JPH04273023A - Ultrasonic reflection type level meter - Google Patents

Abstract

PURPOSE:To conduct highly accurate level measuring with noise effectively excluded by providing a synchronous rectification circuit and a low pass filter on a receiving circuit to make a frequency of a synchronous signal conformable with that of an ultrasonic wave to be transmitted. CONSTITUTION:A synchronous rectification circuit 10 and a low pass filter 11 connected to its output side are provided on a receiving circuit of a receiver, an output side of the low pass filter 11 is connected to a control device 2, and a frequency of a synchronous signal of the synchronous rectification circuit 10 is made conformable with that of an ultrasonic wave transmitted from the receiver. When a reflected signal is received and inputted in the synchronous rectification circuit 10, since the inputted signal frequency is conformable with the synchronous signal frequency, a negative half-wave is rectified to be inverted between positive half-waves. This causes the output of a synchronous rectification signal in which the positive half-wave appears in a frequency two times that of the input signal. The synchronous rectification signal is envelope-detected by passing the next low pass filter 11, and an resultant envelope signal is outputted to the control device 2.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] A level meter using ultrasonic waves generally consists of an ultrasonic transmitter, a reflected wave receiver, and a control device for these. The system transmits ultrasonic waves about 20 times, deletes the maximum 2 pieces of detection data and the minimum 2 pieces of data obtained from the received signal, averages the remaining data, and records it on the static strain meter. It has become.

0003

[Problems to be Solved by the Invention] In conventional level meters, when receiving reflected ultrasonic waves in a receiver,
When noise with a wide frequency band such as a metallic sound arrives, it is taken in, resulting in a problem of poor measurement accuracy.

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

[0005]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a transmitter that emits ultrasonic waves of a constant frequency toward a reflecting surface, a receiver that receives the reflected waves, and a transmitter that transmits these waves. In an ultrasonic reflection level meter consisting of a receiver and a receiver control device, the receiving circuit of the receiver is provided with a synchronous rectifier circuit and a low-pass filter connected to its output side, and the output side of the low-pass filter is connected to the receiver circuit. The synchronous rectifier is connected to a control section, and the synchronous signal of the synchronous rectifier circuit is made to match the frequency of the ultrasonic waves transmitted from the transmitter.

[0006]

[Operation] When the reflected signal is received and input to the synchronous rectifier circuit, the frequency of the input signal matches the frequency of the synchronous signal, so the negative half-wave is rectified and folded back between the positive half-waves. . Therefore, a synchronous rectified signal in which a positive half wave appears at twice the frequency 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.

[0007] If the frequency of the input signal deviates from the frequency of the synchronization signal, only the input signal synchronized with this is rectified, so the envelope signal subjected to envelope detection becomes a low-level signal, and the above-mentioned signal It is distinguished as

[0008]

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

[0009] The transceiver 1 consists of a transmitter for ultrasonic signals and a receiver for the reflected waves. The transmitting section includes a separator 3, a waveform shaper 4, an AND circuit 5, a transmitting amplifier 6, and an ultrasonic transmitter 7. Further, the receiving section includes an ultrasonic receiver 8, a receiving amplifier 9, a synchronous rectifier circuit 10, and a low-pass filter 11.

The separator 3 is connected to a power/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 this input terminal 12. Separator 3 separates the signal to obtain internal power. Also, the 40KHz square wave signal for the separated sound source is sent to the AND circuit 5.
At the same time, the signal is input to the synchronous rectifier circuit 10 as a synchronizing signal.

The waveform shaper 4 has a transmission pulse input terminal 13
connected to. The transmission pulse is a rectangular wave pulse that is 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, and the ultrasonic transmitter 7 emits a burst of ultrasonic waves of 40 KHz, which 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 electrical signals. The converted signal is amplified by a receiving amplifier 9 having a band of 10 KHz to 50 KHz, and the amplified signal is input to a synchronous rectifier circuit 10.

As shown in FIG. 2, the synchronous rectifier circuit 10 includes an inverting amplifier 15 with a gain of minus 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 . Further, the above output signal is inputted to the second analog switch 17 through the inverting amplifier 15. In addition, each of these analog switches 16,
17, the 40 KHz sound source signal separated by the separator 3 is input as a synchronization signal, and is input to the second analog switch 17 through the NOT circuit 18. Further, each analog switch 16, 17 is connected to the low pass filter 11.

Now, the 40 KHz reflected signal ((a
) is received and that signal is applied to the first analog switch 16. Since the first analog switch 16 is turned on at the positive half wave of the 40 KHz synchronization signal and turned off at the negative half wave, the signal is applied to the first analog switch 16. A positive half wave of the reflected signal is output during the on time. Further, the phase of the reflected signal applied to the inverting amplifier 15 is inverted by 180 degrees as shown in FIG. 3(b), and the inverted signal is applied to the second analog switch 17. The second analog switch 17 has N
Since the synchronization signal is applied through the OT circuit 18, the second analog switch 17 is turned off when the synchronization signal is a positive half-wave, and turned on when it is a negative half-wave. Therefore, the second analog switch 17 is turned on with a timing shift of half a wavelength from that of the first analog switch 16.

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

On the other hand, if the received signal is, for example, (a) in FIG.
Assuming that the noise is 10 KHz as shown in the figure, the signal whose phase is inverted by 180° after passing through the inverting amplifier 15 is (
b) As shown in the figure, these signals each have 40
It is applied to the first and second analog switches 16 and 17, which are turned on and off by a KHz synchronization signal.

