A non-contact measurement device and method for the DC voltage of an electric wire

Abstract

The present invention discloses a non-contact measurement device and method for the DC voltage of an electric wire. Based on a piezoelectric device, non-contact measurement of the DC voltage of the electric wire is achieved. The measured DC voltage is sampled through capacitive voltage division, and the sampled DC voltage is applied across the electrodes of the piezoelectric device. According to the inverse piezoelectric effect of the piezoelectric device, the distance between the two plates of the piezoelectric device will change with the magnitude and polarity of the sampled voltage, thereby changing its own capacitance. Combining the lock-in amplification technique to measure the capacitance value change of the piezoelectric device and the capacitance value of the sampling capacitor, through the change of capacitance, the sampled voltage can be deduced inversely, and then the measured DC voltage can be deduced inversely. The present invention abandons the mechanical structure part in the traditional vibration capacitance type capacitance measurement method, and adopts the lock-in amplifier technique, which can measure the amplitude and polarity of the DC voltage of the electric wire, and has the advantages of low power consumption, small volume, light weight and high measurement accuracy, and can be widely applied to the field of DC voltage measurement technology.

Description

Technical Field

[0001] The present invention relates to the technical field of DC voltage measurement, and in particular to a non-contact measurement device and method for the DC voltage of an electric wire. Background Art

[0002] Traditionally, the detection of DC voltage or AC voltage of an electric wire requires contact with an object and is completed by conducting current. However, this contact measurement method is sometimes very inconvenient. For example, voltage data cannot be obtained at some nodes where the insulation layer of the line cannot be damaged. Therefore, in recent years, people have begun to study non-contact measurement methods for wire voltage. Since the non-contact measurement technology for AC voltage is relatively mature, the research focus is on the non-contact measurement technology for DC voltage. Compared with traditional contact voltmeters, non-contact voltmeters have the advantages of easy use, high safety, and being unaffected by line insulation, and will become the development direction of future voltage measurement devices.

[0003] There are mainly three existing methods for non-contact measurement of DC voltage. One is the probe method, which places a conductor probe in the electric field formed by a live wire and a reference ground, directly measures the potential difference between the probe and the reference ground, and then calculates the DC voltage of the wire based on the position between the probe and the live wire. The second is to utilize the Pockels effect of certain crystal materials and measure the DC voltage of the wire according to the magnitude of the refraction angle of the birefringence phenomenon. The third is the variable capacitance method, which converts the DC induced voltage signal into an alternating signal by changing the relative position of the two plates of the capacitor, and obtains the DC voltage of the wire to be measured through signal amplification processing.

[0004] Among them, the third variable capacitance method can be implemented in different ways, such as the rotating vane type, the MEMS (Micro-Electro-Mechanical System) lateral vibration type, the vibrating capacitor type, etc. The rotating vane type uses a motor to drive the shielding electrode to rotate, and modulates an AC signal through periodic shielding and releasing of the induction electrode. The MEMS lateral vibration type modulates an AC signal by using the relative position change between the movable comb teeth and the fixed comb teeth. The vibrating capacitor sensor periodically changes the distance between the induction electrode and the object to be measured through longitudinal vibration, and modulates an AC signal on the induction electrode to achieve measurement.

[0005] However, the probe method has the disadvantages that the measurement result drifts with time, the measurement error is large, it cannot be measured online for a long time, and it needs to be zeroed before each measurement. The optical sensor based on the Pockels effect requires optical devices, has a high cost, and is greatly affected by the environmental temperature and floating charges. Among the several technical solutions of the variable capacitance method, the rotating vane type has high power consumption and serious wear; the MEMS lateral vibration type has the disadvantages of low signal-to-noise ratio and unstable measurement results; there are mechanical structures such as cantilever beams in the vibrating capacitor sensor system, and the measurement results are easily affected by the cantilever beam structure and geometric dimensions. Summary of the Invention

[0006] In view of this, the present invention provides a non-contact measurement device and method for the DC voltage of a wire, which realizes the non-contact measurement of the DC voltage of the wire through a piezoelectric device, abandons the mechanical structure part in the traditional vibration capacitance type capacitance measurement method, and has the advantages of low power consumption, small volume, light weight, high measurement accuracy, etc.

