Impedance separation detection circuit and detection method of double alternating current bridge

Abstract

The application provides a double alternating current bridge impedance separation detection circuit and a detection method. One end of a first connecting terminal of a first alternating current bridge is connected with one end of a voltage source and one end of a first connecting terminal of a second alternating current bridge; one end of a second connecting terminal of the first alternating current bridge is connected with one end of a first balance resistor R s1 ; one end of a third connecting terminal of the first alternating current bridge is connected with one end of a second balance resistor R s2 ; the other end of the first balance resistor R s1 is connected with the other end of the second balance resistor R s2 , the other end of the voltage source, one end of a third balance resistor R s3 and one end of a fourth balance resistor R s4 ; the other end of a second connecting terminal of the second alternating current bridge is connected with the other end of the third balance resistor R s3 ; and the other end of a third connecting terminal of the second alternating current bridge is connected with the other end of the fourth balance resistor R s4 . The application can accurately separate the impedance and inductance change amount of a large-range eddy current displacement sensor in a detection process, and more accurately measure the displacement size between an eddy current probe and a target.

Description

Technical Field

[0001] This invention relates to the field of detection circuit technology for large-range eddy current displacement sensors, specifically to a dual AC bridge impedance separation detection circuit and detection method, and in particular to a dual AC bridge impedance separation detection circuit for large-range precision eddy current sensors. Background Technology

[0002] The purpose of the signal demodulation circuit is to accurately measure the change in impedance or inductance with distance. Its quality directly determines the sensor's performance and is the most crucial component of the sensor. An AC bridge is the most commonly used impedance measurement circuit, frequently found in strain gauge circuits. However, in eddy current sensor detection circuits, resistance is a parasitic parameter of the detection signal and needs to be controlled as much as possible. Furthermore, inductance is sensitive to distance but not to temperature. Additionally, previous research indicates that the change in inductance of an eddy current sensor at different locations can be well fitted by an exponential function. Therefore, in the measurement process of an eddy current displacement sensor, only the change in inductance needs to be obtained.

[0003] The traditional AC bridge circuit involved in the eddy current displacement sensor detection circuit is a detection circuit improved from the most basic AC bridge. This circuit separates the inductance and resistance of the detection signal. The bridge input is a 5V, 1MHz AC voltage source, and the output voltage U is an expression for the changes in inductance and resistance, where the real part of the output voltage represents the change in inductance and the imaginary part represents the change in resistance. These two can be separated by phase-sensitive detection. The key prerequisite for this method of separating inductance and resistance is that the changes in inductance and resistance are much smaller than themselves during operation, i.e., R >> ΔR,L >> ΔL. Since the range of eddy current displacement sensors is usually relatively small, the changes in inductance and resistance are very small during operation, thus meeting the above condition. However, for the design of large-range eddy current sensors, the condition R >> ΔR,L >> ΔL cannot be guaranteed when the sensor probe is far from the equilibrium position.

[0004] Patent document CN106093577A discloses a method and circuit for rapid impedance comparison measurement. This method is based on traditional AC bridge technology, using two arbitrary signal generators as two series-connected digital sources to achieve arbitrary vector voltage ratios. The two series-connected impedances being compared, along with the two digital sources, form a four-arm bridge. However, this patent document still fails to meet the requirement that the changes in inductance and resistance during operation are much smaller than their own values.

[0005] Patent document CN103529268B discloses an AC bridge with automatic auxiliary balancing function and its impedance measurement method. This AC bridge includes an AC power supply, a main inductive voltage divider, an auxiliary inductive voltage divider, and a null pointer. The main and auxiliary inductive voltage dividers have the same inductive voltage division ratio, and a negative feedback branch is provided between them, consisting of an active voltage follower, an inverting amplifier, a filter, and an isolation transformer connected in series. The primary side of the isolation transformer is connected to the auxiliary inductive voltage divider. The input terminal of the active voltage follower is connected to the main inductive voltage divider, and the output terminal is connected to the null pointer. The measurement method involves processing the voltage division on the main inductive voltage divider through the negative feedback branch, causing the null pointer branch to automatically obtain ground potential. The bridge can achieve impedance comparison measurement through simple main balancing. However, the technical solution of this patent document differs from that of this application. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a dual AC bridge impedance separation detection circuit and detection method.

