A method for automatically calibrating an inductive displacement sensor

Abstract

The present invention relates to a sensor detection technology, and discloses an automatic calibration inductance displacement sensor detection method, comprising an inductance displacement sensor to be tested, wherein a built-in coil of the inductance displacement sensor is equivalent to an internal resistance rc and an inductance L connected in series, a differential voltage across a sampling resistor and a standard resistor is measured through a detection circuit, a control and operation unit samples the differential voltage across the sampling resistor and the standard resistor, the control and operation unit operates the samples and obtains a calculated value of the standard resistor, the control and operation unit compares the calculated value with a rated value of the standard resistor to obtain a measurement loop gain coefficient Ks, and then the standard resistor is replaced by an inductance displacement sensor, the control and operation unit also samples the differential voltage across the sampling resistor and the inductance displacement sensor, and the impedance of the inductance displacement sensor is calibrated according to the gain coefficient Ks.

Description

Technical Field

[0001] The invention relates to a sensor detection technology, in particular to an automatic calibration inductive displacement sensor detection method. Background Art

[0002] The inductive displacement sensor is realized by sealing an inductive coil in a full metal shell. A measurement circuit is built to apply a periodic excitation signal to the inductive displacement sensor. The sensor emits an electric field or a magnetic field. When the displacement of the detected target changes, the change in the electric field or magnetic field will cause the impedance of the sensor itself to change. This change will affect the excitation signal applied to the sensor by the measurement circuit. The measurement circuit demodulates the change in the excitation signal to obtain the impedance value of the inductive displacement sensor, which is used to judge the displacement state of the target and realize displacement detection.

[0003] Since the inductive displacement sensor works based on electric or magnetic fields, it does not need to contact the detection target during the displacement detection process. It is a non-contact displacement detection, which overcomes the shortcomings of mechanical contacts that are easy to wear, easy to be contaminated, and require a limit mechanism. This type of sensor is gradually replacing the displacement detection mechanism based on mechanical micro switches, and is widely used in the industrial field and military and civil aviation aircraft.

[0004] With the widespread application of inductive displacement sensors, more and more users have proposed harsher operating environments, and expect that in such environments, sensors and their detection technologies can provide higher detection accuracy while also being able to monitor the health status of sensors and detection circuits themselves to expose hidden dangers in advance, and more accurately isolate and diagnose faulty components, thereby ensuring higher application reliability at lower maintenance costs.

[0005] In order to meet the requirements of use in harsh environments, inductive proximity sensor suppliers have developed various detection technologies, including pulse charge and discharge detection circuits based on time domain; low-frequency oscillation circuits based on differential coil compensation; and impedance analysis circuits based on frequency domain. However, these can only calibrate the sensor and its detection circuit before the product leaves the factory. Once the performance status of a component changes during use, the detection circuit cannot automatically complete the compensation, which ultimately leads to performance degradation or even loss of function in the application link. Maintenance personnel cannot even quickly and accurately determine the fault location and can only regularly detect and calibrate the equipment, which brings great inconvenience to the maintenance and guarantee link.

[0006] Although it is possible to simply introduce a switch circuit into the circuit to achieve calibration, the switches used are either relay mechanical contact type or analog switch electronic contact type. Mechanical contact switches have contact arc noise, and are prone to reliability issues such as poor contact after increasing the number of working times; analog switch electronic contacts have on-resistance, which has a large dispersion of on-resistance and a large uncertain temperature drift, which will introduce uncertain factors into the measurement circuit and make the calibration meaningless. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides an automatic calibration inductive displacement sensor detection circuit and a detection method thereof. By building a simple circuit, designing a reasonable signal extraction and calibration method, and implementing a calibration step before measurement, the accuracy of the detection circuit is improved, and the problem that the current detection technology cannot accurately isolate the inductive displacement sensor and the detection circuit fault is effectively solved. At the same time, because a synchronous full differential structure is adopted, the switch contact problem and the uncertain influence of the on-resistance are avoided.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for automatically calibrating an inductive displacement sensor comprises an inductive displacement sensor to be tested, wherein a built-in coil of the inductive displacement sensor is equivalent to an internal resistance rc and an inductance L connected in series, and the method further comprises setting a detection circuit capable of simultaneously measuring the differential voltage across a sampling resistor and a standard resistor, wherein the detection circuit is controlled by a control and operation unit to control a controlled excitation source to output a periodic signal of an excitation test circuit, and the control and operation unit samples the differential voltage across the sampling resistor and the standard resistor, and the control and operation unit performs operations on the samples to obtain a calculated value of the standard resistor, and the control and operation unit compares the calculated value with the rated value of the standard resistor to obtain a measurement loop gain coefficient Ks, and then the standard resistor is replaced by the inductive displacement sensor, and the control and operation unit controls the controlled excitation source to output a periodic signal of the excitation test circuit, and the control and operation unit samples the differential voltage across the sampling resistor and the inductive displacement sensor, and the impedance of the inductive displacement sensor is calibrated according to the above-mentioned gain coefficient Ks.

