Wireless grounding resistance precision monitoring device based on low power consumption

Abstract

The utility model provides a wireless grounding resistance precision monitoring device based on low power consumption, which comprises a power supply circuit, a wireless communication circuit, a measuring circuit and a main control circuit, and is characterized in that the power supply circuit is used for stabilizing, boosting and stabilizing the voltage of a battery and supplying power after positive and negative conversion; the wireless communication circuit is used for wirelessly sending the calculated grounding resistance value to an upper platform or a central control unit, so that a worker can monitor the equipment; the measuring circuit is used for performing amplification, filtering and alternating current-direct current conversion on the acquired grounding resistance signal and then transmitting the signal to the main control circuit to calculate a grounding resistance value; and the main control circuit is electrically connected with the wireless communication circuit and the measuring circuit and is used for controlling the wireless communication circuit to transmit and receive signals, calculating a grounding resistance value, switching working states of the wireless communication circuit and the measuring circuit and automatically awakening the wireless communication circuit and the measuring circuit. According to the wireless grounding resistance precision monitoring device provided by the invention, the wiring complexity and the power consumption are reduced, and the measurement precision is improved.

Description

Technical Field

[0001] The present application relates to the technical field of circuit monitoring, and in particular, to a low-power wireless ground resistance precision monitoring device. Background Art

[0002] The ground resistance online monitor is suitable for transmission line tower grounding, meteorological lightning protection grounding, petrochemical grounding, communication grounding, substation grounding, railway facility grounding, building warehouse grounding, metal loop resistance, electrical equipment grounding and other places.

[0003] Most of the original ground resistance online monitors use wired communication methods based on 485 communication. When facing large oil depots or refineries, the number of sensors will reach dozens or even hundreds, and a lot of manpower and material resources will be wasted in wiring, connection and other issues. The original design uses discrete chips such as operational amplifiers, analog switches or operational amplifiers, digital potentiometers, etc. Because analog switches or digital potentiometers are only powered by power, there will be waveform loss when facing small signals, resulting in measurement deviations; when amplifying, analog switches and digital potentiometers are not pure impedance devices, and there will be capacitance and inductance, which will cause signal waveform distortion, thereby affecting the measurement accuracy. At the same time, the power consumption of the original ground resistance online monitor is in a continuous consumption state after startup, and the power consumption is high. Utility Model Content

[0004] The present application provides a low-power wireless ground resistance precision monitoring device to solve the technical problems of the existing ground resistance online monitoring instrument with complex wiring, high power consumption and low measurement accuracy.

[0005] The technical solutions adopted in this application are as follows:

[0006] A low-power wireless ground resistance precision monitoring device includes a power supply circuit, a wireless communication circuit, a measurement circuit, and a main control circuit, wherein:

[0007] The power supply circuit is used to stabilize, boost and stabilize the battery voltage, and then perform positive and negative conversion to supply power;

[0008] The wireless communication circuit is used to wirelessly send the calculated ground resistance value to the upper platform or central control unit for the staff to monitor the equipment;

[0009] The measuring circuit is used to amplify, filter and convert the collected grounding resistance signal into AC / DC and then transmit it to the main control circuit to calculate the grounding resistance value;

[0010] The main control circuit is electrically connected to the wireless communication circuit and the measuring circuit, and is used to control the transmission and reception of signals of the wireless communication circuit, calculate the grounding resistance value, switch the working state of the wireless communication circuit and the measuring circuit, and automatically wake up.

[0011] Furthermore, the power supply circuit includes a 3.3V voltage stabilizing circuit, a voltage boosting circuit, a voltage stabilizing circuit, and a negative power supply circuit, wherein:

[0012] The 3.3V voltage stabilizing circuit is used to stabilize the battery voltage to 3.3V to supply power to the main control circuit;

[0013] The boost circuit is used to boost the battery voltage to 5.5V as a regulated power supply; to supply power to the amplifier in the measurement circuit;

[0014] The voltage stabilizing circuit is used to stabilize the 5.5V voltage output by the boost circuit to 5V, and is used to supply power to the positive power supply of the amplifier in the measuring circuit, and to provide conversion between positive and negative power supplies;

[0015] The negative power supply circuit is electrically connected to the voltage stabilizing circuit and is used to convert the 5V voltage output by the voltage stabilizing circuit into -5V to supply the negative power supply of the amplifier in the measuring circuit.

