CN116222360A - LVDT displacement sensor data acquisition method - Google Patents
LVDT displacement sensor data acquisition method Download PDFInfo
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- 238000004364 calculation method Methods 0.000 claims abstract description 16
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- 238000013480 data collection Methods 0.000 claims description 4
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- H—ELECTRICITY
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- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
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- H03M1/12—Analogue/digital converters
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- G—PHYSICS
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- 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
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
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Abstract
The application provides a data acquisition method of an LVDT displacement sensor, which comprises the steps of controlling a digital-to-analog converter DAC to cooperate with a driving circuit to generate sine wave excitation signals; the coil outputs an induction signal based on the excitation signal, and the induction signal is output to the analog-to-digital converter ADC through the signal processing circuit; the method comprises the steps of controlling an analog-to-digital converter ADC to continuously collect dynamic induction signals of a coil by a collection method with collection frequency being 2N times of an excitation signal and collection times being N times of the whole period of the excitation signal, and deducing and calculating the amplitude of the induction signals by applying a discrete Fourier transform principle; and calculating the displacement of the LDVT displacement sensor according to the amplitude of the induction coil. According to the method, the amplitude of the induction signal is deduced and calculated by applying the principle of discrete Fourier transform, and the temperature drift error, the zero point error and the phase error generated due to hardware in the calculation of the amplitude of the induction signal are avoided by using a mathematical method; the invention has excellent precision through practical test.
Description
Technical Field
The application relates to the technical field of displacement sensors, in particular to a data acquisition method of an LVDT displacement sensor.
Background
LVDT (Linear Variable Differential Transformer) is an abbreviation of linear variable differential transformer, belonging to the linear displacement sensor. The working principle is simply referred to as a core-movable transformer. It is composed of a primary coil, one or two secondary coils, iron core, coil skeleton and casing. An alternating signal is applied to the primary coil, the secondary coil generates a corresponding induction signal, and when the iron core is moved, the signal amplitude of the induction signal changes, and the displacement of the iron core movement is in proportional relation with the amplitude of the induction signal. During operation of the LVDT displacement sensor, the movement of the core cannot exceed the linear range of the coil, otherwise a nonlinear value will be generated, so that all LVDT displacement sensors have a linear range.
As shown in fig. 1, for an LVDT displacement sensor having two secondary coils, winding directions of the two secondary coils are opposite, when the core is at the middle position, the amplitudes of induction signals generated by the two secondary coils are equal and opposite, and an output equivalent voltage is zero; when the iron core deviates from the central position, the amplitude of the induction signals generated by the two secondary coils changes, the output equivalent voltage is not zero, and the displacement change can be obtained by calculating the amplitude of the induction signals of the two secondary coils.
In the conventional test method, an RC oscillating circuit is required to generate an excitation signal input at one side of the primary coil of the LVDT, and an RC low-pass filter circuit is required to process an output signal at one side of the secondary coil of the LVDT to convert a dynamic signal into a static level signal for measurement.
However, the RC oscillator and the RC low pass filter circuit may be affected by the ambient temperature, resulting in inaccurate measurement results.
Disclosure of Invention
In order to enable a detection result to be more accurate, the application provides a data acquisition method of an LVDT displacement sensor.
The data acquisition method of the LVDT displacement sensor provided by the application adopts the following technical scheme:
an LVDT displacement sensor data collection method, comprising:
controlling a digital-to-analog converter DAC to cooperate with a driving circuit to generate a sine wave excitation signal;
the coil outputs an induction signal based on a sine wave excitation signal, and the induction signal is processed by the signal processing circuit and then is output to the analog-to-digital converter ADC;
controlling an analog-to-digital converter ADC, and controlling the analog-to-digital converter ADC to continuously acquire dynamic induction signals of a coil by using an acquisition method with acquisition frequency being 2N times of an excitation signal and acquisition times being N times of the whole period of the excitation signal;
and calculating the amplitude of the induction signal based on the acquired original value by adopting the principle of discrete Fourier transform, and calculating the displacement based on the amplitude.
By adopting the technical scheme, the analog-to-digital converter ADC is utilized to continuously collect the induction signals output by the coil and calculate the displacement, and compared with the method for collecting the static level by utilizing the RC low-pass filter circuit, the calculated displacement is more accurate.
Optionally, the controlling the DAC to cooperate with the driving circuit to generate the sine wave excitation signal includes:
the DAC outputs a step wave, the driving circuit is a low-pass filter circuit formed by operational amplifiers, and the step wave is changed into a sine wave after passing through the low-pass filter circuit.
Optionally, the coil outputs an induction signal based on a sine wave excitation signal, and the induction signal is processed by a signal processing circuit and then output to an analog-to-digital converter ADC, including:
the signal processing circuit is a signal amplifying circuit formed by operational amplifiers.
