CN109974570B - Differential inductance type displacement sensor and measuring method - Google Patents
Differential inductance type displacement sensor and measuring method Download PDFInfo
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Abstract
The invention discloses a differential inductance type displacement sensor and a measuring method, comprising a response circuit and a processing circuit, wherein the response circuit comprises a near sensing coil and a far sensing coil, the near sensing coil is close to a target, and the far sensing coil is positioned between the near sensing coil and the processing circuit; the processing circuit comprises an analog-to-digital converter (ADC), a driving logic module and a processing logic module; the near sensing coil and the far sensing coil are respectively connected with the processing circuit through connecting cables; the driving logic module is used for periodically and synchronously exciting the two sensing coils of the response circuit; the response is output to the analog-to-digital converter ADC through the differential amplifier INA, and the processing logic module samples the difference response voltage through the analog-to-digital converter ADC to obtain response waveform characteristics and calculate and convert the response waveform characteristics into the detected approaching distance.
Description
[ technical field ] A method for producing a semiconductor device
The invention belongs to the field of sensors, and relates to a differential inductance type displacement sensor and a measuring method.
[ background of the invention ]
The position and the stroke of a transmission part need to be detected in the operation control processes of manufacturing, metallurgy, chemical industry, electric power traffic, biomedical science and aerospace, so that the research of a displacement sensor is generally concerned and valued in the industry and becomes a hot spot of continuous development; among them, the inductive displacement sensor (differential IPS) has the advantages of no mechanical contact, safety, durability, reliability, strong environmental adaptability, etc., and can be widely applied, especially in the aviation field with high requirements; with the development of large-scale and automatic aircrafts, the monitoring requirements of the target position of a transmission part become more and more, and monitoring points on the outer side of the aircraft are in severe environments such as dust, oil stain, water mist, icing, acousto-optic interference, low temperature in cruising and the like, so that high requirements are provided for the environmental adaptability of a displacement sensor. The environment temperature range of aviation displacement detection is-55- +125 ℃, and the relative position change of the differential IPS detection sensing coil and the target is angle or straight line change. The angle change detection range is usually 0-30 degrees, and the measurement precision of 0.2-0.5 degrees is usually required; the linear variation range is usually 1-5 mm, and the measurement precision of 0.2-1.0 mm is generally required; the continuously improved differential IPS is used for dynamic control of airplane landing gear, cabin door, wing panel, engine reverse thrust and the like, adopts a fully-closed structure, is resistant to pollution and severe environment, and plays an indispensable role in detection of movement positioning of airborne electromechanical components.
However, due to the particularity of the space environment, the general industrial type differential IPS has difficulty meeting the specification requirements in the field of aviation:
aviation reliability requirements limit computation-intensive algorithms, and avoid the use of process control components, such as single-chip Microcomputers (MCUs) and Digital Signal Processors (DSPs), because such components contain a large number of register units, any logic state error can cause control failure; the number of maneuvering displacement detection points on the aircraft is more and more, most of the detection points belong to causal working relations, the failure probability is increased due to process control components, the common high-precision industrial differential IPS for measuring inductance based on a phase detection method uses MCU or DSP process control components, and the performance index of the whole aviation machine is difficult to ensure (the mean time between failure and failure (MTBF) is required to be more than 200000 h).
The environment requirement of the airborne equipment on the aviation has stricter limitation and wider frequency range on the test standard of radio frequency energy emission than the common industrial general electromagnetic compatibility standard of the same type; the common industrial differential IPS can not meet the requirement of the test standard, for example, a magnetic resistance type proximity sensor uses a large current larger than 500mA to drive a sensing coil, and generates switching value output related to the distance by using the change of the magnetic resistance, so as to obtain the measured proximity distance. Due to electromagnetic oscillation in the open magnetic circuit of the sensing coil, the limit of radio frequency energy emission cannot be met.
The sensing coil is wound by a high-temperature-resistant enameled wire (oxygen-free copper), the temperature coefficient is 3950 ppm/DEG C, the working temperature range of the avionic device is (-55- +125 ℃), and the total temperature drift of the corresponding resistance component is larger than 71%, so that a large distance measurement error is caused.
The general differential IPS digital detection method is characterized by applying sinusoidal excitation to a sensing coil, collecting the response voltage (current) waveform of the sensing coil, separating the resistance and inductance components of the differential IPS sensing coil according to the phase and amplitude difference of the waveform, comparing a set threshold value or a table look-up method to obtain the detected approach distance, improving the distance measurement precision by inhibiting the resistance temperature drift of the coil, and quantitatively outputting. Due to the complex control process, MCU or DSP parts are needed, the power consumption and hardware cost are high, and the MTBF performance is difficult to reach the standard.
The general differential IPS simulation detection method is characterized in that step excitation is applied to a sensing coil, the magnitude of a response value at a fixed moment is compared with the magnitude of a set threshold value, the magnitude relation (qualitative measurement) between a detected approaching distance and the set threshold value can be obtained, the circuit is simple, the detection method can be compensated by a customized thermistor, but the working temperature range is narrow, the distance measurement precision is low, the temperature parameter drift of a simulation element is limited, and the stability is limited.
According to the traditional differential IPS analog detection method used in the field of aviation, a voltage-controlled oscillator is used for periodically exciting a sensing coil, response current is converted into output voltage in direct proportion to inductance through an analog circuit, compared with a set threshold value, a pulse output signal representing an approaching distance is obtained, a narrow pulse starting trigger of the oscillator locks a displacement signal output by a comparator, and stable level output is obtained through filtering. The approach distance threshold value can be set by selecting parameters of the simulation element, however, instability caused by temperature drift of the simulation element needs compensation adjustment, only qualitative output is required, and the function is limited.
A novel digital differential IPS detection method special for aviation is provided at present, and the method uses a programmable logic device to control an analog-to-digital converter to apply step excitation to a sensing coil, performs high-speed sampling on a response waveform for a period of time, and completes waveform integral value calculation. A one-dimensional lookup table is established according to the relation between the value and the proximity distance to obtain the proximity distance, the lookup table method simplifies calculation, and verification by using a process control assembly is avoided, so that the measurement resolution of +/-0.1 mm can be achieved by measuring 0-5 mm at normal temperature. However, the method cannot separate the resistance and inductance components of the differential IPS sensing coil, and the measurement error caused by the change of the ambient temperature is too large to be matched with the ideal measurement resolution. Accurate measurement over the full temperature range cannot be achieved.
The dimension reduction table look-up method reduces the complexity of on-line calculation, greatly compresses the scale of the look-up table, improves the reliability and has potential for performance development; however, further deep analysis shows that the change range of the fixed time sampling value in the model along with the approaching distance is limited due to the nonlinear distribution relationship between the inductance component of the sensing coil and the approaching distance, which is about 27% of the dynamic range of an analog-to-digital converter (ADC), the actual conversion utilization rate is low, the measurement resolution which is expected to be improved is limited, and the bottleneck for continuously improving the detection accuracy of the differential IPS method is formed.