[0010] On the basis of the above scheme and as a preferred scheme of the above scheme: when sampling with a standard resistor, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us, and the differential voltage across the calibration resistor is amplified and input into the control and operation unit as the output voltage Uz, and the control and operation unit synchronously samples Us and Uz n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n), and the control and operation unit operates on the two signal sequences to obtain the calculated value of the standard resistor When the inductive displacement sensor replaces the standard resistor and samples, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us', and the differential voltage across the inductive displacement sensor to be tested is amplified and input into the control and operation unit as the output voltage Uz'. The control and operation unit synchronously samples Us' and Uz' n times and filters them according to a certain sampling interval Δt to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n). The control and operation unit operates on the two signal sequences to obtain the impedance calculation value of the inductive displacement sensor.

[0011] On the basis of the above scheme and as a preferred scheme of the above scheme: the detection circuit comprises: fixing one end of the inductance displacement sensor to the standard resistor and connecting it to the positive input end of the amplifier A3; the other end of the inductance displacement sensor is simultaneously connected to the SA1 terminal of the switch one and the SB1 terminal of the switch two; the other end of the standard resistor is simultaneously connected to the SA2 terminal of the switch one and the SB2 terminal of the switch two; the output terminal SA of the switch one is connected to the sampling resistor and the negative input end of the amplifier A1, and the other end of the sampling resistor is connected to the output end of the amplifier A1; the output terminal SA of the switch one is connected to the negative input end of the amplifier A2; the output end of the amplifier A1 is connected to the positive input end of the amplifier A2; the output terminal SB of the switch two is connected to the negative input end of the amplifier A3; the output end of the amplifier A2 is connected to the control and operation unit; the output end of the amplifier A3 is connected to the control and operation unit, and the controlled excitation source is controlled by the control and operation unit and simultaneously connected to the inductance displacement sensor (2) to be tested, the standard resistor and the positive input end of the amplifier A3.

[0012] On the basis of the above scheme and as a preferred scheme of the above scheme: the control and operation unit is a digital signal processor DSP, a single-chip microcomputer MCU, a programmable logic device CPLD / FPGA, a RISC microprocessor ARM, a hardware multiplier and a divider.

[0013] On the basis of the above scheme and as a preferred scheme of the above scheme: the controlled excitation source is an oscillator circuit, a digital signal processor DSP, a single-chip microcomputer MCU, a single-chip digital frequency synthesis chip DDS, a programmable logic device CPLD / FPGA, and a RISC microprocessor ARM.

[0014] On the basis of the above scheme and as a preferred scheme of the above scheme: the amplifiers A1, A2, A3 are dedicated amplifiers, amplifier circuits composed of independent operational amplifiers, and amplifier circuits composed of discrete semiconductors.

[0015] On the basis of the above scheme and as a preferred scheme of the above scheme: the switch one and the switch two are switch circuits implemented by analog multiplexers, single-channel analog switches, multi-channel analog switches, relays, and various switches.

[0016] On the basis of the above scheme and as a preferred scheme of the above scheme: the method steps are as follows:

[0017] (1) The control and operation unit controls the controlled excitation source to output a periodic signal for stimulating the test circuit;

[0018] (2) The control and calculation unit controls the terminal SA2 of switch 1 to be connected to the terminal SA. At the same time, the control unit controls the terminal SB2 of switch 2 to be connected to the terminal SB, thereby connecting the standard resistor to the measurement circuit.

[0019] (3) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us. At the same time, amplifier A3 extracts the differential voltage across the calibration resistor and outputs the voltage Uz.

