JP2840656B2 - Peak detection type ultrasonic thickness gauge - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse reflection type ultrasonic thickness gage, and more particularly to a bottom echo or a bottom echo at an output of a receiving amplifier (hereinafter simply referred to as a “receiver”). The present invention relates to improvement of a circuit for detecting backside echo.

(Prior art)

In a conventional pulse reflection type ultrasonic thickness gage, a received echo signal output from a receiving amplifier is input to a voltage comparator, and then a predetermined value input to another input terminal of the voltage comparator. The voltage is compared with a voltage to be compared (hereinafter, referred to as “reference voltage”) which is a constant DC voltage, and a detection pulse is output from the voltage comparator when the voltage of the received echo signal exceeds the reference voltage. Here, the time counter is set to zero when the thickness of the material to be measured is zero (ZERO).
Since it starts from a point, the value of the time measurement counter is held by the above-described detection pulse, and the thickness value of the material to be measured can be obtained by multiplying this value by the sound velocity value in the material to be measured. As described above, in the conventional pulse reflection type ultrasonic thickness gauge, the thickness value of the measurement material is measured by comparing the DC voltage (reference voltage) having a predetermined fixed value with the voltage of the received echo signal. The measurement detection point was determined.

FIG. 1 shows an example of such a conventional pulse reflection type ultrasonic thickness gauge. FIG. 2 shows the first
FIG. 3 is a diagram showing an input waveform of a receiver of the conventional device shown in FIG. The operation of this conventional apparatus will be described with reference to FIGS. 1 and 2. First, an electric pulse P (see FIG. 2 (FIG. 2)) generated synchronously by a pulse transmitter 2 controlled by a synchronous signal generator 1 a)) is converted into an ultrasonic pulse by the probe 3. The ultrasonic pulse is incident on the measured material 4 from the upper surface 5 of the measured material 4 (thickness is T) through a couplant layer (not shown) such as machine oil, and the bottom surface (or The light is reflected from the back surface 7 and returns to the probe 3. Then, the bottom echo pulse A as an electric pulse in the probe 3
(FIG. 2A). This bottom surface echo pulse A is a time ta after the generation of the electric pulse P until the ultrasonic pulse reciprocates with the probe 3 through the material 4 to be measured.
Occurs. As is apparent, this time ta is substantially equivalent to the thickness equivalent time, that is, the ultrasonic pulse is applied to the material 3 to be measured.
Is the time required to reciprocate through the thickness T. The voltage of the bottom echo pulse A is amplified and output by the receiver 8,
The voltage of the amplified bottom echo pulse A is converted to a DC voltage by an automatic gain control (AGC) circuit 9 and fed back to the receiver 8. The output voltage of the receiver 8 that operates as a feedback amplifier together with the AGC circuit 9 is input to the voltage comparator 10. The voltage comparator 10 also receives the reference voltage E generated by the reference voltage generator 11, and if the voltage of the bottom echo pulse A exceeds the reference voltage E, the detection pulse D (FIG. 2 (b))
Is output to the data hold circuit 15. When the detection pulse D is input, the data hold circuit 15 holds the time count value ta of the counter 13 and outputs it to the arithmetic circuit 16.

On the other hand, after the synchronization signal generator 1 outputs a control signal for generating an electric pulse P to the pulse transmitter 2, the ultrasonic pulse converted from the electric pulse P as described above reaches the upper surface 5 of the material 4 to be measured. When the arrival time has elapsed, a ZERO point pulse corresponding to the ZERO position of the thickness measurement is output from the ZERO generator 12, and the counter 13 is reset. Since the counter 13 counts the unit time pulse generated by the reference clock generator 14, the data held by the detection pulse D as described above corresponds to the time (corresponding to the thickness T of the material 4 to be measured). Count value) ta.

Next, the arithmetic circuit 16 performs an arithmetic operation by multiplying the time count value ta input from the data hold circuit 15 by the sound speed value in the material 4 to be measured set by the sound speed calculating means 17 and input therefrom. The calculation result is output to the digital (or analog) display 18 as a measured value of the thickness T of the workpiece 4. The display 18 finally displays the input measurement value as the thickness T.
Display as

By the way, in the apparatus shown in FIG. 1, a material to be measured 4 contains a resin processed product such as FRP (glass fiber reinforced plastic) as a dissimilar material layer 6 (here, two layers are provided). FIGS. 2 (c) and 2 (e) show waveforms input to the receiver 8 in the case and when the structure of the material 4 to be measured is composed of particles, for example, as in cast iron. Here, the pulse M is another unnecessary echo in the material 4 to be measured. Since the reference voltage E is fixed in the conventional apparatus as described above, before detecting the echo (bottom echo) A from the bottom surface of the material 4 to be measured, in the case of FIG. As shown in FIG. 4D, echoes L ₁ from two different material layers 6 which are constituent materials of the material to be measured.
And L ₂ , and in the case of FIG. 2 (e), an echo from particles of the tissue of the material to be measured 4 is detected as shown in FIG. 2 (f), and the bottom surface for measuring the thickness is measured. A stable and accurate thickness measurement cannot be performed because it cannot be distinguished from Echo A.

