CN114428220A - High-precision series measurement method for asymmetric factors of differential transformer - Google Patents
High-precision series measurement method for asymmetric factors of differential transformer Download PDFInfo
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Abstract
The invention discloses a high-precision series measurement method for asymmetric factors of a differential transformer, wherein the differential transformer comprises two primary coils L1 and L2 and a secondary coil L3, and the high-precision series measurement method comprises the following steps: the two primary coils L1, L2 are connected in series; after an AC carrier source is connected with an external resistor R1, an AC carrier signal V is input into two primary coils L1 and L2 which are connected in seriesP(ii) a A voltage signal V containing the asymmetry factor of the primary coil is induced by the secondary coil L3L3Amplifying to obtain a voltage signal V containing an asymmetry factorsout(ii) a Will voltage signal VsoutSequentially carrying out alternating current amplification, demodulation and filtering to obtain a direct current voltage signal Vd(ii) a Obtaining and obtaining an asymmetric factor and a direct current voltage signal V according to the amplification, alternating current amplification, demodulation and filtering parametersdAnd according to a DC voltage signal VdAnd calculating to obtain the asymmetry factor of the primary coil. The invention can realize the asymmetric factor of the primary coil in the differential transformerAnd (6) measuring.
Description
Technical Field
The invention belongs to the technical field of capacitance displacement sensing measurement, and particularly relates to a high-precision series measurement method for asymmetric factors of a differential transformer.
Background
A high-precision capacitance displacement sensor is taken as a traditional non-contact sensor and is mainly applied to an inertia measuring device for measuring capacitance change, such as an accelerometer and the like. The high-precision capacitance displacement sensor mainly comprises a capacitance bridge, a front-end circuit, a modulation-demodulation and low-pass filter circuit and the like. At present, high-precision capacitance displacement sensors based on transformer bridges are widely applied to space electrostatic accelerometers and inertial sensors. In the space inertial sensor, a capacitance displacement sensing circuit measures the variation of the position of the inspection quality in the probe, and the inspection quality in the probe is controlled to be at a zero position through the control of a feedback circuit.
The transformer bridge circuit converts the capacitance signal into a voltage signal, the voltage signal is transmitted to a post-stage circuit through an amplifying circuit, and two differential primary coils of the transformer bridge circuit are perfectly symmetrical under an ideal condition but cannot be realized in reality, so that the asymmetry of the primary coils can generate false displacement signals. Meanwhile, for the design and manufacture of the transformer, the primary coil generates asymmetry due to factors such as a coil winding mode, the unevenness of a magnetic core, a glue pouring process and the like.
Therefore, the asymmetry of the differential transformer needs to be measured to measure the magnitude of the sensing offset caused by the asymmetry of the primary coil, so as to provide a reference for the design and manufacturing process of the transformer.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a high-precision series measurement method for asymmetric factors of a differential transformer, which can measure the asymmetric factors of a primary coil in the differential transformer.
To achieve the above object, in a first aspect, the present invention provides a high-precision series measurement method of an asymmetry factor of a differential transformer including two primary coils L1, L2 and a secondary coil L3, the method including the steps of:
(1) connecting the two primary coils L1, L2 in series;
(2) after an AC carrier source is connected with an external resistor R1, an AC carrier signal V is input into two primary coils L1 and L2 which are connected in seriesP；
(3) A voltage signal V containing the asymmetry factor of the primary coil is induced by the secondary coil L3L3Amplifying to obtain a voltage signal V containing an asymmetry factorsout；
(4) The voltage signal V is converted into a voltage signalsoutSequentially carrying out alternating current amplification, demodulation and filtering to obtain a direct current voltage signal Vd；
(5) Obtaining and obtaining an asymmetry factor and a DC voltage signal V according to the amplification, AC amplification, demodulation and filtering parametersdAccording to the transfer function of (4), and according to the DC voltage signal V obtained in step (4)dAnd calculating to obtain the asymmetry factor of the primary coil.
The invention provides a high-precision series measurement method for asymmetric factors of a differential transformer, which converts asymmetric factors of a primary coil in the differential transformer into output of a secondary coil through high-frequency modulation, and converts the output into a stable direct-current voltage signal V after the processes of amplification, alternating-current amplification, demodulation, filtering and the likedAccording to the asymmetry factor and the DC voltage signal VdThe transfer function of the differential transformer can calculate the magnitude of the asymmetric factor of the differential transformer, and the measurement of the asymmetric factor of the differential transformer is realized. And the parameters of amplification and alternating current amplification are designed, so that the gain is improved, small signals of the asymmetric factors of the differential transformer are converted and amplified, the measurement resolution of the asymmetric factors is improved, and high-precision measurement is realized.
