CN102012209B - Digital transmission demodulating method of differential transformer displacement transducer - Google Patents
Digital transmission demodulating method of differential transformer displacement transducer Download PDFInfo
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- CN102012209B CN102012209B CN2010102988370A CN201010298837A CN102012209B CN 102012209 B CN102012209 B CN 102012209B CN 2010102988370 A CN2010102988370 A CN 2010102988370A CN 201010298837 A CN201010298837 A CN 201010298837A CN 102012209 B CN102012209 B CN 102012209B
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Abstract
The invention relates to a digital transmission demodulating method of a differential transformer displacement transducer, belonging to a method for processing signals for accurately measuring the small displacement of an object by using an LVDT (Linear Variable Differential Transformer). The method comprises the following steps of: driving a primary coil of the LVDT by a transformer manufactured by a field programmable gate array (FPGA), collecting the output signals Va and Vb of two secondary coils of the LVDT, carrying out digital demodulation on the collected output signals Va and Vb of the two secondary coils of the LVDT in the formula of S=(Va-Vb)/(Va+Vb), and detecting signals of the LVDT by the mapping relationship between the actual displacement of the LVDT iron core and the S. The addition and subtraction as well as the demodulation method of the division are used on the secondary coil signals in the LVDT, and the actual displacement of the LVDT iron core is obtained by a moving average algorithm and the mapping relationship. The invention reduces the noise interference to the measuring result and greatly reduces the measuring error.
Description
Technical field
The differential transformer displace numeral becomes send demodulation method to relate to the method for the signal of the accurate Measuring Object micro-displacement of a kind of processing and utilizing LVDT.
Background technology
Differential transformer displace adopts electromagnetic induction principle energy measurement micro-displacement, and its English name is linear variable differential transformer, is called for short LVDT, and its structure is seen Fig. 1.Adopt epoxy resin, materials such as stainless steel are used not enameled wire coiling on skeleton in collinear footpath as coil rack.Different with traditional power transformer, LVDT is a magnetic-coupled measuring sensor a little less than a kind of open-flux path: 1, two secondary coil 2 of primary coil of coiling on skeleton; Its working method depends on moving of in coil rack iron core 3, when elementary coil 1 is supplied with the alternating voltage (pumping signal) of certain frequency, thereby iron core 3 move in coil just changed space magnetic field distribute changed at the beginning of; Mutual induction amount between the secondary coil, secondary coil 2 just produces induction electromotive force, along with the difference of iron core position; Mutual induction amount is also different; The induction electromotive force that excitation produces is also different, and so just the displacement (actual iron core is to keep contacting through measuring staff and measured object, just the displacement of testee) with iron core 3 becomes voltage signal output; Because two secondary coil 2 polarity of voltages are opposite; So the output of sensor is the poor of two secondary coil 2 voltages, its voltage difference and displacement linear when iron core 3 is in position, twice level coil 2 middles twice level coil 2 induced voltages equate but phase place is opposite that its voltage difference is zero; When iron core 3 past moving right, the voltage of the secondary coil induction on the right is greater than the left side.The voltage difference size of two-stage coil 2 outputs forms linear change (the real segment part of first quartile) with iron core 3 displacements, and this is the effective measurement range of LVDT (half the).The difference of coil 2 output voltages is not linear with iron core 3 displacements when iron core 3 continues past moving right, and this is buffering, non-measurement zone (phantom line segments).Otherwise, when iron core 3 moves as the same from twice level coil centre positions to the left side.Zero point, the real segment on both sides generally was the measurement range of symmetry, and only the both is AC signal and phase differential 180 ", as shown in Figure 2.
Generally speaking; Signal detecting method utilization carrier amplifier to differential transformer displace (LVDT) is commonly used is accomplished, and carrier amplifier is made up of demodulator circuit module, interchange amplification module, LPF functional module and oscillator commonly used again.Simple method obtains the amplitude modulation continuous voltage from each secondary coil exactly, through rectification, subtract each other, shows the position of iron core through the DC voltage of output.Original signal in this method has been passed through intermediate links such as rectification, plus-minus and has just been obtained d. c. voltage signal, can make error very big like this, can not obtain accurate iron core position.
