JPS6131912A - Ultrasonic thickness meter - Google Patents

Abstract

PURPOSE:To perform high-precision thickness detection by providing an M-scale counter in front of a display counter, radiating an ultrasonic wave to the same inspection point N times, and counting a clock corresponding to a reflected wave at every time and displaying the grand total result. CONSTITUTION:A transmitting and receiving probe 2 is arranged on the surface of a material 1 to be inspected. A pulser 3 is excited to generate an ultrasonic wave, which propagates in the material 1 to be inspected and is reflected by the bottom surface, so that the reflected wave is received by the probe 2. The received signal is supplied to a receiving amplifier 4 and a comparing circuit 5b the set number N of times of measurement with the actual number of times of measurement. The number N of times indicates the frequency of the measurement of the ultrasonic thickness meter which is performed while the measurement position of the object material 1 is fixed. A gate circuit 5a receives the output of the amplifier 4 and outputs a pulse signal setting a clock counting section to the M-scale counter 8a when the number of times of measurement at the same measurement position is less than N. Decimal counters 8b-8d count the output of a counter 8a to make a decimal 3-digit display on display circuits 10a-10c. Thus, the high-precision thickness detection is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ultrasonic thickness meter that measures the thickness of a material to be inspected using ultrasonic waves.

[Background of the invention]

The configuration of a conventional ultrasonic thickness needle is shown in FIG. 1, and its time chart is shown in FIG. 2. Transmitting/receiving probe 2 on the surface of the material to be tested
Place. Since the balsa 3 is a pulse power source for ultrasonic oscillation, the excitation of the balsa 3 generates ultrasonic waves, which pass through the inside of the material to be examined and are reflected at the bottom surface, and this reflected wave is used for transmission and reception. The wave is received by probe 2. This received signal passes through a reception amplifier 4 and a gate circuit 5 and becomes an input to a gate 70.

FIG. 2 shows a signal 22 consisting of a transmitted wave and a bottom echo when a transmitted pulse 21 is applied. The output of gate circuit 5 is shown as signal 23. This signal 23 is at H level during the period from the rise of the transmitted wave until the bottom echo is received, and the gate 7 is opened.

Clock circuit 6 generates clock signal 24, and gate 7 allows the clock to pass while signal 23 is at H level. The counter 8 counts the output clocks of the gate 7. The arithmetic circuit 9 takes in the count value of the counter 8,
Calculate the wall thickness of the test material l. The display circuit IO displays this calculation result.

The oscillation frequency of ultrasonic waves is usually as high as several MHz.

On the other hand, the frequency of the clock pulse 24 is
(Clock oscillator) There is a smaller variation than K.

For example, in a crystal oscillator, its oscillation error is 1O-6×(
±100). However, as mentioned above, since the oscillation frequency of ultrasonic waves is several MHz, selecting a signal of this frequency results in an error of about ±100 Hz.

This error is a value that cannot be ignored in thickness detection, and becomes an obstacle to accurate thickness detection.

Furthermore, the speed of sound varies depending on the material and temperature of the material being tested.

For this reason, the constant of the multiplication performed in the arithmetic circuit 9 must be made variable, and implementing this requires a complex circuit configuration, which is difficult to implement in ultrasonic thickness gauges that require smaller size and lighter weight. is difficult.

[Purpose of the invention]

An object of the present invention is to provide a super thick needle with a simple circuit configuration that enables high detection accuracy.

[Summary of the invention]

The aspects of the present invention are as follows.

■ Measures against errors in the clock generation source ■ Simplification of the processing circuit ■ Measures against temperature changes in the speed of sound For this purpose, an M-adic counter was provided in the front stage of the force counter. Furthermore, ultrasonic waves are emitted N times to the same inspection location,
Clock counting corresponding to the reflected wave is performed each time. This N
This makes it possible to accurately display plate thickness based on the comprehensive counting results. Here, M and N have an optimal combination relationship.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the ultrasonic thickness gauge of the present invention. Fourth
The figure is the time chart. The ultrasonic thickness gauge includes an ultrasonic probe 2, a balsa 3, a preamplifier 4, and a gate circuit 5.
a, comparison circuit 5b, clock source 6, AND gate 7, counters 8a, 8b, 8c, 8d, indicators 10a, 10b
, 10c.

The difference from the conventional example shown in FIG. 1 is the gate circuit 5a.

Comparison circuit 5b, counters 8a-8d1 indicators 10a-1
It is at the point where 0c is set.

The comparison circuit 5b compares the set number of measurements N and the actual number of counts. Here, the set number of measurements N is an instruction value to fix the measurement location of the material 1 to be inspected and perform the ultrasonic thickness measurement N times on the fixed measurement location. This comparison circuit 5b activates the gate circuit 5a only when the number of measurements at the same measurement point is N times or less. In FIG. 4, the interval of one transmission/reception cycle is defined as t.