[0007] In a first aspect, an embodiment of the present invention provides a non-contact measurement device for the DC voltage of a wire, including a sampling copper sheet, a piezoelectric device, a sine signal generation circuit, a lock-in amplifier circuit, an analog-to-digital conversion circuit, and a microcontroller module;

[0008] The sampling copper sheet is used to form a first sampling capacitance with the target measurement wire;

[0009] The piezoelectric device forms a second sampling capacitance. The piezoelectric device is used to perform voltage division sampling on the target measurement DC voltage to obtain a sampling voltage; wherein, the second sampling capacitance matches the sampling voltage according to the inverse piezoelectric effect of the piezoelectric device;

[0010] The sine signal generation circuit is used to generate a sine excitation voltage;

[0011] The lock-in amplifier circuit is used to obtain the first node voltage at the connection between the sampling copper sheet, the sine signal generation circuit and the lock-in amplifier circuit, and obtain a first output voltage according to the sine excitation voltage combined with the first node voltage;

[0012] And, it is used to obtain the second node voltage at the connection between the piezoelectric device, the sine signal generation circuit and the lock-in amplifier circuit, and obtain a second output voltage according to the sine excitation voltage combined with the second node voltage;

[0013] The analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the circuit analog signal to obtain a digital signal; the digital signal includes the sine excitation voltage, the first node voltage, the second node voltage, the first output voltage, and the second output voltage;

[0014] The microcontroller module is used to determine the first sampling capacitance of the sampling copper sheet, the second sampling capacitance and the sampling voltage of the piezoelectric device according to the digital signal of the analog-to-digital conversion circuit, and determine the target measurement DC voltage according to the first sampling capacitance, the second sampling capacitance and the sampling voltage.

[0015] Optionally, the measurement device further includes a display module for displaying the voltage value of the target measurement DC voltage, and the display module is electrically connected to the microcontroller module.

[0016] Optionally, the measuring device further includes a DC power supply module, which is connected to the sine signal generating circuit, the lock-in amplifier circuit, the analog-to-digital conversion circuit, the microcontroller module, and the display module. The DC power supply module is used to supply power to the measuring device.

[0017] Optionally, the measuring device further includes a first single-pole double-throw switch, a second single-pole double-throw switch, and a third single-pole double-throw switch; the sine signal generating circuit is connected to the gate terminal of the first single-pole double-throw switch; the sampling copper sheet is connected to the gate terminal of the second single-pole double-throw switch; the lock-in amplifier circuit is connected to the gate terminal of the third single-pole double-throw switch; the contact 1 of the first single-pole double-throw switch, the contact 1 of the second single-pole double-throw switch, and the contact 1 of the third single-pole double-throw switch are connected in sequence; the contact 2 of the first single-pole double-throw switch and the contact 2 of the second single-pole double-throw switch are both connected to the contact 2 of the third single-pole double-throw switch, and the piezoelectric device is disposed between the contact 2 of the first single-pole double-throw switch and the contact 2 of the second single-pole double-throw switch;

[0018] Wherein, when the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed to the contact 1, the lock-in amplifier circuit is configured to obtain a first node voltage at the connection between the sampling copper sheet, the sine signal generating circuit, and the lock-in amplifier circuit, and obtain a first output voltage according to the sine excitation voltage and the first node voltage;

[0019] When the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed to the contact 2, the lock-in amplifier circuit is configured to obtain a second node voltage at the connection between the piezoelectric device, the sine signal generating circuit, and the lock-in amplifier circuit, and obtain a second output voltage according to the sine excitation voltage and the second node voltage.

[0020] Optionally, the measuring device further includes a first resistor, a second resistor, and a third resistor; one end of the first resistor is connected to the contact 2 of the third single-pole double-throw switch, and the other end is connected to the GND terminal; the second resistor is disposed between the contact 2 of the first single-pole double-throw switch and the contact 2 of the third single-pole double-throw switch; the third resistor is disposed between the contact 1 of the first single-pole double-throw switch and the contact 1 of the second single-pole double-throw switch.

[0021] In a second aspect, an embodiment of the present invention provides a non-contact measurement method for the DC voltage of a wire using a non-contact measurement device for the DC voltage of a wire as described in the first aspect of the embodiment of the present invention, including:

[0022] Performing voltage sampling on a target measurement wire through the measuring device;

[0023] A circuit analog signal is obtained from the result of the voltage sampling, and an analog-to-digital conversion is performed according to the circuit analog signal to obtain a digital signal;

[0024] According to the digital signal, a first sampling capacitance of the sampling copper sheet, a second sampling capacitance of the piezoelectric device, and a sampling voltage are determined;

[0025] A target measured DC voltage is determined according to the first sampling capacitance, the second sampling capacitance, and the sampling voltage;

[0026] Wherein, the digital signal includes a sinusoidal excitation voltage, a first node voltage, a second node voltage, a first output voltage, and a second output voltage.

