CN110006331B - Wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system - Google Patents
Wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system Download PDFInfo
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Abstract
The invention discloses a wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system which comprises a strain sensor and a strain signal conversion functional block, wherein the strain signal conversion functional block is sequentially connected with a fixed gain amplification functional block, a filtering module, a program control amplification module and a microcontroller functional block, the strain signal conversion functional block is also connected with a bridge source functional block and a bridge recovery functional block during compaction, and a hardware return-to-zero functional block is also connected between a reference end of the fixed gain amplification functional block and the microcontroller functional block; the fixed gain amplification functional block adopts a low-noise differential input type instrument amplifier, the positive input end and the negative input end of the low-noise differential input type instrument amplifier are respectively connected with a grounding capacitor, and an interelectrode capacitor is connected between the fixed gain amplification functional block and the program control amplification module. The invention realizes the strain signal conditioning with high precision, wide range, anti-interference and miniaturization, and has higher integration level, more complete functions and smaller package.
Description
Technical Field
The invention relates to the technical field of measurement and control, in particular to a wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system.
Background
Strain is often adopted in a material mechanics test to characterize the material damage evolution processThe local strain evolution process of the over-measured material can be used for predicting and evaluating the damage of the material. The energetic material part belongs to a high elastic modulus material, the internal stress distribution of the energetic material part changes under the excitation of load outside force or heat and the like, and the change of the strain of each point can be observed by arranging strain sensors at multiple points. The strain variation range of the energetic material component is about 10 under the excitation of force or thermal load0～104Mu epsilon, and strain values on different orders of magnitude have different structural strength and structural mechanical significance, which puts demands on wide-range measurement and high-precision measurement spanning 4 orders of magnitude. Along with the development of equipment towards high reliability, the demand for implanted online monitoring of structural weak parts in the equipment is greater and greater, and a direct demand is provided for miniaturization of a strain test system. Compared with a half-bridge and full-bridge strain measurement method, the single-arm bridge has the advantages of few transmission lines, simple line connection and the like, and is widely applied to the field of normal-temperature strain test engineering. The existing conditioning technology suitable for strain measurement of a static single-arm bridge cannot meet the requirements of wide high precision, wide range, miniaturization, low power supply and low power consumption of a strain test system in implanted online monitoring.
Disclosure of Invention
The invention aims to provide a wide-range high-precision conditioning system for a resistance type strain measurement signal of a static single-arm bridge, which is used for solving the problems that the conditioning system for strain measurement of the static single-arm bridge in the prior art cannot meet the requirements of an implanted online monitoring on high precision and wide range of a strain test system, and cannot meet the requirements of a low power supply and low power consumption.
The invention solves the problems through the following technical scheme:
a wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system comprises a strain sensor and a strain signal conversion functional block which is connected with the strain sensor and used for converting mechanical strain into microvolt voltage, wherein the output end of the strain signal conversion functional block is sequentially connected with a fixed gain amplification functional block, a filtering module, a program control amplification module and a microcontroller functional block, the strain signal conversion functional block is also sequentially connected with a bridge source functional block used for providing power for the strain signal conversion functional block and a bridge compaction time recovery functional block used for collecting bridge source voltage in real time, the bridge compaction time recovery functional block is connected with the microcontroller functional block, and a hardware return-to-zero functional block is further connected between the reference end of the fixed gain amplification functional block and the microcontroller functional block; the bridge source functional block adopts a special power supply integrated circuit, and the extraction functional block designs and calculates the lowest bit number of analog-to-digital conversion according to the allowable error of the bridge source functional block during bridge compaction; the fixed gain amplification functional block adopts a low-noise differential input type instrument amplifier, the positive input end and the negative input end of the low-noise differential input type instrument amplifier are respectively connected with a grounding capacitor, and an interelectrode capacitor is connected between the fixed gain amplification functional block and the program control amplification module.