Summary of the invention
In order to reflect the position of iron core exactly, the present invention provides a kind of digital demodulation method, not only gained secondary coil signal is adopted plus-minus method, also adopts the method for removing, and uses a kind of mapping relations to draw the real displacement value of iron core, reduces error greatly.
To achieve these goals; The present invention utilizes the transmitter of being made by field programmable gate array (FPGA) to drive the primary coil of LVDT; And the output signal Va and the Vb of two secondary coils of collection LVDT; This transmitter comprises the storer that is made up of FLASH or SRAM, drives the digital to analog converter (D/A) of LVDT primary coil, two analog to digital converters (A/D) of two secondary coils of sampling LVDT, and digital output module, comprise the signal demodulating algorithm and with the transmitter software of host computer signal procedure; The digital demodulation that the output signal Va and the Vb of two secondary coils of the LVDT that collects makes S=(Va-Vb)/(Va+Vb) is handled; Utilize the actual displacement amount of LVDT iron core and the mapping relations between the S to realize the input to LVDT, this disposal route may further comprise the steps:
Each storer in A, the initialization transmitter,
B, FPGA produce the sine wave exciting signal of changeable frequency, are input to LVDT primary coil input end through D/A,
C, two A/D of employing gather the analog output signal of two secondary coils of LVDT simultaneously, are converted into digital signal,
D, the actual displacement amount of setting up the LVDT iron core and the mapping relations between the measuring amount,
E, utilize the method for S=(Va-Vb)/(Va+Vb) to carry out digital demodulation, the gained result carried out digital error correction and digital filtering, the data storage of error correction in FLASH,
F, revised result deliver to digital output module, export to host computer with the data of floating-point format, and export with analog form through digital-to-analog conversion simultaneously, are used for outside instrument and come the indication measurement result.
Among the described step B; Sinusoidal excitation signal is produced by Direct Digital Synthesizer (DDS); And the heel one-level has the power amplifier of fixed ampllitude function, and the major clock of DDS and FPGA is synchronous, is the megahertz level; FPGA realizes the control to DDS through frequency control word and amplitude control word, and its control method comprises the steps:
B1, in FLASH, write excitation frequency word and amplitude control word,
B2, the reading frequency control word writes DDS frequency control register through the PI0 port from FLASH, from FLASH, reads the amplitude control word simultaneously, sees the amplitude control signal through the PIO port off to power amplifier,
B3, process DDS generation sinusoidal wave data, process D/A are converted into analog sine, the processing of process power amplifier just obtains the pumping signal of corresponding frequencies, corresponding amplitude again.
And through the collection moment of DDS synchronizing signal control A/D, gathering constantly is the peak point of the sine value of pumping signal.
In order to obtain accurate iron core displacement, step D has adopted a kind of calibration process to set up the actual displacement amount of LVDT iron core and the mapping relations between the measuring amount, and this process comprises the steps:
D1, FLASH duty controller are connected FLASH with CPU;
D2, the LVDT sensor is installed on the testboard bay; High-grade displacement indicator is housed on the stand; Measurement point evenly is set in the full scale of LVDT sensor, and the intensive more gained error correction of measurement point table is accurate more, and transmitter software reads uncorrected calculated value and is sent to host computer through the path; By the upper computer software record, artificial simultaneously displacement actual value through host computer keyboard input testboard bay top offset this moment indicator;
D3, upper computer software are after obtaining abundant measured value and actual value; Adopt the linear difference algorithm to obtain the conversion table of input and output; This table sends transmitter software by upper computer software to through USB interface, writes the FLASH storer by transmitter software.
In step e, adopt the moving average filtering algorithm as digital filtering.
Beneficial effect of the present invention: the disposal route that adopts output signal Va and Vb to two secondary coils to make S=(Va-Vb)/(Va+Vb); Overcome the excessive shortcoming of noise in the past; And by DDS generation sinusoidal excitation signal; And carry out digital error correction and digital filtering, make the measuring accuracy of displacement very high.
Description of drawings
Fig. 1 differential transformer displace (LVDT) structural representation;
Fig. 2 differential transformer displace (LVDT) fundamental diagram;
Fig. 3 differential transformer displace of the present invention (LVDT) numeral becomes send the hardware configuration among the demodulation method embodiment;
Fig. 4 differential transformer displace of the present invention (LVDT) numeral becomes send the software flow pattern among the demodulation method embodiment.
