CN106370096A - Measurement circuit and measuring method of LVDT (Linear Variable Differential Transformer) - Google Patents
Measurement circuit and measuring method of LVDT (Linear Variable Differential Transformer) Download PDFInfo
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- CN106370096A CN106370096A CN201610846356.6A CN201610846356A CN106370096A CN 106370096 A CN106370096 A CN 106370096A CN 201610846356 A CN201610846356 A CN 201610846356A CN 106370096 A CN106370096 A CN 106370096A
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- lvdt
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/003—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination
Abstract
The invention discloses a measurement circuit of an LVDT (Linear Variable Differential Transformer). The measurement circuit comprises a sinusoidal pulse width modulator, a signal conditioning circuit, a linear variable differential transformer, a first sampling circuit, a second sampling circuit and a controller; the sinusoidal pulse width modulator is used for outputting pulse width and frequency-adjustable rectangular wave signals; the input end of the signal conditioning circuit is connected with the sinusoidal pulse width modulator; the signal conditioning circuit outputs amplitude and frequency adjustable sinusoidal wave signals; the primary coil of the linear differential transformer is connected with the output end of the signal conditioning circuit to receive the sinusoidal wave signals as LVDT excitation signals; the secondary coil of the linear differential transformer outputs LVDT differential signals; the input end of the first sampling circuit is connected with the primary coil; the input end of the second sampling circuit is connected with the secondary coil; and the controller is connected with the output end of the first sampling circuit and the output end of the second sampling circuit and is used for performing amplitude normalization processing to output an LVDT linear position. With the measurement circuit of the LVDT, relatively complicated analog circuit parameter adjustment is avoided, zero-point residual voltage, phase drift and sensor nonlinearity can be effectively compensated. The measurement circuit has the advantages of high stability and can reduce measurement errors.
Description
Technical field
The present invention relates to lvdt field of measuring technique, it is more particularly related to a kind of measuring circuit of lvdt and
Its measuring method.
Background technology
Linear variable differential transformer (LVDT) (linear variable differential transformer, lvdt) is a kind of line
Property displacement transducer, it is configured to a differential transformer, including the primary coil, the two groups of secondary coils and that are wound in tubbiness
The iron core of individual dilval.Iron core is a moving part, and its position affects the magnetic coupling between primary and secondary winding.Secondary coil is of the same name
End links together, and output signal is the difference of two coil signals.When primary coil has ac-excited signal, secondary coil is defeated
Go out to exchange differential wave amplitude and phase place reflects the linear position of iron core.rvdt(rotary variable differential
Transformer, Rotary Variable Differential transformator) principle is identical with this, and export differential signal amplitude and reflect iron core with phase place
Angle position.
In prior art, the measuring circuit of general lvdt, it is made up of discrete analog device or Analogous Integrated Electronic Circuits, wherein
Relatively more representational be adi integrated circuit ad698.But, this analoglike measuring circuit generally has the disadvantages that 1.
Circuit is based on analog device and constitutes, and analog device parameter regulation is loaded down with trivial details, and easily introduces error and drift；2. work as iron core zero
During point, in theory, the magnetic flux being coupled to secondary coil is identical, therefore the differential wave of secondary output is zero；In fact, due to line
, can there is residual voltage at zero in the reasons such as the imbalance of circle, parasitic capacitance, bleeder resistance；Compensation circuit can be introduced to eliminate zero
Point residual voltage, can introduce nonlinearity erron in zero crossings simultaneously；3. demodulator circuit needs to refer to the output work of oscillating circuit
For reference signal, when sensor output is with reference signal same phase, demodulator circuit can work well, but each in signal chains
Link all there may be phase shift, needs to be introduced into the phase shift that analogue phase adjusts in circuit compensation signal chains, there is also compensation simultaneously
Low precision and the problem of drift, adjust loaded down with trivial details；4.lvdt sensor is decided by its construction, can exist certain non-linear, especially
It is when close to full scale, its output signal exists roll-offs, and can affect its effective range；Need to introduce a non-linear school
Positive circuit, in analog systemss, there is also correction accuracy poor, drift, adjust loaded down with trivial details the problems such as.
