SU1362589A1 - Method of measuring the voltage on welding rods - Google Patents

Abstract

The invention relates to welding production, namely to electrical equipment for contact welding, and can be used to measure the active voltage drop across a welding contact in various welding quality control systems. The invention improves the accuracy of the change. The method of measuring the voltage on the welding electrodes is as follows: the total voltage of the useful signal and interference is measured, and the signal is compensated for by interfering the measurement circuit into the welding circuit. The change in the geometrical dimensions of the measuring circuit under the action of the perpendicular component of the magnetic induction acting on it is converted into an electrical signal. Then, the received electrical signal is differentiated, the moment of time is equal to its kula, and at this moment the voltage is measured on the welding electrodes. Such a solution improves the quality of the welded joint by increasing the voltage measurement accuracy on the welding electrodes, which is achieved with the exception of the error due to the nonlinearity of the resistance of the welding gap, the electrode - electrode. 5 il. C /) g / 2 oo O) oo ao oo; o. 2

Description

The invention relates to welding production, namely to electrical equipment for resistance welding, and can be used to measure the active voltage drop across a welding contact in various welding quality control systems.

The aim of the invention is to improve the measurement accuracy.

FIG. 1 shows a block diagram of a device that implements the proposed method; in fig. 2 is a block diagram of an inductance measurement unit; in fig. 3-5-time diagrams of the operation of the device that implements the proposed method.

The essence of the invention is as follows.

The voltage UK, taken from the measurement loop, is the sum of the voltage of the useful signal and the noise voltage Un

and, with and “+ Un (1)

at the same time, uE is the voltage drop across the welding electrodes, and Un is the interference voltage induced by the magnetic flux F, which covers the measuring circuit, i.e.

.. AF

(2)

The magnitude of the flux Φ of the magnetic induction B through the surface S, “stretched over the contour covering this flow, can be determined if the vector magnetic potential A is known from this contour. To determine the flow, it is sufficient to calculate the circulation of this quantity along the contour Φ Mdl, (3)

where A is the projection of the vector magnetic potential on the direction of integration;

dl - contour element.

Physical measurement of magnitude A is difficult, OAHaj o, from the expression

A rotBj (4)

it follows that there is a hard relationship between the values of A and S, which can be used to estimate the value of A from the measurement results of B., From (4), it follows that B and A are mutually perpendicular. The contour in the direction of integration has a measurable physical parameter P, the value of which depends on B, i.e.

p KilBf, (5)

where IBJ is the modulus of induction component perpendicular to the direction of integration; K | - constant coefficient. If Ф is a magnetic flux that does not change the direction within the surface S of the contour, then, using expressions (3 and 5), we write

f (gPdl. (6)

From (6) it follows that the magnetic flux Φ can be indirectly measured at certain time intervals when its direction

five

relative to the contour is unchanged. The physical parameter P can be the relative elongation of Al / f under the action of a magnetic field (magnetostriction effect).

The effect of magnetostriction leads to a change in the length of the circuit and, as a consequence, to a change in its inductance. Changes in the inductance, proportional to the magnitude of the magnetic flux, are transformed into voltage, which can be differentiated

0 determine the point in time when the interference voltage is zero. By measuring the voltage at the welding gap at this point, the voltage amplitude of the electrode - electrode is determined at the time when

r the interference voltage is zero.

The device implementing the proposed method comprises measuring circuit 1, inductance measurement unit 2, differentiation unit 3, null organ 4, current sensor 5, multiplier 6, adder 7, coincidence circuit 8, amplifier 9 for tracking and memorization. Inductance measurement unit 2 comprises a bridge circuit 10, a rectifier 11, a high pass filter 12, a frequency generator 13. A circuit 1 connects the welding gap electrode-electrode to the input of the inductor measurement unit 2 and the first input of the adder 7, and the output of the inductor measurement unit 2 is connected to the input of the differentiation unit 3 and the first input of the coincidence circuit 8, and the output

The Q of differentiation unit 3 is connected to the input of a null organ 4, the output of which is connected to the second input of the matching circuit 8, while the output of the matching circuit 8 is connected to the first input of the tracking and memorizing amplifier 9, the output of which is connected to the first input of the multiplier 6, the output of the multiplier 6 is connected to the second input of the adder 7, and the second input of the multiplier 6 is connected to the output of the current sensor 5 connected to the welding circuit, and the output of the adder 7 is connected to the second input of the tracking and storing amplifier 9. The output of the frequency generator 13 is connected to the input of the bridge circuit 10, the output of which is connected to the rectifier 11, while the output of the rectifier 11 is connected to the input

g filter 12 high pass.

The voltage measurement is carried out as follows.

The magnetic flux Φ (t) (Fig. 1) arising under the action of the welding current affects the measuring circuit 1 made of a magnetostrictive material, for example, nickel, and measures its linear dimensions, i.e. length 1o, the value of D1 (t). The reduction in the magnetic dimensions of the circuit causes a proportional change in inductance, which, in turn,

5 is proportional to the change in the magnetic flux / Ф (() / (fig. Za, b). If the initial (without the floor) circuit length was about, and the initial inductance LO, then the relative change in inductance due to the flux Φ (t) is:

W / F (1) /,

which is reflected in the graphs in FIG. For, b. The presence of the module is explained by the clarity of the magnetostriction effect, i.e. any direction of flow causes a decrease in the length of the circuit, and therefore its inductance. Measurement of inductance is performed by block 2 (Fig. 2). K. Bridge circuit 10 is supplied with the high voltage Ui (Fig. 3a) from generator 13. In the absence of magnetic flux, the bridge is balanced, i.e.

