LVDT displacement sensor capable of identifying electromagnetic interference and identification method

Abstract

The present invention relates to an LVDT displacement sensor capable of identifying electromagnetic interference, belonging to the field of electronic components, wherein the sensor comprises an oscillator, a buffer, a primary coil, two secondary coils, a movable iron core and a signal conditioning circuit, and also comprises a mode adjustment circuit; the oscillator is connected to the buffer, the buffer is connected to the primary coil, one end of the two secondary coils is grounded, and the other end is connected to the signal conditioning circuit, and the movable iron core is arranged between the primary coil and the two secondary coils; the mode adjustment circuit is connected to one of the secondary coils, and the sensor is placed in different modes by controlling the connection or disconnection of the secondary coil with the signal conditioning circuit, thereby determining whether the sensor is subject to electromagnetic interference. The present invention can realize the identification of high-frequency electromagnetic interference and low-frequency magnetic field interference through low-complexity hardware design and lightweight software algorithm, and provide security authentication for the output data of LVDT in complex electromagnetic environment.

Description

Technical Field

[0001] The present invention relates to the field of electronic components, and in particular to an LVDT displacement sensor capable of identifying electromagnetic interference and an identification method. Background Art

[0002] The linear displacement sensor commonly used in the fields of aerospace and industrial automation is the linear variable differential transformer (LVDT); it is mainly composed of a primary coil, two symmetrical secondary coils, a movable iron core, a measuring rod, an internal excitation source (such as an oscillator) and a signal processing circuit. The iron core moves with the movement of the measured object, converting the displacement into the change in the mutual inductance between the primary coil and the secondary coil, which is ultimately reflected in the change in the output voltage of the secondary coil.

[0003] In the field of aerospace and industrial automation, there is a demand for measuring a variety of displacements, such as the position of the aircraft joystick, pedal position, valve displacement, cylinder displacement, and rolling clearance measurement. In the application scenario of measuring the position of the aircraft joystick, the LVDT converts the pilot's control instructions into electrical signals and sends them to the flight control computer. Whether it can work normally is directly related to the aircraft control and even flight safety. The LVDT working signal is weak, and it contains a large number of analog circuit devices inside, which is very sensitive to high-frequency electromagnetic interference; at the same time, its front-end sensor element contains coils, which are also very sensitive to low-frequency magnetic field interference. External electromagnetic interference signals can cause the output of the LVDT to shift, causing its upper controller to receive erroneous sensor data and may lead to serious consequences.

[0004] In the prior art, there is a simulation method for analyzing and compensating the sensitivity of LVDT to magnetic field radiation in Ansys Maxwell. First, a physical structure model of LVDT is established in Ansys Maxwell, and then an excitation source and a signal processing circuit are added to the physical structure model in the Maxwell CircuitEditor module; then the output characteristic curve of LVDT under normal working conditions and external magnetic field interference conditions is simulated; finally, a magnetic shielding layer is added to the outer shell of LVDT, and the influence of the shielding layer on the output characteristic curve of LVDT is simulated and analyzed, and it is verified that the shielding layer can improve the anti-interference ability of LVDT to magnetic field radiation. However, this method only focuses on the magnetic sensitivity characteristics of LVDT, and only improves the ability of LVDT to resist magnetic field interference, but does not improve the ability of LVDT to detect magnetic field interference itself, nor does it involve the anti-interference ability of LVDT to external high-frequency electromagnetic fields. Therefore, this method cannot comprehensively improve the ability of LVDT to resist electromagnetic interference attacks. A high temperature and strong radiation resistant LVDT sensor is also disclosed, whose coil winding is covered with an insulating compound and the gaps between the coils are filled with insulating compounds, which can withstand higher temperatures and radiation doses than loose wires. At the same time, the coil of the LVDT sensor is made of chromium-niobium bronze, which is a high temperature and radiation resistant material. Its radiation and high temperature resistance performance are better than copper wire, so that the LVDT sensor can operate stably in the radiation environment of a nuclear power plant. However, the high temperature and strong radiation resistant LVDT sensor disclosed in this way can withstand high temperatures and strong nuclear radiation, but its ability to resist electromagnetic interference attacks is not enhanced. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, provide an LVDT displacement sensor capable of identifying electromagnetic interference and an identification method, and solve the deficiencies of the prior art.

[0006] The object of the present invention is achieved by the following technical solutions: an LVDT displacement sensor capable of identifying electromagnetic interference, the sensor comprising an oscillator, a buffer, a primary coil, two secondary coils, a movable iron core and a signal conditioning circuit, and also comprising a mode adjustment circuit;

[0007] The oscillator is connected to the buffer, the buffer is connected to the primary coil, one end of the two secondary coils is grounded, and the other end is connected to the signal conditioning circuit, and the movable iron core is arranged between the primary coil and the two secondary coils;

[0008] The mode adjustment circuit is connected to one of the secondary coils, and controls the connection or disconnection between the secondary coil and the signal conditioning circuit to put the sensor in different modes, thereby determining whether the sensor is subject to electromagnetic interference.

