WO2021008234A1 - 连续调制超声波精确测距方法、装置及系统 - Google Patents

连续调制超声波精确测距方法、装置及系统 Download PDF

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Publication number
WO2021008234A1
WO2021008234A1 PCT/CN2020/091999 CN2020091999W WO2021008234A1 WO 2021008234 A1 WO2021008234 A1 WO 2021008234A1 CN 2020091999 W CN2020091999 W CN 2020091999W WO 2021008234 A1 WO2021008234 A1 WO 2021008234A1
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Prior art keywords
wave signal
sine wave
signal
amplitude
echo
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PCT/CN2020/091999
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English (en)
French (fr)
Inventor
焦迪
李建国
应继伟
汪邦运
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上海菲伽智能科技有限公司
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Publication of WO2021008234A1 publication Critical patent/WO2021008234A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/523—Details of pulse systems
    • G01S7/526—Receivers
    • G01S7/527—Extracting wanted echo signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/539—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Definitions

  • the present invention relates to the technical field of engineering measurement, in particular to an ultrasonic distance measurement method, device and system.
  • LVDT Linear Variable Differential Transformer
  • the cost of a monitoring system composed of LVDT is relatively high.
  • the use of ultrasonic distance measurement principle to realize displacement monitoring has the advantages of non-contact, large-scale and low-cost.
  • using the principle of ultrasonic distance measurement to achieve displacement monitoring accuracy is usually around 1mm (millimeters), which cannot meet some occasions that require high-precision level settlement information.
  • Ultrasound is essentially an elastic mechanical wave with a vibration frequency greater than or equal to 20KHz (kilohertz), which is mostly generated by piezoelectric ultrasonic transducers.
  • 20KHz kilohertz
  • the ultrasonic transducer When the ultrasonic transducer is excited by an alternating electrical signal within its frequency response range, the ultrasonic transducer mechanically oscillates, causing the gas molecules near the space where the ultrasonic transducer is located to vibrate, thereby changing the space near the ultrasonic transducer.
  • Sound pressure (vibration of gas molecules in the air) produces a series of ultrasonic waves through the transfer of energy between gas molecules.
  • the ultrasonic waves will be reflected on the interface between the two media. Assuming that the propagation rate of ultrasonic waves in a certain medium is known, calculate the time required from the ultrasonic transducer to receive the reflected ultrasonic echo from the ultrasonic transducer to the ultrasonic transducer. The distance between the reflective interfaces.
  • ultrasonic time difference method At present, most distance measurements using ultrasonic waves use the ultrasonic time difference method.
  • several pulse signals are used to excite the ultrasonic transducer to emit ultrasonic waves, and the ultrasonic waves are reflected by the measured object and then receive ultrasonic echo; then the time difference from the point when the ultrasonic wave is sent to the point when the reflected wave is received is calculated, and the time difference The product of the ultrasonic wave velocity is divided by 2 to obtain the distance between the ultrasonic emission point and the measured object.
  • This method is also called "radar measurement”.
  • the ultrasonic transducer starts to oscillate from a static state and emits ultrasonic waves under the excitation of an electric pulse signal, and the establishment of a stable ultrasonic oscillation requires a transition process, as shown in Figure 1a and Figure 1b, where Figure 1a shows the vibration of the ultrasonic vibrator.
  • Figure 1a shows the vibration of the ultrasonic vibrator.
  • Figure 1b is the stop diagram of the ultrasonic vibrator, that is, the ultrasonic transducer needs to go through a transition from zero to steady amplitude oscillation from static activation to output ultrasonic amplitude.
  • the amplitude of the ultrasonic wave changes according to the normal increasing law.
  • the receiving point is a cluster of which the amplitude changes with the ultrasonic transducer from static to steady state. Echo signal that changes with process and measurement range changes. Therefore, the arrival time of the echo measured by the amplitude discrimination method is ambiguous and unstable, and it is difficult to determine the precise time of the echo arrival. This becomes the key factor that the conventional radar measurement method cannot obtain high measurement accuracy, and the pulse signal is used to stimulate the ultrasonic emission.
  • the transducer has transient frequency spectrum characteristics, and the generated ultrasonic amplitude has further uncertainty.
  • the amplitude of the ultrasonic signal propagating in natural space attenuates sharply with the increase in the distance of the measured target. At the same time, it is interfered by the space noise, which will make a superimposed contribution to the echo signal, causing irregular fluctuations of the echo signal, and further increasing Identify the error of the arrival time of the echo signal.
  • the present invention provides a continuously modulated ultrasonic accurate ranging method, device and system, which effectively solves the technical problem of insufficient measurement accuracy in the existing ultrasonic ranging.
  • a continuously modulated ultrasonic accurate ranging method including:
  • the distance to the measured target is calculated according to the starting time point and the arrival time point to complete the ranging.
  • the formed first sine wave signal is used to drive the transmitting ultrasonic transducer to vibrate, that is, a continuous signal with constant amplitude-frequency characteristics is used to excite the transmitting ultrasonic transducer, which effectively avoids intermittent excitation of the ultrasonic transceiver transducer ( Including the instability caused by the transmitting ultrasonic transducer and the receiving ultrasonic transducer; in addition, the moment when the second sine wave signal is amplitude modulated by the first sine wave signal is taken as the starting time point, and according to the echo signal The second sine wave signal determines the arrival time point of the echo signal, which is different from the measurement method of the traditional amplitude discrimination method, and accurately obtains the transmission and reception time point of the ultrasonic signal.
  • zero-crossing trigger is performed on the second sine wave signal after automatic gain control to obtain the arrival time point of the echo signal.
  • the arrival time point of the echo signal is accurately determined by performing a zero-crossing trigger on the second sine wave signal.
  • the step of forming the first sine wave signal and the second sine wave signal is included:
  • Frequency division of the first square wave signal obtains a second square wave signal, and a second sine wave signal is formed according to the second square wave signal.
  • the first sine wave signal and the second sine wave signal are formed according to the same square wave signal, wherein the first sine wave signal is directly formed by the first square wave signal, and the second sine wave signal is formed by the first square wave signal.
  • the signal is formed after frequency division to ensure that the phase difference between the first sine wave signal and the second sine wave signal remains unchanged, and amplitude modulation is performed after the starting point of the ranging timing is reached.
  • the method before using the second sine wave signal to perform amplitude modulation on the first sine wave signal, the method further includes the step of timing according to the first sine wave signal or the second sine wave signal:
  • the starting time point of the ranging timing is determined by counting the digital pulse signals, so as to precisely control the time of amplitude modulation.
  • the starting time of the ranging timing is pre-set by the relevant personnel. It is usually set to a certain moment when the amplitude of the transmitting ultrasonic transducer becomes stable, avoiding the transmitting ultrasonic transducer and reaching a steady state from the initial mechanical oscillation. The transition process between the two can effectively solve the technical problem that the echo signal arrival time cannot be accurately determined in the existing ultrasonic ranging.
  • a bandpass filter with a center frequency as the second sine wave frequency filters the half-wave signal to obtain a second sine wave signal, and completes the demodulation of the echo signal.
  • any continuous time sequence or signal can be expressed as an infinite superposition of sine wave signals of different frequencies.
  • the half-wave signal after precision half-wave rectification is superimposed by sine wave signals of different frequencies, amplitudes and phases, so that after the half-wave signal is obtained, the pure first can be demodulated by filtering.
  • Two sine wave signals greatly improve the accuracy of the measurement at the time of arrival.
  • the preset ratio is overmodulated.
  • the piezoelectric ultrasonic vibrator in the ultrasonic transceiving transducer has the physical properties of large residual vibration inertia, and a certain percentage of overmodulation is performed during the amplitude modulation process to enhance the second signal carried in the echo signal.
  • the modulation ratio of the sine wave signal (increase the modulation degree of the envelope), thereby greatly enhancing the signal-to-noise ratio.
  • the present invention also provides a continuously modulated ultrasonic precision ranging device, which is characterized in that it comprises:
  • the microprocessor unit is used to calculate the distance to the measured target according to the starting time point formed by the starting time forming unit and the arrival time point determined by the echo arrival time processing unit;
  • the first sine wave forming unit is connected to the microprocessor unit and used to form the first sine wave signal
  • the second sine wave forming unit is connected to the microprocessor unit for forming a second sine wave signal
  • Amplitude modulation and driving unit used to use the first sine wave signal formed by the first sine wave forming unit to excite the transmitting ultrasonic transducer to vibrate, and used to use the second sine wave forming unit to form at a starting time of the ranging timing Amplitude modulates the first sine wave signal by the second sine wave signal of
  • the starting time forming unit is used to determine the starting time point of the ranging timing
  • the front receiving unit is used to receive the echo signal reflected by the target
  • An amplitude demodulation unit configured to perform amplitude demodulation on the echo signal received by the pre-receiving unit to obtain a second sine wave signal
  • the echo arrival time processing unit is configured to perform automatic gain control on the second sine wave signal demodulated by the amplitude demodulation unit, and determine the arrival time point of the echo signal according to the second sine wave signal after gain control.
  • the formed first sine wave signal is used to drive the transmitting ultrasonic transducer to vibrate, that is, a continuous signal with constant amplitude-frequency characteristics is used to excite the transmitting ultrasonic transducer, which effectively avoids intermittent excitation of the ultrasonic transceiver transducer ( Including the instability caused by the transmitting ultrasonic transducer and the receiving ultrasonic transducer; in addition, the moment when the second sine wave signal is amplitude modulated by the first sine wave signal is taken as the starting time point, and according to the echo signal The second sine wave signal determines the arrival time point of the echo signal, which is different from the measurement method of the traditional amplitude discrimination method, and accurately obtains the transmission and reception time point of the ultrasonic signal.
  • a zero-crossing trigger is performed on the second sine wave signal after automatic gain control to obtain the arrival time point of the echo signal.
  • the arrival time point of the echo signal is accurately determined by performing a zero-crossing comparison of the second sine wave signal.
  • the microprocessor unit is also used to generate a first square wave signal according to a preset frequency
  • the first sine wave forming unit forms a first sine wave signal according to the first square wave signal
  • the second sine wave forming unit divides the frequency of the first square wave signal to obtain a second square wave signal, and forms a second sine wave signal according to the second square wave signal.
