JPS6310793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection circuit that processes a received signal in, for example, an ultrasonic level meter.

BACKGROUND ART Conventionally, ultrasonic measuring devices have been widely used as non-contact methods for measuring the flow rate of an object to be measured and the distance to the object. The operation of such an ultrasonic measuring device is to emit ultrasonic pulses toward an object to be measured in a repetitive cycle, and measure the propagation time of the ultrasonic pulses to determine the distance to the object or the flow rate of the object. This is a way to know. A circuit configuration diagram of an ultrasonic level meter using such a method is shown in FIG. 1, and the configuration and operation of this ultrasonic level meter will be briefly explained. In FIG. 1, numeral 1 indicates periodic (for example
This is a timing pulse generation circuit that outputs a pulse signal with a period of 100ms, and the output of this circuit is supplied to the ultrasonic oscillation circuit 2, variable time width voltage generation circuit 7 (hereinafter abbreviated as TVG voltage generation circuit), and flip-flop 11, respectively. be done. The ultrasonic oscillation circuit 2 generates an ultrasonic signal for a certain period of time based on the periodic pulse of the timing pulse generation circuit 1, and supplies it to the drive circuit 3. The drive circuit 3 is a circuit that amplifies the ultrasonic signal generated by the ultrasonic oscillation circuit 2, and the ultrasonic signal amplified here is supplied to the transducer 5 via the switching circuit 4. The transducer 5 converts the ultrasonic signal into an ultrasonic wave, emits it toward the surface to be measured 6 , and receives the ultrasonic wave reflected from the surface to be measured 6 . The ultrasonic waves reflected by the surface to be measured 6 are converted into ultrasonic signals again by the transducer 5, and then sent to the voltage control amplifier 8 (hereinafter referred to as VCA) via the switching circuit 4.
Controlled Amp.).
VCA8 together with TVG voltage generation circuit 7 is called
A TVG (Time Varing Gain) amplification circuit 13 is configured. The operation of this circuit 13 will now be explained with reference to FIG. Figure 2 shows timing generation circuit 1
Pulse signal waveform, gain waveform of VCA8,
The input waveform and output waveform of VCA8 are shown respectively. In the figure, reference numeral 13 is a waveform representing noise due to emitted ultrasonic waves and residual vibrations associated therewith, and reference numeral 14 is a waveform representing a received signal due to reflected ultrasonic waves. The amplitude of the received signal 14 increases as the reception time becomes later (i.e., the amplitude of the measured surface 6
The further away the transducer and transducer 5 are), the smaller it becomes.
The result is corrected by the TVG amplifier circuit.
As shown in the waveform shown in the figure, the output of VCA8 is such that only the received wave is amplified, and at the same time the noise during ultrasonic emission is removed.
(abbreviated as AGC circuit) 9. AGC circuit 9
is a circuit that stabilizes the amplitude of the received signal, which cannot be stabilized by the TVG amplifier circuit 7 alone. Note that the properties of the received signal not only attenuate monotonically over time, but also change from moment to moment due to changes in the state of the reflecting surface and the state within the ultrasonic propagation path. The received signal whose amplitude has been made constant by the AGC circuit 9 is supplied to a comparator 10 and compared with a preset reference level. When the received signal level is higher than the reference level, a detection signal is output from the comparator 10 and supplied to a flip-flop 11 (hereinafter abbreviated as FF11). FF11 is set by the periodic pulse of the timing pulse generation circuit 1,
The output of the FF 11 becomes a binary signal "1" and is supplied to the time output value conversion circuit 12, and the comparator 10
The FF 11 is reset by the detection signal output from the FF 11. The time output value conversion circuit 12 is FF11
Calculate the ratio of the current level value to the set level value using the time the output of is at the "1" level, and convert it into a predetermined signal, for example, a 4 to 20 mA current signal or a 1 to 5 V voltage signal. This is a circuit that outputs

However, the conventional ultrasonic level meter configured as described above has the following drawbacks.

(1) In addition to normal reflected waves, the received signal includes various types of ultrasonic noise flying through the air, as well as induced noise mixed in from cables and the like. As mentioned earlier, the TVG amplifier circuit 13
Although this method is effective for reflected wave signals that become weaker as the reception time becomes later, it is susceptible to the opposite effect from randomly occurring reception noise as described here. As a means for removing such reception noise, a filter with a large time constant is used in the output circuit to prevent sudden changes in the output, but the provision of this filter has drawbacks such as slow response speed.

(2) TVG amplifier circuit 1 to amplify the received wave
3 and AGC circuit 9 are used in series,
Each adjustment is difficult.