In one embodiment, the method further comprises:
(6) adjusting the frequency of said AC carrier wave source to obtainTaking and according to the DC voltage signal V of the AC carrier signal at different frequenciesdAnd obtaining the change condition of the asymmetry factor along with the frequency.
In one embodiment, the AC carrier signal VPIs an alternating voltage signal from 10kHz to 200 kHz.
In one embodiment, in step (3), the voltage signal V is converted into a voltage signalL3The amplification is performed by a charge amplification circuit, wherein,
the charge amplification circuit comprises a charge amplifier U1, a feedback impedance and a blocking capacitor C1, wherein the inverting input end of the charge amplifier U1 is connected with one end of the secondary coil L3 through the blocking capacitor C1, the non-inverting input end of the charge amplifier U1 and the other end of the secondary coil L3 are grounded, and the output end of the charge amplifier U1 is connected with the inverting input end of the charge amplifier U1 through the feedback impedance.
In one embodiment, the feedback impedance includes a feedback resistor and a feedback capacitor, and the feedback resistor and the feedback capacitor are connected in parallel.
In one embodiment, in step (4), the voltage signal V is converted into a voltage signalsoutThe AC amplification is carried out by an AC amplification circuit, wherein,
the alternating current amplifying circuit comprises a capacitor C2, a resistor R2, a resistor R3 and an operational amplifier U2, wherein the inverting input end of the operational amplifier U2 is connected with one end of the resistor R2 and one end of the resistor R3 respectively, the other end of the resistor R2 is connected with the output end of the charge amplifier U1 through the capacitor C2, the other end of the resistor R3 is connected with the output end of the operational amplifier U2, and the non-inverting input end of the operational amplifier U2 is grounded.
In one embodiment, in step (4), the ac amplified voltage signal V is obtainedsoutDemodulation is carried out through a demodulation circuit, the demodulation circuit adopts an analog switch, and the input end of the analog switch is connected with the output end of the operational amplifier U2.
In one embodiment, in step (4), the AC amplified and demodulated power is usedPressure signal VsoutThe filtering is performed by a low-pass filter circuit, wherein,
the low-pass filter circuit comprises an operational amplifier U3, capacitors C3-C4 and resistors R4-R7, wherein the inverting input end of the operational amplifier U3 is respectively connected with one end of the resistor R4, one end of the resistor R5 and one end of the capacitor C3, and the other end of the resistor R4 is connected with one output end of the analog switch; a non-inverting input end of the operational amplifier U3 is respectively connected with one end of the resistor R6, one end of the resistor R7 and one end of the capacitor C4, one end of the resistor R6 is connected with the other output end of the analog switch, and the other end of the resistor R7 and the other end of the capacitor C4 are grounded; the output end of the operational amplifier U3 is respectively connected with the other end of the resistor R5 and the other end of the capacitor C3.
In a second aspect, the present invention provides a capacitance displacement sensing measurement method, including the high precision series measurement method described above.
The capacitance displacement sensing measurement method provided by the invention considers the asymmetry of two primary coils in a differential transformer in an actual high-precision capacitance displacement sensor, and adopts the serial connection mode of the primary coils and alternating current carrier signals V with different frequenciesPConverting the asymmetry factor of the primary coil into the output voltage of the secondary coil by measuring the AC carrier signals V of different frequenciesPDC voltage signal V at different frequenciesdThe change condition of the asymmetry factor along with the frequency can be obtained, the sensing offset caused by the asymmetry of the primary coil can be measured according to the change condition, and accurate measurement of displacement of different inertial measurement devices is realized.
Drawings
FIG. 1 is a flow chart of a method for high-precision serial measurement of asymmetry factor of a differential transformer according to an embodiment;
FIG. 2 is a circuit schematic of a charge amplification circuit according to an embodiment;
FIG. 3 is a schematic circuit diagram of an AC amplifying circuit according to an embodiment;
FIG. 4 is a graph of the transfer function of the AC amplifying circuit provided in FIG. 3;
FIG. 5 is a circuit schematic of a low pass filter circuit provided by one embodiment;
fig. 6 is a graph of the transfer function of the low pass filter circuit provided in fig. 5.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problem that the asymmetry of two primary coils in the traditional capacitance displacement detection circuit causes a false displacement signal, the invention provides a high-precision series measurement method for the asymmetry factor of a differential transformer, which comprises the following steps of S10-S50 as shown in FIG. 1, and the detailed steps are as follows:
s10, the two primary coils L1 and L2 in the differential transformer are connected in series.
