Residual current measuring circuit and device thereof

Abstract

The invention discloses a residual current measuring circuit and a device thereof. The circuit comprises an I / V conversion unit, an anti-aliasing filtering unit, a secondary amplification unit, an A / D sampling unit and a microprocessor unit which are connected in sequence, the I / V conversion unit is used for converting an input original residual current signal into a voltage signal; the anti-aliasing filtering unit is used for filtering and denoising the voltage signal to obtain a denoised signal; the secondary amplification unit is used for carrying out secondary amplification on the de-noised signal to obtain an amplified signal; the A / D sampling unit is used for converting the amplified signal into a digital signal and transmitting the digital signal to the microprocessor, the completeness of the measured signal can be guaranteed through the measures of preventing the current signal to be measured from shunting and the filtering combination circuit, and the precision and authenticity of residual current measurement are improved.

Description

Technical Field

[0001] The invention relates to the field of current monitoring, and in particular to a residual current measuring circuit and a device thereof. Background Art

[0002] Due to cable aging, insulation damage or equipment leakage in the low-voltage power distribution system, the current in the distribution circuit does not flow back to the power supply, resulting in residual (leakage) current to the ground. If these problems are not discovered in time, it may cause damage to the running equipment, or even cause serious accidents such as building fires and personal injuries.

[0003] Therefore, to ensure safety, low-voltage power distribution systems are generally equipped with residual current monitoring devices. Existing residual current monitoring devices are easily interfered by the external environment, resulting in low measurement accuracy. Summary of the invention

[0004] The invention provides a residual current measuring circuit and a device thereof, which are used to solve the technical problem that the residual current monitoring device has low precision.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A residual current measurement circuit comprises: an I / V conversion unit, an anti-aliasing filter unit, a secondary amplification unit, an A / D sampling unit and a microprocessor unit connected in sequence;

[0007] The I / V conversion unit is used to convert the input original residual current signal into a voltage signal;

[0008] The anti-aliasing filter unit is used to filter and de-noise the voltage signal to obtain a de-noised signal;

[0009] The secondary amplification unit is used to perform secondary amplification on the denoised signal to obtain an amplified signal;

[0010] The A / D sampling unit is used to convert the amplified signal into a digital signal and transmit it to the microprocessor.

[0011] Preferably, the I / V conversion unit includes a resistor R1, a resistor R2, an operational amplifier IC1 and a capacitor C1; the resistor R1 and the capacitor C1 form a parallel RC circuit, a first end of the parallel RC circuit is connected to a first end of the resistor R2, a second end of the parallel RC circuit is connected to an output end of the operational amplifier IC1, a second end of the resistor R2 is connected to a first input end of the operational amplifier IC1, and a second input end of the operational amplifier IC1 is grounded.

[0012] Preferably, the anti-aliasing filtering unit includes: a resistor R3, a resistor R4, a capacitor C2, a capacitor C3, and an operational amplifier IC2; the first end of the resistor R3 is connected to the output end of the operational amplifier IC1; the second end of the resistor R3 is respectively connected to the first end of the resistor R4 and the first end of the capacitor C3, the second end of the resistor R4 is respectively connected to the first end of the capacitor C2 and the first input end of the operational amplifier IC2, and the second input end of the operational amplifier IC2 is connected to its output end; the second end of the capacitor C2 is grounded; the second end of the capacitor C3 is connected to the second input end of the operational amplifier IC2.

[0013] Preferably, the secondary amplification unit includes: a resistor R5, a resistor R6, a resistor R7, a capacitor C4, a capacitor C5, and an operational amplifier IC3; the capacitor C4 and the capacitor C5 form a parallel RC circuit, the first end of the resistor R6 is connected to the output end of the operational amplifier IC2, the second end of the resistor R6 is respectively connected to the first end of the parallel RC circuit, the first end of the resistor R7, and the first end of the capacitor C5, and the second end of the capacitor C5 is grounded; the second end of the resistor R7 is connected to the first end of the operational amplifier IC3, the second end of the operational amplifier IC3 is grounded, and the second end of the parallel RC circuit is connected to the output end of the operational amplifier IC3.