[0007] A dual AC bridge impedance separation detection circuit according to the present invention includes: a reference bridge, a measuring bridge, and a voltage source connected in parallel; the reference bridge includes a first AC bridge and a first balancing resistor R. s1 and the second balancing resistor R s2 The measuring bridge includes a second AC bridge and a third balancing resistor R. s3 and the fourth balancing resistor R s4 ;

[0008] The first connection terminal of the first AC bridge is connected to one end of the voltage source and the first connection terminal of the second AC bridge, respectively; the second connection terminal of the first AC bridge is connected to the first balancing resistor R. s1 One end of the first AC bridge is connected to the second balancing resistor R, which serves as the first detection terminal. s2 One end, and serves as the second detection end;

[0009] The first balancing resistor R s1 The other end is connected to the second balancing resistor R. s2 The other end, the other end of the voltage source, the third balancing resistor R s3 one end and the fourth balancing resistor R s4 One end of the second AC bridge is grounded; the second connection terminal of the second AC bridge is connected to the third balancing resistor R. s3 The other end serves as the third detection terminal; the third connection terminal of the second AC bridge is connected to the four balancing resistors R. s4 The other end serves as the fourth detection end.

[0010] Preferably, the voltages output from the reference bridge and the measuring bridge have a phase difference;

[0011] The detection signal is the phase difference between the output voltages of the measuring bridge and the reference bridge.

[0012] Preferably, the measuring bridge and the reference bridge are switched via an analog switch;

[0013] When the switch is switched to the reference bridge, the output voltage phase of the reference bridge is:

[0014]

[0015] Where γ is the phase angle of the numerator in the formula for the output voltage signal of the bridge, γ' is the phase angle of the denominator in the formula for the output voltage signal of the bridge, ΔL is the change in inductance L of the sensor relative to the initial bridge equilibrium position, ΔR is the change in AC resistance R of the sensor relative to the initial bridge equilibrium position, ω is the angular frequency, ω=2πf, f is the operating frequency of the voltage source.

[0016] When the switch is switched to the measuring bridge, the output voltage phase of the measuring bridge is:

[0017]

[0018] Preferably, the resistance values ​​of both the first balancing resistor and the second balancing resistor exceed (ωL). 2 15 times.

[0019] Preferably, the voltages output from the reference bridge and the measuring bridge are demodulated by a lock-in amplifier.

[0020] Preferably, the real part of the output voltage is obtained using a reference signal with a 0-degree phase angle, and the imaginary part of the output voltage is obtained using a reference signal with a 90-degree phase angle.

[0021] Preferably, the phase difference between the output voltages of the reference bridge and the measurement bridge is obtained by performing algebraic operations on the real and imaginary parts of the output signals of the reference bridge and the measurement bridge.

[0022] The present invention also provides a sensor displacement and temperature detection method, based on the above-mentioned dual AC bridge impedance separation detection circuit, comprising the following steps:

[0023] Step 1: Within the preset temperature range, the AC resistance of the eddy current probe coil increases accordingly with the rise in temperature. There is a corresponding functional relationship between its resistance and temperature. The current ambient temperature of the eddy current sensor in a static state is measured by calibrating this functional relationship.

[0024] Step 2: The inductance of the eddy current probe has an exponential relationship with the measured displacement of the target. By calibrating the coefficient of this exponential relationship, the relationship between the sensor probe displacement and the change in inductance is calibrated, and the target displacement is measured.

