CN110133370B - Measuring instrument and measuring method based on surface acoustic wave sensor - Google Patents
Measuring instrument and measuring method based on surface acoustic wave sensor Download PDFInfo
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- CN110133370B CN110133370B CN201910370387.2A CN201910370387A CN110133370B CN 110133370 B CN110133370 B CN 110133370B CN 201910370387 A CN201910370387 A CN 201910370387A CN 110133370 B CN110133370 B CN 110133370B
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Abstract
The invention discloses a measuring instrument and a measuring method based on a surface acoustic wave sensor.A physical quantity of an object to be measured is converted into a variable quantity of surface acoustic wave frequency through the SAW sensor to output a surface acoustic wave signal, the amplitude of the surface acoustic wave signal is stabilized through an AGC circuit to obtain a sinusoidal signal with controllable amplitude, the sinusoidal signal after the amplitude stabilization is filtered to remove noise waves through a first-order active band-pass filter, the sinusoidal signal is further shaped into a square wave signal through a shaping circuit, the shaped square wave signal is secondarily filtered through a second-order RC filter, then the frequency of the surface acoustic wave signal is calculated through an FPGA frequency measuring circuit to obtain the frequency of the surface acoustic wave signal, the frequency of the surface acoustic wave signal is; the invention adopts the AGC circuit and the shaping circuit, and can carry out frequency measurement of electric signals with a large amplitude range; and the accuracy and precision of the measuring result are greatly improved by adopting an equal-precision frequency measurement method.
Description
Technical Field
The invention relates to the technical field of instruments and meters, in particular to a measuring instrument and a measuring method based on a surface acoustic wave sensor.
Background
Frequency is one of the most important parameters in modern electronic circuits and is of great importance in many fields. In the present day, a Surface Acoustic Wave (SAW) sensor is a sensor that uses a SAW device as a sensing element, reflects measured information by a change in the speed or frequency of a SAW in the SAW device, and converts the information into an electrical signal for output. The surface acoustic wave sensor can accurately measure physical and chemical information, such as temperature, stress, gas density and the like. Various types including surface acoustic wave pressure sensors, surface acoustic wave temperature sensors, surface acoustic wave bio-gene sensors, surface acoustic wave chemical gas phase sensors, and smart sensors have been developed. The usage of the surface acoustic wave sensor is also more and more widespread, and the measuring instrument based on the surface acoustic wave sensor on the market at present generally has the following defects:
firstly, the method comprises the following steps: the price is generally higher, and common consumers are difficult to bear;
secondly, the method comprises the following steps: the traditional measuring instrument lacks an Automatic Gain Control (AGC) shaping circuit and is difficult to carry out shaping measurement on a large-amplitude signal;
thirdly, the method comprises the following steps: low measurement precision, poor stability and longer reaction time.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a measuring instrument and a measuring method based on a surface acoustic wave sensor, and solves the problems that the traditional measuring instrument based on the surface acoustic wave sensor is difficult to measure large-amplitude signals, low in measuring precision, poor in stability, long in reaction time and high in price.
