JPS62162959A - Multiplexer type dac circuit for flaw detector - Google Patents

Abstract

PURPOSE:To detect a defect signal with a constant level by charging the capacitor of a waveform generating circuit with a short-distance current from a short- distance current source and also charging the capacitor to the opposite polarity from the short-distance current with a long-distance current from a long-distance current source. CONSTITUTION:When probes are switched in synchronism with PRF, a storage circuit 13 sets a set value Nn or Nf corresponding to the switched probe for the short-distance current source or long-distance current source. Then, when a short-distance switch 6 is turned on at specific timing, the short-distance current source charges the capacitor of the waveform generating circuit 4 with the short-distance current In. Further, when a short-distance switch is turned on, the long-distance current source charges the capacitor with the long-distance current If to the opposite polarity from the charging with the current In. Thus, the sensitivity to a defect signal from an object of flaw detection is corrected corresponding to the propagation distance of an ultrasonic wave to obtain the defect signal having the constant level regardless of the propagation distance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a flaw detector BDAc (distance sensitivity correction) circuit using a multiplexer method that corrects the sensitivity to a defect signal from an object to be tested according to the propagation distance of ultrasonic waves. Regarding.

[Conventional technology]

FIG. 5 is a diagram showing the principle of flaw detection using an ultrasonic flaw detector. The ultrasonic waves transmitted from the probe 20 are transmitted to the object to be inspected 21.
The ultrasonic probe (
(not shown). In this case, the object to be flawed 2
If the length of the ultrasonic wave 1 in the propagation direction is long (if the defect is near the bottom surface, the defect wave will be attenuated and the level of the defect signal will be lowered.

The defect signal (or bottom surface signal) attenuates exponentially as the ultrasonic propagation distance increases, as shown in FIG. 6(a). In order to obtain a constant 1/pel defect signal regardless of the ultrasonic propagation distance, the gain for the defect signal of the ultrasonic flaw detector must be adjusted according to the ultrasonic propagation distance, as shown in Figure 6(b). Just try to change it. for that purpose,
All that is required is to change the attenuation amount of the defect signal as shown in Figure 6 (C).

Conventional ultrasonic flaw detector distance sensitivity correction circuit (hereinafter referred to as DAC)
) (Yo, determine the maximum propagation distance of ultrasonic waves in advance, make the propagation distances O to L correspond to numbers from 1 to -No (Nn is 100, for example), and set the appropriate value according to the propagation distance. You are supposed to input the number N. DA(l yo N
When is input, the capacitor is charged with a current of I=KN (where K is a constant), and the charging characteristic curve lv! of the capacitor at this time is used as the attenuation characteristic curve to obtain a defect signal of a constant level. .

[Problem that the invention seeks to solve]

FIG. 7 is a characteristic diagram of an attenuation characteristic curve in such a conventional DAC. In FIG. 7, the horizontal axis shows the propagation distance of ultrasonic waves corresponding to time, and the vertical axis shows the correspondence to capacitor voltage. This i0i decay characteristic line has a set value N=10
The interval between the set value N=11 and the set value N=11 is 0.91t (seconds), and the interval between the set value N=50 and the set value N=51 is 0.04 t (seconds).
t (seconds) or set value N = 99 and set value N = 10
0.01t (seconds). This is a problem because as the propagation distance of the ultrasonic wave becomes longer, the interval between the curves becomes wider with respect to the set value N, and it becomes difficult to obtain a defect signal of a constant level.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a multiplexer type flaw detection type DAC circuit that can obtain a defect signal of a constant level regardless of the propagation distance of ultrasonic waves.

[Means for solving problems]

Therefore, in the present invention, a plurality of probes are sequentially switched in synchronization with the pulse repetition frequency, and the reflected waves from the object to be inspected in response to the ultrasonic waves transmitted from the switched probes are used as a monitor signal. In a multiplexer-type flaw detector DAC circuit that performs deep detection, the short-range current I corresponds to the set value N11. a short-distance current source that outputs a long-distance current ■1 corresponding to a set value Nf; a long-distance current source that outputs a long-distance current ■1 corresponding to a set value Nf;
.

a waveform generation circuit composed of a capacitor of a predetermined capacity that is charged in the opposite direction by , a short-range switch that outputs the short-range current In to the waveform generation circuit, and a long-range current ■,
The set value Nn and the set value Nt are stored for each of the plurality of probes and a long distance switch that outputs the signal to the waveform generation circuit, and each time the probe is switched, the set value Nn and the set value Nt are stored. The set value Nf and the set value Nn corresponding to the tentacle are set at close range gi? DA for multiplexer type flaw detector equipped with a memory circuit set to H current source and long distance m current source
Configure the C circuit.

