Clamp-on ac voltage probe

Abstract

The present application provides a kind of clamping type AC voltage probe for easily measuring high voltage AC voltage.The clamping type AC voltage probe (1) includes: clamping part (2), clamping cable (CBL) as the object of measurement;Electrode (E) is arranged in a manner facing the cable (CBL) clamped by the clamping part (2);Parallel circuit (5), capacitor (C1) and resistor (R1) are connected in parallel, one end (P1) is connected to electrode (E);Resistor (R2), one end is connected to the other end (P2) of parallel circuit (5), the other end is connected to circuit ground;Capacitor (C2), one end is connected to the other end (P2) of parallel circuit (5), the other end is connected to circuit ground;And amplifier (A1), one end (P1) or the other end (P2) of parallel circuit (5) is connected to the input terminal, and the signal input to the input terminal is amplified and output.

Description

Technical Field

[0001] This invention relates to a clamping AC voltage probe for clamping a cable being measured. Background Technology

[0002] Previously, a voltage detection device was known that detected the AC voltage of the object being detected by generating a reference voltage to reduce the potential difference between the AC voltage of the object being detected and the reference voltage, that is, by generating a reference voltage that is the same voltage as the AC voltage of the object being detected (for example, see Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-25918 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, according to the voltage detection device, a reference voltage identical to the AC voltage of the object being detected needs to be generated. Therefore, for example, when the AC voltage of the object being detected is a high voltage of several hundred to several thousand volts, a circuit for generating such a high voltage is required. The circuit for generating such a high voltage is costly and does not easily reproduce the AC waveform of the detected high voltage.

[0008] The purpose of this invention is to provide a clamp-on AC voltage probe that makes it easy to measure high-voltage AC voltage.

[0009] Technical means to solve the problem

[0010] An example of the clamping AC voltage probe of the present invention includes: a clamping part for clamping a cable as the object of measurement; an electrode disposed facing the cable clamped by the clamping part; a parallel circuit in which a first capacitor and a first resistor are connected in parallel, one end of which is connected to the electrode; a second resistor, one end of which is connected to the other end of the parallel circuit and the other end of which is connected to the circuit ground; a second capacitor, one end of which is connected to the other end of the parallel circuit and the other end of which is connected to the circuit ground; and an amplifier connected to one or the other end of the parallel circuit at an input terminal, which amplifies and outputs the signal input to the input terminal.

[0011] The effects of the invention

[0012] This type of clamp-on AC voltage probe is easy to measure high-voltage AC voltages. Attached Figure Description

[0013] Figure 1This is a perspective view showing an example of the structure of a clamping AC voltage probe according to an embodiment of the present invention.

[0014] Figure 2 It's perspective. Figure 1 The clamping arm and frame are shown in the front view of the interior through the front wall.

[0015] Figure 3 It means Figure 1 The circuit diagram shows an example of the electrical structure of a clamp-on AC voltage probe.

[0016] Figure 4 It means Figure 3 The circuit diagram shows another example of the electrical structure of a clamp-on AC voltage probe.

[0017] [Explanation of Symbols]

[0018] 1: Clamp-on AC voltage probe

[0019] 2: Clamping part

[0020] 3: Frame

[0021] 4: Coaxial cable

[0022] 5: Parallel circuit

[0023] 21, 22: Clamping arms

[0024] 23, 24: Screw holes

[0025] 25: Screws

[0026] 26: Nut

[0027] 27: Shaft

[0028] 28: Containment Space

[0029] 31: Circuit board

[0030] 32: Conductive layer

[0031] 211, 221: Retaining groove

[0032] A1: Amplifier

[0033] C1: Capacitor (First Capacitor)

[0034] C2: Capacitor (Second Capacitor)

[0035] Cx: Electrostatic capacitance

[0036] CBL: Cable

[0037] E: Electrode

[0038] P1: One end

[0039] P2: The other end

[0040] R1: Resistor (first resistor)

[0041] R2: Resistor (Second Resistor)

[0042] T1, T2, T3: terminals

[0043] Va: Input voltage

[0044] Vin: Cable voltage

[0045] W: Wiring Detailed Implementation

[0046] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. Furthermore, structures marked with the same symbols in the drawings represent the same structures, and their descriptions are omitted.

[0047] Figure 1 The clamp-on AC voltage probe 1 shown generally includes: a clamping part 2 for clamping the cable CBL, which is the object to be measured; and a generally box-shaped frame 3 connected to the clamping part 2. The frame 3 is connected to a measuring device such as an oscilloscope or a data logger via a coaxial cable 4.