  • the first sine wave signal and the second sine wave signal are formed according to the same square wave signal, wherein the first sine wave signal is directly formed by the first square wave signal, and the second sine wave signal is formed by the first square wave signal.
  • the signal is formed after frequency division to ensure that the phase difference between the first sine wave signal and the second sine wave signal remains unchanged, and amplitude modulation is performed after the starting point of the ranging timing is reached.
  • the initial moment forming unit after zero-crossing comparison of the first sine wave signal or the second sine wave signal to form a digital pulse signal, it is counted; when the count reaches a preset value, it is determined that it has reached The starting time point of the ranging timing; and controlling the amplitude modulation and driving unit to use the second sine wave signal to amplitude modulate the first sine wave signal.
  • the starting time point of the ranging timing is determined by counting the digital pulse signals, so as to precisely control the time of amplitude modulation.
  • the starting time of the ranging timing is pre-set by the relevant personnel. It is usually set to a certain moment when the amplitude of the transmitting ultrasonic transducer becomes stable, avoiding the transmitting ultrasonic transducer and reaching a steady state from the initial mechanical oscillation. The transition process between the two can effectively solve the technical problem that the echo signal arrival time cannot be accurately determined in the existing ultrasonic ranging.
  • the received echo signal is subjected to precise half-wave rectification to obtain a half-wave signal, and the half-wave signal is processed by a band-pass filter whose center frequency is the second sine wave frequency.
  • the second sine wave signal is filtered to complete the demodulation of the echo signal.
  • any continuous time sequence or signal can be expressed as an infinite superposition of sine wave signals of different frequencies.
  • the half-wave signal after precision half-wave rectification is superimposed by sine wave signals of different frequencies, amplitudes and phases, so that after the half-wave signal is obtained, the pure first can be demodulated by filtering.
  • Two sine wave signals greatly improve the accuracy of the measurement at the time of arrival.
  • the preset ratio is overmodulated.
  • the piezoelectric ultrasonic vibrator in the ultrasonic transceiving transducer has the physical properties of large residual vibration inertia, and a certain percentage of overmodulation is performed during the amplitude modulation process to enhance the second signal carried in the echo signal.
  • the modulation ratio of the sine wave signal (increase the modulation degree of the envelope), thereby greatly enhancing the signal-to-noise ratio.
  • the present invention also provides a continuously modulated ultrasonic accurate ranging system, including the above-mentioned continuously modulated ultrasonic accurate ranging device, and further includes:
  • the stainless steel tube cylinder filled with transformer insulating oil, and the flat floating sheet placed on the surface of the transformer insulating oil surface, the continuous modulation ultrasonic precision distance measuring device is placed in the stainless steel tube cylinder at a certain distance above the transformer insulating oil, and the measurement The distance between the floating plate and the flat plate.
  • a novel technical processing method is adopted to provide a low-cost, large measurement range (monitoring height of more than 1 meter) using continuous modulation ultrasonic time difference method to achieve high-precision ranging system, which can be applied to the needs High measurement accuracy and the occasions that require a large range of distance measurement, such as engineering level settlement monitoring that requires high measurement accuracy, it is especially suitable for accurate ranging and positioning of underwater targets, compared to the use of LVDT or capacitive settlement monitoring
  • the method of sensor ranging has an excellent cost performance.
  • Figure 1a is a diagram of the vibration of the ultrasonic vibrator
  • Figure 1b is a diagram of the vibration of the ultrasonic vibrator
  • FIG. 2 is a schematic flowchart of an implementation manner of a continuous modulation ultrasonic accurate ranging method in the present invention
  • Figure 3 is a schematic diagram of the amplitude modulation wave after amplitude modulation in the present invention.
  • Fig. 4 is a block diagram of a continuously modulated ultrasonic accurate ranging device in the present invention.
  • 1-microprocessor unit 2-first sine wave forming unit, 3-second sine wave forming unit, 4-amplitude modulation and driving unit, 5-initial time forming unit, 6-pre-receiving unit, 7- Amplitude demodulation unit, 8-echo arrival time processing unit, 9-power supply conversion unit.
  • Fig. 2 is a schematic diagram of the flow of an implementation of the continuous modulation ultrasonic accurate ranging method.
  • the ultrasonic ranging method includes:
  • S10 uses the first sine wave signal to excite the transmitting ultrasonic transducer to vibrate
  • S20 uses the second sine wave signal to amplitude modulate the first sine wave signal at a preset starting time point of the ranging timing
  • S30 receives the echo signal reflected by the target under test, and demodulates it to obtain a second sine wave signal
  • S40 performs automatic gain control on the second sine wave signal obtained by demodulation, and determines the arrival time point of the echo signal according to the second sine wave signal after gain control;
  • S50 calculates the distance to the measured target according to the starting time point and the arrival time point to complete the ranging.
  • the first sine wave signal (carrier signal) oscillating at a preset frequency starts to excite the transmitting ultrasonic transducer SPS1, and the transmitting ultrasonic transducer SPS1 in a static state is at Driven by the first sine wave signal, it starts to oscillate and gradually transitions to a steady state within a certain period of time, as shown in Figure 1a.
  • the second sine wave signal (beacon signal) is used to amplitude modulate the first sine wave signal, and the amplitude modulated wave signal after amplitude modulation is used to continuously stimulate transmission
  • the amplitude modulated wave signal I obtained after amplitude modulation is shown in Figure 3 (the abscissa is time t, and the ordinate is amplitude A).
  • the ultrasonic signal emitted by the transmitting ultrasonic transducer SPS1 reaches the measured target and is reflected to form an echo signal, which is received by the receiving ultrasonic transducer SPS2.
  • the receiving ultrasonic transducer SPS2 After receiving the echo signal, the receiving ultrasonic transducer SPS2 immediately demodulates it to obtain the second sine wave signal, and then performs automatic gain control on the second sine wave signal obtained by demodulation, and performs automatic gain control on the second sine wave signal obtained by the The second sine wave signal determines the arrival time point tx of the echo signal. Finally, according to the time difference between the arrival time point tx and the starting time point t1, combined with the ultrasonic wave velocity, the precise distance L between the ultrasonic emission point and the measured target reflection point is calculated.
  • the speed C of ultrasonic propagation in free space is related to the ambient temperature T, as shown in equation (1):
  • the distance L between the ultrasonic transmitting point and the measured target is as shown in formula (2):
  • ⁇ tx (tx-t 1 )/2, which is the actual arrival time of the echo signal.
  • the formation process of the first sine wave signal and the second sine wave signal is: after the ranging system is powered on at t0, the microprocessor generates a continuous first square wave signal with a preset frequency and a duty cycle of 50%, and The first square wave signal forms a first sine wave signal. At the same time, the first square wave signal is frequency-divided to obtain a second square wave signal, and a second sine wave signal is formed according to the second square wave signal.
  • the frequency of generating the first square wave signal is specifically the center frequency of the ultrasonic transceiver transducer (including the transmitting ultrasonic transducer SPS1 and the receiving ultrasonic transducer SPS2).
  • the microprocessor forms a 40KHz constant frequency constant amplitude continuous first square wave signal, and then forms a 40KHz first sine wave signal according to the first square wave signal, that is, the frequency of the first sine wave signal also works for the ultrasonic transceiver transducer The center frequency.
  • the frequency division ratio is set according to the actual situation, for example, it can be set to divide by 64, divide by 32, or divide by 24. , Even two-way frequency, etc., there is no specific limitation here.
  • the operating center frequency of the ultrasonic transceiver transducer is 40KHz.
  • the microprocessor After the system is powered on at t0, the microprocessor immediately generates and sends a first square wave signal with a stable frequency of 40KHz and a duty cycle of 50%.
  • the first square wave signal passes through a second-order bandpass filter to obtain a pure The 40KHz constant frequency and constant amplitude first sine wave signal as the carrier signal.
  • the microprocessor sends the first square wave signal of 40KHz to the frequency divider, and the second square wave signal of 625Hz (Hertz) is obtained by dividing the frequency by 64 (using the same 40KHz first square wave signal to obtain the 625Hz signal.
  • the purpose of the second square wave signal is to ensure that the phase difference between the second square wave signal obtained by frequency division and the first square wave signal remains unchanged).
  • the second square wave signal passes through another second-order band pass filter, That is, a pure 625 Hz constant frequency and constant amplitude second sine wave signal as a beacon signal is obtained.
  • the second sine wave signal of 625 Hz is used to amplitude modulate the first sine wave signal of 40KHz, and the amplitude modulation wave signal is controlled to continue to excite the transmitting ultrasonic transducer SPS1 in a balanced driving manner .
  • the starting time point t1 of the ranging timing for amplitude modulation is pre-set according to the vibration state of the transmitting ultrasonic transducer SPS1 in the actual application.
  • the specific value is not limited here, as long as it meets the time period of the transmitting ultrasonic transducer SPS1
  • the amplitude becomes stable.
  • the method for determining the starting time point t 1 of the ranging timing is also not limited. For example, in one embodiment, after the ranging system is powered on at time t 0 , the trigger timer starts timing and reaches the starting point of the ranging timing. after the time point t 1 the second sine wave signal fed to amplitude modulator.
  • the starting time point t 1 of the ranging timing is determined according to the timing of the first sine wave signal or the second sine wave signal, specifically: the first sine wave signal or the second sine wave signal is compared after zero crossing A digital pulse signal is formed, and the obtained digital pulse signal is counted; when the count reaches a preset value, it is determined that the starting time point t 1 of the ranging timing is reached.
  • the frequency divider divides the first square wave signal of 40KHz by 64 to obtain the second square wave signal of 625Hz, and after forming the second sine wave signal according to the second square wave signal, the second sine wave signal It is sent out in two ways, one of which is sent to the input of the integrated analog switch connected to the modem, and the other is processed by a high-speed zero-crossing trigger comparator to form a digital pulse signal (the rising edge corresponds to the zero-crossing time of the second sine wave signal) ). After that, use a four-digit binary counter with an initial output state of zero to count the digital pulse signal.
  • the counter output bit Q2Q1Q0 corresponds to the logical digital value "100"
  • the output bit Q2 is determined by The zero jump becomes 1
  • the jump signal is detected by the microprocessor and the integrated analog switch is controlled to turn on, and the second sine wave signal is sent to the amplitude modulator as the modulation signal to amplitude modulate the first sine wave signal.
