CN110631469A

CN110631469A - Automatic calibration system and method based on LVDT sensor

Info

Publication number: CN110631469A
Application number: CN201910869143.9A
Authority: CN
Inventors: 李建国; 应继伟; 焦迪; 殷建国; 汪邦运
Original assignee: Shanghai Figa Intelligent Technology Co Ltd
Current assignee: Shanghai Figa Intelligent Technology Co Ltd
Priority date: 2019-09-16
Filing date: 2019-09-16
Publication date: 2019-12-31

Abstract

The invention discloses an automatic calibration system and method based on an LVDT sensor, the system comprises a constant frequency and constant amplitude signal generating unit, a channel gating and LVDT driving unit, an access gating low noise preamplifier unit, a program control gain unit and a microprocessor unit, the output end of the constant-frequency and constant-amplitude signal generating unit is connected with the input end of the channel gating and LVDT driving unit, the output end of the channel gating and LVDT driving unit is connected with the input end of the access gating low-noise preamplification unit, the output end of the access gating low-noise preamplification unit is connected with the input end of the microprocessor unit, the output end of the microprocessor unit is respectively connected with the input end of the channel gating and LVDT driving unit and the input end of the program control gain unit, the output end of the program control gain unit is connected with the input end of the access gating low-noise preamplification unit.

Description

Automatic calibration system and method based on LVDT sensor

Technical Field

The invention belongs to the field of manufacturing of detecting instruments, and relates to an automatic calibration system and method based on an LVDT sensor.

Background

At present, a vibrating string type strain sensor is widely applied in the fields of engineering buildings, bridges, reservoir dams and the like. The vibrating wire type strain sensor is generally applied to the field of geotechnical engineering particularly due to the advantages of simple structure and strong anti-interference capability.

However, vibrating wire strain sensors have also been the subject of extensive debate in the industry due to their apparent technical shortcomings. The vibrating wire strain sensor with the tensioned metal string as the sensitive element has the advantages that after the length of the string is determined, the change of the natural vibration frequency can show the magnitude of the tension borne by the string, and a certain relation between the frequency and the stress can be obtained through certain conversion. With the continuous and intensive research and analysis of the vibrating wire type strain sensor, and the combination of the practical failure cases applied in engineering, the inherent physical defects of the vibrating wire type strain sensor are gradually revealed: 1. the vibrating wire strain sensor is not suitable for long-term monitoring. It is well known that any object will deform when subjected to an external force; meanwhile, any object can generate the expansion and contraction phenomenon under the condition that the temperature difference changes, and the vibrating wire type strain sensor is not affected by the factors. The vibrating wire of the vibrating wire type strain sensor is tensioned and fixed on the elastic diaphragms at the two ends, so that the two ends of the vibrating wire are influenced by superposition of certain tension and gravity; the vibrating wire will inevitably deform. The relative positions of the internal molecules or ions of the tensioned vibrating wire are changed in a peristalsis mode, and meanwhile additional internal forces between atoms and molecules are generated to counteract the external force and try to restore to the state before deformation. When the balance is reached, the additional internal force is equal to the external force and opposite to the external force. Theoretically, the internal stress of a desired single crystal metal material does not yield permanently within the elastic limit under load conditions. However, since the metal material actually used is of a polycrystalline structure, there are a large number of internal crystal defects; in the situation that the temperature difference is not changed greatly, due to the crystal phase difference and the short-range diffusion of atoms, the material is subjected to micro plastic deformation; when the temperature difference is increased, the phenomena of atom long-range diffusion and lattice dislocation slip tending to be severe occur in the material, and the continuous accumulation of the microscopic plastic deformation evolves into the macroscopic plastic deformation along with the time. The metal can generate micro plastic deformation in the elastic stress range, and the mechanism of dislocation short-range slip, solute atom directional dissolution, directional vacancy flow, crystal sliding and the like in the crystal can be successfully explained. The physical mechanism that occurs on the wire also occurs on the vibrating wire that is tensioned at both ends in the vibrating wire strain sensor. 2. The vibrating wire strain sensor has serious temperature effect. Since the linear thermal expansion coefficient of the vibrating wire strain sensor is related to the material, machining precision, shape and the like, before the sensor is used, the vibrating wire strain sensor needs to be calibrated and compensated in a single body. 3. The vibrating wire type strain sensor is not suitable for being used in the measurement occasion of complex deformation. According to the theory that the steel body deforms under the action of external force and the volume of the steel body does not change under the action of material mechanics and elasticity mechanics, if the steel body is compressed and deformed axially under pressure, the radial direction inevitably expands and deforms along the principle of volume invariance, and the effect of radial expansion is related to the shape and the material of the steel body, so that the change of radial expansion is a distribution function along the axial direction. If the distribution function of the axial change is not uniform, the vibrating wire in the vibrating wire type strain sensor arranged on the steel body is twisted, and the twisting phenomenon can be converted into axial additional external force, so that the measurement of the vibrating wire type strain sensor is inaccurate. Therefore, it is not surprising that a failure is often detected in the detection of a construction stress or the like using a vibrating wire strain sensor.

The strain and stress monitoring in various building projects is an important measurement index, the true condition of a building member under a stress condition is objectively reflected by accurately measuring the strain or stress of various materials used in the building projects and various supports used in foundation pit enclosures under the stress condition, and reliable and accurate data are provided for the engineering construction and the use and operation processes, so that a multichannel self-adaptive self-fixed elevation precision LVDT data acquisition system which has high precision, is irrelevant to radial change, has small temperature coefficient, high automation degree (no need of manual interference) and is convenient for data interaction and a measurement method thereof are necessary to research and develop.

Disclosure of Invention

An ideal engineered microstrain monitoring system would be: 1. the method has the advantages that the measured data are accurate and reliable, 2, a convenient information interaction mode is provided for users, 3, the energy supply of a monitoring system does not need manual intervention in principle, and 4, the monitoring frequency is set flexibly.

The invention aims to provide a multichannel self-adaptive fixed elevation precision LVDT data acquisition and measurement system and method for a human-computer interaction interface, which have solar energy and power supply adapter energy supplement, extremely accurate axial detection precision, insensitivity to radial deformation, a self-calibration function for range-gain of various LVDT sensors, a self-adaptive function for processing system gain, an extremely small temperature coefficient, wireless remote GPRS data interaction, a short-range wireless or wired networking function and convenience.

In order to fully illustrate and understand the principles of the present invention and the technical approaches adopted, it is necessary to understand the manner in which microstrain stress monitoring is currently performed in engineering construction.

Take the excavation of steel structure support in deep foundation pit as an example. In the excavation process of the deep foundation pit, in order to prevent the collapse of the edge of the foundation pit, a reinforced concrete continuous wall needs to be constructed around the excavated foundation pit, and because the pressure of a soil body is huge, the constructed continuous wall needs to be appropriately supported, and a supporting beam is generally formed by two modes: reinforced concrete supporting beam and steel structural support beam. The steel structure supporting beam is a construction mode widely adopted internationally, and is also a trend of a supporting method in deep foundation pit excavation and maintenance engineering in China. The stress condition (deformation condition) of the steel support beam of the steel support structure is accurately measured, so that the safety of the whole engineering construction is related, and by means of accurately measuring the stress (deformation) of the steel support beam, the aims of reversely verifying the correctness of design calculation and reducing the construction cost can be fulfilled. The stress and micro-strain of the steel structure supporting beam are monitored by adopting high-precision and high-sensitivity LVDT micro-strain sensors, and the LVDT micro-strain sensors are arranged at key stress positions of the supporting beam (the arrangement position is required to accord with the Saint-Venn principle). And the measurement data of the sensors at the monitoring points are transmitted to a monitoring management station in a cable connection mode.

The invention relates to a multichannel self-adaptive self-fixed high-precision LVDT data acquisition and measurement system and a method.

The multichannel self-adaptive self-fixed high-precision LVDT data acquisition and measurement system is used for realizing that: the method comprises the steps of realizing constant-frequency amplitude-stabilized excitation on an LVDT sensor with 32 channels (in an embodiment, the number of the channels can be expanded as required) in a time division multiplexing mode, conditioning output response signals of the LVDT sensor (including system gain self-adaption, automatic calibration of the LVDT sensor, extraction of final conditioning signals of the LVDT of each channel by adopting quick true effective value processing, judgment of the motion direction of the sensor, 16-bit A/D sampling and calculation), realizing wireless networking among monitoring points in a short-range wireless mode, providing data interaction in a Bluetooth wireless mode, providing remote GPRS wireless data interaction, providing a solar energy and power adapter charging function, and providing a high-stability low-noise power supply for related units. The LVDT sensor group is composed of a plurality of LVDT sensors and corresponding machinery.