[0025] Step 3: Under different temperature conditions, the exponential relationship coefficient calibrated in Step 2 is different. Combining Step 1 and Step 2, determine the actual target displacement and inductance change function relationship under the current ambient temperature, calibrate the exponential coefficient of the detection signal and sensor displacement that has a unique correspondence with the inductance change, and obtain the actual displacement value without temperature drift under the current environment.

[0026] The relationship between the detection signal and the sensor displacement is calibrated under different temperature conditions to obtain the true displacement value without temperature drift.

[0027] Preferably, in step 1, the change in the detection signal represents a change in temperature, and its phase difference is represented by the real and imaginary parts of the two-point bridge output voltage:

[0028]

[0029] Among them, R s R is the balancing bridge resistance of the first AC bridge, and R is the AC resistance of the sensor probe when the bridge is in its initial balanced position. Let be the vector composed of the real and imaginary parts of the output voltage from the first AC bridge. Let be the vector composed of the real and imaginary parts of the output voltage from the second AC bridge.

[0030] Preferably, in step 2, the change in the detection signal represents the change in inductance, and its phase difference is represented by the real and imaginary parts of the two-point bridge output voltage:

[0031]

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. This invention can accurately separate the impedance and inductance changes of a large-range eddy current displacement sensor during the detection process, and more accurately measure the displacement between the eddy current probe and the target.

[0034] 2. This invention utilizes the relationship between the sensor coil resistance and ambient temperature in a static state to achieve self-temperature compensation of the sensor.

[0035] 3. This invention can accurately obtain the inductance change of the eddy current sensor at different positions within its measurement range by using the phase difference of the output voltage signals of the two bridges under different conditions, thus avoiding unreasonable simplifications in the sensor measurement circuit design in the prior art. Attached Figure Description

[0036] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0037] Figure 1 This is a circuit diagram of the dual AC bridge impedance separation detection circuit of the present invention;

[0038] Figure 2 This is a schematic diagram illustrating the application of the dual bridge circuit in one embodiment;

[0039] Figure 3 This is a circuit diagram of a traditional AC bridge circuit. Detailed Implementation

[0040] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0041] Example 1:

[0042] Figure 1 As shown, this embodiment provides a dual AC bridge impedance separation detection circuit, including: a reference bridge, a measuring bridge, and a voltage source connected in parallel; the reference bridge includes a first AC bridge and a first balancing resistor R. s1 and the second balancing resistor R s2 The measuring bridge includes a second AC bridge and a third balancing resistor R. s3 and the fourth balancing resistor R s4 The first connection terminal of the first AC bridge is connected to one end of the voltage source and the first connection terminal of the second AC bridge, respectively; the second connection terminal of the first AC bridge is connected to the first balancing resistor R. s1 One end of the first AC bridge is connected as the first detection terminal; the third connection terminal of the first AC bridge is connected to the second balancing resistor R. s2 One end of the resistor serves as the second detection terminal; the first balancing resistor R s1 The other end is connected to the second balancing resistor R. s2 The other end, the other end of the voltage source, the third balancing resistor R s3 one end and the fourth balancing resistor R s4 One end of the first AC bridge is grounded; the second connection terminal of the second AC bridge is connected to the third balancing resistor R. s3 The other end serves as the third detection terminal; the third connection terminal of the second AC bridge is connected to four balancing resistors R. s4 The other end serves as the fourth detection terminal. The resistance values ​​of both the first and second balancing resistors exceed (ωL).2 15 times.

[0043] The measuring bridge and the reference bridge are switched via an analog switch;

[0044] When the switch is switched to the reference bridge, the output voltage phase of the reference bridge is:

[0045]

[0046] Where γ is the phase angle of the numerator in the formula for the output voltage signal of the bridge, γ' is the phase angle of the denominator in the formula for the output voltage signal of the bridge, ΔL is the change in inductance L of the sensor relative to the initial bridge equilibrium position, ΔR is the change in AC resistance R of the sensor relative to the initial bridge equilibrium position, ω is the angular frequency, ω=2πf, f is the operating frequency of the voltage source.