The strain sensor is connected with the strain signal conversion functional block to convert mechanical strain into microvolt voltage, the bridge source circuit provides power for the strain signal conversion functional block, microvolt strain signals are connected with the low-noise differential input type instrument amplifier to realize primary amplification, signals after the primary amplification are connected with the low-pass filter to realize filtering, signals after the filtering are subjected to secondary amplification through the program control amplification module, and signals after the secondary amplification are subjected to analog-to-digital conversion and then input into the microcontroller functional block to realize signal acquisition. The extraction functional block acquires the bridge source voltage in real time during bridge compaction, and the hardware zeroing functional block outputs the zero-resetting reference voltage of the low-noise differential input type instrumentation amplifier after digital-to-analog conversion by measuring the strain signal input under zero load, so that high-precision hardware zeroing is realized. The high-precision test of the strain signal is realized by utilizing signal processing methods for improving the signal quality, such as differential input and differential output of primary amplification, differential input of secondary amplification, capacitance alternating current filtering of a transmission line, interstage low-pass filtering and the like, wherein the capacitance alternating current filtering of the transmission line is arranged at the positive and negative signal ends of a differential input signal of a fixed gain amplification functional block and is realized by adopting a direct capacitance grounding mode; and the interstage low-pass filtering receives the signal of the fixed gain amplification functional block, and the signal is output to the program control gain amplification module after being filtered by the low-pass filter.
Further, the method can be used for preparing a novel materialGround, gain A of the fixed gain amplification block1The design method comprises the following steps:
step S100: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
The method specifically comprises the following steps:
step S110: output voltage deviation delta U caused by resistance precision error under no load in single-arm strain test of computing equal-arm bridgein：
Wherein: k represents a sensitivity coefficient of the strain sensor; u shapesRepresents the wheatstone bridge voltage; r1Representing a characteristic resistance value of the single-arm strain sensor; r2～R4Respectively representing the bridge arm resistances in the equal-arm bridge; Δ R2～ΔR4Respectively representing the error value, Δ R, of the bridge arm resistance1Representing the maximum deviation value of the characteristic resistance value of the single-arm strain sensor; e.g. of the type2～e4Respectively representing the error rates of the bridge arm resistances, where e1Representing a maximum error rate of deviation of the single-arm strain sensor from the characteristic resistance value;
step S120: equivalent input noise voltage DeltaU due to internal noise of fixed gain amplifiernrmsThe calculation method comprises the following steps:
wherein: b is a low-pass filtering bandwidth designed in static strain measurement;
Vnan equivalent input noise voltage for the fixed gain amplification block;
step S130: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Step S200: determining the gain A of a fixed gain amplification block1The method specifically comprises the following steps:
according to the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Determining the gain A of a fixed gain amplification block1，
Wherein, URefAdSIs the reference voltage of the fixed gain amplification block;
is the minimum gain value of the program-controlled amplification module.
Furthermore, the program-controlled amplification module comprises a program-controlled gain amplification functional block, an ADC (analog to digital converter) and a program-controlled gain resistor, wherein the input end of the program-controlled gain amplification functional block is connected with the filtering module, the output end of the program-controlled gain amplification functional block is connected with the input end of the ADC, and the output end of the ADC is connected with the microcontroller functional block.
Further, the program-controlled gain of the program-controlled gain amplification function block
Where i identifies the programmed gain level, i ═ 1,2,3, 4; programmable gain
The selection method comprises the following steps:
step A1: setting the initial gain of the program-controlled gain amplification functional block to the highest gain before testing
Step A2: judging signal U amplified by program control gain amplification functional blockinWhether or not to be at
To (c) to (d); if the current gain is within the interval, the gain is not adjusted, the current gain is the gain selected by the current measurement, and the process is finished;
if the upper limit value is higher than the upper limit value, the next step is carried out:
step A3: and reducing the one-stage programmable gain level and returning to the step A2.
Further, still include:
step A4: the gain of the last measurement in the subsequent measurement is the initial gain value;
step A5: after measurement, whether the amplified signal is
In the above-mentioned manner,
if yes, selecting the current gain as the gain selected by the current measurement, and ending;
if the upper limit value is higher than the upper limit value, the step A6 is carried out;
if the value is lower than the lower limit value, the step A7 is executed;
step A6: reducing the one-level program control gain level, and returning to the step A5;
step A7: and increasing the one-stage programmable gain level and returning to the step A5.