Content of the invention
For weak point present in above-mentioned technology, the present invention provides a kind of measuring circuit of lvdt and its measurement side
Method, it is to avoid relatively cumbersome analog circuit parameters are adjusted, and effectively compensate for residual voltage at zero, phase drift, sensor non-thread
Property, stability height, reduce measurement error.
In order to realize according to object of the present invention and further advantage, the present invention is achieved through the following technical solutions:
The present invention provides a kind of measuring circuit of lvdt, comprising:
Sine pulse width modulator, it is used for the square-wave signal of output pulse width and frequency-adjustable；Described square wave letter
Number pulse width press sinusoidal regulation；
Signal conditioning circuit, its input is connected to described sine pulse width modulator, for described square-wave signal according to
Secondary it is filtered with processing and amplifying with the sine wave signal of output amplitude and frequency-adjustable；
Linear variable differential transformer (LVDT), its primary coil is connected to described signal conditioning circuit outfan to receive described sine wave
Signal exports lvdt differential wave as lvdt pumping signal, described secondary coil；
First sample circuit, its input is connected to described primary coil, for adopting to described lvdt pumping signal
Sample；
Second sample circuit, its input is connected to described secondary coil, for adopting to described lvdt differential wave
Sample；And,
Controller, it is connected respectively to described first sample circuit outfan and described second sample circuit outfan, uses
Process in amplitude normalization is made with respect to described lvdt pumping signal to described lvdt differential wave to export lvdt linear position；
Wherein, the frequency of described square-wave signal is that the sample frequency and described second of described first sample circuit is adopted respectively
The integral multiple of the sample frequency of sample circuit.
Preferably, described controller is provided with four communication ends:
First communication ends are connected to the pulse to adjust described Square wave pulses of the input of described sine pulse width modulator
Width and frequency；
Second communication ends are connected to described first sample circuit outfan to receive the described lvdt excitation letter through over-sampling
Number；
Third communication end is connected to described second sample circuit outfan to receive the differential letter of described lvdt through over-sampling
Number；
As the outfan of controller, the described lvdt through described controller normalized is linear for output at fourth communication end
Position.
Preferably, described signal conditioning circuit includes described Square wave pulses being carried out filtering high fdrequency components successively and putting
The big low pass filter processing and power amplifier；
Described low pass filter is connected to described sine pulse width modulator outfan, and described power amplifier output connects
To described primary coil.
Preferably, described first sample circuit include successively described lvdt pumping signal being carried out filtering high fdrequency components and
First frequency overlapped-resistable filter of sampling and the first analog-digital converter；
Described first frequency overlapped-resistable filter input is connected to described primary coil；Described first AfD converter output
It is connected to described second communication ends.
Preferably, described second sample circuit includes successively described lvdt differential wave being amplified, filtering high frequency
The instrument amplifier of component and sampling, the second frequency overlapped-resistable filter and the second analog-digital converter；
Described instrument amplifier input is connected to described secondary coil, and described second AfD converter output is connected to
Described third communication end.
Preferably, described signal conditioning circuit also includes the electric capacity for AC coupled, and described electric capacity is located at described work(
Between rate amplifier and described primary coil.
A kind of measuring method of lvdt, comprises the following steps:
Sine pulse width modulator produces pulse width and the square-wave signal of frequency-adjustable, processes through signal conditioning circuit,
The sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT) primary coil；
Sine pulse width modulator produces pulse width and the square-wave signal of frequency-adjustable, processes through signal conditioning circuit,
The sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT) primary coil；
The lvdt differential wave of the lvdt pumping signal to primary coil input and secondary coil output carries out sampling simultaneously,
Direct current biasing is gone to process；
Carry out digit phase synchronous demodulation to going the lvdt differential wave after direct current biasing；
Enter respectively to going the lvdt pumping signal after direct current biasing and the lvdt differential wave after digital Phase synchronization demodulation
Row smoothing processing；
It is inclined that the sensor zero point offset signal being stored by controller carries out zero point to the lvdt differential wave of smooth output
Shift correction；
With the lvdt pumping signal after smoothing processing as reference, amplitude is made to the lvdt differential wave after zero migration correction
Normalized, exports lvdt linear position；
Wherein, the sampling of described lvdt pumping signal and described lvdt differential wave respectively with described square-wave signal
Produce synchronous；
The synchronizing signal of described digit phase synchronous demodulation is described square-wave signal.