[ summary of the invention ]
The present invention is directed to overcoming the above-mentioned disadvantages of the prior art and providing a differential inductive displacement sensor and a measuring method thereof
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a differential inductive displacement sensor comprising:
the response circuit comprises a near sensing coil and a far sensing coil, the near sensing coil is close to the target, and the far sensing coil is positioned between the near sensing coil and the processing circuit; and
the processing circuit comprises an analog-to-digital converter (ADC), a driving logic module and a processing logic module; the near sensing coil and the far sensing coil are respectively connected with the processing circuit through connecting cables; the driving logic module is used for periodically and synchronously exciting the two sensing coils of the response circuit; the response is output to an analog-to-digital converter ADC through a differential amplifier INA;
the processing logic module samples the difference response voltage through the analog-to-digital converter ADC, obtains response waveform characteristics, and calculates and converts the response waveform characteristics into a detected approaching distance.
The invention also discloses a measuring method adopting the differential inductive displacement sensor, which comprises the following steps:
(1) establishing a detection circuit of a differential IPS: the differential IPS is a symmetrical response circuit formed by two sensing coils, the near sensing coil is closer to a target, and the sensitivity of an inductance component to displacement is high; the far sensing coil is positioned between the near sensing coil and the processing circuit; the environmental temperature influences of the resistance components of the near sensing coil and the far sensing coil are the same; the two symmetrical responses are subjected to difference and amplification and output to an analog-to-digital converter (ADC) for digital processing;
(2) establishing a difference IPS table look-up algorithm: after responding to the unique inflection point of the waveform, establishing two independent constraint relations through twice sampling, and realizing the table look-up calculation of the proximity distance through the unique corresponding relation between the sampling vector and the environment variable formed by the temperature and the proximity distance;
(3) dimension reduction of a difference IPS table look-up algorithm: setting the second sampling moment to be large enough, separating the constraint relation between the sampling vector and the proximity distance and the environmental temperature, splitting the two-dimensional lookup table into a plurality of table heads or indexes, and simplifying the two-dimensional lookup table into two one-dimensional lookup tables by combining a linear interpolation method;
(4) and (3) calibrating differential IPS: under the set calibration temperature, a precision translation stage is used, the approach distances between the sensor and the target are controlled to reach all calibration points in sequence, the corresponding relation between a first sampling value and the approach distances is recorded, and a high-temperature lookup table and a low-temperature lookup table are obtained;
(5) the calculation of the temporary lookup table is simplified: high and low temperature look-up tables are calculated and stored as M by off-line calculation during calibrationiAnd NiA constructed calibration operator;
(6) on-line lookup calculation of differential IPS: in the detection process, a temporary lookup table is generated by calculation by using the calibration operator and the second real-time sampling value, and the detected approaching distance is obtained by searching the temporary lookup table by using the first sampling value.
Compared with the prior art, the invention has the following beneficial effects:
the response circuit comprises a far sensing coil and a near sensing coil which are symmetrical, and the responses of the two symmetrical circuits are subjected to difference amplification and then sampled, so that the detection sensitivity is improved. The invention is used for various systems of landing gear, passenger and cargo cabin door, aileron, thrust reverser and the like of aviation and spacecraft. With the gradual opening of civil aviation and military markets, the invention has wide application and great economic and social benefits. Compared with the prior art and products, the invention can avoid using process control components such as a single chip microcomputer, a digital signal processor and the like, utilizes simple high-reliability components and parts, combines an innovative circuit structure and a digital processing algorithm, and obviously improves the sensitivity and the resolution of the sensor. The digital separation of the impedance parameters of the sensing coil enhances the temperature adaptability of the sensor and reduces the measurement error. Wide application prospect and great economic and social benefits.
The method of the invention continues the linear interpolation and the table look-up method in the dimension reduction table look-up method, inherits the advantage of low calculation complexity of the dimension reduction table look-up method, increases the ratio of two fixed-time sampling values in the dynamic range of the analog-to-digital converter ADC by the differential IPS of the differential structure, and improves the effective ranging resolution of the differential IPS; and, the differential IPS can enhance the anti-interference capability of the system and the adaptability to the length of the connecting cable. The differential-dimensionality reduction differential IPS designed by the invention uses 61 lookup table units to realize numerical decoupling calculation of the impedance vector of the sensing coil. The performance verification of the differential IPS shows that compared with the single-end differential IPS, the measurement resolution is improved from 135.5LSB/0.10mm to 1201.4LSB/0.10mm, the interpolation calculation error is reduced from 99.376 mu m to-3.240 mu m, and the improved differential-dimension-reduction differential IPS has obvious measurement precision advantage in the similar differential IPS method.
[ description of the drawings ]
FIG. 1 is a circuit configuration diagram of a differential inductive displacement sensor;
FIG. 2 is an equivalent circuit diagram of a proximity sensing coil;
FIG. 3 is a graph of the inductance component of the proximity sensing coil versus proximity distance;
FIG. 4 is a waveform of a response of a single-ended inductive displacement sensor;
FIG. 5 is a response waveform of a differential inductive displacement sensor;
FIG. 6 is a non-linear relationship of differential response and ambient temperature;
fig. 7 is a graph of the maximum response variation of differential and single-ended sensors over the dynamic range of an analog-to-digital converter ADC.
[ detailed description ] embodiments
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present disclosure. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present. In addition, if a layer/element is "on" another layer/element in one orientation, then that layer/element may be "under" the other layer/element when the orientation is reversed.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1-7, the differential inductive displacement sensor of the present invention is mainly composed of a sensing coil and a processing circuit. The sensing coil is an iron core coil wound by an oxygen-free copper wire, and the local open magnetic field of the sensing coil is changed along with the distance between the coil and the target, so that the sensing coil is expressed as the sensitive characteristic of inductance component; the processing circuit applies excitation to the sensing coil, detects response at the measuring node, calculates IPS inductance parameters and outputs the approach distance between the sensing coil and the target; the sensing coil comprises a resistance component and an inductance component, wherein the inductance component is very small in change along with temperature, is very sensitive to close distance and represents the size of the close distance; the resistance component varies slightly with the approach distance, but its temperature drift is not negligible. IPS for aircraft generally requires: the displacement measurement precision of 0.2-1.0 mm is achieved within the range of 1-5 mm, the temperature coefficient of a sensing coil formed by winding a high-temperature-resistant oxygen-free copper wire is 3950 ppm/DEG C, and the total drift caused by the temperature change of resistance and inductance components of the sensing coil exceeds 71% within the range of-55 to +125 ℃ of the working environment temperature, so that the IPS measurement precision is influenced. For this reason, suppressing the temperature drift of the resistance component becomes a key issue that revolutionizes IPS design.