[0020] (4) The control and operation unit synchronously samples Us and Uz in step (3) n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n);

[0021] (5) The control and operation unit operates the two signal sequences in step (4) to obtain a calculated value of the standard resistance;

[0022] (6) The control and operation unit compares the calculated value in step (5) with the rated value of the standard resistor to obtain the measurement loop gain coefficient Ks;

[0023] (7) The control and calculation unit controls the terminal SA1 of switch 1 to be connected to the terminal SA. At the same time, the control unit controls the terminal SB1 of switch 2 to be connected to the terminal SB, connecting the inductance displacement sensor to be tested to the measurement circuit;

[0024] (8) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us'. At the same time, amplifier A3 extracts the differential voltage across the inductance displacement sensor to be tested and outputs the voltage Uz'.

[0025] (9) The control and operation unit synchronously samples Us' and Uz' in step (8) n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n);

[0026] (10) Control and Calculation The two signal sequences in step (9) are calculated to obtain the impedance calculation value of the inductive displacement sensor. The impedance of the inductive displacement sensor is calibrated according to the gain coefficient Ks in step (6).

[0027] On the basis of the above scheme and as a preferred scheme of the above scheme: steps (1) to (10) are continuously repeated to complete periodic automatic calibration, impedance measurement and fault diagnosis and isolation.

[0028] On the basis of the above scheme and as a preferred scheme of the above scheme: in the step (6), when the gain coefficient Ks exceeds the preset reasonable distribution range, the test circuit fault is reported, the current measurement is terminated, and the self-test function of the measurement circuit is realized; when the gain coefficient Ks is distributed within the preset range, the test circuit is reported to be normal, and the next measurement is carried out;

[0029] In the step (10), the calibrated impedance of the inductance displacement sensor is compared with the preset reasonable distribution range. When the calculated value exceeds the preset reasonable distribution range, the inductance displacement sensor fault is reported; the current cycle measurement is terminated, and the inductance displacement sensor health test function is realized;

[0030] In the step (10), the impedance of the inductive displacement sensor is calibrated to obtain the corresponding relationship between the impedance and displacement of the inductive displacement sensor, and a lookup table is established. After the impedance measurement of the inductive displacement sensor is completed, the current displacement state of the inductive displacement sensor is obtained through the lookup table, and quantitative displacement information is output.

[0031] The beneficial effects of the present invention are as follows: switch 1 and switch 2 inserted in the measuring loop are turned on under the orderly control of the control unit, and before measuring the impedance of the inductive displacement sensor, the standard resistor is first measured to obtain the gain coefficient of the measuring loop, and the inductive displacement sensor is calibrated according to the calibration coefficient when measuring, which can improve the measurement accuracy. At the same time, the positions of multiple groups of linkage switches in the signal chain are creatively designed, so that the extraction of differential signals is not affected by the switch on-resistance, thereby improving the detection reliability. At the same time, the measuring loop can be self-diagnosed, and when measuring the inductive displacement sensor, once the measurement result is abnormal, the measuring circuit and the object to be measured can be isolated, thereby achieving low-cost and high-efficiency maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram showing a simple calibration method according to the present invention;

[0033] Figure 2 The dispersion characteristics of the on-resistance of the switch of the common model simulation of the present invention;

[0034] Figure 3 The temperature characteristics of the on-resistance of the switch are simulated for the common models of the present invention;

[0035] Figure 4 It is an equivalent principle diagram of the simple calibration method of the present invention;

[0036] Figure 5 The schematic diagram of the detection circuit and the detection method of the present invention is shown in FIG.

[0037] Figure 6 The automatic calibration equivalent principle diagram of the present invention is shown in FIG.

[0038] Figure 7 This is the measurement equivalent principle diagram of the inductive displacement sensor of the present invention.

[0039] In the figure: controlled excitation source-1, inductive displacement sensor-2, standard resistor-3, switch one-4, switch two-5, sampling resistor-6, control and operation unit-7, amplifier-A1, amplifier-A2, amplifier-A3. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0041] See also Figure 1-7 A simple method to achieve calibration is Figure 1 As shown, a switch SW is inserted into the loop. The on-resistance of this switch when it is turned on is rw. There is dispersion in the on-resistance when two groups of three contacts are turned on. Figure 2 The dispersion characteristics of the on-resistance of common analog switches are shown. Figure 3 The temperature characteristics of the on-resistance of a commonly used analog switch are shown. Figure 2 and Figure 3 It can be seen that there are great differences in the on-resistance of analog switches between channels, between chips, and when the temperature changes. The on-resistance characteristics of other types of analog switches are similar and will not be repeated here.

