CN201637504U - High-sensitivity ultrasonic thermometer - Google Patents

Abstract

The utility model relates to a high-sensitivity ultrasonic thermometer comprising an ultrasonic temperature sensor, an ultrasonic transducer driving circuit and an ultrasonic return signal processing circuit, wherein the ultrasonic temperature sensor comprises two ultrasonic transducers and an airtight metal tube body filled with air; the ultrasonic transducer driving circuit mainly comprises D/A (Analog/Digital) converting circuit and a power amplifying circuit; the ultrasonic return signal processing circuit mainly comprises a filter circuit, an amplifying circuit, an A/D (Digital/Analog) converting circuit, a FPGA (Field Programmable Gate Array) and a CPU (Central Processing Unit). The ultrasonic transducer driving circuit drives the transducers to send ultrasonic waves out, and the ultrasonic return signal processing circuit precisely measures the transmission time of the ultrasonic waves in the tube body. The transmission speed of the ultrasonic waves in air changes along with the change of the temperature so that as long as the transmission time of the ultrasonic waves in the tube body is measured at different temperatures, the measurement of the temperature can be realized. Due to the adoption of high-precision ultrasonic wave transmission time measuring circuit and algorithm, the high-sensitivity ultrasonic thermometer can realize high-precision temperature measurement, wherein the precision of temperature measurement depends on the measurement precision of the transmission time of the ultrasonic waves, and the measurement range depends on the length of the tube body.

Description

A kind of high-sensitivity ultrasonic thermometer

Technical field

The utility model belongs to sophisticated sensor and detection technique field, is specifically related to a kind of thermometer with the ultrasonic technology precisely measuring temperature.

Background technology

Hyperacoustic notable feature is the frequency height, thereby wavelength is short, and the diffraction phenomenon is little, and good directionality can direction propagation, runs into impurity or interphase during propagation and just has significant reflection.Along with development of electronic technology, ultrasonic technology more and more is applied to the precision measurement of temperature etc.

When ultrasound wave was propagated in medium, velocity of propagation changed with the variation of state parameters such as temperature, pressure.The hundreds of approximately rice of velocity of propagation per second increased with the temperature rising when ultrasound wave was propagated in gas, and air middle pitch speed is 331.4 meter per seconds in the time of 0 ℃, is 340 meter per seconds in the time of 15 ℃, 1 ℃ of the every rising of temperature, and velocity of sound increases by 0.6 meter per second approximately.Record transmission range ultrasound wave travel-time under different temperatures when constant, just can record temperature.For example, hyperacoustic speed is 344 meter per seconds in the time of 20 ℃, and hyperacoustic speed is 344.6 meter per seconds in the time of 21 ℃, if hyperacoustic transmission range is 0.3 meter, then hyperacoustic transmission time is 8.7209 * 10 in the time of 20 ℃ ^-4Second, hyperacoustic transmission time is 8.7057 * 10 in the time of 21 ℃ ^-4Second, hyperacoustic transmission time difference is 1.52 * 10 in the time of 21 ℃ and 20 ℃ the time ^-6Second.Guarantee to measure and reach 0.001 ℃ Measurement Resolution, require the resolution of ultrasonic transmission time measurement to reach and could realize 1～2 nanosecond.If with conventional hyperacoustic transmission time of timer counter circuit measuring, then the frequency of clock circuit will reach 1G at least, this obviously is difficult to realize for instrument development.

Summary of the invention

The utility model is at the problems referred to above, the high-sensitivity ultrasonic temperature survey meter that a kind of Measurement Resolution can reach 0.001 ℃ is disclosed, it has adopted ultrasonic temperature sensor, FPGA circuit and software segmentation interpolation algorithm, can under the prerequisite that guarantees the measurement real-time, realize the measurement of nanosecond ultrasonic transmission time, thereby realize the high-precision temperature measurement.