When the multichannel adaptive self-determination high-precision LVDT data acquisition and measurement system is powered on, a microprocessor in the system waits for receiving a setting instruction of a working mode of the system, wherein the setting instruction comprises the number and the independent number of the LVDT sensors to be sampled, the sampling frequency, and the upper limit and lower limit alarm information of the measurement data of each single sensor. The operating mode setting parameters may be received in three ways: 1. the method comprises the following steps of carrying out field programming on a microprocessor of the system through an external serial port, 2, providing man-machine interaction between a liquid crystal touch display screen configured by the system and the microprocessor, and 3, interacting between the system and a GPRS remote wireless data interaction network. After receiving the working parameters, the multichannel adaptive self-fixed high-precision LVDT data acquisition and measurement system firstly acquires the power supply condition information of the system, and if the power supply of a lithium battery pack configured by the system is normal, the initialization process of each accessed LVDT sensor is started; otherwise, the information that the system needs to supplement the electric energy is sent to the different places through the remote wireless GPRS network. Since each type of LVDT sensor has different output responses (different sensitivities) under the same input excitation, the initialization process includes: 1. the sensitivity of each accessed LVDT sensor is automatically measured and stored in a nonvolatile memory of the system so as to realize the automatic calibration function; 2. and automatically adjusting the gain of the sensor in the data conditioning process according to the measured value of the sensitivity of each LVDT sensor, thereby realizing the self-adaptive function of data conditioning.

After initialization and the set measuring time is up, the invention carries out measurement on each accessed LVDT sensor in a time-sharing mode through a gating integrated analog switch under the control of a configured microprocessor: the microprocessor gives the coded address to the relevant integrated analog switch and the LVDT sensor of the corresponding channel is accessed to the system. The microprocessor obtains an n KHZ digital pulse signal with extremely stable repetition frequency after frequency division by a configured crystal oscillator clock source, the digital pulse signal obtains a bipolar sine-form fundamental wave after passing through a multi-feedback band-pass filter, and the fundamental wave excites a primary winding of a related selected LVDT sensor after being amplified and driven by a funnel-type instrument amplifier; double-end response signals sent by the selected LVDT sensors are read into the zero-drift instrument amplifier after being gated by the corresponding integrated analog switches; at this point, the gain of the zero drift instrumentation amplifier is automatically configured by the microprocessor based on the sensitivity parameters stored in the non-volatile memory at initialization of the selected LVDT sensor.

The signal is amplified and converted by a zero drift instrument amplifier to be converted into a single-ended measurement signal, and then is further purified by a multiplex feedback band-pass filter. 1. The signal is converted into a direct current signal by a fast sampling high-precision true effective value processing circuit, and finally a high-precision measurement value is obtained after 16-bit AD conversion; and 2, judging the motion direction of the double-end signal output by the LVDT sensor by a direction judging circuit respectively according to the voltage of each end relative to the reference ground (circuit ground) of the circuit. The invention realizes the direction discrimination of the measurement signal by the following modes: the LVDT sensor outputs a response double-ended signal, the voltages UA and UB to earth at each end of the LVDT sensor are respectively buffered (in order not to influence the differential measurement value), and proportional subtraction processing is carried out, so that even if the difference between the UOA and the UOB is small, a considerable difference UC can still be obtained after the proportional differential subtraction processing, the UC obtains a '0' or '1' signal after an integrated comparator, and the '0' or '1' signal represents two relative movement directions of the armature of the LVDT sensor.

And repeating the operation process until all the accessed LVDT sensors are sampled, sending the sampling data of each sensor and the corresponding environment temperature data through various configured communication circuits, finishing the measurement, and enabling the system to enter a sleep state until the next measurement time is up to be automatically awakened. The communication circuit sends measurement information according to a selected communication mode after receiving measurement data sent by the multichannel self-adaptive self-calibration high-precision LVDT data acquisition and measurement system, wherein remote wireless GPRS communication is default and can not be changed; and short-range wireless communication bluetooth and WIFI are optional. In order to ensure the measurement accuracy of the multichannel self-adaptive self-fixed high-accuracy LVDT data acquisition and measurement system, the system adopts an ARM M7 microprocessor (STM32H750) with 16-bit AD sampling, so that the requirements on the stability of system power supply and a reference source are higher, and the system adopts an ultrahigh-accuracy reference source (ADR4530) with the temperature drift coefficient less than or equal to 2 ppm/DEG C.

In order to adapt to a long-term unattended monitoring environment, the multichannel self-adaptive fixed-elevation precision LVDT data acquisition and measurement system adopts a 37 ampere-hour and 4.2V high-capacity parallel lithium battery pack for power supply, and is assisted by a solar charging circuit and provided with a power adapter charging interface. In order to safely and properly charge the parallel lithium battery pack, a solar energy and alternating current hybrid charging management system special for the high-capacity parallel lithium battery pack is developed, the maximum charging current of the solar energy and alternating current hybrid charging management system for realizing charging is 1.5 amperes, namely the parallel lithium battery pack is charged by C/18.5 of the capacity of the distributed battery pack, and the energy can be supplemented in principle on 2 sunny days. The matched 37 ampere-hour parallel lithium battery pack can maintain enough working power supply for more than 1.5 months under the condition of full load monitoring 24 times per day; during the period, only two clear days are needed, and the battery pack can recover the full energy. Therefore, the multichannel self-adaptive self-fixed high-precision LVDT data acquisition and measurement system does not need manual intervention to recover energy supplement in principle, and the charging port of the power adapter is also configured in the system in the invention in consideration of unpredictability of weather factors.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: and converting a double-end signal output by the LVDT sensor into a single-end signal by adopting a zero-drift instrument amplifier, and performing linear compensation on the gain of the zero-drift instrument amplifier and the ambient temperature in order to further inhibit the temperature drift of converting the double-end signal into the single-end signal.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: a fast sampling true effective value processing mode is adopted to obtain and convert the output signal of the LVDT sensor, and the traditional mode of processing the signal of the LVDT sensor by adopting phase-sensitive detection is abandoned.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: the solar energy charging, the high-capacity lithium battery energy storage and the power supply mode of providing an energy interface by a power adapter are adopted, and the long-term normal operation of the system can be realized without human intervention in principle.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method, for LVDT sensor processing flow is: a constant-frequency constant-amplitude standard signal source (6.0P-P V, 2.5KHz sine wave) is used as an input signal of a funnel type amplifier with two gain coefficients. After the LVDT sensor is driven by the funnel amplifier, the output response of the LVDT sensor is conditioned by links such as a program control gain zero drift instrument amplifier, a noise suppression band-pass filter, a quick sampling true effective value and the like, and then is sampled by a 16-bit A/D of a microprocessor.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: during initialization, a funnel type amplifier with two gain coefficients (0.8 and 0.4) is adopted to drive the LVDT sensors so as to obtain the output response coefficient of each connected LVDT sensor.

A multichannel self-adaptive self-fixed high-precision LVDT data acquisition and measurement system and method are characterized in that an output response coefficient SS and sensitivity KS of a universal LVDT sensor are determined as reference (taking Shenzhen Shang as a product with the SDVG20-VA measuring range of 2.5 mm of science and technology development Limited company as an example):

setting a programmable gain zero drift instrument amplifier at a certain fixed gain A (in the embodiment, A is 2), connecting a constant-frequency 2.5KHz and constant-amplitude 3.0VRMS (volt) standard signal source into an input end (VIN0.8) of a gain coefficient of a funnel type amplifier 0.8 to drive an LVDT sensor, and obtaining V0.8S after an AD sampling value of output response of the LVDT sensor; a constant-frequency constant-amplitude standard signal source is connected to an input end (VINS0.4) of a funnel type amplifier driving LVDT sensor with a gain coefficient of 0.4, and output response of the constant-frequency constant-amplitude standard signal source is V0.4S after an AD sampling value; so output response delta: VS ═ D0.8S-D0.4S, input signal increment: v ═ VIN0.8-VIN0.4 ═ 3 × 0.8) - (3 × 0.4), KS ═ VS/. v, and KS is the output response coefficient of the universal LVDT sensor. And storing the obtained KS into a nonvolatile memory of the microprocessor.

