CN115425932A - Piezoelectric accelerometer signal conditioning method and circuit for low-frequency vibration measurement - Google Patents
Piezoelectric accelerometer signal conditioning method and circuit for low-frequency vibration measurement Download PDFInfo
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Abstract
The invention belongs to the technical field of electric digital data processing, and discloses a piezoelectric accelerometer signal conditioning method and circuit for low-frequency vibration measurement. The method comprises the following steps: selecting a plurality of IC piezoelectric accelerometers to be reversely butted and installed to form two branches for pairing use, so that sensed alternating acceleration signals are opposite in phase; a matching transistor pair is used for forming a multi-path constant current source for supplying power; a plurality of instrument amplifier chips form a differential amplifying circuit, and a direct current coupling connection mode is adopted to introduce a plurality of IC piezoelectric accelerometer signals into the differential amplifying circuit so as to double the sensitivity of alternating acceleration signals while offsetting direct current bias voltage; subtracting the approximate direct current bias voltage to be zero; common mode noise is further suppressed by utilizing the high common mode rejection ratio characteristic of the instrument amplifier chip through two-stage differential amplification. The invention further inhibits common mode noise and improves the signal-to-noise ratio of the low-frequency broadband test signal through two-stage differential amplification.
Description
Technical Field
The invention belongs to the technical field of electrical digital data processing, and particularly relates to a signal conditioning method and circuit of an IC piezoelectric accelerometer for low-frequency vibration measurement.
Background
The built-in IC type piezoelectric accelerometer integrates and encapsulates the traditional piezoelectric acceleration sensitive element and the preamplifier circuit into a whole, has the characteristics of anti-interference, low noise, long-line transmission of test signals and the like, is developed into a standardized product system, and adopts a standard coaxial cable connector as an output interface, wherein the coaxial output interface is a 2-line system: the shielded wire is used as the ground wire, and the core wire is formed by combining the power supply wire and the signal output wire into a whole. When the device is used, the core wire is connected with a constant current source on one hand to supply power for an internal IC circuit; and meanwhile, the core wire is connected with a direct current blocking capacitor, and the measured acceleration alternating signal is output while the direct current bias voltage is blocked.
The piezoelectric accelerometer is used for low-frequency vibration measurement and aims to solve the problem of high output impedance, the piezoelectric accelerometer with an internal IC (integrated Circuit) and a pre-amplification circuit integrated in the piezoelectric accelerometer complete an impedance matching process and reduce output impedance, but a field effect transistor amplifier adopted by the pre-amplification circuit in the piezoelectric accelerometer with the internal IC needs to be supplied with power by an external constant current source, and a power supply line is also a signal output line, so that a direct current bias voltage of the field effect transistor amplifier needs to be isolated by an external blocking capacitor, and then an alternating current signal is coupled and output, so that the selection of the external blocking capacitor is important, and ideally, the loss of an alternating current signal is reduced to the minimum while the direct current voltage is effectively isolated. However, as known from the basic knowledge of electronic circuits, when a capacitor is operated in a circuit and an alternating signal passes through the capacitor, capacitance exists always, and the magnitude of the capacitance is related to the operating frequency. The piezoelectric ceramic sensitive element is used for measuring the piezoelectric accelerometer by low-frequency micro-vibration, the working frequency of the piezoelectric element can be as low as 0.05Hz, and the capacitive reactance of a blocking capacitor (the lower the frequency is, the larger the capacitance value of the required blocking capacitor is) is correspondingly as high as hundreds of kilohms, so that high requirements are provided for impedance matching; the capacitive reactance of the blocking capacitor is considered as a part of the internal resistance of the accelerometer with the built-in IC for analysis, and the external blocking capacitor of the traditional signal conditioning circuit influences the low-frequency response of the accelerometer when the piezoelectric accelerometer is actually used.
Through the above analysis, the problems and defects of the prior art are as follows: when the piezoelectric accelerometer is actually used for low-frequency vibration measurement, the low-frequency response of the sensor is usually required, and the signal-to-noise ratio of the measurement is also concerned, but the IC type piezoelectric accelerometer in the prior art has poor anti-interference and noise reduction performance, and cannot avoid using a capacitive device to isolate direct-current voltage at the same time, so that the signal-to-noise ratio effect in the test is poor, and the test sensitivity precision is influenced.
Disclosure of Invention
In order to overcome the problems in the related art, the disclosed embodiments of the present invention provide a method and a circuit for conditioning signals of a piezoelectric accelerometer for low-frequency vibration measurement. In particular to a signal conditioning method and a signal conditioning circuit of an IC piezoelectric accelerometer for low-frequency vibration measurement.
The technical scheme is as follows: a piezoelectric accelerometer signal conditioning method and circuit for low frequency vibration measurement includes:
s1, selecting two IC piezoelectric accelerometers to be reversely butted and installed on an adaptive installation seat to form two branches, wherein the two branches are used in a matched mode, the vibration pickup directions are opposite, so that sensed alternating acceleration signals are opposite in phase, and the power supply working modes of internal ICs are the same;
s2, two paths of constant current sources are formed by matching transistor pairs to supply power to the IC circuits in the two paired IC piezoelectric accelerometers, so that the direct current bias voltages of the two IC circuits are approximately equal;
s3, forming a composite differential amplification circuit by using a plurality of instrument amplifier chips, introducing two IC piezoelectric accelerometer signals into the differential amplification circuit in a direct current coupling connection mode, and doubling the sensitivity of an alternating acceleration signal while offsetting a direct current bias voltage; subtracting the approximate direct current bias voltage to be zero;
s4, the high common-mode rejection ratio characteristic of the composite differential amplifier of the integrated instrument amplifier chip is utilized, two-stage differential amplification is carried out, the first stage adopts a symmetrical cross input mode, the input characteristic difference introduced by the potential difference of the input end is reduced, the balance of the input end is improved, and therefore the common-mode rejection ratio of the differential circuit is improved; and the second stage further suppresses common-mode noise through differential operation on the basis of the differential output of the first stage.