[0048] The clamping part 2 includes a pair of clamping arms 21 and 22. The base end of the clamping arm 21 is supported by a shaft 27 mounted on the frame 3. The clamping arm 21 is able to swing about the shaft 27. Retaining grooves 211 and 221 for inserting the cable CBL are formed on the facing surfaces of the clamping arms 21 and 22.

[0049] Clamping arm 21 applies force to clamping arm 22 via a torsion spring (not shown in the diagram). The force applied by the torsion spring clamps cable CBL between clamping arm 21 and clamping arm 22.

[0050] Reference Figure 2 The clamping arm 22 is fixedly connected to the frame 3. Furthermore, the clamping arm 22 can also swing in the same way as the clamping arm 21.

[0051] The clamping arms 21, 22 and the frame 3 are made of insulating material, such as resin.

[0052] A receiving space 28 is provided inside the clamping arm 22. The receiving space 28 communicates with the internal space of the frame 3. An electrode E, which is generally plate-shaped, is disposed in the receiving space 28. The electrode E may be formed as a conductor pattern on a printed wiring substrate, or it may be a metal plate. The electrode E is disposed facing or in contact with the inner wall surface of the holding groove 221 of the clamping arm 22. Thus, the electrode E is disposed facing the cable CBL clamped by the clamping part 2, through the wall of the holding groove 221, which is made of insulating material.

[0053] A circuit board 31 is housed in the frame 3. The terminals T3 of the circuit board 31 are connected to the electrode E via wiring W1.

[0054] A conductive layer 32, indicated by a shadow line, is formed on the inner wall surface of the receiving space 28 of the clamping arm 22 and the frame 3, except for the portion located between the cable CBL and the electrode E clamped by the clamping part 2.

[0055] The conductive layer 32 can be, for example, a metal foil such as aluminum foil, a layer coated with a conductive coating, a plating layer, or a metal plate. Figure 2 In the example shown, no conductive layer 32 is formed on the wall of the retaining groove 221 located between the cable CBL clamped by the clamping part 2 and the electrode E, or on the periphery of the electrode E.

[0056] Therefore, the outer wall of the clamping AC voltage probe 1 is insulating, and at least the portion of the inner wall of the frame 3 and the inner wall of the clamping arm 22, except for the portion located between the cable CBL and the electrode E clamped by the clamping part 2, is conductive.

[0057] The outer wall of the clamp-type AC voltage probe 1 is insulated, thus reducing the possibility of damage to the clamp-type AC voltage probe 1 even when, for example, the conductor portion of the cable CBL is exposed, current flows from the cable CBL to the electrode E or the circuit board 31. Furthermore, the safety of the user operating the clamp-type AC voltage probe 1 is improved.

[0058] In addition, by including the conductive layer 32, electromagnetic noise from the external environment can be reduced.

[0059] Furthermore, electrode E is not necessarily limited to the example of being disposed inside the clamping part 2 and arranged facing the cable CBL with an insulating material as a barrier. Electrode E may also be disposed exposed in the retaining groove 221 and facing each other in contact with the cable CBL.

[0060] Near the front ends of clamping arms 21 and 22, screw holes 23 and 24 are formed, which pass through the free-size holes of clamping arms 21 and 22 when they are closed. A nut 26 is installed on the side of the screw hole 24 of clamping arm 22 opposite to that of clamping arm 21. Thus, by inserting a screw 25 into the screw hole 24 from the screw hole 23 side and tightening the screw 25 and nut 26, the clamping arms 21 and 22 can securely clamp the cable CBL.

[0061] As described below, the clamp-on AC voltage probe 1 detects the AC voltage of the cable CBL via the electrostatic capacitance Cx generated by aligning the conductor of the cable CBL with the electrode E. The electrostatic capacitance Cx is inversely proportional to the distance between the conductor of the cable CBL and the electrode E. Therefore, the shorter the distance, the greater the electrostatic capacitance Cx, and the easier it is to detect the AC voltage. Furthermore, if the distance changes, the voltage level obtained via the electrostatic capacitance Cx will change.

[0062] On the other hand, the clamping arms 21 and 22, relying solely on the force applied by the torsion springs (not shown in the diagram), result in insufficient clamping force on the cable CBL. This creates a gap between the cable CBL and the retaining groove 221, increasing the distance between them and potentially reducing the electrostatic capacitance Cx. Furthermore, the cable CBL oscillates, causing changes in the distance between them and potentially altering the electrostatic capacitance Cx.