[For production]

In the multiplexer-type flaw detector DAC with the above configuration, when the probe is switched in synchronization with the pulse repetition frequency, the memory circuit stores the set values N1 and Nf corresponding to the switched probe as short-range currents. Source and remote current source. Next, when the short-range switch is turned on at a predetermined timing, the short-range current source charges the capacitor of the waveform generation circuit with the short-range current I0, and when the long-range switch is turned on, the long-range current source charges the long-range current I0. ■The short-distance current ■Charges the capacitor of the waveform generation circuit with the opposite polarity to that of charging by A.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block circuit diagram of a multiplexer type flaw detection DAC circuit according to the present invention. In Figure 1,
1 is an offset current source that outputs an offset current In of a predetermined magnitude, and 2 is a short-range current I, = K, IN' for the setting 4fINn.

(Here, Kn is a constant) A short-distance digital-to-analog converter (Kinomi 11 & fa flow source) that outputs 3 is a long-distance @flow If = for the set value Nf, /Nf (Kf is 4 is the offset current In or near g! A waveform generating circuit 5 (which generates a waveform by generating an offset current I0 6 is a short distance switch for flowing the short distance current I11 to the waveform generation circuit 4; 7 is a long distance switch for flowing the long distance current If to the waveform generation circuit 4; 8 is a long distance switch for flowing the long distance current If to the waveform generation circuit 4; A clock pulse generation circuit that outputs a clock pulse of a predetermined frequency; 9 is a clock pulse generator;
The number of pulses of the pulse generation circuit 8 is counted, and when the counted value reaches the preset value C1, the waveform generation circuit 4 is activated by the short-range current If by outputting a count-up signal.
A short-distance counter 10 (10) counts the number of pulses from the lock pulse generation circuit 8 and outputs a count-up signal when the count reaches the preset value Ct. A long-distance counter 11 measures the charging start timing of the waveform generation circuit 4 by the current counter 11, and a counter 11 calculates an offset based on the count-a-turn signal of the short-range counter 9 and the count-a-turn signal of the long-range counter 10. A waveform generation control circuit 12 controls the current source Sochi 5, the short distance switch 6, and the long distance switch 7 to turn on and off. When the capacitor reaches a predetermined voltage (13 is an amplitude control circuit that maintains that voltage, for each of the plurality of probes,
Set value Nn, N(.

Preset value C1 of short distance counter 9 and long distance counter 1
A preset value at of 0 is stored, and each time the probe is switched in synchronization with the pulse repetition frequency (hereinafter referred to as PRF signal), the set value N fi corresponding to the switched probe is stored. , N t, preset values C7, C1
, respectively short-range digital/analog converter 2,
This is a memory circuit that connects the long-distance digital/analog converter 3, the short-distance counter 9, and the long-distance counter 10.

If any number from 1 to N (N is 100, for example) is input, which corresponds to the minimum propagation distance O to the maximum propagation distance glL of ultrasonic waves in the long-distance digital/analog converter 3. , outputs a long-distance current If=Kf/Nf for the input number Nt.

This recirculating section fi as current (1) charges the capacitor of the waveform generating circuit 4.

FIG. 2 is a characteristic diagram of the charging characteristic curve of the capacitor of the waveform generating circuit 4 charged by the speed ratio S current (1), that is, the attenuation characteristic curve of the DAC circuit for the multiplex 7-tube type flaw detector according to the present invention. In FIG. 2, the horizontal axis corresponds to the propagation distance of the ultrasonic wave with time, and the vertical axis corresponds to the voltage of the capacitor, as in the above-mentioned FIG. 7. This charging characteristic curve has a set value N f = 10 and a set value N t = 1
1, the interval o, it (seconds) between the set value N@=50 and the set value Nt=51, and the set value Nf=9
The interval 0.1t (second) between 9 and the set value N = 100 is equal. Therefore, for every certain propagation distance of the ultrasound, 1
Two curves are obtained, and distance compensation can be performed with a small number of settings Nt.

In this embodiment, the return R current 11=K(/Nf) is output for the input number N+, but the long distance current r, -e KtNr (here, K is a constant , e is a common logarithm).The charging characteristic curve, that is, the attenuation characteristic curve in this case is shown in FIG.
Interval between f=90 and set value Nf-=89: 0.25t
(Seconds) Interval between set value Nf=51 and set value Nf-50 0
．． 09t (seconds) and set value Nf=O and set value Nt=0
The interval is 0.026t (seconds). Therefore, an appropriate number of curves can be obtained whether the ultrasonic propagation distance is short or long, and distance compensation can be performed with a small number of settings Nf.

Next, a multiplexer type flaw detector DAC according to the present invention
The overall operation of the circuit will be explained with reference to FIG.

Figure 4 shows only the offset current source 1, short-range digital/analog converter 2, long-range digital/analog converter 3, off-celler 1-switch 5, short-range switch 6, long-range switch 7, and waveform generation port Ft84. This is what is shown.

(1) Each time the probe is switched in synchronization with the PRF signal from the memory circuit 131, the set values Nn, Nt and preset values C1, Ct corresponding to the switched probe are stored in short-range digital format. - Analog converter 2, long-distance digital-to-analog converter 3, near fifl counter 9 and far [I'r! ) Set to J rank 10.