S20, after the external resistor R1 is connected by the AC carrier source, the AC carrier signal V is input into the two primary coils L1 and L2 which are connected in seriesP。
Specifically, the connection relationship between the ac carrier source and the differential transformer includes a connection mode a and a connection mode b, where the connection mode a is: the alternating current carrier source is connected with the homonymous end of one primary coil L1 through an external resistor R1, the synonym end of the primary coil L1 is connected with the synonym end of the other primary coil L2, and the homonymous end of the primary coil L2 is grounded. The connection mode b is as follows: the alternating current carrier source is connected with the synonym end of one primary coil L1 through an external resistor R1, the synonym end of the primary coil L1 is connected with the synonym end of the other primary coil L2, and the synonym end of the primary coil L2 is grounded. The connection mode can be selected according to the actual situation, and this embodiment is not limited.
When the two primary coils L1, L2 are asymmetrical in the present embodiment, the ac carrier signal VPAfter voltage division by the external resistor R1 and the primary coil and mutual inductance of the primary coil L1, the primary coil L2 and the secondary coil L3, a voltage signal V containing an asymmetric factor of the primary coil is induced in the secondary coil L3L3According to the principle of partial voltage and mutual induction voltage calculation, the following results are obtained:
in the formula, L0Represents the common mode value of the primary coil L1 and L2 inductances; (alpha1-α2) Denotes the asymmetry factor of the primary windings L1 and L2 in a differential transformer, where α1Indicating the primary winding L1 of the differential transformer with respect to the common mode value L0A difference factor of2Indicating the primary winding L2 of the differential transformer with respect to the common mode value L0A difference factor of (d); vPIs an expression for the frequency with which,
s represents the expression of angular frequency in the complex frequency domain, which can be written as s ═ j ω; l is3Represents the inductance value of the secondary coil L3; r1Indicating the resistance of the external resistor R1.
In addition, α is1、α2The comprehensive difference factor caused by the asymmetry of the coupling factor K and the asymmetry of the inductance value L of the two primary coils L1, L2 to the secondary coil L3 of the differential transformer is introduced by the mutual inductance relationship between the primary coil and the secondary coil of the transformer, and the specific relationship is derived as follows:
in the formula, M1M represents the mutual inductance factor of the primary coil L1 and the secondary coil L32Represents the mutual inductance of the primary coil L2 and the secondary coil L3; k1Denotes the coupling factor, K, of the primary coil L1 with the secondary coil L32Is the coupling factor of primary coil L2 with secondary coil L3; etaLPresentation inductanceThe degree of asymmetry of the light beam is,
wherein L is1Represents the inductance value, L, of the primary coil L12The inductance value of the primary coil L2 is indicated.
From the above expression, the voltage signal VL3Is in communication with an alternating current carrier signal VPAC voltage signal of the same frequency, and AC carrier signal VPIs a function related to the frequency f, the voltage signal VL3Is related to an asymmetry factor (alpha)1-α2) A function related to the frequency f.
S30, inducing a voltage signal V containing the asymmetry factor of the primary coil from the secondary coil L3L3Amplifying, specifically, amplifying by charge or instrument to obtain voltage signal V containing asymmetry factorsout。
In step S30, the voltage signal V induced by the secondary coilL3In the microvolt range, facilitating subsequent voltage signal VL3The obtained voltage signal V is required to be measuredL3Amplifying to obtain a voltage signal V containing an asymmetry factorsout。
S40, converting the voltage signal VsoutSequentially carrying out alternating current amplification, demodulation and filtering to obtain a direct current voltage signal Vd。
S50, obtaining and obtaining an asymmetry factor and a direct current voltage signal V according to the parameters of amplification, alternating current amplification, demodulation and filteringdAccording to the transfer function of (a), and according to the direct voltage signal V obtained in step S40dAnd calculating to obtain the asymmetry factor of the primary coil.