[0014] Preferably, it further comprises a zeroing unit, the input end of the zeroing unit is connected to the output end of the microprocessor, and the output end of the zeroing unit is connected to the output end of the I / V conversion unit; the microcontroller is used to send a signal to the zeroing signal to control the zeroing unit to perform zeroing processing on the voltage signal output by the I / V conversion unit;

[0015] and / or

[0016] The measuring circuit further comprises any one or more of the following units:

[0017] Display unit, communication unit, alarm unit and power cut-off unit;

[0018] The display unit, the communication unit, the alarm unit and / or the power cut-off unit are connected to the microprocessor.

[0019] Preferably, when the residual current measurement circuit includes a zeroing unit, the zeroing unit includes: a digital-to-analog converter IC4, an operational amplifier IC5 and a resistor R8; the input end of the digital-to-analog converter IC4 is connected to the output end of the microprocessor, the output end of the digital-to-analog converter IC4 is connected to the first input end of the operational amplifier IC5, and the second input end of the operational amplifier IC5 is grounded; the feedback signal end of the digital-to-analog converter IC4 is connected to the output end of the operational amplifier IC5, the output end of the operational amplifier IC5 is connected to the first end of the resistor R8, and the second end of the resistor R8 is connected to the second input end of the operational amplifier IC1.

[0020] A residual current measuring device comprises a shell and a PBC board arranged in the shell, wherein the PBC board is printed with the above-mentioned residual current measuring circuit.

[0021] Preferably, it further comprises a first insulating support and a second insulating support, the parallel RC circuit of the I / V conversion unit is erected between the first insulating support and the second insulating support, and the first end of the parallel RC circuit is passed through the first insulating support, the second end of the parallel RC circuit of the I / V conversion unit is passed through the second insulating support, a first avoidance hole and a second avoidance hole are provided on the PBC board, the first avoidance hole corresponds to the first insulating support, the second avoidance hole corresponds to the second insulating support, the first insulating support is connected to the signal output terminal of the external device through the first avoidance hole, and the second insulating support is connected to the signal output terminal of the external device through the second avoidance hole.

[0022] Preferably, the housing comprises a first shielding box and a second shielding box, the first shielding box is used to shield the I / V conversion unit on the PBC board; the second shielding box is used to shield the entire PBC board.

[0023] Preferably, the first shielding box is a Permalloy shielding box, and the second shielding box is a conductive and continuous silicon steel shielding box with gaps or holes on the surface of the shielding body and a metal braided mesh conductive elastic material filled therein.

[0024] and / or

[0025] The first insulating support and the second insulating support are both connected to the signal output end of the external device through a low-leakage coaxial shielded cable.

[0026] The present invention has the following beneficial effects:

[0027] 1. The residual current measurement circuit and device of the present invention can ensure the integrity of the measurement signal and improve the accuracy and authenticity of the residual current measurement by preventing the current signal to be measured from being shunted and the filtering combination circuit.

[0028] 2. In the preferred solution, through the overall EMC combination design of the PCB board, high-frequency and low-frequency electromagnetic interference can be filtered out in a harsh electromagnetic harmonic environment to ensure the reliability of residual current measurement.

[0029] 3. In the preferred embodiment, the present invention constructs a residual current data management strategy, and uses the residual current as a reference for daily maintenance of factory equipment, which can prevent electrical safety accidents of equipment and improve the economic benefits of the factory.

[0030] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1 is a hardware principle block diagram of a measuring device in a preferred embodiment of the present invention;

[0033] Figure 2 A diagram of a current transmitter signal measurement device in a preferred embodiment of the present invention;

[0034] Figure 3 is a circuit topology diagram of an I / V conversion unit in a preferred embodiment of the present invention;

[0035] Figure 4 is a circuit topology diagram of an anti-aliasing filter unit in a preferred embodiment of the present invention;

[0036] Figure 5 is a circuit topology diagram of a secondary amplification unit in a preferred embodiment of the present invention;

[0037] Figure 6 is a circuit topology diagram of a zero adjustment unit in a preferred embodiment of the present invention;

[0038] Figure 7 is a schematic structural diagram of a shielding box in a preferred embodiment of the present invention;

[0039] Figure 8 The figure is a schematic diagram of a polytetrafluoroethylene insulating support and its assembly in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0041] Embodiment 1:

[0042] In order to solve the following problems, the present invention provides a residual current measurement circuit and device with high precision that can adapt to harsh electromagnetic environments:

[0043] (1) Solve the problem of noise introduction that may be generated by the residual current signal (transmitter secondary side) introduced into the measurement device.