Further, the hardware return-to-zero function block includes a return-to-zero DAC, and the step of calculating and outputting the return-to-zero voltage value in the return-to-zero DAC is as follows:
the method comprises the following steps: obtaining a measurement output at no load
Simultaneously recording the program control gain of the program control amplification module corresponding to the output
Step two: meterCalculating the initial value of return-to-zero voltage
Step three: resetting the initial value of the voltage through the microcontroller functional block and the reset DAC
Transmitting to the reference voltage terminal of the fixed gain amplification function block as the initial value of the reference voltage input terminal
Step four: the fast return-to-zero calculation controller is designed by adopting an automatic control theory, and the return-to-zero voltage value is calculated by the following steps:
(1) with set zero-return strain output value UosAs input quantity, real-time strain output value UoAs controlled quantity and feedback quantity, output return-to-zero voltage UzThe controlled object consists of a fixed gain amplification functional block and a program control amplification module;
(2) calculating the return-to-zero voltage U by using a continuous quantity adjusting method with an integral initial valuez：
Wherein the content of the first and second substances,
is an initial value of integration, numerically the output value of the fixed gain amplification block collected at the moment of test start return to zero, i.e.
e (t) is a set return-to-zero strain value UosAnd the strain output value U not completely returning to zerooI.e. e (t) Uos(t)-Uo(t)；Kp、TiAnd TdAn adjustment value for adjusting the zeroing efficiency;
(3) when the return-to-zero voltage is calculated, the strain output value is set to be 0 mu epsilon, the controller can quickly realize that the real-time strain output is lower than 1 mu epsilon, and after the return-to-zero process is stopped, the output value of the return-to-zero voltage controller at the stopping moment is the return-to-zero voltage value during strain measurement.
In order to avoid the problem of oscillation of the acquired return-to-zero voltage caused by the precision, noise, interference and the like of electronic elements, an automatic control theory is adopted to design a fast return-to-zero calculation controller, so that a stable return-to-zero voltage value can be quickly calculated, and efficient return-to-zero is realized.
Further, the bridge source voltage extraction functional block comprises a bridge voltage accurate measurement circuit, the bridge voltage accurate measurement circuit is used for realizing the resolution meeting the span of 4 orders of magnitude, and the realization method of the bridge voltage accurate measurement circuit is as follows:
1) according to strain output value
Calculating the lower bound εMinMinimum number of bits N satisfying the lower bound measure when 1 mu epsilonPoSa：
Wherein A is1The gain of the fixed gain amplification block;
the program control gain of the program control gain amplification functional block;
the highest gain of the program control gain amplification functional block;
2) the resolution of strain voltage is controlled in strain acquisition, and the sampling resolution of a strain signal is the same as that of a bridge source power supply;
3) the voltage digital-to-analog conversion resolution design method of the return-to-zero DAC comprises the following steps:
calculating an error value delta U under the sampling resolution according to the designed maximum return-to-zero errorOAdThe calculation formula is as follows:
calculating the number of return-to-zero digital-to-analog conversion bits NDacError value of output Δ UODaNumerically, on
By error value Δ UODaNot greater than the maximum return-to-zero error, and calculating the minimum return-to-zero digital-to-analog conversion digit N of the error value of the sampling resolutionDacNamely:
4) equivalent input noise voltage delta U of fixed gain amplification blocknrmsShould be numerically below the lower limit εMinOutput voltage of lower strain signal conversion function block
Half of, numerically
Further, the method for suppressing errors caused by bridge source noise and drift in the bridge source functional block comprises:
the (I) bridge source functional block adopts a special power supply integrated circuit and is in accordance with the maximum allowable error delta U of the bridge sourceAllowPowerDesigning the lowest analog-to-digital conversion number of the stoping function block during bridge compaction:
maximum error delta U of bridge source functional blockpower≤1.5×ΔUAllowPower；
Lowest order of analog-to-digital conversion
Wherein, URefAdFor reference voltages for analog-to-digital conversion in the extraction function during bridge compaction, n being in analog-to-digital conversionA minimum number of analog-to-digital conversion bits;
(II) simultaneously measuring bridge source voltage and strain signals, calculating a bridge source voltage value and a strain value after high-frequency peak interference is suppressed by a sliding window mean value filtering method, and calculating by adopting a bridge source voltage-to-strain value compensation method to obtain a strain value, specifically:
the strain signal value tested by the strain measurement system is set as
After the system is calibrated, a strain value epsilon can be calculated;
the bridge source voltage and strain value measurement after mean value processing is calculated by adopting a sliding window mean value calculation method, and the calculation formula is as follows:
obtaining the bridge pressure value in the measurement process
And strain measurements εt；
By the formula
And calculating a strain value.
