JPH10339624A - Ultrasonic wave thickness meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure thickness with precision in short time. SOLUTION: For a thickness of a steel plate 11, such reciprocation time as ultrasonic wave is reflected in a plurality of times between a front surface 11a and a rear surface 11b is measured with a timing counter circuit 17, and reciprocation frequency is counted with a reciprocation counter circuit 19, and a calculation circuit 18 calculates based on time, frequency, and sound speed. Since a measured time is longer than the amount equal to one reciprocation, even if a frequency of clock signal from a clock circuit 16 is not so high, a measurement error can be smaller easily for higher precision. Since high precision measurement can be done with a single application of ultrasonic wave, a high precision measurement in a short time is allowed compared to where a measurement is done at a single reciprocation after ultrasonic wave is applied and the next measurement is done after a reflection echo from repetition is fully attenuated, which is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic thickness gauge for measuring the thickness of a measuring object such as a metal plate.

[0002]

2. Description of the Related Art Conventionally, ultrasonic waves have been used to measure the thickness of, for example, a bottom plate of an oil tank.
If ultrasonic waves are used, only from one surface side such as a metal plate,
Since the thickness can be measured non-destructively, it can be relatively easily measured whether or not the thickness of the bottom plate of the oil tank or the like is reduced by corrosion, as compared with other methods.

FIG. 3 shows a basic configuration of thickness measurement using ultrasonic waves. A vibrator 2 is mounted on the surface 1 a of the steel plate 1. The vibrator 2 is a transducer, and outputs electric high frequency output from the ultrasonic oscillator 3 to the steel plate 1.
Converts to mechanical vibrations inside. The converted mechanical vibration is
The ultrasonic wave propagates through the steel sheet 1, is reflected on the back surface 1b, and returns to the front surface 1a. This reflected wave is electrically detected as a back echo by the vibrator 2 and input to the input circuit 4.

As shown in FIG. 4, when a pulsed high-frequency output is applied to the vibrator 2 at time t0 from the ultrasonic oscillator 3,
At time t1, the back side echo is also input to the input circuit 4 in a pulse shape. The gate circuit 5 supplies a clock signal of a constant period w generated by the clock circuit 6 to the counter circuit 7 from time t0 to time t1. The count value n of the counter circuit 7 corresponds to a time nxw in which the ultrasonic wave makes one round trip between the front surface 1a and the back surface 1b of the steel plate 1. The arithmetic circuit 8
From the time n × w corresponding to the count value of the counter circuit 7 and the sound velocity c in the steel plate 1, the thickness d between the front surface 1a and the back surface 1b of the steel plate 1 is calculated as in the following first formula. I do.

D = n × w × c / 2 (1)

[0006]

The sound velocity in the steel sheet 1 as shown in FIG. 3 is 5,000 to 6,000 m / s for longitudinal waves.
ec is known. For convenience of calculation, c = 5000 m / sec and d = 1 mm.
In the digital measurement as shown in FIG. 4, a counting error of one digit is unavoidable for the clock signal. The signal needs to be counted. Therefore, n = 100, and from the first equation,
w = 0.04 μsec is obtained. The frequency of this clock signal is 25 MHz, which is close to the operable upper limit of a general semiconductor integrated circuit such as a CMOS. To further increase the measurement accuracy, for example, to 0.1%, the frequency of the clock signal must be 250 MHz.
The measuring device becomes expensive. In order to increase the accuracy at a low clock signal frequency, the number of measurements must be increased and the error must be statistically reduced, so that the thickness measurement takes time.

An object of the present invention is to provide an ultrasonic thickness gauge capable of measuring a thickness with high accuracy in a short time.

[0008]

According to the present invention, the time required for ultrasonic waves to be applied from one surface of an object to be measured and the ultrasonic waves reflected and returned from the other surface to be detected, and the sound speed in the object to be measured are reduced. In the ultrasonic thickness gage for measuring the thickness of the object to be measured, the ultrasonic wave is applied from one surface, and then the reflected wave is reflected by the other surface. The ultrasonic wave is repeatedly reflected between one surface and the other surface, and a counting means for counting the number of reciprocations, and the reflection which is repeated a plurality of times between the other surface after the ultrasonic wave is applied from one surface. Time measuring means for measuring the time required until a wave is detected by the detecting means, and calculating means for calculating the thickness of the object to be measured based on the time measured by the time measuring means and the number of reciprocations counted by the counting means. And including That is an ultrasonic thickness gauge.

According to the present invention, the detecting means detects the reflected wave after reciprocating a plurality of times by repeating the reflection between one surface and the other surface of the object to be measured, and the elapsed time from the application of the ultrasonic wave. Is clocked by the clock means. The number of reciprocations due to repetition of reflection is counted by the counting means,
From the time measured by the timer means, the number of reciprocations counted by the counting means, and the speed of sound in the measurement object, calculate the distance that the ultrasonic wave propagated in multiple round trips, and measure it as the distance equivalent to one-way propagation for one time The thickness of the object can be determined.