The technical solution adopted in the utility model is:

A kind of high-sensitivity ultrasonic thermometer is used to realize that Measurement Resolution is better than 0.001 ℃ precision temperature measurement.Thus, the high-precision ultrasonic thermometer that the utility model proposes comprises ultrasonic transducer E1, ultrasonic transducer E2, D/A change-over circuit, power amplification circuit, signal amplification circuit, filtering circuit, A/D change-over circuit, on-site programmable gate array FPGA and central processing unit CPU;

Described ultrasonic temperature sensor is to be made of ultrasonic transducer E1, ultrasonic transducer E2 and a body, the relative two ends that are installed in the body of described ultrasonic transducer E1 with ultrasonic transducer E2, body is airtight withstand voltage, wherein is full of the gas as the ultrasound wave medium.

Described central processing unit CPU connects on-site programmable gate array FPGA, control on-site programmable gate array FPGA sine wave output drive signal, one tunnel output of on-site programmable gate array FPGA connects the D/A change-over circuit, by the D/A change-over circuit described sine wave drive signal is changed, the D/A change-over circuit connects power amplification circuit again, signal is amplified, power amplification circuit is connected with ultrasonic transducer E1, signal is inputed to described ultrasonic transducer E1, and this ultrasonic transducer E1 converts described this input signal to mechanical vibration and produces ultrasonic signal;

Described ultrasonic transducer E2 receives the ultrasonic signal that described ultrasonic transducer E1 sends, mechanical vibration are converted to electric signal, the output ultrasonic wave echoed signal, and by with its amplifying circuit that is connected successively, filtering circuit and A/D change-over circuit, make described ultrasonic echo signal after amplification, filtering and A/D conversion, input to on-site programmable gate array FPGA successively; The digital sine conversion of signals that D/A converter is used for that FPGA is sent is an analog sinus signals, and power amplification circuit is used to amplify the power of this sinusoidal signal, makes it enough energy drives ultrasonic transducer E1.It is digital signal that described A/D converter is mainly used in a ultrasonic echo analog signal conversion, and input FPGA.

Described on-site programmable gate array FPGA sample simultaneously the sine wave drive signal of output and the ultrasonic echo signal of input, and sampled data left in the internal memory; Described FPGA circuit major function has two: first function is to produce the digital sine signal under the control of CPU, and this signal converts simulating signal to through D/A converter, and amplifies rear drive transducer E1 through power amplification circuit.Second function is to finish the ultrasonic echo signals sampling, and the data existence is configured in the memory block of FPGA inside.

Described central processing unit CPU reads sampled data from the on-site programmable gate array FPGA internal memory, accurately calculate the pairing moment of ultrasonic propagation time terminal point by the segmentation interpolation algorithm; Then, determine the pairing moment of ultrasonic propagation time starting point according to the sine wave drive signal of output.Thereby accurately determine the transmission time of ultrasound wave between two transducer E1, E2.Last CPU accurately calculates its corresponding temperature according to ultrasound wave different transmission times between two transducer E1, the E2 in the ultrasonic temperature sensor body.

Described transducer E1 is a piezoelectric transducer, can be the electrical signal conversion with certain energy mechanical vibration, and when the frequency of signal was in the frequency of ultrasonic scope, transducer E1 was electrical signal conversion a ultrasonic signal.Transducer E2 also is a piezoelectric transducer, and mechanical vibration are converted to electric signal, and when ultrasonic signal affacted on the ultrasonic transducer E2, it was converted to electric signal to ultrasonic signal, and this signal can be referred to as the ultrasonic echo signal.

The sinusoidal ultrasonic signal of periodicity of ultrasonic transducer E1 emission some, after this signal is propagated in gas and is arrived transducer E2, excitation transducer E2 produces the ultrasonic echo signal, the continuous pump of the ultrasonic signal that the amplitude of echoed signal receives along with transducer and increasing gradually, when pumping signal stops, the mechanical vibration of transducer still can continue under action of inertia and decay gradually, the amplitude of echoed signal also reduces gradually, therefore the ultrasonic echo signal is a luffing cyclical signal, and its cycle is corresponding to the cycle of ultrasonic signal.That cycle of echoed signal amplitude maximum is corresponding to the cycle of last sent that ultrasonic signal of transducer E1.