[0044] (2) After the residual current signal (transmitter secondary side) is introduced into the measuring device, because the impedance of the PCB measurement board is not infinite (generally above 200MΩ), there is signal current shunting, resulting in a certain amount of current leakage. In order to maintain the integrity of the measured current signal to the greatest extent, measures must be taken to prevent current leakage.

[0045] (3) For the noise introduced by the PCB measurement board itself and the external noise that has not been filtered out, measures need to be taken to amplify the useful signal and filter out the interference noise to improve the accuracy and authenticity of the signal measurement.

[0046] (4) In the factory power distribution environment, there are many electromagnetic harmonics. In order to adapt to the high-precision measurement of residual current in harsh electromagnetic environments, appropriate EMC design measures must be taken to shield electromagnetic harmonic interference.

[0047] (5) Adopt effective management strategies for the collected residual current information to prevent electrical safety accidents of equipment.

[0048] In order to solve the above technical problems, it is necessary to effectively measure the residual current of the power distribution system, such as Figure 1-2 As shown, the residual current measuring device in the present invention comprises a housing and a PBC board arranged in the housing, the PBC board is printed with the above-mentioned residual current measuring circuit, and the residual current measuring circuit comprises an I / V conversion unit, an anti-aliasing filter unit, a secondary amplification unit, an A / D sampling unit, a microprocessor unit, a display unit, a communication unit, an alarm unit and a power cut-off unit connected in sequence. The I / V conversion unit is used to convert the input original residual current signal into a voltage signal; the anti-aliasing filter unit is used to filter and de-noise the voltage signal to obtain a de-noised signal; the secondary amplification unit is used to perform secondary amplification on the de-noised signal to obtain an amplified signal; the A / D sampling unit is used to convert the amplified signal into a digital signal and transmit it to the microprocessor, the display unit, the communication unit, the alarm unit and the power cut-off unit are all connected to the microprocessor, the display unit is preferably an LCD display, the communication unit is an Internet of Things communication interface, the alarm unit is an audio-visual alarm device, and the power cut-off unit is a power cut-off interface.

[0049] In the present invention, the working process of the residual current measuring device is as follows:

[0050] First, the current transmitter signal (transmitter secondary side) is introduced into the measuring device, and a high-impedance, low-drift operational amplifier is used in the device to convert the residual current signal into a voltage signal (I / V conversion). Then, it is sent to the microprocessor for processing after anti-aliasing filtering, secondary amplification, and A / D acquisition. At the same time, the system also has a zeroing circuit to perform zeroing correction on the initial I / V signal. The collected residual current information is displayed locally or warned, and sent to the database of the monitoring center through the Internet of Things communication interface. By monitoring the historical data and real-time data of the database, timely warnings and troubleshooting are carried out to prevent electrical safety accidents of equipment.

[0051] The phase conductor and neutral line of the power distribution circuit pass through the high-precision current transmitter. Under normal circumstances, due to the balance of current in each phase, the phase sum of the current on the primary side of the transmitter (including the neutral line) is zero. However, when someone is electrocuted or other leakage faults occur, residual (leakage) current is generated. At this time, the phase sum of the current on the primary side of the transmitter is not zero and is converted into a small current signal on the secondary side. When introducing a small current signal into this measurement device, the key point is to avoid introducing external noise, such as Figure 2 As shown, the measures taken are: low-leakage coaxial shielded cable is used to introduce the small current signal into the measuring device, and the shielding layer of the cable is grounded close to the front end of the signal source to avoid the introduction of noise.

