of the characteristic to be measured of the transducer which turns out to be harmful to the precision of measuring the diameter of a wire.

The present invention aims to propose a method for measuring the diameter of a wire in which the bridge is balanced so as to make it possible to improve the accuracy of measuring the diameter of a wire and to linearize the translation into diameter of the wire of the measured capacitor capacity
This object is achieved by the fact that in the method of measuring the diameter of a wire consisting in placing between the two identical electrodes of the transducer, electrically connected to each other, a wire to be measured so that it is arranged symmetrically by compared to the electrodes and forms with them, a capacitor to constitute in turn with the secondary of a transformer the branch of a bridge, according to the invention, before placing between the electrodes of the transducer the wire to be measured, symmetrically places a standard wire of given diameter forming therewith a capacitor, which the bridge is balanced, that after placing the wire to be measured between the transducer electrodes, the measuring bridge is rebalanced by moving the electrodes of the transducer or one of the electrodes thereof and the wire to be measured and that the diameter of the wire to be measured is determined as a function of the distance between the electrodes.

 In this way, the method of measuring the diameter of a wire according to the invention makes it possible to increase the precision of measuring the diameter of a wire and to improve the quality of the wire produced.

 Other objects, advantages and characteristics of the invention will appear on reading the description of an embodiment of the method without limitation and made with reference to the accompanying drawing in which the single figure represents the electrical diagram in principle of a device for measuring the diameter of a wire applying a method of measuring the diameter of a wire according to the invention.

 The device for measuring the diameter of a wire implementing the method for measuring the diameter of a wire according to the invention comprises two identical and interconnected transducer electrodes 1 and 2, one of which, 2, is connected to a zero indicator 3 and to an adjustable back-up capacitor 4 connected in turn to the secondary of a transformer 5, the primary of which is connected to a generator 6 of the alternating voltage.

 A standard wire 7 of given diameter is placed between the electrodes l and 2, electrically connected to the secondary of the transformer 5 or a measuring wire 8 symbolized in the drawing by a broken line and also electrically connected to the secondary of the transformer 5 .

 There is thus a bridge of which one of the branches is composed of the electrodes 1 and 2 of the transducer forming with the standard wire 7 or the wire to be measured 8, a capacitor and the secondary of the transformer 59 the other branch of the bridge is constituted by the auxiliary capacitor 4 and the secondary of the transformer 5, the zero indicator 3 serving as a diagonal.

 The method of measuring the diameter of a wire according to the invention consists in placing, symmetrically between the electrodes 1 and 2 of the transducer, the standard wire 7 of given diameter so that it forms, with these electrodes, a capacitor. Next, the bridge is balanced by adjusting the capacity of the auxiliary capacitor 4. Then, symmetrically placed between the same electrodes 1 and 2, the measuring wire 8 forming, with these, a capacitor. The bridge is again balanced by displacement of the electrodes 1 and 2 of the transducer and the diameter of the wire to be measured 8 is a function of the distance between the electrodes 1 and 2.

 According to another particular embodiment of the method according to the invention, the bridge is balanced by moving one of the electrodes of the transducer, for example the electrode 1 and the wire to be measured 8, and the diameter of the wire to be determined is determined. also measure 8 from the distance between the electrodes.

 We will now examine in more detail the criteria for measuring the diameter of a wire according to the invention.

où:
E est la constante diélectrique;
2l1 est la distance séparant les électrodes 1 et 2 du transducteur;
2r1 est le diamètre du fil étalon 7.The capacity of the transducer capacitor in the presence of standard wire 7 has the expression:

or:
E is the dielectric constant;
2l1 is the distance between electrodes 1 and 2 of the transducer;
2r1 is the diameter of the standard wire 7.

où:
212 est la distance entre les electrodes 1 et 2 du transducteur;
2r2 est le diamètre du fil à mesurer 8.After balancing the bridge and placing the measuring wire 8 in the transducer, the capacitance of the capacitor is expressed by the formula:

or:
212 is the distance between electrodes 1 and 2 of the transducer;
2r2 is the diameter of the wire to be measured 8.

The bridge is rebalanced by moving the electrodes 1 and 2 of the transducer, or one of the electrodes 1 of the transducer and the wire to be measured 8, until C1 = C2. The diameter of the wire 8 is then determined as a function of the distance between the electrodes 1 and 2 from the expression.

 The method of measuring the diameter of a wire according to the invention makes it possible to improve the accuracy of measuring the diameter of a wire. For example in the range of diameters between 1 μm and 300 μm, the relative error in measuring the diameter of such a wire does not exceed 0.2%, and for a wire diameter of 300 μm and beyond is 0.07%.

Thus the absolute error of the measurement of a wire of 10 µm in diameter is 0.02 µm.

 The high speed of measurement, combined with high precision, makes it possible to abandon the weighing process currently used for measuring the diameter of a wire, to significantly improve the quality of the wire produced, to reduce the measurement time, d 'increase the productivity of the equipment, replace the dies in good time during the drawing process because the wear of a die can be judged on the wire diameter.

 Of course, the invention is not limited to the embodiments described and shown and it is capable of numerous variants accessible to those skilled in the art, without departing from the spirit of the invention. 'invention.

Claims (1)

 Method for measuring the diameter of a wire consisting in placing symmetrically between two identical electrodes and electrically connected to each other of a transducer, a wire to be measured forming, with these, a capacitor which in turn constitutes the secondary d '' a transformer, a branch of a measuring bridge, characterized in that before having the wire to be measured (8) between the electrodes (1 and 2) of the transducer, one places between these electrodes (1 and 2) symmetrically with respect thereto a standard wire (7) of given diameter forming with these electrodes a capacitor, which equilibrates the measurement bridge, which is placed between the electrodes (1 and 2) of the transducer a wire to be measured (8), that the balance of the bridge is restored by displacement of the electrodes (1 and 2) of the transducer, or of one of the electrodes (1) of the transducer and of the wire to be measured (8), and that 'the diameter of the wire to be measured (8) is determined as a function of the distance between the electrodes.