This invention was made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a signal detection circuit that is resistant to noise, has a fast response speed, and does not require adjustment in an ultrasonic measuring device. a variable gain amplifier that amplifies the received signal received by the variable gain amplifier; a converter that converts the amplitude of the output signal of the variable gain amplifier into digital amplitude data; While controlling the gain of the gain amplifier, from among the received signals received by the ultrasonic transducer, a regular received signal corresponding to the ultrasound that has been properly emitted from the measurement target and returned is identified. , comprising an arithmetic control circuit (for example, a microcomputer) that outputs a measurement result corresponding to the elapsed time from when the ultrasonic transducer emits an ultrasonic wave until a regular received signal is obtained; If the reception time at which the next normal received signal is expected to be obtained cannot be determined, the arithmetic control circuit determines the time from when the ultrasonic transducer emits an ultrasonic wave until when the next ultrasonic wave is emitted. Over the entire period, the amplitude data is captured while increasing the gain of the variable gain amplifier over time, and when amplitude data equal to or greater than a predetermined value is obtained, it is assumed that a normal received signal has been obtained. While the gain of the variable gain amplifier is once fixed and the reception time is determined, if the reception time can be determined, the reception time is determined every time an ultrasonic wave is emitted by the ultrasonic transducer. Repeatedly capturing the amplitude data obtained in a certain time period before and after,
The present invention is characterized in that the gain of the variable gain amplifier is controlled so that these amplitude data are constant, and the measurement results are output.

An embodiment of the present invention will be described below with reference to the drawings. Before explaining the embodiments, the basic idea of the invention will be explained. Generally, ultrasonic level meters are used to continuously measure the level of powder, liquid, etc., but the rate of change in these levels is usually relatively slow. Ripples on the liquid surface can be considered as the fastest level change, but the height of these waves can be considered to be sufficiently small (for example, 5% or less) relative to the measurement span. In other words, if normal reflected wave reception is being performed, the change in the repeatedly measured value should be within a certain range (determined by the maximum rate of change in level or the maximum value of the height of the liquid). . Therefore, by limiting the reception of reflected waves to a narrow range before and after the previous reception time, stable measurement that is resistant to disturbance noise becomes possible. This invention focuses on this, digitizes the amplitude of the previous received signal and measures it with a microcomputer, and based on this measurement result, calculates the time period in which the next received signal exists and the gain of the next receiving amplifier.
It was decided by a microcomputer program. In addition, according to such a method, by limiting the reception period to a narrow range, the attenuation of the received signal due to time can be almost ignored within the period, so that TVG control used in the TVG amplifier circuit is not necessary. Also, immediately after turning on the power,
If the reflected wave is lost, it is necessary to search for the reflected wave throughout the measurement range, but in that case, there is no need to determine the exact reception time, so there is no need to perform AGC control.

FIG. 3 is a block diagram showing the configuration of one embodiment of the present invention. In this figure, parts corresponding to those in FIG. 1 are given the same reference numerals, and their explanations will be omitted. In FIG. 3, reference numeral 14 denotes an arithmetic control circuit that controls the transmission and reception timing of ultrasonic waves, controls the gain of the VCA 8 during reception, and calculates the output value of the output circuit 18, and is configured using, for example, a microcomputer. This arithmetic control circuit 14 includes an ultrasonic oscillation circuit 2, a DAC (digital-to-analog conversion circuit) 1
5. Transfers necessary signals to and from each of the ADC (analog-to-digital converter) 17 and the output circuit 18.
The DAC 15 converts the signal from the arithmetic control circuit 14 into a VCA
This is a digital-to-analog converter that converts the VCA 8 control signal into a VCA 8 control signal, and its output is supplied to the control terminal of the VCA 8. The output of the VCA 8 controlled by the DAC 15 is supplied to the detection circuit 16. The detection circuit 16 is
This is a circuit that detects the envelope of the received signal amplified by VCA8, and the output of this detection circuit 16 is output from ADC17.
is supplied to The ADC 17 is an analog-to-digital converter that digitizes the output of the detection circuit 16, and is composed of, for example, a 4-bit comparator.
The output circuit 18 converts the output value calculated by the arithmetic control circuit 14 into a standard signal of current or voltage, and in FIG.
This is a circuit included in a part of the .

Next, the operation of the circuit shown in FIG. 3 will be explained with reference to the flowchart shown in FIG. First, when measurement is started, the arithmetic control circuit 14 outputs.
The start pulse 20 causes ultrasonic waves to be emitted into the air in the same manner as in conventional ultrasonic level meters (step S ₁ in FIG. 4). Thereafter, the arithmetic control circuit 14 performs two different controls based on the previous measurements (step S ₂ ). That is, the first
This control is performed when the reception time of the reflected wave is unpredictable (this is immediately after the power is turned on, or when the reflected wave is incorrectly received continuously), and the DAC1 is activated at the same time as the ultrasonic wave is emitted.
Increase the gain of VCA8 over time via 5
TVG control is carried out, and in parallel, the received signal received via the ADC 17 is read and the amplitude is checked (step S ₃ ). If there is a received signal exceeding the preset amplitude, the arithmetic control circuit 14 fixes the gain of the VCA 8 to the gain value at that time (step S ₄ ), and starts the ultrasonic emission operation again (step S _{1 )} . ). If the received signal is smaller than the set amplitude, that is, if the reception signal detection fails, the process does not proceed to step _S4 and proceeds to step _S1.
The same rotation is repeated until the received signal is obtained (omitted in Fig. 4).