Designing a high-precision bridge source circuit in the strain signal conversion functional block according to the principles of miniaturization, low power consumption and high precision, and selecting a special power supply integrated circuit according to main error sources such as noise, temperature drift and the like of a power supply device; designing a bridge source voltage recovery circuit according to the bridge source allowable error and calculating the lowest bit number of analog-to-digital conversion of the recovery circuit; a method for suppressing errors such as bridge source interference, noise and the like in high-precision strain measurement is designed, and the function of suppressing errors caused by bridge source noise and drift in high-precision strain measurement is achieved.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the technical indexes of the high-precision strain measurement conditioning system, the maximum allowable error and the precision requirement of each functional block are decomposed and designed, and the high-precision performance design of the whole conditioning system is realized; and an integrated circuit which meets the requirements of basic functions and high-precision anti-interference and low-noise performance of the circuit and has higher integration level, more complete functions, smaller package and lower power supply requirement is selected to realize the circuit function.
(2) The invention realizes the function of replacing part of hardware by software so as to reduce the number of hardware devices and realize the miniaturization design of the whole conditioning system.
(3) The invention adopts a self-adaptive program control gain method to realize the high-magnification two-stage amplification of the low-order measurement value after the first-stage amplification and the low-magnification two-stage amplification of the high-order measurement value after the first-stage amplification, and finally realizes the wide range of +/-100～104Mu epsilon) high precision measurement required by the strain test + - (+ 5 mu epsilon).
(4) The invention relates to a wide-range high-precision test signal processing general method for realizing the same test precision with 4 magnitude spans, which comprises the following steps: the influence of various noises and interferences on a test signal is inhibited through hardware technologies such as differential input, alternating current signal small-capacitance filtering, intermediate-level low-pass filtering, line anti-interference design and the like; the influence of the signal conversion resolution on the test precision is eliminated through the design of bridge source voltage recovery resolution, strain signal acquisition resolution, return-to-zero voltage digital-to-analog conversion resolution and the like; by means of hardware zeroing, two-stage amplification and second-stage program control amplification, the influence of noise of a preposed instrument amplifier, bridge resistance precision, component temperature drift and noise of other components on the test precision can be eliminated.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 is a flow chart of a gain selection method for a programmable gain amplification block;
FIG. 3 is a functional diagram of a fast calculation control system for return-to-zero voltage values.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Example 1:
with reference to fig. 1, a wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system comprises a strain sensor and a strain signal conversion functional block connected with the strain sensor and used for converting mechanical strain into microvolt-level voltage, wherein the output end of the strain signal conversion functional block is sequentially connected with a fixed gain amplification functional block, a filtering module, a program control amplification module and a microcontroller functional block, the strain signal conversion functional block is further sequentially connected with a bridge source functional block used for providing power for the strain signal conversion functional block and a bridge compaction time recovery functional block used for collecting bridge source voltage in real time, the bridge compaction time recovery functional block is connected with the microcontroller functional block, and a hardware return-to-zero functional block is further connected between the reference end of the fixed gain amplification functional block and the microcontroller functional block; the bridge source functional block adopts a special power supply integrated circuit, and the extraction functional block designs and calculates the lowest bit number of analog-to-digital conversion according to the allowable error of the bridge source functional block during bridge compaction; the fixed gain amplification functional block adopts a low-noise differential input type instrument amplifier, the positive input end and the negative input end of the low-noise differential input type instrument amplifier are respectively connected with a grounding capacitor, and an interelectrode capacitor is connected between the fixed gain amplification functional block and the program control amplification module.