In steps S40 and S50, the amplified voltage signal V may be used to obtain more intuitive and stable measurement resultssoutAmplified again and then demodulated into a DC voltage signal VdThen filtering and removing the high-frequency signal to obtain a low-frequency direct-current voltage signal V containing the asymmetric factor of the differential transformerd. Then according to the parameters of amplification, AC amplification, demodulation and filtering to obtain the asymmetry factor and DC voltage signal VdBy measuring the DC voltage signal VdThe relation with the transfer function can be calculated to obtain the asymmetry factor (alpha) of the primary coil1-α2)。
In order to further improve the measurement resolution of the asymmetric factor and realize high-precision measurement, amplification, alternating current amplification, demodulation and filtering parameters can be correspondingly adjusted to improve the gain, so that small signals of the asymmetric factor of the differential transformer are converted and amplified, and high-precision measurement is realized.
In the high-precision serial measurement method for the asymmetric factor of the differential transformer provided by this embodiment, the asymmetric factor of the primary coil in the differential transformer is converted into the output of the secondary coil through high-frequency modulation, and then converted into the stable dc voltage signal V after the processes of amplification, ac amplification, demodulation, filtering, and the likedAccording to the asymmetry factor and the DC voltage signal VdThe transfer function of the differential transformer can calculate the magnitude of the asymmetric factor of the differential transformer, and the measurement of the asymmetric factor of the differential transformer is realized. And the parameters of amplification and alternating current amplification are designed, so that the gain is improved, small signals of the asymmetric factors of the differential transformer are converted and amplified, the measurement resolution of the asymmetric factors is improved, and high-precision measurement is realized.
In one embodiment, considering that the inductance value of the coil is frequency-dependent, in order to more accurately realize the measurement of the asymmetry factor of the transformer, the improved high-precision series measurement method of the present invention may further include step S60, which is detailed as follows:
s60, adjusting the frequency of the AC carrier source, obtaining and according to the DC voltage signal V of the AC carrier signal at different frequenciesdAnd obtaining the change condition of the asymmetry factor along with the frequency.
In step S60, the ac carrier signal V may be adjustedPThe frequency of the voltage measuring instrument can measure direct current voltage signals V under different frequenciesdThe change of the asymmetry factor of the differential transformer along with the frequency is further measured, so that the differential transformer is convenient to subsequently utilize to carry out capacitance displacement measurement on different inertia measurement devices, and reliable reference is provided.
It should be noted that, the differential transformer is generally applied in the range from 1kHz to 1MHz, and when the frequency is higher than the self-resonant frequency, the coil externally shows a capacitive characteristic, and cannot normally operate. In general, in the range of 10kHz to 200kHz, the coil of the differential transformer in mH magnitude exhibits a stable inductance state, and after the inductance state is higher than 200kHz, the inductance and the distributed capacitance in a single coil resonate due to the existence of the distributed capacitance, so that the alternating current carrier signal V provided by the embodiment cannot work normallyPMay be set to 10kHz to 200 kHz.
In one embodiment, in step S30, the voltage signal V may be amplified by a charge amplifying circuit or an instrument amplifying circuitL3Performing charge or instrument amplification, the present embodiment uses a charge amplifying circuit to amplify the voltage signal VL3For illustration of charge amplification, as shown in fig. 2, the charge amplification circuit includes a charge amplifier U1, a feedback impedance, and a dc blocking capacitor C1.
Specifically, taking the connection mode of the ac carrier source and the differential transformer provided in the above embodiment as an example as a connection mode a, the connection relationship between the amplifying circuit and the differential transformer provided in this embodiment is as follows: the inverting input terminal of the charge amplifier U1 is connected with the dotted terminal of the secondary coil L3 through a blocking capacitor C1, the non-inverting input terminal of the charge amplifier U1 and the unlike terminal of the secondary coil L3 are grounded, and the output terminal of the charge amplifier U1 is connected with the inverting input terminal thereof through a feedback impedance. Similarly, it can be seen that when the ac carrier source and the differential transformer are connected in the connection mode b, the connection relationship between the amplifying circuit and the differential transformer provided in this embodiment is not described herein again.
Due to the voltage signal V induced by the secondary coil L3L3The magnitude is in microvoltage magnitude, so that a subsequent direct current blocking capacitor C1 can be connected and then amplified by a charge amplifier U1 to obtain a voltage signal V containing an asymmetric factorsout，
In the formula, ZfRepresenting the impedance value of the feedback impedance. Specifically, the feedback impedance is used as a feedback resistor (resistance value is R)2) And feedback capacitance (capacitance value)Is C2) For example, the impedance of the feedback impedance can be expressed as
Further, in order to obtain a more intuitive and stable measurement result, a first-stage alternating current amplification circuit can be connected to the output end of the charge amplifier U1 for further amplification, and the voltage signal V after alternating current amplification is subjected to demodulation circuitsoutDemodulating the signal into a direct current voltage signal, and then filtering a high-frequency signal by a low-pass filter circuit to obtain a low-frequency direct current voltage signal V containing asymmetric factors of a differential transformerd. Then, according to the circuit parameters, the asymmetry factor and the DC voltage signal V can be obtaineddBy measuring a direct voltage signal VdThe primary coil asymmetry factor can be calculated.