[0027] Optionally, the determining the first sampling capacitance of the sampling copper sheet, the second sampling capacitance of the piezoelectric device, and the sampling voltage according to the digital signal includes:

[0028] Determining the first sampling capacitance according to the sinusoidal excitation voltage and the first node voltage;

[0029] Determining an equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sinusoidal excitation voltage, the second node voltage, and the second output voltage;

[0030] Determining the second sampling capacitance according to the first sampling capacitance and the equivalent capacitance;

[0031] Determining the sampling voltage according to the second sampling capacitance.

[0032] Optionally, the determining the equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sinusoidal excitation voltage, the second node voltage, and the second output voltage includes:

[0033] Determining the amplitude of the second node voltage according to the amplitude of the second output voltage and the sinusoidal excitation voltage;

[0034] Determining the equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the amplitude of the sinusoidal excitation voltage and the amplitude of the second node voltage.

[0035] Optionally, the determining the sampling voltage according to the second sampling capacitance includes:

[0036] Determining the sampling voltage according to the second sampling capacitance in combination with the initial parameters of the piezoelectric device;

[0037] Wherein, the initial parameters are the parameters of the piezoelectric device without voltage division sampling, and the initial parameters include an initial capacitance, an initial thickness, a piezoelectric coefficient, and an elastic modulus.

[0038] The present invention realizes non-contact measurement of the DC voltage of an electric wire based on a piezoelectric device. The DC voltage to be measured is sampled by capacitor voltage division, and the sampled DC voltage is applied across the electrodes of the piezoelectric device. According to the inverse piezoelectric effect of the piezoelectric device, the distance between the two plates of the piezoelectric device will increase or decrease with the magnitude and polarity of the sampled voltage, thereby changing its own capacitance. Combining the lock-in amplification technology to measure the changed capacitance value of the piezoelectric device and the capacitance value of the sampling capacitor, through the change of the capacitance, the sampled voltage can be deduced inversely, and then the DC voltage to be measured can be deduced inversely. The present invention abandons the mechanical structure part in the traditional vibration capacitive capacitance measurement method, has the advantages of low power consumption, small volume and light weight, and uses the lock-in amplifier technology to measure the change of the capacitance, can measure the amplitude and polarity of the DC voltage of the electric wire, and also has the advantage of high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic structural diagram of a non-contact measurement device for the DC voltage of an electric wire provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic structural diagram of a measurement state of a non-contact measurement device for the DC voltage of an electric wire provided by an embodiment of the present invention;

[0041] Figure 3 is a schematic structural diagram of another measurement state of a non-contact measurement device for the DC voltage of an electric wire provided by an embodiment of the present invention;

[0042] Figure 4 is based on the Figure 2 front-end circuit measurement structure principle schematic diagram provided by an embodiment of the present invention;

[0043] Figure 5 is based on the Figure 3 front-end circuit measurement structure principle schematic diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The following will clearly and completely describe the concept, specific structure and technical effects generated by the present invention in combination with the embodiments and the drawings, so as to fully understand the purpose, features and effects of the present invention.

[0045] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0046] In addition, all the connection relationships mentioned in the text do not simply refer to direct connection of components, but rather refer to the formation of a better connection structure by adding or reducing connection accessories according to specific implementation situations. Each technical feature in the present invention can be interactively combined on the premise of not conflicting with each other.

[0047] In a first aspect, an embodiment of the present invention provides a non-contact measurement device for the DC voltage of an electric wire, including a sampling copper sheet, a piezoelectric device, a sine signal generation circuit, a lock-in amplifier circuit, an analog-to-digital conversion circuit, and a microcontroller module;

[0048] The sampling copper sheet is used to form a first sampling capacitor with the target measurement electric wire;

[0049] The piezoelectric device forms a second sampling capacitor. The piezoelectric device is used to perform voltage division sampling on the target measurement DC voltage to obtain a sampling voltage; wherein, the second sampling capacitor matches the sampling voltage according to the inverse piezoelectric effect of the piezoelectric device;