  • the transmitting ultrasonic transducer SPS1 After the transmitting ultrasonic transducer SPS1 outputs a 40KHz constant amplitude sine wave of 0.0064s (second), it starts to connect the second sine wave signal to the amplitude modulator, and uses the amplitude modulated amplitude modulation wave signal to excite the transmitting ultrasonic wave. Energy device SPS1. In this example, during 0.0064s before the second sine wave signal is added, the transmitting ultrasonic transducer SPS1 has gone through 256 complete constant amplitude sine wave excitation cycles of 40KHz and has entered a steady state. In other examples, the number of timing digital pulses can be adjusted according to actual conditions.
  • the reflection point of the target is reflected to form an echo signal, and then the echo signal is precision half-wave rectified to obtain a half-wave signal, and the center frequency is the first A band-pass filter with two sine wave frequencies filters the half-wave signal to obtain a second sine wave signal.
  • the amplitude of the second sine wave signal obtained by demodulation is related to the measurement distance. If you directly trigger the zero-crossing of the demodulated second sine wave signal to determine the arrival time of the echo signal, a slight time error will occur at the zero-crossing point. Therefore, in order to achieve high-precision measurement, automatic gain control (AGC) is performed on the second sine wave signal obtained by demodulation to make its amplitude constant and ensure that there is no time error at the zero-crossing point during the zero-crossing trigger.
  • AGC automatic gain control
  • the second sine wave signal with the same amplitude after automatic gain processing is compared with zero-crossing to form a digital pulse signal Vtx and a zero-crossing trigger is performed.
  • the rising edge (time t x ) of the digital pulse signal Vt x is the echo signal Time of arrival.
  • the gain control of the second sine wave signal obtained by demodulation changes linearly and inversely with the gain voltage control voltage, that is, when the measurement distance increases, the amplitude of the second sine wave signal decreases, and the gain voltage control The voltage also decreases, the control gain of the second sine wave signal becomes larger; when the measuring distance decreases, the amplitude of the second sine wave signal increases, and the gain voltage control voltage also increases, then the control gain of the second sine wave signal increases. The control gain is reduced.
  • the system receives the echo signal (at the starting time point t x of the ranging timing, the amplitude modulated wave signal obtained by modulating the first sine wave signal of 40KHz with the second sine wave signal of 625 Hz stimulates the transmitting ultrasonic transducer After SPS1), the differential amplification process is performed by a low-noise high common-mode rejection ratio operational amplifier, so that the echo signal floating relative to the system reference ground is converted to the system reference ground, amplified and suppressed common-mode noise Echo signal; after that, the echo signal is precision half-wave rectified and passed through a fourth-order bandpass filter with a center frequency of 625Hz, and the first sine wave signal of 40KHz is filtered out, and a pure 625Hz second is demodulated Sine wave signal; then the second sine wave signal obtained by demodulation is automatically gain controlled, and the second sine wave signal after gain control is passed through a high-speed zero-crossing comparator to obtain a digital pulse signal Vt x ;
  • the pulse signal
  • the microprocessor in the microprocessor unit When a zero-crossing point appears in the digital pulse signal Vtx, the microprocessor in the microprocessor unit generates an interrupt signal TEND, and the time when the microprocessor responds to the interrupt is the arrival time point of the echo signal t x (corresponding to the rising edge of the zero-crossing point of the digital pulse signal Vtx).
  • the system excites the transmitting ultrasonic transducer SPS1 with the first sine wave signal of 40KHz, and the echo signal received by the receiving ultrasonic transducer after reflection is also of equal amplitude
  • the output of the fourth-order band-pass filter with a center frequency of 625Hz is zero; the output of the echo signal after amplitude modulation through the fourth-order band-pass filter with a center frequency of 625Hz is the second sine of 625Hz
  • the wave signal is based on this to achieve the purpose of this embodiment.
  • the piezoelectric ultrasonic vibrator in the ultrasonic transceiving transducer has the physical property of large residual inertia, therefore, in another embodiment, when the second sine wave signal is used to amplitude modulate the first sine wave signal, the super The preset ratio is adjusted to enhance the modulation ratio of the second sine wave signal carried in the echo signal (increase the modulation degree of the envelope), thereby greatly enhancing the signal-to-noise ratio.
  • the ratio of overshoot can be set according to the ultrasonic transceiver transducer used in the actual application, such as overshoot 1/100, overshoot 2/100 or more.
  • FIG. 4 is a block diagram of the continuous modulation ultrasonic precision ranging device provided by the present invention. It can be seen from the figure that the ultrasonic ranging device includes: a microprocessor unit 1, a first sine wave forming unit 2, a second Sine wave forming unit 3, amplitude modulation and driving unit 4, starting time forming unit 5, pre-receiving unit 6, amplitude demodulating unit 7 and echo arrival time processing unit 8, wherein the output terminal of microprocessor unit 1 Are respectively connected to the input ends of the first sine wave forming unit 2 and the second sine wave forming unit 3, and the output ends of the first sine wave forming unit 2 and the second sine wave forming unit 3 are respectively connected to the input of the amplitude modulation and driving unit 4
  • the output terminal of the second sine wave forming unit 3 is also connected to the input terminal of the starting time forming unit 5, the output terminal of the starting time forming unit 5 is connected to the input terminal of the microprocessor unit 1, and the front receiving unit
  • the output end of 6 is connected to the input end of
  • the microprocessor unit 1 controls the first sine wave forming unit 1 to form a first sine wave signal and output it to the amplitude modulation and driving unit, while controlling the second sine wave
  • the forming unit 2 forms a second sine wave signal.
  • the amplitude modulation and driving unit 4 receives the first sine wave signal, it immediately excites the transmitting ultrasonic transducer SPS1 with the first sine wave signal, and the transmitting ultrasonic transducer SPS1 in a static state is driven by the first sine wave signal. It starts to oscillate and gradually transitions to a steady state within a certain period of time, as shown in Figure 1a.
  • the microprocessor unit 1 controls the second sine wave signal to enter the amplitude modulation and driving unit 4, and then the amplitude modulation and driving unit 4 uses the first
  • the second sine wave signal amplitude modulates the first sine wave signal, and the amplitude modulated wave signal after amplitude modulation is used to continuously excite the transmitting ultrasonic transducer SPS1.
  • the ultrasonic signal emitted by the transmitting ultrasonic transducer SPS1 reaches the target and is reflected to form an echo signal, which is received by the receiving ultrasonic transducer SPS2 in the pre-receiving unit 6.
  • the amplitude demodulation unit 7 After the receiving ultrasonic transducer SPS2 receives the echo signal, the amplitude demodulation unit 7 then demodulates it to obtain the second sine wave signal, and then the echo arrival time processing unit 8 demodulates the second sine wave signal Perform automatic gain control, and determine the arrival time point t x of the echo signal according to the second sine wave signal after gain control. Finally, the microprocessor unit 1 calculates the precise distance L between the ultrasonic emission point and the measured target reflection point according to the time difference between the arrival time point t x and the starting time point t 1 , combined with the ultrasonic wave speed, as (1) and formula (2).
  • the formation process of the first sine wave signal and the second sine wave signal is: after the ranging system is powered on at time t0, the microprocessor unit 1 generates a continuous first square wave signal with a preset frequency and a duty cycle of 50% and sends them separately Into the first sine wave forming unit 2 and the second sine wave forming unit 3, the first sine wave forming unit 2 forms a first sine wave signal according to the first square wave signal and sends it to the amplitude modulation and driving unit 4.
  • the second sine wave forming unit 3 divides the frequency of the first square wave signal to obtain a second square wave signal, and forms a second sine wave signal according to the second square wave signal.
  • the frequency of generating the first square wave signal is specifically the center frequency of the ultrasonic transceiver transducer (including the transmitting ultrasonic transducer SPS1 and the receiving ultrasonic transducer SPS2). Assuming that the center frequency of the ultrasonic transceiver transducer is 40KHz, then The microprocessor forms a 40KHz constant frequency constant amplitude continuous first square wave signal, and then forms a 40KHz first sine wave signal according to the first square wave signal, that is, the frequency of the first sine wave signal also works for the ultrasonic transceiver transducer The center frequency.
  • the frequency division ratio is set according to the actual situation, for example, it can be set to divide by 64, divide by 32, or divide by 24. , Or even two-way frequency, there is no specific limitation here.
  • the working center frequency of the ultrasonic transceiver transducer is 40KHz
  • the microprocessor unit includes a unit for providing the first square wave signal and the initial reset signal for the first sine wave forming unit and the second sine wave forming unit
  • the microprocessor includes a unit for providing the first square wave signal and the initial reset signal for the first sine wave forming unit and the second sine wave forming unit
  • the microprocessor includes a unit for providing the first square wave signal and the initial reset signal for the first sine wave forming unit and the second sine wave forming unit The microprocessor;
  • the first sine wave forming unit includes a second-order band-pass filter for transforming the first square wave signal into a 40KHz first sine wave signal;
  • the second sine wave forming unit includes a A frequency divider for dividing the frequency of the first sine wave signal, and a second-order band pass filter for transforming the second sine wave signal into a second sine wave signal;
  • the amplitude modulation and drive unit includes a frequency divider for amplitude modulation
  • the microprocessor in the microprocessor unit immediately generates and sends a first square wave signal with a stable frequency of 40KHz and a duty cycle of 50%.
  • the first square wave After the signal passes through the second-order band pass filter in the first sine wave forming unit, a pure 40KHz constant frequency and constant amplitude first sine wave signal is obtained as a carrier signal.
  • the microprocessor sends the first square wave signal to the frequency divider in the second sine wave forming unit, which is divided by 64 to obtain a second square wave signal of 625 Hz (Hertz).
  • the second square wave signal passes After the second-order band pass filter in the second sine wave forming unit, a pure 625 Hz constant frequency and constant amplitude second sine wave signal as a beacon signal is obtained.
  • the amplitude modulation integrated circuit in the amplitude modulation and drive unit uses the second sine wave signal of 625Hz to amplitude modulate the first sine wave signal of 40KHz, and controls the amplitude modulation wave through the balance driver The signal continues to excite the transmitting ultrasonic transducer SPS1 in a balanced driving manner.
  • the amplitude modulated wave signal I obtained after amplitude modulation is shown in Figure 3.