[0016] Furthermore, the main control circuit includes a microcontroller U4, capacitors C9, C10, C11, C12, C14, C20, C21, C22, resistors R1, R4, R6, a magnetic bead L4, a crystal oscillator X1 and pin headers J1, J5. The capacitors C9, C10, C11, and C14 are arranged in parallel and one end is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the resistor R4 is connected to a +3.3V power supply, and the other end is connected to a positive electrode of the capacitor C12, and a negative electrode of the capacitor C12 is connected to a GND end, and a switch SW1 is connected in parallel between the capacitor C12 and the positive and negative electrodes; one end of the resistor R6 is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the capacitor C20 is connected to a GND end, and the other end is connected to an OSC32_IN pin of the microcontroller U4, and one end of the capacitor C22 is connected to The positive electrode of the magnetic bead L4 is connected to the +3.3V power supply, and the negative electrode is respectively connected to the VDDA pin of the microcontroller U4 and the capacitor C21, and the other end of the capacitor C21 is connected to the GND end; the pin header J1 includes two interfaces, wherein the first interface is connected to the +3.3V power supply, and the second interface is respectively connected to the BOOTO / PH3 pin of the microcontroller U4 and the resistor R1, and the other end of the resistor R1 is connected to the GND end; the pin header J5 includes four interfaces, wherein the first interface is connected to the GND end, the second interface is connected to the SWCLK pin of the microcontroller U4, the third interface is connected to the SWDIO pin of the microcontroller U4, and the fourth interface is connected to the GND end.

[0017] Furthermore, the microcontroller U4 adopts a STM32L431 microcontroller.

[0018] Furthermore, the wireless communication circuit includes a Lora module U3, capacitors C1 and C2, and pins J2, J3, and J4, wherein: the GND pin of the Lora module U3 is grounded, the VCC pin is connected to the positive electrode of the battery, and the capacitors C1 and C2 are arranged in parallel between the GND pin and the VCC pin of the Lora module U3; the first interface of the pin header J2 is grounded, the second interface is connected to the M1 pin of the Lora module U3, and the third interface is connected to the M1_IO pin of the microcontroller U4; the first interface of the pin header J3 is grounded, the second interface is connected to the M0 pin of the Lora module U3, and the third interface is connected to the M0_IO pin of the microcontroller U4; the first interface of the pin header J4 is connected to the positive electrode of the battery, the second interface is grounded, the second interface is connected to the M0 pin of the Lora module U3, the third interface is respectively connected to the TXD_1 pin of the microcontroller U4 and the RXD pin of the Lora module U3, and the fourth interface is respectively connected to the RXD_1 pin of the microcontroller U4 and the TXD pin of the Lora module U3.

[0019] Furthermore, the measuring circuit comprises:

[0020] A first-stage amplifier circuit is used to amplify the collected ground resistance signal;

[0021] The first bandpass filter is used to remove high and low frequency interference in the first-stage amplification circuit, allowing only signals of specific frequencies to pass through, reducing environmental interference, and sending the output signal to the second-stage amplification circuit;

[0022] The secondary amplifier circuit amplifies the signal output by the first bandpass filter to a set ideal range value to prevent the signal from being too large or too small from affecting the measurement accuracy;

[0023] The second band-pass filter is used to remove the high and low frequency interference that is not removed by the first band-pass filter, reduce the ripple interference, and send the output signal to the signal conversion circuit;

[0024] The signal conversion circuit is used to convert the AC analog signal output by the second bandpass filter into a DC signal.