In one embodiment, referring to fig. 3, the ac amplifying circuit includes a capacitor C2, a resistor R2, a resistor R3, and an operational amplifier U2, wherein an inverting input terminal of the operational amplifier U2 is connected to one end of the resistor R2 and one end of the resistor R3, the other end of the resistor R2 is connected to an output terminal of the amplifying circuit (the charge amplifier U1) through the capacitor C2, the other end of the resistor R3 is connected to an output terminal of the operational amplifier U2, and a non-inverting input terminal of the operational amplifier U2 is grounded.
In the present embodiment, the capacitor C2 is used for isolating the dc signal; the resistors R2 and R3 determine the amplification factor of the AC amplifying circuit so as to satisfy the AC carrier signal VPHas a frequency of 10kHz to 200kHz, the AC amplifying circuit is a high-pass amplifying circuit, and further amplifies the output signal VsoutIs a Vout2. The resistance values of the resistors R2 and R3 in the ac amplifying circuit provided by this embodiment are both R3The capacitance values of the capacitors C3-C4 are all C3For example, the transfer function of the circuit is
As shown in fig. 4.
In one embodiment, the demodulation circuit is used for amplifying the output signal V of the AC amplification circuitout2The signal is multiplied by a square wave signal with same frequency and same phase to obtain a double frequency signal with a central frequency band of 0 and symmetrical positive and negative, and the circuit design of the signal can adopt an analog switch to realize the extraction of a half period signal, wherein the input end of the analog switch is connected with the output end of an operational amplifier U2.
In one embodiment, referring to fig. 5, the low pass filter circuit includes an operational amplifier U3, capacitors C3-C4 and resistors R4-R7, an inverting input terminal of the operational amplifier U3 is connected to one end of the resistor R4, one end of the resistor R5 and one end of the capacitor C3, respectively, and the other end of the resistor R4 is connected to an output terminal of the analog switch; the non-inverting input end of the operational amplifier U3 is respectively connected with one end of a resistor R6, one end of a resistor R7 and one end of a capacitor C4, one end of a resistor R6 is connected with the other output end of the analog switch, and the other end of a resistor R7 and the other end of the capacitor C4 are grounded; the output end of the operational amplifier U3 is connected with the other end of the resistor R5 and the other end of the capacitor C3 respectively.
In this embodiment, the output signal V of the AC amplifying circuit is usedout2Obtaining low-frequency signal after passing through a demodulation circuit and a low-pass filter circuit, and collecting direct-current voltage signal V output by the low-pass filter circuitdAnd dividing the transfer function of the circuit design about the asymmetry factor to obtain the magnitude of the asymmetry factor of the differential transformer. The resistances of the resistors R4-R7 in the low-pass filter circuit provided by the embodiment are all R4The capacitance values of the capacitors C3-C4 are all C4For example, the transfer function of the circuit is
As shown in fig. 6.
According to the high-precision series measurement method for the asymmetric factors of the differential transformer, the asymmetric factors of the primary coil of the differential transformer are converted into the output of the secondary coil through high-frequency modulation, amplified through the front-end amplifying circuit and the alternating-current amplifying circuit, converted into stable direct-current signals through the demodulating circuit and the low-pass filter circuit, and divided by the transfer function of the circuit design, so that the asymmetric factors of the differential transformer can be calculated. And the parameters of the front-end amplifying circuit and the alternating current amplifying circuit can be designed, so that the gain is improved, small signals of the asymmetric factors of the differential transformer are converted and amplified, the measurement resolution of the asymmetric factors is improved, and high-precision measurement is realized.
The invention also provides a capacitance displacement sensing measurement method which comprises the high-precision series measurement method for the asymmetric factors of the differential transformer.