[0009] The mode adjustment circuit includes switch devices M1 and M2; the switch device M1 is connected to the signal conditioning circuit, and the switch device M2 is connected to the second control voltage;

[0010] The switch device M1 is connected to the switch device M2 and a first control voltage, and is also connected to ground via a resistor;

[0011] When the first control voltage control switch device M1 is disconnected and the second control voltage control switch device M2 is closed, the secondary coil is connected to the signal conditioning circuit and the sensor is in normal mode. When the first control voltage control switch device M1 is closed and the second control voltage control switch device M2 is disconnected, the secondary coil is disconnected from the signal conditioning circuit and the sensor is in self-test mode. By judging whether the outputs in the two modes satisfy the constraint relationship, it is judged whether it is affected by electromagnetic interference.

[0012] The constraints include Among them, O n and O c are the outputs in normal mode and self-test mode when the movable core is displaced, d n and d c are the outputs in normal mode and self-test mode when the movable core has no displacement and there is no electromagnetic interference, respectively. 1 and k 2 They are the slopes of the calibration curves corresponding to the normal mode and the self-test mode respectively;

[0013] If the movable core is displaced, the output in normal mode and self-test mode is O n and O c If the constraint relationship is satisfied, it is determined that there is no electromagnetic interference; if the constraint relationship is not satisfied, it is determined that there is electromagnetic interference.

[0014] The signal conditioning circuit comprises an adder, a half-wave rectifier and a low-pass filter; an oscillator provides a sinusoidal wave excitation with an angular frequency of ω for the primary coil, and two secondary coils generate an induction signal whose amplitude varies approximately linearly with the position of the iron core and has a phase difference of 180° to the adder, and the two induction signals are added and amplified by the adder, and then the signal processed by the adder is taken as a positive half cycle or a negative half cycle by a half-wave rectifier, and finally the signal component greater than or equal to ω is filtered out by a low-pass filter and a DC bias component is added, so as to obtain a non-negative output signal including the size and direction information of the measured displacement.

[0015] The electromagnetic interference identification method comprises:

[0016] The first control voltage and the second control voltage are used to control the on / off states of the switch devices M1 and M2 so that the sensor is in the normal mode or the self-test mode, and the corresponding calibration curve slopes k in the normal mode and the self-test mode are obtained.1 and k 2 ;

[0017] Get the output of the sensor in normal mode and self-test mode when the movable core has no displacement and there is no electromagnetic interference. n and d c ;

[0018] Get the output of the sensor in normal mode and self-test mode when the movable core is displaced n and O c ;

[0019] By judging whether the outputs in the two modes satisfy the constraint relationship, it is determined whether the sensor is subject to electromagnetic interference.

[0020] The step of controlling the on / off states of the switch devices M1 and M2 by the first control voltage and the second control voltage to put the sensor in the normal mode or the self-test mode specifically includes:

[0021] When the first control voltage controls the switch device M1 to be disconnected and the second control voltage controls the switch device M2 to be closed, the secondary coil connected to the switch device M2 is connected to the signal conditioning circuit, and the sensor is in a normal mode;

[0022] When the first control voltage controls the switch device M1 to be closed and the second control voltage controls the switch device M2 to be opened, the secondary coil connected to the switch device M2 is disconnected from the signal conditioning circuit, and the sensor is in a self-test mode.

[0023] The constraints include If the outputs in the two modes satisfy the constraint relationship at this time, it is determined that the sensor is not subject to electromagnetic interference at this time, otherwise it is determined that the sensor is subject to electromagnetic interference.

[0024] The present invention has the following advantages: an LVDT displacement sensor and identification method capable of identifying electromagnetic interference, which can realize the identification of high-frequency electromagnetic interference and low-frequency magnetic field interference through low-complexity hardware design and lightweight software algorithm, and provide security authentication for the output data of LVDT in complex electromagnetic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a circuit diagram of the present invention;

[0026] Figure 2 Schematic diagram of the calibration curves of the two modes. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application provided below in conjunction with the drawings is not intended to limit the scope of protection of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. The present invention is further described below in conjunction with the drawings.

[0028] like Figure 1 As shown, the present invention specifically relates to an LVDT displacement sensor capable of identifying electromagnetic interference, which includes an oscillator, a buffer, a primary coil, two secondary coils, a movable iron core and a signal conditioning circuit. The movable iron core moves with the movement of the object to be measured, thereby changing the mutual inductance between the primary coil and the secondary coil. The signal conditioning circuit includes an adder, a half-wave rectifier and a low-pass filter.

