JPS60312A - Ultrasonic thickness meter - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by counting up clock pulses applied to the plate thickness of a member to be measured on the basis of a previously fixed zero point at the preceding measurement in a prescribed range and varying the zero point of a zero point calibrating circuit in proportion to the counted value. CONSTITUTION:An R-SF/F14 outputs a square wave by regarding the decay timing of a monostable multivibrator 12 to be used as a zero point compensating circuit as a zero point and the period from the zero point to the receiving timing as the pulse width related to the plate thickness. An integration counter 19 integrates all clock pulses outputted from a conversion circuit 17 in each measuring opertion. A display part 21 having decimal 4-digit structure is connected to the output side of the integration counter 17 through a decoder/driver 20. After completing the measurement of 160 times, the plate thickness corresponding to the integrated value of the integration counter 19 is displayed with 1/100mm. unit by a control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic thickness gauge, and more particularly to an ultrasonic thickness gauge that improves accuracy by correcting measurement deviations caused by the structure of a split probe.

The ultrasonic thickness gauge can easily measure the thickness of metal parts such as steel, copper, and aluminum, as well as plates and tubes made of non-metallic materials such as plastic, glass, and porcelain, without having to choose the type. This measuring instrument can easily measure the center of a plate, which is impossible with a micrometer, and is widely used in various industrial fields. There are two types of thickness measurements using ultrasonic thickness gauges: the so-called resonance method and the pulse method. The latter utilizes the relationship that the round trip time of an ultrasonic pulse is proportional to the thickness of a plate made of the same material. Specifically, the probe is kept in contact with the plate, and the ultrasonic pulse is Calculate the time required from the complete emission to the reception of the reflected wave reflected by the other surface of the plate,
The board thickness is calculated from this time and the sound velocity in the board, and is displayed digitally. This pulse method is generally popular because it has good accuracy and is easy to handle.

One of the probes used in the ultrasonic thickness gauge using the pulse method is a split type probe as shown in FIG.

This split type probe 1 has a transmitting transducer 4 and a receiving transducer 5 with shoes 2 and 3 divided into right and left parts, and a shielding plate 6 provided between them. 6 is pressed against the plate material 8 side, which is the member to be measured, by a compression spring 7 to prevent vibrations from being transmitted along the surface of the plate material 80 from the transmitting side to the receiving side, thereby making it possible to measure the thickness of a thin plate.

However, in this split type probe 1, when the thickness of the plate 8 changes, the geometric path of the pulse changes to I, n, II in FIG.
The relationship between the plate thickness and the pulse path length is not perfect. For this reason, the relationship between the measured value and the actual plate thickness is as shown in the solid line in Figure 2 (when the plate thickness is 6 decoys and both are adjusted so that each stroke is 1-1), and as shown in Figure 3. A maximum deviation of about 0.181 g occurred.

In FIGS. 2 and 3, the deviation changes linearly when the plate thickness is from 1 mm to 12 mg, and remains constant from 12 to 30. This is because the range from 12 to 30 is near the focal path of the segmented probe and becomes a stable region. Cankan Ochisha-', 1' without correcting measurement deviation due to such plate thickness! , if left unattended, it will not be much of a problem when performing measurements with coarse accuracy on the order of n, but depending on the user's request, 1/1o to 1/I OQ
When attempting to perform measurements with a precision of 1K, the error becomes large and the credibility of the lower digit values becomes poor, making it impractical. On the other hand, in order to perform correction, a table according to the correction curves shown in Figs. 2 and 3 is stored in the memory in advance, and the actual value is read out as data from the memory using the measured value as an address. This results in a complicated and large circuit configuration, resulting in an increase in weight, and there are disadvantages in that it takes a huge amount of time and effort to create a program.

The present invention has been made in view of the above-mentioned drawbacks of the prior art.
It is an object of the present invention to provide an ultrasonic thickness gauge that is small, lightweight, and has a simple configuration and that improves measurement accuracy by correcting measurement deviations of a segmented probe.