[0047] When the switch is switched to the measuring bridge, the output voltage phase of the measuring bridge is:

[0048]

[0049] The voltages output from the reference bridge and the measuring bridge have a phase difference, and the detection signal is the phase difference between the output voltages of the measuring bridge and the reference bridge.

[0050] The voltages output from the reference bridge and the measuring bridge are demodulated by a lock-in amplifier. The real part of the output voltage is obtained using a reference signal with a 0-degree phase angle, and the imaginary part is obtained using a reference signal with a 90-degree phase angle. The phase difference between the output voltages of the reference bridge and the measuring bridge is obtained by performing algebraic operations on the real and imaginary parts of the output signals.

[0051] This embodiment also provides a sensor displacement and temperature detection method. Based on the above-described dual AC bridge impedance separation detection circuit, the eddy current sensor inductance is sensitive to displacement detection but insensitive to temperature, while the AC resistance is more sensitive to temperature. Figure 2 The dual-bridge circuit in the circuit switches to obtain two bridge signals. By performing algebraic operations on the real and imaginary parts of the output signals of the reference bridge and the measurement bridge, the phase difference between the output voltages of the reference bridge and the measurement bridge is obtained, thereby separating the resistor and the inductor. That is, when the detection position is fixed, the AC resistance related to the ambient temperature is obtained through this circuit. When the sensor is working normally, the relationship between the detected displacement and the change in inductance is obtained through this circuit. The change in inductance has a unique correspondence with the circuit detection signal. The sensitivity of the AC resistance to temperature is used to detect the ambient temperature around the sensor, and the sensitivity of the inductance to the detected displacement is used to detect the target displacement.

[0052] Specifically, the steps include the following:

[0053] Step 1: Within a preset temperature range, the AC resistance of the eddy current probe coil increases accordingly with rising temperature. A functional relationship exists between its resistance and temperature. This functional relationship is calibrated to measure the current ambient temperature of the eddy current sensor in a static state. Changes in the detected signal represent changes in temperature, and the phase difference is represented by the real and imaginary parts of the two-point bridge output voltage:

[0054]

[0055] Among them, R s R is the balancing bridge resistance of the first AC bridge, and R is the AC resistance of the sensor probe when the bridge is in its initial balanced position. Let be the vector composed of the real and imaginary parts of the output voltage from the first AC bridge. Let be the vector composed of the real and imaginary parts of the output voltage from the second AC bridge.

[0056] Step 2: The inductance of the eddy current probe has an exponential relationship with the measured displacement of the target. By calibrating this exponential coefficient, the relationship between the sensor probe displacement and the inductance change is further calibrated, and the target displacement is measured. The change in the detected signal represents the change in inductance, and its phase difference is represented by the real and imaginary parts of the two-point bridge output voltage:

[0057]

[0058] Step 3: Under different temperature conditions, the exponential relationship coefficient calibrated in Step 2 is different. Combining Step 1 and Step 2, determine the actual target displacement and inductance change function relationship under the current ambient temperature, calibrate the exponential coefficient of the detection signal and sensor displacement that has a unique correspondence with the inductance change, and obtain the actual displacement value without temperature drift under the current environment.

[0059] Example 2:

[0060] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0061] This embodiment provides a design method for a dual AC bridge impedance separation detection circuit for a large-range precision eddy current sensor. The dual AC bridge impedance separation detection circuit is an improvement on the most basic AC bridge. The most basic AC bridge includes an eddy current probe itself forming one bridge arm, and a reference bridge arm consisting of a coil of the same specification as the eddy current probe or a common equivalent inductor and resistor. Its bridge output voltage is:

[0062]

[0063] Where L and R are the inductance and AC resistance of the eddy current sensor probe coil at the equilibrium position, j is the imaginary unit, ω is the angular frequency (ω = 2πf), f is the operating frequency of the voltage source, and ΔL and ΔR are the changes in inductance and resistance relative to L and R during the movement of the measured target, respectively. R is the input power for the bridge circuit. ss This is the balancing resistor for the bridge circuit.