Hyperacoustic travel-time is exactly the corresponding time interval between that a bit and on the echoed signal that receives of transducer E2 arbitrarily on the ultrasonic signal that sends of transducer E1.The key of ultrasonic transmission time measurement is to determine the starting point and the terminal point in travel-time.The starting point in travel-time can be the specific pairing moment on the ultrasonic signal that sends of transducer E1, the terminal point of time be on the echoed signal with corresponding that pairing moment of ultrasonic signal unique point.

Echoed signal is a Variable Amplitude cyclical signal, and the most characteristic ripple is that ripple of amplitude maximum in its waveform, can be referred to as characteristic wave, and characteristic wave is corresponding to last ripple of ultrasonic signal.In characteristic wave, the most characteristic point is zero crossing and peak point, can select the unique point of zero crossing as echoed signal.The unique point moment corresponding is exactly the terminal point in travel-time, and is corresponding with it, and the pairing moment of zero crossing of last that ripple can be defined as the starting point in travel-time in the ultrasonic signal waveform.

Because ultrasonic signal is that FPGA produces under the control of CPU, the starting point in travel-time, just the zero crossing moment corresponding of last that ripple of ultrasonic signal is easy to determine accurately that by CPU its precision depends on the running frequency of FPGA.

The terminal point in travel-time, just the pairing moment of zero crossing is determined by the segmentation interpolation algorithm in the echoed signal characteristic wave.The segmentation interpolation algorithm is according to the waveform in that cycle of peak amplitude maximum in the at first definite echoed signal of the A/D sampled signal of the ultrasonic echo of storing among the FPGA; Determine former and later two sampled points of zero crossing (ratio zero is big, and a ratio zero is little) pairing moment then; Be benchmark with former and later two sampled points of zero crossing at last, with fitting method sampled point is segmented interpolation, determine the pairing moment of echoed signal zero crossing, i.e. in the pairing moment of ultrasonic propagation time terminal point, its precision depends primarily on the resolution of A/D sampling.

The principle of work of the high-precision ultrasonic thermometer that the utility model proposes is as follows: the relative body two ends that are installed in ultrasonic transducer E2 of ultrasonic transducer E1, central processing unit CPU control on-site programmable gate array FPGA sine wave output drive signal, allow signal input to described ultrasonic transducer E1 by D/A change-over circuit and power amplification circuit successively, this ultrasonic transducer E1 converts described this input signal to mechanical vibration and produces ultrasonic signal.

Described ultrasonic transducer E2 receives the ultrasonic signal that described ultrasonic transducer E1 sends, and output ultrasonic wave echoed signal, by filtering circuit the ultrasonic echo signal that ultrasonic transducer E2 sends is carried out filtering, after amplifying by amplifying circuit again, by the A/D change-over circuit echoed signal is sampled, sampled data is stored in earlier in the memory block that is configured in the FPGA.

After sampling is finished, central processing unit CPU is at first launched hyperacoustic data according to FPGA and is determined the pairing moment of ultrasonic propagation time starting point, read the A/D sampled data of ultrasonic echo signal then in the FPGA, employing accurately calculates the pairing moment of ultrasonic propagation time terminal point by the segmentation interpolation algorithm, and then accurately determines the transmission time of ultrasound wave between two transducer E1, E2.CPU accurately calculates its corresponding temperature according to ultrasound wave different transmission times between two transducer E1, the E2 in the ultrasonic temperature sensor body then.

The utility model can be realized the measurement of the ultrasonic transmission time of nanosecond precision owing to the hardware circuit and the software algorithm of subdivision that have adopted based on FPGA, thereby realizes that resolution is better than 0.001 ℃ high-precision temperature measurement, and guarantees good real-time.The utility model can be widely used in fields such as precision temperature measurement and control.