The differential IPS according to the present invention has a specific structure as shown in fig. 1. The differential IPS is a symmetrical response circuit formed by two sensing coils, and the response is output to the ADC after being subjected to difference and amplification; the near coil is closer to the target, its inductive component LinThe sensitivity to displacement is high; the far coil is arranged between the near coil and the processing circuit, is relatively far away from the target, and has an inductance component LifLess displacement sensitivity of (d); resistive component r of the near and far coilsinAnd rifThe same environmental temperature effect is obtained; the parameter values for a typical IPS are: inductance component L of the near coilinThe variation is about 4.9-9.5 mH; inductance component L of remote coilifThe variation becomes significantly smaller; resistance component r at 20 DEG CinAnd rifAbout 13.2 omega, the temperature drift is 3950 ppm/DEG C, and the change is about 9.3-18.7 omega within the range of ambient temperature of-55 to +125 ℃. For the manufacturing deviation of the coil, the impedance vector of the far coil is 95% of that of the front coil, and the displacement sensitivity of the inductance component of the far coil is 10% of that of the near coil; according to the current-limiting condition that the coil current is less than 20mA, the current-limiting resistor R of the discharge loopnAnd RfAnd is chosen to be 300 omega.
The near and far coils form a symmetrical response circuit, and the driving logic module passes through the switch tube MnAnd MfPeriodically and synchronously exciting sensing coil, two symmetrical measuring nodesThe above responses are output through a differential amplifier INA (INA), and the processing logic module samples the differential response voltage through an ADC (analog to digital converter), acquires the response waveform characteristics, and calculates and converts the response waveform characteristics into the detected approaching distance. The near and far coils are connected with the processing circuit through equal-length cables: the integrated IPS cable is short, and cable distribution parameters can be ignored; the non-integrated IPS is formed by connecting a plurality of sensing detection units to a multi-channel processing circuit through cables. The connecting cable is equivalent to a resistor rwAnd equivalent inductance LwIn series with the equivalent capacitance CpAnd (4) connecting in parallel. Measured for a typical unshielded twisted pair cable, Lw＝457nH/m，rw84.7pF/m, equivalent capacitance Cp72.4 pF/m. The parasitic parameters of the cable are far smaller than the impedance vector of the sensing coil, the temperature drift influence is relatively negligible, the cable resistance can be calculated and separated by a circuit equation like the resistance component of the sensing coil, and the influence of temperature change on detection is well inhibited.
Mathematical model of sensor
The equivalent circuit structures corresponding to the near coil and the far coil are the same. Equivalent circuit of the near coil, as shown in FIG. 2, inductance component LinResistance component rinEquivalent inductance component L of the cablewnAnd an equivalent resistance rwnForm a series circuit, can incorporate Lin+Lwn＝Lan，rin+rwn＝ran。UsThe driving logic periodically closes the switch tube for direct current driving voltage, and step excitation of the circuit is realized. Due to LanAnd cable equivalent capacitance CpnThe equivalent circuit is a second-order inertial system. U for measuring voltage response waveform of nodeCn(t) represents, which is also the equivalent capacitance CpnThe response voltage of (c); u shapeLn(t) represents LanThe response voltage of (c); i.e. iLn(t) and iCn(t) each represents a flow of LanAnd CpnThe current of (2).
The equivalent circuit is constrained in the form of a second order differential equation. Slave Us +Warp Rn、ran、LanTo Us -Current loop and slave Cpn +(Ucn +) Warp ran、LanTo Cpn -(Ucn -) The current loop of (A) corresponds to two independent Kirchhoff (KVL) equations
Substituted into energy storage element CpnAnd LanVoltage-current condition (VCR) of (A) to (B) to obtain
Wherein the variable is the response voltage UCn(t) and the inductor current iLn(t) of (d). Elimination of iLn(t) obtaining a compound containing only UCnDifferential equation of (t)
The characteristic root of the equation is
The form of the feature root determines the characteristics of the response waveform. When the characteristic root is two conjugate complex numbers, the second-order inertia system is in an underdamped state, and response waveform oscillation is attenuated. When the characteristic root is two real numbers, the second-order inertia system is in an over-damping state, the response waveform of the measurement node is firstly raised from low (mainly caused by capacitance charging) and then gradually lowered (mainly caused by inductance charging) along with the time, and finally converges to the response voltage final value controlled by pure resistance voltage division, and the response waveform only has one inflection point after the zero moment. The characteristic root is a critical state of two states when the characteristic root is two equal real numbers.
And at a fixed delay moment after the rising edge of the step excitation is generated, acquiring a plurality of sampling points on the response waveform, and calculating the parameters of the electronic element of the tested circuit by using a table look-up method by using a sampling vector, wherein an equation set of a constraint look-up table is required to have a solution to the input of the sampling vector and only one solution is required. The requirement is that the curves forming the system of equations are (locally) monotonous. Only when the second-order inertia system is in an over-damping state, the response waveform only has one inflection point, and the response characteristic before the inflection point is formed by charging parasitic capacitance in an equivalent circuit. Because the capacitor is a cable distributed parasitic capacitor, the alternating current impedance of the capacitor is far smaller than that of the sensing coil, and the influence on the response waveform is quickly reduced along with the charging approaching saturation; the main characteristics of the response waveform after the inflection point moment are restricted by the inductive charging of the sensing coil.
