CN117606526A - LVDT digital demodulation system - Google Patents
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- CN117606526A CN117606526A CN202311543042.5A CN202311543042A CN117606526A CN 117606526 A CN117606526 A CN 117606526A CN 202311543042 A CN202311543042 A CN 202311543042A CN 117606526 A CN117606526 A CN 117606526A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K7/00—Modulating pulses with a continuously-variable modulating signal
- H03K7/08—Duration or width modulation ; Duty cycle modulation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
- G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
- G01D5/22—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils
- G01D5/2291—Linear or rotary variable differential transformers (LVDTs/RVDTs) having a single primary coil and two secondary coils
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/54—Testing for continuity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
- H03M1/124—Sampling or signal conditioning arrangements specially adapted for A/D converters
- H03M1/1245—Details of sampling arrangements or methods
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- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Power Engineering (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
A kind of LVDT digital demodulation system, the sine wave generating circuit receives the double-circuit complementary SPWM signal that SPWM generating module produced, demodulate the double-circuit complementary differential sine signal as the primary signal, input to LVDT primary side and synchronous rectification circuit, LVDT secondary side outputs the sine signal correlated with LVDT displacement, namely the secondary side signal; the synchronous rectification circuit processes the input primary side signal and secondary side signal according to the synchronous reversing signal to generate a primary side half-wave rectification signal and a secondary side half-wave rectification signal; the active filter circuit respectively processes the input primary half-wave rectification signal and the secondary half-wave rectification signal to obtain a primary direct current signal and a secondary direct current signal; the AD sampling circuit carries out signal conditioning and real-time acquisition on the input primary side direct current signal and secondary side direct current signal, and sends a direct current signal acquisition result to the LVDT position demodulation module; and the LVDT position demodulation module extracts an LVDT position signal through ratio calculation according to the acquisition result.
Description
Technical Field
The invention relates to a digital demodulation method of an LVDT sensor, in particular to a precise measurement method of linear displacement in a position servo control system.
Background
LVDT sensors are widely used for linear displacement detection in position servos. LVDTs are abbreviations for linear variable differential transformers and the principle of operation can be described simply as core-movable transformers. An LVDT sensor typically includes four signal lines, including two primary side signal lines and two secondary side signal lines. The displacement detection principle is that a sine voltage signal is input on a primary side signal wire, and then the amplitude of a secondary side output sine voltage signal is extracted, wherein the amplitude is in direct proportion to linear displacement.
Demodulation is typically performed using ADI company AD598/AD 698. The principle is that the primary side voltage amplitude and the secondary side voltage amplitude of the LVDT are detected through synchronous demodulation, and the position demodulation is carried out in a mode of dividing the secondary side amplitude by the primary side amplitude. Therefore, the proportional coefficient error caused by the temperature drift of the primary side signal and the secondary side signal of the LVDT can be eliminated, and the temperature performance and the stability are improved. But the frequency and the amplitude of the primary excitation voltage are configured through external resistors and capacitors. In addition, the realization mode of synchronous demodulation needs to be compensated by an external resistance-capacitance phase-shifting circuit, has higher requirements on resistance-capacitance precision and temperature drift, is not flexible enough, and cannot be compatible with multiple LVDTs.
Disclosure of Invention
The invention solves the technical problems that: overcomes the defects of the prior art and provides an LVDT position demodulation system meeting the high-precision use requirement.
The solution of the invention is as follows: the LVDT digital demodulation system comprises a sine wave generation circuit, a synchronous rectification circuit, an active filter circuit, an AD sampling circuit, an LVDT position demodulation module and an SPWM generation module;
the sine wave generating circuit receives the double-path complementary SPWM signal generated by the SPWM generating module, demodulates the double-path complementary differential sine signal to serve as a primary side signal, inputs the primary side signal of the LVDT and the synchronous rectifying circuit, and outputs a sine signal related to displacement of the LVDT, namely a secondary side signal, by the secondary side of the LVDT;
the synchronous rectification circuit processes the input primary side signal and secondary side signal according to the synchronous reversing signal to generate a primary side half-wave rectification signal and a secondary side half-wave rectification signal;
the active filter circuit respectively processes the input primary half-wave rectification signal and the secondary half-wave rectification signal to obtain a primary direct current signal and a secondary direct current signal;
the AD sampling circuit carries out signal conditioning and real-time acquisition on the input primary side direct current signal and secondary side direct current signal, and sends a direct current signal acquisition result to the LVDT position demodulation module;
and the LVDT position demodulation module extracts an LVDT position signal through ratio calculation according to the acquisition result.