[0064] The dual AC bridge impedance separation detection circuit specifically includes: one AC bridge equipped with a sufficiently large balancing resistor as a reference bridge, and the other AC bridge as a measuring bridge equipped with a balancing resistor configured based on the difference between the probe inductive reactance and the resistance value. The detection signal is the phase difference between the output voltages of the measuring bridge and the reference bridge.

[0065] The measuring bridge and the reference bridge are switched via an analog switch. When the switch is switched to the reference bridge, the phase of the bridge output voltage is:

[0066]

[0067] When the switch is switched to the measuring bridge, the phase of the bridge output voltage is:

[0068]

[0069] The above method can be used for both sensor displacement measurement and measurement of the ambient temperature of the sensor. The specific steps include:

[0070] S1: The change in the sensor's detection signal under normal static conditions is mainly caused by temperature changes. At this time, the change in the detection signal represents the temperature change, and its phase difference can be represented by the real and imaginary parts of the two-point bridge output voltage:

[0071]

[0072] Here, R s The balancing bridge resistors of the first AC bridge are, i.e. Figure 1 R in s1 R is the AC resistance of the sensor probe when it is in the initial equilibrium position of the bridge circuit. Let be the vector composed of the real and imaginary parts of the output voltage from the first AC bridge. This is a vector composed of the real and imaginary parts of the output voltage from the second AC bridge. The current ambient temperature of the eddy current sensor in a static state can be measured through calibration.

[0073] S2: The change in the detected signal during sensor operation is mainly caused by the change in inductance. At this time, the change in the detected signal represents the change in inductance, and its phase difference can be represented by the real and imaginary parts of the two-point bridge output voltage:

[0074]

[0075] By calibrating the relationship between the sensor probe displacement and inductance change, the target displacement can be measured.

[0076] S3: By calibrating the relationship between the detection signal and the sensor displacement under different temperature conditions, the true displacement value without temperature drift is finally obtained.

[0077] This embodiment proposes a design method for an AC bridge impedance separation detection circuit for a large-range precision eddy current sensor. Two AC bridges are established under different equilibrium conditions: one is a reference bridge, and the other is a measurement bridge. The phase of the input AC signal changes as it passes through these two bridges, resulting in a phase difference between the voltages output from the two bridge circuits. The voltages are demodulated by a lock-in amplifier. The real part of the output voltage is obtained using a reference signal with a 0-degree phase angle, and the imaginary part is obtained using a reference signal with a 90-degree phase angle. The phase difference between the output voltages of the two bridge circuits is obtained by performing algebraic operations on the real and imaginary parts of the output signals from the reference bridge and the measurement bridge. This phase difference can represent the change in inductance of the eddy current probe when it is displaced relative to the target.

[0078] Example 3:

[0079] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0080] This embodiment provides a design method for a dual AC bridge impedance separation detection circuit for a large-range precision eddy current sensor. The dual AC bridge impedance separation detection circuit is an improvement on the most basic AC bridge. The most basic AC bridge includes an eddy current probe itself forming one bridge arm, and a reference bridge arm consisting of a coil of the same specifications as the eddy current probe or a common equivalent inductor and resistor. Its bridge output voltage is:

[0081]

[0082] Where L and R are the inductance and AC resistance of the eddy current sensor probe coil at the equilibrium position, j is the imaginary unit, ω is the angular frequency (ω = 2πf), f is the operating frequency of the voltage source, and ΔL and ΔR are the changes in inductance and resistance relative to L and R during the movement of the measured target, respectively. R is the input power for the bridge circuit. ss This is the balancing resistor for the bridge circuit.

[0083] The dual AC bridge impedance separation detection circuit specifically includes: one of the AC bridges is equipped with a sufficiently large first balancing resistor R. s1 Second balancing resistor R s2As a reference bridge, another AC bridge is used as a measuring bridge, with a balancing resistor configured based on the difference between the probe's inductive reactance and resistance, i.e., R. s3 =R s4 ωL-R, the detection signal is the phase difference between the output voltage of the measurement bridge and the reference bridge.