[0063] However, the clamping AC voltage probe 1 can securely clamp the cable CBL by using screws 25 to fasten clamping arms 21 and 22, thus reducing the possibility of a decrease in electrostatic capacitance Cx caused by an increase in the phase distance or a change in electrostatic capacitance Cx caused by the swing of the cable CBL.

[0064] Alternatively, the nut 26 can be positioned on the side of the screw hole 23, and the screw 25 can be inserted through the screw hole 24. Alternatively, the nut 26 can be omitted, and a screw groove can be formed in the screw hole 23 or the screw hole 24.

[0065] Figure 3 The clamp-on AC voltage probe 1 shown includes an electrode E, a parallel circuit 5, a resistor R2 (second resistor), a capacitor C2 (second capacitor), an amplifier A1, and terminals T1 and T2. The parallel circuit 5 is a parallel circuit of capacitor C1 (first capacitor) and resistor R1 (first resistor). The parallel circuit 5, resistor R2, capacitor C2, amplifier A1, and terminals T1 and T2 are formed on the circuit board 31.

[0066] Figure 3 In the diagram, the electrostatic capacitance formed by the cable CBL facing the electrode E is represented by the electrostatic capacitance Cx.

[0067] Electrode E via Figure 2 The wiring shown, including terminal T3, is connected to one end P1 of the parallel circuit 5. The other end P2 of the parallel circuit 5 is connected to the circuit ground via capacitor C2. Additionally, the other end P2 of the parallel circuit 5 is connected to the circuit ground via resistor R2. The circuit ground is connected to conductive layer 32.

[0068] One end P1 of the parallel circuit 5 is connected to the input terminal of amplifier A1. The output terminal of amplifier A1 is connected to terminal T1. Terminal T2 is connected to the circuit ground.

[0069] Terminal T1 is connected to the core wire of coaxial cable 4, and terminal T2 is connected to the shield wire of coaxial cable 4. Thus, the output signal of amplifier A1 is output to a measuring device such as an oscilloscope or data logger via coaxial cable 4. Furthermore, the output signal of amplifier A1 is not limited to examples output via coaxial cable; it can also be output via twisted-pair cable or multi-core cable. Additionally, the output signal line of amplifier A1 and the power supply line for the amplifier A1 can be included in a single cable. From the viewpoint of reducing noise, it is more preferable to provide a separate power supply cable for amplifier A1 from the output signal cable.

[0070] The cable CBL is not particularly limited; for example, it is assumed to be a power cable for driving the motor of an electric vehicle. In the case of a power cable for driving the motor of an electric vehicle, the AC voltage, which is the output of the self-inverter and is a rectangular wave periodic waveform based on pulse width modulation (PWM), becomes the object of measurement. In this case, the assumed voltage is alternating current (AC) of 200V to 1000V, and the measured waveform is a pulse with a frequency equivalent to 1kHz to 1MHz.

[0071] The AC voltage of cable CBL is applied to one end P1 of parallel circuit 5 via electrostatic capacitor Cx.

[0072] For example, in the case of a rectangular wave periodic waveform based on PWM, the rising and falling of the rectangular wave contains high-frequency components. Therefore, in order to accurately measure the voltage waveform of the cable CBL, it is necessary to detect both the low-frequency component corresponding to the period of the rectangular wave and the high-frequency component corresponding to the rising and falling of the rectangular wave.

[0073] Therefore, based on the clamp-on AC voltage probe 1, a series circuit of resistor R1 and capacitor C2 is constructed. The series circuit of resistor R1 and capacitor C2 is a so-called integrating circuit, which functions as a low-pass filter to allow low-frequency components to pass through.

[0074] Since the voltage between the terminals of capacitor C2 and resistor R1 is added together and applied to the input terminals of amplifier A1, the low-frequency component corresponding to the period of the rectangular wave can be input to amplifier A1 according to the series circuit of resistor R1 and capacitor C2.

[0075] Furthermore, based on the clamp-type AC voltage probe 1, a series circuit of capacitor C1 and resistor R2 is constructed. This series circuit of capacitor C1 and resistor R2 is a so-called differentiating circuit, functioning as a high-pass filter that allows high-frequency components to pass through.

[0076] Since the voltage between the terminals of resistor R2 and capacitor C1 is added together and applied to the input terminals of amplifier A1, the high-frequency components corresponding to the rise and fall of the rectangular wave can be input to amplifier A1 according to the series circuit of capacitor C1 and resistor R2.

