JPH076820B2 - Ultrasonic reflection level meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level meter for detecting the level of a reflecting surface by reflected waves of ultrasonic waves, and is used as, for example, a snow depth level meter.

[0002]

2. Description of the Related Art A level meter using ultrasonic waves is generally composed of an ultrasonic wave transmitter, a reflected wave receiver and a control device for these waves. Of the ultrasonic wave of about 20 times, delete the maximum 2 pieces and the minimum 2 pieces of the detection data obtained from the received signal, average the remaining data, and record it in the static strain gauge. Has become.

[0003]

In the conventional level meter, when the reflected wave of the ultrasonic wave is received by the receiver,
When a noise with a wide frequency band such as a metallic sound arrives, the noise is captured, and there is a problem that the measurement accuracy is poor.

Therefore, an object of the present invention is to provide an ultrasonic reflection type level meter having high measurement accuracy by improving the receiving circuit.

[0005]

In order to solve the above-mentioned problems, the present invention relates to a transmitter for reflecting ultrasonic waves of a constant frequency toward a reflecting surface, a receiver for receiving the reflected waves, and a receiver for these waves. In an ultrasonic reflection level meter consisting of a transmitter and a control device for a receiver, a synchronous rectification circuit and a low-pass filter connected to the output side are provided in the receiving circuit of the receiver, and the output side of the low-pass filter is provided. Is connected to the control section, and the
Inversion 1 inverting amplifier, first and second analog switches
And the first analog switch, which is composed of a NOT circuit.
Input the received signal to the second switch
Signal is input through the inverting amplifier, and the first analog signal is input.
It is transmitted from the above transmitter as a synchronous signal of the log switch.
2nd analog while inputting the signal for ultrasonic sound source
The sound source signal is used as the switch synchronization signal in the NOT operation.
The input is made through a circuit .

[0006]

When the reflected signal is received and input to the synchronous rectification circuit, the frequency of the input signal matches the frequency of the synchronous signal, so that the negative half-wave is rectified and folded back between the positive half-waves. . Therefore, a synchronous rectification signal in which a positive half wave appears at a frequency twice that of the input signal is output. The signal is envelope-detected by passing through the next low-pass filter, and the envelope signal is output to the control section.

If the frequency of the input signal deviates from the frequency of the synchronizing signal, only the input signal at the timing synchronized with this is rectified, so the envelope signal subjected to the envelope detection becomes a low level signal, and Is discriminated against.

[0008]

EXAMPLE FIG. 1 shows an example of a snow depth level meter. In the figure, 1 is a transceiver, and 2 is a control device.

The transmitter / receiver 1 comprises an ultrasonic signal transmitter and a reflected wave receiver. The transmission unit is composed of a separator 3, a waveform shaper 4, an AND circuit 5, a transmission amplifier 6 and an ultrasonic transmitter 7. The receiving unit is composed of an ultrasonic receiver 8, a receiving amplifier 9, a synchronous rectifying circuit 10 and a low pass filter 11.

The separator 3 is connected to the power source / sound source input terminal 12. A signal obtained by superimposing a 40 KHz rectangular wave for a sound source on a DC power source is input to the input terminal 12. The separator 3 separates the signal and obtains an internal power supply. Also, the separated 40 KHz rectangular wave signal for the sound source is AND circuit 5
To the synchronous rectification circuit 10 as a synchronous signal.

The waveform shaper 4 has a transmission pulse input terminal 13
Connected to. The transmission pulse is a rectangular wave pulse input a predetermined number of times every 1 msec, and is shaped into a rectangular wave by the waveform shaper 4.

When the sound source signal separated by the separator 3 and the waveform-shaped transmission pulse are input to the AND circuit 5,
A 40 KHz sound source signal is generated every 1 ms. This signal is amplified by the transmission amplifier 6, ultrasonic waves of 40 KHz are transmitted in a burst form in the ultrasonic wave transmitter 7, and are emitted toward the snow surface S.

The ultrasonic waves reflected from the snow surface S are received by the ultrasonic receiver 8 and converted into electric signals. The converted signal is amplified by the reception amplifier 9 having a band of 10 KHz to 50 KHz, and the amplified signal is input to the synchronous rectification circuit 10.