In one embodiment, in step S1, the plurality of IC piezoelectric accelerometers are the same model.
In one embodiment, in step S2, the circuit structure of each constant current source of the plurality of constant current sources is identical.
In one embodiment, in step S3, the composite differential amplifying circuit is divided into two stages of differential amplification: the input stage positive and negative input ends are input in a crossed manner, so that the input characteristic difference caused by reference potential imbalance is reduced, after two paths of signals are subtracted in two first-stage instrument amplifier chips at the input ends, common-mode signals are reduced, differential-mode signals are enhanced, and then the signals enter a second-stage instrument amplifier chip for differential amplification; the whole composite differential amplifying circuit channel is not provided with a blocking capacitor; the signals of the IC piezoelectric accelerometers are introduced into a differential amplifying circuit, after the direct current bias voltages are subtracted, the direct current bias voltages output by the two IC piezoelectric accelerometers are equal and are zero after the direct current bias voltages are subtracted, and the alternating acceleration signals are 180-degree phase-opposite in phase difference and are doubled after the direct current bias voltages are subtracted.
In one embodiment, in step S4, the composite differential amplifier is divided into two stages of differential amplification, the input stage is cross-input at the positive and negative input ends, and the two paths of signals are cross-subtracted in the two first instrumentation amplifier chips at the input ends, and then enter the second instrumentation amplifier chip for subtraction and difference.
In one embodiment, after step S4, the signal is output and then enters an integrating circuit, and is fed back to the reference potential input end of the final instrument amplifier to form a servo feedback loop, so as to reduce zero drift.
Another object of the present invention is to provide a piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement, comprising:
a front-end circuit formed by a field effect tube follower is arranged in an IC piezoelectric accelerometer and used for sensing the phase reversal of alternating acceleration signals;
the matched transistor pairs form two paths of constant current sources which are relatively consistent and supply power to the front-end circuit; the composite differential amplification circuit is formed by a plurality of instrument amplifier chips and is used for introducing a plurality of IC piezoelectric accelerometer signals into the differential amplification circuit in a direct current coupling connection mode, so that the sensitivity of alternating acceleration signals is doubled while the direct current bias voltage is counteracted; subtracting the approximate direct current bias voltage to be zero; and the common-mode noise is further suppressed by utilizing the high common-mode rejection ratio characteristic of the instrument amplifier chip and through two-stage differential amplification.
In one embodiment, the front end circuitry comprises:
the system comprises a plurality of IC piezoelectric accelerometers, a plurality of low-frequency IC piezoelectric accelerometers are reversely mounted in a butt joint mode to form two branches which are used in a matched mode, and sensed alternating acceleration signals are in opposite phase;
and the field effect tube follower converts the charge signal of the piezoelectric element into a voltage signal in a drain following mode and outputs the voltage signal.
In one embodiment, the matched transistor pair comprises: the constant current sources respectively supply power to the corresponding IC piezoelectric accelerometers at the same time, and the generated direct current bias voltages are consistent.
In one embodiment, the composite differential amplifier is divided into two stages of differential amplification: the positive and negative input ends of the input stage are input in a crossed manner, so that the input characteristic difference caused by reference potential imbalance is reduced, after two paths of signals are subtracted in two first-stage instrument amplifier chips at the input ends respectively, common-mode signals are naturally reduced, differential-mode signals are enhanced, and then the signals enter a second-stage instrument amplifier chip for differential amplification;
the signal enters an integrating circuit after being output, and is fed back to the reference potential input end of the final instrument amplifier to form a servo feedback loop, so that zero drift of a low-frequency circuit is inhibited.
By combining all the technical schemes, the invention has the advantages and positive effects that:
first, aiming at the technical problems existing in the prior art and the difficulty in solving the problems, the technical problems to be solved by the technical scheme of the present invention are closely combined with results, data and the like in the research and development process, and some creative technical effects are brought after the problems are solved. The specific description is as follows:
in order to meet the requirement of signal-to-noise ratio during low-frequency broadband vibration measurement and adapt to a universal coaxial cable output interface of a built-in IC type piezoelectric accelerometer, the invention provides a signal conditioning method and a hardware circuit of the internally-mounted IC piezoelectric accelerometer for low-frequency broadband vibration measurement, which comprises the following steps: two accelerometers of the same type with good consistency are selected for reverse butt joint installation and paired use; a double-path constant current source which is relatively consistent is formed by matching transistors and geminate transistors and supplies power to an IC inside the accelerometer, so that the consistency of two low-frequency measurement branches is improved;
a differential amplification circuit is formed by a plurality of instrument amplifier chips, and a direct current coupling connection mode is adopted to introduce a piezoelectric accelerometer signal into the differential amplification circuit so as to multiply the sensitivity of an alternating acceleration signal while offsetting a direct current bias voltage; the signal loss caused by the direct current capacitor capacitive reactance in the circuit when a single piezoelectric accelerometer is used is avoided, and the static working point change introduced by the front end and the rear end of the direct current capacitor with large capacitance value is avoided, so that the static working point during low-frequency measurement is relatively stable while the signal to noise ratio is improved.