[0077] That is, the low-frequency component corresponding to the period of the rectangular wave and the high-frequency component corresponding to the rise and fall of the rectangular wave overlap and are input to the input terminal of amplifier A1. Therefore, the AC voltage waveform detected from cable CBL can be amplified with good accuracy by amplifier A1 and output to the measuring device.

[0078] Furthermore, the resistance value R1 is very large compared to the impedance of capacitor C1. Specifically, for example, the resistance value R1 can be set to 1MΩ to 1GΩ. For example, if the assumed frequency f is set to 1kHz to 1MHz and the capacitor C1 is set to 1nF, then the impedance |Z| of capacitor C1 relative to 1kHz is 1 / (2π×10⁻⁶). 3 ×10 -9 =159kΩ, the impedance |Z| of capacitor C1 relative to 1MHz is 1 / (2π×10) 6 ×10 -9 =159Ω.

[0079] Therefore, the resistance value R1 is more than 6.3 times greater than the impedance |Z| of capacitor C1 at a frequency f of 1kHz, and more than 6300 times greater than the impedance |Z| of capacitor C1 at a frequency f of 1MHz. Consequently, most of the AC current detected from cable CBL flows through the series circuit of electrostatic capacitor Cx, capacitor C1, and capacitor C2.

[0080] As a result, since the current flowing through resistor R1 can be largely ignored, the cable voltage Vin of cable CBL is divided by the series circuit of electrostatic capacitor Cx, capacitor C1, and capacitor C2, and the input voltage Va input to amplifier A1 can be approximated by the following formula (1).

[0081] Va=Vin×(CxC2+CxC1) / (C1C2+CxC2+CxC1)…(1) where the electrostatic capacitance of capacitor C1 is set as C1 and the electrostatic capacitance of capacitor C2 is set as C2.

[0082] Thus, according to the clamp-type AC voltage probe 1, the cable voltage Vin is divided, and the reduced input voltage Va is input to the amplifier A1. Therefore, as described in Patent Document 1, it is easy to measure the high voltage AC voltage without setting up a circuit to generate a high voltage.

[0083] For example, the electrostatic capacitor Cx can be set to 0.1pF to 10pF, the electrostatic capacitor C1 to 0.1nF to 10nF, and the electrostatic capacitor C2 to 1nF to 100nF. When Cx = 0.1pF, C1 = 0.1nF, and C2 = 1nF, according to equation (1), Va = Vin × 0.001. Furthermore, when Cx = 10pF, C1 = 10nF, and C2 = 100nF, according to equation (1), Va = Vin × 0.001.

[0084] That is, the cable voltage Vin can be reduced to 1 / 1000 of the input voltage Va and input to amplifier A1. In this case, even if the cable voltage Vin is 1kV, the input voltage Va input to amplifier A1 is 1V, so it is easy to measure the high voltage cable voltage Vin.

[0085] Amplifier A1 is a so-called amplifier circuit that amplifies the input signal and outputs it. Amplifier A1 is preferably a component with a high input impedance, such as an amplifier constructed using a junction field-effect transistor (FET) or a metal-oxide-semiconductor FET (MOSFET).

[0086] As described above, the AC current detected by electrode E from cable CBL flows through the series circuit of capacitors Cx, C1, and C2, causing the cable voltage Vin to be divided, and the input voltage Va is input to amplifier A1. However, when the input impedance of amplifier A1 is low, the detected AC current flowing into amplifier A1 decreases, reducing the current flowing through the series circuit of capacitors Cx, C1, and C2, and thus lowering the input voltage Va. Therefore, the detection accuracy of the cable voltage Vin may decrease.

[0087] However, by setting the input impedance of amplifier A1 to a high impedance, the current flowing into the input terminals of amplifier A1 can be reduced. As a result, the possibility of a decrease in the detection accuracy of cable voltage Vin can be reduced.

[0088] The output signal of amplifier A1 is output to the measuring device via terminal T1 and coaxial cable 4. Thus, the AC voltage waveform of cable CBL can be observed using the measuring device.

[0089] Furthermore, such as Figure 4 As shown, the input terminal of amplifier A1 can also be connected to the other end P2 instead of to one end P1. However, sometimes it is desirable to adjust the filter characteristics of a low-pass filter containing resistor R1 and capacitor C2, and a high-pass filter containing capacitor C1 and resistor R2, according to the frequency or waveform of the signal to be detected. When the circuit constants of capacitors C1 and C2 change along with this adjustment of filter characteristics, and the voltage division ratio in the series circuit of capacitor Cx, capacitor C1, and capacitor C2 changes, the detection level input to amplifier A1 changes when the input terminal of amplifier A1 is connected to the other end P2.