As shown in FIG. 2, the synchronous rectification circuit 10 includes an inverting amplifier 15 having a gain of -1, first and second analog switches 16 and 17, and a NOT circuit 18.
The output signal of the receiving amplifier 9 is directly input to the first analog switch 16. The output signal is input to the second analog switch 17 through the inverting amplifier 15. In addition, each of these analog switches 16,
The 40 KHz sound source signal separated by the separator 3 is input to 17 as a synchronization signal, but is input to the second analog switch 17 through a NOT circuit 18. The analog switches 16 and 17 are connected to the low pass filter 11.

Now, the reflected signal of 40 KHz ((a) in FIG. 3)
Is received and the signal is applied to the first analog switch 16, the first analog switch 16 receives 40
Since the positive half wave of the KHz synchronization signal turns on and the negative half wave turns off, the positive half wave of the reflected signal is output during the on time. The phase of the reflected signal applied to the inverting amplifier 15 is inverted by 180 degrees as shown in FIG. 3B, and the inverted signal is applied to the second analog switch 17. Since the synchronization signal is applied to the second analog switch 17 through the NOT circuit 18, the second analog switch 17 is turned off when the synchronization signal has a positive half-wave and turned on when the synchronization signal has a negative half-wave. Therefore, the second analog switch 17 is turned on with a timing shifted by half a wavelength from the first analog switch 16.

The signal applied to the low-pass filter 11 is, as shown in FIG. 3 (c), the positive half-wave of the received input signal, and the negative half-wave is folded into the positive side. It becomes a synchronous rectification signal with the obtained waveform. When this periodic rectified signal passes through the low-pass filter 11, the high-frequency component is removed and the envelope signal is subjected to envelope detection, as shown in FIG. This signal is output from the reception pulse output terminal 20 to the control device 2 as a reception pulse.

On the other hand, if the received signal is, for example, noise of 10 KHz as shown in FIG. 4 (a), the signal whose phase is inverted by 180 ° through the inverting amplifier 15 is as shown in FIG. 4 (b). Then, these signals are applied to the first and second analog switches 16 and 17 which are turned on and off by the synchronization signal of 40 KHz, respectively.

Therefore, the signal applied to the low-pass filter 11 has a waveform chopped at 40 KHz, as shown in FIG. When a signal having such a waveform is passed through the low-pass filter 11, the envelope signal becomes a signal having a low level of 40 KHz as shown in FIG.

As described above, since the level of the envelope signal has a clear level difference between the normal input signal and the noise signal, it is possible to discriminate them by comparing them with an appropriate reference level in the control device. .

However, such a discrimination means alone may cause erroneous detection when the level of the envelope signal of the noise signal is high. Therefore, as another discrimination means, detection data of snow depth obtained based on the envelope signal (data corresponding to the distance H from the transceiver 1 to the snow surface S)
Takes advantage of the fact that it is smaller than or equal to the data corresponding to the distance Ho to the ground surface L, and there is no possibility that the relationship will be reversed. That is, the data corresponding to the distance Ho is detected in advance and stored as reference data, the reference data is compared with the detection data, and the detection data exceeding the reference data is excluded.

Such a determination process is performed by the control device 2
Performed in. The control device 2 is the CPU 2
1, ROM 22, RAM 23, counter 24, timer counter 25, A / D converter 26, PI / O2
7, each of which transmits and receives a signal through the bus line 28 based on a program stored in the ROM 22.

Further, the control device 2 includes an oscillator 2
9, a frequency divider 30, a power supply unit 31, an addition unit 32, a waveform shaper 33, an amplifier 34, and a level discriminator 35 are provided.
The signal generated by the oscillator 29 is frequency-divided and input to the adding unit 32 as a 40 KHz sound source signal, superimposed on the DC power source input from the power source unit 31, and input from the power source / tone source output terminal 36 to the transceiver 1. Output to the terminal 12.

Further, the transmission signal output through the PI / O 27 is passed through the waveform shaper 33, and is output from the transmission pulse output terminal 37 to the input terminal 13 of the transceiver 1.

An amplifier 34 is connected to the reception pulse input terminal 38, and the amplified signal is passed through a level discriminator 35 to P
It is input to the I / O 27. In the level discriminator 35, the level of the envelope signal below a certain level is excluded.

The control by the CPU 21 is as follows.
This is performed by a program stored in the ROM 22. The flow chart of the program is as shown in FIG.