[0052] I / V conversion unit

[0053] In order to improve the measurement precision and accuracy, there are two key points in this link: first, use a suitable circuit to perform high-precision I / V conversion on the front current signal (small current signal on the secondary side of the transmitter) while suppressing noise; second, avoid small current signals from generating current shunts on the PCB measurement board. The measures taken are:

[0054] a) First, the preamplification of the current signal uses a high-precision op amp IC1 with extremely low input bias current. In order to improve the sensitivity of weak current measurement, the jumper resistor R1 is increased to reduce the shunt of the measured current. At the same time, the feedback resistor R1 of IC1 uses a sheet glass glaze high resistance, which has a series of advantages such as good moisture resistance, small temperature drift, small size, and not easy to be polluted by dust and particles. The thermal noise and contact noise of the glass glaze resistor are ideal. A small capacitor C1 is connected in parallel to the feedback resistor, and a low-leakage polystyrene capacitor is selected to provide noise suppression and loop compensation.

[0055] Specifically, Figure 3As shown, the I / V conversion unit in the present invention includes a resistor R1, a resistor R2, an operational amplifier IC1 and a capacitor C1; the resistor R1 and the capacitor C1 form a parallel RC circuit, the first end of the parallel RC circuit is connected to the first end of the resistor R2, the second end of the parallel RC circuit is connected to the output end of the operational amplifier IC1, the second end of the resistor R2 is connected to the first input end of the operational amplifier IC1, and the second input end of the operational amplifier IC1 is grounded.

[0056] b) Second, to avoid current shunt caused by small current signal on the PCB measurement board, the current signal input lead cannot be directly soldered on the PCB board of the measurement device (the insulation resistance of the PCB board is generally above 200MΩ). This method uses a polytetrafluoroethylene insulating support to isolate the measurement components from the PCB board, so that the measurement components maintain sufficient insulation resistance to prevent current from being shunted through the PCB board and losing the authenticity and integrity of the current signal to be measured. Figure 2 , Figure 3 , Figure 8 shown.

[0057] like Figure 8 As shown in the figure, the PCB board insulation support is made of polytetrafluoroethylene, and there is a through hole in the middle to facilitate the insertion of component pins. During installation, first embed the polytetrafluoroethylene insulation support into the pre-opened hole on the PCB board, and then install the pins of components such as R1 and C1 through the insulation support to avoid contact between the components and the PCB board, thereby achieving the isolation effect of the components and the PCB board.

[0058] Anti-aliasing filter unit

[0059] In the process of measuring small current signals, some noise will inevitably be introduced. How to identify noise and eliminate its influence is very important. This method proposes to select appropriate R and C parameters according to the characteristics and frequency of the sampling signal, and calculate the cutoff frequency according to the Nyquist sampling theorem (i.e., sampling frequency fs≤fmax). Figure 4 The anti-aliasing filter unit shown in the figure adopts an active second-order filter design and uses a low-noise operational amplifier to amplify useful signals and filter out noise interference. When the signal to be measured passes through the anti-aliasing filter circuit, the noise greater than the set cutoff frequency aliased in the signal can be filtered out. At the same time, the front and rear stages can be isolated to prevent the large signal circuit of the rear stage from interfering with the small current signal conversion circuit of the front stage, thereby improving the signal-to-noise ratio.

[0060] Specifically, the anti-aliasing filtering unit includes: a resistor R3, a resistor R4, a capacitor C2, a capacitor C3, and an operational amplifier IC2; the first end of the resistor R3 is connected to the output end of the operational amplifier IC1; the second end of the resistor R3 is respectively connected to the first end of the resistor R4 and the first end of the capacitor C3, the second end of the resistor R4 is respectively connected to the first end of the capacitor C2 and the first input end of the operational amplifier IC2, and the second input end of the operational amplifier IC2 is connected to its output end; the second end of the capacitor C2 is grounded; the second end of the capacitor C3 is connected to the second input end of the operational amplifier IC2.

[0061] Secondary amplifier unit

[0062] When the current signal to be measured is converted by I / V and anti-aliasing filtering circuit, the output voltage is generally in the mV level. In order to improve the precision and accuracy of signal acquisition, it is also necessary to undergo signal amplification processing. After signal amplification, the signal is about one-quarter to three-quarters of the input reference voltage of the A / D converter, and then collected and converted by the A / D converter. The specific circuit is as follows Figure 5 As shown. A resistor-capacitor T-type filter is used to filter out certain burrs, and then the signal is amplified by an operational amplifier and sent to the subsequent detection circuit. According to the filtering principle, the low-pass cutoff frequency is calculated by the selected R and C parameters. The low-pass cutoff frequency of the RC circuit filter should be greater than the signal frequency to filter out noise.

