JPH03122586A - Method for threshold value repeated renewal type synthesis of received ultrasonic pulse signal confirming trigger - Google Patents

Abstract

PURPOSE:To accurately measure the propagation time of an ultrasonic pulse signal by employing an one-shot variable threshold value type receiving ultrasonic pulse signal confirming trigger synthesizing circuit. CONSTITUTION:In this one-shot threshold value repeated renewal type received ultrasonic pulse signal confirming trigger synthesizing circuit, the threshold values formed from the n-th receiving signal and the (n-1)-th receiving signal before one therefrom, that is, the nearest part receiving signal are used to synthesize the n-th received signal confirming trigger RIT. The gate of the counter provided to the outside is opened by the n-th RIT and closed by the (n+1)-th RI to make it possible to obtain the count value corresponding to the propagation time of the ultrasonic signal between transmitting and receiving parts.

Description

[Detailed Description of the Invention] 3.1 Field of Industrial Application Devices that utilize the propagation time of ultrasonic waves include ultrasonic flowmeters, ultrasonic level meters, and ultrasonic distance meters.

In these devices, it is important to accurately detect the timing at which the ultrasonic pulse signal arrives at the transducer of the receiving section, and the present invention can be effectively used for this purpose.

3.2 Conventional techniques and problems Conventional methods for detecting the arrival of ultrasonic pulse signals include setting a certain threshold so that a specific peak in the rising portion of the received wave can be identified, and detecting the amplitude of the received wave. A common method is to consider a time point beyond this point to be the arrival of a pulse signal. However, when a fixed threshold value is used, the amplitude of the received signal may fluctuate greatly when there is turbulence or temperature unevenness in the flow of the medium between the transmitting and receiving transducers.

(a) The phase of the received signal confirmation trigger is unreasonably shifted.

(b) Mistaking the peak of the received signal.

(c) In the worst case, a so-called mis-trigger occurs in which a peak cannot be detected. This phenomenon causes errors in the above-mentioned measuring instruments.

Figure 1 shows, as an example, how a mistrigger occurs corresponding to (b). In this figure, 1 is the 0 level of the received signal, 2 is a constant threshold level, 3 is the received signal when the amplitude is large, and 4 is the received signal when the amplitude is large. This is the received signal when the amplitude is smaller than this. Also, 5 is the timing when 3 becomes equal to 2 for the first time,
6 is the timing when 4 becomes equal to 2 for the first time, 7 is the trigger that is output at the timing of 5, and 8 is the trigger that is output at the timing of 6. It can be clearly seen that even if the received ultrasound signals arrive at the same time, the timing at which the trigger is output is different.

Mistriggering as described above occurs because if a certain threshold value is set, it will not be possible to respond to changes in the amplitude of the received signal due to changes in the medium conditions between the transmitting and receiving transducers. happen.

This invention aims to solve the above problems. The outline is as follows. n is a number representing the arrival order of the received signal, and q is 0 or a positive integer and is a constant. A certain number of q from nth to n+q
The operation of updating the threshold value to the threshold value created from the received ultrasound signal that arrived before +1 ultrasound signal arrives is repeated, and for a short time after updating the threshold value, the difference between the transmitting and receiving transducers Changes in media conditions are almost negligible. Therefore, it is possible to respond to changes in the state of the medium between the transmitting and receiving transducers at any given time.

3. A received ultrasonic pulse signal confirmation trigger synthesis circuit that repeatedly updates the threshold value every 31 shots and its operation A typical embodiment of the present invention is shown in FIG.

This circuit can be operated as a constant threshold value repeatedly updated received ultrasonic pulse signal confirmation trigger synthesis circuit according to a control signal from an external controller. However, for the sake of clarity, here, the operation as a reception ultrasonic pulse signal confirmation trigger synthesis circuit of the type where q=0, that is, the threshold value is repeatedly updated for each shot, will be explained. In this received ultrasonic pulse signal confirmation trigger synthesis circuit that repeatedly updates the threshold value for each shot, the threshold is created from the n-th received signal and the n-1th received signal one step before it, that is, the most recent past received signal. Figure 3 shows a timing chart of the operation.The timing chart shows, from the top, the received signal, the threshold value, and the peak holder 10 that detects the peak value of the received signal. output.

A reset signal for controlling the reset switch 12 that discharges the peak hold capacitor 11, an output of the sample holder 13, an S/H signal for controlling the sample hold switch 14 of the sample holder 13, and a reception signal that is the output of the comparator 17. confirmation trigger RIT,
The order is in the order of the count time of an external counter. The reset signal and S/H signal are given from an external controller.

In this synthesis circuit, the received signal is input to a peak holder 10 and a comparator 17.

This circuit operates as follows based on control signals from an external controller. First, when a reset signal is input to the reset switch 12, the peak holt capacitor 11
after it is discharged.

