An automatic calibration inductance displacement sensor detection circuit

Abstract

The application discloses an automatic calibration inductance displacement sensor detection circuit for detecting an inductance displacement sensor, which comprises a controlled excitation source, an inbuilt coil of the inductance displacement sensor equivalent to a series connection of an internal resistance rc and an inductance L, the controlled excitation source is controlled by a control and operation unit and is connected to the inductance displacement sensor, a standard resistance and an amplifier A3 at the same time, one end of the inductance displacement sensor is connected to a switch one and a switch two at the same time, one end of the standard resistance is connected to the switch one and the switch two at the same time, the output of the switch one is connected to a sampling resistance, the other end of the sampling resistance is connected to an output end of an amplifier A1, the switch one is connected to a negative input end of the amplifier A2, the output end of the amplifier A1 is connected to a positive input end of the amplifier A2, a terminal SB of the output of the switch two is connected to a negative input end of the amplifier A3, the output of the amplifier A2 is connected to the control and operation unit, and the output of the amplifier A3 is connected to the control and operation unit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inductive displacement sensor, and particularly relates to an automatic calibration inductive displacement sensor detection circuit. BACKGROUND

[0002] In order to meet the use requirements in harsh environments, inductive proximity sensor suppliers have developed various detection technologies, including time-domain-based pulse charging and discharging detection circuit, low-frequency oscillation circuit based on differential coil compensation, and frequency-domain-based impedance analysis circuit. However, these can only calibrate the sensor and its detection circuit before the product is shipped. Once the performance state of a component changes during use, the detection circuit cannot automatically complete compensation, which eventually leads to performance degradation or even loss of function in the application link. Maintenance personnel cannot quickly and accurately determine the fault location, and can only regularly detect and calibrate the equipment, which brings great inconvenience to the maintenance support link.

[0003] Although a switch circuit can be simply introduced into the circuit to achieve calibration, the switch used is a relay mechanical contact type or an analog switch electronic contact type. The mechanical contact switch has contact arc noise and reliability problems such as poor contact after a large number of operations. The analog switch electronic contact has a large dispersion of on-resistance, and there is a large uncertain temperature drift, which introduces uncertain factors into the measurement loop and loses the meaning of calibration. SUMMARY

[0004] The present application aims at providing an automatic calibration inductive displacement sensor detection circuit, which can be used for inductive displacement sensor detection.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] The application discloses an automatic calibration inductance displacement sensor detection circuit, which comprises a controlled excitation source, an inductance displacement sensor to be detected, a standard resistor, a switch one, a switch two, a sampling resistor, an amplifier A1, an amplifier A2, an amplifier A3, a control and operation unit, wherein the controlled excitation source is controlled by the control and operation unit and is connected to the inductance displacement sensor to be detected, the standard resistor and the positive input end of the amplifier A3 at the same time; the other end of the inductance displacement sensor is connected to the SA1 terminal of the switch one and the SB1 terminal of the switch two at the same time; the other end of the standard resistor is connected to the SA2 terminal of the switch one and the SB2 terminal of the switch two at the same time; 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; and the output end of the amplifier A3 is connected to the control and operation unit.

[0007] 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 hardware divider.

[0008] 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).

[0009] As a preferred scheme of the above scheme, the amplifiers A1, A2 and A3 are special-purpose amplifiers, amplification circuits composed of independent operational amplifiers or amplification circuits composed of discrete semiconductors.

[0010] As a preferred scheme of the above scheme, the switch one and the switch two are analog multiplexers, single-channel analog switches, multi-channel analog switches, relays or switch circuits realized by various switches.

[0011] The automatic calibration inductance displacement sensor detection circuit of the present application can be used for inductance displacement sensor detection, and through simple circuit construction, reasonable signal extraction and calibration method design, the calibration step can be implemented before measurement, the precision of the detection circuit is improved, and the problem that the current detection technology cannot accurately isolate the inductance displacement sensor and the detection circuit fault is effectively solved. Meanwhile, the synchronous full differential structure is adopted, so that the switch contact problem and the uncertain influence of on-resistance are avoided. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The present application detection circuit and its detection method schematic diagram of the present application;

[0013] Figure 2 The present application automatic calibration equivalent schematic diagram of the present application;

[0014] Figure 3 The present application inductance displacement sensor measurement equivalent schematic diagram of the present application.

[0015] In the figure:

[0016] Controlled excitation source-1, inductance 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

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0018] Referring to Figures 1-3 An automatic calibration inductance displacement sensor detection circuit, the principle is as follows Figure 1As shown, including controlled excitation source 1, to be measured inductance displacement sensor 2 built-in coil equivalent to internal resistance rc and inductance L in series, standard resistance 3, switch one 4, switch two 5, sampling resistance 6, amplifier A1, amplifier A2, amplifier A3, control and operation unit 7, the controlled excitation source 1 is controlled by control and operation unit 7 and simultaneously connected to be measured inductance displacement sensor 2, standard resistance 3 and amplifier A3 positive input end, inductance displacement sensor 2 the other end is connected to switch one 4 SA1 terminal and switch two 5 SB1 terminal simultaneously; The other end of the standard resistance 3 is connected to the SA2 terminal of the switch one 4 and the SB2 terminal of the switch two 5 simultaneously; The output terminal SA of the switch one 4 is connected with the sampling resistance 6 and the negative input end of the amplifier A1, and the other end of the sampling resistance 6 is connected with the output end of the amplifier A1; The output terminal SA of the switch one 4 is connected with the negative input end of the amplifier A2; The output end of the amplifier A1 is connected with the positive input end of the amplifier A2; The output terminal SB of the switch two 5 is connected with 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.