  • the starting time point t 1 of the ranging timing for amplitude modulation is pre-set according to the vibration state of the transmitting ultrasonic transducer SPS1 in the actual application.
  • the method for determining the starting time point t 1 of the ranging timing is also not limited.
  • the timer in the starting time forming unit 5 is triggered to start Timing, after reaching the starting time point t 1 of the ranging timing, the second sine wave signal is sent to and controlled by the amplitude modulator to perform amplitude modulation.
  • the starting time forming unit 5 performs timing according to the first sine wave signal or the second sine wave signal to determine the starting time point t 1 of the ranging timing, specifically: the first sine wave signal or the second sine wave signal After the wave signal is compared with zero crossing, a digital pulse signal is formed, and the obtained digital pulse signal is counted; when the count reaches a preset value, it is determined that the starting time point t 1 of the ranging timing is reached.
  • the second sine wave forming unit includes a frequency divider and a second-order bandpass filter, and also includes an integrated analog switch for controlling the on and off of the second sine wave signal;
  • the starting time forming unit includes An integrated comparator used to transform the second sine wave signal into a digital pulse signal and an integrated counter used to count the digital pulse signal;
  • the microprocessor in the microprocessor unit is also used to provide an interrupt for the initial moment formation unit service.
  • the frequency divider in the second sine wave forming unit divides the 40KHz first square wave signal by 64 to obtain a 625Hz second square wave signal, and forms a second sine wave signal according to the second square wave signal.
  • the second sine wave forming unit sends out the second sine wave signal in two ways, one of which is sent to the input end of the integrated analog switch connected to the modem, the other is sent to the starting time forming unit, the second The sine wave signal is subjected to high-speed zero-crossing comparison by the integrated comparator in the initial time forming unit to form a digital pulse signal as the trigger signal of the integrated counter (the rising edge corresponds to the zero-crossing time of the second sine wave signal).
  • the transmitting ultrasonic transducer SPS1 After the transmitting ultrasonic transducer SPS1 outputs a 40KHz constant amplitude sine wave of 0.0064s (second), it starts to connect the second sine wave signal to the amplitude modulator in the amplitude modulation and driving unit 4, and uses the amplitude modulation.
  • the amplitude modulated wave signal excites the transmitting ultrasonic transducer SPS1.
  • the transmitting ultrasonic transducer SPS1 has gone through 256 complete constant amplitude sine wave excitation cycles of 40KHz and has entered a steady state.
  • the amplitude demodulation unit 7 After receiving the echo signal, the amplitude demodulation unit 7 then performs precise half-wave rectification on the echo signal to obtain a half-wave signal, and filters the half-wave signal with a band-pass filter with the center frequency of the second sine wave frequency to obtain the first Two sine wave signals, and the echo arrival time processing unit 8 determines the arrival time point t x of the echo signal according to the second sine wave signal obtained by demodulation.
  • the echo arrival time processing unit 8 performs automatic gain control (AGC) on the second sine wave signal obtained by demodulation to make the amplitude constant and ensure that there is no time error at the zero crossing point when the zero crossing is triggered. .
  • AGC automatic gain control
  • the second sine wave signal with the same amplitude after zero-crossing comparison forms a digital pulse signal Vt x and performs a zero-crossing trigger.
  • the rising edge (time t x ) of the digital pulse signal Vt x is the echo signal The point of arrival.
  • the gain control of the second sine wave signal demodulated by the echo arrival time processing unit 8 varies linearly and inversely with the gain voltage control voltage, that is, when the measurement distance increases, the second sine wave signal
  • the gain voltage control voltage also decreases, the control gain of the second sine wave signal becomes larger; when the measuring distance decreases, the amplitude of the second sine wave signal increases, and the gain voltage control voltage also increases, then The control gain of the second sine wave signal is reduced.
  • the pre-receiving unit includes a receiving ultrasonic transducer SPS2 and an operational amplifier; the amplitude demodulation unit includes a precision half-wave rectifier circuit and a fourth-order band pass filter.
  • the echo arrival time processing unit includes an integrated comparator. Since the integrated comparator constitutes a zero-crossing trigger structure, when there is no signal input, its output state is uncertain, which can easily cause oscillations. Therefore, the integrated comparator is usually designed as a hysteresis mode with a small hysteresis value. That is, the amplitude of the input signal of the integrated comparator will affect the time point when the threshold is crossed. In order to eliminate the fluctuation at the time of passing the threshold point caused by the fluctuation of the signal amplitude, an automatic gain control chip for performing automatic gain control processing on the second sine wave signal obtained by demodulation is provided in the echo arrival time processing unit.
  • the receiving ultrasonic transducer SPS2 in the front receiving unit receives the echo signal (at the starting time point t x of the ranging timing, the second sine wave signal of 625 Hz is used to modulate the first sine wave signal of 40KHz
  • the second sine wave signal of 625 Hz is used to modulate the first sine wave signal of 40KHz
  • the precision half-wave rectifier circuit in the amplitude demodulation unit performs precision half-wave rectification on the echo signal and passes through a fourth-order band-pass filter with a center frequency of 625 Hz , Filter out the 40KHz first sine wave signal and demodulate the pure 625Hz second sine wave signal
  • the automatic gain control chip through the gain control voltage input from the gain control
  • the zero-crossing trigger occurs in the integrated comparator, which is the microcomputer in the microprocessor unit.
  • the processor generates an interrupt signal TEND, and the time when the microprocessor responds to the interrupt is the arrival time point t x of the echo signal.
  • TEND the time when the microprocessor responds to the interrupt is the arrival time point t x of the echo signal.
  • the system excites the transmitting ultrasonic transducer SPS1 with the first sine wave signal of 40KHz, and the echo signal received by the receiving ultrasonic transducer after reflection is also of equal amplitude
  • the output of the fourth-order band-pass filter with a center frequency of 625Hz is zero; the output of the echo signal after amplitude modulation through the fourth-order band-pass filter with a center frequency of 625Hz is the second sine of 625Hz
  • the wave signal is based on this to achieve the purpose of this embodiment.
  • the amplitude modulation and driving unit 4 uses the second sine wave signal to compare the first sine wave signal.
  • the amplitude modulation and driving unit 4 uses the second sine wave signal to compare the first sine wave signal.
  • overshoot the preset ratio.
  • the receiving ultrasonic transducer SPS2 cannot respond to the overmodulated echo signal due to inertia, so the modulation ratio of the second sine wave signal carried in the echo signal is enhanced to a certain extent (Increase the modulation degree of the envelope), thereby greatly enhancing the signal-to-noise ratio.
  • the ratio of overshoot can be set according to the ultrasonic transceiver transducer used in the actual application, such as overshoot 1/100, overshoot 2/100 or more.
  • the microprocessor unit 1 also includes an RS485 communication chip and a temperature sensor chip.
  • the RS485 communication chip is used to realize the communication between the continuously modulated ultrasonic precision ranging device and the outside world, which can achieve a transmission distance of up to 1000m; for the temperature sensor chip To correct the speed of ultrasound.
  • a temperature sensor chip of model DS1624 was used to correct the ultrasonic propagation rate from -10 to 70°C in real time, and the measurement accuracy reached 0.032°C.
  • the present invention also provides a continuously modulated ultrasonic precision ranging system.
  • the ranging system also includes: a stainless steel tube filled with transformer insulating oil, and The flat plate float used to reflect and transmit the ultrasonic signal emitted by the ultrasonic transducer SPS1 on the surface of the transformer insulating oil surface (the diameter of the flat plate float is slightly smaller than the inner diameter of the stainless steel cylinder), and the continuous modulation ultrasonic precision ranging device is placed in the stainless steel cylinder A certain distance above the insulating oil of the transformer in the cylinder, measure the distance to the flat floating piece.
  • the continuously modulated ultrasonic precision ranging device For the setting distance of the continuously modulated ultrasonic precision ranging device, set it according to the position of the ultrasonic transceiver transducer, as long as the blind area of the ultrasonic signal is satisfied.
  • the continuously modulated ultrasonic precision ranging device is set in the transformer insulating oil About 50 cm above, when the transmitting ultrasonic transducer and the receiving ultrasonic transducer are not set in the same position, even no blind spot measurement can be achieved.
  • the high-precision ranging method according to the continuous modulation ultrasonic time difference method can achieve a measurement range of 1 meter and above, and a measurement accuracy of 0.1 mm (millimeter), which can be applied to the need for high measurement accuracy and a large range of distance measurement. It is especially suitable for accurate ranging and positioning of underwater targets.