[Problems to be solved by the invention]

As described above, a conventional pulse-reflection type superconducting type in which a measurement detection point of a thickness value of a measuring material is obtained by comparing a DC voltage (reference voltage) of a predetermined (fixed) value with a voltage of a received echo signal. When measuring the thickness of a composite material, cast iron, a material coated on a surface, or the like, a sonic thickness gauge uses a reflected wave (from a so-called ultrasonic discontinuity point, such as the above-mentioned different material layer, before the bottom surface echo). Echo) was detected, so measurement using the bottom surface echo could not be performed. In order to eliminate such a defect, distance sensitivity compensation for correcting attenuation in the length direction of the ultrasonic wave propagation path is performed, or the frequency of the ultrasonic wave to be incident on the material to be measured is reduced to reduce the material of the material to be measured. Increasing the permeability of tissue has conventionally been performed.

However, in this method, (I) since the reference voltage of the comparator is a fixed DC voltage,
When the DUT changes, the reference voltage and the amplification of the receiver must be changed, which is inconvenient. (II) Differences in materials and compositions between individual DUTs,
Due to the difference in the state of contact between the ultrasonic sensor and the surface of the material to be measured, there have been problems such as that the level of the received echo changes and stable measurement cannot be performed.

[Means for solving the problem]

In order to solve the problems of the prior art as described above, on the assumption that the amplitude of unnecessary echoes other than at least the bottom echo is smaller than that of the bottom echo, the present invention provides a reception output group of reception echoes. Provided is an ultrasonic thickness gauge which detects a bottom surface echo by detecting an echo having the highest height and measures the thickness of a material to be measured.

[Action]

As described above, the peak detection type ultrasonic thickness gage according to the present invention detects the peak of the echo from the material to be measured, and the bottom echo is more than the other unnecessary echoes for thickness measurement regardless of the received echo level. When the height is high, the bottom echo is detected stably and the thickness is reliably measured. If the echo from the ultrasonic discontinuity point is higher than the bottom echo, the target material is recognized as a defective material having tissue separation, lamination, and the like inside the material.

〔Example〕

FIG. 3 is a block diagram showing a preferred embodiment of the present invention, and FIG. 4 is a diagram showing waveforms appearing at some points of the circuit of FIG. 3 at the time of peak detection.

The apparatus of the embodiment of the present invention shown in FIG. 3 has substantially the same configuration as that of FIG. 1 except that the reference voltage generator 11 in the conventional apparatus of FIG. Therefore,
In FIG. 3, the same or corresponding components as those of the conventional apparatus of FIG. 1 are denoted by the same reference numerals.

Next, referring to FIG. 4, FIG. 4 (a) shows that, similarly to FIG. 2 (a), an electric pulse P is first generated, and an ultrasonic pulse obtained by converting the electric pulse P is generated in the material 4 to be measured. , And returns to the probe 3 and is converted again to generate a bottom surface echo pulse A. FIG. 4 (b)
Integrating circuit only for echoes from the measured material other than the transmission pulse
A select gate generating circuit (not shown in FIG. 3) provided in the apparatus of FIG.
The state where the select gate is turned on after the end of the transmission pulse width is shown. FIG. 4C shows a waveform selectively extracted by the select gate. Integrator circuit 19
As a result, the bottom echo pulse A is integrated into a waveform shown in FIG. 4D, and is input to the voltage comparator 10 as a reference voltage. FIG. 4 (e) shows the receiver 8 for the voltage comparator 10.
The waveform of the output signal is shown by a solid line, and the integrated waveform of the output of the integration circuit 19 is shown by a broken line. In the hatched portion in FIG. 4E, the voltage level of the output signal of the receiver 8 is higher than the level of the integrated waveform voltage which is the reference voltage. Therefore, the waveform of the output signal of the voltage comparator 10 is as shown in FIG. Therefore, for example, the bottom of the bottom echo can be detected using the falling point of the pulse as a measurement point of the above-mentioned time ta as shown by the downward arrow in FIG. 4 (f). As is apparent from FIG. 4 (e), the measurement point at the time ta is strictly delayed in time from the top of the bottom echo pulse A, but this is due to the influence of the time constant of the integration circuit. Because there is a delay in the rise of the waveform,
It is easily possible for those skilled in the art to make a constant delay even if the input signal level changes.