The micrometer stage with 0.2 micrometer accuracy is used, the amplifier of the programmable gain zero drift instrument is set at a certain fixed gain A (in the embodiment, A is 2), and a constant-frequency constant-amplitude standard signal source is connected to the input end of a funnel type amplifier driving LVDT sensor with 0.8 gain coefficient. The universal LVDT sensor was locked to the micrometer stage and the output response VCWS1 was obtained. Adjusting the micrometer stage to change by 0.2 micrometer to obtain output response VCWS 2; calculating V ═ VCWS 2-VCWS 1 to obtain VDCW ═ V (0.2 micrometers); VDCW is the output voltage amplitude (a/D converted voltage value) corresponding to a 0.2 micron variation of the conventional LVDT sensor. And storing the KS and the VDCW into a nonvolatile memory of a microprocessor. Once the first and second initialization steps are completed, the acquisition system in the subsequent production only needs to store KS and VDCW values into the memory and quote the KS and VDCW values.

When the invention is put into operation, the initialization process is firstly carried out (the initialization operation is started by the system when the sensor is used later or is powered off or damaged sensors are replaced). The accessed LVDT sensors are sequentially selected through the high-performance integrated analog switch, and the V (VIN) is equal to VIN0.8-VIN0.4 and V (V) is repeated to the accessed LVDT sensors automatically and sequentially under the condition of gain A of the program control amplifier

VOUTN ═ VOUTN0.8-VOUTN0.4, KN ═ VOUTN/. VIN operation, thereby obtaining KN for each access sensor; the KN is also automatically stored in non-volatile memory in the microprocessor (these values do not change unless an LVDT sensor failure is replaced or cancelled). During measurement, the invention automatically compares the measured value of the LVDT of the selected channel N (corresponding to a specific LVDT sensor) with the standard K value according to the corresponding KN, and the compared coefficient is used as the basis for the microprocessor to select the gain of the amplifier of the program control gain zero-drift instrument, so that the LVDT sensors with different sensitivities can obtain proper gain AN for amplification (no saturation occurs). Note that: during normal measurement, the funnel type amplifier is always in a 0.8 gain coefficient input state.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: the KN of each LVDT sensor obtained by the above measures is also used to achieve automatic calibration. The specific process is as follows: determining the gain AN of the microprocessor for automatically selecting the amplifier of the program-controlled gain zero-drift instrument according to the KN value obtained by each accessed LVDT sensor to obtain AN AD conversion value DATN, and calculating DZHN ═ DATN multiplied by A/AN, namely: DZHN is the value of gain a used to convert the measured value DATN to a generic LVDT; and finally, calculating LN (DZHN multiplied by KS/KN) multiplied by 0.2 micrometer to obtain the displacement measurement value of the Nth access LVDT sensor, thereby realizing automatic calibration.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: the method comprises the steps that a crystal oscillator frequency division mode is adopted to generate a square wave signal with extremely accurate frequency, the square wave signal is fed to a control input end of an integrated analog switch, a data input end of the integrated analog switch is connected with a reference source, and the integrated analog switch outputs a chopping signal with constant frequency and constant amplitude under the control of the square wave signal. And extracting fundamental waves of the chopped wave signals by adopting a multi-feedback band-pass filtering mode, wherein the constant-frequency constant-amplitude fundamental waves are used as input excitation signals of a driver of the LVDT sensor.

A multichannel adaptive self-fixed high precision LVDT data acquisition and measurement system and method is characterized in that: the Bluetooth mode is adopted to provide information interaction for a user using a mobile phone, the LORA wireless communication mode is adopted to realize local networking among monitoring points, and the remote wireless GPRS mode is adopted to provide information interaction for a remote monitoring station.

The multichannel self-adaptive high-precision LVDT data acquisition and measurement system comprises a constant-frequency constant-amplitude signal generating unit, a channel gating and LVDT driving unit, an access gating low-noise preamplification unit, a program control gain unit, a true effective value rapid sampling unit, a motion direction judging unit and a microprocessor unit, wherein the output end of the constant-frequency constant-amplitude signal generating unit is connected with the input end of the channel gating and LVDT driving unit, the output end of the channel gating and LVDT driving unit is connected with the input end of the access gating low-noise preamplification unit, the output end of the access gating low-noise preamplification unit is respectively connected with the input end of the true effective value rapid sampling unit and the input end of the motion direction judging unit, the output end of the true effective value rapid sampling unit and the output end of the motion direction judging unit are respectively connected with the input end of the microprocessor unit, the output end of the microprocessor unit is respectively connected with the input end of the constant-frequency constant-amplitude signal generating unit and the input end of the program control gain unit, and the output end of the program control gain unit is connected with the input end of the access gating low-noise preamplification unit.

Further, the constant-frequency and constant-amplitude signal generating unit comprises an integrated analog switch and a zero-drift operational amplifier, the square wave signal output by the microprocessor unit controls the on-off of the integrated analog switch, so that the signal output by the integrated analog switch is a constant-frequency and constant-amplitude square wave signal, and the zero-drift operational amplifier is connected with the integrated analog switch and is used for converting the constant-frequency and constant-amplitude square wave signal into a constant-frequency and constant-amplitude bipolar sine wave signal.

Further, the channel gating and LVDT driving unit includes an integrated analog switch and an integrated funnel-type instrumentation amplifier, and the microprocessor unit controls the integrated analog switch to connect a bipolar sine wave signal of constant frequency and constant amplitude to an input terminal of the integrated funnel-type instrumentation amplifier, so that the microprocessor unit obtains a response coefficient of an accessed LVDT sensor.

Further, the access gating low-noise pre-amplification unit comprises a zero-drift low-noise variable-gain instrument amplifier and a resistor, and the microprocessor unit selects a resistor with matched gain for the zero-drift low-noise variable-gain instrument amplifier according to the stored sensitivity value.

Furthermore, the real effective value rapid sampling unit comprises an integrated real effective value chip and is used for rapidly converting the sine wave signal output by the access gating low-noise preamplification unit into a high-precision direct current signal.

Furthermore, the motion direction judging unit comprises three integrated operational amplifiers and an integrated comparator, two signals output and responded by the two ends of the LVDT sensor are respectively amplified through the integrated operational amplifiers, the two amplified signals are subjected to proportional difference through the other integrated operational amplifier, and the output signal of the integrated operational amplifier is used as the input signal of the quasi-zero-crossing comparator formed by the integrated comparator.

Further, the device also comprises a display and communication unit which is connected with the microprocessor unit.

The multichannel adaptive high-precision LVDT data acquisition and measurement method comprises the following steps:

acquiring a clock signal;

acquiring an output signal of the sensor after correcting the sensitivity based on the clock signal;

obtaining detection information of the sensor based on the output signal, wherein the detection information comprises a measurement value and a movement direction;

wherein the sensor is an LVDT sensor.

Further, the acquiring the clock signal includes:

setting working parameters;

based on the operating parameters, a clock signal is derived.

Further, the setting of the operating parameter includes one of the following modes:

setting working parameters by a JTAG interface;

setting working parameters through human-computer interaction;

and the GPRS remote wireless data interaction sets working parameters.

Further, the operating parameters include one or more of the following combinations:

sensor number, collection frequency, collection time, and alarm information of upper and lower limits of measurement values.

Further, the clock signal is a frequency stabilization signal obtained by frequency division of the crystal oscillator.

Further, the acquiring, based on the clock signal, the output signal of the sensor after the sensitivity correction includes:

an excitation signal of the sensor is acquired.

Further, the acquiring an excitation signal of the sensor comprises:

chopping a reference source to obtain a digital signal;

extracting a fundamental wave of the digital signal;

and amplifying the fundamental wave to obtain an excitation signal of the sensor.

Further, the obtaining a measurement value of the sensor based on the output signal includes:

amplifying the output signal to obtain a measurement signal;

purifying the measurement signal;

the measurement signal is converted into a direct current signal.

Further, the deriving a direction of motion of the sensor based on the output signal comprises:

and obtaining the motion direction information of the sensor based on the comparison of the double-end output response signals of the sensor.