And controlling the parameter ranges of the sensing coil and the cable to enable the corresponding inertial system to be in an over-damping state, and performing sampling and table look-up calculation by using the part after the inflection point moment of the response waveform. The relevant parameters need to satisfy the conditions
(RnCpnran+Lan)2-4RnCpnLan(Rn+ran)>0 (5)
The parasitic capacitance of the cable is a main factor causing the second-order inertial behavior of the response waveform, and the shorter the length of the cable is, the closer the response waveform is to a first-order system, and the farther the response waveform is from an underdamped state. Therefore, the cable length is a main factor that affects whether the above-mentioned constraint condition is satisfied. The above constraint relationship can be considered as the relationship between the magnitude of the parasitic capacitance of the cable and the corresponding inertial system damping state:
f(Cpn)＝(Rnran)2Cpn 2-2RnLan(ran+2Rn)Cpn+Lan 2>0 (6)
all parameters in the formula are characterized by physical quantities, which are positive and real. So that the quadratic function f (C)pn) Has an upward opening and has a positive coordinate of the axis of symmetry. f (C)pn) Passing point (0, L)an 2) There are two focal points with horizontal zero coordinate axis, and the abscissa of the two focal points is set as C0LAnd C0R. And when CpnLess than constant C0LOr greater than a constant C0RWhen f (C)pn) The function value of (1) is positive, and the second-order inertial system is in over-resistanceA nylon state; cpnGreater than constant C0LAnd is less than a constant C0RWhen f (C)pn) The function value of (1) is negative, and the inertial system is in an underdamped state; cpnIs equal to a constant C0LOr C0RWhen f (C)pn) The function value of (a) is zero, and the inertial system is in a critical damping state. Constant C0LAnd C0RThe formula can be used to calculate:
using sensing coil parameters of typical aviation-specific IPS and equivalent measurement parameters of a specific cable at normal temperature (r)in13.2 Ω), typically close to a distance threshold of 3.5mm (L)in5.1mH), the cable length is 100m, the equivalent circuit parameters obtained by calculation are: equivalent inductance Lan5.15mH, equivalent capacitance CpnEquivalent resistance r of 7.24nFan21.67 Ω. Selective current limiting resistor Rn300 Ω, constant C0L＝13.80nF，C0R45.40 μ F. Due to Cpn<C0LFor a sensor coil with typical parameters, a 100m long cable is used, and the second-order inertial system is in an over-damped state. The cable length will not normally exceed 20m, so the second order inertial system is stable in an over-damped state.
From the damping state of the equation, the solution of the system of equations can be made clear
Wherein, the general solution constant An1And An2Can be solved by using initial conditions; the solution Q (t) can be determined from the excitation signal.
The drive logic controls the on-off of the switch tube, periodic step excitation is applied to the sensing coil, and all energy storage devices finish discharging after sufficient delay before the rising edge of the step excitation appears. Therefore, the rising edge of the step stimulus produces a zero state response. As can be seen from the equivalent circuit, the step signal is just established (corresponding to 0)+Time of day), total equivalent inductance LanEquivalent capacitance C of cable as short circuitpnMeasuring node voltage U as open circuitCnSubject only to the total equivalent resistance ranAnd a current limiting resistor RnHigh voltage U for step excitationSAnd (4) partial pressure restriction. Get the special solution of the equation
The initial condition of the equivalent circuit in the zero state is the total equivalent inductance LanDischarging completely, and the current in the inductor is zero; equivalent capacitance C of cablepnAnd the capacitor is completely discharged, and the voltage on the capacitor is zero. Obtaining system zero state constraints in conjunction with VCR
Substituting the initial conditions into the formula (8) and the formula (2) to obtain a general solution constant A of the equationn1And An2Two independent constraints of
Thereby solving for the common solution constant. The solution for the inertial system is:
wherein, USIs a step drive high level.
The relationship of the inductance component of the proximity coil to the proximity distance is obtained by calibration, as shown in fig. 3. When U is turnedSResponse waveforms for various approach distances (20 ℃,10m cable) were plotted at 3.3V, as shown in fig. 4, all response characteristics were in an over-damped state; each response has a unique inflection point after time zero. The inflection point moment is constrained by
The response waveform of the unique inflection point moment after the moment greater than zero is in monotone decreasing distribution. The time domain characteristics of the sensor coil reflect the approaching distance between the sensor coil and the target, and form a functional relation.
The coil parameters can be calculated by only using the response loop of the near coil and collecting the voltage of the measurement node of the near coil through the ADC, so that the near distance is obtained. Single-ended IPS based on earlier studies herein have been mass produced. However, the main disadvantages of such IPS are: the change of the approach distance causes the change range of the response waveform at the sampling moment, the occupation ratio in the dynamic range of the ADC is very small, the sensitivity of the sensor is greatly limited, and the change is specifically shown as follows:
in order to counteract the inconsistency of the ADC reference source and the step-drive power supply, the same power supply is selected to supply power to the ADC reference source and the step-drive module. The ADC sampling value directly reflects the proportion of the response waveform in the step excitation high level, the design requirement of the power supply is reduced, and the calibration process is simplified. However, the single-ended response accounts for a limited proportion of the high level of the step excitation along with the variation of the approach distance;
in order to tolerate the deviation of mechanical manufacturing, generally, the range of 0-1.0 mm is not detected; the range of 1.0-5.0 mm is the main detection range. However, the sensitivity of the sensor coil has a nonlinear relationship with the proximity distance (fig. 3), and the detection sensitivity is high in the secondary range where the proximity distance is small, and is low in the primary detection range where the proximity distance is large.
As shown in fig. 4, the time when the change amount of the single-ended response with the change of the distance is large is about 18.24 μ S, and at this time, the response waveform change amount is 738.7mV within the range of 0-7 mm (accounts for 22% in the ADC dynamic range); 273.6mV (8.3% in percentage) in the range of 1.0-7.0 mm. In practical application, only less than 8.3% of ADC dynamic range can be fully utilized, and IPS detection sensitivity is limited.
A far coil is added on the single-ended IPS and assembled between the near coil and a processing circuit to form a differential IPS. Since the far coil is far from the target, its inductance component is less affected by the change in the proximity distance than the near coil. A symmetric drive circuit is designed for the near and far coils. The response at the measurement node is differenced and amplified by a differential amplifier INA and re-sampled. To improve the ratio of response variation over the dynamic range of the ADC. The response of which is constrained to an equation of
The response of the differential IPS can be found using the response of a single-ended IPS, and as shown in fig. 5, the ratio of the amount of change in the near and far coils in the ADC dynamic range is significantly improved by differencing the amplified signals with respect to the response of the coil. The inductance component sensitivity of the far coil is set to decrease to 10% of that of the near coil. Considering process variations, assume that there is a 5% deviation in the resistive and inductive components of the near coil from that of the far coil. The cable length was set to 20m and the gain a was set to 10. The time when the response variation with the distance variation is large is about 22.26 mus, and the response variation is 2470.3mV in the range of 1-7 mm (accounting for 75% in the dynamic range of the ADC). The response waveform has a unique inflection point.