Therefore, the signal applied to the low-pass filter 11 has a waveform chopped at 40 KHz, as shown in FIG. 3(c). When a signal having such a waveform is passed through the low-pass filter 11, the envelope signal becomes a low-level signal of 40 KHz, as shown in the figure (d).

As mentioned above, since there is a clear level difference in the level of the envelope signal between the normal input signal and the noise signal, the control device can discriminate between the two by comparing them with an appropriate reference level. .

However, such a discrimination means alone may cause false detection when the level of the envelope signal of the noise signal is high. Therefore, as another means of discrimination, the snow depth detection data obtained based on the envelope signal (data corresponding to the distance H from the transceiver 1 to the snow surface S) is It takes advantage of the fact that the data is smaller than or equal to the corresponding data and cannot have an inverse relationship. That is, data corresponding to the distance Ho is detected in advance and stored as reference data, the reference data is compared with the detected data, and detected data exceeding the reference data is eliminated.

Such judgment processing is carried out by the control device 2.
It will be held in The control device 2 is a CPU 2
1, ROM22, RAM23, counter 24, timer counter 25, A/D converter 26, PI/O2
7, each of which transmits and receives signals through the bus line 28 based on the program stored in the ROM 22.

The control device 2 also includes an oscillator 2.
9, a frequency divider 30, a power supply section 31, an adder section 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 as a 40 KHz sound source signal to the adder 32, superimposed on the DC power input from the power supply section 31, and input to the transceiver 1 from the power supply/sound source output terminal 36. Output to terminal 12.

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

An amplifier 34 is connected to the received pulse input terminal 38, and the amplified signal is passed through a level discriminator 35 to P
It is input to I/O27. This level discriminator 35 excludes envelope signals whose level is below a certain level.

The control by the CPU 21 described above is as follows:
This is performed by a program stored in the ROM 22. The program is shown in a flowchart as shown in FIG.

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

[0027] When the measurement cycle is started, Fig. 1,
As shown in FIG. 6, a signal A in which the sound source signal is added to the power
The transmission pulse B at 1 ms intervals is input to the transceiver 1, and the 40KHz sound source signal C, which is separated from the internal power supply by the separator 3, and the transmission pulse B are added to the AND circuit 5.
A 40 KHz sound source burst signal D is input to the transmission amplifier 6 every ms, and a burst-shaped ultrasonic wave E is further transmitted from the ultrasonic transmitter 7 toward the snow surface S (step ■).
. Also, at the same time as the start of the measurement cycle, the counter 2
4 is given a start signal F.

When the ultrasonic reflected wave G is received (step ①), the envelope signal detected by the envelope through the synchronous rectifier circuit 10 and the low-pass filter 11 is input to the control device 2, and is then passed through the amplifier 34. It is discriminated by a level discriminator 35. Further, a stop signal K is given to the counter 24, and the counter 24 is stopped. This determines the propagation time t of the ultrasonic wave.

On the other hand, the level-discriminated signal is compared with reference data (data corresponding to the aforementioned distance Ho to the ground surface) as detection data (step 2). 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 2). If the detected data is larger than the reference data, delete the detected data and redo the measurement (step ■).

[0030] Ultrasonic waves are transmitted 20 times in 5 minutes, so it is determined whether or not the detection data for 20 times in 5 minutes has been stored in memory (step ■), and when it reaches 20 times, the maximum value is 2.
, the minimum value of 2 data is deleted (same as ■), and the remaining 16
Average the data (same as ■) and record it on the static strain meter (same as ■)
).

[0031] If the data detected 20 times within 5 minutes is not stored in memory, all the stored data is deleted, the measurement is stopped for 5 minutes, and then resumed.

[0032]

[Effects of the Invention] As described above, the present invention provides a receiving circuit with a synchronous rectifier circuit and a low-pass filter, and by matching the frequency of the synchronous signal of the synchronous rectifier circuit with the frequency of the ultrasonic wave to be transmitted, noise can be reduced. can be effectively eliminated and highly accurate level measurements can be performed.

[Brief explanation of the drawing]

[Figure 1] Block diagram of the embodiment

[Figure 2] Block diagram of synchronous rectifier circuit

[Figure 3] Waveform diagram

[Figure 4] Waveform diagram

[Figure 5] Flowchart

[Figure 6] Timing chart

[Explanation of symbols]

1 Transmitter/receiver 2 Control device 3 Separator 4 Waveform shaper 5 AND circuit 6 Transmission amplifier 7 Ultrasonic transmitter 8 Ultrasonic receiver 9 Receiving amplifier 10 Synchronous rectifier circuit 11 Low pass filter 12 Power/sound source input terminal 13 Transmission pulse input terminal 15 Inverting amplifier 16 First analog switch 17 Second analog switch 18 NOT circuit 20 Receive 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/sound source output terminal 37 Transmission pulse output terminal 38 Receive pulse input terminal

Claims (1)

[Claims] Claim 1: An ultrasonic reflection level meter comprising a transmitter that emits 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 this case, a synchronous rectification circuit and a low-pass filter connected to the output side of the synchronous rectification circuit are provided in the receiving circuit of the above-mentioned receiver, and the output side of the low-pass filter is connected to the control section, and the synchronization signal of the above-mentioned synchronous rectification circuit is transmitted. An ultrasonic reflection type level meter characterized by matching the frequency of ultrasonic waves transmitted from the device.