Preferably, after amplitude normalization is processed, further comprise the steps of:
According to the sensing station-output corresponding relation look-up table of described controller storage, by the non-linear school of lvdt
Positive module is to correct the non-linear of lvdt linear position signal.
Preferably, described amplitude normalization is processed, and refers to:
Controller receives sampled lvdt pumping signal, calculates its virtual value；
Controller will receive the virtual value divided by lvdt pumping signal for the lvdt differential wave after zero migration correction.
The present invention at least includes following beneficial effect:
The lvdt measuring circuit that the present invention provides, sine pulse width modulator produces the square wave of pulse width and frequency-adjustable
Signal to signal conditioning circuit, make by the primary coil of the sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT)
For lvdt pumping signal, secondary coil output lvdt differential wave；Controller with through over-sampling, go direct current biasing process after lvdt
Pumping signal is reference, to through over-sampling, go direct current biasing, digit phase synchronous demodulation, at smooth and zero migration correction
Lvdt differential wave after reason carries out amplitude normalization process, realizes the output of lvdt linear position, and simulation that need not be loaded down with trivial details is electric
Road parameter regulation, it is to avoid the impact to circuit parameter such as the component tolerance of general analog circuit, aging, drift, digital form
The influence factor of set parameter is less, and stability is higher, reduces measurement error；Meanwhile, compared to analog compensation
Method is realized complex and can be introduced new error, the present invention can effectively compensate for residual voltage at zero, phase drift with
And sensor nonlinear.
Part is embodied by the further advantage of the present invention, target and feature by description below, and part also will be by this
Invention research and practice and be understood by the person skilled in the art.
Brief description
Fig. 1 is the schematic diagram of lvdt measuring circuit of the present invention；
Fig. 2 is the flow chart of lvdt measuring method of the present invention.
Specific embodiment
The present invention is described in further detail below in conjunction with the accompanying drawings, to make those skilled in the art with reference to description literary composition
Word can be implemented according to this.
It should be appreciated that used herein such as " have ", "comprising" and " inclusion " term do not allot one or many
The presence of individual other element or a combination thereof or interpolation.
Embodiment 1
The present invention provides a kind of measuring circuit of lvdt, comprising:
Sine pulse width modulator 10, it is used for the square-wave signal of output pulse width and frequency-adjustable；Square-wave signal
Pulse width press sinusoidal regulation；
Signal conditioning circuit 20, its input is connected to sine pulse width modulator 10, for entering successively to square-wave signal
Row filtering and processing and amplifying are with the sine wave signal of output amplitude and frequency-adjustable；
Linear variable differential transformer (LVDT) 30, its primary coil 31 is connected to signal conditioning circuit outfan 20 to receive sine wave letter
Number as lvdt pumping signal, secondary coil 32 exports lvdt differential wave；
First sample circuit 40, its input is connected to primary coil 31, for sampling to lvdt pumping signal；
Second sample circuit 50, its input is connected to secondary coil 32, for sampling to lvdt differential wave；With
And,
Controller 60, it is connected respectively to the first sample circuit 40 outfan and the second sample circuit 50 outfan, is used for
Make amplitude normalization to lvdt differential wave with respect to lvdt pumping signal to process to export lvdt linear position；
Wherein, the frequency of square-wave signal is sample frequency and second sample circuit 50 of the first sample circuit 40 respectively
The integral multiple of sample frequency.