The strain sensor is connected with the strain signal conversion functional block to convert mechanical strain into microvolt voltage, the bridge source circuit provides power for the strain signal conversion functional block, microvolt strain signals are connected with the low-noise differential input type instrument amplifier to realize primary amplification, signals after the primary amplification are connected with the low-pass filter to realize filtering, signals after the filtering are subjected to secondary amplification through the program control amplification module, and signals after the secondary amplification are subjected to analog-to-digital conversion and then input into the microcontroller functional block to realize signal acquisition. The extraction functional block acquires the bridge source voltage in real time during bridge compaction, and the hardware zeroing functional block outputs the zero-resetting reference voltage of the low-noise differential input type instrumentation amplifier after digital-to-analog conversion by measuring the strain signal input under zero load, so that high-precision hardware zeroing is realized. The high-precision test of the strain signal is realized by utilizing signal processing methods for improving the signal quality, such as differential input and differential output of primary amplification, differential input of secondary amplification, capacitance alternating current filtering of a transmission line, interstage low-pass filtering and the like, wherein the capacitance alternating current filtering of the transmission line is arranged at the positive and negative signal ends of a differential input signal of a fixed gain amplification functional block and is realized by adopting a direct capacitance grounding mode; and the interstage low-pass filtering receives the signal of the fixed gain amplification functional block, and the signal is output to the program control gain amplification module after being filtered by the low-pass filter.
Example 2:
based on embodiment 1, the gain A of the fixed gain amplification functional block1The design method comprises the following steps:
step S100: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
The method specifically comprises the following steps:
step S110: output voltage deviation delta U caused by resistance precision error under no load in single-arm strain test of computing equal-arm bridgein：
Wherein: k represents a sensitivity coefficient of the strain sensor; u shapesRepresents the wheatstone bridge voltage; r1Representing a characteristic resistance value of the single-arm strain sensor; r2～R4Respectively representing the bridge arm resistances in the equal-arm bridge; Δ R2～ΔR4Respectively representing the error value, Δ R, of the bridge arm resistance1Representing the maximum deviation value of the characteristic resistance value of the single-arm strain sensor; e.g. of the type2～e4Respectively representing the error rates of the bridge arm resistances, where e1Representing a maximum error rate of deviation of the single-arm strain sensor from the characteristic resistance value;
step S120: of fixed gain amplifiersEquivalent input noise voltage Δ U due to internal noisenrmsThe calculation method comprises the following steps:
wherein: b is a low-pass filtering bandwidth designed in static strain measurement;
Vnan equivalent input noise voltage for the fixed gain amplification block;
step S130: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Step S200: determining the gain A of a fixed gain amplification block1The method specifically comprises the following steps:
according to the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Determining the gain A of a fixed gain amplification block1，
Wherein, URefAdSIs the reference voltage of the fixed gain amplification block;
is the minimum gain value of the program-controlled amplification module.
Example 3:
on the basis of embodiment 1 or 2, the program-controlled amplification module includes a program-controlled gain amplification functional block, an ADC, and a program-controlled gain resistor, an input end of the program-controlled gain amplification functional block is connected to the filtering module, an output end of the program-controlled gain amplification functional block is connected to an input end of the ADC, and an output end of the ADC is connected to the microcontroller functional block.
Further, the program-controlled gain of the program-controlled gain amplification function block
Where i identifies the programmed gain level, i ═ 1,2,3, 4; programmable gain
The selection method (2) is shown in fig. 2:
step A1: setting the initial gain of the program-controlled gain amplification functional block to the highest gain before testing
Step A2: judging signal U amplified by program control gain amplification functional blockinWhether or not to be at
To (c) to (d); if the current gain is within the interval, the gain is not adjusted, the current gain is the gain selected by the current measurement, and the process is finished;
if the upper limit value is higher than the upper limit value, the next step is carried out:
step A3: and reducing the one-stage programmable gain level and returning to the step A2.
Further, still include:
step A4: the gain of the last measurement in the subsequent measurement is the initial gain value;
step A5: after measurement, whether the amplified signal is
In the above-mentioned manner,
if yes, selecting the current gain as the gain selected by the current measurement, and ending;
if the upper limit value is higher than the upper limit value, the step A6 is carried out;
if the value is lower than the lower limit value, the step A7 is executed;
step A6: reducing the one-level program control gain level, and returning to the step A5;
step A7: and increasing the one-stage programmable gain level and returning to the step A5.