[0050] The sine signal generation circuit is used to generate a sine excitation voltage;

[0051] The lock-in amplifier circuit is used to obtain the first node voltage at the connection of the sampling copper sheet, the sine signal generation circuit, and the lock-in amplifier circuit, and obtain a first output voltage according to the sine excitation voltage and the first node voltage;

[0052] And, it is used to obtain the second node voltage at the connection of the piezoelectric device, the sine signal generation circuit, and the lock-in amplifier circuit, and obtain a second output voltage according to the sine excitation voltage and the second node voltage;

[0053] The analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the circuit analog signal to obtain a digital signal; the digital signal includes the sine excitation voltage, the first node voltage, the second node voltage, the first output voltage, and the second output voltage;

[0054] The microcontroller module is used to determine the first sampling capacitor of the sampling copper sheet, the second sampling capacitor and the sampling voltage of the piezoelectric device according to the digital signal of the analog-to-digital conversion circuit, and determine the target measurement DC voltage according to the first sampling capacitor, the second sampling capacitor, and the sampling voltage.

[0055] It should be noted that the piezoelectric device includes, but is not limited to, piezoelectric devices made of piezoelectric materials such as quartz, piezoelectric ceramics, and new polymer materials (such as polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, etc.). Specifically, due to the inverse piezoelectric effect of the piezoelectric device, the second sampling capacitor changes with the change of the sampling voltage.

[0056] In some embodiments, the measuring device further includes a display module for displaying the voltage value of the target measured DC voltage, and the display module is electrically connected to the microcontroller module.

[0057] In some embodiments, the measuring device further includes a DC power supply module, which is connected to the sine signal generating circuit, the lock-in amplifier circuit, the analog-to-digital conversion circuit, the microcontroller module, and the display module, and the DC power supply module is used to supply power to the measuring device.

[0058] In some embodiments, the measuring device further includes a first single-pole double-throw switch, a second single-pole double-throw switch, and a third single-pole double-throw switch; the sine signal generating circuit is connected to the gate terminal of the first single-pole double-throw switch; the sampling copper sheet is connected to the gate terminal of the second single-pole double-throw switch; the lock-in amplifier circuit is connected to the gate terminal of the third single-pole double-throw switch; contact 1 of the first single-pole double-throw switch, contact 1 of the second single-pole double-throw switch, and contact 1 of the third single-pole double-throw switch are connected in sequence; contact 2 of the first single-pole double-throw switch and contact 2 of the second single-pole double-throw switch are both connected to contact 2 of the third single-pole double-throw switch, and the piezoelectric device is disposed between contact 2 of the first single-pole double-throw switch and contact 2 of the second single-pole double-throw switch;

[0059] Wherein, when the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed to contact 1, the lock-in amplifier circuit is used to obtain the first node voltage at the connection between the sampling copper sheet, the sine signal generating circuit, and the lock-in amplifier circuit, and obtain a first output voltage according to the sine excitation voltage combined with the first node voltage;

[0060] When the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed to contact 2, the lock-in amplifier circuit is used to obtain the second node voltage at the connection between the piezoelectric device, the sine signal generating circuit, and the lock-in amplifier circuit, and obtain a second output voltage according to the sine excitation voltage combined with the second node voltage.

[0061] In some embodiments, the measuring device further includes a first resistor, a second resistor, and a third resistor; one end of the first resistor is connected to contact 2 of the third single-pole double-throw switch, and the other end is connected to the GND terminal; the second resistor is disposed between contact 2 of the first single-pole double-throw switch and contact 2 of the third single-pole double-throw switch; the third resistor is disposed between contact 1 of the first single-pole double-throw switch and contact 1 of the second single-pole double-throw switch.

[0062] Second aspect, an embodiment of the present invention provides a non-contact measurement method for the DC voltage of a wire by applying a non-contact measurement device for the DC voltage of a wire as described in the first aspect of the embodiment of the present invention, including:

[0063] Performing voltage sampling on the target measurement wire through the measurement device;

[0064] Obtaining a circuit analog signal from the result of the voltage sampling, and performing analog-to-digital conversion on the circuit analog signal to obtain a digital signal;

[0065] Determining a first sampling capacitance of the sampling copper sheet, a second sampling capacitance of the piezoelectric device, and a sampling voltage according to the digital signal;

[0066] Determining the target measurement DC voltage according to the first sampling capacitance, the second sampling capacitance, and the sampling voltage;

[0067] Wherein, the digital signal includes a sinusoidal excitation voltage, a first node voltage, a second node voltage, a first output voltage, and a second output voltage.