The present invention includes a counter that counts clock pulses applied to the plate thickness during pre-measurement of a member to be measured using a predetermined zero point within a predetermined range, and a zero point calibration circuit that adjusts the zero point in proportion to the counted value of the counter. The above objective is achieved by providing a variable zero point adjustment circuit.

First, the principle of the correction method of the present invention will be explained. The time interval between transmission and reception in the pulse method is the sum of the path time within the plate 8 and the path time of the shoes 2 and 3 in FIG. For this reason, ultrasonic thickness gauges have traditionally been equipped with a zero point calibration circuit that delays the zero point by a predetermined delay time (the time the ultrasonic pulse passes through shoes 2 and 3) from the transmission timing, and the The plate thickness is calculated at time intervals. By the way, shifting the zero point of the zero point calibration circuit forward is equivalent to making a correction of 10, and shifting it backward is equivalent to making a correction of -. Perform all plate thickness measurements of the member to be measured using a zero point fixed in a predetermined position,
By varying the zero point of the zero point calibration circuit by the amount of correction corresponding to the plate thickness, the amount of correction for the next measurement (main measurement) is set.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 4 to 8.

Here, in FIG. 3 cited earlier, one correction is required because there is a ten deviation from the thickness 1 to 6, and ten correction is necessary because there is one deviation from 6+im, but in this example Now, as shown by the dotted lines in Figures 2 and 3, set the deviation in advance to be 0 when the plate thickness is 0, and always perform ten correction. Tens correction shall be applied in proportion to the thickness, and a fixed tens correction shall be applied after the 12th ball.

In addition, since the plate thickness is measured by counting the clock pulses of the asynchronous oscillator, averaging is performed to calculate the plate thickness by integrating the measured values multiple times (160 times in this example) to eliminate variations in the measured values. We will use this method to adjust the correction amount at the initial stage (16 times) of this measurement work.

The reason why the correction amount adjustment period is set to be multiple times is to avoid variations in the measured values during this period.

FIG. 4 is a block diagram of an ultrasonic thickness gauge using a split type probe according to the present invention, and FIG. 5 is a timing chart. In FIG. 4, a split type probe 1 is pressed down closely from above to a plate 8, which is a member to be measured, through an oil film or the like. The transmitting transducer 4 of the split type probe 1 includes a transmitting circuit 10. A receiving circuit 11 is connected to the receiving vibrator 5 . A monostable multivibrator 12, which is an example of a zero point calibration circuit, is connected to the transmission circuit IO. This monostable multivibrator 12 is configured so that a start trigger is input from an external control circuit (not shown) when starting one measurement, and when this trigger pulse is input, the internal state is immediately reversed. , the output that was previously "low" becomes ")"
・It becomes "I". This “high” state is for timing Ck
After continuing for a time T determined by the output voltage U of the D/A converter 13 multiplied by the circuit constant C9 of the L circuit, the voltage applied to one end of the circuit 2 and the voltage +V, R2tD-mVc, it returns to "low" again. The output voltage U of the D/A converter 13 increases stepwise by 1 step from U=O to U=Umax, and when U increases by 1 step (=ΔU), the delay time increases. The structure is such that T becomes shorter by Δt.

Energized by the rise change of the monostable multivibrator 12 from "low" to "high", the transmitting circuit 10 generates a single pulse, and the transmitting vibrator 4 performs electro-acoustic conversion to generate an ultrasonic wave. Force the pulse to be transmitted. This ultrasonic pulse is applied to shoe 2. The signal is received by the receiving transducer 5 via the plate material 8 and the shoe 3ff.