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Abstract

一种连续调制超声波精确测距方法、装置及系统，方法包括：使用第一正弦波信号激励发射超声波换能器振动（S10）；在预先设定的测距计时起始时刻点使用第二正弦波信号对第一正弦波信号进行振幅调制（S20）；接收被测目标反射的回波信号，并对其解调得到第二正弦波信号（S30）；对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点（S40）；根据起始时刻点和到达时刻点计算与被测目标之间的距离（S50）。其以区别于传统振幅甄别法的测量方式，精确得到超声波信号的收发时间点，尤其对解调得到的第二正弦波信号进行自动增益控制，进一步提高到达时刻点的测量精度，进而精确的得到与被测目标间的距离。

Description

连续调制超声波精确测距方法、装置及系统 技术领域
本发明涉及工程测量技术领域，尤其涉及一种超声波测距方法、装置及系统。
背景技术
在工程建设领域中，通常需要对建筑物的沉降实施监测，而沉降监测的本质是对建筑物下沉位移的监测。目前有许多方法可实现对位移的精确监测，例如采用LVDT((Linear Variable Differential Transformer，线性可变差动变压器)传感器实现高精度的位移监测。但是，采用LVDT方式构成的监测系统成本较高，尤其在大量程沉降监测场合，成本将急剧上升。与现有的大多数水准沉降监测方法相比，利用超声测距原理实现位移监测具有非接触、大量程、廉价的优点。然而，鉴于超声波的物理性质，利用超声测距原理实现位移监测的精度通常在1mm(毫米)左右，并不能满足某些需要获得高精确水准沉降信息的场合。
要提高超声波测距的精度，需从超声波的物理机理入手，寻找影响测量精度的内在原因，以提出解决方法。超声波本质上是一种振动频率大于或等于20KHz(千赫兹)的弹性机械波，当前大多使用压电式超声换能器来产生。当超声换能器被施以其频响范围内的交变电信号激励时，超声换能器发生机械振荡，引起超声换能器所处空间附近的气体分子振动，从而改变所处空间附近的声压(空气中气体分子振动)，通过气体分子间能量的传递，产生一系列的超声波。根据超声波从一种传播介质入射到另一种介质时传输速率会发生变化的物理特性，超声波将在这两种介质的分界面上发生反射。假定超声波在某种介质中的传播速率是已知的，计算从超声波换能器发出超声波到超声波换能器接收到被反射回来的超声回波所需的时间，即可获得超声换能器与反射界面间的距离。
目前，利用超声波进行距离测量大多采用超声波时差法。在该方法中，以数个脉冲信号激励超声换能器发射超声波，超声波经被测物反射后接收超声回波；进而计算超声波发出时刻点到反射波被接收到时刻点的时间差，将该时间差与超声波波速的乘积被2除便得到超声发射点与被测物间的距离，这种方式亦被称为“雷达测量法”。众所周知，超声波换能器在电脉冲信号的激励下由静态开始振荡并发射超声波，而超声波稳定振荡的建立需要一个过渡过程，如图1a和图1b所示，其中，图1a为超声振子起振图(横轴为时间t，纵轴为振幅A)，图 1b为超声振子停振图，即超声波换能器由静态启动到输出超声波的振幅需要经历一段由零到稳幅振荡的过渡过程。在该过程中，超声波的振幅按照正态增幅规律进行变化，也就是说，虽然超声激励时刻是已知的，但接收点得到是一簇其振幅随超声波换能器由静止到稳态的过渡过程及测量量程变化而变化的回波信号。以此，使用振幅甄别法测定的回波到达时刻是模糊且不稳定的，难以确定回波到达的精确时刻，成为常规雷达测量法无法得到高测量精度的关键因素，且使用脉冲信号激励超声发射换能器具有瞬变频谱特性，产生的超声波振幅具有进一步的不确定性。另外，在自然空间传播的超声波信号振幅随被测目标距离的增加急剧衰减，同时受到空间噪声的干扰，会对回波信号产生叠加贡献，引起回波信号的无规律涨落，进一步增大了甄别回波信号到达时间点的误差。
发明内容
针对上述现有技术的不足，本发明提供了一种连续调制超声波精确测距方法、装置及系统，有效解决了现有超声波测距中测量精度不够的技术问题。
为了实现上述目的，本发明通过以下技术方案实现：
一种连续调制超声波精确测距方法，包括：
使用第一正弦波信号激励发射超声波换能器振动；
在预先设定的测距计时起始时刻点使用第二正弦波信号对第一正弦波信号进行振幅调制；
接收被测目标反射的回波信号，并对其解调得到第二正弦波信号；
对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点；
根据所述起始时刻点和到达时刻点计算与被测目标之间的距离，完成测距。
在本技术方案中，使用形成的第一正弦波信号驱动发射超声波换能器振动，即采用了幅频特性恒定的连续信号激励发射超声波换能器，有效避免了断续激励超声波收发换能器(包括发射超声波换能器和接收超声波换能器)带来的不稳定性；另外，将第二正弦波信号对第一正弦波信号振幅调制的时刻作为起始时刻点，并根据回波信号中的第二正弦波信号确定回波信号的到达时刻点，以区别于传统振幅甄别法的测量方式，精确得到了超声波信号的收发时间点。再有，在确定回波信号到达时刻点之前，对解调得到的第二正弦波信号进行自动增益控制，将第二正弦波信号的振幅调整为一致，使得回波信号中第二正弦波信号的振幅不会受到测量距离的变化及空间噪声的影响，进一步提高了回波信号到达时刻点的确定精度。
进一步优选地，在根据增益控制后的第二正弦波信号确定回波信号的到达时刻点中：对 自动增益控制后的第二正弦波信号进行过零触发，得到回波信号的到达时刻点。
在本技术方案中，通过对第二正弦波信号进行过零触发的方式精确确定回波信号的到达时刻点。
进一步优选地，在使用第一正弦波信号激励发射超声波换能器振动之前，包括形成第一正弦波信号和第二正弦波信号的步骤：
根据预设频率生成第一方波信号，根据所述第一方波信号形成第一正弦波信号；
对所述第一方波信号分频得到第二方波信号，根据所述第二方波信号形成第二正弦波信号。
在本技术方案中，第一正弦波信号和第二正弦波信号根据同一方波信号形成，其中，第一正弦波信号由第一方波信号直接形成，第二正弦波信号由第一方波信号分频后形成，以确保第一正弦波信号和第二正弦波信号间的相位差保持不变，在测距计时起始时刻点达到后进行振幅调制。
进一步优选地，使用第二正弦波信号对第一正弦波信号进行振幅调制之前，还包括根据第一正弦波信号或第二正弦波信号计时的步骤：
对第一正弦波信号或第二正弦波信号进行过零比较形成数字脉冲信号；
对数字脉冲信号进行计数；
当计数达到预设值，判定到达测距计时起始时刻点。
在本技术方案中，通过对数字脉冲信号计数方式确定测距计时起始时刻点，以精确地控制振幅调制的时刻。这里的测距计时起始时刻点由相关人员预先设定，通常设定为发射超声波换能器的振幅趋于稳定的某一时刻，避开发射超声波换能器由起始机械振荡达到稳态之间的过渡过程，进而有效解决现有超声波测距中不能准确确定回波信号到达时刻的技术问题。
进一步优选地，在对所述回波信号进行振幅解调得到第二正弦波信号中：
对所述回波信号进行精密半波整流得到半波信号；
以中心频率为第二正弦波频率的带通滤波器对所述半波信号进行过滤得到第二正弦波信号，完成对所述回波信号的解调。
由傅立叶变换原理可知，任何连续的时序或信号，都可以表示为不同频率的正弦波信号的无限叠加。在本技术方案中，精密半波整流后的半波信号由不同频率、振幅和相位的正弦波信号叠加而成，是以得到半波信号之后，通过滤波的方法即可解调出纯净的第二正弦波信号，大大提高了到达时刻点测量的精度。
进一步优选地，在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比 例。
在本技术方案中，由超声波收发换能器中压电超声振子具有较大余振惯性的物理性质，在振幅调制的过程中进行一定比例的超调，以增强回波信号中携带的第二正弦波信号的调制比例(增加包络线的调制度)，从而大大增强了信噪比。
本发明还提供了一种连续调制超声波精确测距装置，其特征在于，包括：
微处理器单元，用于根据起始时刻形成单元形成的起始时刻点和回波到达时刻处理单元确定的到达时刻点计算与被测目标之间的距离；
第一正弦波形成单元，与微处理器单元连接，用于形成第一正弦波信号；
第二正弦波形成单元，与微处理器单元连接，用于形成第二正弦波信号；
振幅调制及驱动单元，用于使用第一正弦波形成单元形成的第一正弦波信号激励发射超声波换能器振动，及用于在一测距计时起始时刻点使用第二正弦波形成单元形成的第二正弦波信号对第一正弦波信号进行振幅调制；
起始时刻形成单元，用于确定作为测距计时起始时刻点；
前置接收单元，用于接收测目标反射的回波信号；
振幅解调单元，用于对前置接收单元接收的回波信号进行振幅解调得到第二正弦波信号；
回波到达时刻处理单元，用于振幅解调单元解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点。
在本技术方案中，使用形成的第一正弦波信号驱动发射超声波换能器振动，即采用了幅频特性恒定的连续信号激励发射超声波换能器，有效避免了断续激励超声波收发换能器(包括发射超声波换能器和接收超声波换能器)带来的不稳定性；另外，将第二正弦波信号对第一正弦波信号振幅调制的时刻作为起始时刻点，并根据回波信号中的第二正弦波信号确定回波信号的到达时刻点，以区别于传统振幅甄别法的测量方式，精确得到了超声波信号的收发时间点。再有，在确定回波信号到达时刻点之前，对解调得到的第二正弦波信号进行自动增益控制，将第二正弦波信号的振幅调整为一致，使得回波信号中第二正弦波信号的振幅不会受到测量距离的变化及空间噪声的影响，进一步提高了回波信号到达时刻点的确定精度。
进一步优选地，在回波到达时刻处理单元中：对自动增益控制后的第二正弦波信号进行过零触发，得到回波信号的到达时刻点。
在本技术方案中，通过对第二正弦波信号进行过零比较的方式精确确定回波信号的到达时刻点。
进一步优选地，所述微处理器单元还用于根据预设频率生成第一方波信号；
所述第一正弦波形成单元根据所述第一方波信号形成第一正弦波信号；
所述第二正弦波形成单元对所述第一方波信号分频得到第二方波信号，并根据所述第二方波信号形成第二正弦波信号。