Next, the second control is performed when the reception time of the reflected wave is almost known by the first control, or when normal reflected waves are repeatedly received, and the reception time is around the expected reception time based on the previous measurement. Read signals in a narrow range (step _S6 ). Next, by comparing the amplitude of the read signal with the set value, you can check whether reception has failed or not.
Then, it is determined whether the gain of VCA 8 is good or bad (step _S7 ). If the signal detected during TVG control (first control) is not a regular reflected wave, the step
A reception failure is determined in _S7 , but a reception failure may also occur even if normal reception operations are repeated due to changes in the reflective surface or the like. However, reception failures in such cases may occur repeatedly, for example, 5
It never occurs. Therefore, in the case of reception failure, the number of times is checked in the next step _S8 , and if failure continues (for example, five or more times), the process returns to the first control from the sixth time onward. On the other hand, even if reception is successful, if the amplitude fluctuation each time is large, accurate reception time cannot be determined. In this case, the measurement cycle each time is about 100ms, and it is thought that the amplitude of the received signal will not change drastically in continuous measurements.
Determine the gain of VCA 8 (step S ₉ ). Based on the received signal measured in this manner, the arithmetic control circuit 14 calculates and outputs the value of the output to be supplied to the output circuit 18, so that the output value from the output circuit 18 corresponds to the level to be measured. Current or voltage is output (step S ₁₀ ).

In this way, the present invention predicts the time of the next received wave based on the previous received signal.
Since the gain of the VCA 8 is determined, the signal is detected only in a narrow range before and after the expected reception time, and is not affected by randomly generated noise. Furthermore, there is no need to use a filter with a large time constant in the output circuit 18, and the response speed can be increased. Further, in this invention, the arithmetic control circuit 14
Since a microcomputer or the like is used for this purpose, one voltage control amplifier (VCA 8) can fulfill the roles of the TVG amplifier 13 and the AGC amplifier 9 all at once, simplifying the circuit configuration and eliminating the need for adjustments.

According to the present invention, there is provided a variable gain amplifier that amplifies a received signal received by an ultrasonic transducer, a converter that converts the amplitude of an output signal of the variable gain amplifier into digital amplitude data, and the converter. The arithmetic and control circuit that takes in the amplitude data output from the arithmetic and control circuit sequentially analyzes the condition of the received signal, and controls the gain of the variable gain amplifier based on the results. Identifying a legitimate reception signal corresponding to the emitted and returned ultrasonic wave, and after the ultrasonic receiver emits the ultrasonic wave,
Since the measurement result corresponding to the elapsed time until a normal received signal is obtained is output, the following advantages can be obtained.

The influence of noise can be removed.

Faster response time.

The circuit configuration becomes simpler.

There is no need for adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional ultrasonic level meter, FIG. 2 is a waveform diagram to explain the circuit operation of FIG. 1, and FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention. 4 are flowcharts illustrating the operation of an embodiment of the present invention. 5... Transmitter/receiver, 8... VCA (variable gain amplifier circuit), 14... Arithmetic control circuit, 15... Digital-to-analog converter (DAC), 17... Analog-to-digital converter (ADC).

Claims (1)

[Claims] 1. A variable gain amplifier that amplifies a received signal received by an ultrasonic transducer; a converter that converts the amplitude of the output signal of the variable gain amplifier into digital amplitude data; and the converter. While controlling the gain of the variable gain amplifier while taking in the amplitude data output from the an arithmetic control circuit that identifies a regular received signal corresponding to a sound wave and outputs a measurement result corresponding to an elapsed time from when the ultrasonic transducer emits an ultrasonic wave until a regular received signal is obtained; If the reception time at which the next normal reception signal is expected to be obtained cannot be determined, the arithmetic and control circuit transmits the next ultrasound after the ultrasound transducer emits the ultrasound. The amplitude data is captured while increasing the gain of the variable gain amplifier over time until the signal is emitted, and when amplitude data equal to or higher than a predetermined value is obtained, a normal received signal is obtained. Once the gain of the variable gain amplifier is fixed and the reception time is determined, if the reception time can be determined, each time an ultrasonic wave is emitted by the ultrasonic transducer. The method further comprises repeatedly capturing the amplitude data obtained in a certain time period before and after the reception time, controlling the gain of the variable gain amplifier so that the amplitude data becomes constant, and outputting the measurement result. Characteristic signal detection circuit.