Example 4:
on the basis of embodiment 3, as shown in fig. 3, the hardware return-to-zero functional block includes a return-to-zero DAC, and the step of calculating and outputting the return-to-zero voltage value in the return-to-zero DAC is as follows:
the method comprises the following steps: obtaining a measurement output at no load
Simultaneously recording the program control gain of the program control amplification module corresponding to the output
Step two: calculating the initial value of the return-to-zero voltage
Step three: resetting the initial value of the voltage through the microcontroller functional block and the reset DAC
Transmitting to the reference voltage terminal of the fixed gain amplification function block as the initial value of the reference voltage input terminal
Step four: the fast return-to-zero calculation controller is designed by adopting an automatic control theory, and the return-to-zero voltage value is calculated by the following steps:
(1) with set zero-return strain output value UosAs input quantity, real-time strain output value UoAs controlled quantity and feedback quantity, output return-to-zero voltage UzThe controlled object consists of a fixed gain amplification functional block and a program control amplification module;
(2) calculating the return-to-zero voltage U by using a continuous quantity adjusting method with an integral initial valuez：
Wherein the content of the first and second substances,
is an initial value of integration, numerically the output value of the fixed gain amplification block collected at the moment of test start return to zero, i.e.
e (t) is a set return-to-zero strain value UosAnd the strain output value U not completely returning to zerooI.e. e (t) Uos(t)-Uo(t)；Kp、TiAnd TdAn adjustment value for adjusting the zeroing efficiency;
(3) when the return-to-zero voltage is calculated, the strain output value is set to be 0 mu epsilon, the controller can quickly realize that the real-time strain output is lower than 1 mu epsilon, and after the return-to-zero process is stopped, the output value of the return-to-zero voltage controller at the stopping moment is the return-to-zero voltage value during strain measurement.
In order to avoid the problem of oscillation of the acquired return-to-zero voltage caused by the precision, noise, interference and the like of electronic elements, an automatic control theory is adopted to design a fast return-to-zero calculation controller, so that a stable return-to-zero voltage value can be quickly calculated, and efficient return-to-zero is realized.
Further, the bridge source voltage extraction functional block comprises a bridge voltage accurate measurement circuit, the bridge voltage accurate measurement circuit is used for realizing the resolution meeting the span of 4 orders of magnitude, and the realization method of the bridge voltage accurate measurement circuit is as follows:
1) according to strain output value
Calculating the lower bound εMinMinimum number of bits N satisfying the lower bound measure when 1 mu epsilonPoSa：
Wherein a1 is the gain of the fixed gain amplification block;
the program control gain of the program control gain amplification functional block;
the highest gain of the program control gain amplification functional block;
2) the resolution of strain voltage is controlled in strain acquisition, and the sampling resolution of a strain signal is the same as that of a bridge source power supply;
3) the voltage digital-to-analog conversion resolution design method of the return-to-zero DAC comprises the following steps:
calculating an error value delta U under the sampling resolution according to the designed maximum return-to-zero errorOAdThe calculation formula is as follows:
calculating the number of return-to-zero digital-to-analog conversion bits NDacError value of output Δ UODaNumerically, on
By error value Δ UODaNot greater than the maximum return-to-zero error, and calculating the minimum return-to-zero digital-to-analog conversion digit N of the error value of the sampling resolutionDacNamely:
4) equivalent input noise voltage delta U of fixed gain amplification blocknrmsShould be numerically below the lower limit εMinOutput voltage of lower strain signal conversion function block
Half of, numerically
Example 5:
on the basis of embodiment 1, the method for suppressing errors caused by bridge source noise and drift in the bridge source functional block is as follows:
the (I) bridge source functional block adopts a special power supply integrated circuit and is in accordance with the maximum allowable error delta U of the bridge sourceAllowPowerDesigning the lowest analog-to-digital conversion number of the stoping function block during bridge compaction:
maximum error delta U of bridge source functional blockpower≤1.5×ΔUAllowPower；
Lowest order of analog-to-digital conversion
Wherein, URefAdThe reference voltage of the analog-to-digital conversion in the extraction functional block during bridge compaction is used, and n is the minimum analog-to-digital conversion digit in the analog-to-digital conversion;
(II) simultaneously measuring bridge source voltage and strain signals, calculating a bridge source voltage value and a strain value after high-frequency peak interference is suppressed by a sliding window mean value filtering method, and calculating by adopting a bridge source voltage-to-strain value compensation method to obtain a strain value, specifically:
the strain signal value tested by the strain measurement system is set as
After the system is calibrated, a strain value epsilon can be calculated;
the bridge source voltage and strain value measurement after mean value processing is calculated by adopting a sliding window mean value calculation method, and the calculation formula is as follows:
obtain the measurement processBridge pressure value of
And strain measurements εt；
By the formula
And calculating a strain value.