Here, when the output waveform of the receiver 8 is the same as the waveform of FIG. 2 (c) as shown in FIG. 5 (a), that is, when there are two different material layers 6 inside the material 4 to be measured. As an example,
Explain that even if the thickness cannot be measured accurately with the conventional ultrasonic thickness meter, the peak detection type ultrasonic thickness meter according to the present invention enables accurate and stable measurement of the thickness. .

FIGS. 5 (b) and 5 (c) show the waveforms of the select gate and the selected and extracted waveforms, similarly to the waveform diagrams of FIGS. 4 (b) and 4 (c), respectively. If the input waveform to the integrating circuit 19 is as shown in FIG. 5 (c), its output waveform, that is, the waveform of the reference voltage signal input to the voltage comparator 10 is shown in FIG. 5 (d). Will be able to In FIG. 5 (e), the waveform of the signal input from the receiver 8 to the voltage comparator 10 is shown by a solid line, the waveform of the reference voltage signal is shown by a broken line, and the hatched portion is detected. Fig. 5 (f)
Are output from the voltage comparator 10 to the data hold circuit 15. Since the data from the counter is held at the falling edge of the output pulse from the voltage comparator 10, the data held until the end indicates the data of the last pulse, that is, the data of the bottom surface echo pulse A. Can be measured, the time ta substantially corresponding to the thickness T.

The present invention is not limited to the above embodiment,
For example, a pulse output from a voltage comparator, which is a circuit component of the analog-digital converter, can be used as a peak detection signal. The method is not limited to the above-described embodiment as long as the counting is performed by detecting the peak of the waveform of the bottom echo or the back echo.

〔The invention's effect〕

As described above, when the peak of the echo is detected by the peak detection type ultrasonic thickness gauge according to the present invention, the bottom surface is higher than other unnecessary echoes for thickness measurement regardless of the received echo level. Echo can be detected stably and thickness can be measured reliably. Also, if the height of the echo from the ultrasonic discontinuity point is higher than the bottom echo, measure up to the discontinuity point, and when the thickness is different from the expected value, It can be recognized as a defective material having peeling, lamination, etc. inside the material.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a conventional pulse reflection type ultrasonic thickness gage, and FIG. 2 is a diagram showing measurement by the conventional pulse reflection type ultrasonic thickness gage shown in FIG. FIG. 3 is a block diagram showing a configuration of a peak detection type ultrasonic thickness gage according to an embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the peaks shown in FIG. FIG. 5 is a waveform diagram for explaining measurement by a detection type ultrasonic thickness gage. FIG. 5 is a peak detection type ultrasonic thickness gage shown in FIG. 3 when there is a heterogeneous material layer in a material to be measured. FIG. 6 is a waveform diagram for explaining measurement by the STA. In these drawings, the same reference numerals indicate the same or corresponding parts. In these drawings, reference numeral 1 denotes a synchronization signal generator,
2 is a pulse transmitter, 3 is a probe, 4 is a material to be measured, 5 is a top surface of the material to be measured, 6 is a layer of a different material, 7 is a bottom surface of the material to be measured,
8 is a receiver, 9 is an automatic gain control circuit, 10 is a voltage comparator,
11 is a reference voltage comparator, 12 is a ZERO generator, 13 is a counter, 14 is a reference clock generator, 15 is a data hold circuit, 16 is a calculation circuit, 17 is a sound speed calculation means, 18 is a display, 19
Indicates an integrating circuit.

Claims (1)

(57) [Claims] 1. A peak detection type ultrasonic thickness gage for measuring the thickness of a material to be measured by ultrasonic waves, wherein the thickness of the material to be measured is received by an output of a receiving amplifier circuit for receiving a reflected wave from the material to be measured. The wave output signal is integrated, and the obtained output waveform is input to the voltage comparator as a reference voltage of the next output waveform, and the peak value of the next received echo signal obtained from the reference voltage is higher than the reference voltage. When the reference voltage is high, the reference voltage is updated and data is sequentially held, and the data of the output pulse that generated the last remaining reference voltage is converted into the peak of the maximum amplitude echo signal among the received echoes. A peak detection type ultrasonic thickness gauge, comprising: a signal processing circuit for detecting the thickness as an ultrasonic wave.