[0025] Furthermore, the first-stage amplifier circuit includes a resistor R13, diodes D2 and D3, and a variable gain amplifier U8. The variable gain amplifier U8 includes a dual-channel amplifier circuit, and the amplification factor is adjusted by a program, wherein the positive electrodes of the resistor R13 and the diode D2 are connected to the collected ground resistance signal and the INA pin of the variable gain amplifier U8, the negative electrode of the resistor R13 and the positive electrode of the diode D3 are grounded, the negative electrode of the diode D3 is connected to the negative electrode of the diode D2, and the OUTA pin of the variable gain amplifier U8 is connected to the first bandpass filter;

[0026] The secondary amplification circuit is formed by an internal circuit between the INB pin and the OUTB pin of the variable gain amplifier U8, wherein the INB pin is connected to the output end of the first bandpass filter, and the OUTB pin is connected to the input end of the second bandpass filter.

[0027] Furthermore, the first bandpass filter includes resistors R10 and R11, capacitors C23, C24, C26, C27, an operational amplifier U7.1 and an adjustable potentiometer R12, wherein:

[0028] The positive electrode of the capacitor C23 is connected to the OUTA pin of the variable gain amplifier U8 through the resistor R10, and the negative electrode is connected to the output end of the operational amplifier U7.1. The positive electrode of the capacitor C26 is connected to one end of the adjustable potentiometer R12, and the negative electrode is connected to the negative input end of the operational amplifier U7.1. The other end of the adjustable potentiometer R12 is grounded, the positive input end of the operational amplifier U7.1 is grounded, the negative input end of the power supply of the operational amplifier U7.1 is connected to a -5V voltage and is grounded through a capacitor C27, the positive input end of the power supply of the operational amplifier U7.1 is connected to a +5V voltage and is grounded through a capacitor C24, the resistor R11 is connected between the negative electrode of the capacitor C23 and the negative electrode of the capacitor C26, the resistor R11 is connected between the positive electrode of the capacitor C23 and the positive electrode of the capacitor C26 through a line conduction, and the output end of the operational amplifier U7.1 is connected to the INB pin of the variable gain amplifier U8.

[0029] Furthermore, the second bandpass filter includes resistors R18 and R21, capacitors C31 and C35, an operational amplifier U7.2 and an adjustable potentiometer R23, wherein: the positive electrode of the capacitor C31 is connected to the OUTB pin of the variable gain amplifier U8 through the resistor R18, the negative electrode is connected to the negative input terminal of the operational amplifier U7.2, the positive input terminal of the operational amplifier U7.2 is grounded, and the output terminal of the operational amplifier U7.2 is connected to the input terminal of the signal conversion circuit; the positive electrode of the capacitor C35 is connected to one end of the adjustable potentiometer R23, the negative electrode is connected to the output terminal of the operational amplifier U7.2, and the other end of the adjustable potentiometer R23 is grounded; the resistor R21 is connected and arranged between the negative input terminal and the output terminal of the operational amplifier U7.2.

[0030] Furthermore, the signal conversion circuit includes capacitors C29, C30, C32, C33, C34, resistors R14-R17, R19, R20, R22, PNP transistors Q1 and Q2, operational amplifiers U9.1 and U9.2, wherein:

[0031] The positive electrode of the capacitor C30 is connected to the output end of the second bandpass filter, and the negative electrode is connected to the resistor R17 and the negative input end of the operational amplifier U9.1 in sequence. The positive input end of the operational amplifier U9.1 is grounded through the resistor R20, and the positive and negative power supply input ends of the operational amplifier U9.1 are respectively connected to the +5V voltage and the -5V voltage; one end of the resistor R16 is respectively connected to the collector and base of the PNP transistor Q1 and the negative input end of the operational amplifier U9.1, and the other end is connected to the emitter of the PNP transistor Q2; the emitter of the PNP transistor Q1 is connected to the base of the PNP transistor Q2, and the collector of the PNP transistor Q2 is respectively connected to the output end of the operational amplifier U9.1 and the emitter of the PNP transistor Q1; the resistor R19 One end is connected to the emitter of the PNP transistor Q2, and the other end is connected to the negative input terminal of the operational amplifier U9.2. The positive input terminal of the operational amplifier U9.2 is grounded, and the output terminal of the operational amplifier U9.2 is respectively connected to the positive electrodes of capacitors C32, C33, and C34 and the ADC pin of the microcontroller U4, and the negative electrodes of the capacitors C32, C33, and C34 are grounded; the positive electrode of the capacitor C29 is connected to the negative input terminal of the operational amplifier U9.2, and the negative electrode is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R15 is connected to the negative input terminal of the operational amplifier U9.2, and the other end is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R14 is connected to the circuit between the capacitor C30 and the resistor R17, and the other end is connected to the negative input terminal of the operational amplifier U9.2.