The peak holder 10 detects the peak value of the first received signal. When the 0th order S/H signal is input, this peak value is held in the sample holder capacitor 15 and divided appropriately by the voltage divider 16. The detected signal is output to the comparator 17 as a threshold value for comparison with the second received signal. The peak holder 10 discharges the peak hold capacitor 11 with the reset switch 12 before the second received signal arrives, and prepares to detect the peak value of the second received signal. When the second received signal arrives, the comparator 17 generates a trigger R indicating that the second received signal has been confirmed at the moment the instantaneous value of the received signal exceeds the threshold.
IT is output. The RIT is similarly output for the received signals after the third note. Note that there is no need to consider the RIT for the first received signal.

The above-mentioned synthesis circuit is generally used by being provided in a receiving section of an ultrasonic transmitting/receiving device. The RIT is input to the ultrasonic transmitter, which generates the next ultrasonic signal. Therefore, the time interval between the n-th RIT and the (n+1)-th RIT is the propagation time of the ultrasound signal. In other words, the n-th RIT opens the gate of the external counter,
If the gate is closed at the (n+1)th RIT, a count value corresponding to the propagation time of the ultrasonic signal between the transmitting and receiving sections is obtained. If the counter gate is opened at the n-th RIT and the counter gate is closed at the n+r-th (r is an integer) RIT, a count value corresponding to r times the propagation time of the ultrasonic signal between the transmitting and receiving sections can be obtained. A count time of 3 corresponds to the case where r=2.

3.4 - Repetitive threshold value Repetitive update type received ultrasonic pulse signal confirmation trigger synthesis circuit From the explanation in 3.3, the peak value is reset (discharged) by the reset switch 12 of the peak holder 10, and then the peak value is It is easy to see that if the timing to hold and the timing to sample this with the sample holder 13 are appropriately selected, the circuit in Figure 1 and Figure 2 operates as a general threshold value repetitive update type received ultrasonic pulse signal confirmation trigger synthesis circuit. .

3.5 Effects of the invention As a result of adopting a variable threshold type receiving ultrasonic pulse signal confirmation trigger synthesis circuit for each shot, most of the problems described in 3.2 have been solved, and the ultrasonic pulse between the transmitting and receiving transducers is We were able to measure the signal propagation time extremely accurately. In principle, it is a good idea to create a threshold value based on the most recent received signal, and a variable threshold type received ultrasonic pulse signal confirmation trigger synthesis circuit for each shot corresponding to q = 0 is used. The effect is greatest when it is adopted, and the effect becomes smaller as +q becomes larger.

[Brief explanation of the drawings] Figure 1 shows an example of how a mistrigger occurs (when the peak of the received signal is mixed up) 9 Figure 2 shows a circuit example 9 of a threshold value repetitive update type received ultrasonic pulse signal confirmation trigger synthesis circuit 3 is an example of the timing chart. 1: 0 level of received signal 2 constant threshold level 3: Received signal with large amplitude 4: Received signal with smaller amplitude than 3: Timing 6:4 when 3 becomes equal to 2 for the first time is 2 Trigger 8 is output at timing 7:5, which is equal to
:Trigger output at the timing of 6 10: Peak holder 11: Peak hold capacitor 12: Reset switch 13: Sample holder 14: Sample hold switch 15: Sample hold capacitor 16: Voltage divider 17: Comparator RIT: Received signal confirmed Trigger (output of comparator) indicating that

Claims (1)

[Claims] 1. As stated in the main text, an ultrasonic pulse signal is intermittently emitted from an ultrasonic transducer in a transmitter, which is received by a receiving ultrasonic transducer in a receiver, and In a device that measures the time required for a sound wave pulse signal to arrive from a transmitter to a receiver, n is a number representing the order of arrival of the received signals, q is 0 or a positive integer and a constant, and the nth received signal Detect the peak value of the received signal that arrived earlier than , hold a value approximately proportional to this peak value, give this to the comparator as an update threshold input, and compare this with the nth to n+qth A method in which the comparator sequentially compares the received signal with the received signal and synthesizes triggers for confirming the arrival of each of the nth to n+q received signals. 2 As stated in the text and shown in the drawings, attach the peak holder (1
0), a sample holder (13), a voltage divider (16), and a comparator (17), and depending on the control signal from the controller provided outside the circuit, the reception signal that arrived before the nth received signal is The peak value of the signal is detected by the peak holder (10), and this peak value is transferred to the sample holder (10).
3), divide the voltage appropriately with the voltage divider (16), and then give it to the comparator (17) as an update threshold input. This and the nth to n+q received signals are input to the comparator (17). Repetitive threshold value update type reception ultrasonic pulse signal confirmation in which the operation of sequentially comparing in (17) and synthesizing triggers to confirm the arrival of the n-th to n+q-th received signals is performed repeatedly. Trigger synthesis circuit