Embodiment
Embodiment below in conjunction with among Fig. 3, the 4 couples of the present invention specifically describes.
The present invention can pass through Fig. 3, a kind of transmitter shown in 4 is realized, the hardware of transmitter mainly comprises display screen and keyboard and power supply, the clock/reset of the soft nuclear of NIOSII CPU, DDS, D/A converter, A/D converter, FLASH duty controller, FLASH and SRAM storer, active arrangement chip, USB interface, CH452.Like Fig. 3, we are referred to as hardware in the FPGA sheet to be drawn in the interior hardware of dashed rectangle, and the hardware outside square frame is referred to as hardware outside the FPGA sheet.
Present embodiment can be measured 2 to 16 LVDT sensors simultaneously, and the practical implementation method is referring to Fig. 3, Fig. 4, and step is following:
1, each storer of initialization (FLASH and SRAM etc.), why selecting with FLASH storage data is that data are not lost after the power down because FLASH belongs to nonvolatile memory, and the SRAM storer is used for the operating software code.
2, power on after, active arrangement chip configuration FPGA, from the active arrangement chip load software code to SRAM and the operation.
3, in FLASH, write excitation frequency word and amplitude control word through USB interface and CFI interface.
The reading frequency control word writes DDS frequency control register through the PIO port from FLASH; From FLASH, read the amplitude control word simultaneously; See 4 amplitude control signal through the PIO port off to power amplifier, can select 16 sensor accesses wherein to carry out the signal demodulation through the keyboard of CH452.
4, through the processing of DDS, D/A converter, power amplifier produce frequency 50 megahertzes sine wave exciting signal (with the dominant frequency clock of FPGA be synchronous; All be 50 megahertzes); Be input to the primary coil input end of differential transformer displace (LVDT) through D/A converter; The 1/4 phase place place in each cycle of DDS; Be the peak value place of pumping signal, to A/D control with resolve module and send a synchronizing pulse, A/D control and resolve module and under the driving of synchronizing pulse, control A/D converter and carry out analog to digital conversion.
5, two A/D converters are gathered the analog output signal of two secondary coils simultaneously, are converted into 16 digital signal.
6, FLASH duty controller inserts the CFI interface of 10NIOS II CPU with FLASH, and it is motionless to keep the LVDT iron core to be positioned at position, range stage casing, in different frequency responses image data and record down is set.The accuracy computation method is maximal value and the difference of minimum value and the ratio of full scale resolution in the data of gathering; Be precision=(maximal value-minimum value)/65536; The whole of digital transmitter output at present are displacement relative values, and its transmitter output valve corresponding with the LVDT range is-65535～+ 65536, does not have unit; According to the range of used LVDT, the displacement of this value through converting and can obtaining having long measure.
7, carry out calibration operation, calibration operation is that the LVDT sensor is installed on the testboard bay, and high-grade displacement indicator is housed on the stand, and measurement point evenly is set in the full scale of LVDT sensor, and the intensive more gained error correction of measurement point table is accurate more.Transmitter software reads uncorrected calculated value and is sent to host computer through the path, by the upper computer software record, and artificial simultaneously displacement actual value through host computer keyboard input stand top offset this moment indicator.Upper computer software adopts the linear difference algorithm to obtain 17 inputs after obtaining abundant measured value and actual value, the conversion table of 32 outputs, and promptly this table size is 512kbyte; This table sends transmitter software by upper computer software to through USB interface, writes the FLASH storer by transmitter software.
8, utilize the method for S=(Va-Vb)/(Va+Vb) to carry out digital demodulation; With the moving average algorithm income value is handled, obtained original shift value and give the error correction module, the error correction module adds that as the address NIOS IICPU selects control word through the 2bit error correction table that PIO sends here with 17 original shift value; Form 20 bit address; Deliver to FLASH and revise from reading error value wherein, the result who obtains delivers to the transformation result register, and serial/parallel modular converter converts 32 bit parallel results into 32 bit serial data; Be sent to the serial/parallel modular converter outside the FPGA sheet with serial mode through Port Multiplier, obtain 32 parallel synchronous output.Parallel synchronous output is delivered to the D/A converter that is used to simulate output simultaneously and is obtained simulating signal output, can be shown by the display screen of CH452.