In above-mentioned embodiment, sine pulse width modulator (sinusoidal pulse width modulation, spwm)
The pulse width of the square-wave signal of 10 generations to be adjusted according to the sine wave needed for excitation lvdt.Signal conditioning circuit 20 is to square
Shape ripple signal is filtered processing, and after filtering high fdrequency components, can recover modulated signal, i.e. sine wave needed for excitation lvdt
Signal.The modulating frequency changing sine pulse width modulator 10 can adjust the frequency of the sine wave encouraging lvdt.By sinusoidal pulsewidth
The pulse width of manipulator 10 is multiplied by a different scale factor, can adjust the amplitude of the sine wave of excitation lvdt.Sinusoidal
Pulse width modulator 10 can be unipolarity or bipolar manner.
As a kind of specific embodiment, signal conditioning circuit 20 includes successively Square wave pulses being carried out filtering high frequency
The low pass filter 21 of component and processing and amplifying and power amplifier 22；Low pass filter 21 is connected to sine pulse width modulator 10
Outfan, power amplifier 22 outfan is connected to primary coil 31.Power amplifier 22 amplification low pass device 21 demodulates
Sine wave signal, with adapt to lvdt primary coil 31 driving power requirement.As further preferred, signal conditioning circuit 20
Also include the electric capacity 23 for AC coupled, electric capacity 23 is located between power amplifier 22 and primary coil 31.
As a kind of specific embodiment, controller 60 is provided with four communication ends: the first communication ends 61 are connected to sine
The input of pulse width modulator 10 is to adjust pulse width and the frequency of Square wave pulses；Second communication ends 62 are connected to first and adopt
Sample circuit 40 outfan is to receive the lvdt pumping signal through over-sampling；It is defeated that third communication end 63 is connected to the second sample circuit 50
Go out end to receive the lvdt differential wave through over-sampling；Fourth communication end 64, as the outfan of controller, exports via controller
The lvdt linear position of 60 normalizeds.
As a kind of specific embodiment, the first sample circuit 40 includes successively lvdt pumping signal being carried out filtering height
First frequency overlapped-resistable filter 41 of frequency component and sampling and the first analog-digital converter 42；First frequency overlapped-resistable filter 41 input is even
It is connected to primary coil 31；First analog-digital converter 42 outfan is connected to the second communication ends 62.Second sample circuit 50 include according to
The secondary instrument amplifier 51 that lvdt differential wave is amplified, filters with high fdrequency components and sampling, the second frequency overlapped-resistable filter
52 and second analog-digital converter 53；Instrument amplifier 51 input is connected to secondary coil 32, and the second analog-digital converter 53 exports
End is connected to third communication end 63.Instrument amplifier 51 is used for amplifying the lvdt differential wave of secondary coil 32 output.Instrument is put
Lvdt differential wave after big device 51 amplifies is adopted higher than the second sample circuit 50 by the second frequency overlapped-resistable filter 52 rejection frequency
The high-frequency signal of sample frequency half；The lvdt pumping signal of primary coil by the first frequency overlapped-resistable filter 41 rejection frequency is higher than
The high-frequency signal of the first sample circuit 40 sample frequency half, to meet nyquist sampling theorem, realizes sampling.
Controller 60 can be microcontroller (mcu) or digital signal processor (dsp).Controller 60 controls first respectively
Analog-digital converter 42 and the second analog-digital converter 53 are gone forward side by side line amplitude normalized with obtaining corresponding sampled value, by the 4th
Communication ends 64 export lvdt linear position.First communication ends 61 of used controller 60, can adjust sine pulse width modulator 10
The pulse width of square-wave signal of output and frequency.
The lvdt measuring circuit that the present invention provides, sine pulse width modulator 10 produces the rectangle of pulse width and frequency-adjustable
Ripple signal to signal conditioning circuit 20, the primary of the sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT) 30
Coil 31 exports lvdt differential wave as lvdt pumping signal, secondary coil 32；Controller 60 with through over-sampling, go direct current inclined
After putting process, lvdt pumping signal is reference, to through over-sampling, remove direct current biasing, digit phase synchronous demodulation, smooth and zero
Lvdt differential wave after point offset correction is processed carries out amplitude normalization process, realizes the output of lvdt linear position, need not
Loaded down with trivial details analog circuit parameters are adjusted, it is to avoid the shadow to circuit parameter such as the component tolerance of general analog circuit, aging, drift
Ring, the influence factor of the parameter set by digital form is less, and stability is higher, reduces measurement error.