In order to achieve the above purpose, the invention adopts the following technical scheme: a measuring instrument based on a surface acoustic wave sensor is characterized in that: the device comprises an acoustic surface wave sensor, an AGC circuit, a first-order active band-pass filter, a shaping circuit, a second-order RC filter, an FPGA frequency measurement circuit, a singlechip and an LCD display screen; the method comprises the steps that physical quantity of an object to be measured is converted into surface acoustic wave frequency variable quantity through an SAW sensor to output surface acoustic wave signals, the surface acoustic wave signals are subjected to amplitude stabilization through an AGC circuit to obtain sine signals with controllable amplitudes, noise waves of the sine signals after amplitude stabilization are filtered through a first-order active band-pass filter, the sine signals are shaped into square wave signals through a shaping circuit, the square wave signals after shaping are subjected to secondary filtering through a second-order RC filter, then the signals are calculated through an FPGA frequency measurement circuit to obtain the frequency of the surface acoustic wave signals, the frequency of the surface acoustic wave signals is input into a single chip microcomputer, physical quantity to be measured is obtained through calculation and stored in the single chip microcomputer, and the.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the AGC circuit comprises a two-stage amplifying circuit, a detection circuit and a single-threshold voltage comparison circuit which are connected in sequence, wherein the input end of the two-stage amplifying circuit is connected with the output end of the surface acoustic wave sensor, and the output end of the single-threshold voltage comparison circuit is connected to a gain control port of a program-controlled amplifier in the two-stage amplifying circuit to form a closed-loop automatic gain circuit; the two-stage amplifying circuit comprises a program-controlled amplifying circuit and an in-phase proportional amplifying circuit which are sequentially connected; the two-stage amplifying circuit is used for amplifying a surface acoustic wave signal output from the surface acoustic wave sensor; the detection circuit is used for detecting a low-frequency signal from the surface acoustic wave signal output by the two-stage amplification circuit; the single threshold voltage comparison circuit is used for providing discrimination voltage for the program control amplifying circuit in the two-stage amplifying circuit.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the programmable amplifying circuit comprises a programmable amplifier chip, a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, a first direct current power supply V1 and a second direct current power supply V2, wherein a positive gain control resistor end RG + and a negative gain control resistor end RG-of the programmable amplifier chip are connected with two ends of the second resistor R2; the signal positive-level input end VIN + is connected with the surface acoustic wave sensor output port VG1, and the signal negative-level input end VIN-is connected with the resistor R3 and then grounded; the power supply ports Vcc and Vee are respectively connected with the first direct-current power supply V1 and the second direct-current power supply V2 and then grounded; and a gain control port Vg of the programmable amplifier chip is connected with a fifth resistor R5 and then used for receiving an output electric signal of the single-threshold voltage comparison circuit, and an output port OUT is connected with a positive and negative signal input port of the in-phase proportional amplifier circuit.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the in-phase proportional amplifying circuit comprises an in-phase proportional amplifier chip, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a third direct-current power supply V3, a fourth direct-current power supply V4 and a fifth direct-current power supply V5; the negative input port of the in-phase proportional amplifier chip is connected with the ninth resistor R9 and then grounded, and the positive input port is connected with the seventh resistor R7 and then connected with the signal output port of the programmable amplifier chip; the positive power supply port and the negative power supply port are respectively connected with the third direct-current power supply V3 and the fourth direct-current power supply V4 and then grounded, and the auxiliary power supply port is connected with the fifth direct-current power supply V5 and then grounded; and the signal output port is connected with the negative input port after being connected with the eighth resistor R8, and is connected with the tenth resistor R10 to be used as the total output end VF1 of the whole AGC circuit.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the detection circuit comprises an eleventh resistor R11, a twelfth resistor R12, a first capacitor C1 and a diode D1, wherein the eleventh resistor R11 is connected with the first capacitor C1 in parallel, one end of the eleventh resistor is grounded, the other end of the eleventh resistor R11 is connected with the cathode of the diode D1, the anode of the diode D1 is connected with the signal output end of the in-phase proportional amplifying circuit, and the twelfth resistor R12 is connected with the negative signal input end of the single-gate voltage comparison circuit.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the single-threshold voltage comparator circuit comprises a single-threshold voltage comparator chip, a sixth direct-current power supply V6, a seventh direct-current power supply V7, an eighth direct-current power supply V8, a thirteenth resistor R13 and a second capacitor C2, and two power supply ports of the single-threshold voltage comparator chip are respectively connected with the seventh direct-current power supply V7 and the sixth direct-current power supply V6 and then grounded; the positive input port of the single-threshold voltage comparator chip is connected with the eighth direct-current power supply V8 and then grounded, the negative input port is connected with the second capacitor C2 and the thirteenth resistor R13 in sequence and then connected with the output port, and the output port is connected with the program control amplifying circuit and used for forming an automatic gain closed-loop circuit.
