SU855585A2 - Pulse eddy current metal detector - Google Patents

Description

(54) PULSE VORTEX METAL DETECTOR

one

The invention relates to an intrinsically non-destructive means of control using electromagnetic and magnetic methods for the detection of objects from ferrous metals in non-conducting and weakly conducting media.

According to the main author. St. 748319 is a pulsed eddy current detector used for detecting metal objects in various covering media, comprising a pulse generator, a eddy current converter connected to a pulse generator, an indication unit, a series-connected limiter, a comparator, a driver and a trigger with separate start connected between the pulse generator and the unit indication, the source of the reference voltage connected to the second input of the comparator and the one-shot whose input is connected to the generator torus pulses and a second input of the indication unit, and an output - to a second input of latch 1.

In this device, the signal at the trigger output appears when metal enters the control zone, i.e. with an increase in the duration of the transient process t ,,, to the coil of a Pichretok converter (VP). In the absence of metal in the control zone, the duration of the transition process

on the coil, the VP is equal to t −l n / Bn determined by the eigenvalues of the coil: inductance L and activation resistance g. Hitting a magnetic object in the control zone leads to an increase in the duration of the transition process on the coil in - b. Compensation of the initial duration of the transition process 1 /, not carrying useful information, is carried out by selecting

ts corresponding to the duration of the impulse of the univibrator gf, where Cjj is the duration of the impulse that form .vl, and the simultaneous supply of these pulses to the trigger inputs or

20 of any other device that fulfills the function of matching schemas (schemas

AND).

As a result, the duration of the signal at the trigger output (AND schemes) -tpt ,, y.

25 is determined by the increment of the duration of the transition process when metal enters the control zone.

-y -y -y- „iu

-f i & LL

Sigi: on with gn.

 6 o

6P

(prn t; n.t ;,)

A disadvantage of the known device is the effect of temperature and time instability of the duration of the one-shot pulse and the own transient process of the VP li coil, which leads to the appearance of a spurious signal at the output of the trigger (I circuit) and, therefore, at the output of the display unit. A false signal caused by temperature or temporal drift of the device can be eliminated by manually adjusting the pulse duration of the one-shot, or by adjusting the magnitude of the reference voltage supplied to the second input of the comparator. However, the need for manual adjustment of the device makes it difficult to automate the control of industrial products and raw materials in the stream.

The purpose of the invention is to increase the stability of the device and automate the process of control.

The goal is achieved by the fact that a pulse eddy current detector containing a pulse generator, a eddy current transmitter connected to a pulse generator, a display unit, a limiter connected in series, a comparator, a driver and a separate start trigger connected between the pulse generator and the display unit, the source of the reference voltage, connected to the second input of the comparator and the one-shot, the input of which is connected to the pulse generator, and the output to the second input of the trigger is provided two inverters, a coincidence circuit, a charging unit and an integrating amplifier, the inverter inputs connected to the driver and single-oscillator outputs, their outputs are connected to the output of the matching circuit, a trigger with separate start, the matching circuit and the pulse generator are connected through the charging unit to the unit display and an integrating amplifier, the output of which is connected to the second comparator output.

FIG. 1 The block diagram of the proposed pulsed eddy current detector; in fig. 2 is an electrical circuit of the charge unit; FIG. 3–14 are the stress plots on the elements of the block diagram in the absence of a metal gauge; in fig. 1526 - the same, in the presence of a metal object.

The device (Fig. 1) contains a pulse generator 1, an eddy current transmitter 2, a limiter 3, a comparator 4, a driver 5, a single vibrator 6, inverters 7 and 8, a trigger 9 with separate start, a coincidence circuit 10, a charge block 11, integrator the amplifier 12 and the display unit 13, the charging unit circuit with transistors (Fig. 2) have keys 14-16 and the charge capacitor 17.

The device works as follows.