Description of drawings

Fig. 1 is a kind of high-sensitivity ultrasonic thermometer structured flowchart;

Fig. 2 is the drive signal synoptic diagram that is added on the transducer E1;

Fig. 3 is the ultrasonic echo signal schematic representation that receives on the transducer E2;

Fig. 4 is a kind of working principle of hardware synoptic diagram of precisely measuring ultrasonic wave transmission time method;

Fig. 5 a-5b is a synoptic diagram of determining the corresponding moment of ultrasonic propagation time terminal point institute.

Embodiment

Below in conjunction with Figure of description the technical solution of the utility model is described in further detail.

Referring to Fig. 1, this thermometer is mainly by body 10, ultrasonic transducer E111, transducer E212, central processing unit CPU 19, FPGA FPGE118, A/D change-over circuit 17, filtering circuit 16, amplifying circuit 15, power amplification circuit 14, D/A change-over circuit 13, display circuit 20, keyboard circuit 21 and D/A change-over circuit 22 constitute.

Body 10, ultrasonic transducer E111, transducer E212 constitute temperature sensor, the relative two ends that are installed in the body of ultrasonic transducer E1 with ultrasonic transducer E2, and body is airtight withstand voltage, wherein is full of the gas as the ultrasound wave medium.

Display circuit 20 is used to the temperature value that shows that CPU calculates, keyboard circuit 21 is used for to the parameter of input temp meter and operating personnel's authority, D/A change-over circuit 22 converts temperature value to analog current signal from digital signal, 4～20 milliamperes of normalized current signals commonly used in the output Engineering Control.

Referring to Fig. 2, be the drive signal on the ultrasonic transducer E1, it is that the digital sine signal that produces in FPGA converts analog sinus signals to through the D/A change-over circuit, and then forms through the power amplification circuit amplification, the voltage of the V representation signal among the figure, t represents the time.The frequency of this signal is 1MHz, the about 10V of voltage, and the about 1.5A of electric current has about 15 watts electric energy, is enough to drive ultrasonic transducer E1 and converts electrical energy into mechanical energy, sends ultrasonic signal.

Referring to Fig. 3, be the ultrasonic echo signal of on transducer E2, exporting, the voltage of the V representation signal among the figure, t represents the time.When the ultrasonic signal that transducer E1 sends was gone up through propagating into transducer E2 after certain travel-time, transducer E2 was converted to electric energy with the mechanical energy of ultrasonic signal, the output ultrasonic wave echoed signal.The electric signal of transducer E2 output is not before ultrasound wave propagates on the transducer E2, amplitude is zero, after transducer E2 receives ultrasonic signal, the electric signal amplitude of output increases gradually, reduce to decay to zero then gradually, be a luffing periodic signal, that ripple of amplitude maximum is corresponding to last ripple of ultrasonic signal.The frequency of ultrasonic echo signal depends on the frequency of ultrasonic signal, also is 1MHz.

Referring to Fig. 4, after the synchronizing circuit 432 of CPU19 in FPGA18 sent the beginning sample command, FPGA18 started simultaneously to the driving of ultrasonic transducer E111 with to the sampling of ultrasonic transducer E212 output signal.

Digital sine signal generator 431 transmission frequency that are implemented in the FPGA are the sinusoidal signal in 8 cycles of 1MHz, this signal is converted to simulating signal through D/A change-over circuit 13, after power amplification circuit 14 amplifies, be carried on the transducer E111 again, send ultrasonic signal.The electric signal of transducer E212 output is connected to A/D change-over circuit 17 after wave circuit 16 filtering after amplifying through operational amplification circuit 15 after filtration.The sample circuit 433 control A/D change-over circuits 443 of FPGA inside are digital signal with analog signal conversion, and sampled value is deposited in the RAM memory block 434 that is implemented in the FPGA one by one.After sampling was finished, FPGA430 sent sampling done state information to CPU 19, and CPU19 finishes once sampling after receiving sampling done state information.