Further, the comparing of the double-ended output response signals of the sensors comprises:

the difference of the two-ended output response signal comparisons is amplified.

Further, the correcting the sensitivity of the sensor includes:

the sensitivity of the sensor is adjusted to be equal to a standard value, wherein the standard value is set.

Further, the adjusting the sensitivity of the sensor to be equal to a standard value includes:

and adjusting the amplification factor corresponding to the sensitivity of the sensor.

Further, the adjusting the amplification factor corresponding to the sensitivity of the sensor includes:

and switching the selection resistor to adjust the amplification factor.

An automatic calibration system based on an LVDT sensor comprises a constant frequency and constant amplitude signal generating unit, a channel gating and LVDT driving unit, an access gating low-noise preamplifier unit, a program control gain unit and a microprocessor unit, the output end of the constant-frequency and constant-amplitude signal generating unit is connected with the input end of the channel gating and LVDT driving unit, the output end of the channel gating and LVDT driving unit is connected with the input end of the access gating low-noise preamplification unit, the output end of the access gating low-noise preamplification unit is connected with the input end of the microprocessor unit, the output end of the microprocessor unit is respectively connected with the input end of the channel gating and LVDT driving unit and the input end of the program control gain unit, the output end of the program control gain unit is connected with the input end of the access gating low-noise preamplification unit.

Further, the constant-frequency and constant-amplitude signal generating unit comprises a first integrated analog switch and a zero-drift operational amplifier, the square wave signal output by the microprocessor unit controls the on-off of the first integrated analog switch, so that the signal output by the first integrated analog switch is a constant-frequency and constant-amplitude square wave signal, and the zero-drift operational amplifier is connected with the first integrated analog switch and is used for converting the constant-frequency and constant-amplitude square wave signal into a constant-frequency and constant-amplitude bipolar sine wave signal.

Further, the channel gating and LVDT driving unit includes a second integrated analog switch and an integrated funnel-type instrumentation amplifier, and the microprocessor unit controls the second integrated analog switch to access the LVDT sensor and connects a constant-frequency constant-amplitude bipolar sine wave signal to an input end of the integrated funnel-type instrumentation amplifier, so that the microprocessor unit obtains a response coefficient of the accessed LVDT sensor.

Further, the access gating low-noise preamplifier unit comprises a zero drift instrument amplifier and a resistor, and the microprocessor unit selects a resistor with matched gain for the zero drift instrument amplifier to adjust the response coefficient of the LVDT sensor through the program control gain unit according to the stored sensitivity value.

Furthermore, the system also comprises a true effective value rapid sampling unit, wherein the input end of the true effective value rapid sampling unit is connected with the access gating low-noise preamplification unit, and the output end of the true effective value rapid sampling unit is connected with the input end of the microprocessor unit.

The input end of the motion direction judging unit is connected with the access gating low-noise preamplifier unit, and the output end of the motion direction judging unit is connected with the input end of the microprocessor unit.

And further, the system also comprises a hybrid charging and power supply conversion power supply which is used for providing electric energy for the system to work.

An automatic calibration method based on an LVDT sensor comprises the following steps:

acquiring a response coefficient and a sensitivity value of the LVDT sensor;

comparing the response coefficient and the sensitivity value of the LVDT sensor;

adjusting the response coefficient of the LVDT sensor based on a comparison of the response coefficient and the sensitivity value of the LVDT sensor.

Further, the adjusting the response coefficient of the LVDT sensor based on the comparison of the response coefficient and the sensitivity value of the LVDT sensor includes:

and adjusting the corresponding amplification factor of the response coefficient of the LVDT sensor.

and switching the selection resistor to adjust the amplification factor.

Due to the adoption of the technical processing and measuring method, the effect of the invention is obvious:

1. and a zero drift instrument amplifier and linear compensation are adopted to obtain more accurate measurement data.

2. And a fast true effective value processing mode is adopted to acquire and convert the output signal of the LVDT sensor.

3. The gain of the data conditioning circuit has the self-adaptive function to the LVDT sensor which is connected with the data conditioning circuit and has various input-output responses (sensitivity).

4. The LVDT sensor has a self-calibration function for various input-output response (sensitivity) of the connected LVDT.

5. The solar energy and power grid hybrid power supply mode is adopted to charge the configured large-capacity lithium battery pack, and the long-term operation of the manual dry-preheating system is not required in principle.

6. The LVDT sensor is provided with an original excitation signal with extremely accurate frequency by adopting a crystal oscillator frequency division mode, the amplitude of the original excitation signal is stabilized by adopting an integrated analog switch to a reference source chopping mode, and the accurate input excitation signal is provided for the LVDT sensor by adopting a mode of extracting fundamental waves in the original excitation signal and double reference sources by adopting a multi-feedback band-pass filtering mode.

7. Providing communication service for users in a Bluetooth, LORA and GPRS wireless mode; and a network port and RS485 mode is adopted to provide wired communication service for users.

8. The invention provides human-computer interaction for users by adopting the liquid crystal touch screen and a remote wireless GPRS mode.

For a better understanding of the nature and features of the present invention, reference should be made to the following examples and accompanying drawings.

Drawings

FIG. 1 is a block diagram of the multi-channel adaptive high-precision LVDT data acquisition and measurement system according to the present invention;

FIG. 2 is a circuit diagram of the connection between the constant frequency and amplitude signal generating unit and the channel gating and LVDT driving unit according to the present invention;

FIG. 3 is a circuit diagram of an integrated analog switch IC20 according to the present invention;

FIG. 4 is a circuit diagram of an integrated analog switch IC21 according to the present invention;

FIG. 5 is a circuit diagram of an integrated analog switch IC22 according to the present invention;

FIG. 6 is a circuit diagram of an integrated analog switch IC23 according to the present invention;

FIG. 7 is a circuit diagram of an integrated analog switch IC24 according to the present invention;

FIG. 8 is a circuit diagram of an integrated analog switch IC25 according to the present invention;

FIG. 9 is a circuit diagram of an integrated analog switch IC26 according to the present invention;

FIG. 10 is a circuit diagram of the gated low noise pre-amp cell and true valid value fast sampling cell connections of the present invention;

FIG. 11 is a circuit diagram of the microprocessor IC12 of the present invention;

FIG. 12 is a circuit diagram of a motion direction discriminating unit according to the present invention;

FIG. 13 is a circuit diagram of the microprocessor IC14 of the present invention;

FIG. 14 is a circuit diagram of a high precision integrated reference source IC13 in accordance with the present invention;

FIG. 15 is a circuit diagram of an integrated boost converter chip IC4 according to the present invention;

fig. 16 is a circuit diagram of the connection of the integrated boost converter IC5, the integrated low dropout IC6 and the integrated low dropout IC7 according to the present invention;

FIG. 17 is a circuit diagram of an integrated buck chip IC8 in accordance with the present invention;

FIG. 18 is a circuit diagram of the integrated polarity reversing chip IC9 and the negative supply low dropout chip IC10 in accordance with the present invention;

FIG. 19 is a solar charging circuit diagram according to the present invention;

fig. 20 is a diagram of an ac-dc converter circuit according to the present invention.

Detailed Description

The main technical parameters of the embodiment of the invention are as follows: a. 32LVDT sample channels. b. An LVDT sensor with a free movable end is adopted, and two ends of the LVDT sensor are fixed on a measured object, and the length of two ends (fixed ends) of the LVDT sensor is 150 mm. c. And GPRS long-distance wireless data interaction and Bluetooth short-range data interaction modes are adopted. d. The axial movement direction of the measured object is consistent with the movement direction of the LVDT sensor inclined iron. e. The measurement environment temperature range is-10 ℃ to 65 ℃. f. The time interval between two adjacent sampling is 1 hour.

Please refer to fig. 2 to fig. 20. A multichannel self-adaptive self-fixed elevation precision LVDT data acquisition and measurement system is composed of a constant frequency and constant amplitude signal generation unit 1, a channel gating and LVDT driving unit 2, an access gating low-noise preamplification unit 3, a program control gain unit 4, a true effective value rapid sampling unit 5, a motion direction judging unit 6, a microprocessor unit 7, a display and communication unit 8, a conversion power supply unit 9 and a hybrid charging unit 10.