[0090] On the other hand, when the input terminal of amplifier A1 is connected to one end P1, if the electrostatic capacitance of capacitors C1 and C2 is adjusted within a range where the series impedance of capacitors C1 and C2 does not change, the change in the detection level input to amplifier A1 can be suppressed, and the filter characteristics can be adjusted. Therefore, the input terminal of amplifier A1 can also be connected to the other end P2, but it is more preferable to connect it to one end P1.

[0091] That is, an example of the clamping AC voltage probe of the present invention includes: a clamping part for clamping a cable as the object of measurement; an electrode arranged facing the cable clamped by the clamping part; a parallel circuit in which a first capacitor and a first resistor are connected in parallel, one end of which is connected to the electrode; a second resistor, one end of which is connected to the other end of the parallel circuit and the other end of which is connected to the circuit ground; a second capacitor, one end of which is connected to the other end of the parallel circuit and the other end of which is connected to the circuit ground; and an amplifier connected to one end or the other end of the parallel circuit at an input terminal, which amplifies and outputs the signal input to the input terminal.

[0092] According to the structure described, the cable core and electrodes are arranged facing each other, and the electrodes are electrostatically coupled to the cable core. As a result, the AC voltage of the cable is applied to one end of the parallel circuit via the electrostatic capacitance generated between the cable core and the electrodes. Furthermore, a low-pass filter is formed by connecting a first resistor and a second capacitor in series, and a high-pass filter is formed by connecting a first capacitor and a second resistor in series. As a result, by using the low-pass filter to obtain the fundamental frequency of the AC voltage being measured, and using the high-pass filter to obtain the high-frequency components contained in the rising and falling waveforms of the AC voltage, the waveform of the object being measured can be easily and accurately detected. Furthermore, due to the electrostatic coupling between the cable and the electrodes, the direct current from the cable is cut off, and the current obtained from the electrodes becomes alternating current. As a result, regarding the voltage input to the amplifier, the voltage division caused by the electrostatic capacitance between the cable electrodes, the first capacitor, and the second capacitor dominates. Thus, for example, even if the cable voltage is high, the voltage reduced by voltage division will still be input to the amplifier. Therefore, even if the object to be measured is a high voltage, it can be detected without setting up a circuit to generate a high voltage, as described in Patent Document 1. Therefore, if the clamp-type AC voltage probe is used, it is easy to measure the AC voltage of a high voltage.

[0093] In addition, the input terminal of the amplifier is preferably connected to one end of the parallel circuit.

[0094] According to the aforementioned structure, the voltage division ratio of the voltage input to the amplifier is determined by the series impedance of the first and second capacitors. Conversely, when the input terminal of the amplifier is connected to the other end of the parallel circuit, the voltage division ratio of the voltage input to the amplifier is determined by the impedance of the second capacitor. Therefore, when the capacitance of the second capacitor is changed to adjust the characteristics of the low-pass filter, the signal level input to the amplifier also changes. On the other hand, according to the aforementioned structure, since the voltage division ratio of the voltage input to the amplifier is determined by the series impedance of the first and second capacitors, by changing the capacitance of the second capacitor within a range that does not change the series impedance of the first and second capacitors, it is easy to suppress changes in the signal level input to the amplifier and adjust the capacitance of the second capacitor.

[0095] In addition, the resistance value of the first resistor is preferably greater than the impedance of the first capacitor.

[0096] According to the described structure, in the parallel circuit of the first capacitor and the first resistor, more current flows through the first capacitor compared to the first resistor. As a result, the voltage division accuracy achieved by the electrostatic capacitance between the cable electrodes, the first capacitor, and the second capacitor is improved.

[0097] In addition, the input terminal of the amplifier is preferably high impedance.

[0098] According to the structure described, the current flowing from the electrodes into the input terminals of the amplifier can be reduced, thus improving the voltage division accuracy achieved by the electrostatic capacitance between the cable electrodes, the first capacitor, and the second capacitor.

[0099] Furthermore, the amplifier is preferably constructed using a FET.

[0100] The FET has a high input impedance, making it suitable as the amplifier.

[0101] Alternatively, preferably, the clamping portion is constructed using an insulating material, and the electrode is disposed inside the clamping portion and arranged facing the cable, with the insulating material as a barrier.