The measuring instrument based on the surface acoustic wave sensor is characterized in that: the shaping circuit is a double-threshold voltage comparison circuit and comprises a double-threshold voltage comparator chip, a ninth direct-current power supply V9, a tenth direct-current power supply V10, a fourteenth resistor R14 and a fifteenth resistor R15; the positive power supply port and the negative power supply port of the double-threshold voltage comparator chip are respectively connected with a ninth direct-current power supply V9 and a tenth direct-current power supply V10 and then are grounded, a fourteenth resistor R14 is connected between the output port and the positive input port of the double-threshold voltage comparator chip in series, the positive input port of the double-threshold voltage comparator chip is connected with a fifteenth resistor R15 and then is grounded, and the negative input port of the double-threshold voltage comparator chip is connected with the output end of the AGC circuit.
A measuring method of a measuring instrument based on a surface acoustic wave sensor is characterized in that: the method comprises the following steps:
converting physical quantity to be measured into variable quantity of surface acoustic wave frequency through a surface acoustic wave sensor and outputting a surface acoustic wave signal;
secondly, stabilizing the amplitude of the surface acoustic wave signal to obtain a signal with stabilized amplitude;
thirdly, filtering clutter from the signals after stable radiation;
fourthly, shaping the amplitude-stabilized signal into a square wave signal;
fifthly, carrying out secondary filtering on the square wave signal;
sixthly, measuring the frequency of the surface acoustic wave signal according to the filtered square wave signal;
and seventhly, calculating the physical quantity value to be measured according to the measured signal frequency value through a relation between the physical quantity to be measured and the surface acoustic wave frequency.
The measuring method of the measuring instrument based on the surface acoustic wave sensor is characterized in that: and sixthly, measuring the frequency of the surface acoustic wave signal by using an equal-precision frequency measurement method according to the square wave signal.
The invention achieves the following beneficial effects: the invention is based on the surface acoustic wave sensor, is suitable for instruments in various environments and ensures the accuracy of measurement; by adopting an AGC circuit and a shaping circuit, the frequency measurement of the electric signal with a large amplitude range can be carried out; the precision of the measurement result can reach 1.2% through experimental measurement, the signal frequency is measured by adopting an FPGA development board, and the result is output by a single chip microcomputer LCD screen, so that a user can directly and quickly read the measurement result.
Drawings
FIG. 1 is a block diagram of a meter according to the present invention;
FIG. 2 is a circuit diagram of a programmable amplifier in the AGC module of the present invention;
FIG. 3 is a circuit diagram of an in-phase proportional amplifier in the AGC module of the present invention;
FIG. 4 is a diagram of a detection circuit in the AGC module according to the present invention;
FIG. 5 is a circuit diagram of a single threshold voltage comparator in the AGC module of the present invention;
FIG. 6 is a circuit diagram of a first-order active band-pass filter according to the present invention;
FIG. 7 is a circuit diagram of a dual threshold voltage comparator according to the present invention;
FIG. 8 is a circuit diagram of a second order RC filter according to the present invention
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
As shown in the figure, the measuring instrument based on the surface acoustic wave sensor comprises the surface acoustic wave sensor, an AGC circuit, a first-order active band-pass filter, a shaping circuit, a second-order RC filter, an FPGA frequency measurement circuit, a single chip microcomputer and an LCD display screen; converting physical quantity (such as pressure variation) of an object to be measured into variation of surface acoustic wave frequency through a SAW sensor (such as a SAW pressure sensor) to output a surface acoustic wave signal, stabilizing the amplitude of the surface acoustic wave signal through an AGC circuit to obtain a sinusoidal signal with controllable amplitude, filtering clutter of the sinusoidal signal after the amplitude stabilization through a first-order active band-pass filter, further shaping the sinusoidal signal into a square wave signal through a shaping circuit, secondarily filtering the shaped square wave signal through a second-order RC filter, calculating the frequency of the surface acoustic wave signal through an FPGA frequency measurement circuit, inputting the frequency of the surface acoustic wave signal into a singlechip, calculating to obtain the physical quantity (such as pressure variation) to be measured, storing the physical quantity to be measured in the singlechip, and displaying the calculated physical quantity to be measured through an LCD display;
the FPGA frequency measurement circuit adopts an equal-precision frequency measurement method, a signal (standard signal) with a set frequency needs to be input into the FPGA frequency measurement circuit from the outside, and the singlechip is also used for controlling the frequency of the standard signal input into the FPGA frequency measurement circuit;