Dimension reduction table look-up method for differential circuit
In the constraint equation (equation 14) of the differential response circuit, A is fixed gain, UsIs a step-excitation high voltage, R, with fixed parametersnAnd RfIs a current-limiting resistor with fixed parameters, CpnAnd CpfIs a fixed parameter equivalent capacitance of the cable; l isanAnd LafThe total equivalent inductance containing the inductance component of the sensing coil changes along with the change of the approaching distance; ranAnd RafThe total equivalent resistance containing the resistance component of the sensing coil changes along with the change of the environmental temperature; a. then1、An2、Af1、Af2、pn1、pn2、pf1And pf2Are intermediate parameters and can be calculated from other parameters according to the constraints in equation 14; the total equivalent inductance and resistance L of the near and far response loops in equation 14an、Laf、RanAnd RafIs an unknown variable and is affected only by two independent factors, namely the approach distance and the ambient temperature. According to the characteristics of the differential response waveform, two independent constraint relations are established by sampling twice after the unique inflection point of the response waveform, and the sum of the sampling vector and the temperature can be establishedUnique correspondence between proximity-distance-constituting environment variables
Wherein, Ud1And Ud2Is the response value (sample value) at two fixed times, D is the approach distance of IPS and target, T is the ambient temperature, and a is the fixed gain. The inductance component and D can be established by calibrationnThe relationship of (2) (FIG. 3); the relationship of the resistance component to T can be established by the temperature coefficient of resistance (3950 ppm/deg.C). Realizing the table look-up calculation of the proximity distance by the unique corresponding relation between the sampling vector and the environment variable formed by the temperature and the proximity distance, and sampling the vector (U) in real timed1,Ud2) And retrieving the approach distance.
Two-dimensional look-up tables for 14-bit (or higher precision) ADCs are large in scale. Because the differential model improves the ratio of the sampling vector variation range in the dynamic range of the ADC, the method of compressing the lookup table by means of coil parameter definition range is limited. The two-dimensional lookup table is subjected to dimensionality reduction by utilizing approximate linear distribution of sampling vectors and temperature and linear interpolation, and the method is an effective means for reducing storage and retrieval expenses.
With sufficient delay, the differential response approaches the response end value. The equivalent inductance and the parasitic capacitance are considered to be fully charged, and the response final value is only controlled by the voltage division of the resistance in the circuit and is independent of the approaching distance (inductance component). The second sample time is set to "infinity" (greater than 250 μ S in this example), a sample vector (U)d1,Ud2) The constraint relationships with D and T are separated. Equation (15) is simplified to:
thus, with respect to the sampling vector (U)d1,Ud2) And two-dimensional constraints (equation (15)) of the environment vectors (D, T), are reduced to a number of U's corresponding to different T' sd1And constraint of D. Structurally, the two-dimensional lookup table is divided into a plurality of tables with head (index) only related to T and table (content) only related to DA related one-dimensional look-up table.
t1At the optimum value. Let t2Corresponding to the final value of the response, then t1Is the only valid sample in response to a waveform change. Will t1The time when the response waveform changes the most is set to obtain the highest detection resolution. The time when the response waveform changes most in fig. 5 is 22.26 μ S. Since this time is close to the only inflection point of the response (fig. 5), t can be set1The time is prolonged appropriately.
Calibrating U at each constant temperature pointd1The relationship with D cannot be realized in practice. The approximate linear relationship among the relationships is utilized to carry out interpolation calculation, and a small amount of relationships are used to calculate other relationships, so that the constant temperature calibration times can be reduced. Setting t according to typical parameters125.00. mu.S, cable length 20 m. Will Ud1Seen as a function of the arguments D and T. Solve the function Ud1Partial derivative function of (D, T) with respect to T
Calculating partial derivative values corresponding to the groups D, and converting the partial derivative values into numerical values (S) with the unit of the Least Significant Bit (LSB) of the 14-bit ADCd1) As shown in fig. 6. The curves in the diagram reflect the sampling values (S) corresponding to different Dd1) Non-linear with T. The curves in the graph are all close to the horizontal line (constant), then Sd1(T) is close to the diagonal. The nonlinear relationship is most severe when the approach distance is minimal: the accumulated (integrated) deviation over the T variation range is 0.11LSB (14 bit ADC). Therefore, see Sd1There is an approximately linear relationship with T and the total deviation within the typical parameter range is negligible for the sampling resolution of a 14-bit ADC.
Sampling value Sd1Has approximate linear relation with T, and only needs to establish S at two calibration temperatures by calibrationd1Corresponding to D, namely, under the premise of meeting error conditions, the S within the engineering range can be calculated by a calibration table through an interpolation algorithmd1The proximity distance is retrieved corresponding to the lookup table of D. Whereby the two-dimensional look-up table is reduced to two one-dimensional look-up tables.
On-line computing process
Differences in cable length and manufacturing variations lead to sampled values Sd1The corresponding relation of D and D needs to be calibrated once through calibration. Under the set calibration temperature, a precise translation stage is used to control the approach distance between the sensor and the target to reach all calibration points in sequence, and the sampling value S is recordedd1And D. Taking 0.1mm step as an example, each group of one-dimensional lookup tables includes 61 groups of sampling values S within the range of 1-6 mmd1The relation between D and T corresponding to D.
Calibrating a sample value S at two different fixed calibration temperaturesd1In relation to D, i.e. samples S corresponding to 61 sets of index pointsd1And obtaining a high-temperature calibration table and a low-temperature calibration table. The two sets of 61 sampled values (S) are sampled and recorded by means of a precision translation staged1L_10～Sd1L_70And Sd1H_10～Sd1H_70) And corresponding (S) at two calibration temperaturesd2L,Sd2H). This information constitutes the complete calibration data. In the measuring process, the sensor detection circuit obtains a real-time sampling vector (S) through the ADCd1,Sd2). At Sd2The corresponding interpolation position can be used for solving a group of sampling values S by utilizing a high-temperature calibration table and a low-temperature calibration tabled1And D, i.e., a temporary look-up table, to retrieve the approach distance at the current temperature. Real-time measurement of S at ambient temperatured1The relationship between D and D is different from the relationship recorded in the high and low temperature calibration tables. Sd1And T (and S)d2There is a unique correspondence) there is an approximately linear relationship. Sampling value S at real-time temperatured2And the sampling value (S) at the calibration temperatured2L,Sd2H) The proportion relation determines the interpolation proportion for calculating the temporary lookup table, and the temporary lookup table can be obtained through the linear interpolation calculation of the calibration data. Further sampling the real-time value Sd1And carrying out one-dimensional search in the temporary lookup table to obtain the detected approaching distance.
High and low temperature calibration tables and real-time sampling value S are utilized in IPS on-line detection processd2According to the formula
Calculate a temporary look-up table (S)d1T_i). The calculation to generate the temporary lookup table is an online calculation. The introduction of operators further simplifies the online calculation by the method that
Wherein M isiAnd NiIs a scaling operator calculated from the high and low temperature look-up tables. High and low temperature look-up tables are calculated and stored as M by off-line calculation during calibrationiAnd NiAnd forming a calibration operator. During detection, the calculation for generating the temporary lookup table is simplified into a real-time sampling value Sd2And the on-line calculation load is reduced by one multiplication and addition operation with a calibration operator.
