JPS61722A - Measuring apparatus of supersonic wave propagation time - Google Patents

Abstract

PURPOSE:To measure supersonic wave propagation time with stability and precision with possibility of employment of such a stabilized action oscillator as a crystal oscillator, by using an oscillator of a limited variable frequency range as a VCO. CONSTITUTION:A synchronous generating circuit 5, after receiving a starting time signal from a CPU9, issus a start pulse in synchronization with a leading edge of the first pulse from the oscillator 4. A transmission circuit 6 upon receiving this pulse, causes a supersonic wave to be emitted by driving a vibrator 8a. A vibrator 8b completes counting by a signal receiving pulse R issued from the signal receiving circuit 1 and then issues a counting value N to the CPU9. A time difference detecting circuit 3 detects a difference time between the timing of the signal receiving pulse R and the leading edge of the pulse nearerst to this timing among the output pulses from an oscillator and control the oscillator 4 to make the time difference zero. The frequency (f) at this moment is measured by a counter 10. CPU9 performs an arithmetic operation N/f to calculate a T required for the supersonic wave propagation between oscillators 8a, 8b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to an improvement in an ultrasonic propagation time measuring device that can be suitably used, for example, in an ultrasonic flowmeter or an ultrasonic level meter.

[Prior art and its problems]

Figure 1 shows the TLL (Time Lo-ck
1 is a block diagram illustrating the principle of a conventional ultrasonic propagation time measurement device using a method called ed Loop method.

In the figure, 1 is a receiving circuit, 2 is a counter, 3 is a time difference detection circuit, 4 is a voltage controlled oscillator (VCO), 5 is a synchronization generating circuit, 6 is a transmitting circuit, and 5at8b is a vibrator.

The circuit operation is as follows. The transmitter transducer 8a driven by the transmitter circuit 6 sends out ultrasonic pulses into the measurement medium. The receiving side transducer 8b receives the ultrasonic pulse and sends the received output to the receiving circuit 1. On the other hand, the synchronization generating circuit 5 generates a start pulse in synchronization with the pulse output from the oscillator 4. At the same time as starting the transmitting circuit 6, the counter 2 is started.

The counter 2 is configured to send a count end signal to the time difference detection circuit 3 after counting N pulses with a repetition frequency of f from the oscillator 4. N is an appropriately selected integer (preset constant number).

In the time difference detection circuit 3, the ultrasonic pulse is transmitted to the transmitting side transducer 8.
The receiving circuit 1 provides the time t required for propagation in the measurement medium from the receiving side transducer 8b to the receiving side transducer 8b, and the counter 2 is provided with the repetition frequency f. Therefore, the time difference detection circuit 3 controls the repetition frequency of the oscillator 4 during propagation. As a result, the relationship 1=- is established, and by transforming this, it is possible to extract.

Now, in the conventional ultrasonic propagation time measuring device as described above, if the propagation time of the ultrasonic wave from the transmitting side transducer 8a to the receiving side transducer 8b changes significantly due to the influence of water temperature, etc. Following this, the oscillation frequency of the oscillator 4 will also change significantly.

In other words, it is necessary to use an oscillator with a wide variable frequency range as the voltage controlled oscillator 4. Therefore, an oscillator such as a crystal oscillator, which operates stably but has a narrow variable frequency range, cannot be used. Conventional ultrasonic propagation time measurement devices have the disadvantage that they are forced to use an unstable oscillator, which adversely affects measurement accuracy.

[Purpose of the invention]

The present invention has been made in order to eliminate the drawbacks of the prior art as described above, and therefore it is an object of the present invention to provide an oscillator with a relatively narrow variable frequency range even when the ultrasonic propagation time varies considerably. The object of the present invention is to provide a 5e ultrasonic propagation time measuring device.