Embodiment 2
On the basis of embodiment 1, the present embodiment provide a kind of measuring method based on lvdt measuring circuit, it include with
Lower step:
S1, sine pulse width modulator produces pulse width and the square-wave signal of frequency-adjustable, at signal conditioning circuit
Reason, the primary coil of the sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT)；
S2, sine pulse width modulator produces pulse width and the square-wave signal of frequency-adjustable, at signal conditioning circuit
Reason, the primary coil of the sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT)；
S3, the lvdt differential wave of the lvdt pumping signal to primary coil input and secondary coil output is adopted simultaneously
Sample, go direct current biasing process；
S4, carries out digit phase synchronous demodulation to going the lvdt differential wave after direct current biasing；
S5, to the lvdt differential wave after going the lvdt pumping signal after direct current biasing to demodulate with digital Phase synchronization respectively
It is smoothed；
S6, the sensor zero point offset signal being stored by controller carries out zero point to the lvdt differential wave of smooth output
Offset correction；
S7, with the lvdt pumping signal after smoothing processing as reference, makees to the lvdt differential wave after zero migration correction
Amplitude normalization is processed, and exports lvdt linear position；
In above-mentioned embodiment, the sampling product with square-wave signal respectively of lvdt pumping signal and lvdt differential wave
Raw synchronous, refer to the sample frequency frequency with square-wave signal respectively of the first sample circuit 40 and the second sample circuit 50
Identical.
The fixing rhythm and pace of moving things producing according to the intervalometer of controller 60, is updated with the data in software sinusoidal data look-up table
The pulse width of the square-wave signal of sine pulse width modulator 10.Square-wave signal is at the filtering of signal conditioning circuit 20
Reason, after filtering high fdrequency components, recovers modulated signal, i.e. sine wave signal needed for excitation lvdt.Signal conditioning circuit 20 is defeated
Go out the primary coil 31 to linear variable differential transformer (LVDT) 30 for the sine wave signal, as lvdt pumping signal.Change sinusoidal pulse width modulation
The modulating frequency of device 10 can adjust the frequency of the sine wave of excitation lvdt.The pulse width of sine pulse width modulator 10 is multiplied by
One different scale factor, can adjust the amplitude of the sine wave of excitation lvdt.
By the program part of software, turn to respectively through the first analog-digital converter 42 and the second analog-digital converter 53 modulus
The digitized signal setting direct current biasing of output after changing removes algorithm, removes the direct current biasing of sampled value in analog digital conversion.
By digit phase synchronous demodulation algorithm, calculate away the amplitude of the digitized signal modulated signal after direct current biasing
And symbol.The synchronizing signal of digit phase synchronous demodulation is square-wave signal.
The data that smoothing processing refers to by a digital filter demodulates to digital Phase synchronization demodulating algorithm is entered
Row is processed, and obtains a stabilization signal representing lvdt plunger position.
The sensor biased data look-up table being drawn according to the experiment of program storage, then the sensor being stored by controller
Zero offset signal carries out zero migration correction respectively to the lvdt pumping signal of smooth output and lvdt differential wave, to correct
The biasing effect of lvdt, such as residual voltage at zero.
Controller 60 enters line amplitude normalizing to the lvdt differential wave after zero migration correction with respect to lvdt pumping signal
Change is processed, and exports lvdt linear position by controller 60 fourth communication end 64.Amplitude normalization is processed, and refers to: controller
60 receive sampled lvdt pumping signal, calculate its virtual value；Controller 60 will receive after zero migration correction
Lvdt differential wave is divided by the virtual value of lvdt pumping signal.Amplitude normalization, for eliminating pumping signal amplitude of variation to survey
The impact of amount result.