The differential amplification circuit adopts a composite instrument amplifier circuit structure, reduces the fading of a Common Mode Rejection Ratio (CMRR) caused by the level difference of input ends in a higher frequency band through input-stage cross coupling, and inhibits the zero drift of a low-frequency circuit through connecting an integral servo loop at the reference potential input end of a rear-stage instrument amplifier.
Secondly, considering the technical solution as a whole or from the perspective of products, the technical effects and advantages of the technical solution to be protected by the present invention are specifically described as follows:
the invention provides a signal conditioning method and a hardware circuit of an internally-installed IC (integrated circuit) piezoelectric accelerometer for low-frequency broadband vibration measurement, which comprises the following steps: selecting two low-frequency IC piezoelectric accelerometers of the same type with good consistency, carrying out reverse butt joint installation, and pairing for use; a matched transistor pair forms a relatively consistent two-way constant current source to supply power to an IC in the accelerometer; a differential amplifying circuit is formed by a plurality of instrument amplifier chips, and a direct current coupling connection mode is adopted to introduce a piezoelectric accelerometer signal into the differential amplifying circuit, so that the sensitivity of an alternating acceleration signal is doubled while a direct current bias voltage is counteracted; the differential amplification circuit is a composite instrument amplifier formed by a plurality of instrument amplifier chips, and compensates the attenuation of a Common Mode Rejection Ratio (CMRR) caused by the level difference of input ends in a relatively high frequency band through input-end cross coupling, so that the measurement working bandwidth of the accelerometer is ensured; the high common mode rejection ratio characteristic of the instrument amplifier chip is utilized, common mode noise is further suppressed through two-stage differential amplification, and the signal-to-noise ratio of the low-frequency broadband test signal is improved.
Compared with the prior art, the invention has the advantages that:
the invention adopts a method of DC coupling output signal and common mode voltage offset to design a signal conditioning circuit: selecting accelerometers of the same type to be paired with accelerometers to be used, and reversely butting piezoelectric accelerometers with two built-in ICs to form two branches, so that sensed alternating acceleration signals are opposite in phase to each other: the matched transistors are used for aligning the tubes to form a double-path constant current source with good consistency, and the double-path constant current source is used for respectively supplying power to IC circuits in the two accelerometers, so that direct current bias voltages on the two branches are approximately consistent; the signal of the accelerometer of the IC circuit is output to a differential circuit formed by an instrument amplifier, at the moment, direct current bias voltage is counteracted as a common mode signal, and an alternating acceleration signal is an inverted differential mode signal, and is retained after differential subtraction, so that the basic principle of signal processing shows that the amplitude is changed into 2 times of the original value by subtracting two inverted signals, and correspondingly, the measuring sensitivity is doubled; the approximate DC bias voltage is approximate to zero after subtraction, and a blocking capacitor is not needed to isolate the DC voltage, so that the influence of the blocking capacitor used by an AC coupling circuit on low-frequency acceleration measurement is avoided (according to Thevenin's theorem, the capacitive reactance of the blocking capacitor plays a role in voltage division in the circuit to enable an acceleration signal to be lost), a useful acceleration signal is doubled, a useless DC common mode signal is approximate to zero after subtraction, and the signal-to-noise ratio of the test is naturally improved.
Third, as inventive supplementary proof of the claims of the present invention, also appear: the signal conditioning circuit which is in reverse butt joint with the two matched IC piezoelectric accelerometers and is in direct current coupling avoids inherent low-frequency response limitation of an alternating current coupling circuit which adopts a blocking capacitor, so that the effective working frequency band of the piezoelectric accelerometers is expanded to low frequency, the lower frequency limit of the piezoelectric accelerometers is not limited by the performance of the matching circuit any more, and the working frequency characteristic of the piezoelectric elements is better matched. The use of expensive large-capacity and low-loss capacitors is avoided, and the cost performance is improved.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure.