Preferably, the SPWM generating module generates a double-path complementary SPWM signal by modulating the sinusoidal modulation wave compared with a high-frequency triangular carrier signal, and the frequency of the high-frequency triangular carrier signal is 50-200 times of the frequency of the primary side signal.
Preferably, the SPWM generation module is implemented in, but not limited to, an FPGA.
Preferably, the sine wave generating circuit comprises two MFB second-order low-pass filters, which respectively demodulate the input two-way complementary SPWM signals.
Preferably, the synchronous commutation signal is obtained by manually measuring sine signals of the primary side and the secondary side of the LVDT and judging the moment when the phase is zero, namely the commutation point of the synchronous rectification circuit.
Preferably, the device also comprises a double-phase demodulation module, wherein the AD sampling circuit is used for collecting primary side signals and secondary side signals and sending the primary side and secondary side collecting results to the double-phase demodulation module; and the double-phase demodulation module detects the amplitude and the phase of the signal according to the primary and secondary side acquisition result and outputs a synchronous reversing signal to the synchronous rectification circuit.
Preferably, the bi-phase demodulation module outputs a synchronous commutation signal to the synchronous rectification circuit according to the primary and secondary side acquisition result and the amplitude and phase of the detection signal, and the bi-phase demodulation module comprises:
two unit sinusoidal signals f (theta) and f (theta+90 DEG) with orthogonal phases and the same frequency as the excitation frequency are adopted as modulation signals, the modulation signals are multiplied by the acquisition results of the primary side and the secondary side respectively, and then the direct current component X on the X, Y axis of an orthogonal coordinate system is obtained by low-pass filtering E 、Y E 、X F 、Y F ；
Vector synthesis is carried out to obtain the absolute amplitude value R of the primary side signal and the secondary side signal E 、R F And relative phase phi with respect to f (theta) E 、φ F ；
By relative phase phi E 、φ F And judging the moment when the phase is zero, namely the phase change point of the subsequent synchronous rectification circuit, generating and outputting a primary side synchronous phase change signal and a secondary side synchronous phase change signal, wherein the phase change frequency is the same as that of the primary side sinusoidal signal, and outputting a high level by the phase signal when the amplitude of the sinusoidal signal is greater than zero, otherwise outputting a low level.
Preferably, the system also comprises an LVDT health management module, and the bi-phase demodulation module obtains the absolute amplitude value R of the primary side signal and the secondary side signal E 、R F Transmitting to LVDT health management module, according to R F /R E Demodulation to obtain LVDT position L1, combining with relative phase phi E 、φ F And comparing with the LVDT position signal L2 obtained by the DC signal acquisition result, judging whether the LVDT has a disconnection fault, and performing LVDT health management.
Preferably, by X E 、φ E Signal, judge LVDT primary side cable has unilateral broken wire or bilateral broken wireA wire; by X F 、φ F The signal is used for judging whether the LVDT secondary side cable has single-side broken wire or double-side broken wire; i.e. X E， φ E The signal has no mutation, and the primary coil is normal; x is X E， φ E The primary coil has abrupt change, but is not zero, and the primary coil is broken on one side; x is X E， φ E The primary coil is broken on both sides when the mutation exists and is zero; x is X F 、φ F The signal has no abrupt change, and the secondary coil is normal; x is X F 、φ F The signal has abrupt change, but is not zero, and the secondary coil is broken on one side; x is X F 、φ F The signal has abrupt change and is zero, and the double-side coil is broken.
Preferably, the bi-phase demodulation module, the LVDT health management module and the LVDT position demodulation module are implemented in an FPGA.
Compared with the prior art, the invention has the beneficial effects that:
the invention designs an LVDT digital demodulation system based on an FPGA, which comprises two modes of direct current demodulation and alternating current demodulation. Particularly, a bi-phase alternating current demodulation algorithm is adopted, the accuracy and the reliability of alternating current demodulation are improved, sinusoidal excitation voltage configuration, alternating current demodulation, direct current demodulation and synchronous rectification are realized in an FPGA, and then high-accuracy linear displacement detection is realized. Meanwhile, the invention has strong compatibility to different LVDTs, and the parameter configuration method is simple and flexible, and can realize the functions of LVDT disconnection detection and the like.