[0010]

FIG. 1 shows a schematic electrical configuration of an ultrasonic thickness gauge 10 as an embodiment of the present invention.
In order to measure the thickness between the front surface 11a and the back surface 11b of the steel plate 11 to be measured, a transducer 12 including a transducer is mounted on the front surface 11a. The vibrator 12 outputs a high-frequency output given in a pulse form from the ultrasonic oscillator 13,
This is converted into mechanical ultrasonic vibration directed to the bottom surface 11b of the steel plate 11. The vibrator 12 detects a pulse-like reflected echo a plurality of times. The detected reflected echo is amplified by the input circuit 14 and provided to the gate circuit 15. Gate circuit 15
Supplies the clock signal from the clock circuit 16 to the time counter circuit 17 in response to a signal indicating the time point at which the ultrasonic pulse is output from the ultrasonic oscillator 13. The clock signal has a fixed cycle, and the counting operation of the clock counter circuit 17 corresponds to a clock operation. Clock counter circuit 1
The clock value of 7 is input to the arithmetic circuit 18. The timekeeping operation of the timekeeping counter circuit 17 is controlled by a reciprocating counter circuit 19 that counts the number of reflected echoes so as to end when the reflected echoes after a predetermined number of round trips are detected. The predetermined number is, for example, a preset number, and the arithmetic circuit 18 calculates the thickness of the steel sheet 11 based on the number, the time measured by the time counter circuit 17 and the sound speed.

FIG. 2 shows a state in which measurement is performed in the embodiment of FIG. When a pulsed ultrasonic wave is applied at time t10, it is assumed that n reflected echoes are detected by time t1n, such as the first reflected echo at time t11, the second reflected echo at time t12, and so on. . in this case,
The thickness d can be obtained according to the following second equation.

[0012]

(Equation 1)

Here, m is the count value of the time counter circuit 17, w is the cycle of the clock signal, c is the speed of sound in the measurement object at the temperature at the time of measurement, and n is the number of reciprocations. Even if the count value of m includes an error of one digit, the denominator of the second formula includes the number of round trips n. Therefore, if n is large, the effect of the error of one digit can be reduced. Therefore, the measurement accuracy can be improved without increasing the frequency of the clock signal from the clock circuit 16 very much.

In the conventional measuring method as shown in FIG. 4, the timing of the trigger for determining the ultrasonic pulse supply time t0 and the reflected echo detection time t1 for measuring one round trip time is, for example, a gate circuit. 5 is determined as the point in time when the output of the input circuit 3 reaches the threshold. Therefore,
An error due to the setting of a threshold may also occur. In order to reduce such errors, it is necessary to perform a plurality of measurements and statistically process them to increase the measurement accuracy. In multiple measurements, each measurement must be performed with sufficient time to avoid the effects of repeated reflections. turn into.

In this embodiment, after one ultrasonic application,
Since the reflected echoes are detected in a plurality of round trips, the effect of the trigger timing error can be reduced, and the measurement accuracy can be improved. When the plate thickness is thin, the reflected echo returns in a short time, so that the error tends to be large in the conventional method, but in the present embodiment, the attenuation of the reflected echo is small, so that a large number of reciprocations can be performed, High-precision measurement.

Furthermore, in order to detect the number of reciprocating echoes after one ultrasonic wave application, the gain of the input circuit 14 or the like is increased along with the number of echoes, or the threshold value for determining the trigger timing in the gate circuit 15 is set. The level may be lowered. In addition, instead of setting the number of reciprocations in advance, a time point at which the level of the reflected echo falls to a predetermined reference value is set as an end condition, so that highly accurate measurement can be performed within a measurable range. .

[0017]

As described above, according to the present invention, the reflected wave after reciprocating a plurality of times between one surface and the other surface of the object to be measured is detected. The thickness of the object to be measured is calculated from the time from application of ultrasonic waves to detection, the number of reciprocations, and the speed of sound in the object to be measured. Highly accurate measurement values can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of an ultrasonic thickness gauge according to an embodiment of the present invention.

FIG. 2 is a time chart during a thickness measurement according to the embodiment of FIG. 1;

FIG. 3 is a block diagram showing a schematic electrical configuration of a conventional ultrasonic thickness gauge.

FIG. 4 is a time chart during the thickness measurement according to FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic thickness gauge 11 Steel plate 11a Front surface 11b Back surface 12 Transducer 13 Ultrasonic oscillator 14 Input circuit 15 Gate circuit 16 Clock circuit 17 Clock counter circuit 18 Arithmetic circuit 19 Reciprocal counter circuit

Claims (1)

[Claims] An ultrasonic wave is applied from one surface of an object to be measured,
On the other hand, in an ultrasonic thickness gauge that measures the thickness of the measurement target based on the time required until the ultrasonic wave reflected back from the surface is detected and the speed of sound in the measurement target, the ultrasonic wave is transmitted from one surface. After the addition, a detecting means for detecting a reflected wave reflected from the other surface and returning, and an ultrasonic wave detected by the detecting means is repeatedly reflected between the one surface and the other surface to count the number of reciprocations. Counting means, time-measuring means for measuring the time required for reflected waves having traveled back and forth a plurality of times between the other surface after the ultrasonic wave is applied from one surface, and time-measuring means. An ultrasonic thickness meter comprising: a calculating unit that calculates a thickness of a measurement target based on a time period and a number of reciprocations counted by a counting unit.