Ro RS, Lo L o,

and its output voltage is U2 O, (fig. 3g), which takes place between the pulses of the welding current. In the presence of a welding current and, consequently, of a magnetic flux, the initial inductance LO of measuring circuit 1 decreases in proportion to the amplitude of the flow, which causes a corresponding imbalance of the bridge circuit and the appearance of high frequency voltage Uz (output modulated by the flux F (1)) at its output. Since the extension, and hence the inductance, is determined by the flow modulus, the phase of the output voltage LJ2 (Fig. 3g) does not depend on the direction of the flow, therefore, by rectifying Uo by the rectifier 11, obtaining a unipolar voltage Us (Fig. Hz) corresponding to the flow envelope; By filtering the high-pass filter 12 with the unipolar voltage U2, we obtain the voltage U4 (Fig. 4a) corresponding to the flow modulus

U4 no. (T)). ,

which, after differentiation according to formula (2), produces a voltage proportional to the voltage of the disturbance

dU4 (t) dip (1) 1

This operation is performed by differentiation unit 3, and the output voltage of unit 3 is shown in FIG. 46, If

dU4 (t) p

that

dl

and the interference voltage in the formula (1) at the time moment to is also equal to zero Uo (to) 0,

therefore, measuring U8 UK (Fig. 4e) at time point to, we get

U8 (to) U33 (to) - (7)

To determine the moment to, a null organ 4 is used, where the voltage Us is applied. At the exit of the zero-body 4 during the transition

0

input voltage through a zero value, short pulses of m 10 MKS U are formed (Fig. 4c), which through the coincidence circuit 8 are supplied to the first (control, i) input of the tracking and storing amplifier 9. Amplifier 9 is a device that is an amplifier only when there is voltage at the control input, i.e. on the time of action of the strobe pulse (m 10 μs). When the voltage at the control input disappears, the output voltage of the amplifier 9 is fixed at the falling edge of the gate pulse. Strobe pulses Uy (Fig. 4d) are the pulses generated by the null-organ at the moment of time to and transmitted by the circuit 8 to the control input of the amplifier 9. At the same time, the coincidence circuit does not transmit the pulses produced by the zero-organ on the front and to the front edges of the welding current pulse. The gating pulses of them and open the amplifier 9 at times to to time t 10 μs. At this time, its transmission coefficient Yu becomes constant, i.e.

Kz (to) const

5 In measuring circuit 1, under the action of the flux Φ (t), an interference voltage Up is induced, which is added to the useful signal Ie and is fed to the first input of the adder 8 in the form of a voltage Ug (Fig. 4e). A welding current acts at the input of current sensor 5, and a voltage Ug is generated at the output (Fig. 5a).

U9 Kl IcB, (8)

where Kl is a constant coefficient;

ICB - welding current.

Thus, at the output of the sensor 5 current 5 acts a signal geometrically similar to the useful signal

ie R3 IcB, (9)

where Kee is the resistance of the welding contact.

0 The voltage Ug is applied to the input of the multiplier 6, the output voltage Uio of which (Fig. 56) is determined by the product of the voltages applied to the first and second inputs

and, about K2-U9-U | 2. (10)

5 where Cs is a constant coefficient.

Thus, Ug and Uio have the same shape, since Ui2 is a constant voltage (except for the duration of the gate pulse). At the time to gating pulse, the output voltage of the amplifier 9 is defined as

U, 2 (to) K3Un (to) (11)

where Cs is the gain of the amplifier 9

at time to. The output voltage Uio with a multiplier of 5 liters 6 is fed to the inverse (second) input of the adder 7, and the output voltage UN of the adder 7 (Fig. 5c) Un (to) U8 (to) -U, o (to) (12)

Substituting expressions (7) and (10) into (12), we obtain

U ,, (to) U3, (to) -K, -K2-K3U ,, (to) -IcB (to)

(13) Ki K2 K2S can be written as

Uii (to) l + K, К2Кз b (to), (to)

or taking into account (11)

U, 2 (to) -lcB (to) Kl K2 IEE (b). (15)

at the moments of gating to, a change in the output voltage of the device and 10 occurs, which is reflected by the "step in fig. 56. After the gating pulse disappears, the value of Ui2 (Fig. 5d) is fixed at the level determined by (15). Substituting in (10) the value of Ug from (8) and Ui2 from (15), we find that the output voltage of the device, defined as

U, o ((to)

or for any point in time

Uio (to) iaz (1).

In the device, the output voltage is synthesized from a current signal, such as Uss, and the amplitudes of the synthesized and measured signals are equalized at short gating moments (m 10 µs), which allows you to measure the parameters of the synthesized signal

regardless of the presence of interference voltage by any available equipment. This makes it possible to obtain high measurement accuracy, high speed of the quality control system of the welded joint and, as a result, improved quality of the joint itself.

Claims (1)

Invention Formula A method of measuring voltage on welding electrodes, in which the total voltage of a useful signal and interference is measured and the interference signal is compensated as follows: the measuring circuit is placed in the welding circuit, the change in the geometric dimensions of the measuring circuit under the action of the perpendicular magnetic induction component, acting on it is converted into an electrical signal, characterized in that, in order to improve the measurement accuracy, the resulting electrical signal differentiates t, determine the moment of equality of its zero, and at this moment the voltage is measured at the welding electrodes. Fig.Z shg t but of idZ. Editor T. Parfenova Order 5949/9 VNIIPI USSR State Committee for Inventions and Discoveries 113035, Moscow, Zh-35, -Raushska nab. 4/5 Production and printing company, Uzhgorod, ul. Project, 4 FIG. Compiled by V. Gribov Tehred I. VeresKorrektor L. Pilipenko Circulation 970 Subscription