[0029] The oscillator provides a sinusoidal wave excitation with an angular frequency of ω to the primary coil, and then generates an induction signal on the two secondary coils whose amplitude varies approximately linearly with the core position and whose phase difference is 180°, as shown in the following formula:

[0030] V o1 =A 1 ·sin(ωt)(1)

[0031] V o2 =-A 2 ·sin(ωt)(2)

[0032] In the above formula, A 1 and A 2 Respectively represent the amplitudes of the two sensing signals.

[0033] The two sensing signals are first added and amplified by the adder to obtain the following signal:

[0034] V A =k A ·(A 1 -A 2 )·sin(ωt)(3)

[0035] In the above formula, k A represents the gain of the adder. Then according to A 1 and A 2 The half-wave rectifier module takes out VA The positive or negative half cycle of

[0036]

[0037] In the above formula, k B is the gain of the half-wave rectifier and sign(x) is the sign function, defined as follows:

[0038]

[0039] The low-pass filter converts V H The signal components with intermediate frequencies higher than or equal to ω are filtered out and a DC bias component is added to obtain the final non-negative output signal V O .

[0040]

[0041] Finally, V O It also contains the magnitude and direction information of the measured displacement.

[0042] The LVDT working signal is weak, and it contains a large number of analog circuit devices. The PCB traces and interconnecting cables interact with external high-frequency electromagnetic interference signals, generating interference voltage and current, and inducing nonlinear effects of analog devices such as operational amplifiers. In addition, the front-end sensor element of the LVDT contains a coil, which can interact with the external low-frequency magnetic field, generate illegal induction signals, and superimpose with the legal normal working signals, and participate in the subsequent signal conditioning process. Next, the sensitivity of the LVDT to external magnetic field interference is analyzed.

[0043] Assume that the angular frequency of the external magnetic field is ω m , then the output signal of the secondary coil containing the illegal induction signal is:

[0044] V o ′ 1 =A 1 ·sin(ωt)+B 1 ·sin(ω m t+φ m1 )(7)

[0045] V o ′ 2 =-A 2 sin(ωt)-B 2 ·sin(ω m t+φ m2 )(8)

[0046] In the above formula, B 1 and B 2Represent the amplitudes of the two illegal sensing signals, φ m1 and φ m2 They represent their phase differences relative to the original legal sensing signals. Then the output signal of the adder also changes.

[0047]

[0048] The outputs of the half-wave rectifier and the low-pass filter have changed accordingly, denoted as V H ′ and V O ′ From the above analysis process, it can be seen that the illegal induction signal and the original legal induction signal are mixed together and participate in the nonlinear processing of the subsequent circuit, resulting in the legal component in the final output of the LVDT and the illegal component caused by magnetic field interference being coupled together in a nonlinear manner.

[0049] Furthermore, if Figure 1 As shown, two switching devices M1 and M2, both of which are JFET (junction field effect transistor) type, control whether a secondary coil in the LVDT is connected to the back-end signal conditioning circuit, the source of the switching device M2 is connected to the signal conditioning circuit, the drain is connected to one of the secondary coils, and the gate is connected to the second control voltage; the source of the switching device M1 is connected to the drain of the switching device M2, the drain is grounded through a resistor, and the gate is connected to the first control voltage; here, the connection methods of the source and drain of the switching devices M1 and M2 can also be converted to each other.

[0050] When the first control voltage controlled switching device M1 is disconnected and the second control voltage controlled switching device M2 is closed, the secondary coil is connected to the signal conditioning circuit and the sensor is in normal mode. When the first control voltage controlled switching device M1 is closed and the second control voltage controlled switching device M2 is disconnected, the secondary coil is disconnected from the signal conditioning circuit and the sensor is in self-test mode.

[0051] like Figure 2 As shown, there are two calibration curves corresponding to the two modes of the LVDT; the first control voltage and the second control voltage are output by a lightweight software algorithm, and the two switching devices M1 and M2 control the LVDT to switch quickly between the two modes under the action of the external input control signal.

[0052] When the displacement is 0 mm, the outputs of the LVDT in normal mode and self-test mode are d and d.

[0053] nc

[0054] When there is no electromagnetic interference signal, the output of LVDT in normal mode and self-test mode is O and O, which meets the following requirements:

[0055] nc

[0056] Bundle relationship:

[0057]

[0058] In the above formula, k 1 and k 2 They are the slopes of the two calibration curves, among which the value of 2.05 is not universal and different values ​​can be determined according to different LVDTs.