FIG. 1 is a flow chart of a signal conditioning method for an IC piezoelectric accelerometer for measuring low-frequency vibration according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a conventional IC type piezoelectric accelerometer and an external circuit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a counter-docking installation of paired piezoelectric accelerometers provided by an embodiment of the present invention;
FIG. 4 is a schematic diagram of a connection relationship between an accelerometer and a signal conditioning circuit using DC coupling according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a two-way matching constant current source circuit according to an embodiment of the present invention
FIG. 6 is a schematic diagram of a composite differential amplifier circuit provided by an embodiment of the invention;
FIG. 7 is a schematic diagram of a signal conditioning circuit according to an embodiment of the present invention;
in the figure: A. a front-end circuit; a-1, a piezoelectric accelerometer; a-2, a field effect tube follower; B. a pair of matching transistors; C. a composite differential amplifier circuit; c-1, a first-stage instrumentation amplifier chip; c-2, a second-level instrumentation amplifier chip; c-3, final instrument amplifier.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
1. Illustrative examples are illustrated:
the signal conditioning method of the IC piezoelectric accelerometer for low-frequency vibration measurement, provided by the embodiment of the invention, comprises the following steps:
selecting two IC piezoelectric accelerometers of the same type and low frequency with good consistency to be reversely butted and installed to form two branches for matching use, so that sensed alternating acceleration signals are in opposite phase;
forming two relatively consistent constant current sources by using the matched transistor pairs to supply power to the interior of the IC piezoelectric accelerometer; therefore, the direct current bias voltages on the two branches are approximately consistent;
a differential amplifying circuit is formed by a plurality of instrument amplifier chips, and two IC piezoelectric accelerometer signals are introduced into the differential amplifying circuit in a direct current coupling connection mode to double the sensitivity of an alternating acceleration signal while offsetting direct current bias voltage; (ii) a The approximate direct current bias voltage is subtracted to be approximate to zero; the differential amplification circuit is a composite instrument amplifier formed by a plurality of instrument amplifier chips, and compensates the attenuation of a Common Mode Rejection Ratio (CMRR) caused by the level difference of input ends in a relatively high frequency band through input-end cross coupling, so that the measurement working bandwidth of the accelerometer is ensured;
the high common mode rejection ratio characteristic of the instrument amplifier chip is utilized, common mode noise is further suppressed through two-stage differential amplification, and the signal-to-noise ratio of the low-frequency broadband test signal is improved.
The method specifically comprises the following steps:
the piezoelectric accelerometer signal conditioning method for low-frequency vibration measurement comprises the following steps:
firstly, selecting two IC piezoelectric accelerometers A-1 to be reversely butted and installed on an adaptive installation seat to form two branches, wherein the two branches are used in a matched mode, the vibration pickup directions are opposite, so that sensed alternating acceleration signals are opposite in phase, and the power supply working modes of internal ICs are the same;
secondly, two paths of constant current sources are formed by the matched transistor pair B to supply power to the IC circuits in the two paired IC piezoelectric accelerometers A-1, so that the direct current bias voltages of the two IC circuits are approximately equal;
thirdly, a composite differential amplification circuit 3 is formed by a plurality of instrument amplifier chips, signals of two IC piezoelectric accelerometers A-1 are introduced into the differential amplification circuit in a direct current coupling connection mode, and the sensitivity of an alternating acceleration signal is doubled while the direct current bias voltage is counteracted; subtracting the approximate direct current bias voltage to be zero;
fourthly, the high common mode rejection ratio characteristic of the instrument amplifier chip is utilized, two-stage differential amplification is carried out, the first stage adopts a symmetrical cross input mode, the input characteristic difference introduced by the potential difference of the input end is reduced, the balance of the input end is improved, and therefore the common mode rejection ratio of the differential circuit is improved; and the second stage further suppresses common-mode noise through differential operation on the basis of the differential output of the first stage.
Example 1
As shown in fig. 1, a method for conditioning signals of an IC piezoelectric accelerometer for low-frequency vibration measurement according to an embodiment of the present invention includes the following steps:
s101: according to the factory calibration certificate of the IC piezoelectric accelerometer A-1, two sensors with good sensitivity consistency (for example, the sensitivity difference is not more than 0.5 decibel) are selected according to the sensitivity response curve, and the two sensors are oppositely installed.
S102: and a matching transistor is used for forming two paths of constant current source circuits for the tube B, the circuit structures of all constant current sources are consistent, and high-precision resistors are selected to ensure that the circuit performances are approximately consistent.
S103: and a constant current source is used for supplying power to the two IC piezoelectric accelerometers A-1.
S104: and (3) amplifying by using a plurality of instruments to form a composite differential amplifier C: the differential amplification is divided into two stages of differential amplification, the input stage is input in a cross mode at positive and negative input ends, two paths of signals are respectively subjected to cross subtraction in two first instrumentation amplifier chips C-1 at the input ends, and then enter a second-stage instrumentation amplifier chip C-2 for subtraction and differential.
S105: the signal enters an integrating circuit after being output and is fed back to the reference potential input end of the final-stage instrument amplifier C-3 to form a servo feedback loop, and zero drift is reduced.
Example 2
As shown in fig. 2, an operating principle of an IC type piezoelectric accelerometer 1-1 according to an embodiment of the present invention includes:
the IC type piezoelectric accelerometer of the standard interface is shown in fig. 2: the piezoelectric ceramic element T1 and the front-end circuit A1 are integrally packaged, the output interface of the piezoelectric ceramic element T1 is a coaxial connector P1, only two external connecting wires are connected, and one of the two connecting wires is connected with the shielding layer of P1; one is connected with the core wire of the coaxial connector and is used as a common wire for power supply and signal output, and the traditional connection method is as follows: the constant current source supplies power forward, the DC bias voltage is isolated by a DC blocking capacitor C0, and the alternating signal is coupled to the rear stage.
The dc blocking capacitor C0 presents an alternating impedance, which is related to the frequency f:
the lower the frequency is, the larger the alternating current impedance is, and thus, the capacitive device exists in the circuit, which is unfavorable for low-frequency measurement, so that the impedance matching difficulty of a post-stage circuit is increased, the signal integrity of low-frequency signal energy transmitted to a post-stage is reduced, and the low-frequency response of a measurement system is influenced; and the lower the working frequency is, the higher the capacitance value of the required blocking capacitor is, so that the common knowledge of circuit design can know that the stability of the reference potential becomes worse after the alternating signal passes through the blocking capacitor with large capacitance value, and the actual effect of the test is influenced.