[0068] It should be noted that during measurement, the measurement device is placed near the target measurement wire for voltage sampling. On the premise of ensuring safety, the closer the sampling copper sheet of the measurement device is to the target measurement wire, the better.

[0069] In some embodiments, the determining the first sampling capacitance of the sampling copper sheet, the second sampling capacitance of the piezoelectric device, and the sampling voltage according to the digital signal includes:

[0070] Determining the first sampling capacitance according to the sinusoidal excitation voltage and the first node voltage;

[0071] Determining an equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sinusoidal excitation voltage, the second node voltage, and the second output voltage;

[0072] Confirming the second sampling capacitance according to the first sampling capacitance and the equivalent capacitance;

[0073] Determining the sampling voltage according to the second sampling capacitance.

[0074] In some embodiments, the determining the equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sinusoidal excitation voltage, the second node voltage, and the second output voltage includes:

[0075] Determining the amplitude of the second node voltage according to the amplitude of the second output voltage and the sinusoidal excitation voltage;

[0076] Determine the equivalent capacitances of the first sampling capacitor and the second sampling capacitor according to the amplitude of the sine excitation voltage and the amplitude of the second node voltage.

[0077] In some embodiments, the determining the sampling voltage according to the second sampling capacitor includes:

[0078] Determine the sampling voltage according to the second sampling capacitor in combination with the initial parameters of the piezoelectric device;

[0079] Wherein, the initial parameters are the parameters of the piezoelectric device without voltage division sampling, and the initial parameters include an initial capacitance, an initial thickness, a piezoelectric coefficient, and an elastic modulus.

[0080] Next, taking a specific non-contact measurement device for the DC voltage of a wire as an example, the present invention will be further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention:

[0081] Refer to Figure 1 , the non-contact measurement device for the DC voltage of a wire is composed of components and modules such as a single-pole double-throw switch K1, K2, K3, a copper sheet, a piezoelectric device, a resistor R1, a resistor R2, a resistor R3, a sine signal generation circuit, a lock-in amplifier circuit, an analog-to-digital conversion circuit, a microcontroller, a display module, and a DC power supply. The area of the copper sheet is 3-5 times the cross-sectional area of the wire, and the thickness is about 0.1 mm. The purpose is to form a sampling capacitor C1 between the wire and the copper sheet, and the capacitance of the piezoelectric device is C2. The measurement process is divided into two steps. The first step is to find C1, and the second step is to obtain the voltage of the measured wire.

[0082] (1) States of each module when obtaining capacitance C1

[0083] Before measuring the wire voltage, it is necessary to first calibrate the size of the capacitance C1. At this time, the positions of each switch are as Figure 2 shown.

[0084] Refer to Figure 2 , the sine signal generation circuit generates an excitation signal E(t), that is, a sine excitation voltage, which is connected to the resistor R3 through the 1 contact of K1, and then sent to the lock-in amplifier circuit module through the 1 contact of K2 (point M, that is, the first node) and the 1 contact of K3. Then, it passes through the analog-to-digital conversion circuit and is calculated and processed by the microcontroller and stored, preparing for the next step of measuring the wire voltage. The DC power supply provides DC power for each functional module.

[0085] (2) States of each module when measuring the wire voltage

[0086] When measuring the wire voltage, the positions of each switch are as Figure 3 shown.

[0087] Reference Figure 3 When the K2 switch is turned to the 2 contact, C1 and C2 are connected. The sine signal generation circuit generates an excitation signal E(t), which is connected to the resistor R2 through the 2 contact of K1, and then connected to the lock-in amplifier circuit module through the 2 contact (point N, i.e., the second node) of K3. Then, it passes through the analog-to-digital conversion circuit, is calculated and processed by the microcontroller, and then sent to the display module. The DC power supply provides DC power for each functional module.

[0088] Specifically, the measurement principle is as follows:

[0089] First of all, it should be noted that Figure 1 In the shown structural diagram, the analog-to-digital conversion circuit, the microcontroller, the display module, and the DC power supply module are common modules. The sine signal generation circuit module and the lock-in amplifier circuit module are essential modules of this device. However, the relevant circuits of these two modules are also relatively mature, so their internal circuit compositions are not listed here, and only their input and output signals and function descriptions are given.