After amplitude normalization is processed in step s7, also include step s8, according to the sensing station-output of controller storage
Corresponding relation look-up table, corrects the non-linear of lvdt linear position signal by the gamma correction module of lvdt.
In above-mentioned embodiment, the square-wave signal of sine pulse width modulator 10 generation pulse width and frequency-adjustable gives letter
Number modulate circuit 20, primary coil 31 conduct of the sine wave signal of output amplitude and frequency-adjustable to linear variable differential transformer (LVDT) 30
Lvdt pumping signal, secondary coil 32 exports lvdt differential wave；Controller 60 with through over-sampling, go direct current biasing process after
Lvdt pumping signal is reference, to through over-sampling, go to direct current biasing, digit phase synchronous demodulation, smooth and zero migration school
Lvdt differential wave after just processing carries out amplitude normalization process, realizes the output of lvdt linear position, mould that need not be loaded down with trivial details
Intend circuit parameter to adjust, it is to avoid the impact to circuit parameter such as the component tolerance of general analog circuit, aging, drift, numeral
The influence factor of the parameter set by mode is less, and stability is higher, reduces measurement error；Meanwhile, compared to simulation
Compensation method is realized complex and can be introduced new error, and present embodiment can effectively compensate for residual voltage at zero, phase
Position drift and sensor nonlinear.
Embodiment 3
On the basis of embodiment 1 and embodiment 2, the present embodiment provides the measuring circuit of lvdt and its tool of measuring method
Body embodiment.
, it is 2.5khz that lvdt measuring circuit adopts driving frequency, virtual value is 3v's taking mhr500lvdt sensor as a example
Sine-wave excitation, nxp microcontroller lpc1768 selected by controller 60.Lpc1768 has been internally integrated pwm (pulse width
Modulation, pulse width modulation) module, can be used to produce spwm (sinusoidal pulse width
Modulation, Sinusoidal Pulse Width Modulation) signal, that is, be equivalent to the sine pulse width modulator 10 of the present invention.Pwm module when
Clock frequency configuration is 96mhz, pwm period register ntIt is set to 119, therefore frequency f of pwm signalpwmFor:
Interrupted using the general purpose timer within lpc1768, its interruption frequency f is setintFor 80khz.In interrupting service
Update pwm pulse width register, control the first analog-digital converter 42, the sampling of the second analog-digital converter 53 simultaneously, and return as amplitude
One changes calculating is processed.The internal flash memory of lpc1768 stores the sinusoidal wave form amplitude that a cycle hits m is at 32 points and looks into
Look for table data.Update pwm pulse width register, the modulating frequency of pwm pulse width in the interruption service of above-mentioned 80khz
The sinusoidal signal frequency f producingsinFor:
Square-wave signal is filtered process from signal conditioning circuit 20, after filtering high fdrequency components, tune can be recovered
Signal processed, i.e. sine wave signal needed for excitation lvdt.Filtering adopts salung base low pass filter, and setting by frequency is
4khz.Power amplifier 22 adopts amplifier opa544t.Mhr500lvdt sensor input impedance in 2.5khz is 145 ω,
Opa544t can meet driving and require.Virtual value is the sine voltage hunting range of 3v is ± 3*1.414v, and ± 15v power supply supplies
Electricity, meets its hunting range and requires.
Power amplifier 22 outfan capacitance 23 realizes AC coupled.Instrument amplifier 51 selects ina826 instrument
Amplifier.
First frequency overlapped-resistable filter 41 and the second frequency overlapped-resistable filter 52 are respectively adopted single order low pass rc wave filter, cutoff frequency
Rate is set to 25khz.
First analog-digital converter 42 and the second analog-digital converter 53 are respectively adopted ads8519 integrated chip.Highest sample rate
For 250khz, signal input scope maximum ± 10v, requirement can be met.PORT COM is usb interface, based on collection inside lpc1768
The usb controller becoming is realized.