[Key points of the invention]

The key point of the present invention is that in conventional measurement devices, the counter counts a predetermined number of N pulses, whereas in the present invention, the counter counts the oscillator output pulses from the ultrasonic transmission time. The count is started at the reception time of the ultrasonic wave (the number of pulses to be counted is undefined), and the rising (or falling) edge of the output pulse near the reception time is The oscillation frequency of the oscillator is controlled so that the time difference with a specific phase such as When the amount of deviation exactly reaches the unit cycle period at the reference frequency,
The oscillation frequency is set to the reference frequency.

By doing this, the variable range of the oscillation frequency is within a range of ±1 cycle from the base wall frequency.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. In this figure, the same or corresponding elements as in FIG. 1 are given the same reference numerals.

In addition, 9 is a CPU, 10 is a frequency counter that counts the output frequency of the oscillator 4, and 11 is a time pace circuit.

Next, the circuit operation will be explained. The synchronization generation circuit 5 is connected to the CPU 9
After receiving the start timing signal from the oscillator 4, a start pulse is sent out in synchronization with the rising edge of the first pulse from the oscillator 4. The transmitting circuit 6 uses these two tart pulses to drive the receiving side transducer 8a to transmit an ultrasonic wave.

On the other hand, the counter 2 starts counting the output pulses from the oscillator 4 in response to the start pulse from the synchronization generating circuit 5, and ends counting in response to the reception pulse R output from the reception circuit 1 when the transducer 8b receives the ultrasonic wave. Then, the current number 1-KN is output to the CPU 9K.

The time difference detection circuit 3 detects the time difference between the timing of the received pulse R and the pulse rising edge closest to the timing among the output pulses from the oscillator 4, and adjusts the timing of the oscillator 4 so that the time difference becomes zero. Control output frequency.

The controlled frequency f at this time is measured by the frequency counter 10 and output to the CPU 9.・CPU9 is
By performing the calculation N/f, the oscillators 8a and 8b
The time T required for ultrasonic propagation during this period is calculated and output.

FIG. 3 is a circuit diagram showing a specific example of the time difference detection circuit 3 in FIG. 2, and FIGS. 3A and 3B are timing charts of signals of each part in FIG. 3, respectively.

Check Figures 3 and 3A. A pulse with a repetition frequency f from the oscillator 4 is input to the D input terminals of the D-type flip-flops F, F, and a received pulse R from the receiving circuit 1 is input to the clock input terminal C.

Therefore, flip-flops F and F latch the level of the pulse input to the D input terminal from the oscillator 4 (L in this case) at the rising timing of the received pulse B input to the clock input terminal C, and By sending the K output to the oscillator 4 and controlling its oscillation frequency, let's make the time difference Δt between the rising timing of the received pulse R and the rising edge of the pulse from the oscillator 4 closest to the timing to zero. (in this case the frequency increases).

In FIG. 3B, since it is the H level of the pulse input from the oscillator 4 to the D input terminal that is latched at the rising timing of the received pulse R, the flip-flop F,
F attempts to make the time difference Δt zero by sending out the K output from its Q output terminal and controlling the output frequency of the oscillator 4 (in this case, the frequency decreases).

FIG. 4 is a circuit diagram showing a vCO controller 4A located in the 760 oscillator 4, which receives the H level output or L level output from the time difference detection circuit 3 and outputs the CO control voltage.

In the figure, whether an H level output (+ voltage) is input from the detection circuit 3 via a resistor r or an L level output (- voltage) is input.
Depending on whether C is input, the feedback capacitor Co of operational amplifier OP is charged positively or negatively, and C
O control voltage is output from operational amplifier OP and VC
Decrease or increase the output frequency of O. As will be described later, when a reset signal is input from the CPU 9, the switch SW is closed and the capacitor Co is discharged, so the CO control voltage also becomes zero, and the VCO at this time
The oscillation frequency of returns to the reference frequency.

Next, returning to FIG. 2, operations related to the present invention will be explained.