[0019] Among them, the control and operation unit is digital signal processor DSP, single-chip microcomputer MCU, programmable logic device CPLD / FPGA, RISC microprocessor ARM, hardware multiplier and divider.

[0020] Among them, the controlled excitation source is oscillator circuit, digital signal processor DSP, single-chip microcomputer MCU, single-chip digital frequency synthesis chip DDS, programmable logic device CPLD / FPGA, RISC microprocessor ARM.

[0021] Among them, the amplifier A1, A2, A3 is a dedicated amplifier, an amplification circuit composed of independent operational amplifiers, an amplification circuit composed of discrete semiconductors.

[0022] Among them, the switch one and the switch two are analog multiplexer, single-channel analog switch, multi-channel analog switch, relay, switch circuit realized by various switches.

[0023] The automatic calibration inductance displacement sensor detection circuit application and working method are as follows:

[0024] (1) The control and operation unit controls the controlled excitation source to output the periodic signal of the excitation test circuit;

[0025] (2) The control and operation unit controls the terminal SA2 of the switch one to be connected with the terminal SA, at the same time, the control unit controls the terminal SB2 of the switch two to be connected with the terminal SB, and the standard resistance is connected to the measurement loop;

[0026] (3) amplifier A2 extracts the differential voltage across the sampling resistor and outputs a voltage Us, and at the same time, amplifier A3 extracts the differential voltage across the calibration resistor and outputs a voltage Uz;

[0027] (4) the control and operation unit synchronously samples the Us and Uz in step (3) n times at a certain sampling interval Δt and filters to obtain two signal sequences (Us, Δt, n) and (Uz, Δt, n);

[0028] (5) the control and operation unit operates the two signal sequences in step (4) to obtain a calculated value of the standard resistor;

[0029] (6) the control and operation unit compares the calculated value in step (5) with the rated value of the standard resistor to obtain a measurement loop gain coefficient Ks;

[0030] (7) the control and operation unit controls the switch one to connect the terminal SA1 to the terminal SA. At the same time, the control unit controls the switch two to connect the terminal SB1 to the terminal SB, and connects the inductance displacement sensor to be measured into the measurement loop;

[0031] (8) amplifier A2 extracts the differential voltage across the sampling resistor and outputs a voltage Us', and at the same time, amplifier A3 extracts the differential voltage across the inductance displacement sensor to be measured and outputs a voltage Uz';

[0032] (9) the control and operation unit synchronously samples the Us' and Uz' in step (8) n times at a certain sampling interval Δt and filters to obtain two signal sequences (Us', Δt, n) and (Uz', Δt, n);

[0033] (10) the control and operation unit operates the two signal sequences in step (9) to obtain a calculated value of the impedance of the inductance displacement sensor, and calibrates the impedance of the inductance displacement sensor according to the gain coefficient Ks in step (6).

[0034] Further, steps (1) to (10) are repeatedly performed to complete the periodic automatic calibration, impedance measurement and fault diagnosis isolation.

[0035] The method for completing the periodic automatic calibration, impedance measurement and fault diagnosis isolation is that, in step (6), when the gain coefficient Ks exceeds a preset reasonable distribution range, it is reported that the test circuit is faulty, the current measurement is terminated, and the measurement circuit self-test function is realized; when the gain coefficient Ks is distributed within the preset range, it is reported that the test circuit is normal, and the next measurement is performed;

[0036] In step (10), the calibrated inductance displacement sensor impedance is compared with the preset reasonable distribution range. When the calculated value exceeds the preset reasonable distribution range, the inductance displacement sensor is reported to be faulty; the current cycle measurement is terminated, and the inductance displacement sensor health test function is realized.

[0037] In step (10), the inductance displacement sensor impedance is calibrated to obtain the corresponding relationship between the inductance displacement sensor impedance and the displacement, a lookup table is established, and after the inductance displacement sensor impedance measurement is completed, the current inductance displacement sensor displacement state is obtained through the lookup table, and the quantitative displacement information is output.

[0038] The measurement principle of the present application is shown in Figure 1 The control and operation pass through the CT terminal of the switch to control the conduction of the SA2 and SA terminal of the switch 1, and the standard resistance Ra is connected to the measurement circuit. At the same time, the SB2 and SB terminal of the switch 2 are conducted. The equivalent circuit of the measurement circuit is shown in Figure 2 .