[0090] 1. Obtaining C1

[0091] Let the DC voltage of the wire under test be V m , and the output of the sine signal generation circuit is E(t)=A sin(ωt + θ), where A is the amplitude of the sine signal, ω is the angular frequency, and θ is the initial phase. Since E(t) is generally used as the reference signal of the circuit, θ is generally taken as zero, and E(t)=A sinωt. Based on Figure 2 , the front-end circuit measurement schematic diagram for obtaining C1 as shown in Figure 4 can be obtained. Figure 4 In it, u M (t) is the voltage at node M. The function of the lock-in amplifier circuit module is to realize the phase-sensitive detection of the u M (t) signal. Therefore, two input signals are required: E(t) and u M (t). After being processed by the internal circuit, the lock-in amplifier circuit module outputs a voltage U o1 , that is, the first output voltage, which is proportional to the product of the amplitude of the sine excitation signal E(t) and the amplitude of u M (t), and then sent to the subsequent analog-to-digital conversion circuit.

[0092] According to Figure 4 , there is:

[0093]

[0094] Among them, the phase angle is:

[0095]

[0096] (1) Working principle of the lock-in amplifier circuit module

[0097] There are mature modules available for purchase in the lock-in amplifier module market. Its basic function is to extract the amplitude of the product signal of u M (t) and E(t). The working principle of the lock-in amplifier is briefly described below. Inside the lock-in amplifier, first, the multiplication of E(t) and u M (t) is achieved, resulting in:

[0098]

[0099] Then, let the above result pass through a low-pass filter, and we have:

[0100]

[0101] Finally, adjust the phase shift of E(t) so that the phase angle At this time, the output U of the lock-in amplifier o1 is:

[0102]

[0103] (2) Calculate C1

[0104] According to Equation (5), where U o1 , A, ω, and R3 are known, so C1 can be calculated.

[0105] 2. Measure the wire voltage

[0106] Based on Figure 3 , the front-end circuit measurement schematic diagram when measuring the wire voltage as shown in Figure 5 can be obtained. In the figure, u N (t) is the voltage at node N. The function of the lock-in amplifier circuit module is to perform phase-sensitive detection on the u N (t) signal. Therefore, two input signals are required: E(t) and u N (t). After being processed by the internal circuit, the lock-in amplifier circuit module outputs a voltage U o2 , which is proportional to the product of the amplitude of the sine excitation signal E(t) and the amplitude of u N (t), and then sent to the subsequent analog-to-digital conversion circuit. The working principle of the lock-in amplifier circuit module has been described in point 1 above and will not be elaborated here.

[0107] (1) Relationship between the DC voltage V of the wire under test m and the capacitance C2 of the piezoelectric device

[0108] Assume that the plate area of the piezoelectric device without an external voltage is S and the thickness is δ0. Then, the capacitance C of the piezoelectric device 20 is:

[0109]

[0110] Among them, ε is the dielectric constant of the piezoelectric material. When an external voltage V2 is applied to the piezoelectric device, charges Q = V2C appear on the two electrodes of the piezoelectric device at this time. 20 . If the piezoelectric coefficient of the piezoelectric material is d and the elastic modulus is E, according to the inverse piezoelectric effect of the piezoelectric material, the thickness of the piezoelectric material decreases or increases at this time (if V2 is positive, it decreases; if V2 is negative, it increases). The plate area S of the piezoelectric device will also change slightly, which can be ignored. Among them, the thickness change amount of the piezoelectric device is:

[0111]

[0112] At this time, the thickness of the piezoelectric material becomes:

[0113]

[0114] The capacitance at this time is:

[0115]

[0116] Among them, the external voltage V2 of the piezoelectric device is still an unknown quantity. As long as the magnitude of C2 is measured, V2 can be obtained according to Equation (9).

[0117] According to the voltage division relationship of series capacitors, it is very easy to find the relationship between V2 and the DC voltage V of the wire under test m is:

[0118]

[0119] Substituting Equation (10) into Equation (9), the functional relationship between the capacitance C2 of the piezoelectric device and the DC voltage V of the wire under test can be obtained m between.

[0120] (2) Relationship between the output voltage U of the lock-in amplifier o2 and the capacitance C2 of the piezoelectric device

[0121] Referring to Figure 5 , assuming the sinusoidal excitation voltage E(t) = A sinωt, the voltage at node N can be obtained as:

[0122]

[0123] Among them,

[0124]

[0125]

[0126]

[0127] Among them, in formula (14), C Σ is the equivalent capacitance when C1 and C2 are connected in series.