Optionally, the controlling the ADC uses an acquisition method with an acquisition frequency 2N times of the excitation signal and an acquisition frequency N times of the whole period of the excitation signal to control the ADC to continuously acquire the dynamic sensing signal of the coil, including:
the acquisition frequency of the analog-to-digital converter ADC is 2n times of the excitation signal, n is greater than 1, and n is an integer; the acquisition times of the analog-to-digital converter ADC are N times of the whole period of the excitation signal, N is greater than 0, and N is an integer.
Optionally, the calculating the amplitude of the induction signal based on the original value using the principle of discrete fourier transform includes:
the calculation formula is as follows:
wherein X k is the amplitude of the induction signal, N is the total number of acquisitions, N is the serial number of acquisitions, k is the frequency coefficient, and X N is the original value.
In summary, the present application includes at least one of the following beneficial technical effects:
1. the amplitude of the induction signal is deduced and calculated by applying the principle of discrete Fourier transform, and the temperature drift error, zero point error and phase error generated by the reason that the RC oscillator and RC filtering are used by hardware in the calculation of the amplitude of the induction signal are avoided by using a mathematical method;
2. the digital-to-analog converter DAC is matched with the driving circuit to output a sine excitation signal, compared with the RC oscillator, the digital-to-analog converter DAC is less affected by temperature, so that the excitation signal is more stable and is more close to a standard sine wave than the RC oscillator, and the precision after Fourier transform calculation is improved;
3. the analog-to-digital converter ADC is controlled, the acquisition frequency is 2N times of the excitation signal, the acquisition frequency is N times of the whole period of the excitation signal, and the analog-to-digital converter ADC is controlled to acquire the dynamic induction signal of the coil, so that digital filtering is realized, and the deduction calculation result based on the discrete Fourier transform principle is more accurate.
Drawings
Fig. 1 is a schematic diagram of a coil structure in the background of the present application.
Fig. 2 is a flowchart of the entirety of an embodiment of the present application.
Fig. 3 is a block diagram of connections of an embodiment of the present application with respect to circuit portions.
Detailed Description
The present application will be described in further detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
The LVDT displacement sensor comprises a coil, wherein the coil comprises a primary coil and two secondary coils, an iron core is arranged between the primary coil and the secondary coils, and the secondary coils can induce alternating signals passing through the primary coils and further generate induction signals on the secondary coils. When the position of the iron core is moved, the induction signals generated on the two secondary coils are changed, and the distance of the movement of the iron core is calculated by detecting the change of the amplitude of the induction signals, so that the calculation of displacement is realized.
The embodiment of the application discloses a data acquisition method of an LVDT displacement sensor. Referring to fig. 1 and 2, an LVDT displacement data acquisition method includes controlling a digital-to-analog converter DAC to cooperate with a driving circuit to generate a sine wave excitation signal; the coil outputs an induction signal based on the excitation signal, and the induction signal is processed by the signal processing circuit and then is output and transmitted to the analog-to-digital converter ADC; controlling an analog-to-digital converter ADC to continuously acquire dynamic induction signals of a coil by using an acquisition method with acquisition frequency being 2N times of an excitation signal and acquisition times being N times of the whole period of the excitation signal; the amplitude of the induction signal is calculated based on the acquired original value by adopting the principle of discrete Fourier transform, and the displacement is calculated based on the amplitude.
Selecting a singlechip with an internal digital-to-analog converter DAC, and designing a circuit structure according to figure 3;
the single chip microcomputer controls the DAC (digital-to-analog converter) to output a step wave with the frequency of 4m times of the excitation signal, and the step wave outputs a sine excitation signal to the primary coil after passing through the driving circuit, wherein m is an integer larger than 1.
The digital-to-analog converter DAC is matched with the driving circuit to output sine wave excitation signals, so that the stability of the frequency and amplitude of the sine wave can be ensured, the influence of the ambient temperature is very small compared with that of an RC oscillator, the accuracy of a measurement result is improved, and meanwhile, the amplitude of the excitation sine wave can be conveniently changed according to the setting of the input value of the digital-to-analog converter DAC.
The coil outputs an induction signal based on the excitation signal, and the induction signal is processed by the signal processing circuit and then is output to the analog-to-digital converter ADC.
And the signal processing circuit uses an instrument amplifier and designs a circuit with the amplification factor of G=1 to output the sensing signal, so that the output capacity of the sensing signal is enhanced, and the signal stability is improved.
The singlechip controls the two external analog-digital converters ADC to continuously and synchronously collect induction signals of the two secondary coils by using an acquisition mode that the acquisition frequency is 2N times of the excitation signal and the acquisition frequency is N times of the whole period of the excitation signal, wherein N is an integer greater than 1 and N is an integer greater than 0.