[0039] The control and operation unit controls the controlled excitation source OSC to output an excitation signal. Similarly, the current Iz flowing through the standard resistance Ra and the on-resistance rw1 of the switch and the current Is flowing through the standard resistance Rs satisfy the following relationship:

[0040] Iz=Is

[0041] Is flows through the sampling resistance Rs, and the differential is taken by the amplifier A2 to obtain Us. Iz flows through the standard resistance Ra, and under the action of the switch 2, the amplifier A3 only takes the differential of the standard resistance Ra to obtain the differential voltage Uz. At this time, the on-resistance rw1 of the switch 1 is isolated from the amplifier differential loop. As described above, the input leakage current of the amplifier is small enough to be ignored, and the current consumed on the on-resistance rw2 of the switch 2 is also ignored. By designing the switching circuit, the influence of the on-resistance of the switch is isolated, so that Us and Uz satisfy the following relationship:

[0042]

[0043] After sorting, the calculated value of the standard resistance Ra is obtained:

[0044]

[0045] Assuming that the rated resistance value of the standard resistance Ra is Re, the measurement circuit gain coefficient Ks is obtained:

[0046]

[0047] The Uz and Us in the formula are obtained by sampling and are known quantities; the standard resistor Rs is a known quantity, and the standard resistor rated value Re is a known quantity; it is obvious from the above derivation that the on-resistance rw1 of switch 1 and the on-resistance rw2 of switch 2 are unknown quantities, but do not participate in the measurement operation of the calibration link, thereby avoiding the influence of the on-resistance, and the gain coefficient Ks obtained is determined and reliable. The health status of the detection loop is judged according to the size of Ks, and once Ks exceeds the reasonable distribution range, it is determined that the detection circuit fails, and the current period measurement is stopped; if Ks is distributed within the reasonable range, it is determined that the detection circuit is normal, and the measurement is continued.

[0048] The control and operation unit controls the conduction of the A1 and SA terminals of switch 1 through the CT terminal of the switch, and connects the inductance displacement sensor to be measured into the measurement loop. At the same time, the SB1 and SB terminals of switch 2 are conducted. The equivalent circuit of the measurement loop is as shown in Figure 3 .

[0049] As described above

[0050] Iz'=Is'

[0051] The amplifier A2 obtains the differential voltage between the two ends of the sampling resistor Rs as Us', and the amplifier A3 obtains the differential voltage between the two ends of the inductance displacement sensor to be measured as Uz', which satisfies the following relationship:

[0052]

[0053] After arrangement, we obtain:

[0054]

[0055] According to the gain coefficient Ks obtained above, the measurement result is revised again:

[0056]

[0057] In the formula, Uz' and Us' are obtained by sampling and are known quantities; the sampling resistor Rs is a known quantity, and the standard resistor rated value Re is a known quantity; it is also obvious that the on-resistance rw1' of switch 1 and the on-resistance rw2' of switch 2 are unknown quantities, but do not participate in the measurement operation of the inductance displacement sensor to be measured. The impedance Z of the inductance displacement sensor to be measured is calculated according to the above formula L , and the final calibration is performed. According to the calibration result, the health condition of the inductance displacement sensor to be measured is judged. When Z L exceeds the reasonable distribution range, it is determined that the inductance displacement sensor fails, and when Z L is distributed within the reasonable range, the target displacement state is judged according to the size of Z L , and the displacement detection is completed.

[0058] The application provides an automatic calibration inductance 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 precision of the detection circuit is improved, and the problem that the current detection technology cannot accurately isolate the inductance displacement sensor and the detection circuit fault is effectively solved. At the same time, because the synchronous full differential structure is adopted, the switch contact problem and the uncertain influence of on-resistance are avoided.

[0059] The above is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. An auto-calibrating inductive displacement sensor detection circuit, comprising: The controlled excitation source (1), the inductance displacement sensor (2) to be measured, the standard resistance (3), the switch one (4), the switch two (5), the sampling resistance (6), the amplifier A1, the amplifier A2, the amplifier A3, the control and operation unit (7) are connected, the controlled excitation source (1) is controlled by the control and operation unit (7) and is connected to the inductance displacement sensor (2) to be measured, the standard resistance (3) and the positive input end of the amplifier A3 at the same time, the other end of the inductance displacement sensor (2) is connected to the SA1 terminal of the switch one (4) and the SB1 terminal of the switch two (5) at the same time, the other end of the standard resistance (3) is connected to the SA2 terminal of the switch one (4) and the SB2 terminal of the switch two (5) at the same time, the output terminal SA of the switch one (4) is connected to the sampling resistance (6) and the negative input end of the amplifier A1, the other end of the sampling resistance (6) is connected to the output end of the amplifier A1, the output terminal SA of the switch one (4) 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 (5) 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, and the output end of the amplifier A3 is connected to the control and operation unit. The amplifiers A1, A2 and A3 are special-purpose amplifiers, amplification circuits composed of independent operational amplifiers or amplification circuits composed of discrete semiconductors. The switch one and the switch two are analog multiplexers, single-channel analog switches, multi-channel analog switches, relays or switch circuits realized by various switches.

2. The auto-calibrating inductive displacement sensor detection circuit of claim 1, wherein: 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 or a hardware multiplier and divider.

3. The auto-calibrating inductive displacement sensor detection circuit of claim 1, 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 or a RISC microprocessor ARM.

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