the AGC circuit, the first-order active band-pass filter, the shaping circuit, the second-order RC filter and the FPGA frequency measurement circuit can not change the frequency of a plurality of surface acoustic wave signals (SAW signals) output from the SAW sensor, and the frequency measured by the FPGA frequency measurement circuit is equal to the frequency of the SAW signals output from the SAW sensor;
the AGC circuit comprises a two-stage amplifying circuit, a detection circuit and a single-threshold voltage comparison circuit, wherein the input end of the two-stage amplifying circuit is connected with the output end of the SAW sensor, the output end of the two-stage amplifying circuit is connected with the input end of the detection circuit, the output end of the detection circuit is connected with the input end of the single-threshold voltage comparison circuit, and the output end of the single-threshold voltage comparison circuit is connected to a gain control port of a program-controlled amplifier in the two-stage amplifying circuit to form a closed-loop automatic gain circuit. The output signal voltage of the AGC circuit is compared with the discrimination voltage provided by the single-threshold voltage comparison circuit through the program control amplification circuit, namely closed-loop negative feedback, in the two-stage amplification circuit, and the gain of the program control amplification circuit is adjusted, so that the amplitude stabilization of the output signal is realized.
The two-stage amplifying circuit is used for amplifying the SAW signal (such as a pressure signal is a SAW sinusoidal signal) output from the SAW sensor into a high-frequency signal; the detection circuit is used for detecting a low-frequency signal from the high-frequency SAW signal output by the two-stage amplification circuit; the single threshold voltage comparison circuit is used for providing discrimination voltage for the program control amplifying circuit in the two-stage amplifying circuit;
the two-stage amplifying circuit comprises a program-controlled amplifying circuit and an in-phase proportional amplifying circuit which are connected with each other and contain a program-controlled amplifier, and the output end OUT of the program-controlled amplifying circuit is connected with an input pin 3 of the in-phase proportional amplifying circuit.
As shown in fig. 2, the programmable amplifying circuit includes a programmable amplifier chip VCA820, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first dc power supply V1, and a second dc power supply V2, wherein a positive gain control resistor terminal RG + and a negative gain control resistor terminal RG-of the programmable amplifier chip VCA820 are connected to two ends of the second resistor R2 for controlling the gain of the amplifier; the signal positive stage input end VIN + is connected with the SAW sensor output port VG1, and the signal negative stage input end VIN-is connected with the rear of the resistor R3 and then grounded for receiving signals. The power supply ports Vcc and Vee are respectively connected with the first direct current power supply V1 and the second direct current power supply V2 and then grounded for supplying power to the chip. The resistor connection terminal FB is connected with the fourth resistor R4 and then connected with the output terminal OUT for outputting signals, and the port FB can also be directly grounded. The gain control port Vg of the programmable amplifier is connected to the fifth resistor R5 for receiving the output electrical signal of the single-threshold voltage comparison circuit, and is used for controlling the gain together with the gain control resistor terminals RG + and RG-. The ground port GND is grounded, the pin Vref is connected with the resistor R6 and then is grounded, and the output port OUT is connected with a positive and negative signal input port of the in-phase proportional amplifier circuit.
As shown in fig. 3, the in-phase proportional amplifying circuit in the two-stage amplifying circuit includes an in-phase proportional amplifier chip OPA695, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a third dc power supply V3, a fourth dc power supply V4, and a fifth dc power supply V5; the negative input port 2 of the in-phase proportional amplifier chip OPA695 is connected with the ninth resistor R9 and then grounded, and the positive input port 3 is connected with the seventh resistor R7 and then connected with the signal output port OUT of the programmable amplifier VCA820 chip and used for receiving signals output from the programmable amplifying circuit; the positive power supply port 4 and the negative power supply port 7 are respectively connected with the third direct current power supply V3 and the fourth direct current power supply V4 in sequence and then grounded, and the auxiliary power supply port 6 is connected with the fifth direct current power supply V5 and then grounded and used for supplying power to the chip. The signal output port 9 is connected with the eighth resistor R8 and then connected with the negative input port 2, the eighth resistor R8 serves as a feedback resistor, and the gain of the signal can be realized by negative feedback. The signal output port 9 is also connected to a diode D1 in the detector circuit for outputting the amplified signal to the next detector circuit. The signal output port 9 is connected to the tenth resistor R10 and then serves as the total output terminal VF1 of the whole AGC circuit.