在本技术方案中，第一正弦波信号和第二正弦波信号根据同一方波信号形成，其中，第一正弦波信号由第一方波信号直接形成，第二正弦波信号由第一方波信号分频后形成，以确保第一正弦波信号和第二正弦波信号间的相位差保持不变，在测距计时起始时刻点达到后进行振幅调制。
进一步优选地，在所述起始时刻形成单元中，对第一正弦波信号或第二正弦波信号进行过零比较形成数字脉冲信号后，对其进行计数；当计数达到预设值，判定到达测距计时起始时刻点；并控制振幅调制及驱动单元使用第二正弦波信号对第一正弦波信号进行振幅调制。
在本技术方案中，通过对数字脉冲信号计数方式确定测距计时起始时刻点，以精确地控制振幅调制的时刻。这里的测距计时起始时刻点由相关人员预先设定，通常设定为发射超声波换能器的振幅趋于稳定的某一时刻，避开发射超声波换能器由起始机械振荡达到稳态之间的过渡过程，进而有效解决现有超声波测距中不能准确确定回波信号到达时刻的技术问题。
进一步优选地，在振幅解调单元中，对接收到的回波信号进行精密半波整流得到半波信号，并以中心频率为第二正弦波频率的带通滤波器对所述半波信号进行过滤得到第二正弦波信号，完成对所述回波信号的解调。
由傅立叶变换原理可知，任何连续的时序或信号，都可以表示为不同频率的正弦波信号的无限叠加。在本技术方案中，精密半波整流后的半波信号由不同频率、振幅和相位的正弦波信号叠加而成，是以得到半波信号之后，通过滤波的方法即可解调出纯净的第二正弦波信号，大大提高了到达时刻点测量的精度。
进一步优选地，振幅调制及驱动单元在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比例。
在本技术方案中，由超声波收发换能器中压电超声振子具有较大余振惯性的物理性质，在振幅调制的过程中进行一定比例的超调，以增强回波信号中携带的第二正弦波信号的调制比例(增加包络线的调制度)，从而大大增强了信噪比。
本发明还提供了一种连续调制超声波精确测距系统，包括上述连续调制超声波精确测距装置，还包括：
填充有变压器绝缘油的不锈钢管缸筒，及置于所述变压器绝缘油面表面的平板浮片，所述连续调制超声波精确测距装置置于不锈钢管缸筒内变压器绝缘油上方一定距离，测量与平 板浮片之间的距离。
在本技术方案中，采用新颖的技术处理方法，提供了一种成本低廉、测量量程大(监测高度达1米以上)的使用连续调制超声波时差法实现高精度测距的系统，能够适用于需要较高测量精度及需要大量程测定距离的场合，如对测量精度要求较高的工程水准沉降监测，明尤其适用于水下目标的精确测距及定位，相比于使用LVDT或电容式沉降监测传感器进行测距的方法具有极佳的性价比。
附图说明
结合附图，并通过参考下面的详细描述，将会更容易地对本发明有更完整的理解并且更容易地理解其伴随的优点和特征，其中：
图1a为超声振子起振图，图1b为超声振子停振图；
图2为本发明中连续调制超声波精确测距方法一种实施方式流程示意图；
图3为本发明中振幅调制后的调幅波示意图；
图4为本发明中连续调制超声波精确测距装置框图。
附图标记：
1-微处理器单元，2-第一正弦波形成单元，3-第二正弦波形成单元，4-振幅调制及驱动单元，5-起始时刻形成单元，6-前置接收单元，7-振幅解调单元，8-回波到达时刻处理单元，9-供电电源变换单元。
具体实施方式
为使本发明的内容更加清楚易懂，以下结合说明书附图，对本发明的内容作进一步说明。当然本发明并不局限于该具体实施例，本领域内的技术人员所熟知的一般替换也涵盖在本发明的保护范围内。
如图2所示为连续调制超声波精确测距方法一种实施方式流程示意图，从图中可以看出，在该超声波测距方法中包括：
S10使用第一正弦波信号激励发射超声波换能器振动；
S20在预先设定的测距计时起始时刻点使用第二正弦波信号对第一正弦波信号进行振幅调制；
S30接收被测目标反射的回波信号，并对其解调得到第二正弦波信号；
S40对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波 信号确定回波信号的到达时刻点；
S50根据起始时刻点和到达时刻点计算与被测目标之间的距离，完成测距。
在本实施方式中，测距系统在t0时刻通电后，开始以预设频率振荡的第一正弦波信号(载波信号)激励发射超声波换能器SPS1，处于静止状态的发射超声波换能器SPS1在该第一正弦波信号的驱动下开始振荡，并在一定时间内逐步过渡到稳态，如图1a所示。之后，在一预先设定的测距计时起始时刻点t1，使用第二正弦波信号(信标信号)对第一正弦波信号进行振幅调制，并使用振幅调制后的调幅波信号持续激励发射超声波换能器SPS1，振幅调制后得到的调幅波信号I如图3所示(横坐标为时间t，纵坐标为振幅A)。发射超声波换能器SPS1发射的超声波信号到达被测目标后进行反射形成回波信号并被接收超声波换能器SPS2接收。接收超声波换能器SPS2接收到回波信号之后，随即对其进行解调得到其中的第二正弦波信号，之后对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点tx。最后，根据到达时刻点tx和起始时刻点t1间的时间差值，结合超声波波速，计算得到精确的超声波发射点与被测目标反射点间的距离L。
具体，超声波在自由空间传播的速度C与环境温度T有关，如式(1)：
C＝331.4*(1+T/273) 1/2                (1)
当发射超声波换能器SPS1和接收超声波换能器SPS2设置于同一水平位置，超声波发射点与被测目标之间的距离L如式(2)：
L＝(C*Δt x)/2                       (2)
其中，Δtx＝(tx-t 1)/2，为回波信号实际达到时间。
第一正弦波信号和第二正弦波信号的形成过程为：测距系统在t0时刻通电后，微处理器生成预设频率和占空比为50％的连续第一方波信号，并根据该第一方波信号形成第一正弦波信号。与此同时，对第一方波信号进行分频得到第二方波信号，并根据第二方波信号形成第二正弦波信号。生成第一方波信号的频率具体为超声波收发换能器(包括发射超声波换能器SPS1和接收超声波换能器SPS2)工作的中心频率，假定超声波收发换能器工作的中心频率为40KHz，则微处理器形成40KHz恒频恒幅连续的第一方波信号，进而根据该第一方波信号形成40KHz的第一正弦波信号，即第一正弦波信号的频率也为超声波收发换能器工作的中心频率。在对第一方波信号进行分频得到第二方波信号中，分频比根据实际情况进行设定，如，可以设定为64分频、也可以设定为32分频、24分频，甚至是二分频等，这里不做具体限定。
在一实例中，超声波收发换能器工作的中心频率为40KHz。系统在t0时刻通电后，微处理器随即生成40KHz频率稳定、占空比为50％的第一方波信号并送出，该第一方波信号通过 一二阶带通滤波器后，获得纯净的作为载波信号的40KHz恒频恒幅第一正弦波信号。与此同时，微处理器将40KHz的第一方波信号送入分频器，经64分频得到625Hz(赫兹)的第二方波信号(使用同一40KHz第一方波信号分频得到625Hz的第二方波信号的目的是确保分频所得的第二方波信号与第一方波信号间的相位差保持不变)，该第二方波信号通过另一二阶带通滤波器后，即获得纯净的作为信标信号的625Hz恒频恒幅第二正弦波信号。测距计时起始时刻点t 1到达后，使用625Hz的第二正弦波信号对40KHz的第一正弦波信号进行幅度调制，并控制调幅波信号以平衡驱动的方式继续激励发射超声波换能器SPS1。
进行振幅调制的测距计时起始时刻点t1根据实际应用中发射超声波换能器SPS1的振动状态进行预先设定，这里对其具体值不做限定，只要满足发射超声波换能器SPS1经历时间段Δt＝t1-t0的振动后振幅趋于稳定即可。此外，对测距计时起始时刻点t 1的确定方式同样不做限定，如，在一实施方式中，在测距系统t 0时刻通电后，触发计时器开始计时，达到测距计时起始时刻点t 1后将第二正弦波信号送入振幅调制器。在另一实施方式中，根据第一正弦波信号或第二正弦波信号计时确定测距计时起始时刻点t 1，具体：对第一正弦波信号或第二正弦波信号进行过零比较后形成数字脉冲信号，并对得到的数字脉冲信号进行计数；当计数达到预设值，判定到达测距计时起始时刻点t 1。
在一实例中，分频器对40KHz的第一方波信号64分频得到625Hz的第二方波信号，并根据该第二方波信号形成第二正弦波信号后，将第二正弦波信号分两路送出，其中，一路被送至与调制解调器连接的集成模拟开关的输入端，另一路经高速过零触发比较器处理后形成数字脉冲信号(上升沿对应第二正弦波信号过零点的时刻)。之后，使用初始输出状态为零的四位二进制计数器对该数字脉冲信号进行计数，当计数到第4个数字脉冲信号时，计数器输出位Q2Q1Q0对应的逻辑数字值为“100”，输出位Q2由零跳变为1，该跳变信号被微处理器检测到并控制集成模拟开关开通，将第二正弦波信号送入振幅调制器作为调制信号对第一正弦波信号进行振幅调制，同时将该时刻作为测量的起始时刻点t1。这一过程中，振幅调制前等待的时间段Δt＝t 1-t 0可由式(3)精确得出：
Δt＝t 1-t 0＝1×64×4/4000＝0.0064s             (3)
也就是说，发射超声波换能器SPS1输出0.0064s(秒)的40KHz等幅正弦波后，开始向振幅调制器接入第二正弦波信号，并使用振幅调制后的调幅波信号激发发射超声换能器SPS1。在该实例中，第二正弦波信号加入前的0.0064s期间，发射超声换能器SPS1已经历了256个40KHz的完整等幅正弦波激励周期，已进入稳态。在其他实例中，计时数字脉冲的数量可以根据实际情况进行调整。
发射超声波换能器SPS1发射的超声波信号到达被测目标后，被被测目标的反射点反射形成回波信号，随即对回波信号进行精密半波整流得到半波信号，并以中心频率为第二正弦波频率的带通滤波器对半波信号进行过滤得到第二正弦波信号。
由于超声波信号在大气环境下传播时，振幅会随着传输距离的增加而迅速衰减，即解调得到的第二正弦波信号的振幅与测量距离相关。若直接对解调后的第二正弦波信号作过零触发来确定回波信号到达时刻点，在过零点将产生微小的时间误差。是以，为了实现高精度测量，对解调而得的第二正弦波信号进行自动增益控制(AGC)，使之振幅恒定，确保过零触发时过零点无时间误差。之后，将自动增益处理后振幅一致的第二正弦波信号进行过零比较形成数字脉冲信号Vtx并进行过零触发，该数字脉冲信号Vt x的上升沿(时刻t x)即为回波信号的到达时刻点。在一定电压幅度范围内，对解调得到的第二正弦波信号的增益控制随增益压控电压呈线性反比变化，即，当测量距离增加，第二正弦波信号的幅度减小，增益压控电压亦减小，则对第二正弦波信号的控制增益变大；当测量距离减小，第二正弦波信号的幅度增大，增益压控电压亦增大，则对第二正弦波信号的控制增益减小。