The eddy current transducer (VP) 2 is powered by powerful probing current pulses generated by the output stage of the generator 1. The shape of the voltage pulses 1 on the VP coil is shown in FIG. 4. The frequency of operation of the device, as well as the duration of the probe pulses UrsH, is determined by the master stage of the generator 1 (Fig. 3); The voltage pulses U from the coil VP 2 are supplied to the limiter 3, limited to the maximum (Fig. 5) and fed to the input of the comparator 4. The second input of the comparator 4 is supplied with the reference voltage Upn from a stabilized source. As a result, the output

 the comparator 4 produces an impulse, voltage, and) (Fig. 6), the duration of which is determined by the moments of the equality of the voltages at the inputs of the comparator. Since the signal from the VP is a slowly varying value (damping law, close to exponential), with wave levels of the reference voltage Ujj, the trailing edge of the comparator 4 turns out to be closed (Fig. 6). To form the steep edges of this pulse, a shaper 5 is connected to the output of the comparator 4, from which output the generated pulse t (Fig. 7) is fed to one of the trigger inputs with separate start 9 and to the inverter 8. A second pulse is fed to the second trigger input with separate start 9 t ' one-shot 6 (Fig. 8) triggered by the falling edge of the pulse of the generator 1. In addition, a single vibrator pulse b is fed to the input of the inverter 7 and is inverted (Fig. 11). The pulse duration of the one-shot b is chosen equal to or slightly less than 5 times the length of the pulse Z / cf at the output of the former 5 in the absence of metal in the control zone (Fig. 7).

Thus, in the absence of metallic objects in the zone of control Q at the output of the trigger with separate start 9, there is no voltage pulse (if the pulse durations of the ediovibrator are equal

Qg And shaper ti) either has

to;

- minimum duration equal to tif-tQg (Fig. 9). In the event that the duration of a one-shot pulse due to temperature or time drift is greater than the duration.

Claims (1)

Lf, the output pulse U (appears at the output cxeN "10 coincidence (Fig. 12), to the inputs of which inverted pulses are fed from the former 5 and the single vibrator B (Fig. 10 and 11). A signal of a certain duration.,; The output of the flip-flop 9 with a separate start or a skhvgll 10 coincidence is fed to the charging unit 11 and opens the corresponding key 14 or 16 (Fig. 3) The magnitude of the charging voltage U, ap (t) of the capacitor 17 is proportional to the pulse duration of the signal you ij and thanks to the large constant time of the discharge is remembered until the next one Measurements (Fig. 13 and 14). The polarity of the voltage on the capacitor 17 is positive when the pulse EL n.ji is applied to the key 14 from the output of the trigger with separate Lfj start 9 or negative — the pulse is applied to the key 16 (/ and 5 from coincidence circuit 10. As a result, an almost constant voltage Unjop (t) proportional to the pulse duration of the signal is applied to the input of the integrating amplifier 12 and the display unit 13. In order to avoid a charge condenser bypass, the display unit and the integrating amplifier must have high input resistance Before the beginning of the next measurement cycle, the capacitor 17 is discharged by applying a pulse Utbdv.reH of the output of the master oscillator 1 to the transistor switch 15, a shunt-on capacitor 17. From the output of the integrating amplifier 12, which has a large time constant (several seconds) the signal is fed to the second input of the comparator 4, where it is summed with the reference voltage UOP. Thus, when a voltage of one or another polarity arises at the output of unit 11 caused by temperature or time drift of the pulse duration, one-shot, or the own time constant of the VP coil, a signal appears at the output of the integrating amplifier, which causes a change in The level of the reference voltage at the input of the comparator, and consequently, the change in the duration of the janny jibcat driver 5. As a result, the path is self-implanted and the signal at the output of the charging unit is zero. With the appearance of a metric object in the control zone, the transient pulse voltage Vgn on the VP coil increases (Fig. 16), which causes the appearance of a positive polarity signal at the output of the charge unit. Taking into account that the time spent by a metal object in the EP field when monitoring in the process stream or scanning the EP above the object surface is less than the time constant of the integrating amplifier, the useful signal is not compensated and is registered by the display unit (Fig.). Thus, a pulsed eddy current detector can automate the process of control, which increases labor productivity. Claims of the invention Pulsed eddy current detector according to the ed. St. W 748319, differing in the fact that, in order to increase the operation stability and automate the monitoring process, it is additionally equipped with two inverters, a coincidence circuit, a charging unit and an integrating amplifier, the inverter inputs being connected to the driver and single-oscillator outputs, respectively, to the outputs input :: xeNtt3i coincidence, trigger with separate start, coincidence circuit and pulse generator are connected via a charging unit with a display unit and an integrating amplifier, the output of which is connected to the second input Ator. Sources of information taken into account in the examination 1. USSR author's certificate I 748319, cl. G 01 V 3/10, 1978.. : JL 0-tZD-  + fTOW. search-gene Hj / f (Wffl / f -P (l. And-in D d U3ap.eff} and ass gene.