[0063] Specifically, the secondary amplification unit includes: a resistor R5, a resistor R6, a resistor R7, a capacitor C4, a capacitor C5, and an operational amplifier IC3; the capacitor C4 and the capacitor C5 form a parallel RC circuit, the first end of the resistor R6 is connected to the output end of the operational amplifier IC2, the second end of the resistor R6 is respectively connected to the first end of the parallel RC circuit, the first end of the resistor R7, and the first end of the capacitor C5, and the second end of the capacitor C5 is grounded; the second end of the resistor R7 is connected to the first end of the operational amplifier IC3, the second end of the operational amplifier IC3 is grounded, and the second end of the parallel RC circuit is connected to the output end of the operational amplifier IC3.

[0064] Zero adjustment unit

[0065] In order to eliminate the initial error of the small current signal measurement circuit (the influence of DC bias, calibration gain and phase, etc.), so as to improve the quality of the small current signal and the measurement accuracy. This method adds a zero adjustment unit, and the circuit of the zero adjustment unit can be composed of an operational amplifier and a digital-to-analog converter. When the initial small current at the front end is not 0 (such as when no signal is connected), the measurement channel may also output an initial voltage that is not 0. At this time, the appropriate voltage is output through the zero adjustment circuit and synthesized into the small current signal to make the initial output 0. The zero adjustment circuit is as follows Figure 6As shown, by setting the digital input of the digital-to-analog converter, a positive voltage or negative voltage within a certain range is output as a reference voltage, which is synthesized onto the small current signal to be measured (such as Figure 1 shown).

[0066] Specifically, the zeroing unit includes: a digital-to-analog converter IC4, an operational amplifier IC5 and a resistor R8; the input end of the digital-to-analog converter IC4 is connected to the output end of the microprocessor, the output end of the digital-to-analog converter IC4 is connected to the first input end of the operational amplifier IC5, and the second input end of the operational amplifier IC5 is grounded; the feedback signal end of the digital-to-analog converter IC4 is connected to the output end of the operational amplifier IC5, the output end of the operational amplifier IC5 is connected to the first end of the resistor R8, and the second end of the resistor R8 is connected to the second input end of the operational amplifier IC1.

[0067] A / D sampling unit

[0068] After the small current signal is conditioned in the previous step, it is finally collected by an A / D (analog-to-digital) converter and transmitted to a microprocessor. To improve the measurement accuracy, this method uses a 24-bit analog-to-digital converter with no data loss, differential input, low-pass filter, and programmable cutoff frequency. To further filter out the influence of noise, multi-stage RC passive filtering is added to the data acquisition circuit, and the analog-to-digital converter is calibrated by the microprocessor before data reading. To ensure that the power supply does not affect the signal accuracy of the acquisition circuit, this solution also uses a low-noise reference source chip to provide a reference voltage to ensure the long-term stability of the reference voltage.

[0069] case

[0070] In a factory power distribution environment, there are many electromagnetic harmonics. In order to adapt to the high-precision measurement of residual current in a harsh electromagnetic environment, the method and device adopt appropriate EMC design measures to shield electromagnetic harmonic interference.

[0071] This method requires the use of multi-layer PCB design in PCB design, and the use of multi-layer large-area grounding in the design to effectively reduce the signal grounding impedance, isolate and eliminate possible noise interference. When laying out the PCB, the measurement device is placed close to the signal source to reduce leakage paths, noise pickup and capacitive loads.

[0072] When measuring components and assembling, the following key measures should be taken: First, the signal line should use low-leakage coaxial shielded cable and BNC connector, and the shield layer of the cable should be grounded close to the front end of the signal source to avoid the introduction of noise and shielding noise interference (see Figure 2 ); secondly, the leads of the signal input and feedback components (jumper resistors) cannot be directly soldered on the PCB board. Measures must be taken to isolate them from the circuit board so that the measuring components maintain sufficient insulation resistance (see Figure 3 ). This method uses a polytetrafluoroethylene insulating support to isolate the components from the PCB. At the same time, it is required to be welded in a clean workshop to ensure the cleanliness of the PCB and components. If contamination occurs, it will significantly reduce the insulation resistance between the input terminal and the power supply or signal voltage lead, so the component package and the PCB measurement board must be kept clean and dry.