在一实例中，系统接收到回波信号(在测距计时起始时刻点t x，使用625Hz的第二正弦波信号调制40KHz的第一正弦波信号得到的调幅波信号激励发射超声波换能器SPS1)后，首先经低噪声高共模抑制比运算放大器进行差分放大处理，使得相对于系统参考地浮空的回波信号被转换为相对于系统参考地、被放大及抑除了共模噪声的回波信号；之后对该回波信号进行精密半波整流并通过中心频率为625Hz的四阶带通滤波器，将其中40KHz的第一正弦波信号滤除，解调出纯净的625Hz的第二正弦波信号；之后将解调得到的第二正弦波信号进行自动增益控制，再将增益控制后的第二正弦波信号经过高速过零比较器，得到数字脉冲信号Vt x；之后，对该数字脉冲信号Vtx实施过零触发，当数字脉冲信号Vtx中出现过零点时，微处理器单元中的微处理器产生中断信号TEND，微处理器响应该中断的时刻即为回波信号的到达时刻点t x(对应数字脉冲信号Vtx过零点的上升沿)。可以理解，在Δt＝t 1-t 0时间段，系统以40KHz的第一正弦波信号激励发射超声换能器SPS1，经反射后被接收超声换能器接收到的回波信号同样是等幅波，经中心频率为625Hz的四阶带通滤波器后的输出是零；而经振幅调幅后的回波信号经中心频率为625Hz的四阶带通滤波器后的输出是625Hz的第二正弦波信号，基于此实现本实施方式的目的。
由于超声波收发换能器中压电超声振子具有较大余振惯性的物理性质，是以，在另一实施方式中，在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比例，以增强回波信号中携带的第二正弦波信号的调制比例(增加包络线的调制度)，从而大大增强了信噪 比。超调的比例可以根据实际应用中使用的超声波收发换能器进行设定，如，超调1/100、超调2/100甚至更多。
如图4所示为本发明提供的连续调制超声波精确测距装置框图，从图中看出，在该超声波测距装置中包括：微处理器单元1、第一正弦波形成单元2、第二正弦波形成单元3、振幅调制及驱动单元4、起始时刻形成单元5、前置接收单元6、振幅解调单元7及回波到达时刻处理单元8，其中，微处理器单元1的输出端分别与第一正弦波形成单元2和第二正弦波形成单元3的输入端连接，第一正弦波形成单元2及第二正弦波形成单元3的输出端分别与振幅调制及驱动单元4的输入端连接，第二正弦波形成单元3的输出端还与起始时刻形成单元5的输入端连接，起始时刻形成单元5的输出端与微处理器单元1的输入端连接，前置接收单元6的输出端与振幅解调单元7的输入端连接，振幅解调单元7的输出端与回波到达时刻处理单元8的输入端连接，回波到达时刻处理单元8的输出端与微处理器单元1的输入端连接。另外，该超声波测距装置中还包括为各功能单元提供相应电源的供电电源变换单元9，可提供±12V电源和±5V电源，保证连续调制超声波测距系统的正常运行。
在本实施方式中，测距系统在t 0时刻通电后，微处理器单元1控制第一正弦波形成单元1形成第一正弦波信号并输出至振幅调制及驱动单元，同时控制第二正弦波形成单元2形成第二正弦波信号。振幅调制及驱动单元4接收到第一正弦波信号之后，随即以该第一正弦波信号激励发射超声波换能器SPS1，处于静止状态的发射超声波换能器SPS1在该第一正弦波信号的驱动下开始振荡，并在一定时间内逐步过渡到稳态，如图1a所示。起始时刻形成单元5确定预先设定的测距计时起始时刻点达到后，微处理器单元1随即控制第二正弦波信号进入振幅调制及驱动单元4，进而振幅调制及驱动单元4使用第二正弦波信号对第一正弦波信号进行振幅调制，并使用振幅调制后的调幅波信号持续激励发射超声波换能器SPS1。发射超声波换能器SPS1发射的超声波信号到达被测目标后进行反射形成回波信号并被前置接收单元6中的接收超声波换能器SPS2接收。接收超声波换能器SPS2接收到回波信号之后，振幅解调单元7随即对其进行解调得到第二正弦波信号，之后回波到达时刻处理单元8根据对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点t x。最后，微处理器单元1根据到达时刻点t x和起始时刻点t 1间的时间差值，结合超声波波速，计算得到精确的超声波发射点与被测目标反射点间的距离L，如式(1)和式(2)。
第一正弦波信号和第二正弦波信号的形成过程为：测距系统t0时刻通电后，微处理器单元1生成预设频率和占空比为50％的连续第一方波信号并分别送入第一正弦波形成单元2和第二正弦波形成单元3，第一正弦波形成单元2根据该第一方波信号形成第一正弦波信号并 送入振幅调制及驱动单元4。与此同时，第二正弦波形成单元3对第一方波信号进行分频得到第二方波信号，并根据第二方波信号形成第二正弦波信号。生成第一方波信号的频率具体为超声波收发换能器(包括发射超声波换能器SPS1和接收超声波换能器SPS2)工作的中心频率，假定超声波收发换能器工作的中心频率为40KHz，则微处理器形成40KHz恒频恒幅连续的第一方波信号，进而根据该第一方波信号形成40KHz的第一正弦波信号，即第一正弦波信号的频率也为超声波收发换能器工作的中心频率。在对第一方波信号进行分频得到第二方波信号中，分频比根据实际情况进行设定，如，可以设定为64分频、也可以设定为32分频、24分频，甚至是二分频，这里不做具体限定。
在一实例中，超声波收发换能器工作的中心频率为40KHz，微处理器单元中包括一用于为第一正弦波形成单元和第二正弦波形成单元提供第一方波信号及初始复位信号的微处理器；第一正弦波形成单元中包括一用于将第一方波信号变换为40KHz第一正弦波信号的二阶带通滤波器；第二正弦波形成单元中包括一用于对第一正弦波信号进行分频的分频器，及一用于将第二正弦波信号变换为第二正弦波信号的二阶带通滤波器；振幅调制及驱动单元中包括用于进行振幅调制的振幅调制集成电路、用于将振幅调制集成电路送出的振幅调制信号变换为平衡输出驱动模式的平衡驱动器及发射超声换能器SPS1。
在工作过程中，测距系统在t 0时刻通电后，微处理器单元中的微处理器随即生成40KHz频率稳定、占空比为50％的第一方波信号并送出，该第一方波信号通过第一正弦波形成单元中的二阶带通滤波器后，获得纯净的作为载波信号的40KHz恒频恒幅第一正弦波信号。与此同时，微处理器将第一方波信号送入第二正弦波形成单元中的分频器，经64分频得到625Hz(赫兹)的第二方波信号，该第二方波信号通过第二正弦波形成单元中的二阶带通滤波器后，即获得纯净的作为信标信号的625Hz恒频恒幅第二正弦波信号。当测距计时起始时刻点t1到达后，振幅调制及驱动单元中的振幅调制集成电路使用625Hz的第二正弦波信号对40KHz的第一正弦波信号进行幅度调制，并通过平衡驱动器控制调幅波信号以平衡驱动的方式继续激励发射超声波换能器SPS1，具体，振幅调制后得到的调幅波信号I如图3所示。
进行振幅调制的测距计时起始时刻点t 1根据实际应用中发射超声波换能器SPS1的振动状态进行预先设定，这里对其具体值不做限定，只要满足发射超声波换能器SPS1经历时间段Δt＝t 1-t 0的振动后振幅趋于稳定即可。此外，对于测距计时起始时刻点t 1的确定方式同样不做限定，如，在一实施方式中，在测距系统t 0时刻通电后，触发起始时刻形成单元5中的计时器开始计时，达到测距计时起始时刻点t 1后将第二正弦波信号送入并控制振幅调制器进行振幅调制。在另一实施方式中，起始时刻形成单元5根据第一正弦波信号或第二正弦波信号进 行计时确定测距计时起始时刻点t 1，具体：对第一正弦波信号或第二正弦波信号进行过零比较后形成数字脉冲信号，并对得到的数字脉冲信号进行计数；当计数达到预设值，判定到达测距计时起始时刻点t 1。
在一实例中，第二正弦波形成单元中包括分频器和二阶带通滤波器之外，还包括用于控制第二正弦波信号通断的集成模拟开关；起始时刻形成单元中包括用于将第二正弦波信号变换为数字脉冲信号的集成比较器及用于对数字脉冲信号进行计数的集成计数器；微处理器单元中的微处理器还用于为起始时刻形成单元提供中断服务。
在工作过程中，第二正弦波形成单元中的分频器对40KHz的第一方波信号64分频得到625Hz的第二方波信号，并根据该第二方波信号形成第二正弦波信号后，第二正弦波形成单元将该第二正弦波信号分两路送出，其中，一路被送至与调制解调器连接的集成模拟开关的输入端，另一路被送至起始时刻形成单元，第二正弦波信号经起始时刻形成单元中的集成比较器进行高速过零比较后形成数字脉冲信号，作为集成计数器的触发信号(上升沿对应第二正弦波信号过零点的时刻)。之后，使用初始输出状态为零的集成计数器(四位二进制计数器)对该数字脉冲信号进行计数，当其输出位Q 2Q 1Q 0对应逻辑数字值“100”时，输出位Q 2由零跳变为1，微处理器单元中的微处理器产生中断，并控制集成模拟开关开通，将第二正弦波信号被送入振幅调制及驱动单元作为调制信号对第一正弦波信号进行振幅调制，同时将微处理器响应中断的时间作为测量的起始时刻点t 1。这一过程中，振幅调制前等待的时间段Δt＝t 1-t 0可由式(3)精确得出。也就是说，发射超声波换能器SPS1输出0.0064s(秒)的40KHz等幅正弦波后，开始向振幅调制及驱动单元4中的振幅调制器接入第二正弦波信号，并使用振幅调制后的调幅波信号激发发射超声换能器SPS1。在该实例中，第二正弦波信号加入前的0.0064s期间，发射超声换能器SPS1已经历了256个40KHz的完整等幅正弦波激励周期，已进入稳态。
发射超声波换能器SPS1发射的超声波信号到达被测目标后，被被测目标的反射点反射形成回波信号，最终被前置接收单元6中的接收超声波换能器SPS2接收。接收到回波信号之后，振幅解调单元7随即对回波信号进行精密半波整流得到半波信号，并以中心频率为第二正弦波频率的带通滤波器对半波信号进行过滤得到第二正弦波信号，进而回波到达时刻处理单元8根据解调得到的第二正弦波信号确定回波信号的到达时刻点t x。