The direct current coupling circuit can avoid the problems, and after capacitive devices are removed from the circuit, low-frequency signals can be transmitted to a post-stage circuit without loss. However, if the dc bias voltage is to be suppressed, the circuit cannot perform the amplification function, and the dc bias voltage will saturate the circuit in the first stage of amplification. According to the invention, two paired IC piezoelectric accelerometers are adopted and are oppositely installed in a butt joint mode, and output signals are subjected to differential subtraction to counteract direct-current bias voltage.
2) As shown in fig. 3, the paired piezoelectric accelerometer 1-1 according to the embodiment of the present invention is mounted in a reverse docking manner.
The two selected accelerometers with good sensitivity-frequency response test curve consistency are used in pairs, and in the vibration measuring direction, the two IC piezoelectric accelerometers A-1 are oppositely arranged on the installation adapter seat in the reverse direction, so that the measured vibration alternating signals are in opposite phase.
3) As shown in fig. 4, a connection relationship between an accelerometer and a signal conditioning circuit is schematically shown, and a connection manner of a piezoelectric accelerometer signal conditioning circuit is shown in fig. 3, in which a constant current source 1 and a constant current source 2 supply power to two IC piezoelectric accelerometers a-1, respectively, and output signal lines of the two IC piezoelectric accelerometers a-1 are directly connected with an input end of a differential amplifier, i.e., a composite differential amplifier C, to form a connection manner of direct current coupling; the constant current source 1 and the constant current source 2 are constant current sources constituted by a matching transistor pair 2, and the matching transistor pair 2 is a highly uniform transistor produced by an electronic device manufacturer, and the non-uniformity error of the constant current source 1 and the constant current source 2 can be controlled within a very small range.
The constant current source 1 and the constant current source 2 respectively supply power to the two IC piezoelectric accelerometers A-1, and the generated direct current bias voltages are approximately consistent; the mechanical mounting positions of the two IC piezoelectric accelerometers A-1 are opposite; therefore, when measuring vibration, the main component of the direct current bias voltage on the two branches is a common mode signal, while the vibration acceleration alternating signal is in an opposite phase, and the main component is a differential mode signal.
After the common-mode signal and the differential-mode signal enter the composite differential amplifier C, subtracting the common-mode signal to obtain rejection; while the amplitude of the inverted differential mode signal is doubled, i.e. the test sensitivity is doubled.
4) As shown in fig. 5, for a circuit diagram of a matching transistor pair B, that is, a schematic diagram of a dual-path matching constant current source circuit, in order to ensure the consistency of two constant current source branches, a dual-path constant current source is formed by using a tube Q4 of the matching transistor pair B, two triodes with extremely high consistency are arranged inside the Q4, a device which is specially used for matching consistency use occasions and produced by an electronic device manufacturer, and for a single branch, a universal triode constant current source classic circuit is provided, wherein diodes D1, D2, D3, and D4 are zener diodes with the same conduction voltage and volt-ampere characteristics, resistors R3, R4, R5, and R6 are metal foil resistors with high precision and temperature stability, and resistors RL1 and RL2 are load matching resistors.
Taking one of the branches (source 1) as an example:
diodes D1, D2 and R5 are connected in series to form a stable voltage at the base of the triode 1 of the matching transistor pair Q4, which is U D The base-emitter voltage of the triode is U BE And the current gain is beta, the output current of the source 1 is:
similarly, the output current of the source 2 is:
5) As shown in fig. 6, as a schematic circuit diagram of a composite differential amplifier C, that is, as an electrical schematic diagram of a composite differential amplifying circuit, although the IC piezoelectric accelerometer a-1 with better consistency is selected as a front stage, and a dual-path constant current source formed by matched transistor-pair transistors is also used for power supply, the dc bias voltages of two branches are both in the order of several volts (about half of the power supply voltage), and there may be a slight difference between the two branches, and for a differential circuit (whether a transistor discrete component or a differential amplifier with an integrated circuit structure), the difference in dc levels at the positive and negative input ends may cause a change in the operating characteristics of devices inside the input stage of the circuit, and the output common mode error of the differential circuit, which is introduced by the imbalance of the input dc levels, may cause a reduction in the Common Mode Rejection Ratio (CMRR) of the differential circuit in a higher frequency band: with the frequency rising, the Common Mode Rejection Ratio (CMRR) is decreased rapidly, namely in the higher frequency band, the signal to noise ratio of the test is decreased, aiming at the situation, the invention adopts a plurality of instrument amplifiers to form a composite differential amplifier to improve the common mode rejection ratio and expand the working bandwidth:
u1, U2 are integrated difference instrument amplifier (namely C-1), as first grade amplification, its input cross-coupling, respectively restrain common mode signal, amplify the differential mode signal, and the accelerometer of antiphase is as the differential mode signal, makes the sensitivity double. The second stage differential instrumentation amplifier (i.e., C-2) U3 amplifies the difference between the output signals of the preceding stages U1, U2 while rejecting common mode signals. Because the common-mode responses of U1, U2 are correlated, the output common-mode errors caused by the common-mode error voltages are also similar. The common-mode error of U3 appears as a common-mode signal, which is also rejected in the second stage, while the differential signal of the previous stage is further amplified.