[0084] Furthermore, the phase of the output signal from the reference bridge is expressed as the expression for the change in resistance and the change in inductance, and the phase of the output signal from the measurement bridge is the sum of the above expressions for the change in resistance and the change in inductance, and the expression for the change in inductance.

[0085] The total detection signal is the phase of the measured bridge output signal minus the phase of the reference bridge output signal. This allows us to establish a relationship between the detection signal and an expression consisting entirely of the inductance change, thus achieving the goal of detecting the inductance change independently.

[0086] The measuring bridge and the reference bridge are switched via an analog switch. When the switch is switched to the reference bridge, the phase of the bridge output voltage is:

[0087]

[0088] Here, γ is the phase angle of the numerator in the formula for the bridge output voltage signal, and γ′ is the phase angle of the denominator in the formula for the bridge output voltage signal. When the switch is switched to the measuring bridge, the phase of the bridge output voltage is:

[0089]

[0090] The detection circuit design method described above can be used for both sensor displacement measurement and measurement of the ambient temperature of the sensor. Specific steps include:

[0091] S1: The change in the sensor's detection signal under normal static conditions is mainly caused by temperature changes. At this time, the change in the detection signal represents the temperature change, and its phase difference can be represented by the real and imaginary parts of the two-point bridge output voltage:

[0092]

[0093] Here, R s The balancing bridge resistors of the first AC bridge are, i.e. Figure 1 R in s1 R is the AC resistance of the sensor probe when it is in the initial equilibrium position of the bridge circuit. Let be the vector composed of the real and imaginary parts of the output voltage from the first AC bridge. This is a vector composed of the real and imaginary parts of the output voltage from the second AC bridge. The current ambient temperature of the eddy current sensor in a static state can be measured through calibration.

[0094] S2: The change in the detected signal during sensor operation is mainly caused by the change in inductance. At this time, the change in the detected signal represents the change in inductance, and its phase difference can be represented by the real and imaginary parts of the two-point bridge output voltage:

[0095]

[0096] By calibrating the relationship between the sensor probe displacement and inductance change, the target's displacement can be measured.

[0097] S3: By calibrating the relationship between the detection signal and the sensor displacement under different temperature conditions, the true displacement value without temperature drift is finally obtained.

[0098] This embodiment proposes a dual AC bridge detection circuit. By using the phase difference of the output voltage signals of the two bridges under different conditions, the inductance change of the eddy current sensor at different positions within the measurement range can be accurately obtained. This method avoids the unreasonable simplification in the above-mentioned sensor measurement circuit design.

[0099] Example 4:

[0100] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0101] like Figure 3 As shown, this is a detection circuit improved from a traditional AC bridge. This circuit separates the inductance and resistance of the detection signal, and the bridge output voltage... for:

[0102]

[0103] Where L and R are the inductance and AC resistance of the eddy current sensor probe coil at the equilibrium position, j is the imaginary unit, ω is the angular frequency (ω = 2πf), f is the operating frequency of the voltage source, and ΔL and ΔR are the changes in inductance and resistance relative to L and R during the movement of the measured target, respectively. R is the input power for the bridge circuit. s To balance the bridge resistance, this embodiment combines the phase method measurement method. Taking the logarithm of the above equation, the AC bridge output signal is given by the following expression:

[0104]

[0105] here,

[0106]

[0107]

[0108]

[0109]

[0110] From the above formula, it can be seen that when R s When it is large enough, γ′=0, at which point we have

[0111]

[0112] When R s +R=ωL and △R<<R s When +R, there is

[0113]

[0114] Based on the analysis of the two equations above, a preliminary design can be made as follows: Figure 1 The double bridge circuit shown.