In the gate circuit 5a, the comparator circuit 5b has N at the same measurement point.
If the number of measurements is less than or equal to 1, a pulse signal 23 for setting a clock counting period is generated from the output of the amplifier 4. N
When the number of times is exceeded, this gate circuit 5a becomes locked and does not output any output.

The counter 8a is an M-ary counter. Counter 8b~
8d is a IO counter, and in particular, the counter 8b is a counter for the least significant digit, the counter 8C is a digit one digit higher, and the counter 8d is a counter for the most significant digit.

The display circuit 10a*lOb*10c displays the counted values of each of the counters 8b, 8c, and sci. Counters 8b-8d correspond to counter 8 in FIG.

This will be explained in detail below.

Frequency F (MHz) of clock signal 24 of clock source 6
, wall thickness T (+a+) of test material 1, test material 1 8b to 8d
10 up to the order of 0.1 m with the value of wall thickness as it is.
It shall be displayed in three decimal digits.

Letting t be the time from when the ultrasonic wave is emitted until the bottom reflected wave reaches the transmitting/receiving probe. Furthermore, by repeating N times, the total counting result P after N cycles is P * = (t.・F)・N ・・・・・・・・・・・・
・(2) becomes. Substituting equation (1) into (2) yields. On the other hand, the total counting result Pt after the completion of N cycles is P number = 10MT ・・・・・・・・・(
4). Therefore, from equations (3) and (4),
T-・F-N=lOMT song/song (5), 7 NF=5MV...river]...(
6).

Measurement error that occurs when F, M, and V are set, ON is determined using equation (6), and N is rounded off to the first decimal place to make N an integer (this value is referred to as N). Find A(m). Ptr at N is 2TN, F Ptr=□ ・Between songs (7 and N, and 1/l per clock pulse OM (m+
), so it becomes .

The maximum value of the measured plate thickness is T. ,! Then, the maximum error value 'A+m a z is T = TI from equation (8).
This is because it is at the time of IIIg. Assuming that the measurement error is within ±0.1 (w), it is necessary to set the measurement error to within ±0.1 (w).

According to the inventor's experiments, it was confirmed that the sound velocity of transverse waves in a steel plate changes depending on the material and temperature as shown in Fig. 5. Figure 5 shows the speed of sound in the room temperature range, V = 3.176~3
．． 279 (m/ tt s ), the maximum variation is ±0.15% at the block frequency F = 15 MHz, M is an integer between 1≦M≦16, and Tmax =
50 (1111), equation (6), (10)
Integers M and N that satisfy the formula are as shown in FIG.

If M and N are set using this FIG. 6, accurate measurement becomes possible. For example, V=3.23p m/s
When F=15MHz and M=13. N.

= 14, the speed of sound is 3.22 μm/s ~
It can be seen that even with a variation of 3.237 μm/s (that is, a variation of ±0.2%), accurate measurement is possible up to a clock frequency range of ±0.015%.゛As described above, even if the clock frequency varies or the sound speed V changes, by appropriately combining M and N,
Easy and accurate wall thickness measurement is possible.

In the above embodiment, 3-digit decimal display is used, but if the digits are generally displayed in 1O decimal, equation (6) becomes as follows. Furthermore,
In addition to transverse waves, it can also be used for longitudinal wave ultrasound.

〔Effect of the invention〕

According to the present invention, accurate thickness measurement has become possible by appropriately combining M and N.

[Brief Description of the Drawings] Figure 1 is a diagram of a conventional example, Figure 2 is a time chart, Figure 3 is a diagram of an embodiment of the present invention, Figure 4 is a time chart, and Figure 5 is a concrete example of changes in sound speed due to temperature. An example diagram, FIG. 6, is a diagram showing an example of M, N, clock frequency fluctuations, and sound speed fluctuations. l... Test material, 2... Transmission/reception probe, 3... Pulser, 4... Amplifier, 5a... Gate circuit, 5b...
... Comparison circuit, 6... Clock source, 7... AND gate, 8a to 8d... Counter, l Oa-10c.
...Display circuit.

Claims (1)

[Claims] 1. A transmitting/receiving probe that sequentially transmits Nr ultrasonic pulses to the same measurement point on the test material and receives the ultrasonic waves reflected from the bottom surface of the test material, and a transmitting and receiving probe for each of the above times. an M-adic counter that measures the interval up to by counting the clocks of the clock source within the interval;
A display counter that counts the output value of the M-ary counter and performs counting according to the decimal display digit, and a display circuit that displays the count value of the display counter (However, M and Mr are
When the frequency of the above clock source is F, the minimum unit of the minimum display digit when displaying in decimal notation is K, and the ultrasonic sound speed is V,
Under the relational expression NF = (1/2K) MV, M and N are integers determined in advance by giving F, K, and V so that the measurement error is within a predetermined tolerance, but M is not an integer. and N are integer values M and Nr).