Please continue to refer to fig. 2 to fig. 20. The constant-frequency constant-amplitude signal generating unit 1 provides a sine wave excitation signal source with stable frequency and amplitude for the LVDT sensor. The implementation principle is that a 2.5KHz output square wave signal obtained by frequency division of a microprocessor is utilized to chop a reference voltage source through a low-output impedance integrated analog switch, and then a constant-frequency constant-amplitude chopped wave signal is converted into a bipolar sine wave signal VIN through a second-order band-pass filter; therefore, the sine wave signal VIN is also constant frequency and constant amplitude. The input of the constant frequency and constant amplitude signal generating unit 1 is connected with the output of the microprocessor unit 7 and the hybrid charging and power supply conversion power supply 9, and the output of the constant frequency and constant amplitude signal generating unit is sequentially connected with the input of the channel gating and LVDT driving unit 2.

The channel gating and LVDT driving unit 2 is used for sequentially connecting each LVDT sensor into a circuit through an integrated analog switch with low output impedance under the control of the microprocessor, and amplifying and driving the LVDT sensors by using a funnel-type instrument amplifier. When the invention is in an initialization state, firstly, a microprocessor in a microprocessor unit 7 controls an analog switch to connect a constant-frequency constant-amplitude bipolar sine wave signal VIN (frequency is 2.5KHz, amplitude is 3.0VRMS) output by a constant-frequency constant-amplitude signal generating unit 1 to an input end with a gain coefficient of 0.8, namely VIN0.8 of an amplifier of a funnel type instrument, so that an output response Y0.8N of a certain connected LVDT sensor N under the gain coefficient of 0.8 is obtained, and Y0.8N is stored in a microprocessor memory in the microprocessor unit 7; then, under the control of the microprocessor, the constant-frequency constant-amplitude bipolar sine wave signal output by the constant-frequency constant-amplitude signal generating unit 1 is connected to an input end with a gain coefficient of 0.4, namely VIN0.4, of the amplifier of the funnel-type instrument, so that an output response Y0.4N of a certain connected LVDT sensor under the gain coefficient of 0.4 is obtained, and Y0.4N is stored in a microprocessor memory in the microprocessor unit 7; obtained in combination with the 0.8 and 0.4 attenuation coefficients imparted to the input bipolar sine wave signal: v VIN is 0.8-VIN0.4, yonn is Y0.8N-Y0.4N, and the microprocessor obtains the response coefficient of the LVDT sensor by calculating yonn/VIN; and repeating the operations in sequence until the response coefficients of all the access sensors are obtained. Meanwhile, the microprocessor selects the gain coefficient of the corresponding signal conditioning circuit when a certain LVDT sensor N is accessed by gating according to the obtained response coefficient of each LVDT, thereby realizing the purposes of self-calibration and line gain self-adaption described by the technical characteristic paragraph.

The access gating low-noise preamplification unit 3 and the program control gain unit 4 are used for endowing corresponding amplification gain to each sequentially accessed LVDT. The input of the access gating low-noise preamplification unit 3 is sequentially connected with the output of the channel gating and LVDT driving unit 2, a zero drift low-noise variable gain instrument amplifier in the access gating low-noise preamplification unit 3 plays an amplification task, and the gain of the zero drift low-noise variable gain instrument amplifier is determined by a peripheral gain matching resistor controlled by a microprocessor. The output of the preamplifier is connected with the inputs of the true effective value fast sampling unit 5 and the motion direction judging unit 6. When a LVDT sensor is selected and switched in, the microprocessor in the microprocessor unit 7 selects the relevant gain matching resistance for the zero-drift low-noise variable gain instrumentation amplifier according to the sensitivity values stored in the memory at the time of initialization in relation to the LVDT sensor.

The input of the motion direction judging unit 6 is connected with the output of the access gating low-noise preamplification unit 3, and the output of the motion direction judging unit is connected with the input of the microprocessor unit 7. The movement direction determination unit 6 is used for determining the direction (compression or extension) of deformation of the object under the action of external force.

The true effective value fast sampling unit 5 is composed of a true effective value integrated circuit and an ultra-low output impedance integrated analog switch, the input of the true effective value fast sampling unit is connected with the output of the access gating low-noise preamplification unit 3, and the output of the true effective value fast sampling unit is sequentially connected with the input of the microprocessor unit 7. The true effective value fast sampling unit 5 is used for converting the output sinusoidal signal of the access gating low-noise preamplification unit 3 into direct-current voltage, and is assisted with the fast discharge of the high-speed ultra-low output impedance integrated analog switch to complete the fast sampling function.

The display and communication unit 8 is used for realizing wired, short-distance and long-distance wireless communication and realizing bidirectional interaction of data and control instructions. Is connected with the output of the microprocessor unit 7, and the output is respectively connected with the RS485, GPRS, LORA and BLUETEETH communication modules.

The hybrid charging and power conversion power supply 9 is used for providing a plurality of groups of high-quality voltage-stabilizing power supplies for all the components of the invention and providing an alternating current or solar hybrid charging function for the configured large-capacity lithium battery pack.

Please continue to refer to fig. 2 to fig. 20. The composition and principle of each circuit unit of the present invention are further described in detail below.

As shown in fig. 2, the constant frequency and constant amplitude signal generating unit 1 is composed of a low output impedance integrated analog switch IC15(ADG801), a zero-drift operational amplifier IC 16: a (AD8639), resistors R46, R47, R48, R49, R50 and capacitors C58, C59 and C60. The power supply input terminal (VDD) and the signal input terminal of the low output impedance integrated analog switch IC15(ADG801) are both connected to +3R of the reference source, so that when the low output impedance integrated analog switch IC15(ADG801) is turned on, the amplitude of the output signal at the signal output terminal (D) is + 3R. The 2.5KHz square wave signal (OSC) output by the microprocessor unit 7 controls the on/off of the low output impedance integrated analog switch IC15(ADG801), so that the +3R reference source output by it is chopped into a series of constant frequency and constant amplitude square wave signals with the frequency of 2.5KHz and the amplitude of + 3R. Zero drift operational amplifier IC 16: a (AD8639) and its peripheral passive elements constitute a multiple feedback bandpass filter whose center frequency is 2.5KHz, so that the zero-drift operational amplifier IC 16: a (AD8639) outputs a bipolar sine wave with constant frequency and constant amplitude, and the stability of the LVDT excitation signal is ensured.

The following description will be incorporated to describe the channel gate and LVDT driving unit 2 and the access gate low noise preamplifier unit 3, due to the linkage relationship of the circuit processes.

As shown in fig. 2 to 4, the channel gating and LVDT driving unit 2 is composed of an integrated low output impedance analog switch IC17(ADG1636), an integrated funnel type instrumentation amplifier IC18(AD8475), an integrated analog switch IC19(ADG1636), an integrated analog switch IC20(ADG1606), and an integrated analog switch IC21(ADG 1606).

As shown in fig. 5 to 10, the access-gated low noise pre-amplifier unit 3 is formed by integrating analog switches IC22(ADG1606), IC23(ADG1606), IC24(ADG1606), IC25(ADG1606), IC26(ADG1636), IC27(ADG1408), zero drift instrumentation amplifier IC28(INA188), and zero drift operational amplifier IC 16: b (AD8639), resistors R51, R52, R53, R54, R55, R56, R57, R58, R59, R60, R61, R62, R63, R64, R65, R66, R67, R68, R69, R70, R71, R72, R73, R74, R75, R76, R77, capacitors C61, C62, C63, and the like.

The description is divided into three initialization phases:

initialization phase one

Assume that the values of KS, VDCW for the universal LVDT sensor have been obtained in the manner described above and permanently stored in the microprocessor memory.

The initial access of each sensor to the system must execute an initialization process, and when the system is restarted after power failure, the invention can prompt interactive information of 'whether initialization is needed' through a configured touch display screen. The purpose of initialization is to acquire the output response coefficient of each access LVDT sensor, compare the output response coefficient with the sensitivity (based on the SDVG20-VA product with the range of 2.5 mm, which is believed to be the science and technology development Limited company in Shenzhen) of the general LVDT sensor stored in the microprocessor unit 7 by the microprocessor IC12(STM32H750), determine the calculation of the output signal of each access sensor (the automatic calculation of the microprocessor), and provide proper front gain for the single sensor.