(2) When the waveform generation control circuit 11 turns on the offset switch 5 after a certain period of time has elapsed after outputting the I'RF signal, the offset current #1 charges the capacitor of the waveform generation circuit 4 (Fig. 4(a) )reference). When the voltage of the capacitor reaches the offset voltage v0, the amplitude control circuit 12 holds the voltage v0.

(3) When the count value of the short distance counter 9, which counts the number of clock pulses of the clock pulse generation circuit 8, reaches the preset value C1, the short distance counter 9 outputs a count-up signal. When the waveform generation control circuit 11 turns on the short-range switch 6 by outputting the count-a-tub signal, the digital-to-analog converter 2 charges the capacitor of the waveform generation circuit 4 (Fig. 4(b)).
reference).

When the voltage of the capacitor reaches the voltage V, the amplitude control circuit 12 controls the voltage V. hold.

(4) When the count value of the long distance counter 10 that counts the number of clock pulses of the clock pulse generation circuit 8 reaches the preset value Cf, the long distance counter 10 outputs a run 1-up signal. . Waveform generator circuit #'1
] 1 counts up (when the long distance switch 7 is turned on by the output of No. (See FIG. 4(C).) Amplitude control circuit 12: When the voltage of the capacitor reaches O, that voltage is held.

The voltage of the capacitor of the waveform generation circuit 4 that has passed through the amplitude control circuit 12 is used to control the amount of attenuation of the DAC.

Thereafter, each time the probe is switched in synchronization with the PRF signal, the set values Nfl, Nf, and preset values C, . . . - Set the analog converter 2, the long-distance digital/analog converter 3, the short-range counter 9, and the long-range counter IO to control the amount of attenuation of the DAC.

〔Effect of the invention〕

As explained above, according to the present invention, the long-distance current If'' I t/Nt or the long-distance current I, = e K for the set value Nf determined corresponding to the transmission distance of the ultrasonic wave. When outputting tN t and charging a capacitor with this return fsWa current T+, a capacitor charging characteristic curve with approximately equal spacing for each setting @Nf, or with appropriate spacing when the propagation distance is short or long. is obtained, so by using this charging characteristic curve as the attenuation characteristic curve of the DAC,
The effect is that defect signals of a constant level can be obtained regardless of the propagation distance of the ultrasonic waves.

[Brief explanation of drawings]

Figure 1 shows a D for a multi-player type flaw detector according to the present invention.
2 and 953 are professional circuit diagrams of the AC circuit, and FIG. 4 is a charging characteristic curve diagram of the capacitor of the waveform generation circuit charged by the long-range current r of the circuit shown in FIG. Multiplexer method flaw detection related to '? + g m
An explanatory diagram showing the operation of the D A C circuit, Fig. 5 is a diagram of the principle of flaw detection using an ultrasonic flaw detector, Fig. 6 is an explanatory diagram of ultrasonic waves that decay exponentially, and Fig. 7 shows attenuation in a conventional DAC. It is a characteristic diagram of a characteristic curve. DESCRIPTION OF SYMBOLS 1... Offset current source, 2... Short distance digital-analog converter, 3... Long distance digital-analog converter, 4... Waveform generation circuit, 5- Offset switch, 6-... Short distance switch, 7...・Long distance switch
8 ・Clock pulse generation circuit, 9 short distance counter,
DESCRIPTION OF SYMBOLS 10... Long distance counter, 11... Waveform generation control circuit, 12. Amplitude control circuit, 13. Memory circuit.

Claims (2)

[Claims] (1) A plurality of probes are sequentially switched in synchronization with the pulse repetition frequency, and the reflected wave from the object to be tested in response to the ultrasonic waves transmitted from the switched probes is used as a monitor signal to monitor the object to be tested. In a multiplexer-type flaw detector DAC circuit that performs flaw detection, the setting value N_
A short-distance current source outputs a short-distance current I_n corresponding to n, a long-distance current source outputs a long-distance current I_f corresponding to a set value N_f, and a reverse direction is generated by the short-distance current I_n and the long-distance current I_f. a waveform generation circuit configured with a capacitor of a predetermined capacity that is charged with a capacitor; a short-range switch that outputs the short-range current I_n to the waveform generation circuit; The set value N_n and the set value N_f are stored for the distance switch and each of the plurality of probes, and each time the probe is switched, the set value N_f is stored, and each time the probe is switched, the set value N_f is stored. A multiplexer-type DAC circuit for a flaw detector, comprising a memory circuit for setting the set value N_n and the set value N_f in the short-distance current source and the long-distance current source. (2) A patent claim characterized in that the long-distance current I_f is I_f=K_f/N_f or I_f=e^-^(K_f)^(N_f) (where K_f is a constant and e is a common logarithm). A multiplexer-type DAC circuit for a flaw detector as described in Scope 1.