[0128] According to the principle of the lock-in amplifier described above, the output U of the lock-in amplifier circuit o2 is proportional to the product of the amplitude A of the sinusoidal excitation signal E(t) and the amplitude B of u N (t), that is:

[0129]

[0130] (3) According to the output U o2 to obtain the DC voltage V of the wire under test m process

[0131] ① First, from formula (15), obtain B (knowing A, U o2 );

[0132] ② According to formula (12), obtain C ∑ (knowing ω, R1, R2, A, B);

[0133] ③ Then, according to formula (14), obtain C2 (knowing C ∑ , C1);

[0134] ④ Then, according to formula (9), obtain V2 (knowing C2, C 20 , d, E, δ0);

[0135] ⑤ Finally, according to formula (10), obtain V m (knowing V2, C1, C2).

[0136] In summary, aiming at the shortcomings of the existing technology, the present invention proposes a non-contact measurement device and method for the DC voltage of a wire based on a piezoelectric device. The DC voltage to be measured is sampled by capacitive voltage division, and the sampled DC voltage is applied across the electrodes of the piezoelectric device. According to the inverse piezoelectric effect of the piezoelectric device, the distance between the two plates of the piezoelectric device will increase or decrease with the magnitude and polarity of the sampled voltage, thereby changing its own capacitance. By measuring this change in capacitance, the sampled voltage can be deduced, and then the DC voltage to be measured can be deduced. The present invention directly uses a piezoelectric device to achieve non-contact measurement of DC voltage, and adopts a lock-in amplification technology to measure the capacitance value change of the piezoelectric device and the capacitance value of the sampling capacitor, and then obtains the measurement value of the DC voltage according to the relevant measurement values. The beneficial effects of the present invention include: cleverly using the inverse piezoelectric effect of the piezoelectric device itself to change the size of the test capacitor, no longer requiring mechanical structures such as rotating electrodes or cantilever beams, which results in the present invention having the advantages of low power consumption, light weight, and small volume; using a lock-in amplifier technology to measure the change in capacitance can measure the amplitude and polarity of the DC voltage of the wire, and the measurement accuracy is high.

[0137] The above has made a specific description of the preferred embodiment of the present invention. However, the present invention is not limited to the described embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present invention. These equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A non-contact measuring device for the DC voltage of an electric wire, characterized in that, It includes a sampling copper sheet, a piezoelectric device, a sine signal generating circuit, a lock-in amplifier circuit, an analog-to-digital conversion circuit, and a microcontroller module; The sampling copper sheet is used to form a first sampling capacitor with the target measurement wire; The piezoelectric device forms a second sampling capacitor. The piezoelectric device is used to perform voltage division sampling on the target measurement DC voltage to obtain a sampling voltage. Among them, the second sampling capacitor is matched with the sampling voltage according to the inverse piezoelectric effect of the piezoelectric device; The sine signal generating circuit is used to generate a sine excitation voltage; The lock-in amplifier circuit is used to obtain the first node voltage at the connection of the sampling copper sheet, the sine signal generating circuit and the lock-in amplifier circuit, and obtain a first output voltage according to the sine excitation voltage combined with the first node voltage; And, it is used to obtain the second node voltage at the connection of the piezoelectric device, the sine signal generating circuit and the lock-in amplifier circuit, and obtain a second output voltage according to the sine excitation voltage combined with the second node voltage; The analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the circuit analog signal to obtain a digital signal. The circuit analog signal represents the result of voltage sampling of the target measurement wire by the measurement device. The digital signal includes the sine excitation voltage, the first node voltage, the second node voltage, the first output voltage, and the second output voltage; The microcontroller module is used to determine the first sampling capacitor of the sampling copper sheet, the second sampling capacitor and the sampling voltage of the piezoelectric device according to the digital signal of the analog-to-digital conversion circuit, and determine the target measurement DC voltage according to the first sampling capacitor, the second sampling capacitor and the sampling voltage.

2. The non-contact measurement device for the DC voltage of an electric wire according to claim 1, characterized in that It further includes a display module for displaying the voltage value of the target measurement DC voltage. The display module is electrically connected to the microcontroller module.