Although the present invention has been described herein with reference to the illustrated embodiments thereof, which are intended to be preferred embodiments of the present invention, it is to be understood that the invention is not limited thereto, and that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.
Claims (6)
1. A wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system is characterized by comprising a strain sensor and a strain signal conversion function block which is connected with the strain sensor and used for converting mechanical strain into microvolt voltage, wherein the output end of the strain signal conversion function block is sequentially connected with a fixed gain amplification function block, a filtering module, a program control amplification module and a microcontroller function block; the bridge source functional block adopts a special power supply integrated circuit, and the extraction functional block designs and calculates the lowest bit number of analog-to-digital conversion according to the allowable error of the bridge source functional block during bridge compaction; the fixed gain amplification function block adopts a low-noise differential input type instrument amplifier, the positive and negative input ends of the low-noise differential input type instrument amplifier are respectively connected with a grounding capacitor, an interelectrode capacitor is connected between the fixed gain amplification function block and the program control amplification module, and the fixed gain amplification function block is connected with the program control amplification module through the interelectrode capacitorGain A of the constant gain amplification block1The design method comprises the following steps:
step S100: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
The method specifically comprises the following steps:
step S110: output voltage deviation delta U caused by resistance precision error under no load in single-arm strain test of computing equal-arm bridgein：
Wherein: k represents a sensitivity coefficient of the strain sensor; u shapesRepresents the wheatstone bridge voltage; r1Representing a characteristic resistance value of the single-arm strain sensor; r2～R4Respectively representing the bridge arm resistances in the equal-arm bridge; Δ R2～ΔR4Respectively representing the error value, Δ R, of the bridge arm resistance1Representing the maximum deviation value of the characteristic resistance value of the single-arm strain sensor; e.g. of the type2～e4Respectively representing the error rates of the bridge arm resistances, where e1Representing a maximum error rate of deviation of the single-arm strain sensor from the characteristic resistance value;
step S120: equivalent input noise voltage DeltaU due to internal noise of fixed gain amplifiernrmsThe calculation method comprises the following steps:
wherein: b is a low-pass filtering bandwidth designed in static strain measurement;
Vnan equivalent input noise voltage for the fixed gain amplification block;
step S130: calculating the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Step S200: determining the gain A of a fixed gain amplification block1The method specifically comprises the following steps:
according to the maximum input equivalent deviation voltage of the fixed gain amplification functional block under no load
Determining the gain A of a fixed gain amplification block1，
Wherein, URefAdSIs the reference voltage of the fixed gain amplification block;
is the minimum gain value of the program-controlled amplification module.
2. The system for conditioning the wide-range high-precision static single-arm bridge resistance type strain measurement signal according to claim 1, wherein the programmable amplification module comprises a programmable gain amplification functional block, an ADC and a programmable gain resistor, an input end of the programmable gain amplification functional block is connected with the filtering module, an output end of the programmable gain amplification functional block is connected with an input end of the ADC, and an output end of the ADC is connected with the microcontroller functional block.
3. The wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system according to claim 2, wherein the programmable gain of the programmable gain amplification functional block
Where i identifies the programmed gain level, i ═ 1,2,3, 4; programmable gain
The selection method comprises the following steps:
step A1: setting the initial gain of the program-controlled gain amplification functional block to the highest gain before testing
Step A2: judging signal U amplified by program control gain amplification functional blockinWhether or not to be at
To (c) to (d); if the current gain is within the interval, the gain is not adjusted, the current gain is the gain selected by the current measurement, and the process is finished;
if the upper limit value is higher than the upper limit value, the next step is carried out:
step A3: and reducing the one-stage programmable gain level and returning to the step A2.