When the initialization stage one is executed, the microprocessor unit 7 first sends a high level (CS) to the "1, 9" enable pin of the integrated analog switch IC17(ADG1636), sends a high level (CS1) to the "1, 9" enable pin of the IC19(ADG1636), and sends a high level (ENK) to the "1, 9" enable pin of the integrated analog switch IC26(ADG 1636). The integrated analog switches IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(ADG1606), and C25(ADG1606) are supplied with "0, 0, 0, 0" logic level, ENA enable signal at high level "1" and ENB enable signal at high level "0" to the terminals "17, 16, 15, and 14". The integrated analog switch IC27(ADG1408) is sent a "0, 0, 0" (selected gain of 2) to the channel gating terminal pin (1, 16, 15), and the IC27(ADG1408) is sent a high "1" to the enable terminal pin "2". The above arrangement means that: when the enable pin "2" of the extension 33-64 channels (IC27(ADG 1408)) is not used to be low "0", this means that the extension 33-64 channels are used, the first (channel 1) LVDT sensor in the 1-16 channels is sequentially selected, the input of the funnel-type instrumentation amplifier is set to 0.8 gain factor VIN0.8, the default gain of the selected channel gating and LVDT driving unit 2 is "2" times, and the output response V1S0.8 of the first (channel 1) LVDT at the funnel-type instrumentation amplifier input gain of 0.8 is measured; this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Then, the microprocessor unit 7 sends out "1, 0, 0, 0" gating signals to the terminal pins "17, 16, 15, 14" of the integrated analog switch IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(DG1606), IC25(ADG1606), that is, selects the second (channel 2) LVDT sensor, if other conditions are not changed; measuring V2S0.8 the output response of the second LVDT at a funnel-type instrumentation amplifier input gain of 0.8(VIN 0.8); this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Until the strobe signal changes to "1, 1, 1, 1"), the output response V16S0.8 of the sixteenth (channel 16) sensor connected to the LVDT sensor at a funnel-type instrumentation amplifier input gain of 0.8(VIN0.8) was measured and saved.

Then, the microprocessor unit 7 sends a high level (CS) to the "1, 9" enable pin of the integrated analog switch IC17(ADG1636), sends a low level "0" to the "1, 9" enable pin of the IC19(ADG1636) (CS1), and sends a high level (ENK) to the "1, 9" enable pin of the integrated analog switch IC26(ADG 1636). The integrated analog switches IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(ADG1606), and C25(ADG1606) are supplied with "0, 0, 0, 0" logic level, ENA enable signal at high level "0" and ENB enable signal at high level "1" to the terminals "17, 16, 15, and 14". The integrated analog switch IC27(ADG1408) is sent a "0, 0, 0" (selected gain of 2) to the channel gating terminal pin (1, 16, 15), and the IC27(ADG1408) is sent a high "1" to the enable terminal pin "2". The above arrangement means that: when the enable pin "2" of the extension 33-64 channels (IC27(ADG 1408)) is not used to be a low level "0", this means that the extension 33-64 channels are used, the seventeenth (channel 17) LVDT sensor from the 17-32 channels is selected in turn, the input of the funnel-type instrumentation amplifier is set to a gain factor of 0.8(VIN0.8), the default gain of the selected channel gating and LVDT driving unit 2 is a factor of "2", and the output response V17S0.8 of the seventeenth (channel 17) LVDT is measured at an input gain of 0.8(VIN0.8) of the funnel-type instrumentation amplifier; this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Then, the other conditions are not changed, the micro-processor unit 7 sends out "1, 0, 0, 0" gating signals to the terminal pins "17, 16, 15, 14" of the integrated analog switch IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(DG1606), IC25(ADG1606), that is, the eighteenth (channel 18) LVDT sensor is selected; determining the output response V18S0.8 of the eighteenth LVDT at a funnel-type instrumentation amplifier input gain of 0.8(VIN 0.8); this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Until the strobe signal changes to "1, 1, 1, 1"), the output response V32S0.8 of the thirty second (channel 32) access LVDT sensor at a funnel-type instrumentation amplifier input gain of 0.8(VIN0.8) is measured and saved.

Initialization phase two

In the first initialization phase, the microprocessor unit 7 first sends a low level "0" (CS) to the enable pins "1 and 9" of the integrated analog switch IC17(ADG1636), sends a high level (CS1) to the enable pins "1 and 9" of the IC19(ADG1636), and sends a high level (ENK) to the enable pins "1 and 9" of the integrated analog switch IC26(ADG 1636). The integrated analog switches IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(ADG1606), and C25(ADG1606) are supplied with "0, 0, 0, 0" logic level, ENA enable signal at high level "1" and ENB enable signal at high level "0" to the terminal pins "17, 16, 15, and 14". The integrated analog switch IC27(ADG1408) is sent a "0, 0, 0" (selected gain of 2) to the channel gating pin (1, 16, 15) and a high "1" to the enable pin "2" of the IC27(ADG 1408). The above arrangement means that: when the enable pin "2" of the extension 33-64 channels (IC27(ADG 1408)) is low "0", this means that the extension 33-64 channels are used, the first (channel 1) LVDT sensor from the 1-16 channels is selected in turn, the input of the funnel-type instrumentation amplifier is set to a gain factor of 0.4(VIN0.4), the default gain of the selected channel gating and LVDT driving unit 2 is "2" times, and the output response V1S0.4 of the first (channel 1) LVDT at the input gain of the funnel-type instrumentation amplifier of 0.4 is measured; this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Then, the microprocessor unit 7 sends out "1, 0, 0, 0" gating signals to the terminal pins "17, 16, 15, 14" of the integrated analog switch IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(DG1606), IC25(ADG1606), i.e. selects the second (channel 2) LVDT sensor, if other conditions are not changed; measuring V2S0.4 the output response of the second LVDT at an input gain of 0.4(VIN0.4) for the funnel-type instrumentation amplifier; this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Until the strobe signal changes to "1, 1, 1, 1"), the output response V16S0.4 of the sixteenth (channel 16) sensor to the LVDT sensor at a funnel-type instrumentation amplifier input gain of 0.4(VIN0.4) was measured and saved.

Then, the microprocessor unit 7 sends a low level "0" (CS) to the "1, 9" enable pin of the integrated analog switch IC17(ADG1636), sends a low level "0" (CS1) to the "1, 9" enable pin of the IC19(ADG1636), and sends a high level (ENK) to the "1, 9" enable pin of the integrated analog switch IC26(ADG 1636). The integrated analog switches IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(ADG1606), and C25(ADG1606) are supplied with "0, 0, 0, 0" logic level, ENA enable signal at high level "0" and ENB enable signal at high level "1" to the terminals "17, 16, 15, and 14". The integrated analog switch IC27(ADG1408) is sent a "0, 0, 0" (selected gain of 2) to the channel gating terminal pin (1, 16, 15), and the IC27(ADG1408) is sent a high "1" to the enable terminal pin "2". The above arrangement means that: when the enable pin "2" of the extension 33-64 channels (IC27(ADG 1408)) is not used to be a low level "0", this means that the extension 33-64 channels are used, the seventeenth (channel 17) LVDT sensor from the 17-32 channels is selected in turn, the input of the funnel-type instrumentation amplifier is set to a gain factor of 0.4(VIN0.4), the default gain of the selected channel gating and LVDT driving unit 2 is a factor of "2", and the output response V17S0.4 of the seventeenth (channel 17) LVDT is measured at an input gain of 0.4(VIN0.4) of the funnel-type instrumentation amplifier; this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Then, the other conditions are not changed, the micro-processor unit 7 sends out the gating signals of 1, 0, 0, 0 to the terminal pins 17, 16, 15, 14 of the integrated analog switch IC20(ADG1606), IC21(ADG1606), IC22(ADG1606), IC23(ADG1606), IC24(DG1606), IC25(ADG1606), that is, the eighteenth (channel 18) LVDT sensor is selected; determining the output response V18S0.4 of the eighteenth LVDT at a funnel-type instrumentation amplifier input gain of 0.4(VIN 0.4); this value is "permanently" stored in the memory of microprocessor IC12(STM32H750) in microprocessor unit 7. Until the strobe signal changes to "1, 1, 1, 1"), the output response V32S0.4 of the thirty second (channel 32) access LVDT sensor at a funnel-type instrumentation amplifier input gain of 0.4(VIN0.4) is measured and saved.