As shown in fig. 4, the detector circuit includes an eleventh resistor R11, a twelfth resistor R12, a capacitor C1, and a diode D1, wherein the eleventh resistor R11 is connected in parallel with the first capacitor C1, and then one end of the eleventh resistor R11 is grounded, and the other end of the eleventh resistor R11 is connected to the negative pole of the diode D1, so as to form a passive filter, which is an LC filter, and can attenuate high frequency signals unnecessary from the signals output from the in-phase proportional amplifier circuit. The anode of the diode D1 is connected with the signal output port 9 of the in-phase proportional amplifier, the diode is connected in the circuit to play a role in voltage stabilization and rectification, and the twelfth resistor R12 is connected with the negative signal input port 2 of the single-threshold voltage comparator chip OPA 820.
As shown in fig. 5, the single-threshold voltage comparison circuit includes a single-threshold voltage comparator chip OPA820, a sixth dc power supply V6, a seventh dc power supply V7, an eighth dc power supply V8, a thirteenth resistor R13, and a second capacitor C2, wherein power supply ports 4 and 7 of the single-threshold voltage comparator chip are respectively connected to the seventh dc power supply V7 and the sixth dc power supply V6 and then grounded, and the dc power supply is used for supplying power to the single-threshold voltage comparator chip. The positive input port 3 of the single-threshold voltage comparator chip is connected to the eighth dc power supply V8 and then grounded, and the eighth dc power supply V8 supplies a discrimination voltage for comparison with a signal output from the detector circuit. The negative input port 2 is connected with the output port 6 after being sequentially connected with the second capacitor C2 and the thirteenth resistor R13, and the output port 6 is connected with the fifth resistor R5 of the programmable amplifying circuit and then connected with the gain control port Vg of the programmable amplifier chip VCA820, so as to form an automatic gain closed loop.
As shown in fig. 6, the first-order active band-pass filter circuit is used to filter the signal output from the total output port VF1 of the AGC circuit, so as to remove the unwanted high and low frequency signals and keep the useful middle frequency band signal. The first-order active filter circuit comprises a filter chip TL082, a ninth direct current power supply V9, a tenth direct current power supply V10, a fourteenth resistor R14, a fifteenth direct current resistor R15, a third capacitor C3 and a fourth capacitor C4. The positive signal input port 3 of the filter chip TL082 is grounded, the negative signal input port 2 is connected with the third capacitor C3 and the fifteenth resistor R15 in sequence and then serves as a signal total input terminal VF2, and the total input terminal VF2 is used for being connected with a total output terminal VF1 of the upper AGC circuit. Positive and negative power supply ends 7 and 4 of the filter chip are respectively connected with a tenth direct current power supply V10 and a ninth direct current power supply V9 and then grounded, a fourteenth resistor R14 and a fourth capacitor C4 are connected in parallel, then two ends of the fourteenth resistor R14 and two ends of the fourth capacitor C4 are connected with a negative signal input end 2 and a filter chip signal output end 6, and the chip output end 6 is used as a total output end VF3 and is connected with a negative signal input end 2 of a TL084 double-threshold voltage comparator chip of a lower.
As shown in fig. 7, a shaping circuit, i.e., a dual threshold voltage comparison circuit, is used to shape the signal output from the output port VF3 of the first-order active band-pass filter into a square wave signal. The double-threshold voltage comparison circuit comprises a double-threshold voltage comparator chip TL084, an eleventh direct current power supply V11, a twelfth direct current power supply V12, a sixteenth resistor R16 and a seventeenth resistor R17. The positive power supply port 4 and the negative power supply port 11 of the double-threshold voltage comparator chip are respectively connected with a 12 th direct current power supply V12 and an eleventh direct current power supply V11 and then grounded for supplying power to the double-threshold voltage comparator chip, a seventeenth resistor R17 is connected between the output port 1 and the positive input port 3 of the double-threshold voltage comparator chip in series, the seventeenth resistor R17 is a feedback resistor and used for forming negative feedback to achieve the purpose of shaping, the positive input port 3 of the double-threshold voltage comparator chip is connected with a sixteenth resistor R16 and then grounded, the negative input port 2 is connected with the output end VF3 of the first-order active band-pass filter circuit and used for receiving filtered signals, and the shaping signal output end VF4 is connected with the signal input end of the next-order RC.