The singlechip controls the analog-to-digital converter ADC to continuously and synchronously acquire the induction signals of the two secondary coils by using an acquisition mode that the acquisition frequency is 2N times of the excitation signal and the acquisition frequency is N times of the whole period of the excitation signal, and compared with the prior art that an RC oscillator and an RC low-pass filter circuit are adopted, the influence of the environment temperature and the circuit on a measurement result can be reduced; the acquisition frequency of the ADC and the output frequency of the DAC use the same singlechip clock source, so that the acquisition and excitation time sequence are ensured to be aligned strictly, and the precision of the Fourier transform calculation result is improved; the N times integer period of the collected excitation signal is controlled to realize digital filtering, so that the stability of the measured value is improved; when two paths of sensing signals are acquired, the influence of high-frequency noise on the acquisition precision is avoided by using a two-path synchronous acquisition mode.
Deriving the magnitude of the induced signal using the principle of fourier transform, comprising:
the calculation formula is as follows:
formula one;
wherein X k is the amplitude of the induction signal, N is the total number of acquisitions, N is the serial number of acquisitions, k is the frequency coefficient, and X N is the original value;
the amplitude A can be obtained by calculating the two secondary coils 1 and A2 ；
In dynamic signal analysis, signals are often analyzed using fourier transforms, known as the discrete fourier transform formula:
euler formula: e, e j*x ＝cosx+j*sinx；
According to the discrete fourier transform and euler equation, it can be expressed by the following equation:
a second formula;
wherein X k is the amplitude of the induction signal, N is the total number of acquisitions, N is the serial number of acquisitions, k is the frequency coefficient, and X N is the original value.
In the second formula, the calculation formula is expressed in complex form, and when the amplitude of the signal is calculated, the real part is used for calculation, so that the second formula is converted into the first formula.
In actual calculation, X [ n ] and X [ k ] use single-precision floating point numbers to operate, and in order to avoid exceeding the upper limit of the single-precision floating point numbers in the calculation process, X [ n ] uses the ratio of the original value sampled by an analog-to-digital converter ADC to the full range of the analog-to-digital converter ADC.
Illustrating: the excitation signal is designed to be 1kHz, a frequency driving digital-to-analog converter DAC of 32kHz is used for driving a driving circuit to output a 1kHz sine wave, the acquisition frequency is designed to be 8kHz, the calculation result of a formula I shows the amplitude of the 1kHz in a frequency domain when k=1 according to the Fourier transformation principle, 1920 points are continuously acquired, namely 240ms is used for the period of 240 excitation signals, the calculation of the formula I is carried out after the acquisition is completed, and the amplitude A of the induction signals of two coils is obtained 1 、A 2 。
The calculation formula of the test result is as follows:
a formula IV;
the range of values for the test results is-1 to +1;
and obtaining a measurement result, and then carrying out linear fitting compensation to obtain displacement.
The foregoing description of the preferred embodiments of the present application is not intended to limit the scope of the application, in which any feature disclosed in this specification (including abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. That is, each feature is one example only of a generic series of equivalent or similar features, unless expressly stated otherwise.
Claims (5)
1. The LVDT displacement sensor data acquisition method is characterized by comprising the following steps:
controlling a digital-to-analog converter DAC to cooperate with a driving circuit to generate a sine wave excitation signal;
the coil outputs an induction signal based on the excitation signal, and the induction signal is output to an analog-to-digital converter ADC through a signal processing circuit;
controlling an analog-to-digital converter ADC, and controlling the analog-to-digital converter ADC to continuously acquire dynamic induction signals of a coil by using an acquisition method with acquisition frequency being 2N times of an excitation signal and acquisition times being N times of the whole period of the excitation signal;
and deducing and calculating the amplitude of the induction signal based on the acquired original value by adopting the principle of discrete Fourier transform, and calculating the displacement based on the amplitude.
2. The LVDT displacement sensor data collection method of claim 1, wherein the controlling the DAC to cooperate with the driving circuit to generate the sine wave excitation signal comprises:
the DAC outputs a step wave, the driving circuit is a low-pass filter circuit formed by operational amplifiers, and the step wave is changed into a sine wave after passing through the low-pass filter circuit.
3. The LVDT displacement sensor data collection method of claim 1, wherein the coil outputs an induction signal based on a sine wave excitation signal, and the induction signal is processed by a signal processing circuit and then output to an analog-to-digital converter ADC, comprising:
the signal processing circuit is a signal amplifying circuit formed by operational amplifiers.
4. The LVDT displacement sensor data collection method according to claim 1, wherein the controlling the ADC uses a collection mode with a collection frequency 2N times of the excitation signal and a collection frequency N times of the whole period of the excitation signal to control the ADC to continuously collect the dynamic sensing signal of the coil, comprising:
the acquisition frequency of the analog-to-digital converter ADC is 2n times of the excitation signal, n is greater than 1, and n is an integer; the acquisition times of the analog-to-digital converter ADC are N times of the whole period of the excitation signal, N is greater than 0, and N is an integer.
5. A method of LVDT displacement sensor data acquisition according to claim 1, wherein said calculating the amplitude of the induced signal based on the raw value using the principle of the discrete fourier transform comprises:
the calculation formula is as follows:
wherein ,
n is the total collection times, N is the collection serial number, k is the frequency coefficient, and +.>
Is the original value. />
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