[0042] The control and calculation control switch SA2 and SA terminal are turned on through the CT terminal of the switch, and the standard resistor Ra is connected to the measurement circuit. At this time, the equivalent circuit of the measurement circuit is as follows Figure 4 shown.

[0043] The control and operation unit controls the controlled excitation source OSC to output an excitation signal to excite the standard resistor Ra. Since the amplifier A1 works under deep negative feedback conditions, the positive and negative input terminals of the amplifier A1 meet the virtual short condition. At the same time, because the input impedance of the amplifiers A1, A2, and A3 is extremely high, the input leakage currents In1, Ip1, In2, Ip2, In3, and Ip3 of the amplifiers A1, A2, and A3 are negligible. The current Iz flowing through the standard resistor Ra and the switch on-resistance rw1 and the current Is flowing through the standard resistor Rs meet the following relationship:

[0044] Iz=Is

[0045] The current Iz flows through Ra and rw1 to form a voltage drop, and the difference is obtained by amplifier A2 to obtain Us. The current Is flows through Rs to form a voltage drop, and the difference is obtained by amplifier A3 to obtain Uz, satisfying the following relationship:

[0046]

[0047] After sorting, the calculated value of standard resistance Ra is obtained:

[0048]

[0049] Assuming that the rated resistance value of the standard resistor Ra is Re, the measurement loop gain coefficient Ks is obtained:

[0050]

[0051] In the formula, Uz and Us are obtained through sampling and are known quantities; the standard resistor Rs is a known quantity, and the rated value Re of the standard resistor is a known quantity; the above derivation clearly shows that the on-state internal resistance rw of switch 1 participates in the measurement calculation of the calibration link. Figure 2 , Figure 3 Given the simulated switch on-resistance dispersion and temperature characteristics, rw is an uncertain variable, and the Zengxi coefficient Ks obtained using this simple method is uncertain and unreliable. If a switch such as a relay is used, although the switch on-resistance can be controlled, the reliability of the switch is seriously reduced due to repeated switching for a long time, and the problem cannot be fundamentally solved.

[0052] After completing the calibration according to the above steps, the control and calculation unit controls the switch to connect the SA1 and SA terminals, connects the inductance displacement sensor to be measured to the measurement circuit, and re-performs the measurement calculation according to the above method. The switch on-resistance will also be introduced into the measurement link, resulting in erroneous measurement results. The measurement process will not be repeated here.

[0053] Aiming at the problems existing in the simple calibration method, the technical solution of the present invention is described as follows:

[0054] A method for automatically calibrating an inductive displacement sensor comprises an inductive displacement sensor 2 to be tested, wherein a built-in coil of the inductive displacement sensor 2 is equivalent to an internal resistance rc and an inductance L connected in series, and the method further comprises setting a detection circuit capable of simultaneously measuring the differential voltage across a sampling resistor 6 and a standard resistor 3, wherein the detection circuit controls a controlled excitation source 1 by a control and operation unit 7 to output a periodic signal of an excitation test circuit, and the control and operation unit samples the differential voltage across the sampling resistor and the standard resistor, and the control and operation unit performs operations on the samples to obtain a calculated value of the standard resistor, and the control and operation unit compares the calculated value with the rated value of the standard resistor to obtain a measurement loop gain coefficient Ks, and then the standard resistor is replaced by the inductive displacement sensor, and the control and operation unit controls the controlled excitation source to output a periodic signal of the excitation test circuit, and the control and operation unit samples the differential voltage across the sampling resistor and the inductive displacement sensor, and the impedance of the inductive displacement sensor is calibrated according to the above-mentioned gain coefficient Ks.