[0115] In the diagram, the balancing resistor R in the reference bridge... s1 and R s2 Choose a sufficiently large value for the balancing resistor R in the bridge circuit. s3 =R s4 =ωL-R, in this embodiment, ω=2πf, f is the frequency of the bridge input signal, which is 1MHz. When the bridge balance position is selected at a displacement of 5.5mm between the sensor probe and the target, the probe AC ​​resistance R=3.746ohm, the inductance L=38.68uH, and the expression for the bridge output voltage is:

[0116]

[0117] Here, Rs is Figure 2 The balancing resistor of the bridge connected by the switch, that is, R when the switch is switched to the first AC bridge. s =R s1 =R s2 When the switch is switched to the second AC bridge, R s =R s3 =R s4 =ωL-R, where A is the real part of the bridge output voltage and B is the imaginary part of the bridge output voltage.

[0118] (γ-γ′)=arctan(B / A).

[0119] As described above, the present invention switches the measuring bridge and the reference bridge via an analog switch, such as... Figure 2 As shown, when the switch is switched to the reference bridge, the phase of the bridge output voltage is:

[0120]

[0121] At this point, A and B are the real and imaginary parts of the output voltage of the first AC bridge, respectively, denoted as A1 and B1.

[0122] When the switch is switched to the measuring bridge, the phase of the output voltage of the bridge is:

[0123]

[0124] At this time, A and B are respectively the real part and the imaginary part of the output voltage of the second AC bridge, denoted as A2 and B2.

[0125] According to the above analysis, in the reference bridge, there is:

[0126]

[0127] In the measuring bridge, there is:

[0128]

[0129] By subtracting the phase of the output voltage in the measuring bridge from the phase of the output voltage in the reference bridge, the separation of the inductance change amount and the resistance change amount in the output signal can be achieved. The specific expression is:

[0130]

[0131] Here A1, A2, B1, and B2 respectively represent the real part and the imaginary part of the output voltage of the reference bridge and the measuring bridge.

[0132] Since the working time of the eddy current sensor is generally short and it remains stationary most of the time, it is considered that the temperature change during the working time of the eddy current sensor is negligible. Considering the heat dissipation factor, it is assumed that the main unstable factor affecting the output signal of the eddy current sensor is caused by the slow change of the ambient temperature.

[0133] According to the above analysis, when the eddy current sensor remains stationary, the change in the output signal of the bridge is mainly caused by the temperature change. There is R s +R = ωL and ΔL << L. At this time, there is:

[0134]

[0135]

[0136] Using the above formula, the ambient temperature of the eddy current sensor in the stationary state can be calculated. By calibrating the relationship between the output signal of the voltage and the displacement at different temperatures, the true displacement value without temperature drift can be finally obtained.

[0137] The present invention can accurately separate the impedance and inductance change amounts of a large-range eddy current displacement sensor during the detection process, and more accurately measure the displacement size between the eddy current probe and the target.