Claims (5)
1. demodulation method is sent in the change of differential transformer displace numeral; It is characterized in that: utilize the transmitter of making by field programmable gate array (FPGA) to drive the primary coil of LVDT; And the output signal Va and the Vb of two secondary coils of collection LVDT; This transmitter comprises the storer that is made up of FLASH and SRAM, drives the digital to analog converter (D/A) of LVDT primary coil, two analog to digital converters (A/D) of two secondary coils of sampling LVDT, and digital output module, comprise the signal demodulating algorithm and with the transmitter software of host computer signal procedure; The digital demodulation that the output signal Va and the Vb of two secondary coils of the LVDT that collects makes S=(Va-Vb)/(Va+Vb) is handled; Utilize the actual displacement amount of LVDT iron core and the mapping relations between the S to realize the input to LVDT, above-mentioned processing procedure may further comprise the steps:
Each storer in A, the initialization transmitter,
B, field programmable gate array (FPGA) produce the sine wave exciting signal of changeable frequency, are input to LVDT primary coil input end through digital to analog converter (D/A),
C, two analog to digital converters of employing (A/D) are gathered the analog output signal of two secondary coils of LVDT simultaneously, are converted into digital signal,
D, the actual displacement amount of setting up the LVDT iron core and the mapping relations between the measuring amount,
E, utilize the method for S=(Va-Vb)/(Va+Vb) to carry out digital demodulation, the gained result carried out digital error correction and digital filtering, the data storage of error correction in FLASH,
F, revised result deliver to digital output module, export to host computer with the data of floating-point format, and export with analog form through digital-to-analog conversion simultaneously, are used for outside instrument and come the indication measurement result.
2. differential transformer displace numeral as claimed in claim 1 becomes send demodulation method; It is characterized in that: among the described step B; Sine wave exciting signal is produced by Direct Digital Synthesizer (DDS); And the heel one-level has the power amplifier of fixed ampllitude function, and Direct Digital Synthesizer (DDS) is synchronous with the major clock of field programmable gate array (FPGA), is the megahertz level; Field programmable gate array (FPGA) is realized the control to Direct Digital Synthesizer (DDS) through frequency control word and amplitude control word, and its control method comprises the steps:
B1, in FLASH write frequency control word and amplitude control word,
B2, the reading frequency control word writes Direct Digital Synthesizer (DDS) frequency control register through the PIO port from FLASH, from FLASH, reads the amplitude control word simultaneously, sees the amplitude control signal through the PIO port off to power amplifier,
B3, process Direct Digital Synthesizer (DDS) generation sinusoidal wave data, process digital to analog converter (D/A) are converted into analog sine, the processing of process power amplifier just obtains the sine wave exciting signal of corresponding frequencies, corresponding amplitude again.
3. differential transformer displace numeral as claimed in claim 2 becomes send demodulation method, it is characterized in that: the collection through Direct Digital Synthesizer (DDS) synchronizing signal control analog to digital converter (A/D) is the peak point of the sine value of sine wave exciting signal constantly.
4. according to claim 1 or claim 2 differential transformer displace numeral becomes and send demodulation method, and it is characterized in that: step D has adopted following calibration process to set up the actual displacement amount of LVDT iron core and the mapping relations between the measuring amount:
D1, FLASH duty controller are connected FLASH with CPU;
D2, LVDT is installed on the testboard bay; High-grade displacement indicator is housed on the stand; Measurement point evenly is set in the full scale of LVDT, and the intensive more gained error correction of measurement point table is accurate more, and transmitter software reads uncorrected calculated value and is sent to host computer through the path; By the upper computer software record, artificial simultaneously displacement actual value through host computer keyboard input testboard bay top offset this moment indicator;
D3, upper computer software adopt the linear difference algorithm to obtain the conversion table of input and output after obtaining abundant measured value and actual value, and this table sends transmitter software by upper computer software to through USB interface, writes FLASH by transmitter software.