[0055] Furthermore, when sampling with a standard resistor, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us, and the differential voltage across the calibration resistor is amplified and input into the control and operation unit as the output voltage Uz, and the control and operation unit synchronously samples Us and Uz n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n), and the control and operation unit operates on the two signal sequences to obtain the calculated value of the standard resistor; Inductive displacement sensor When sampling after replacing the standard resistor, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us', and the differential voltage across the inductance displacement sensor to be tested is amplified and input into the control and operation unit as the output voltage Uz'. The control and operation unit synchronously samples Us' and Uz' n times and filters them according to a certain sampling interval Δt to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n). The control and operation unit operates on the two signal sequences to obtain the impedance calculation value of the inductance displacement sensor.

[0056] Further, the detection circuit includes fixing one end of the inductance displacement sensor 2 to the standard resistor 3 and connecting it to the positive input terminal of the amplifier A3. The other end of the inductance displacement sensor 2 is simultaneously connected to the SA1 terminal of the switch 1 4 and the SB1 terminal of the switch 2 5; the other end of the standard resistor 3 is simultaneously connected to the SA2 terminal of the switch 1 4 and the SB2 terminal of the switch 2 5; the output terminal SA of the switch 1 4 is connected to the sampling resistor 6 and the negative input terminal of the amplifier A1, and the other end of the sampling resistor 6 is connected to the output terminal of the amplifier A1; the output terminal SA of the switch 1 4 is connected to the negative input terminal of the amplifier A2; the output terminal of the amplifier A1 is connected to the positive input terminal of the amplifier A2; the output terminal SB of the switch 2 5 is connected to the negative input terminal of the amplifier A3; the output terminal of the amplifier A2 is connected to the control and operation unit; the output terminal of the amplifier A3 is connected to the control and operation unit, and the controlled excitation source 1 is controlled by the control and operation unit and simultaneously connected to the inductance displacement sensor 2 to be tested, the standard resistor 3 and the positive input terminal of the amplifier A3.

[0057] The control and operation unit is a digital signal processor DSP, a single-chip microcomputer MCU, a programmable logic device CPLD / FPGA, a RISC microprocessor ARM, a hardware multiplier and a divider.

[0058] Wherein, the controlled excitation source is an oscillator circuit, a digital signal processor DSP, a single-chip microcomputer MCU, a single-chip digital frequency synthesis chip DDS, a programmable logic device CPLD / FPGA, and a RISC microprocessor ARM.

[0059] The amplifiers A1, A2, A3 are dedicated amplifiers, amplifier circuits composed of independent operational amplifiers, and amplifier circuits composed of discrete semiconductors.

[0060] Among them, the switch one and the switch two are switch circuits implemented by analog multiplexers, single-channel analog switches, multi-channel analog switches, relays, and various switches.

[0061] The steps of the above detection circuit application method are as follows:

[0062] (1) The control and operation unit controls the controlled excitation source to output a periodic signal for stimulating the test circuit;

[0063] (2) The control and calculation unit controls the terminal SA2 of switch 1 to be connected to the terminal SA. At the same time, the control unit controls the terminal SB2 of switch 2 to be connected to the terminal SB, thereby connecting the standard resistor to the measurement circuit.

[0064] (3) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us. At the same time, amplifier A3 extracts the differential voltage across the calibration resistor and outputs the voltage Uz.

[0065] (4) The control and operation unit synchronously samples Us and Uz in step (3) n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n);

[0066] (5) The control and operation unit operates the two signal sequences in step (4) to obtain a calculated value of the standard resistance;

[0067] (6) The control and operation unit compares the calculated value in step (5) with the rated value of the standard resistor to obtain the measurement loop gain coefficient Ks;

[0068] (7) The control and calculation unit controls the terminal SA1 of switch 1 to be connected to the terminal SA. At the same time, the control unit controls the terminal SB1 of switch 2 to be connected to the terminal SB, connecting the inductance displacement sensor to be tested to the measurement circuit;

[0069] (8) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us'. At the same time, amplifier A3 extracts the differential voltage across the inductance displacement sensor to be tested and outputs the voltage Uz'.

[0070] (9) The control and operation unit synchronously samples Us' and Uz' in step (8) n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n);

[0071] (10) Control and Calculation The two signal sequences in step (9) are calculated to obtain the impedance calculation value of the inductive displacement sensor. The impedance of the inductive displacement sensor is calibrated according to the gain coefficient Ks in step (6).