The output signal of U3 is fed back to the reference level input pin 5 of U3 through an integral servo loop formed by an operational amplifier U4 (i.e., the final instrumentation amplifier C-3), a resistor R11 and a capacitor C3, wherein a dc voltage error input at a previous stage is also fed back to the previous instrumentation amplifier for cancellation.
Example 2
As shown in fig. 7, an IC piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement according to an embodiment of the present invention includes:
adopt IC piezoelectric accelerometer inside to have leading circuit 1 that field effect transistor follower constitutes, include:
the method comprises the following steps that a plurality of IC piezoelectric accelerometers A-1 and a plurality of IC piezoelectric accelerometers A-1 are selected, two IC piezoelectric accelerometers of the same type and the same type with good consistency are reversely butted and installed to form two branches, and the two branches are paired for use, so that sensed alternating acceleration signals are opposite in phase;
the field-effect tube follower A-2 is respectively composed of field-effect tubes Q1 and Q2, peripheral resistors R1 and Rs1, and R2 and Rs2, and the main structure adopts a source-drain following mode with a conventional and classical structure in electronics to convert charge signals of the piezoelectric elements T1 and T2 into voltage signals for output;
the matched transistor pair B forms a two-way constant current source which is relatively consistent and supplies power for the interior of the IC piezoelectric accelerometer;
a composite differential amplification circuit C formed by a plurality of instrument amplifier chips is divided into two stages of differential amplification: the positive and negative input ends of the input stage are input in a crossed manner, so that the input characteristic difference caused by reference potential imbalance is reduced, after two paths of signals are subtracted in two first-stage instrumentation amplifier chips C-1 at the input ends respectively, common-mode signals are naturally reduced, differential-mode signals are enhanced, and then the signals enter a second-stage instrumentation amplifier chip C-2 for differential amplification; the whole composite differential amplifying circuit C channel does not have any blocking capacitor, so the composite differential amplifying circuit C channel belongs to a connection mode of direct current coupling without capacitors, signals of the IC piezoelectric accelerometer A-1 are introduced into the differential amplifying circuit, after direct current bias voltages are subtracted, because the consistency of the IC piezoelectric accelerometer A-1 is selected before, the direct current bias voltages output by the two IC piezoelectric accelerometers A-1 are approximately equal and are approximately zero after subtraction, and useful alternating acceleration signals are opposite in phase with the phase difference of 180 degrees and are naturally doubled after subtraction, so that the sensitivity of the alternating acceleration signals is doubled while the direct current bias voltages are offset.
In the embodiment of the invention, a composite differential amplifier circuit C formed by a plurality of instrument amplifier chips inhibits the fading of a Common Mode Rejection Ratio (CMRR) caused by the level difference of input ends at a relatively high frequency band through input-stage cross coupling, and ensures the measurement working bandwidth of an accelerometer; through two-stage differential amplification, by utilizing the high common mode rejection ratio characteristic of an instrumentation amplifier chip, the common mode rejection ratio of a conventional instrumentation amplifier reaches more than 100 decibels, namely, a differential mode signal is amplified, common mode interference is suppressed, the gain of the amplified differential mode signal is more than 10000 times of that of the amplified common mode signal, common mode noise is further suppressed, input stage cross coupling input is realized, the difference influence of the input end level is reduced, the fading trend of the Common Mode Rejection Ratio (CMRR) in a high frequency band is slowed down, and the bandwidth is equivalently expanded, so the signal-to-noise ratio of a broadband test signal is improved.
In the embodiment of the invention, the signal differentially amplified by the composite differential amplifying circuit C is output and then enters the integrating circuit to be fed back to the reference potential input end of the final-stage instrument amplifier C-3 to form a servo feedback loop, so that the zero drift of the integrating circuit, namely a low-frequency circuit, is inhibited.
In a preferred embodiment, a low-frequency IC piezoelectric accelerometer A-1 is selected, and sensors with good consistency of sensitivity-frequency response test curves are selected and used in pairs; the paired IC piezoelectric accelerometers are mounted opposite each other on a mating mount.
And a matching transistor pair B and a high-precision resistor are used for forming a double-path constant current source circuit with similar consistency, and the two constant current source circuits are used for respectively supplying power to the internal circuits of the two paired IC piezoelectric accelerometers.
The power supply/signal two-in-one circuits of the two paired IC piezoelectric accelerometers are directly connected to the positive input stage and the negative input stage of the differential amplification circuit (without a DC blocking capacitor of a conventional AC coupling circuit) to form DC coupling connection; the differential amplifier is a composite instrument amplifier circuit formed by a plurality of instrument amplifier chips, and the differential mode signals are amplified and the common mode signals are simultaneously inhibited through input-stage cross coupling and two-stage differential amplification, so that after the power is supplied by a constant current source, direct current bias voltages on power supply/signals of two paired IC type piezoelectric accelerometers are subtracted as common mode voltages, and because the two IC type piezoelectric accelerometers are selected and paired in consistency, and the constant current source is formed by matching transistor pairs, the consistency is also ensured, most direct current bias voltages output by the IC piezoelectric accelerometers are inhibited, and useful measured alternating current signals are inverted differential mode signals (because the two accelerometers are reversely butt-jointed and installed), are effectively amplified, and the sensitivity is doubled.