[0073] A two-layer shielding design combining a Permalloy shielding box and a silicon steel shielding box is used for the PCB measurement board:

[0074] Because the front I / V processes a small current signal and is most sensitive to noise, this method first uses a Permalloy shielding box to shield the components of the front I / V processing. Since Permalloy is a nickel-iron alloy with a high magnetic permeability, the high-frequency electromagnetic harmonics are shielded by grounding the Permalloy shielding box, so that the I / V processing circuit is isolated from the outside, avoiding external high-frequency noise from interfering with the small current signal of the front I / V.

[0075] Secondly, this method uses a silicon steel shielding box as the second layer (outer layer of the PCB board) shielding design to shield the entire PCB board. Silicon steel is an iron-silicon alloy with good electromagnetic shielding effect in low-frequency environments. It can be used to prevent low-frequency electromagnetic harmonics in the power distribution environment from interfering with the PCB board. At the same time, the silicon steel shielding box is grounded through the fixing screws of the PCB board.

[0076] To ensure the shielding effect, the entire shielding surface must be conductive and continuous. Where there are gaps or holes on the shielding surface (such as where the BNC signal cable enters), a metal braided mesh conductive elastic material is used to fill it so that the entire shielding body forms a complete, leak-free shielding layer, and the shielding layer is well grounded.

[0077] Residual Current Data Management Strategy

[0078] In the preferred embodiment, the present invention also provides a residual current data management strategy, which adopts an effective management strategy for the collected residual current to improve the safety of equipment power use and prevent electrical accidents.

[0079] 1) On-site display, warning or action of power distribution: The collected residual current of the equipment is displayed locally on the LCD of the measuring device. When the residual current is close to 30mA, an audible and visual alarm is issued to remind you to check the leakage fault. When the set threshold is reached (such as electric shock), a signal is immediately sent to cut off the power supply.

[0080] 2) The residual current information of the equipment is sent to the central monitoring platform through the IoT communication interface of this device for real-time monitoring, and the residual current of important equipment is stored in the database of the monitoring center background. If there is an abnormal deviation between the real-time data and the historical safety data, when the deviation value reaches the warning threshold, it is prompted that the equipment needs to be repaired or the cable replaced to prevent electrical safety accidents of the equipment.

[0081] In summary, the small current measurement method proposed in the present invention, compared with the existing residual current protector, can ensure the integrity of the measurement signal and improve the accuracy and authenticity of the residual current measurement by preventing the shunting measures of the current signal to be measured and the filtering combination circuit. In addition, the present invention can filter out high-frequency and low-frequency electromagnetic interference in a harsh electromagnetic harmonic environment through the EMC combination design of the PCB board as a whole, thereby ensuring the reliability of the residual current measurement. Finally, the residual current data management strategy proposed in the present invention uses the residual current as a reference for the daily maintenance of factory equipment, which can prevent equipment electrical safety accidents and improve the economic benefits of the factory.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A residual current measurement circuit, characterized in that: include: An I / V conversion unit, an anti-aliasing filter unit, a secondary amplification unit, an A / D sampling unit and a microprocessor unit are connected in sequence; The I / V conversion unit is used to convert the input original residual current signal into a voltage signal; The anti-aliasing filter unit is used to filter and de-noise the voltage signal to obtain a de-noised signal; The secondary amplification unit is used to perform secondary amplification on the denoised signal to obtain an amplified signal; The A / D sampling unit is used to convert the amplified signal into a digital signal and transmit it to the microprocessor.

2. The residual current measurement circuit according to claim 1, characterized in that: The I / V conversion unit includes a resistor R1, a resistor R2, an operational amplifier IC1 and a capacitor C1; the resistor R1 and the capacitor C1 form a parallel RC circuit, a first end of the parallel RC circuit is connected to a first end of the resistor R2, a second end of the parallel RC circuit is connected to an output end of the operational amplifier IC1, a second end of the resistor R2 is connected to a first input end of the operational amplifier IC1, and a second input end of the operational amplifier IC1 is grounded.