4. The wide range high accuracy static single arm bridge resistive strain measurement signal conditioning system of claim 3, further comprising:
step A4: the gain of the last measurement in the subsequent measurement is the initial gain value;
step A5: after measurement, whether the amplified signal is
In the above-mentioned manner,
if yes, selecting the current gain as the gain selected by the current measurement, and ending;
if the upper limit value is higher than the upper limit value, the step A6 is carried out;
if the value is lower than the lower limit value, the step A7 is executed;
step A6: reducing the one-level program control gain level, and returning to the step A5;
step A7: and increasing the one-stage programmable gain level and returning to the step A5.
5. The wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system according to claim 1, wherein the hardware zeroing functional block comprises a zeroing DAC, and the step of calculating and outputting a zeroing voltage value in the zeroing DAC is as follows:
the method comprises the following steps: obtaining a measurement output at no load
Simultaneously recording the program control gain of the program control amplification module corresponding to the output
Step two: calculating the initial value of the return-to-zero voltage
Step three: resetting the initial value of the voltage through the microcontroller functional block and the reset DAC
Transmitting to the reference voltage terminal of the fixed gain amplification function block as the initial value of the reference voltage input terminal
Step four: the fast return-to-zero calculation controller is designed by adopting an automatic control theory, and the return-to-zero voltage value is calculated by the following steps:
(1) with set zero-return strain output value UosAs input quantity, real-time strain output value UoAs controlled quantity and feedback quantity, output return-to-zero voltage UzThe controlled object consists of a fixed gain amplification functional block and a program control amplification module;
(2) calculating the return-to-zero voltage U by using a continuous quantity adjusting method with an integral initial valuez：
Wherein the content of the first and second substances,
is an initial value of integration, numerically the output value of the fixed gain amplification block collected at the moment of test start return to zero, i.e.
e (t) is a set return-to-zero strain value UosAnd the strain output value U not completely returning to zerooI.e. e (t) Uos(t)-Uo(t)；Kp、TiAnd TdAn adjustment value for adjusting the zeroing efficiency;
(3) when the return-to-zero voltage is calculated, the strain output value is set to be 0 mu epsilon, the controller can quickly realize that the real-time strain output is lower than 1 mu epsilon, and after the return-to-zero process is stopped, the output value of the return-to-zero voltage controller at the stopping moment is the return-to-zero voltage value during strain measurement.
6. The wide-range high-precision static single-arm bridge resistance type strain measurement signal conditioning system according to claim 5, wherein the bridge source voltage extraction functional block comprises a bridge voltage precision measurement circuit, the bridge voltage precision measurement circuit is used for realizing the resolution meeting the span of 4 orders of magnitude, and the implementation method of the bridge voltage precision measurement circuit is as follows:
1) according to strain output value
Calculating the lower bound εMinMinimum number of bits N satisfying the lower bound measure when 1 mu epsilonPoSa：
Wherein A is1The gain of the fixed gain amplification block;
the program control gain of the program control gain amplification functional block;
for the highest gain of the programmable gain amplification block, K represents the sensitivity coefficient of the strain sensor, UsRepresents the wheatstone bridge voltage; u shapeRefAdThe reference voltage is the reference voltage of the analog-to-digital conversion in the stoping function block during the bridge compaction, and epsilon represents a strain value;
2) the resolution of strain voltage is controlled in strain acquisition, and the sampling resolution of a strain signal is the same as that of a bridge source power supply;
3) the voltage digital-to-analog conversion resolution design method of the return-to-zero DAC comprises the following steps:
calculating an error value delta U under the sampling resolution according to the designed maximum return-to-zero errorOAdThe calculation formula is as follows:
calculating the number of return-to-zero digital-to-analog conversion bits NDacError value of output Δ UODaNumerically, on
By error value Δ UODaNot greater than the maximum return-to-zero error, and calculating the minimum return-to-zero digital-to-analog conversion digit N of the error value of the sampling resolutionDacNamely:
4) equivalent input noise voltage delta U of fixed gain amplification blocknrmsShould be numerically below the lower limit εMinOutput voltage of lower strain signal conversion function block
Half of, numerically
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