The operation of the snow depth level gauge of the embodiment will be described with reference to this flow chart, the timing chart shown in FIG. 6 and the block diagram of FIG.

When the measurement cycle is started, as shown in FIG.
As shown in FIG. 6, a signal A obtained by weighting the sound source signal to the power source
And the transmission pulse B at 1 ms intervals is input to the transceiver 1,
The 40 KHz sound source signal C and the transmission pulse B, which are separated from the internal power supply by the separator 3, are added to the AND circuit 5 for 1 ms.
40 KHz sound source burst signal D for each transmission amplifier 6
To the snow surface S from the ultrasonic transmitter 7 (step). Further, the start signal F is given to the counter 24 at the same time as the start of the measurement cycle.

When the reflected wave G of the ultrasonic wave is received (step), the envelope signal subjected to the envelope detection through the synchronous rectification circuit 10 and the low-pass filter 11 is input to the control device 2 and the level is passed through the amplifier 34. It is discriminated by the discriminator 35. Further, the stop signal K is given to the counter 24, and the counter 24 is stopped. This makes it possible to determine the propagation time t of the ultrasonic waves.

On the other hand, the level-discriminated signal is compared with reference data (data corresponding to the above-mentioned distance Ho to the ground surface) as detection data (step). When the detected data is smaller than or equal to the reference data, it is stored in the RAM 23 together with the data of the propagation time t (step). When the detected data is larger than the reference data, the detected data is deleted and the measurement is performed again (step).

Since ultrasonic waves are transmitted 20 times in 5 minutes, it is judged whether or not the detection data of 20 times is stored in 5 minutes (step).
And the minimum value of 2 data are deleted (same), and the remaining 16
The individual data are averaged (same) and recorded on a static strain gauge (same).

If the detected data is not stored 20 times in 5 minutes, all the stored data are deleted, the measurement is suspended for 5 minutes, and then restarted.

[0032]

As described above, according to the present invention, the receiving circuit is provided with the synchronous rectifying circuit and the low-pass filter, and the frequency of the synchronizing signal of the synchronous rectifying circuit is made to coincide with the frequency of the ultrasonic wave to be transmitted. It can be effectively eliminated and highly accurate level measurement can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a block diagram of a synchronous rectification circuit.

[Figure 3] Waveform diagram

[Figure 4] Waveform diagram

FIG. 5: Flow chart

FIG. 6 is a timing chart.

[Explanation of symbols]

 1 Transmitter / Receiver 2 Control Device 3 Separator 4 Waveform Shaper 5 AND Circuit 6 Transmitter Amplifier 7 Ultrasonic Transmitter 8 Ultrasonic Receiver 9 Receive Amplifier 10 Synchronous Rectifier Circuit 11 Low Pass Filter 12 Power Supply / Sound Source Input Terminal 13 Transmitted Pulse Input Terminal 15 Inverting amplifier 16 First analog switch 17 Second analog switch 18 NOT circuit 20 Received pulse output terminal 21 CPU 22 ROM 23 RAM 24 Counter 25 Timer counter 26 A / D converter 27 PI / O 28 Bus line 29 Oscillator 30 Frequency divider 31 Power Supply Section 32 Addition Section 33 Waveform Shaper 34 Amplifier 35 Level Discriminator 36 Power Supply / Sound Source Output Terminal 37 Transmit Pulse Output Terminal 38 Receive Pulse Input Terminal

Claims (1)

[Claims] 1. An ultrasonic reflection level meter comprising a transmitter that reflects ultrasonic waves of a constant frequency toward a reflecting surface, a receiver that receives the reflected waves, and a control device for these transmitters and receivers. In the above, the receiving circuit of the receiver is provided with a synchronous rectification circuit and a low-pass filter connected to the output side thereof, the output side of the low-pass filter is connected to the control section, and the synchronous rectification circuit has a gain
Inverting amplifier of switch 1 and first and second analog switches
A NOT circuit, and the first analog switch
Input the received signal to the second analog switch
Signal is input through the inverting amplifier, and the first analog
The super signal transmitted from the transmitter as a switch synchronization signal.
The sound source signal of the sound wave is input and the second analog switch
Switch is used as the synchronizing signal of the switch
An ultrasonic reflection type level meter characterized by inputting through .