High precision: and the detection precision of the LVDT is improved in the links of excitation signal generation, phase detection, synchronous rectification and the like.
High versatility: the exciting voltage, exciting frequency and synchronous rectification phase-change point can be modified by software to adapt to LVDTs with different measuring ranges and different impedances. The signal to noise ratio of the sensor signal is improved, and the position detection precision is improved.
High suitability: the controllable parameters are multiple and easy to modify, different driving voltages and excitation frequencies can be conveniently generated through FPGA software configuration, and synchronous rectification phase-change points can be adaptively adjusted to adapt to LVDTs with different input impedance and output impedance, so that the signal-to-noise ratio of sensor signals is improved, and the position detection precision is improved.
Health management: amplitude and phase of the primary side and the secondary side are detected in real time through bi-phase demodulation, whether the LVDT is broken or not is judged, and the phenomenon that feedback data mutation causes larger misoperation of the servo driver is prevented.
The immunity is strong: the large common mode interference existing in the servo system can be effectively restrained.
Compared with the existing schemes at home and abroad, the technical scheme has the characteristics of high precision, high universality, high adaptability, full autonomy and controllability and the like. And LVDT health management is realized, the reliability of a servo system is improved, and the basic technology is mature and easy to realize.
Drawings
FIG. 1 is a basic constitution of the present invention
FIG. 2 is a schematic diagram of a sine wave generating circuit
FIG. 3 is a diagram of a two-phase demodulation scheme
Fig. 4 is a schematic diagram of a synchronous rectifying circuit
Fig. 5 active filter circuit and dc position demodulation schematic diagram
Detailed Description
The invention is further illustrated with reference to figures 1-5 and examples.
The invention provides an LVDT position demodulation system meeting high-precision use requirements. As shown in fig. 1, the device comprises a sine wave generating circuit, a synchronous rectifying circuit, an active filter circuit, an AD sampling circuit, an LVDT position demodulation module and an SPWM generating module. In this embodiment, the preferred embodiment further includes a bi-phase demodulation module and an LVDT health management module, where the SPWM generating module, the LVDT position demodulation module, the bi-phase demodulation module, and the LVDT health management module are implemented in an FPGA chip.
As shown in fig. 2, the sine wave generating circuit is used for generating the primary sine signal of the LVDT, and is implemented by adopting an SPWM generating module and an active filter circuit. And the FPGA chip is used for modulating to generate a double-path complementary SPWM signal. The realization principle is that the two-way complementary sinusoidal modulation wave is compared with two-way high-frequency triangular carrier signals with the same amplitude and the same frequency, and the two-way complementary SPWM1 signal and the SPWM2 signal are generated through modulation. The SPWM1 signal and the SPWM2 signal pass through the MFB second-order low-pass filter 1 and the MFB second-order low-pass filter 2, and a two-way high-precision differential sine wave (primary side signal) is demodulated and input to the primary side of the LVDT. A sinusoidal signal (secondary signal) related to LVDT displacement is output by the LVDT secondary. Wherein the SPWM signal is implemented by, but not limited to, an FPGA. The method realized by the FPGA has high precision and strong applicability, and the excitation frequency and amplitude can be changed by modifying software so as to adapt to LVDT with different coil impedances and improve the signal-to-noise ratio of the feedback signal.
And the synchronous rectification circuit rectifies the sine full-wave signal into a single-side half-wave signal. The principle is shown in fig. 4. The primary side signal and the secondary side signal output the primary side inverted signal and the secondary side inverted signal through the inverting circuit 5 and the inverting circuit 6. The primary signal and the primary inverted signal are input to the analog channel selector 7. Selectively outputting a primary side signal and a primary side opposite-phase signal according to a primary side synchronous commutation signal output by the FPGA to generate a primary side half-wave rectification signal; similarly, the secondary side signal and the secondary side inverted signal are input to the analog channel selector 8. And selectively outputting the secondary side signal and the secondary side opposite-phase signal according to the secondary side synchronous commutation signal output by the FPGA to generate a secondary side half-wave rectification signal. Compared with a common diode rectifying circuit, the circuit has the advantage of low on-resistance, can reduce signal attenuation and improve detection accuracy.