Here, the signal is subjected to acoustic-electrical conversion and then sent to the receiving circuit 11. This receiving circuit 11 has a signal amplification function as well as an automatic gain adjustment function (AGCJ), so that the amplitude of the received waveform is constant regardless of the plate thickness.The output of this receiving circuit 11 The side is an R-S free lag flop (hereinafter abbreviated as rkL-sF/FJ) 14 R
(reset) terminal. On the other hand, this R-8
The S (set) terminal of the F/li'14 is connected to the output side of the monostable multivibrator 12 via the inverting circuit 22, and the output side of the monostable multivibrator 12 is connected to the S (set) terminal of the F/li'14. Change from “high” to “low” 1″
Then, it enters a set state and makes the Q terminal output "high", and on the other hand, when a reception signal is input from the receiving circuit 11, it enters a reset state and makes the Q terminal output "low". The R-8F/F14 configured in this way takes the falling timing of the monostable multi-novel ibrator 12 from "NO1 J" to "LOW" as a zero point, and calculates the board thickness from this zero point to the reception timing. It has the function of outputting a square wave as the associated Norms width.

The Q terminal of the 8F/F 14 is connected to one input terminal of an AND circuit 15. An asynchronous oscillator 16 is connected to the other input terminal of this AND circuit 15, and while a square wave is input to this AND circuit 15 from the R-8F/F 14, the gate is open, and the clock of the oscillator 16 < The signal is sent to a conversion circuit 17 connected to the output side. This conversion circuit 17 is based on the fact that when the speed of sound in a member changes due to a difference in the material of the member to be measured, the pulse width of the square wave output of R-8F/F14 related to the above-mentioned plate thickness changes even if the plate thickness is the same. , AND according to the sound speed set in the sound speed setting unit 18 such as a DIP switch group.
It has the function of thinning out pulses from the output pulse train of the circuit 15 at a constant rate, and outputting the same number of pulses when the plate thickness is the same, regardless of the difference in material.

To be more specific, when the speed of sound is high, the plate thickness is estimated to be thinner, so the rate of thinning is reduced, and when the speed of sound is slow, the plate thickness is estimated to be thicker, so the rate of thinning is increased.

An integration counter 19 serving as a plate thickness measuring circuit is connected to the output side of the conversion circuit 17. This integration counter 1
9 has a function of counting the clock pulses sent out from the conversion circuit 17, and is configured to be able to count all the clock pulses related to 160 measurements for averaging if the VC is ugly. It's been done. Also,
The clock pulse output of the conversion circuit 17 is input to the idD/A converter 13. This D/A converter 13 includes, for example, a counter section (not shown) that counts clock pulses output from the conversion circuit 17, and a ladder circuit (not shown) connected to the bit terminal of each digit of this counter section. Each time a clock pulse is input from the outside, the count value of the counter increases by 1, and a voltage that increases by 1 step (=ΔU) in proportion to this count value is output from the ladder circuit. ing.

This D/A converter 13 performs measurements from the first time to the 16th time out of the 160 repeated measurements, or when the count value of the counter reaches "n" before the 16th time, until it becomes [nJ]. While integrating all the clock pulses sent from the conversion circuit 17, the analog voltage corresponding to the integrated value is output, and when the 16th measurement is completed or the counted value reaches jnJ before the 16th measurement, the counter section After being held, the output voltage value U(16) or Un is fixed at that time.

The reason why the integration is stopped when the count value of the counter reaches rnJ is to keep the correction amount constant after the plate thickness is 12 m in FIG. 3, and the value of n will be described later.

The output voltage U of this D/A converter 13 is applied to one end of the circuit 2 forming the timing C circuit of the monostable multivibrator 12, and the charging current of the capacitor C changes depending on the magnitude of this voltage U. Changes in size. Since U increases each time a measurement is completed, the delay time T until the voltage at the left terminal 12A reaches a predetermined threshold by charging after the capacitor C is discharged by being energized by the trigger FLs. becomes shorter each time. This delay time reduction amount τ (correction amount K) is set to change in proportion to U, with the voltage U of the converter 13 at D/ being 0 as a reference. When one measurement is completed, the zero point of the zero point calibration circuit moves forward by 7b, so the next measurement will be R, -8.
The pulse width of the square wave output by F/F 14 becomes longer,
The correction will be made in the direction of increasing the plate thickness. This operation is performed in a sequential manner from the first time to the 16th time, or when the count value of the counter section of the IJ/A converter 13 reaches rnJ before the 16th time, up to that number of times, and is set as a correction amount adjustment period. When 16 measurements have been completed or when E has reached 1'nJ, the shortening amount τ(16) proportional to the output voltage of the D/A converter 13 or the constant correction amount K(16) determined by τh becomes the following. The measurement is repeated up to the 160th time. Figures 6 and 7 show the changes in the correction amount for the unit thickness Todoroki 9 at the end of each measurement from the first time to 16@ (from 0 to 12 m) and the changes in the correction amount using plate thickness as a parameter. The plate thickness and correction i at the end of the 16th cycle are shown in
The relationship with K is shown in Figure 8. The constant of the CR circuit for timing of the stable multivibrator 12, the applied voltage of R1 +■, the step voltage distribution ΔU\i of the A/D converter 13
The line diagram in FIG. 8 and the dotted line in FIG. 3 are set to match.