[0138] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A dual AC bridge impedance separation detection circuit, characterized in that, include: A reference bridge, a measuring bridge, and a voltage source are connected in parallel; the reference bridge includes a first AC bridge and a first balancing resistor. R s1 and the second balancing resistor R s2 The measuring bridge includes a second AC bridge and a third balancing resistor. R s3 and the fourth balancing resistor R s4 ; The first connection terminal of the first AC bridge is connected to one end of the voltage source and the first connection terminal of the second AC bridge, respectively; the second connection terminal of the first AC bridge is connected to the first balancing resistor. R s1 One end of the first AC bridge is connected to the second balancing resistor, which serves as the first detection terminal. R s2 One end, and serves as the second detection end; First balancing resistor R s1 The other end is connected to the second balancing resistor. R s2 The other end, the other end of the voltage source, the third balancing resistor R s3 one end and the fourth balancing resistor R s4 One end of the second AC bridge is grounded; the second connection terminal of the second AC bridge is connected to the third balancing resistor. R s3 The other end serves as the third detection terminal; the third connection terminal of the second AC bridge is connected to the four balanced resistors. R s4 The other end, and serves as the fourth detection end; The measuring bridge and the reference bridge are switched via an analog switch; The inductance of the bridge at the equilibrium position is: L The resistance values ​​of both the first balancing resistor and the second balancing resistor exceed [a certain value]. 15 times, in, ω Angular frequency, ω =2πf, f The operating frequency of the voltage source. When the switch is switched to the reference bridge, the output voltage phase of the reference bridge is: ； in, γ The phase angle of the numerator in the formula for the output voltage signal of the bridge is [missing information]. γ ' is the phase angle in the denominator of the formula for the output voltage signal of the bridge circuit. L Inductance of the sensor relative to the initial bridge balance position L The change R AC resistance of the sensor relative to the initial bridge balance position R The change in; When the switch is switched to the measuring bridge, the output voltage phase of the measuring bridge is: 。 2. The dual AC bridge impedance separation detection circuit according to claim 1, characterized in that, The voltages output from the reference bridge and the measuring bridge have a phase difference, and this phase difference is independent of the resistance, thus achieving impedance separation. The detection signal is the phase difference between the measuring bridge and the reference bridge, which is only related to the inductance.

3. The dual AC bridge impedance separation detection circuit according to claim 2, characterized in that, The voltages output from the reference bridge and the measuring bridge are demodulated by a lock-in amplifier.

4. The dual AC bridge impedance separation detection circuit according to claim 3, characterized in that, The real part of the output voltage is obtained using a reference signal with a 0-degree phase angle, and the imaginary part of the output voltage is obtained using a reference signal with a 90-degree phase angle.

5. The dual AC bridge impedance separation detection circuit according to claim 4, characterized in that, The phase difference between the output voltages of the reference bridge and the measurement bridge is obtained by performing algebraic operations on the real and imaginary parts of the output signals of the reference bridge and the measurement bridge.

6. A method for sensor displacement and temperature detection, characterized in that, The dual AC bridge impedance separation detection circuit according to any one of claims 1 to 5 includes the following steps: The dual AC bridge includes bridge arms formed by the eddy current probe itself, and reference bridge arms formed by coils of the same specifications as the eddy current probe or ordinary equivalent inductors and resistors. Step 1: Within the preset temperature range, the AC resistance of the eddy current probe coil increases accordingly with the rise in temperature. There is a corresponding functional relationship between its resistance and temperature. The current ambient temperature of the eddy current sensor in a static state is measured by calibrating this functional relationship. Step 2: The inductance of the eddy current probe has an exponential relationship with the measured displacement of the target. By calibrating the coefficient of this exponential relationship, the relationship between the sensor probe displacement and the change in inductance is calibrated, and the target displacement is measured. Step 3: Under different temperature conditions, the exponential relationship coefficient calibrated in Step 2 is different. Combining Step 1 and Step 2, determine the actual target displacement and inductance change function relationship under the current ambient temperature, calibrate the exponential coefficient of the detection signal and sensor displacement that has a unique correspondence with the inductance change, and obtain the actual displacement value without temperature drift under the current environment. The relationship between the detection signal and the sensor displacement is calibrated under different temperature conditions to obtain the true displacement value without temperature drift.

7. The sensor displacement and temperature detection method according to claim 6, characterized in that, In step 1, the change in the detected signal represents the change in temperature, and its phase difference is represented by the real and imaginary parts of the two-point bridge output voltage: ； in, R s The balancing bridge resistors of the first AC bridge, R The AC resistance of the sensor probe when it is in the initial equilibrium position of the bridge circuit. Let be the vector composed of the real and imaginary parts of the output voltage from the first AC bridge. Let be the vector composed of the real and imaginary parts of the output voltage from the second AC bridge.

8. The sensor displacement and temperature detection method according to claim 6, characterized in that, In step 2, the change in the detection signal represents the change in inductance, and its phase difference is represented by the real and imaginary parts of the two-point bridge output voltage: 。

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