As shown in Table 1, the calibration data is composed of 61 sets of calibration operators MiAnd NiComposition of (S) in the original calibration data2L,S2H) Has been calculated and mixed in the scaling operator MiAnd NiIn (3), separate recording is not necessary. The IPS on-line detection and calculation process comprises the following steps:
1) applying step excitations to the proximal and distal coils;
2) obtaining a real-time sample vector (S) at two fixed delay instantsd1,Sd2)；
3) Will Sd2Performing 61 times of multiply-add operation to obtain a temporary lookup table (S) in place of formula (18)d1T_i)；
4) Using Sd1Comparing with the data in the temporary lookup table in the order of the search distance from small to large when Sd1Greater than the data (S) in the temporary look-up tabled1T_i) Stopping retrieval when the search is finished;
5) and determining the measured approaching distance as the position of a calibration point for stopping retrieval, wherein the position corresponds to x multiplied by 0.1mm in the table.
Table 1 lookup table storage, calculation and retrieval process
Thereby obtaining a difference IPS calculation method based on the table look-up. The method has the advantages of low storage and retrieval overhead, simple online calculation and avoidance of using process control components such as MCU or DSP.
Evaluation of Effect
A direct advantage of differential IPS is the large fraction of the change in response with distance over the ADC dynamic range. The sampling precision of the ADC is fully utilized. Using a typical parameter (t)125.00 μ S,20m cable), the maximum sample variation range for single-ended IPS and differential IPS is calculated, as shown in fig. 7. The maximum sampling variation range does not change much with the ambient temperature. Under the same conditions (1-7 mm), the maximum variation ranges of single-ended and differential IPS are 7.9% and 71.2% of the dynamic range of ADC, respectively.
And the dynamic range of the ADC is fully utilized, and the detection sensitivity of the IPS is improved. Differential and single-ended IPS detection sensitivity (t) at different approach distances and temperatures125.00 mus, 20m cable) is shown in table 2. The unit LSB/0.10mm in the table indicates the amount of change (in LSB of 14-bit ADC) that can be caused to the response waveform for every 0.1mm interval under the corresponding conditions. The detection sensitivity of both IPS decreases slowly with decreasing temperature and increases significantly with decreasing approach distance, with the maximum occurring at the lowest temperature and the lowest approach distance: the differential IPS is 1201.4LSB/0.10 mm; single-ended IPS is 135.5LSB/0.10 mm. The detection sensitivity of differential IPS under this condition is 8.8 times that of single-ended IPS.
TABLE 2 comparison of detection sensitivity
Due to the application of linear interpolation, a sufficiently small difference error is required to match the enhancement of the IPS detection sensitivity. This is the key to linear interpolation. The high and low calibration temperatures were set at 100 and 20 c and the differential error for differential and single-ended IPS was calculated for different approach distances and temperatures, as shown in table 3. The difference error (absolute value) of the two IPS increases with the extent to which the temperature is away from the high and low calibration temperatures. The difference error of the differential IPS is positive within the high and low calibration temperature range, and negative outside, and the law is opposite to that of the single-end IPS. The difference error (absolute value) of differential IPS increases with decreasing approach distance, the rule being opposite to that of single-ended IPS, which is a key advantage of the differential structure: although the differential error of the differential IPS is larger than that of the single-ended IPS in the part (upper left corner and upper right corner) in table 3, the significant increase in the detection sensitivity of the differential IPS (table 2) can cancel the distance error generated by the increase in the differential error as the approach distance decreases.
TABLE 3 distribution and comparison of Difference errors
Table 4 is a mapping of the difference error over distance. The data distribution shows that as the approach distance decreases, the differential IPS detection sensitivity increases significantly, not only offsetting the effect of increasing the difference error, but also causing the distance error to decrease as the approach distance decreases. The distribution of single-ended IPS difference errors, as opposed to differential IPS, increases the approach distance, increases the difference error, while decreasing the detection sensitivity. The fraction of increased difference error in reduced detection sensitivity is amplified and the range error increases at an accelerated rate. The maximum distance error of single-ended IPS is 99.376 μm (-55 ℃ C. 7.00 mm); the maximum distance error for differential IPS is-3.240 μm, only 3.3% of single-ended IPS. The practical value is obviously improved.
TABLE 4 mapping of differential error over approach distance
Aiming at the inductive displacement sensor, the invention assembles sensing coils at two positions close to and far away from a target and designs two groups of symmetrical response loops. By synchronous excitation two responses are generated, which are differentially amplified by a differential amplifier INA and then sampled by the ADC at two instants. And searching the approaching distance between the IPS and the target by using a new structure algorithm and a dimensionality reduction look-up table method for the sampling value. The performance improvement of the displacement sensor is obtained, and the method specifically comprises the following steps:
1. the difference value of the two changes of response changing with the approaching distance is differentially amplified by the differential amplifier INA, the ratio of the variation in the dynamic range of the ADC is obviously increased, and the calculation shows that the ratio can be improved from 8.3% to 75%, so that the conversion capability of the high-precision ADC is fully utilized, and the sensitivity and the resolution of the sensor ranging are greatly improved;
2. the two-dimensional lookup table is subjected to dimension reduction through linear interpolation by utilizing the approximate linear distribution of the sampling vector and the ambient temperature, so that the storage and retrieval expenses are obviously reduced;
3. analytical calculations show that differential IPS is also advantageous: as the approach distance decreases, the difference error of the differential IPS increases, but the detection sensitivity significantly increases, which cancels the effect of increasing the difference error and also causes the distance error to decrease as the approach distance decreases; at-55 ℃ and 1.0mm, the maximum distance error of the differential IPS is 72% of that of the single-ended IPS; at the temperature of minus 55 ℃ and 7.0mm, the maximum distance error of the differential IPS is only 3.3 percent of that of the single-ended IPS, so that the practical value is obviously improved;
4. as is known, the differential amplification structure can suppress common-mode signals, effectively resist the influence of external electromagnetic interference on a response loop, and improve the IPS electromagnetic compatibility;
5. the near sensing coil and the far sensing coil are in the same environment, and the influence of temperature change is differentially inhibited;
6. the near sensing coil and the far sensing coil are assembled in the same shell, and the detection controller is connected through equal-length cables, so that the influence of the cables is differentially inhibited, and the adaptability of the connection length is improved;
7. the differential-dimensionality-reduction IPS detection method is small in storage and retrieval, online calculation complexity is reduced, the use of a process control assembly can be omitted, resistance and inductance components of a sensing coil are separated through numerical decoupling calculation, and temperature adaptability of the IPS is improved.
According to specific requirements, the INA gain of the differential amplifier is increased, part of quantitative measurement with low engineering value and small ranging range is abandoned, and certain design flexibility can be expanded by replacing ranging resolution with higher target ranging.