The principle of bi-phase demodulation is shown in figure 3. The primary side signal and the secondary side signal of the LVDT are sampled in real time through the AD sampling circuit 3 and the AD sampling circuit 4 and input into the FPGA. Then two unit sinusoidal signals f (theta) and f (theta+90 DEG) with orthogonal phases and the same frequency as the exciting frequency are adopted as modulation signals, the modulation signals are multiplied by a primary side signal and a secondary side signal respectively, and then the direct current component X on the X, Y axis of an orthogonal coordinate system is obtained through FPGA software low-pass filtering E 、Y E 、X F 、Y F Finally, vector synthesis is carried out to obtain the absolute amplitude value R of the primary side signal and the secondary side signal E 、R F And relative phases phiE, phiF with respect to F (θ). At this time, two functions are realized by the FPGA: 1. by relative phase phi E 、φ F Judging the moment when the phase is zero, namely the phase change point of the subsequent synchronous rectification circuit, generating and outputting a primary side synchronous phase change signal and a secondary side synchronous signal by the FPGAThe commutation frequency of the commutation signal is the same as that of the sinusoidal signal. When the sine signal amplitude is larger than zero, the synchronous phase change signal outputs a high level, otherwise, outputs a low level. It should be noted that: the phase change point of the synchronous rectification circuit is solidified in the FPGA program, and the double-phase demodulation method can conveniently realize phase detection, but is not required. The sine signals of the primary side and the secondary side of the LVDT can be manually measured, the moment when the phase is zero is judged, namely the phase change point of the synchronous rectification circuit, and half-wave rectification is realized by adjusting the phase lag.
The principle of active filter circuit and DC position demodulation is shown in FIG. 5. The primary half-wave rectified signal passes through an active filter circuit 9 to generate a primary direct current signal T1. The secondary half-wave rectified signal is passed through an active filter circuit 10 to produce a secondary dc signal T2. And the signals of the T1 and the T2 are conditioned and collected in real time through an AD sampling circuit 11, and the LVDT direct current position demodulation result L2 is obtained through ratio calculation T2/T1 and gain calculation.
Absolute amplitude R obtained by bi-phase demodulation F 、R E Through R F /R E Demodulating to obtain an LVDT position L1; l1 amplitude combined with relative phase signal phi E 、φ F The method can be compared with the demodulation result L2 of the direct current position of the LVDT so as to judge whether the LVDT has a disconnection fault or not and carry out LVDT health management. Specifically, the following judgment can be adopted to execute:
by X E 、φ E The signal can judge whether the LVDT primary cable has single-side broken wire or double-side broken wire; by X F 、φ F The signal can judge whether the LVDT secondary side cable has single-side broken wire or double-side broken wire. I.e. X E， φ E The signal has no mutation, and the primary coil is normal; x is X E， φ E The primary coil has abrupt change, but is not zero, and the primary coil is broken on one side; x is X E， φ E The primary coil is broken on both sides when the mutation exists and is zero; x is X F 、φ F The signal has no abrupt change, and the secondary coil is normal; x is X F 、φ F The signal has abrupt change, but is not zero, and the secondary coil is broken on one side; x is X F 、φ F The signal has abrupt change and is zero, and the double sides of the secondary coil are broken;
the invention has two functions of high-precision LVDT DC position demodulation and double-phase demodulation, and realizes high-reliability LVDT health management. Meanwhile, the amplitude and frequency of the primary excitation voltage of the LVDT and the phase of the synchronous rectification circuit can be conveniently adjusted, so that the LVDT is suitable for various LVDTs. The characteristics are not available in the existing products. The adopted circuit can adopt different software and hardware implementation modes, and can also be used as an extension implementation scheme of the invention.
Although the present invention has been described in terms of the preferred embodiments, it is not intended to be limited to the embodiments, and any person skilled in the art can make any possible variations and modifications to the technical solution of the present invention by using the methods and technical matters disclosed above without departing from the spirit and scope of the present invention, so any simple modifications, equivalent variations and modifications to the embodiments described above according to the technical matters of the present invention are within the scope of the technical matters of the present invention.