As shown in fig. 8, the second-order RC filter circuit includes an input port VF5, an output port VF6, an eighteenth resistor R18, a nineteenth resistor R19, a fifth capacitor C5, and a sixth capacitor C6. The resistor R18 is connected with the capacitor C5 to form a first-order RC filter, the resistor R19 is connected with the capacitor C6 to form a first-order RC filter, and the first-order RC filter and the second-order RC filter are superposed to form a second-order RC filter. After the signal is input into the second-order RC filter circuit from the input port VF5 and is output from the output port VF6, the circuit can effectively filter the noise wave existing in the input signal. The input port VF5 of the circuit is connected with the output port VF4 of the shaping circuit, and the output port VF6 of the circuit is connected with the input end of the FPGA frequency measurement circuit.
The FPGA frequency measurement circuit adopts an FPGA development board of Xilinx Artix-7XC7A35T model, and the FPGA development board measures the frequency of a signal input to the FPGA development board by using an equal-precision frequency measurement method through verilog language programming; and the signal input end of the FPGA development board is connected with the output end VF6 of the second-order RC filter circuit.
The single chip microcomputer adopts the single chip microcomputer of STM32F103ZET model, can put into the relational expression of the physical quantity of awaiting measuring and surface acoustic wave frequency in advance through its built-in memory module, and built-in calculation treater can calculate the physical quantity calculated value that corresponds with input frequency, shows the calculated value of physical quantity through the LCD display screen.
A measuring method of a measuring instrument based on a surface acoustic wave sensor comprises the following steps:
converting physical quantity to be measured into variable quantity of surface acoustic wave frequency through a surface acoustic wave sensor and outputting a surface acoustic wave signal;
secondly, stabilizing the amplitude of the surface acoustic wave signal to obtain a signal with stabilized amplitude;
thirdly, filtering clutter from the signals after stable radiation;
fourthly, shaping the amplitude-stabilized signal into a square wave signal;
fifthly, carrying out secondary filtering on the square wave signal;
sixthly, measuring the frequency of the surface acoustic wave signal by using the filtered square wave signal by using an equal-precision frequency measurement method;
and seventhly, calculating the physical quantity value to be measured according to the measured signal frequency value through a relation between the physical quantity to be measured and the surface acoustic wave frequency.
The invention takes a surface acoustic wave pressure sensor as an example, and the relation between the pressure value P and the measurement frequency delta f is as follows: Δ f ═ mP, can be,
wherein f is0Beta is a positive proportionality constant < 1, and mu, a, c, E, h are parameters related to the internal structure of the sensor.