The software section of controller 60 is based on keil mdk arm development environment and develops.Lpc1768cpu clock frequency sets
It is set to 96mhz, program runs on internal ram, improve than running on speed during flash.Timer interruption frequency is 80khz, two
1200 instructions can be run between secondary interruption.The length of interrupt service routine not can exceed that 1200 instructions limit.Software master
Body is write with c language, and time-critical code assembler language is write.
32 sampled values of the storage of array sine wave signal a cycle of 32 elements are utilized, each array unit in software
Plain 32 bit wides.Three pointers are respectively directed to array head, array tail and next data.Next data pointer is in each customizer
Interrupt in service from increasing, when reaching array tail, be reset to array head.Interrupt next numeral in service according to pointer indication at each
To array element be assigned to pwm pulse width register.
The conversion value of timer interrupt service sampling two-way analog digital conversion, sample rate is 80khz.
Before digital demodulation, the sampling of secondary coil 32 output signal of lvdt need to first pass through direct current biasing and remove algorithm
Remove removing DC bias.Front 320 sampled values are averaging, i.e. the sampled value in 10 cycles, the meansigma methodss of sinusoidal signal are zero, institute
It is direct current biasing with this meansigma methods.Each sampled value all deducts this meansigma methods, just obtains the signal of AC coupled.
The synchronizing signal of Phase synchronization digital demodulation blocks is pwm signal.Pulse width symbol to pwm and sampled value
Symbol carries out xor operation: during two signal homophases, symbol is identical, and result is logical zero；Two signal inversion are that symbol is different, knot
Fruit is logic 1.The logical value of front 32 XORs determines the phase place of lvdt secondary coil 32 sampling by majority voting algorithm.
The next stage of software is digital filter, and demodulating data is smoothed after the process of this step, stable output.Using
Moving average filter, the width of sliding window can cover front 16 demodulation values.
Determine sensor zero point offset signal beforehand through experiment, and store.Sensor bias correction module is by upper level
The output data of module all deducts this offset signal.Realize sensor bias correction.
Apply the pumping signal of different amplitudes, amplitude output signal is also different.In order to overcome the impact of excitation amplitude shift,
Controller 60 adopts amplitude normalization algorithm.Implementation method is: real-time sampling pumping signal value, is calculated its virtual value, then
The data after sensor bias correction, all divided by the pumping signal virtual value calculating, realize normalization.
By the lvdt output valve measuring under experimental calibration diverse location, retouch and determine curve.Further according to most preferably each fixed point
With the deviation of best fit straight line, calculate the corrected value of each point, and tables of data is stored in the flash memory of lpc1768.Non-thread
Property correcting algorithm according to the corrected value correction final output of difference, form the linear of output.
It should be noted that being related to measuring circuit and its measurement side of lvdt in embodiment 1, embodiment 2 and embodiment 3
The example of method, is all applied to rvdt sensor.
Although embodiment of the present invention is disclosed as above, it is not restricted to listed in description and embodiment
With.It can be applied to various suitable the field of the invention completely.Can be easily for those skilled in the art
Realize other modification.Therefore under the general concept being limited without departing substantially from claim and equivalency range, the present invention does not limit
In specific details with shown here as the legend with description.
Claims (9)
1. a kind of measuring circuit of lvdt is it is characterised in that include:
Sine pulse width modulator, it is used for the square-wave signal of output pulse width and frequency-adjustable；Described square-wave signal
Pulse width presses sinusoidal regulation；
Signal conditioning circuit, its input is connected to described sine pulse width modulator, for entering successively to described square-wave signal
Row filtering and processing and amplifying are with the sine wave signal of output amplitude and frequency-adjustable；
Linear variable differential transformer (LVDT), its primary coil is connected to described signal conditioning circuit outfan to receive described sine wave signal
As lvdt pumping signal, described secondary coil exports lvdt differential wave；
First sample circuit, its input is connected to described primary coil, for sampling to described lvdt pumping signal；
Second sample circuit, its input is connected to described secondary coil, for sampling to described lvdt differential wave；With
And,
Controller, it is connected respectively to described first sample circuit outfan and described second sample circuit outfan, for right
Described lvdt differential wave is made amplitude normalization with respect to described lvdt pumping signal and is processed to export lvdt linear position；
Wherein, the frequency of described square-wave signal is the sample frequency of described first sample circuit and described second sampling electricity respectively
The integral multiple of the sample frequency on road.