In the preferred embodiment of the present invention, the inside of the IC piezoelectric accelerometer 1 is discussed by taking the circuit structure of a common low-frequency IC piezoelectric accelerometer as an example: the main front-end circuit in the IC piezoelectric accelerometer A-1 is a field effect tube follower which is composed of a matching resistor R1, a current limiting resistor Rs1 and a junction field effect tube Q1, and T1 is a piezoelectric element; likewise, the IC piezoelectric accelerometer a-1 includes: the IC piezoelectric accelerometer 1 and the IC piezoelectric accelerometer 2 are selected products with the same model and good consistency.
The IC piezoelectric accelerometer 1 and the IC piezoelectric accelerometer 2 are powered by two matched constant current sources to form two measuring branches. The double-path matching constant current source is a typical constant current source circuit consisting of a matching transistor pair transistor Q4, voltage-regulator tube diodes D1, D2, D3 and D4 and high-precision resistors R3, R4, R5 and R6, and the typical constant current source circuit is supplied with power through a power supply/signal output two-in-one line of the IC piezoelectric accelerometer 1 and the IC piezoelectric accelerometer 2 after passing through load matching resistors RL1 and RL2 respectively; meanwhile, the power supply/signal output two-in-one lines of the IC piezoelectric accelerometer 1 and the IC piezoelectric accelerometer 2 are respectively connected with the positive input end and the negative input end of the differential amplification circuit to form direct current coupling. At this time, the signal input to the differential amplifier circuit includes not only the alternating acceleration signal but also a dc bias voltage.
In the preferred embodiment of the present invention, IC piezoelectric accelerometer 1 and IC piezoelectric accelerometer 2 are mounted in opposite directions as shown in fig. 3, and the two alternating acceleration signals are opposite-phase differential mode signals.
In the preferred embodiment of the invention, the differential amplification circuit is a composite amplifier mainly composed of instrumentation amplifiers U1, U2 and U3, wherein U1 and U2 form a first-stage differential amplification circuit, the input ends of which are cross-coupled, so that the influence of Common Mode Rejection Ratio (CMRR) change caused by level difference of the input ends is reduced; direct current bias voltage of the preceding stage circuit is subtracted, alternating acceleration signals are doubled, and then the signals enter a second-stage differential amplifier U3, common mode signals are further restrained, differential mode signals are amplified, common Mode Rejection Ratio (CMRR) is improved, and therefore signal-to-noise ratio during accelerometer measurement is improved.
In the preferred embodiment of the present invention, the operational amplifier U4, the resistor R11 and the capacitor C3 form an integrating circuit, the resistor R12 is an input end balancing resistor, and the dc offset voltage and the very low frequency zero offset at the output end of the differential amplifier are integrated and fed back to the reference voltage input end (pin 5) of the second stage differential amplifier U3 to form a servo loop, so that the low frequency cut-off frequency of the circuit is determined by the RC time constant, for example, the resistor R11 takes 10M ohms, and the C3 takes 10 microfarads, and the low frequency cut-off frequency (-3 dB) of the circuit is about 0.02Hz, which meets the requirement of low frequency acceleration measurement.
In the above embodiments, the description of each embodiment has its own emphasis, and reference may be made to the related description of other embodiments for parts that are not described or recited in any embodiment.
2. The application example is as follows:
by adopting the technical scheme of the invention, the lower limit of the measuring frequency of the piezoelectric accelerometer can be expanded to the low-frequency end, and the magnetoelectric vibration sensor commonly used in seismology can be functionally replaced, so that the magnetoelectric vibration sensor is used in the technical fields of seismic monitoring, mineral seismic prospecting and the like.
3. Evidence of the relevant effects of the examples:
by adopting the technical scheme of the invention, the limit of the matched alternating current coupling signal conditioning circuit on the low-frequency response characteristic when the traditional IC type accelerometer is used in a single body is avoided. According to Thevenin's theorem, the lower limit of the frequency is no longer limited by the capacitive reactance of the blocking capacitor; compared with the characteristics and natural properties of the direct current coupling circuit and the alternating current coupling circuit, the signal conditioning circuit can better match the working frequency characteristics of the piezoelectric element; and the technical scheme of the accelerometer reverse butt joint and the signal differential processing enables common mode noise signals to be further inhibited, the amplitude of useful differential mode signals is doubled, and the signal-to-noise ratio of the piezoelectric accelerometer during low-frequency measurement is improved while the sensitivity is improved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope of the present invention disclosed herein, which is within the spirit and principle of the present invention, should be covered by the present invention.
Claims (10)
1. A piezoelectric accelerometer signal conditioning method for low-frequency vibration measurement is characterized by comprising the following steps:
s1, selecting two IC piezoelectric accelerometers (A-1) to be reversely butted and installed on an adaptive installation seat to form two branches, wherein the two IC piezoelectric accelerometers (A-1) are used in a matched mode, the vibration pickup directions are opposite, so that sensed alternating acceleration signals are opposite in phase, and the power supply working modes of internal ICs are the same;
s2, two paths of constant current sources are formed by the matched transistor pair (B) to supply power to the IC circuits in the two paired IC piezoelectric accelerometers (A-1), so that the direct-current bias voltages of the two IC circuits are equal;
s3, a composite differential amplification circuit (3) is formed by a plurality of instrument amplifier chips, signals of two IC piezoelectric accelerometers (A-1) are introduced into the differential amplification circuit in a direct current coupling connection mode, the direct current bias voltage is counteracted, meanwhile, the sensitivity of an alternating acceleration signal is doubled, and the direct current bias voltage is zero after subtraction;
s4, by utilizing the high common-mode rejection ratio characteristic of a composite differential amplifier (C) of the integrated instrument amplifier chip, through two-stage differential amplification, the first stage adopts a symmetrical cross input mode, reduces the input characteristic difference introduced by the potential difference of the input end, and improves the balance of the input end, thereby improving the common-mode rejection ratio of a differential circuit; the second stage further suppresses common mode noise through differential operation on the basis of the differential output of the first stage.