[0072] Furthermore, steps (1) to (10) are continuously repeated to complete periodic automatic calibration, impedance measurement, and fault diagnosis and isolation.

[0073] The method for completing the periodic automatic calibration, impedance measurement and fault diagnosis isolation is that in the step (6), when the gain coefficient Ks exceeds the preset reasonable distribution range, the test circuit fault is reported, the current measurement is terminated, and the self-test function of the measurement circuit is realized; when the gain coefficient Ks is distributed within the preset range, the test circuit is reported to be normal, and the next measurement is performed;

[0074] In the step (10), the calibrated impedance of the inductance displacement sensor is compared with the preset reasonable distribution range. When the calculated value exceeds the preset reasonable distribution range, the inductance displacement sensor fault is reported; the current cycle measurement is terminated, and the inductance displacement sensor health test function is realized;

[0075] In the step (10), the impedance of the inductive displacement sensor is calibrated to obtain the corresponding relationship between the impedance and displacement of the inductive displacement sensor, and a lookup table is established. After the impedance measurement of the inductive displacement sensor is completed, the current displacement state of the inductive displacement sensor is obtained through the lookup table, and quantitative displacement information is output.

[0076] The measuring principle of the present invention is as follows Figure 5 As shown, the control and operation control the SA2 of switch 1 and the SA terminal through the CT terminal of the switch, and connect the standard resistor Ra to the measurement circuit. At the same time, the SB2 of switch 2 and the SB terminal are connected. The equivalent circuit of the measurement circuit is as follows Figure 6 shown.

[0077] The control and calculation unit controls the controlled excitation source OSC to output an excitation signal. Similarly, the current Iz flowing through the standard resistor Ra and the switch on-resistance rw1 and the current Is flowing through the standard resistor Rs satisfy the following relationship:

[0078] Iz=Is

[0079] Is flows through the sampling resistor Rs, and the amplifier A2 takes the difference as Us. Iz flows through the standard resistor Ra. Under the action of switch 2, amplifier A3 only takes the difference of the standard resistor Ra to obtain the differential voltage Uz. At this time, the on-resistance rw1 of switch 1 is isolated outside the amplifier differential loop. As described above, the input leakage current of the amplifier is so small that it can be ignored, and the current consumed by the on-resistance rw2 of switch 2 is also negligible. By designing this switching circuit, the influence of the switch on-resistance is isolated, so Us and Uz satisfy the following relationship:

[0080]

[0081] After sorting, the calculated value of standard resistance Ra is obtained:

[0082]

[0083] Assuming that the rated resistance value of the standard resistor Ra is Re, the measurement loop gain coefficient Ks is obtained:

[0084]

[0085] In the formula, Uz and Us are obtained through sampling and are known quantities; the standard resistance Rs is a known quantity, and the rated value Re of the standard resistance is a known quantity; it is obvious from the above derivation that although the on-resistance rw1 of switch 1 and the on-resistance rw2 of switch 2 are unknown quantities, they are not involved in the measurement calculation of the calibration link, thus avoiding the influence of the on-resistance, and the obtained gain coefficient Ks is certain and reliable. The health status of the detection circuit is judged according to the size of Ks. Once Ks exceeds the reasonable distribution range, it is judged that the detection circuit is faulty and the current cycle measurement is stopped; if Ks is distributed within a reasonable range, it is judged that the detection circuit is normal and the measurement continues.

[0086] The control and operation unit controls the A1 and SA terminals of switch 1 through the CT terminal of the switch to connect the inductance displacement sensor to be measured to the measurement circuit. At the same time, the SB1 and SB terminals of switch 2 are connected. The equivalent circuit of the measurement circuit is as follows: Figure 7 shown.

[0087] Same as above

[0088] Iz'=Is'

[0089] The amplifier A2 obtains the differential voltage Us' across the sampling resistor Rs, and the amplifier A3 obtains the differential voltage Uz' across the inductance displacement sensor to be measured, satisfying the following relationship:

[0090]

[0091] After sorting, we get:

[0092]

[0093] According to the gain coefficient Ks obtained previously, the measurement results are corrected again:

[0094]

[0095] In the formula, Uz' and Us' are obtained through sampling and are known quantities; the sampling resistor Rs is a known quantity, and the rated value of the standard resistor Re is a known quantity; it can also be clearly seen that although the on-resistance rw1' of switch 1 and the on-resistance rw2' of switch 2 are unknown quantities, they do not participate in the measurement operation of the inductor displacement sensor to be measured. According to the above formula, the impedance Z of the inductor displacement sensor to be measured is calculated. L , and the final calibration is performed. The health of the inductive displacement sensor to be tested is determined based on the calibration results. L If the inductance displacement sensor is out of the reasonable distribution range, it is judged that the inductance displacement sensor is faulty. L When the distribution is within a reasonable range, according to Z L The size determines the target displacement state and completes the displacement detection.