3. The residual current measurement circuit according to claim 2, characterized in that: The anti-aliasing filtering unit includes: a resistor R3, a resistor R4, a capacitor C2, a capacitor C3, and an operational amplifier IC2; the first end of the resistor R3 is connected to the output end of the operational amplifier IC1; the second end of the resistor R3 is respectively connected to the first end of the resistor R4 and the first end of the capacitor C3, the second end of the resistor R4 is respectively connected to the first end of the capacitor C2 and the first input end of the operational amplifier IC2, and the second input end of the operational amplifier IC2 is connected to its output end; the second end of the capacitor C2 is grounded; the second end of the capacitor C3 is connected to the second input end of the operational amplifier IC2.

4. The residual current measurement circuit according to claim 3, characterized in that: The secondary amplification unit includes: a resistor R5, a resistor R6, a resistor R7, a capacitor C4, a capacitor C5, and an operational amplifier IC3; the capacitor C4 and the capacitor C5 form a parallel RC circuit, the first end of the resistor R6 is connected to the output end of the operational amplifier IC2, the second end of the resistor R6 is respectively connected to the first end of the parallel RC circuit, the first end of the resistor R7, and the first end of the capacitor C5, and the second end of the capacitor C5 is grounded; the second end of the resistor R7 is connected to the first end of the operational amplifier IC3, the second end of the operational amplifier IC3 is grounded, and the second end of the parallel RC circuit is connected to the output end of the operational amplifier IC3.

5. The residual current measurement circuit according to claim 2, characterized in that: It also includes a zeroing unit, the input end of the zeroing unit is connected to the output end of the microprocessor, and the output end of the zeroing unit is connected to the output end of the I / V conversion unit; the microcontroller is used to send a signal to the zeroing signal to control the zeroing unit to perform zeroing processing on the voltage signal output by the I / V conversion unit; and / or The measuring circuit further comprises any one or more of the following units: Display unit, communication unit, alarm unit and power cut-off unit; The display unit, the communication unit, the alarm unit and / or the power cut-off unit are connected to the microprocessor.

6. The residual current measurement circuit according to claim 5, characterized in that: When the residual current measurement circuit includes a zeroing unit, the zeroing unit includes: a digital-to-analog converter IC4, an operational amplifier IC5 and a resistor R8; the input end of the digital-to-analog converter IC4 is connected to the output end of the microprocessor, the output end of the digital-to-analog converter IC4 is connected to the first input end of the operational amplifier IC5, and the second input end of the operational amplifier IC5 is grounded; the feedback signal end of the digital-to-analog converter IC4 is connected to the output end of the operational amplifier IC5, the output end of the operational amplifier IC5 is connected to the first end of the resistor R8, and the second end of the resistor R8 is connected to the second input end of the operational amplifier IC1.

7. A residual current measuring device, characterized in that: The invention comprises a shell and a PBC board arranged in the shell, wherein the PBC board is printed with the residual current measurement circuit as claimed in any one of claims 1 to 6.

8. The residual current measuring device according to claim 7, characterized in that: It also includes a first insulating support and a second insulating support, the parallel RC circuit of the I / V conversion unit is set between the first insulating support and the second insulating support, and the first end of the parallel RC circuit is passed through the first insulating support, and the second end of the parallel RC circuit of the I / V conversion unit is passed through the second insulating support, and a first avoidance hole and a second avoidance hole are arranged on the PBC board, the first avoidance hole corresponds to the first insulating support, and the second avoidance hole corresponds to the second insulating support, the first insulating support is connected to the signal output end of the external device through the first avoidance hole, and the second insulating support is connected to the signal output end of the external device through the second avoidance hole.

9. The residual current measuring device according to claim 7, characterized in that: The housing comprises a first shielding box and a second shielding box, wherein the first shielding box is used to shield the I / V conversion unit on the PBC board; and the second shielding box is used to shield the entire PBC board.

10. The residual current measuring device according to claim 9, characterized in that: The first shielding box is a Permalloy shielding box, and the second shielding box is a conductive and continuous silicon steel shielding box with gaps or holes on the surface of the shielding body and filled with a metal braided mesh conductive elastic material. and / or The first insulating support and the second insulating support are both connected to the signal output end of the external device through a low-leakage coaxial shielded cable.

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