Claims (10)
1. An LVDT digital demodulation system, characterized by: the device comprises a sine wave generating circuit, a synchronous rectification circuit, an active filter circuit, an AD sampling circuit, an LVDT position demodulation module and an SPWM generating module;
the sine wave generating circuit receives the double-path complementary SPWM signal generated by the SPWM generating module, demodulates the double-path complementary differential sine signal to serve as a primary side signal, inputs the primary side signal of the LVDT and the synchronous rectifying circuit, and outputs a sine signal related to displacement of the LVDT, namely a secondary side signal, by the secondary side of the LVDT;
the synchronous rectification circuit processes the input primary side signal and secondary side signal according to the synchronous reversing signal to generate a primary side half-wave rectification signal and a secondary side half-wave rectification signal;
the active filter circuit respectively processes the input primary half-wave rectification signal and the secondary half-wave rectification signal to obtain a primary direct current signal and a secondary direct current signal;
the AD sampling circuit carries out signal conditioning and real-time acquisition on the input primary side direct current signal and secondary side direct current signal, and sends a direct current signal acquisition result to the LVDT position demodulation module;
and the LVDT position demodulation module extracts an LVDT position signal through ratio calculation according to the acquisition result.
2. The system according to claim 1, wherein: the SPWM generating module generates a double-path complementary SPWM signal through the comparison of a sinusoidal modulation wave and a high-frequency triangular carrier signal, and the frequency of the high-frequency triangular carrier signal is 50-200 times of the frequency of a primary side signal.
3. The system according to claim 1 or 2, characterized in that: the SPWM generation module is implemented by, but not limited to, an FPGA.
4. The system according to claim 1, wherein: the sine wave generation circuit comprises two MFB second-order low-pass filters, and the two input double-path complementary SPWM signals are demodulated respectively.
5. The system according to claim 1, wherein: and (3) judging the moment when the phase is zero by manually measuring sine signals of the primary side and the secondary side of the LVDT, namely obtaining a synchronous reversing signal by a phase change point of the synchronous rectifying circuit.
6. The system according to claim 1, wherein: the AD sampling circuit is used for collecting primary side signals and secondary side signals and sending primary side and secondary side collecting results to the double-phase demodulation module; and the double-phase demodulation module detects the amplitude and the phase of the signal according to the primary and secondary side acquisition result and outputs a synchronous reversing signal to the synchronous rectification circuit.
7. The system according to claim 6, wherein: the double-phase demodulation module detects the amplitude and the phase of the signal according to the primary and secondary side acquisition result, and outputs a synchronous reversing signal to the synchronous rectification circuit, wherein the synchronous reversing signal comprises:
using two phases in quadrature, frequency and excitation frequencyThe same unit sine signals f (theta) and f (theta+90 DEG) are taken as modulation signals, multiplied by the primary and secondary side acquisition results respectively, and then low-pass filtered to obtain a direct current component X on the X, Y axis of an orthogonal coordinate system E 、Y E 、X F 、Y F ；
Vector synthesis is carried out to obtain the absolute amplitude value R of the primary side signal and the secondary side signal E 、R F And relative phase phi with respect to f (theta) E 、φ F ；
By relative phase phi E 、φ F And judging the moment when the phase is zero, namely the phase change point of the subsequent synchronous rectification circuit, generating and outputting a primary side synchronous phase change signal and a secondary side synchronous phase change signal, wherein the phase change frequency is the same as that of a primary side sinusoidal signal, and outputting a high level by the synchronous phase change signal when the amplitude of the sinusoidal signal is greater than zero, otherwise outputting a low level.
8. The system according to claim 7, wherein: also included is an LVDT health management module,
the bi-phase demodulation module obtains the absolute amplitude value R of the primary side signal and the secondary side signal E 、R F Transmitting to LVDT health management module, according to R F /R E Demodulation to obtain LVDT position L1, combining with relative phase phi E 、φ F And comparing with the LVDT position signal L2 obtained by the DC signal acquisition result, judging whether the LVDT has a disconnection fault, and performing LVDT health management.
9. The system according to claim 8, wherein: by X E 、φ E The signal is used for judging whether the LVDT primary side cable has single-side broken wire or double-side broken wire; by X F 、φ F The signal is used for judging whether the LVDT secondary side cable has single-side broken wire or double-side broken wire; i.e. X E， φ E The signal has no mutation, and the primary coil is normal; x is X E， φ E The primary coil has abrupt change, but is not zero, and the primary coil is broken on one side; x is X E， φ E The primary coil is broken on both sides when the mutation exists and is zero; x is X F 、φ F Signal noThe secondary coil is normal due to mutation; x is X F 、φ F The signal has abrupt change, but is not zero, and the secondary coil is broken on one side; x is X F 、φ F The signal has abrupt change and is zero, and the double-side coil is broken.
10. The system according to claim 8, wherein: the double-phase demodulation module, the LVDT health management module and the LVDT position demodulation module are realized in an FPGA.
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