The SAW signal output from the SAW sensor has different amplitudes and larger amplitude change, the invention can process the sensor signal with larger amplitude change, and has the capability of measuring larger or smaller signals which is not possessed by other similar products in the market.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A measuring instrument based on a surface acoustic wave sensor is characterized in that: the device comprises an acoustic surface wave sensor, an AGC circuit, a first-order active band-pass filter, a shaping circuit, a second-order RC filter, an FPGA frequency measurement circuit, a singlechip and an LCD display screen; converting physical quantity of an object to be detected into variable quantity of surface acoustic wave frequency through a surface acoustic wave sensor to output a surface acoustic wave signal, stabilizing the amplitude of the surface acoustic wave signal through an AGC circuit to obtain a sinusoidal signal with controllable amplitude, filtering clutter of the sinusoidal signal after amplitude stabilization through a first-order active band-pass filter, further shaping the sinusoidal signal into a square wave signal through a shaping circuit, performing secondary filtering on the shaped square wave signal through a second-order RC filter, calculating the frequency of the surface acoustic wave signal through an FPGA frequency measurement circuit, inputting the frequency of the surface acoustic wave signal into a single chip microcomputer, calculating to obtain physical quantity of the object to be detected and storing the physical quantity of the object to be detected in the single chip microcomputer, and displaying the calculated physical quantity;
the AGC circuit comprises a two-stage amplifying circuit, a detection circuit and a single-threshold voltage comparison circuit which are connected in sequence, wherein the input end of the two-stage amplifying circuit is connected with the output end of the surface acoustic wave sensor, and the output end of the single-threshold voltage comparison circuit is connected to a gain control port of a program control amplifying circuit in the two-stage amplifying circuit to form a closed-loop automatic gain circuit; the two-stage amplifying circuit comprises a program-controlled amplifying circuit and an in-phase proportional amplifying circuit which are sequentially connected; the two-stage amplifying circuit is used for amplifying a surface acoustic wave signal output from the surface acoustic wave sensor; the detection circuit is used for detecting a low-frequency signal from the surface acoustic wave signal output by the two-stage amplification circuit; the single threshold voltage comparison circuit is used for providing discrimination voltage for the program control amplifying circuit in the two-stage amplifying circuit.
2. A saw sensor based meter as claimed in claim 1, wherein: the programmable amplifying circuit comprises a programmable amplifier chip, a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, a first direct current power supply V1 and a second direct current power supply V2, wherein a positive gain control resistor end RG + and a negative gain control resistor end RG-of the programmable amplifier chip are connected with two ends of the second resistor R2; the signal positive-level input end VIN + is connected with the surface acoustic wave sensor output port VG1, and the signal negative-level input end VIN-is connected with the resistor R3 and then grounded; the power supply ports Vcc and Vee are respectively connected with the first direct-current power supply V1 and the second direct-current power supply V2 and then grounded; and a gain control port Vg of the programmable amplifier chip is connected with a fifth resistor R5 and then used for receiving an output electric signal of the single-threshold voltage comparison circuit, and an output port OUT is connected with a positive and negative signal input port of the in-phase proportional amplification circuit.
3. A saw sensor based meter as claimed in claim 1, wherein: the in-phase proportional amplifying circuit comprises an in-phase proportional amplifier chip, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a third direct-current power supply V3, a fourth direct-current power supply V4 and a fifth direct-current power supply V5; the negative input port of the in-phase proportional amplifier chip is connected with the ninth resistor R9 and then grounded, and the positive input port is connected with the seventh resistor R7 and then connected with the signal output port of the programmable amplifier chip; the positive power supply port and the negative power supply port are respectively connected with the third direct-current power supply V3 and the fourth direct-current power supply V4 and then grounded, and the auxiliary power supply port is connected with the fifth direct-current power supply V5 and then grounded; and the signal output port is connected with the negative input port after being connected with the eighth resistor R8, and is connected with the tenth resistor R10 to be used as the total output end VF1 of the whole AGC circuit.
4. A saw sensor based meter as claimed in claim 1, wherein: the detection circuit comprises an eleventh resistor R11, a twelfth resistor R12, a first capacitor C1 and a diode D1, wherein the eleventh resistor R11 is connected with the first capacitor C1 in parallel, one end of the eleventh resistor is grounded, the other end of the eleventh resistor R11 is connected with the cathode of the diode D1, the anode of the diode D1 is connected with the signal output end of the in-phase proportional amplifying circuit, and the twelfth resistor R12 is connected with the negative signal input end of the single-gate voltage comparison circuit.
5. A saw sensor based meter as claimed in claim 1, wherein: the single-threshold voltage comparator circuit comprises a single-threshold voltage comparator chip, a sixth direct-current power supply V6, a seventh direct-current power supply V7, an eighth direct-current power supply V8, a thirteenth resistor R13 and a second capacitor C2, and two power supply ports of the single-threshold voltage comparator chip are respectively connected with the seventh direct-current power supply V7 and the sixth direct-current power supply V6 and then grounded; the positive input port of the single-threshold voltage comparator chip is connected with the eighth direct-current power supply V8 and then grounded, the negative input port is connected with the second capacitor C2 and the thirteenth resistor R13 in sequence and then connected with the output port, and the output port is connected with the program control amplifying circuit and used for forming an automatic gain closed-loop circuit.