[0096] The present invention provides an automatic calibration inductive displacement sensor detection circuit and a detection method thereof. By building a simple circuit, designing a reasonable signal extraction and calibration method, and implementing a calibration step before measurement, the accuracy of the detection circuit is improved, and the problem that the current detection technology cannot accurately isolate the inductive displacement sensor and the detection circuit fault is effectively solved. At the same time, because a synchronous full differential structure is adopted, the switch contact problem and the uncertain influence of the on-resistance are avoided.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An automatic calibration inductive displacement sensor detection method, the automatic calibration inductive displacement sensor detection method comprising an inductive displacement sensor (2) to be tested, wherein the built-in coil of the inductive displacement sensor (2) is equivalent to an internal resistance rc and an inductance L connected in series, characterized in that The method further comprises providing a detection circuit capable of simultaneously measuring the differential voltage across the sampling resistor (6) and the standard resistor (3), wherein the detection circuit controls the controlled excitation source (1) to output a periodic signal of the excitation test circuit by a control and operation unit (7), and the control and operation unit samples the differential voltage across the sampling resistor and the standard resistor, and the control and operation unit performs operation on the sampled value to obtain a calculated value of the standard resistor, and the control and operation unit compares the calculated value with the rated value of the standard resistor to obtain a measurement loop gain coefficient Ks, and then replaces the standard resistor with an inductance displacement sensor, and similarly controls the controlled excitation source to output a periodic signal of the excitation test circuit by the control and operation unit, and the control and operation unit samples the differential voltage across the sampling resistor and the inductance displacement sensor, and calibrates the impedance of the inductance displacement sensor according to the above gain coefficient Ks.

2. The automatic calibration inductive displacement sensor detection method according to claim 1, characterized in that: When sampling with a standard resistor, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us, and the differential voltage across the calibration resistor is amplified and input into the control and operation unit as the output voltage Uz. The control and operation unit synchronously samples Us and Uz n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n), and the control and operation unit operates on the two signal sequences to obtain the calculated value of the standard resistor; Inductive displacement sensor replacement When sampling after the standard resistor, the differential voltage across the sampling resistor is amplified and input into the control and operation unit as the output voltage Us', and the differential voltage across the inductance displacement sensor to be measured is amplified and input into the control and operation unit as the output voltage Uz'. The control and operation unit synchronously samples Us' and Uz' n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n). The control and operation unit operates on the two signal sequences to obtain the impedance calculation value of the inductance displacement sensor.

3. The automatic calibration inductive displacement sensor detection method according to claim 2, characterized in that: The detection circuit comprises: one end of the inductive displacement sensor (2) is fixedly connected to the standard resistor (3) and connected to the positive input terminal of the amplifier A3; the other end of the inductive displacement sensor (2) is simultaneously connected to the SA1 terminal of the switch one (4) and the SB1 terminal of the switch two (5); the other end of the standard resistor (3) is simultaneously connected to the SA2 terminal of the switch one (4) and the SB2 terminal of the switch two (5); the output terminal SA of the switch one (4) is connected to the sampling resistor (6) and the negative input terminal of the amplifier A1, and the other end of the sampling resistor (6) is connected to the positive input terminal of the amplifier A1. A1 output terminal is connected; the output terminal SA of the switch one (4) is connected to the negative input terminal of the amplifier A2; the output terminal of the amplifier A1 is connected to the positive input terminal of the amplifier A2; the output terminal SB of the switch two (5) is connected to the negative input terminal of the amplifier A3; the output terminal of the amplifier A2 is connected to the control and operation unit; the output terminal of the amplifier A3 is connected to the control and operation unit, and the controlled excitation source (1) is controlled by the control and operation unit and is simultaneously connected to the inductance displacement sensor (2) to be measured, the standard resistor (3) and the positive input terminal of the amplifier A3.