由于超声波信号在大气环境下传播时，振幅会随着传输距离的增加而迅速衰减，即解调得到的第二正弦波信号的振幅与测量距离相关。若直接对解调后的第二正弦波信号作过零触发来确定回波信号到达时刻点，在过零点将产生微小的时间误差。是以，为了实现高精度测量，回波到达时刻处理单元8对解调而得的第二正弦波信号进行自动增益控制(AGC)，使之振 幅恒定，确保过零触发时过零点无时间误差。之后，经自动增益处理后振幅一致的第二正弦波信号过零比较后形成数字脉冲信号Vt x并进行过零触发，该数字脉冲信号Vt x的上升沿(时刻t x)即为回波信号的到达时刻点。在一定电压幅度范围内，回波到达时刻处理单元8对解调得到的第二正弦波信号的增益控制随增益压控电压呈线性反比变化，即，当测量距离增加，第二正弦波信号的幅度减小，增益压控电压亦减小，则对第二正弦波信号的控制增益变大；当测量距离减小，第二正弦波信号的幅度增大，增益压控电压亦增大，则对第二正弦波信号的控制增益减小。
在一实例中，前置接收单元中包括一接收超声波换能器SPS2及一运算放大器；振幅解调单元中包括一精密半波整流电路及一四阶带通滤波器。回波到达时刻处理单元中包括一集成比较器。由于集成比较器构成过零触发结构时，在没有信号输入时，其输出状态是不确定的，极易引起震荡，是以通常将集成比较器设计成一个具有小的回差值的迟滞模式，即集成比较器输入信号振幅的大小会影响越过阀值的时间点。为了消除信号幅度涨落引起过阀值点时刻的涨落，在回波到达时刻处理单元中设置一用于对解调得到的第二正弦波信号实行自动增益控制处理的自动增益控制芯片。
在工作过程中，前置接收单元中的接收超声波换能器SPS2接收到回波信号(在测距计时起始时刻点t x，使用625Hz的第二正弦波信号调制40KHz的第一正弦波信号得到的调幅波信号激励发射超声波换能器SPS1)后，首先经低噪声高共模抑制比运算放大器进行差分放大处理，使得相对于系统参考地浮空的回波信号被转换为相对于系统参考地、被放大及抑除了共模噪声的回波信号；之后振幅解调单元中的精密半波整流电路对该回波信号进行精密半波整流并通过中心频率为625Hz的四阶带通滤波器，将其中40KHz的第一正弦波信号滤除，解调出纯净的625Hz的第二正弦波信号；之后自动增益控制芯片(通过自动增益控制芯片中增益控制脚输入的增益控制电压对第二正弦波信号的幅度进行控制，增益控制电压由输入的第二正弦波信号得到，且增益控制电压越小，控制增益越大；增益控制电压越大，控制增益越小)对解调得到的第二正弦波信号进行自动增益控制，再将增益控制后的第二正弦波信号经过集成比较器，得到数字脉冲信号Vt x，在该集成比较器中发生过零触发，为微处理器单元中的微处理器产生中断信号TEND，微处理器响应该中断的时刻即为回波信号的到达时刻点t x。可以理解，在Δt＝t 1-t 0时间段，系统以40KHz的第一正弦波信号激励发射超声换能器SPS1，经反射后被接收超声换能器接收到的回波信号同样是等幅波，经中心频率为625Hz的四阶带通滤波器后的输出是零；而经振幅调幅后的回波信号经中心频率为625Hz的四阶带通滤波器后的输出是625Hz的第二正弦波信号，基于此实现本实施方式的目的。
由于超声波收发换能器中压电超声振子具有较大余振惯性的物理性质，是以，在另一实施方式中，振幅调制及驱动单元4在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比例。虽然在振幅调制时进行了超调，但是接收超声波换能器SPS2由于惯性，无法响应超调的回波信号，是以一定程度上增强了回波信号中携带的第二正弦波信号的调制比例(增加包络线的调制度)，从而大大增强了信噪比。超调的比例可以根据实际应用中使用的超声波收发换能器进行设定，如，超调1/100、超调2/100甚至更多。
此外，微处理器单元1中还包括RS485通信芯片和温度传感芯片，RS485通信芯片用于实现连续调制超声波精确测距装置与外界的通信，可实现高达1000m的传输距离；温度传感芯片用于修正超声波的波速。在一实例中，采用型号为DS1624的温度传感芯片，实时修正从-10～70℃环境温度变化的超声波传播速率，测量精度达0.032℃。
本发明还提供了一种连续调制超声波精确测距系统，在该测距系统中除了包括上述连续调制超声波精确测距装置之外，还包括：填充有变压器绝缘油的不锈钢管缸筒，及置于变压器绝缘油面表面的用于反射发射超声波换能器SPS1发射的超声波信号的平板浮片(平板浮片的直径略小于不锈钢圆筒内径)，连续调制超声波精确测距装置置于不锈钢管缸筒内变压器绝缘油上方一定距离，测量与平板浮片之间的距离。对于连续调制超声波精确测距装置的设置距离，根据其中的超声波收发换能器的位置进行设定，只要满足超声波信号的盲区即可，如，将连续调制超声波精确测距装置设置在变压器绝缘油上方约50厘米处，当发射超声波换能器和接收超声波换能器不设置在同一位置时，甚至可以实现无盲区测量。
在本实施方式中，依据连续调制超声波时差法高精度测距方法可达到1米及以上的测量量程、0.1mm(毫米)的测量精度，能够适用于需要较高测量精度及需要大量程测定距离的场合，明尤其适用于水下目标的精确测距及定位。

Claims (13)

  1. 一种连续调制超声波精确测距方法，其特征在于，包括：
    使用第一正弦波信号激励发射超声波换能器振动；
    在预先设定的测距计时起始时刻点使用第二正弦波信号对第一正弦波信号进行振幅调制；
    接收被测目标反射的回波信号，并对其解调得到第二正弦波信号；
    对解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点；
    根据所述起始时刻点和到达时刻点计算与被测目标之间的距离，完成测距。
  2. 如权利要求1所述的连续调制超声波精确测距方法，其特征在于，在根据增益控制后的第二正弦波信号确定回波信号的到达时刻点中：对自动增益控制后的第二正弦波信号进行过零触发，得到回波信号的到达时刻点。
  3. 如权利要求1或2所述的连续调制超声波精确测距方法，其特征在于，在使用第一正弦波信号激励发射超声波换能器振动之前，包括形成第一正弦波信号和第二正弦波信号的步骤：
    根据预设频率生成第一方波信号，根据所述第一方波信号形成第一正弦波信号；
    对所述第一方波信号分频得到第二方波信号，根据所述第二方波信号形成第二正弦波信号。
  4. 如权利要求1或2所述的连续调制超声波精确测距方法，其特征在于，使用第二正弦波信号对第一正弦波信号进行振幅调制之前，还包括根据第一正弦波信号或第二正弦波信号计时的步骤：
    对第一正弦波信号或第二正弦波信号进行过零比较形成数字脉冲信号；
    对所述数字脉冲信号进行计数；
    当计数达到预设值，判定到达测距计时起始时刻点。
  5. 如权利要求1或2所述的连续调制超声波精确测距方法，其特征在于，在对所述回波信号进行振幅解调得到第二正弦波信号中，包括：
    对所述回波信号进行精密半波整流得到半波信号；
    以中心频率为第二正弦波频率的带通滤波器对所述半波信号进行过滤得到第二正弦波信号，完成对所述回波信号的解调。
  6. 如权利要求1或2所述的连续调制超声波测距方法，其特征在于，在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比例。
  7. 一种连续调制超声波精确测距装置，其特征在于，包括：
    微处理器单元，用于根据起始时刻形成单元形成的起始时刻点和回波到达时刻处理单元确定的到达时刻点计算与被测目标之间的距离；
    第一正弦波形成单元，与微处理器单元连接，用于形成第一正弦波信号；
    第二正弦波形成单元，与微处理器单元连接，用于形成第二正弦波信号；
    振幅调制及驱动单元，用于使用第一正弦波形成单元形成的第一正弦波信号激励发射超声波换能器振动，及用于在一测距计时起始时刻点使用第二正弦波形成单元形成的第二正弦波信号对第一正弦波信号进行振幅调制；
    起始时刻形成单元，用于确定测距计时起始时刻点；
    前置接收单元，用于接收测目标反射的回波信号；
    振幅解调单元，用于对前置接收单元接收的回波信号进行振幅解调得到第二正弦波信号；
    回波到达时刻处理单元，用于振幅解调单元解调得到的第二正弦波信号进行自动增益控制，并根据增益控制后的第二正弦波信号确定回波信号的到达时刻点。
  8. 如权利要求7所述的连续调制超声波精确测距装置，其特征在于，在回波到达时刻处理单元中：对自动增益控制后的第二正弦波信号进行过零触发，得到回波信号的到达时刻点。
  9. 如权利要求7或8所述的连续调制超声波精确测距装置，其特征在于，
    所述微处理器单元还用于根据预设频率生成第一方波信号；
    所述第一正弦波形成单元根据所述第一方波信号形成第一正弦波信号；
    所述第二正弦波形成单元对所述第一方波信号分频得到第二方波信号，并根据所述第二方波信号形成第二正弦波信号。
  10. 如权利要求7或8所述的连续调制超声波精确测距装置，其特征在于，在所述起始时刻形成单元中，对第一正弦波信号或第二正弦波信号进行过零 比较形成数字脉冲信号后，对其进行计数；当计数达到预设值，判定到达测距计时起始时刻点；微处理器单元控制振幅调制及驱动单元使用第二正弦波信号对第一正弦波信号进行振幅调制。
  11. 如权利要求7或8所述的连续调制超声波精确测距装置，其特征在于，在振幅解调单元中，对接收到的回波信号进行精密半波整流得到半波信号，并以中心频率为第二正弦波频率的带通滤波器对所述半波信号进行过滤得到第二正弦波信号，完成对所述回波信号的解调。
  12. 如权利要求7或8所述的连续调制超声波测距装置，其特征在于，振幅调制及驱动单元在使用第二正弦波信号对第一正弦波信号进行振幅调制时，超调预设比例。
  13. 一种连续调制超声波精确测距系统，其特征在于，包括如权利要求7-12任意一项所述的连续调制超声波精确测距装置，还包括：
    填充有变压器绝缘油的不锈钢管缸筒，及置于所述变压器绝缘油面表面的平板浮片，所述连续调制超声波精确测距装置置于不锈钢管缸筒内变压器绝缘油上方一定距离，测量与平板浮片之间的距离。
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