3. The non-contact measuring device for DC voltage of an electric wire according to claim 2, characterized in that, It further includes a DC power supply module. The DC power supply module is connected to the sine signal generating circuit, the lock-in amplifier circuit, the analog-to-digital conversion circuit, the microcontroller module and the display module. The DC power supply module is used to supply power to the measurement device.

4. The non-contact measurement device for the DC voltage of an electric wire according to claim 1, characterized in that, It further includes a first single-pole double-throw switch, a second single-pole double-throw switch, and a third single-pole double-throw switch. The sine signal generating circuit is connected to the gate end of the first single-pole double-throw switch. The sampling copper sheet is connected to the gate end of the second single-pole double-throw switch. The lock-in amplifier circuit is connected to the gate end of the third single-pole double-throw switch. The contact 1 of the first single-pole double-throw switch, the contact 1 of the second single-pole double-throw switch, and the contact 1 of the third single-pole double-throw switch are connected in sequence. The contact 2 of the first single-pole double-throw switch and the contact 2 of the second single-pole double-throw switch are both connected to the contact 2 of the third single-pole double-throw switch. The piezoelectric device is arranged between the contact 2 of the first single-pole double-throw switch and the contact 2 of the second single-pole double-throw switch; Wherein, when the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed at contact 1, the lock-in amplifier circuit is configured to obtain the first node voltage at the connection between the sampling copper sheet, the sine signal generation circuit, and the lock-in amplifier circuit, and obtain a first output voltage based on the sine excitation voltage and the first node voltage; When the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are all closed at contact 2, the lock-in amplifier circuit is configured to obtain the second node voltage at the connection between the piezoelectric device, the sine signal generation circuit, and the lock-in amplifier circuit, and obtain a second output voltage based on the sine excitation voltage and the second node voltage.

5. The non-contact measurement device for the DC voltage of an electric wire according to claim 4, characterized in that, It further includes a first resistor, a second resistor, and a third resistor; one end of the first resistor is connected to contact 2 of the third single-pole double-throw switch, and the other end is connected to the GND terminal; the second resistor is disposed between contact 2 of the first single-pole double-throw switch and contact 2 of the third single-pole double-throw switch; the third resistor is disposed between contact 1 of the first single-pole double-throw switch and contact 1 of the second single-pole double-throw switch.

6. A non-contact measurement method for the DC voltage of an electric wire using the non-contact measurement device for the DC voltage of an electric wire according to any one of claims 1 to 5, characterized in that, Comprising: Performing voltage sampling on the target measurement wire through the measurement device; Obtaining a circuit analog signal based on the result of the voltage sampling, and performing analog-to-digital conversion on the circuit analog signal to obtain a digital signal; Determining a first sampling capacitance of the sampling copper sheet, a second sampling capacitance of the piezoelectric device, and a sampling voltage according to the digital signal; Determining the target measurement DC voltage according to the first sampling capacitance, the second sampling capacitance, and the sampling voltage; Wherein, the digital signal includes a sine excitation voltage, a first node voltage, a second node voltage, a first output voltage, and a second output voltage.

7. A non-contact measurement method for the DC voltage of an electric wire according to claim 6, characterized in that, The determining the first sampling capacitance of the sampling copper sheet, the second sampling capacitance of the piezoelectric device, and the sampling voltage according to the digital signal includes: Determining the first sampling capacitance according to the sine excitation voltage and the first node voltage; Determining an equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sine excitation voltage, the second node voltage, and the second output voltage; Confirming the second sampling capacitance according to the first sampling capacitance and the equivalent capacitance; Confirming the sampling voltage according to the second sampling capacitance.

8. A non-contact measurement method for the DC voltage of an electric wire according to claim 7, characterized in that, The determining the equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the sine excitation voltage, the second node voltage, and the second output voltage includes: Determining the amplitude of the second node voltage according to the amplitude of the second output voltage and the sine excitation voltage; Determining the equivalent capacitance of the first sampling capacitance and the second sampling capacitance according to the amplitude of the sine excitation voltage and the amplitude of the second node voltage.

9. A non-contact measurement method for the DC voltage of an electric wire according to claim 7, characterized in that, The confirming the sampling voltage according to the second sampling capacitance includes: Determining the sampling voltage according to the second sampling capacitance in combination with the initial parameters of the piezoelectric device; Among them, the initial parameters are the parameters of the piezoelectric device without voltage division sampling, and the initial parameters include the initial capacitance, initial thickness, piezoelectric coefficient, and elastic modulus.

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