As already explained in 5, in the CPU 9, the count value N from the counter 2 and the controlled frequency from the 1 oscillator 4 (this is now the reference frequency), the propagation time of the ultrasonic wave increases due to changes in the temperature of the medium, etc. Then, the timing of the received pulse R from the receiving circuit 1 is also delayed, and the timing of the 3rd B pulse is delayed.
In FIG. 3B, the time difference Δt increases. Eventually, the output frequency of the oscillator 4 is controlled so that this time difference Δt becomes zero (in this case, as can be seen from FIG. 3B, the time length corresponding to the number of negative pulses N increases). Therefore, the frequency will decrease, and let this decreased frequency be f).

CI) U 9, upon detecting this frequency (pulse repetition relationship), sends a reset signal to the oscillator 4,
When the switch SW in the figure is closed to discharge the capacitor Co, the oscillation frequency from the oscillator 4 is forcibly reset from f to the reference frequency ro. the result,
Immediately before reset, in FIG. 3B, the received pulse R
Assuming that the (rising) timing of R and the rising edge S1 of the pulse of frequency f match (Δt is controlled to zero), immediately after reset, the (rising) timing of the received pulse R will be the same as the rising edge S1 of the pulse with frequency f. This coincides with the rising edge S2 of the pulse, and the repetition frequency of the pulse at this time becomes the reference station wave number fO.

The above explanation is for the case where the propagation time of the ultrasonic wave increases, but the same thing can be said when the propagation time of the ultrasonic wave decreases.

FIG. 5 shows the flow of the operations of the CPU 9 as described above. In FIG. 2, the above-described operation of the CPU 9 is started and ended by an interrupt signal output from the time base circuit 11.

FIG. 5 (A) shows an expanded initial operation, (B) shows a normal operation, and (C) shows a control operation using an interrupt. There is no need to explain these charts again.

〔Effect of the invention〕

As explained above, according to the present invention, since an oscillator with a small variable frequency range is used as a VCO, it is possible to use an oscillator with stable operation such as a crystal oscillator, and as a result, measurement of ultrasonic propagation time becomes stable. There are five advantages in that it can be done with high precision.

In addition, there is no need for the conventional work such as selectively setting the number of pulses N to be counted by the counter according to the length of the propagation time to be measured, which has the advantage of ease of handling. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the principle of a conventional ultrasonic propagation time measuring device, a second enlarged block diagram showing an embodiment of the present invention, and FIG. 3 is a specific example of the time difference detection circuit 3 in FIG. The circuit diagrams shown in Figure 3A and @3B are timing charts of various signals in Figure 3, respectively. Figure 4 is a circuit diagram showing an example of vCO included in the oscillator 4, Figure 5. is a flowchart showing the flow of the operation of the CPU in FIG. 2; Code explanation 1... Receiving circuit, 2... Counter, 3
......Time difference detection circuit, 4...Voltage controlled oscillator (VCO), 4A...■CO controller, 5...Synchronization generation circuit, 6... ...Transmission circuit, 8a, 8b...A vibrator, 9...CP
U, 10... lap v, number counter, '11・hit・
Time Base Circuit Agent Patent Attorney Akio Namiki Patent Attorney Kiyoshi Matsuzaki Figure 1 Figure 2 Figure 3 Figure 3A Figure 38 AIl

Claims (1)

[Claims] 1) An ultrasonic wave transmitter and a wave receiver placed apart from each other in a measurement medium, and an ultrasonic wave receiver that starts counting output pulses from the oscillator in synchronization with the wave transmission time in the wave transmitter. a counter that finishes counting in synchronization with the time of reception; and means for detecting a time difference between the reception time and a specific phase, such as a rising or falling edge, of the output pulse in the vicinity of the time; means for controlling the oscillation frequency of the oscillator so that the time difference becomes zero, and ultrasonic waves propagate between the transmitter and receiver based on the value of the controlled oscillation frequency and the count number by the counter. The time required for (
means for determining the propagation time (hereinafter referred to as propagation time); and means for monitoring the amount of deviation of the oscillation frequency of the oscillator which is controlled in response to the variation of the propagation time and deviates from a certain reference frequency value; An ultrasonic propagation time measurement device comprising: means for resetting the oscillation frequency of the oscillator to the reference frequency when the amount of deviation reaches a unit cycle period at the reference frequency.