In the capacitance displacement sensing and measuring method provided by this embodiment, in consideration of asymmetry of two primary coils in a differential transformer in an actual high-precision capacitance displacement sensor, the primary coils are connected in series and alternating current carrier signals V with different frequenciesPConverting the asymmetry factor of the primary coil into the output voltage of the secondary coil by measuring the AC carrier signals V of different frequenciesPDC voltage signal V at different frequenciesdThe change condition of the asymmetry factor along with the frequency can be obtained, the sensing offset caused by the asymmetry of the primary coil can be measured according to the change condition, and accurate measurement of displacement of different inertial measurement devices is realized.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A method for high precision series measurement of the asymmetry factor of a differential transformer comprising two primary coils L1, L2 and a secondary coil L3, characterized in that it comprises the steps of:
(1) connecting the two primary coils L1, L2 in series;
(2) after an AC carrier source is connected with an external resistor R1, an AC carrier signal V is input into two primary coils L1 and L2 which are connected in seriesP；
(3) A voltage signal V containing the asymmetry factor of the primary coil is induced by the secondary coil L3L3Amplifying to obtain voltage signal containing asymmetry factorVsout；
(4) The voltage signal V is converted into a voltage signalsoutSequentially carrying out alternating current amplification, demodulation and filtering to obtain a direct current voltage signal Vd；
(5) Obtaining and obtaining an asymmetry factor and a DC voltage signal V according to the amplification, AC amplification, demodulation and filtering parametersdAccording to the transfer function of (4), and according to the DC voltage signal V obtained in step (4)dAnd calculating to obtain the asymmetry factor of the primary coil.
2. A high accuracy serial measurement method according to claim 1, characterized in that the method further comprises:
(6) adjusting the frequency of the AC carrier source to obtain and obtain a DC voltage signal V according to the AC carrier signal at different frequenciesdAnd obtaining the change condition of the asymmetry factor along with the frequency.
3. A high accuracy serial measurement method according to claim 2, characterized in that the alternating carrier signal VPIs an alternating voltage signal from 10kHz to 200 kHz.
4. A high accuracy serial measurement method according to claim 1, characterized in that in step (3), the voltage signal V is measuredL3The amplification is performed by a charge amplification circuit, wherein,
the charge amplification circuit comprises a charge amplifier U1, a feedback impedance and a blocking capacitor C1, wherein the inverting input end of the charge amplifier U1 is connected with one end of the secondary coil L3 through the blocking capacitor C1, the non-inverting input end of the charge amplifier U1 and the other end of the secondary coil L3 are grounded, and the output end of the charge amplifier U1 is connected with the inverting input end of the charge amplifier U1 through the feedback impedance.
5. A high accuracy series measurement method according to claim 4, wherein said feedback impedance comprises a feedback resistor and a feedback capacitor, said feedback resistor and said feedback capacitor being connected in parallel.
6. A high accuracy serial measurement method according to claim 4, characterized in that in step (4), the voltage signal V is measuredsoutThe AC amplification is carried out by an AC amplification circuit, wherein,
the alternating current amplifying circuit comprises a capacitor C2, a resistor R2, a resistor R3 and an operational amplifier U2, wherein the inverting input end of the operational amplifier U2 is connected with one end of the resistor R2 and one end of the resistor R3 respectively, the other end of the resistor R2 is connected with the output end of the charge amplifier U1 through the capacitor C2, the other end of the resistor R3 is connected with the output end of the operational amplifier U2, and the non-inverting input end of the operational amplifier U2 is grounded.
7. A high accuracy serial measurement method according to claim 6, characterized in that in step (4), the voltage signal V after AC amplification is obtainedsoutDemodulation is carried out through a demodulation circuit, the demodulation circuit adopts an analog switch, and the input end of the analog switch is connected with the output end of the operational amplifier U2.
8. A high-precision serial measurement method according to claim 7, wherein in step (4), the voltage signal V is amplified and demodulated by ACsoutThe filtering is performed by a low-pass filter circuit, wherein,
the low-pass filter circuit comprises an operational amplifier U3, capacitors C3-C4 and resistors R4-R7, wherein the inverting input end of the operational amplifier U3 is respectively connected with one end of the resistor R4, one end of the resistor R5 and one end of the capacitor C3, and the other end of the resistor R4 is connected with one output end of the analog switch; a non-inverting input end of the operational amplifier U3 is respectively connected with one end of the resistor R6, one end of the resistor R7 and one end of the capacitor C4, one end of the resistor R6 is connected with the other output end of the analog switch, and the other end of the resistor R7 and the other end of the capacitor C4 are grounded; the output end of the operational amplifier U3 is respectively connected with the other end of the resistor R5 and the other end of the capacitor C3.
9. A capacitance displacement sensing measurement method, comprising the high-precision series measurement method according to any one of claims 1 to 8.
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