The differential-dimensionality reduction IPS detection method provided by the invention uses 61 lookup table units to realize numerical decoupling calculation of the impedance vector of the sensing coil. The performance verification shows that compared with the IPS sampled by a single-coil response loop, the measurement resolution is improved from 135.5LSB/0.10mm to 1201.4LSB/0.10mm, the interpolation calculation error is reduced from 99.376 mu m to-3.240 mu m, and the method has obvious measurement precision advantage in similar IPS methods.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (6)
1. A method of measuring a differential inductive displacement sensor, the method employing a differential inductive displacement sensor, the sensor comprising:
the response circuit comprises a near sensing coil and a far sensing coil, the near sensing coil is close to the target, and the far sensing coil is positioned between the near sensing coil and the processing circuit; and
the processing circuit comprises an analog-to-digital converter (ADC), a driving logic module and a processing logic module; the near sensing coil and the far sensing coil are respectively connected with the processing circuit through connecting cables; the driving logic module is used for periodically and synchronously exciting the two sensing coils of the response circuit; the response is output to an analog-to-digital converter ADC through a differential amplifier INA;
the connecting cable comprises a first connecting cable connected with the near sensing coil and a second connecting cable connected with the far sensing coil, and the first connecting cable comprises a resistor r connected in serieswnAnd an inductance LwnAnd is connected to the capacitor CpnParallel connection; the second connecting cable comprises a resistor r connected in serieswfAnd an inductance LwfAnd is connected to the capacitor CpfParallel connection;
the processing logic module samples the difference response voltage through the analog-to-digital converter ADC to obtain response waveform characteristics, and calculates and converts the response waveform characteristics into a detected approaching distance;
the drive logic module passes through a switch tube MnAnd a switching tube MfPeriodically and synchronously exciting the sensing coil; wherein, the switch tube MnIs connected with the first connectionCable connected, switch tube MfIs connected with a second connecting cable; the first connecting cable outputs the response to the positive input terminal of the differential amplifier INA, and the second connecting cable outputs the response to the negative input terminal of the differential amplifier INA; characterized in that the method comprises the following steps:
(1) establishing a detection circuit of a differential IPS: the differential IPS is a symmetrical response circuit formed by two sensing coils, the near sensing coil is closer to a target, and the sensitivity of an inductance component to displacement is high; the far sensing coil is positioned between the near sensing coil and the processing circuit; the environmental temperature influences of the resistance components of the near sensing coil and the far sensing coil are the same; the two symmetrical responses are subjected to difference and amplification and output to an analog-to-digital converter (ADC) for digital processing;
the specific method for outputting the two symmetrical responses to the analog-to-digital converter ADC for digital processing is as follows:
inductance component L of the proximity sensing coilinThe sensitivity to displacement is higher than the inductance component L of the remote sensing coilifDisplacement sensitivity of (d); resistance component r of near and far sensing coilsinAnd rifThe same environmental temperature effect is obtained;
the driving logic module passes through a switch tube MnAnd MfPeriodically and synchronously passing through a current-limiting resistor RnAnd RfExciting the sensing coil, outputting responses on the two symmetrical measurement nodes through a differential amplifier INA, sampling differential response voltage through an analog-to-digital converter ADC by a processing logic module, acquiring response waveform characteristics, and calculating and converting the response waveform characteristics into a measured approaching distance;
taking the equivalent circuit of the near sensing coil as an example: inductance component LinResistance component rinEquivalent inductance component L of the cablewnAnd an equivalent resistance rwnForm a series circuit, incorporate Lin+Lwn＝Lan，rin+rwn＝ran；UsThe driving logic periodically closes the switch tube for direct current driving voltage to realize step excitation on the circuit; u for measuring voltage response waveform of nodeCn(t) represents the equivalent capacitance CpnThe response voltage of (c); u shapeLn(t) represents LanThe response voltage of (c); i.e. iLn(t) and iCn(t) each represents a flow of LanAnd CpnThe current of (a);
the equivalent circuit is constrained in the form of a second order differential equation, slave Us +Warp Rn、ran、LanTo Us -Current loop and slave Cpn +Warp ran、LanTo Cpn -The current loop corresponds to two independent kirchhoff equations, Cpn +Namely node Ucn +，Cpn -Namely node Ucn -The kirchhoff equation is as follows:
substituted into energy storage element CpnAnd LanVoltage-current conditions of (a) to obtain:
solving general solution constant A of second order differential equation by combining initial condition of energy storage element and excitation signaln1And An2And a special solution Q (t) to obtain the equation solution:
wherein, USIs a step excitation high level;
a far sensing coil is added on the differential IPS with the single-ended structure and assembled between the near sensing coil and the processing circuit to form the differential IPS; the response on the measurement node is subjected to difference calculation through a differential amplifier INA, amplified and re-sampled so as to improve the proportion of response variation in the dynamic range of an analog-digital converter ADC; the response constraint equation is as follows:
wherein A is fixed gain, UsIs a step-excitation high voltage, R, with fixed parametersnAnd RfIs a current-limiting resistor with fixed parameters, CpnAnd CpfIs a fixed parameter equivalent capacitance of the cable; l isanAnd LafThe total equivalent inductance containing the inductance component of the sensing coil changes along with the change of the approaching distance; ranAnd RafThe total equivalent resistance containing the resistance component of the sensing coil changes along with the change of the environmental temperature; a. then1、An2、Af1、Af2、pn1、pn2、pf1And pf2All parameters are intermediate parameters and can be calculated by other parameters according to the constraint in the formula; total equivalent inductance and resistance L of the medium and far response loopsan、Laf、RanAnd RafIs an unknown variable;
constrained by the formula (4), the differential IPS response waveform has a unique inflection point after the excitation zero moment;
(2) establishing a difference IPS table look-up algorithm: after responding to the unique inflection point of the waveform, establishing two independent constraint relations through twice sampling, and realizing the table look-up calculation of the proximity distance through the unique corresponding relation between the sampling vector and the environment variable formed by the temperature and the proximity distance;
(3) dimension reduction of a difference IPS table look-up algorithm: setting the second sampling moment to be large enough, separating the constraint relation between the sampling vector and the proximity distance and the environmental temperature, splitting the two-dimensional lookup table into a plurality of table heads or indexes, and simplifying the two-dimensional lookup table into two one-dimensional lookup tables by combining a linear interpolation method;
(4) and (3) calibrating differential IPS: under the set calibration temperature, a precision translation stage is used, the approach distances between the sensor and the target are controlled to reach all calibration points in sequence, the corresponding relation between a first sampling value and the approach distances is recorded, and a high-temperature lookup table and a low-temperature lookup table are obtained;
(5) the calculation of the temporary lookup table is simplified: high and low temperature look-up tables are calculated and stored as M by off-line calculation during calibrationiAnd NiConstructed scaling operators；
(6) On-line lookup calculation of differential IPS: in the detection process, a temporary lookup table is generated by calculation by using the calibration operator and the second real-time sampling value, and the detected approaching distance is obtained by searching the temporary lookup table by using the first sampling value.