6. A saw sensor based meter as claimed in claim 1, wherein: the shaping circuit is a double-threshold voltage comparison circuit and comprises a double-threshold voltage comparator chip, a ninth direct-current power supply V9, a tenth direct-current power supply V10, a fourteenth resistor R14 and a fifteenth resistor R15; the positive power supply port and the negative power supply port of the double-threshold voltage comparator chip are respectively connected with a ninth direct-current power supply V9 and a tenth direct-current power supply V10 and then are grounded, a fourteenth resistor R14 is connected between the output port and the positive input port of the double-threshold voltage comparator chip in series, the positive input port of the double-threshold voltage comparator chip is connected with a fifteenth resistor R15 and then is grounded, and the negative input port of the double-threshold voltage comparator chip is connected with the output end of the AGC circuit.
7. A measuring method of a measuring instrument based on a surface acoustic wave sensor is characterized in that: the method comprises the following steps:
firstly, converting physical quantity of an object to be detected into variable quantity of surface acoustic wave frequency through a surface acoustic wave sensor and outputting a surface acoustic wave signal;
secondly, stabilizing the amplitude of the surface acoustic wave signal to obtain a signal with stabilized amplitude;
thirdly, filtering clutter from the signals after stable radiation;
fourthly, shaping the filtered and impurity-removed signal into a square wave signal;
fifthly, carrying out secondary filtering on the square wave signal;
sixthly, measuring the frequency of the surface acoustic wave signal according to the filtered square wave signal;
seventhly, calculating the physical quantity value of the object to be measured according to the measured signal frequency value through a relational expression between the physical quantity of the object to be measured and the frequency of the surface acoustic wave;
the measuring instrument based on the surface acoustic wave sensor comprises:
the device comprises a surface acoustic wave sensor, an AGC circuit, a first-order active band-pass filter, a shaping circuit, a second-order RC filter, an FPGA frequency measurement circuit, a single chip microcomputer and an LCD display screen; converting physical quantity of an object to be detected into variable quantity of surface acoustic wave frequency through a surface acoustic wave sensor to output a surface acoustic wave signal, stabilizing the amplitude of the surface acoustic wave signal through an AGC circuit to obtain a sinusoidal signal with controllable amplitude, filtering clutter of the sinusoidal signal after amplitude stabilization through a first-order active band-pass filter, further shaping the sinusoidal signal into a square wave signal through a shaping circuit, performing secondary filtering on the shaped square wave signal through a second-order RC filter, calculating the frequency of the surface acoustic wave signal through an FPGA frequency measurement circuit, inputting the frequency of the surface acoustic wave signal into a single chip microcomputer, calculating to obtain physical quantity of the object to be detected and storing the physical quantity of the object to be detected in the single chip microcomputer, and displaying the calculated physical quantity;
the AGC circuit comprises a two-stage amplifying circuit, a detection circuit and a single-threshold voltage comparison circuit which are connected in sequence, wherein the input end of the two-stage amplifying circuit is connected with the output end of the surface acoustic wave sensor, and the output end of the single-threshold voltage comparison circuit is connected to a gain control port of a program control amplifying circuit in the two-stage amplifying circuit to form a closed-loop automatic gain circuit; the two-stage amplifying circuit comprises a program-controlled amplifying circuit and an in-phase proportional amplifying circuit which are sequentially connected; the two-stage amplifying circuit is used for amplifying a surface acoustic wave signal output from the surface acoustic wave sensor; the detection circuit is used for detecting a low-frequency signal from the surface acoustic wave signal output by the two-stage amplification circuit; the single threshold voltage comparison circuit is used for providing discrimination voltage for the program control amplifying circuit in the two-stage amplifying circuit.
8. The method as claimed in claim 7, wherein the method comprises the following steps: and sixthly, measuring the frequency of the surface acoustic wave signal by using an equal-precision frequency measurement method according to the square wave signal.
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