5. send demodulation method like claim 1 or 2 or 3 described differential transformer displace numeral changes, it is characterized in that: in step e, said digital filtering is the moving average filtering algorithm.
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| CN2010102988370A CN102012209B (en) | 2010-09-29 | 2010-09-29 | Digital transmission demodulating method of differential transformer displacement transducer |
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| CN2010102988370A CN102012209B (en) | 2010-09-29 | 2010-09-29 | Digital transmission demodulating method of differential transformer displacement transducer |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US8712710B2 (en) * | 2011-05-13 | 2014-04-29 | Honeywell International Inc. | Method and apparatus for detection of LVDT core fallout condition |
| CN102426472B (en) * | 2011-08-19 | 2014-03-26 | 徐华中 | Hardware-in-the-loop generator and use method thereof |
| CN102818513B (en) * | 2012-07-31 | 2015-05-13 | 沈阳黎明航空发动机(集团)有限责任公司 | Demodulating device of linear variable differential transformer, and soft demodulating method thereof |
| CN103237362B (en) * | 2013-03-28 | 2016-05-04 | 浙江大学 | A kind of mobile node of wireless sensor network for pick up calibration |
| CN106264525A (en) * | 2015-06-09 | 2017-01-04 | 思澜科技（成都）有限公司 | Bio-impedance testing system based on frequency domain broadband signal and method thereof |
| CN105608279B (en) * | 2015-12-29 | 2018-10-16 | 北京经纬恒润科技有限公司 | A kind of differential transformer displacement transducer emulation design method and device |
| CN105865318A (en) * | 2016-03-30 | 2016-08-17 | 杭州和利时自动化有限公司 | Non-phase-sensitive digital demodulation system and method applied to LVDT displacement sensor |
| CN106647505A (en) * | 2016-12-27 | 2017-05-10 | 北京润科通用技术有限公司 | Signal processing system and method for RVDT |
| CN107121154A (en) * | 2017-05-04 | 2017-09-01 | 宁波拓普智能刹车系统有限公司 | A kind of induction displacement transducer of intelligent braking |
| CN110828003B (en) * | 2019-11-15 | 2022-03-11 | 中国原子能科学研究院 | Signal processing system |
| CN110853778B (en) * | 2019-11-18 | 2021-09-28 | 中国核动力研究设计院 | Irradiation device for realizing real-time measurement of axial length change of fuel element |
| CN111367256B (en) * | 2020-03-03 | 2022-03-29 | 中国船舶重工集团公司第七0七研究所九江分部 | RVDT steering hand wheel control device and automatic detection method |
| CN112197793B (en) * | 2020-09-30 | 2022-03-22 | 四川新川航空仪器有限责任公司 | LVDT sensor |
| CN113494931A (en) * | 2021-06-01 | 2021-10-12 | 中国航空工业集团公司沈阳飞机设计研究所 | Digital demodulation method and device for LVDT or RVDT signals |
| CN114427824B (en) * | 2021-12-16 | 2023-07-25 | 洛阳轴承研究所有限公司 | Magnetic bearing rotor axial displacement measurement method |
| CN114216389B (en) * | 2022-02-08 | 2022-04-22 | 北京航空航天大学 | Testing and analyzing device for LVDT displacement sensor |
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| CN2243064Y (en) * | 1995-03-08 | 1996-12-18 | 阜新市传感技术研究所 | Non-linear compensation modulation-demodulation amplifier |
| US5661397A (en) * | 1995-09-22 | 1997-08-26 | H. R. Textron Inc. | Demodulator circuit for determining position, velocity and acceleration of displacement sensor independent of frequency or amplitude changes in sensor excitation signal |
| CN2519236Y (en) * | 2002-01-22 | 2002-10-30 | 南京师范大学 | Intelligent high precision geometric sense detecting equipment |
| US7391202B2 (en) * | 2006-02-21 | 2008-06-24 | The Boeing Company | Linear variable differential transformer (LVDT) system using an inductance of an LVDT primary as a micro-power excitation carrier frequency to lower a drive power |
| CN101373143B (en) * | 2008-10-21 | 2010-08-25 | 上海微电子装备有限公司 | Method for detecting LVDT sensor signal |
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