[0102] According to the structure, even when the cable core is in contact with the clamping part, the voltage of the cable will not be directly applied to the electrode, thus improving the safety of the clamping AC voltage probe.

[0103] Alternatively, preferably, it further includes a frame, which is connected to the clamping part and houses the parallel circuit, the second resistor, the second capacitor and the amplifier. The outer wall of the frame is insulating and the inner wall is conductive. The circuit is grounded and connected to the conductive inner wall.

[0104] According to the structure, the outer wall surface of the frame that the user comes into contact with can be made insulated to improve safety, and the conductive inner wall surface can reduce electromagnetic noise from the external environment.

[0105] Additionally, preferably, the clamping portion has a receiving space for accommodating the electrode, the outer wall surface of the clamping portion is insulating, and the inner wall surface of the receiving space is conductive, except for the portion located between the electrode and the cable, and the circuit is grounded and connected to the conductive inner wall surface of the receiving space.

[0106] According to the structure, the outer wall surface of the clamping part that the user contacts can be made insulated to improve safety, and the conductive part of the inner wall surface can reduce electromagnetic noise from the external environment.

[0107] Alternatively, preferably, the clamping part clamps the cable by a pair of clamping arms, the base end of at least one of the pair of clamping arms is supported by a shaft, the at least one clamping arm is swaying about the shaft, and a screw hole is formed near the front end of the pair of clamping arms to receive a screw for fastening the pair of clamping arms.

[0108] According to the described structure, a pair of clamping arms can be fastened with screws, thus securely clamping the cable. Therefore, gaps are less likely to form between the cable and the clamping arms, and the electrostatic capacitance between the cable electrodes is stable. As a result, the cable voltage can be easily detected using a clamp-on AC voltage probe.

Claims

1. A clamp-on AC voltage probe, comprising: The clamping part clamps the cable being measured. The electrodes are arranged facing the cable clamped by the clamping part; In a parallel circuit, the first capacitor and the first resistor are connected in parallel, with one end connected to the electrode. The second resistor has one end connected to the other end of the parallel circuit and the other end connected to the circuit ground. The second capacitor has one end connected to the other end of the parallel circuit and the other end connected to the circuit ground. as well as An amplifier, the input terminal of which is connected to the other end of the parallel circuit, amplifies and outputs the signal input to the input terminal.

2. A clamp-on AC voltage probe, comprising: The clamping part clamps the cable being measured. The electrodes are arranged facing the cable clamped by the clamping part; In a parallel circuit, the first capacitor and the first resistor are connected in parallel, with one end connected to the electrode. The second resistor has one end connected to the other end of the parallel circuit and the other end connected to the circuit ground. The second capacitor has one end connected to the other end of the parallel circuit and the other end connected to the circuit ground. as well as An amplifier, the input terminal of which is connected to one end of the parallel circuit, amplifies and outputs the signal input to the input terminal.

3. The clamping AC voltage probe according to claim 1 or 2, wherein the resistance value of the first resistor is greater than the impedance of the first capacitor.

4. The clamp-on AC voltage probe according to claim 1 or 2, wherein the input terminal of the amplifier is high impedance.

5. The clamping AC voltage probe according to claim 4, wherein the amplifier is configured using a field-effect transistor.

6. The clamping AC voltage probe according to claim 1 or 2, wherein the clamping part is constructed of an insulating material. The electrode is disposed inside the clamping portion and is arranged facing the cable in a manner that separates it from the insulating material.

7. The clamping AC voltage probe according to claim 1 or 2 further includes a frame, the frame being connected to the clamping part and housing the parallel circuit, the second resistor, the second capacitor, and the amplifier. The outer wall of the frame is insulating, and the inner wall is conductive. The circuit is grounded and connected to the conductive inner wall.

8. The clamping AC voltage probe according to claim 7, wherein the clamping portion has a receiving space for receiving the electrode. The outer wall of the clamping part is insulating, and the inner wall of the receiving space is conductive, except for the portion located between the electrode and the cable. The circuit is grounded and connected to the conductive inner wall of the receiving space.

9. The clamping AC voltage probe according to claim 1 or 2, wherein the clamping part clamps the cable by a pair of clamping arms. The base end of at least one of the pair of clamping arms is supported by a shaft. The at least one clamping arm is capable of swinging about the axis. Screw holes are formed near the front end of the pair of clamping arms to receive screws used to fasten the pair of clamping arms.

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