In each measurement operation, the clock pulses output from the conversion circuit 17 are set to VC so that they are all counted by the integration counter 19. A four-digit display unit 21 is connected, and when 160 measurements are completed, the integration counter 19 is displayed by a control circuit (not shown).
The plate thickness corresponding to the integrated value is displayed to the nearest 1/100.

θ−, the overall operation of the above embodiment will be explained.

Here, an averaging method is used to measure the plate thickness by accumulating 160 measured values, and an example is assumed in which the integrated value 100 of 160 times on the integration counter 19 corresponds to a display of 1.00 m. Take it. At this time, the count value [l, which is held by the empty section of the D/A converter 13 before performing 16 measurements, is the integrated value for 16 measurements of a plate thickness of 12.00 mm, and is 60.

First, when the sound speed corresponding to the material of the plate material 8 is set in the sound speed setting section 1B and the device is operated, R, -sF is set by the action of the control circuit.
/F14 is reset, and the integration counter 19
And the counter section of the D/A converter 13 is cleared. Therefore, the output of the 1)/A converter 13 becomes 0. In this state, the control circuit outputs the first trigger pulse to the monostable multivibrator 12 (see Figure 5).When the trigger pulse is input to this monostable multivibrator 12, the output is inverted, and at this rising edge, the transmitting circuit 10
generates a single pulse and causes the transmitting transducer 4 to transmit the ultrasonic pulse. Further, when the monostable multivibrator 12 rotates again after the initial delay time T has elapsed, R-8F/F14 is set with this timing as the zero point. When the ultrasonic pulse is reflected by the plate 8 and received by the receiving transducer 5, it is sent to the box-8F/F 14 via the receiving circuit 11, and is reset to the box-8F/F 14f. This R-8F/
While F14 is in the set state, a clock pulse is output from the AND circuit 15. These clock pulses are thinned out in accordance with the speed of sound in a conversion circuit 17, and then counted by an integration counter 19, and also counted by a D/A converter 13, and a corresponding analog voltage U(1) is output. l) In response to the output change of the /A converter 13,
The delay time T of the monostable multivibrator 12 is shorter than To by τ(1). That is, for the next measurement, τ(1)
Correction K(1) will be made by the amount.

The control circuit then outputs a second trigger pulse to the monostable multivibrator 12. In response to this trigger pulse, the monostable multivibrator 12 is reversed, and the transmitting circuit 10, transmitting vibrator 4, plate material 8, and receiving vibrator 5 are connected in the same manner as described above.
, the pulse circulates with the receiving circuit 11. As a result of the first measurement, 几-8F/F 14 showed that τ(1
), and it takes a long time to be reset by the output of the receiving circuit 11. Therefore, the conversion circuit 17 outputs clock pulses whose number is increased by the correction amount K (IJO). This clock pulse is added to the first count value in the integration counter 19 and counted, and /A converter 13 also integrates and counts. Therefore, the output of the D/A converter 13 is U(
As U(2) and rz are larger than twice υ, the delay time T is also shorter than T by τ(2), and for the third measurement, τ
A correction amount K(2) proportional to (2) will be made. After repeating the same operation 16 times, the plate thickness θ~
In the case of up to 12 m, the correction amount K increases according to Fig. 6, and when the 16 correction amount adjustment period ends, the correction amount K (16) that changes in proportion to the plate thickness is obtained (see Fig. 7). ). This correction amount K (16) corresponds to the dotted line A-H in FIG. ! Further, when the plate thickness is 12W or more and the count value of the counter section of the D/A converter 13 reaches 120 before completing 16 measurements, the counter section is held and the output of the D/A converter 13 is is U120 (=
It becomes constant at 120XΔU), and the amount of shortening for subsequent measurements becomes constant due to the thickness, resulting in a correction amount of 12@ which is independent of the plate thickness (see Fig. 7). This correction amount corresponds to the dotted line B-C in FIG.