[0059] Under the influence of electromagnetic interference signals, the quantitative relationship between the output offsets of the LVDT in the two modes is uncontrollable, so equation (10) is not true with a high probability. For high-frequency electromagnetic interference signals, this is because the switching of the secondary coil caused by the switching of the JFET causes a significant change in the field line coupling characteristics of the LVDT, which causes a significant change in the nonlinear effects of analog circuit devices such as operational amplifiers in the two modes; for low-frequency magnetic fields, this is because the legal and illegal components in the final output of the LVDT are coupled in a nonlinear manner. Therefore, by detecting whether a set of outputs of the LVDT in the two modes satisfies equation (11), the identification of high-frequency electromagnetic interference and low-frequency magnetic field interference can be achieved simultaneously. In order to further improve the recognition success rate, both secondary coils can be designed to be switchable separately, so that there are three calibration curves, and the constraint relationship is further strengthened.

[0060] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used for various other combinations, modifications and improvements, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. An LVDT displacement sensor capable of identifying electromagnetic interference, the sensor comprising an oscillator, a buffer, a primary coil, two secondary coils, a movable core and a signal conditioning circuit, characterized in that: Also included is a mode adjustment circuit; The oscillator is connected to the buffer, the buffer is connected to the primary coil, one end of the two secondary coils is grounded, and the other end is connected to the signal conditioning circuit, and the movable iron core is arranged between the primary coil and the two secondary coils; The mode adjustment circuit is connected to one of the secondary coils, and controls the connection or disconnection of the secondary coil with the signal conditioning circuit to put the sensor in different modes, thereby determining whether the sensor is subject to electromagnetic interference; The mode adjustment circuit includes switch devices M1 and M2; the switch device M1 is connected to the signal conditioning circuit, and the switch device M2 is connected to the second control voltage; The switch device M1 is connected to the switch device M2 and a first control voltage, and is also connected to ground via a resistor; When the first control voltage control switch device M1 is disconnected and the second control voltage control switch device M2 is closed, the secondary coil is connected to the signal conditioning circuit, and the sensor is in normal mode; when the first control voltage control switch device M1 is closed and the second control voltage control switch device M2 is disconnected, the secondary coil is disconnected from the signal conditioning circuit, and the sensor is in self-test mode; judging whether the outputs in the two modes satisfy the constraint relationship, and then judging whether it is subject to electromagnetic interference; The constraints include ,in, and They are the outputs in normal mode and self-test mode when the movable core is displaced. and They are the outputs in normal mode and self-test mode when the movable core has no displacement and there is no electromagnetic interference. and They are the slopes of the calibration curves corresponding to the normal mode and the self-test mode respectively; Output in normal mode and self-test mode if the movable core is displaced and If the constraint relationship is satisfied, it is determined that there is no electromagnetic interference; if the constraint relationship is not satisfied, it is determined that there is electromagnetic interference.

2. An electromagnetic interference identification method based on an LVDT displacement sensor capable of identifying electromagnetic interference, characterized in that: The electromagnetic interference identification method comprises: The sensor is placed in normal mode or self-test mode by adjusting the on / off state of the switch devices M1 and M2 in the control mode adjustment circuit through the first control voltage and the second control voltage, and the slope of the calibration curve corresponding to the normal mode and the self-test mode is obtained. and ; Get the output of the sensor in normal mode and self-test mode when the movable core has no displacement and there is no electromagnetic interference and ; Get the output of the sensor in normal mode and self-test mode when the movable core is displaced and ; By judging whether the outputs in the two modes satisfy the constraint relationship, it is possible to judge whether the sensor is subject to electromagnetic interference. The constraints include , if the outputs in the two modes satisfy the constraint relationship, then it is judged that the sensor is not subject to electromagnetic interference, otherwise it is judged that it is subject to electromagnetic interference; The mode adjustment circuit is connected to one of the secondary coils of the sensor, and controls the connection or disconnection of the secondary coil with the signal conditioning circuit to put the sensor in different modes, thereby determining whether the sensor is subject to electromagnetic interference; The switch device M1 is connected to the signal conditioning circuit in the sensor, and the switch device M2 is connected to the second control voltage; the switch device M1 is connected to the switch device M2 and the first control voltage, and is also grounded through a resistor.

3. The electromagnetic interference identification method based on the LVDT displacement sensor capable of identifying electromagnetic interference according to claim 2, characterized in that: The step of controlling the on / off states of the switch devices M1 and M2 by the first control voltage and the second control voltage to put the sensor in the normal mode or the self-test mode specifically includes: When the first control voltage controls the switch device M1 to be disconnected and the second control voltage controls the switch device M2 to be closed, the secondary coil connected to the switch device M2 is connected to the signal conditioning circuit, and the sensor is in a normal mode; When the first control voltage controls the switch device M1 to be closed and the second control voltage controls the switch device M2 to be opened, the secondary coil connected to the switch device M2 is disconnected from the signal conditioning circuit, and the sensor is in a self-test mode.

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