2. the measuring circuit of lvdt as claimed in claim 1 is it is characterised in that described controller is provided with four communication ends:
First communication ends are connected to the input of the described sine pulse width modulator pulse width to adjust described Square wave pulses
And frequency；
Second communication ends are connected to described first sample circuit outfan to receive the described lvdt pumping signal through over-sampling；
Third communication end is connected to described second sample circuit outfan to receive the described lvdt differential wave through over-sampling；
Fourth communication end is as the outfan of controller, the linear position of described lvdt through described controller normalized for the output
Put.
3. the measuring circuit of lvdt as claimed in claim 1 or 2 is it is characterised in that described signal conditioning circuit is included successively
Described Square wave pulses are carried out filter with low pass filter and the power amplifier of high fdrequency components and processing and amplifying；
Described low pass filter is connected to described sine pulse width modulator outfan, and described power amplifier output is connected to institute
State primary coil.
4. the measuring circuit of lvdt as claimed in claim 2 is it is characterised in that described first sample circuit is included successively to institute
State lvdt pumping signal to carry out filtering high fdrequency components and the first frequency overlapped-resistable filter sampled and the first analog-digital converter；
Described first frequency overlapped-resistable filter input is connected to described primary coil；Described first AfD converter output connects
To described second communication ends.
5. the measuring circuit of lvdt as claimed in claim 2 is it is characterised in that described second sample circuit is included successively to institute
State lvdt differential wave and be amplified, filter the instrument amplifier of high fdrequency components and sampling, the second frequency overlapped-resistable filter and
Two analog-digital converters；
Described instrument amplifier input is connected to described secondary coil, and described second AfD converter output is connected to described
Third communication end.
6. the measuring circuit of lvdt as claimed in claim 1 is it is characterised in that described signal conditioning circuit is also included for handing over
The electric capacity of stream coupling, described electric capacity is located between described power amplifier and described primary coil.
7. the method that a kind of measuring circuit of lvdt as any one of claim 1-6 for application carries out lvdt measurement, its
It is characterised by, comprise the following steps:
Sine pulse width modulator produces pulse width and the square-wave signal of frequency-adjustable, processes through signal conditioning circuit, output
The sine wave signal of amplitude and frequency-adjustable to linear variable differential transformer (LVDT) primary coil；
The lvdt differential wave of the lvdt pumping signal to primary coil input and secondary coil output carries out sampling simultaneously, goes directly
Stream bias treatment；
Carry out digit phase synchronous demodulation to going the lvdt differential wave after direct current biasing；
Put down respectively to going the lvdt pumping signal after direct current biasing and the lvdt differential wave after digital Phase synchronization demodulation
Sliding process；
The sensor zero point offset signal being stored by controller carries out zero migration school to the lvdt differential wave of smooth output
Just；
With the lvdt pumping signal after smoothing processing as reference, amplitude normalizing is made to the lvdt differential wave after zero migration correction
Change is processed, and exports lvdt linear position；
Wherein, the sampling of the described lvdt pumping signal and described lvdt differential wave generation with described square-wave signal respectively
Synchronous；
The synchronizing signal of described digit phase synchronous demodulation is described square-wave signal.
8. the measuring method of lvdt as claimed in claim 7 is it is characterised in that after amplitude normalization process, further comprise the steps of:
According to the sensing station-output corresponding relation look-up table of described controller storage, by the gamma correction mould of lvdt
Block is to correct the non-linear of lvdt linear position signal.
9. the measuring method of lvdt as claimed in claim 7 or 8, it is characterised in that described amplitude normalization is processed, refers to
It is:
Controller receives sampled lvdt pumping signal, calculates its virtual value；
Controller will receive the virtual value divided by lvdt pumping signal for the lvdt differential wave after zero migration correction.
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