After sampling finished, CPU19 at first accurately determined the pairing moment T of starting point in the ultrasonic signal according to the data of the digital sine signal generator 431 in the FPGA _QD

CPU19 sends the read data order then, reads the data that are temporary in the RAM memory block 434, the pairing moment of accurate Calculation ultrasonic propagation time terminal point.

The pairing moment of ultrasonic transmission end time is by analyzing and calculate and realize with the segmentation interpolation algorithm all sampled datas of echoed signal.Referring to Fig. 5 a, the ultrasonic echo signal of analysis ultrasonic transducer E2 output for the repeatability that guarantees to measure, should extract the terminal point of ultrasonic transmission time as can be known in the waveform of peak amplitude maximum.In the complete cycle of this waveform, the most tangible two unique points are peak point and zero crossing, zero crossing are defined as the easier acquisition high precision of time reference of echoed signal.

Referring to Fig. 5 a, the computing method in the pairing moment of ultrasonic transmission end time of the present utility model are:

At first the A/D sampled point is compared in pointwise, and the maximal value of finding out sampled point just can be determined can be referred to as the eigenwert waveform to this waveform by the waveform of amplitude maximum easily;

Secondly, participate in Fig. 5 b, determine the pairing zero crossing P of ultrasonic transmission end time ₀The sampled point P in front and the sampled point P+1 in back, obviously the sampled value of sampled point P is greater than zero in characteristic wave, and the sampled value of sampled point P+1 is less than zero;

At last, as benchmark, can accurately calculate zero crossing P with sampled point P and 2 moment corresponding of P+1 with the segmentation interpolation algorithm ₀In the pairing moment, concrete computing method are as follows:

If the sample frequency of A/D is F _A/D, the time between adjacent two sampled points is to be T in the sampling period _A/DIs N from first sampled point to the hits the sampled point P, and the sampled value of sampled point P correspondence is V1, and the pairing moment of sampled point P is T1; The sampled value of sampled point P+1 correspondence is V2; The pairing moment of sampled point P is T1, sampled point P and zero crossing P ₀Between time be T2, zero crossing P ₀Moment corresponding is T _ZD, hyperacoustic transmission time is T, then:

$T_{A/D}=\frac{1}{F_{A/D}}$

$\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">T</figure-callout>}1=N\&times;\frac{1}{F_{A/D}}$

In the less zone of near zero-crossing point, sinusoidal wave waveform approaches straight line, can determine T2 according to the method for linear interpolation:

$T2=\frac{1}{V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1}\&times;\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1\&times;T_{A/D}$

Then the pairing moment of zero crossing, promptly the pairing moment of ultrasonic transmission end time is:

$T_{\mathrm{ZD}}=\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">T</figure-callout>}1+T2=N\&times;\frac{1}{F_{A/D}}+\frac{1}{V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1}\&times;T_{/\mathrm{AD}}\&times;\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1$

From following formula as can be known, the ultrasonic transmission end time corresponding resolution constantly be:

$R=\frac{1}{V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1}\&times;T_{/\mathrm{AD}}$

Participate in Fig. 5 b, the frequency of supposing the ultrasonic echo signal is 1M, and then the cycle is 1us; The resolution of A/D is 12, the amplitude of signal can be divided into 4096 parts so, if the sample frequency of A/D is 32MHz, then arrive in the negative peaked half period in the positive maximal value of sine wave, can adopt 16 points at most, if sinusoidal wave positive maximal value is regarded as straight line to the waveform in the negative peaked half period, then obviously as can be known:

$V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1=\frac{4096}{16}=256$

Observe sinusoidal wave positive maximal value and arrive the interior waveform of negative peaked half period as can be seen, the near zero-crossing point slope of a curve is much larger than near the slope of a curve peak value, then

V2-V1＞256

$R=\frac{1}{V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1}\&times;T_{/\mathrm{AD}}<\frac{1}{256}\&times;T_{/\mathrm{AD}}=\frac{1}{256}\&times;\frac{1}{32}\&times;1\mathrm{\&mu;s}=0.122\mathrm{ns}$

Referring to Fig. 5, hyperacoustic transmission time is:

$T=T_{\mathrm{ZD}}-T_{\mathrm{QD}}=N\&times;\frac{1}{F_{A/D}}+\frac{1}{V2-\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HSA00000108731500022.png"\; state="\{\{state\}\}">V</figure-callout>}1}\&times;T_{/\mathrm{AD}}\&times;V1-T_{\mathrm{QD}}$

Because the pairing moment of ultrasonic transmission start time can accurately be determined, then the resolution of ultrasonic transmission time measurement depend on the ultrasonic transmission end time corresponding resolution constantly, so the resolution of ultrasonic transmission time measurement is less than 0.122 nanosecond.Be installed in the transducer E1 at body two ends and the distance between the E2 and fix, record ultrasound wave travel-time between transducer E1 and E2 under different temperatures, just can record temperature.For example, the speed of ultrasound wave in gas is 344 meter per seconds in the time of 20 ℃, and the speed in the time of 21 ℃ is 344.6 meter per seconds, if the distance between transducer E1 and the E2 is 0.3 meter, then hyperacoustic transmission time is 8.7209 * 10 in the time of 20 ℃ ^-4Second, hyperacoustic transmission time is 8.7057 * 10 in the time of 21 ℃ ^-4Second, hyperacoustic transmission time difference is 1.52 * 10 in the time of 21 ℃ and 20 ℃ the time ^-6Second.As mentioned above, the resolution of ultrasonic transmission time measurement is better than 1.0 * 10 ^-9Second, can realize that then resolution is better than 0.001 ℃ temperature survey.Gas in the airtight body is when temperature variation, and significant change also takes place its pressure, and the variation of temperature and pressure all can influence the velocity of propagation of ultrasound wave in gas, thereby has increased thermometric sensitivity.

Claims (1)

1. high-sensitivity ultrasonic thermometer, it is characterized in that: it comprises ultrasonic temperature sensor, D/A change-over circuit, power amplification circuit, signal amplification circuit, filtering circuit, A/D change-over circuit, on-site programmable gate array FPGA and central processing unit CPU;

Described ultrasonic temperature sensor is to be made of ultrasonic transducer E1, ultrasonic transducer E2 and a body, the relative two ends that are installed in the body of described ultrasonic transducer E1 with ultrasonic transducer E2, body is airtight withstand voltage, wherein is full of the gas as the ultrasound wave medium;

Described central processing unit CPU connects on-site programmable gate array FPGA, control on-site programmable gate array FPGA sine wave output drive signal, one tunnel output of on-site programmable gate array FPGA connects the D/A change-over circuit, by the D/A change-over circuit described sine wave drive signal is changed, the D/A change-over circuit connects power amplification circuit again, signal is amplified, power amplification circuit is connected with ultrasonic transducer E1, signal is inputed to described ultrasonic transducer E1, and this ultrasonic transducer E1 converts described this input signal to mechanical vibration and produces ultrasonic signal;

Described ultrasonic transducer E2 receives the ultrasonic signal that described ultrasonic transducer E1 sends, mechanical vibration are converted to electric signal, the output ultrasonic wave echoed signal, and by with its amplifying circuit that is connected successively, filtering circuit and A/D change-over circuit, make described ultrasonic echo signal after amplification, filtering and A/D conversion, input to on-site programmable gate array FPGA successively;

Described on-site programmable gate array FPGA sample simultaneously the sine wave drive signal of output and the ultrasonic echo signal of input, and sampled data left in the internal memory;

Described central processing unit CPU reads sampled data from the on-site programmable gate array FPGA internal memory, accurately calculate the pairing moment of ultrasonic propagation time terminal point by the segmentation interpolation algorithm; Sine wave drive signal according to output is determined the pairing moment of ultrasonic propagation time starting point, thereby accurately determine the transmission time of ultrasound wave between two transducer E1, E2, CPU accurately calculates its corresponding temperature according to ultrasound wave different transmission times between two transducer E1, the E2 in the ultrasonic temperature sensor body again.

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