Initialization phase three

During the initialization phase three, the microprocessor IC12(STM32H750) in the microprocessor unit 7 operates on the collected data: vin ═ (Vin0.8-Vin0.4),. VNS ═ (VNS 0.8-VNS 0.4), KN ═ VNS/. Vin. Wherein: the output response coefficient of KN to the nth sensor, N being 1, 2, … … 32. When the invention finishes initialization and enters a normal measurement mode, the KN value determines the sensitivity of each access sensor, determines the calculation mode of the output response of the corresponding LVDT sensor, and determines the appropriate gain to be provided by the access gating low-noise pre-amplification unit 3 and the program control gain unit 4. The invention relates to a SDVG20-VA product with the range of 2.5 mm, which is automatically calibrated for various LVDT sensors and is believed to be science and technology development Limited company, wherein the sensor has the highest sensitivity in the same series of products, so that the access gating low-noise preamplification unit 3 and the program control gain unit 4 provide the lowest 2-time gain for the sensor. The gain adaptive control is performed by the following procedure: as is known, the microprocessor IC12(STM32H750) of the microprocessor 7 stores therein the values of the output response coefficients KS and VDCW associated with the SDVG20-VA product with a 2.5 mm measurement range, and the operation is performed in accordance with the adaptive and self-calibration method described above to obtain the measurement values of other connected LVDT sensors besides the conventional LVDT sensor.

When a certain LVDT sensor is connected to the system, the output response coefficient KX is obtained after initialization. The gain calculation formula G of the zero drift instrumentation amplifier IC27(INA188) in the access gated low noise preamplifier unit 3 is 1+50K Ω/RG, where: g is the gain and RG is an external matching resistor that sets the gain of the zero drift instrumentation amplifier IC27(INA 188). According to the invention, the gain BX automatically corresponding to the access gating low-noise preamplification unit 3 is determined according to the KX value obtained when a certain sensor is initialized, the gain BX is calculated and judged by a microprocessor, the selected zero drift instrument amplifier IC28(INA188) provides BN gain for the sensor, the microprocessor gates the relevant channel of the integrated analog switch IC25(ADG1636) according to the BN value, the output end of the channel is connected with a corresponding resistance network in series, and the selected resistance network is the external gain matching resistor of the zero drift instrument amplifier IC28(INA 188). The microprocessor gates the associated channel of the integrated analog switch IC25(ADG1636) according to the following: calculating α X ═ KX/KS (generally, the relationship 1 is always satisfied ≦ α X), and calculating β X ═ 1/α X from α X, where β X is a gain coefficient required for the access sensor. The microprocessor stores a coefficient β N (N ═ 1, 2, … 8) (β 1, β 2, β 3, β 4, β 5, β 6, β 7, β 8) corresponding to the gain (2, 4, 8, 10, 15, 20, 40, 81), compares β X, β N ≦ β X ≦ β N +1, and if β X ≦ β N or β N +1, β X takes a value of β N or β N + 1; and if the beta N is less than the beta X and less than the beta N +1, taking the value of the beta N. Microprocessor IC12(STM32H750) will always maintain these β X values unless reinitialized or power down restarted. The microprocessor calculates the measured value of a certain connected LVDT sensor: assuming that the quantized read value is converted to CN, the access gating low-noise pre-amplification unit 3 provides β N gain for it, and β X is obtained by actual initialization, and the final measured value is corrected to CN × (β X/β N).

As shown in fig. 10, the true effective value fast sampling unit 5 is composed of an integrated true effective value chip IC29(AD8436), an ultra-low output impedance integrated analog switch chip IC30(ADG801), resistors R78, R79, R80, capacitors C64, C65, C66, C67, C68, C69, and C70; the method is used for quickly converting the sine wave signal output by the access gating low-noise preamplification unit 3 into a high-precision direct current signal. The output (dc signal) of the true-significand fast sampling unit 5 is connected to the a/D input of the micro-processor unit 7. Traditionally, the output signal of the LVDT sensor is acquired using a phase sensitive detection method. Considering the high-precision signal processing occasion, the phase-sensitive detection mode needs to use a crystal diode in a circuit and adverse characteristics (forward voltage drop and drift of the forward voltage drop along with the ambient temperature) of the diode during small signal processing, and the adverse factors of the phase-sensitive detection mode can be effectively avoided by adopting the real effective value to quickly sample. In the invention, an integrated true effective value conversion chip AD8436 is adopted to convert sine waves into direct current. In order to ensure that the integrated true-root-mean-square conversion chip AD8436 outputs a low-noise direct-current signal, a filtering element with a large inertia coefficient needs to be added to the output end of the integrated true-root-mean-square conversion chip AD8436, so that the sampling rate of subsequent a/D sampling is affected. In order to solve the contradiction between high-precision signal processing and quick sampling, the invention adopts a mode of quickly releasing stored charges for an inertial element network which is connected in series with the output end of an integrated true effective value conversion chip AD 8436: the implementation method is that an integrated analog switch chip IC29(ADG801) with the output impedance of only 0.4 omega is used, and after the microprocessor finishes the A/D conversion of the low-noise direct current signal output by the true effective value conversion chip AD8436, the residual voltage of an inertial filter network connected in series at the output end of the true effective value conversion chip AD8436 is quickly released. By this technical means, the sampling rate can be increased from 1 HZ/s to 1 KHz/s.

As shown in fig. 12, the motion direction determination unit 6 is used to determine the motion direction of the armature when the LVDT sensor receives an external force. The invention utilizes VOA and VOB signals respectively obtained relative to a circuit reference ground of double-end output response of an LVDT sensor to realize the judgment of the motion direction of an armature: the LVDT sensor double-ended output is responsive to VOA-VOB for data measurement differential signals, VOA and VOB being two signals with the same output phase, and the LVDT sensor is composed of a excitation input coil and two identical output coils TA and TB symmetrically located on both sides of the input excitation coil, assuming their outputs to circuit reference ground are VOA and VOB, respectively. When the midpoint of the armature is at the midpoint of an excitation coil of the LVDT sensor, performing differential processing on the output responses VOA and VOB, wherein the output is zero; when the armature moves away from the midpoint and is biased toward TA under the action of an external force, the output amplitude of the VOA increases and the output amplitude of the VOB decreases. Thus, the direction of motion of the armature can be determined by using the positive or negative half-waves of VOA and VOB: when the full wave rectification of VOA minus the full wave rectification of VOB is greater than zero, the armature is biased toward TA motion and vice versa. In the illustrated example, to minimize the effect on the measurement data, the VOA and VOB signals are integrated into operational amplifier IC 31: a (OPA1654), IC 31: d (OPA1654) is subjected to in-phase following processing of a high impedance input. Integrated operational amplifier IC 31: b (OPA1654), IC 31: c (OPA1654), resistors R81, R82, R83, R86, R87, R88, and diodes D15, D16, D17, and D18 form a two-way precision rectifying circuit, which is used for integrating the operational amplifier IC 31: a (OPA1654), IC 31: the outputs of the D (OPA1654) are respectively subjected to precise full-wave rectification, and the bipolar sine waves are changed into two paths of pulsating direct current signals. The integrated operational amplifier IC32(AD8638), the resistors R84, R85, R89 and R90 form a differential proportional amplifier, and two paths of pulsating direct current signals VDA and VDB enter the in-phase end and the anti-phase end of the integrated operational amplifier IC32(AD8638) through the resistors R84 and R89 respectively. After the two paths of pulsating direct current signals are subjected to proportional differential processing formed by an integrated operational amplifier IC32(AD8638), output signals of the two paths of pulsating direct current signals serve as signals of an integrated comparator IC 33: a (LM293) is used for forming an input signal of the quasi-zero-crossing comparator. When VOA-VOB is greater than zero, the integrated comparator IC 33: a outputs high level '1', and conversely outputs low level '0', thereby realizing the judgment of the motion direction of the armature.

As shown in fig. 13 and 14, the microprocessor unit 7 includes a microprocessor IC14(STM32F750), a high-precision integrated reference source IC13(ADR4530), a reset switch K2, a capacitor C47, C48, C49, C50, C51, C52, C53, C54, C55, C56, C57, a resistor R40, R41, R42, R43, R44, R45, a zener diode W2 (2AP9), W3(2AP9), W4(2AP9), W5(2AP9), W6(2AP9), W7(2AP9), a crystal oscillator JZ1(32.768KHz), and JZ2(25 MHz). The microprocessor unit 7 is used for completing data interaction and macroscopic control of all system operations such as access channel gating control, sensor sensitivity calibration, adaptive gain control, communication module information interaction and control, touch display screen interaction and the like.