In this way, when the correction amount adjustment period ends, the counter section of the A/D converter 13 is held and fixed at the desired correction amount shown by the dotted line in FIG. 3, and the same measurement operation is repeated up to 160 times. returned.

The clock pulses associated with each plate thickness measurement from the first time, including the correction amount, are successively integrated in the integration counter 19. When the 160 measurements are completed, the integration counter 19
The integrated value is converted into a BCD code by the decoder/donniver 20, and displayed on the display section 21 as the averaged and corrected board thickness.

According to this embodiment, during the correction amount adjustment period, the clock pulse = 2D/A converter related to each plate thickness measurement value is sequentially integrated and outputs the corresponding voltage to shorten the delay time of the monostable multivibrator. This makes it possible to automatically make corrections according to the plate thickness with an extremely simple and easy configuration.Furthermore, the initial stage, which is 1/10th of the multiple measurements required to perform averaging, can be made automatically. Since the final correction amount is determined in the step 1 and the correction is performed successively from the first time to the 16th time, the existence of the correction amount adjustment period has almost no effect on measurement accuracy, and the averaging It becomes possible to fully demonstrate the effects of improved measurement accuracy and stabilization. In addition, since the correction amount adjustment period is included in the main measurement performed by averaging, the overall measurement time is shorter than when the correction amount adjustment period is performed as a pre-measurement (preliminary measurement) before the main measurement. It is possible to do this.

In the above embodiment, the delay time of the monostable multi-bi break was set by the time constant of the timing circuit, but it can also be set by counting the oscillation period of the clock oscillator by a predetermined number. , the configuration may be configured to reduce this count number to compensate, and
After adjusting the correction amount in one or more pre-measurements, the main measurement may be performed by averaging one or more times.

As explained above, the present invention makes it possible to measure thicknesses of 1/10 to 1/100 g x N degrees by correcting the measurement deviation of the split type probe with a compact, lightweight, and simple configuration. This provides an ultrasonic thickness gauge that is fully compatible with the increasing sophistication of manufacturing management.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the measurement state of the split type probe, and Fig. 2 is a diagram showing the relationship between the measured value and the actual value when measuring the entire plate thickness using the split type probe. 3 is a diagram showing the relationship between measured values and deviations in FIG. 2, FIG. 4 is a block diagram of an ultrasonic thickness gauge according to an embodiment of the present invention, FIG. 5 is a timing chart, and FIG. 7 and 7 are explanatory diagrams of the operation of the ultrasonic thickness gauge shown in FIG. 4, and FIG. 8 is a diagram showing the relationship between plate thickness and correction amount in the ultrasonic thickness gauge shown in FIG. 4. . DESCRIPTION OF SYMBOLS 1... Split type probe, 8... Plate material, 12... Monostable multivibrator, 13... D/A converter,
16...Asynchronous oscillator, 19... Integration counter.

Claims (1)

[Claims] (1) A split type probe that transmits and receives ultrasonic waves through the member to be measured, a zero point calibration circuit that delays the zero point by a predetermined delay time from the transmission timing, and a board that counts clock pulses from this zero point to the reception timing. In an ultrasonic thickness gage equipped with a measurement circuit for increasing the thickness, a counter counts clock pulses within a predetermined range for measuring the thickness of a member to be measured at a predetermined zero point; An ultrasonic thickness gage comprising: a zero point adjustment circuit that varies the zero point of the zero point calibration circuit in proportion to the count value of the counter.