4. The automatic calibration inductive displacement sensor detection method according to claim 1 or 3, characterized in that: The control and operation unit is one of the following: a digital signal processor DSP, a single-chip microcomputer MCU, a programmable logic device CPLD / FPGA, a RISC microprocessor ARM, a hardware multiplier and a divider.

5. The automatic calibration inductive displacement sensor detection method according to claim 1 or 3, characterized in that: The controlled excitation source is one of the following: an oscillator circuit, a digital signal processor DSP, a single-chip microcomputer MCU, a single-chip digital frequency synthesis chip DDS, a programmable logic device CPLD / FPGA, and a RISC microprocessor ARM.

6. The automatic calibration inductive displacement sensor detection method according to claim 3, characterized in that: The amplifiers A1, A2, A3 are one of the following: dedicated amplifiers, amplifier circuits composed of independent operational amplifiers, and amplifier circuits composed of discrete semiconductors.

7. The automatic calibration inductive displacement sensor detection method according to claim 3, characterized in that: The switch 1 and the switch 2 are one of the following: an analog multiplexer, a single-channel analog switch, a multi-channel analog switch, a relay, or a switch circuit implemented by various switches.

8. The automatic calibration inductive displacement sensor detection method according to claim 3, characterized in that: The method steps are as follows: (1) The control and operation unit controls the controlled excitation source to output a periodic signal for the excitation test circuit; (2) The control and calculation unit controls the terminal SA2 of switch 1 to be connected to the terminal SA. At the same time, the control unit controls the terminal SB2 of switch 2 to be connected to the terminal SB, thereby connecting the standard resistor to the measurement circuit. (3) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us. At the same time, amplifier A3 extracts the differential voltage across the calibration resistor and outputs the voltage Uz. (4) The control and operation unit synchronously samples Us and Uz in step (3) n times at a certain sampling interval Δt and filters them to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n); (5) The control and operation unit operates the two signal sequences in step (4) to obtain a calculated value of the standard resistance; (6) The control and operation unit compares the calculated value in step (5) with the rated value of the standard resistor to obtain the measurement loop gain coefficient Ks; (7) The control and operation unit controls the terminal SA1 of the switch 1 to be connected to the terminal SA; At the same time, the control unit controls the terminal SB1 of the switch 2 to be connected to the terminal SB, and connects the inductance displacement sensor to be tested to the measurement circuit; (8) Amplifier A2 extracts the differential voltage across the sampling resistor and outputs the voltage Us'. At the same time, amplifier A3 extracts the differential voltage across the inductance displacement sensor to be tested and outputs the voltage Uz'. (9) The control and operation unit synchronously samples Us' and Uz' in step (8) n times according to a certain sampling interval Δt and filters them to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n); (10) Control and Calculation The two signal sequences in step (9) are calculated to obtain the impedance calculation value of the inductive displacement sensor. The impedance of the inductive displacement sensor is calibrated according to the gain coefficient Ks in step (6).

9. The automatic calibration inductive displacement sensor detection method according to claim 8, characterized in that: Repeat steps (1) to (10) to complete periodic automatic calibration, impedance measurement, and fault diagnosis and isolation.

10. The automatic calibration inductive displacement sensor detection method according to claim 8 or 9, characterized in that: In the step (6), when the gain coefficient Ks exceeds the preset reasonable distribution range, the test circuit fault is reported, the current measurement is terminated, and the self-test function of the measurement circuit is realized; when the gain coefficient Ks is distributed within the preset range, the test circuit is reported to be normal, and the next measurement is carried out; In the step (10), the calibrated impedance of the inductive displacement sensor is compared with a preset reasonable distribution range; When the calculated value exceeds the preset reasonable distribution range, the inductance displacement sensor fault is reported; the current cycle measurement is terminated, and the inductance displacement sensor health test function is realized; In the step (10), the impedance of the inductive displacement sensor is calibrated to obtain the corresponding relationship between the impedance of the inductive displacement sensor and the displacement, and a lookup table is established. After the impedance measurement of the inductive displacement sensor is completed, the current displacement state of the inductive displacement sensor is obtained through the lookup table, and quantitative displacement information is output.

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