As shown in fig. 11, the display and communication unit 8 is equipped with a touch-sensitive lcd panel to constitute a human-computer interaction function, using the microprocessor IC12(STM32F750) resource port "89, 90" terminal pins (RX1, TX 1). The invention is configured with GPRS serial port, uses IC12(STM32F750) resource port '51, 52' terminal pin (RX3, TX 3); the invention is provided with an RS485 serial port, and uses IC12(STM32F750) resource port '53, 54' terminal pins (RX2, TX 2); the present invention is configured with a LORA module using IC12(STM32F750) resource port "46, 47" pins (RX4, TX 4).

As shown in fig. 15 to fig. 18, the conversion power supply 9 includes an integrated boost conversion chip IC4(TPS55340), an IC5 (TPS55340), an integrated low voltage differential chip IC5 (ADP3330-5), an integrated buck chip IC5 (LM2594), an integrated polarity conversion chip IC5 (TPS63700), a negative power supply low voltage differential chip IC5 (LT19645-5), patch power inductors L5, resistors R5, capacitors C5, C; and the required +5P, +5.0, +5D, -5.0, + 3.3V stable direct current power supply is provided for each component power supply. The input voltage of the conversion power supply 9 is 3-4.2V (namely, the output of the single-group lithium battery pack). The +5P is a direct current unit which provides output current of up to 1.5A for the large-screen touch liquid crystal screen and the GPRS remote wireless communication module; +5.0 and-5.0 provide high-stability working power for the linear circuit of the invention; +5D is a DC stabilized voltage supply provided by the digital circuit part of the invention; +3.3 provides operating power for the processor.

The hybrid charging unit 10 is configured to perform hybrid charging on a lithium battery pack configured in a system by using an ac adapter and a solar power generation method, where the ac adapter is in a priority mode in a charging sequence. Typically, a high capacity lithium battery pack (charged 4.2 volts 37.2AH) configured for the system can maintain normal operation of the system for one month without energy compensation; in the period, the battery pack can be fully charged only in two sunny days, and the electric energy supply of a system does not need to be interfered by people in principle. Under special conditions, the battery pack can be charged by the AC adapter, and the hybrid charging unit can automatically block the solar power generation output on occasions when the battery pack is charged by the AC adapter.

As shown in fig. 19, the solar charging portion of the hybrid charging unit 10 includes a solar charging chip IC1 (BQ24650), resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, fuses F1 and F2, diodes D1(SS510), D1(SS 1), a power tube BG1(IRF7351), a patch power inductor L1, a negative temperature coefficient field effect resistor R1, and light emitting diodes LD1 and LD 1. The solar charging part charges a lithium battery pack with an open-circuit output voltage of 21.5 volts and a normal output power of 20 watts to 37.2AH and 4.2 volts.

As shown in fig. 20, the ac-dc conversion portion is composed of a monolithic ac-dc conversion chip IC2(TOP266), a three-terminal regulator (TL431),

resistors

14, 15, 16, 17, 18, 19, R20, R21, R22, R23, R24, R25, R26, capacitors C12, C13, C14, C15, C16, C17, electrolytic capacitors E1, E2, E3, E4, E5, a fuse F3, inductors L2, L3, a high-frequency transformer T1, a linear optocoupler OP1(TLV817), crystal diodes D4, D5, D6, D7, D8, D9, D10, a transient stabilivolt W1(P6KE200), and the like. In general, a solar charging part provides charging electric quantity for a lithium battery pack, and if solar charging cannot be obtained for a long time, an AC-DC adapter can be used for charging; the output of the adapter is designed to be 24 volts, so that when the adapter is accessed, the output of solar energy is automatically blocked by the anti-reverse-biased diodes D1 and D2.

The method provided by the invention realizes the monitoring of micro strain, micro-scale change, mechanical quantity and the like of high-precision engineering using various LVDT sensors and provides a convenient calibration means for the occasions using a large number of LVDT heavy checkpoints, thereby greatly reducing the fussy high-precision calibration work for a large number of LVDT sensors and providing a quick and high-precision self-adaptive measurement method for the automatic monitoring and detecting occasions. The invention is especially suitable for the occasions with severe environment and high-precision and rapid measurement requirements, such as engineering monitoring, nuclear facilities (equipment), aviation equipment, engines and the like.

Claims

1. An automatic calibration system based on an LVDT sensor is characterized by comprising a constant-frequency constant-amplitude signal generating unit, a channel gating and LVDT driving unit, an access gating low-noise preamplifier unit, a program control gain unit and a microprocessor unit, the output end of the constant-frequency and constant-amplitude signal generating unit is connected with the input end of the channel gating and LVDT driving unit, the output end of the channel gating and LVDT driving unit is connected with the input end of the access gating low-noise preamplification unit, the output end of the access gating low-noise preamplification unit is connected with the input end of the microprocessor unit, the output end of the microprocessor unit is respectively connected with the input end of the channel gating and LVDT driving unit and the input end of the program control gain unit, the output end of the program control gain unit is connected with the input end of the access gating low-noise preamplification unit.

2. The LVDT sensor-based automatic calibration system according to claim 2, wherein the constant frequency and constant amplitude signal generating unit comprises a first integrated analog switch and a zero-shift operational amplifier, wherein the square wave signal outputted from the microprocessor unit controls on/off of the first integrated analog switch, so that the signal outputted from the first integrated analog switch is a constant frequency and constant amplitude square wave signal, and the zero-shift operational amplifier is connected to the first integrated analog switch for converting the constant frequency and constant amplitude square wave signal into a constant frequency and constant amplitude bipolar sine wave signal.

3. The LVDT sensor-based automatic scaling system according to claim 3, wherein the channel gating and LVDT driving unit includes a second integrated analog switch and an integrated funnel-type instrumentation amplifier, the microprocessor unit controlling the second integrated analog switch to access the LVDT sensor and connecting a constant frequency and constant amplitude bipolar sine wave signal to an input of the integrated funnel-type instrumentation amplifier to enable the microprocessor unit to obtain a response coefficient of the accessed LVDT sensor.

4. The LVDT sensor-based automatic scaling system of claim 4, wherein the access-gated low noise preamplifier unit includes a zero drift instrumentation amplifier and a resistor, and the microprocessor unit adjusts the response coefficient of the LVDT sensor by selecting a gain-matched resistor for the zero drift instrumentation amplifier via the programmable gain unit based on the stored sensitivity value.

5. The LVDT sensor-based automatic scaling system according to claim 1, further comprising a true effective value fast sampling unit having an input coupled to the access gate low noise preamplifier unit and an output coupled to an input of the microprocessor unit.

6. The LVDT sensor-based automatic scaling system of claim 5, wherein the true effective value fast sampling unit comprises an integrated true effective value chip for fast converting the output sine wave signal of the access gate low noise pre-amplification unit into a high precision direct current signal.

7. The LVDT sensor-based automatic scaling system according to claim 1, further comprising the motion direction discrimination unit, an input of the motion direction discrimination unit being connected to the access gate low noise preamplifier unit, and an output of the motion direction discrimination unit being connected to an input of the microprocessor unit.

8. The LVDT sensor based automatic scaling system according to claim 7, wherein the motion direction sensing unit includes three integrated operational amplifiers and an integrated comparator, wherein two signals in response to the outputs of the two terminals of the LVDT sensor are amplified by the integrated operational amplifiers respectively, and wherein the two amplified signals are scaled and differentiated by the other integrated operational amplifier, and wherein the output signal of the integrated operational amplifier is used as an input signal of the quasi-zero comparator formed by the integrated comparator.

9. An automatic calibration method based on an LVDT sensor, which is characterized by comprising the following steps:

acquiring a response coefficient and a sensitivity value of the LVDT sensor;

10. The LVDT sensor-based auto-calibration method of claim 9, wherein the adjusting the response coefficient of the LVDT sensor based on the comparison of the response coefficient of the LVDT sensor and the sensitivity value comprises:

and switching the selection resistor, and adjusting the amplification factor corresponding to the response coefficient of the LVDT sensor.