2. Method for piezoelectric accelerometer signal conditioning for low frequency vibration measurement according to claim 1, characterized in that in step S1 the plurality of IC piezoelectric accelerometers (a-1) are of the same model.
3. The method for conditioning a signal of a piezoelectric accelerometer for low frequency vibration measurement according to claim 1, wherein in step S2, the circuit structure of each constant current source of the multiple constant current sources is identical.
4. The piezoelectric accelerometer signal conditioning method for low frequency vibration measurement according to claim 1, wherein in step S3, the composite differential amplification circuit (C) is divided into two stages of differential amplification: the input stage positive and negative input ends are input in a crossed manner, the input characteristic difference caused by reference potential imbalance is reduced, two paths of signals are subtracted in two first-stage instrument amplifier chips (C-1) at the input ends respectively, then common-mode signals are reduced, differential-mode signals are enhanced, and then the signals enter a second-stage instrument amplifier chip (C-2) for differential amplification; the whole channel of the composite differential amplifying circuit (C) is not provided with a blocking capacitor; the signals of the IC piezoelectric accelerometers (A-1) are introduced into a differential amplifying circuit, after the direct current bias voltages are subtracted, the direct current bias voltages output by the two IC piezoelectric accelerometers (A-1) are equal and are zero after the direct current bias voltages are subtracted, and the alternating acceleration signals are 180-degree phase differences and are doubled after the direct current bias voltages are subtracted.
5. The method for conditioning signals of a piezoelectric accelerometer for low-frequency vibration measurement according to claim 1, wherein in step S4, the composite differential amplifier (C) is divided into two stages of differential amplification, the input stages are cross-input at the positive and negative input terminals, and the two signals are cross-subtracted in two first instrumentation amplifier chips (C-1) at the input terminals and then enter a second instrumentation amplifier chip (C-2) for subtraction and differential.
6. The method for conditioning a piezoelectric accelerometer signal for low frequency vibration measurement according to claim 1, wherein after step S4, the signal is outputted and then fed back to the reference potential input terminal of the final instrumentation amplifier (C-3) to form a servo feedback loop, thereby reducing zero drift.
7. A piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement implementing the piezoelectric accelerometer signal conditioning method for low frequency vibration measurement of any one of claims 1 to 6, wherein the piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement comprises:
a front-end circuit (A) formed by a field effect tube follower is arranged in the IC piezoelectric accelerometer and used for sensing the phase reversal of alternating acceleration signals;
the matched transistor pair (B) forms a two-way constant current source which is relatively consistent and supplies power to the front-end circuit (A);
the composite differential amplification circuit (C) is formed by a plurality of instrument amplifier chips and is used for introducing signals of a plurality of IC piezoelectric accelerometers (A-1) into the differential amplification circuit in a direct current coupling connection mode, so that the sensitivity of an alternating acceleration signal is doubled while the direct current bias voltage is counteracted; subtracting the approximate direct current bias voltage to be zero; and the common-mode noise is further suppressed by utilizing the high common-mode rejection ratio characteristic of the instrument amplifier chip and through two-stage differential amplification.
8. Piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement according to claim 7, characterized in that the front end circuit (A) comprises:
the system comprises a plurality of IC piezoelectric accelerometers (A-1), wherein the IC piezoelectric accelerometers (A-1) are reversely mounted in a butt joint mode at low frequency to form two branches which are used in a matched mode, so that sensed alternating acceleration signals are opposite in phase;
and the field effect transistor follower A-2 converts the charge signal of the piezoelectric element into a voltage signal for output in a drain following mode.
9. The piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement of claim 7, wherein the matched transistor pair (B) comprises: the constant current sources respectively and simultaneously supply power to the corresponding IC piezoelectric accelerometers (A-1), and the generated direct current bias voltages are consistent.
10. Piezoelectric accelerometer signal conditioning circuit for low frequency vibration measurement according to claim 7, characterized in that the composite differential amplifier (C) is divided into two stages of differential amplification: the input stage positive and negative input ends are input in a crossed manner, the input characteristic difference caused by reference potential imbalance is reduced, two paths of signals are subtracted in two first-stage instrument amplifier chips (C-1) at the input ends respectively, common-mode signals are naturally reduced, differential-mode signals are enhanced, and then the signals enter a second-stage instrument amplifier chip (C-2) for differential amplification;
the signal enters an integrating circuit after being output, and is fed back to the reference potential input end of a final-stage instrument amplifier (C-3) to form a servo feedback loop, so that zero drift of a low-frequency circuit is suppressed.
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| CN117155325A (en) * | 2023-11-01 | 2023-12-01 | 中国海洋大学 | Signal conditioning method and conditioning circuit of vector hydrophone |
| CN117155325B (en) * | 2023-11-01 | 2024-01-30 | 中国海洋大学 | Signal conditioning method and conditioning circuit of vector hydrophone |
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