2. The measurement method according to claim 1, wherein the specific method of the step (2) is as follows:
according to the differential response waveform characteristics, after the unique inflection point of the response waveform, two independent constraint relations are established through twice sampling, and the unique corresponding relation between the sampling vector and the environment variable formed by the temperature and the approaching distance is established:
wherein, Ud1And Ud2Is the response value at two fixed times, D is the approach distance of the differential IPS and the target, T is the ambient temperature, a is the fixed gain; realizing the table look-up calculation of the proximity distance by the unique corresponding relation between the sampling vector and the environment variable formed by the temperature and the proximity distance, and sampling the vector (U) in real timed1,Ud2) And retrieving the approach distance.
3. The measurement method according to claim 2, wherein the specific method of the step (3) is as follows:
the second sampling instant is set to "infinity", and the vector of samples (U)d1,Ud2) The constraint relationships with D and T are separated, and equation (5) is simplified as:
thus, with respect to the sampling vector (U)d1,Ud2) And two-dimensional constraints of the environment vector (D, T), reduced to a number of U's corresponding to different T' sd1And constraint of D;
t1at the bestA value; let t2Corresponding to the final value of the response, then t1Is only one effective sampling in the process of responding to the change of the waveform; will t1Setting the time when the response waveform changes maximally to obtain the highest detection resolution;
calibrating U at each constant temperature pointd1And D, performing interpolation calculation by using an approximate linear relation among the relations;
sampling value Sd1Has approximate linear relation with T, and establishes S at two calibration temperatures by calibrationd1The relation corresponding to D can calculate the S within the engineering range by the calibration table through the interpolation algorithm on the premise of meeting the error conditiond1Retrieving the approach distance corresponding to the lookup table of D; whereby the two-dimensional look-up table is reduced to two one-dimensional look-up tables.
4. The measurement method according to claim 3, wherein the specific method of the step (4) is as follows:
under the set calibration temperature, the approach distance between the sensor and the target is controlled to reach all calibration points in sequence, and the sampling value S is recordedd1And D;
calibrating a sample value S at two different fixed calibration temperaturesd1Relation with D, setting the number of calibration points as N, i.e. corresponding to the sampling values S of N sets of calibration pointsd1Obtaining a high-temperature calibration table and a low-temperature calibration table; sampling and recording the two groups of N sampling values and corresponding (S) at two calibration temperaturesd2L,Sd2H)；
Sd1An approximately linear relation exists between T and T; a temporary lookup table is calculated through linear interpolation of calibration data and used for retrieving the approach distance at the current temperature; sampling value S in real timed1Performing one-dimensional retrieval in the temporary lookup table to obtain the detected approaching distance;
high and low temperature calibration tables and real-time sampling value S are utilized in the differential IPS on-line detection processd2According to the formula:
calculate a temporary look-up table Sd1T_iFor retrieving the approach distance.
5. The measurement method according to claim 4, wherein the specific method of the step (5) is as follows:
the method for introducing operators to further simplify online calculation is as follows:
wherein M isiAnd NiIs a calibration operator calculated from the high and low temperature look-up tables; high and low temperature look-up tables are calculated and stored as M by off-line calculation during calibrationiAnd NiA constructed calibration operator; during detection, the calculation for generating the temporary lookup table is simplified into a real-time sampling value Sd2And a multiplication and addition operation with the scaling operator.
6. The measurement method according to claim 5, wherein the specific method of the step (6) is as follows:
the calibration data is calibrated by each N groups of calibration operators MiAnd NiComposition of (S) in the original calibration data2L,S2H) Has been calculated and mixed in the scaling operator MiAnd NiPerforming the following steps; the differential IPS on-line detection and calculation process comprises the following steps:
(6-1) applying step excitation to the near sensing coil and the far sensing coil;
(6-2) obtaining real-time sampling vectors (S) at two fixed delay instantsd1,Sd2)；
(6-3) adding Sd2Substituting formula (8) to perform multiplication and addition operation for N times to obtain temporary lookup table Sd1T_i；
(6-4) use of Sd1Comparing with the data in the temporary lookup table in the order of the search distance from small to large when Sd1Is larger than the data S in the temporary lookup tabled1T_iStopping retrieval when the search is finished;
and (6-5) determining the measured approaching distance as the position of the calibration point at which the retrieval is stopped.
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| CN113295080B (en) * | 2020-04-09 | 2023-04-21 | 上海信朴臻微电子有限公司 | Displacement sensor, displacement analysis system and analysis method |
| CN112284230B (en) * | 2020-10-09 | 2021-11-16 | 珠海格力电器股份有限公司 | Displacement detection device, displacement monitoring method and compressor |
| CN112161675B (en) * | 2020-11-03 | 2024-03-26 | 常州市鼎兴电子有限公司 | Design method for optimal matching parameters of capacitive liquid level sensor |
| CN112684510B (en) * | 2020-12-04 | 2024-03-29 | 西安理工大学 | Logic test excitation device of magnetic induction type proximity sensor for aviation |
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| US3405322A (en) * | 1966-06-22 | 1968-10-08 | Westinghouse Electric Corp | Load transient reflection suppressor with differential inductor means interposed in parallel line circuits between the source and load |
| GB1233234A (en) * | 1968-10-23 | 1971-05-26 | ||
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| CN101929832A (en) * | 2009-06-23 | 2010-12-29 | 冉进 | Method for measuring high-accuracy linear displacement |
| CN102778677B (en) * | 2012-05-29 | 2014-11-05 | 上海无线电设备研究所 | Long-distance pulse compression and short-distance pulse envelope detection delay measurement combined distance measuring method |
| CN204556804U (en) * | 2015-04-16 | 2015-08-12 | 三峡大学 | A kind of magnetic field measuring device of magnetic element |
| CN105928449B (en) * | 2016-04-28 | 2018-07-17 | 西安交通大学 | A kind of data processing method of inductive displacement transducer |
| CN206192263U (en) * | 2016-11-30 | 2017-05-24 | 山东盛康电气有限公司 | Tension for appearance displacement detect sensor |
| CN106767952B (en) * | 2017-02-28 | 2018-12-07 | 西安交通大学 | A kind of interference elimination method of inductive displacement transducer |
| CN207908433U (en) * | 2017-10-27 | 2018-09-25 | 中国石油化工股份有限公司 | Transient electromagnetic defectoscope Noise Suppression Device |
| CN109470311B (en) * | 2018-12-17 | 2019-09-06 | 吉林大学 | A kind of double hidden probe-type silo grain multi-parameter RF on-line measuring device and detection methods |
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