[0032] Compared with the prior art, this application has the following beneficial effects:

[0033] The present application adopts a two-stage amplification measure to make the signal reach the optimal amplification range, eliminates the influence of the signal amplitude on the measurement, improves the measurement accuracy, reduces the influence of the capacitance and inductance of the device on the amplification and measurement, and at the same time, there will be no signal loss when facing small signals. A new measurement circuit is adopted to convert the collected AC signal into a DC signal, which improves the measurement accuracy and can accurately measure the grounding resistance value of the grounding loop, with a maximum resolution of 0.001Ω and an accuracy of up to ±1%;

[0034] This application is battery-powered, has multiple working states and can automatically wake up, so that the device works in low-power mode, reduces device power consumption, and extends the device's service life, with a working time of more than 3 years;

[0035] This application uses wireless communication for data transmission, which greatly reduces the workload of wiring and connection and reduces the equipment failure rate. The equipment can be networked according to the actual situation on site, with a transmission distance of 500m-2000m.

[0036] In addition to the above-described purposes, features and advantages, the present application also has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0038] Figure 1 This is a schematic diagram of the composition principle of a low-power wireless ground resistance precision monitoring device according to a preferred embodiment of the present application.

[0039] Figure 2 This is a schematic diagram of the power supply circuit principle of a low-power wireless ground resistance precision monitoring device according to a preferred embodiment of the present application.

[0040] Figure 3 This is a schematic diagram of the main control circuit principle of a low-power wireless ground resistance precision monitoring device according to a preferred embodiment of the present application.

[0041] Figure 4 This is a schematic diagram of the wireless communication circuit principle of a low-power wireless ground resistance precision monitoring device according to a preferred embodiment of the present application.

[0042] Figure 5 This is a schematic diagram of the measurement circuit principle of a low-power wireless ground resistance precision monitoring device according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0043] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0044] Reference Figure 1 The preferred embodiment of the present application provides a low-power wireless ground resistance precision monitoring device, including a power supply circuit, a wireless communication circuit, a measurement circuit, and a main control circuit, wherein:

[0045] The power supply circuit is used to stabilize, boost and stabilize the battery voltage, and then perform positive and negative conversion to supply power;

[0046] The wireless communication circuit is used to wirelessly send the calculated ground resistance value to the upper platform or central control unit for the staff to monitor the equipment;

[0047] The measuring circuit is used to amplify, filter and convert the collected grounding resistance signal into AC / DC and then transmit it to the main control circuit to calculate the grounding resistance value;

[0048] The main control circuit is electrically connected to the wireless communication circuit and the measuring circuit, and is used to control the transmission and reception of signals of the wireless communication circuit, calculate the grounding resistance value, switch the working state of the wireless communication circuit and the measuring circuit, and automatically wake up.

[0049] The present embodiment adopts a two-stage amplification measure to make the signal reach the optimal amplification range, eliminates the influence of the signal amplitude on the measurement, improves the measurement accuracy, reduces the influence of the capacitance and inductance of the device on the amplification and measurement, and at the same time there is no signal loss when facing small signals. A new measurement circuit is adopted to convert the collected AC signal into a DC signal, which improves the measurement accuracy and can accurately measure the grounding resistance value of the grounding loop with a maximum resolution of 0.001Ω and an accuracy of ±1%. The present embodiment is battery-powered, has multiple working states and can be automatically awakened, so that the device works in a low-power mode, reduces the power consumption of the device, and prolongs the use time of the device, with a working time of more than 3 years. The present embodiment adopts wireless communication for data transmission, which greatly reduces the workload of wiring, connection, etc. and reduces the failure rate of the equipment. The equipment can be networked according to the actual situation on site, with a transmission distance of 500m to 2000m.

[0050] Specifically, Figure 2 As shown, the power supply circuit includes a 3.3V voltage stabilizing circuit, a voltage boosting circuit, a voltage stabilizing circuit, and a negative power supply circuit, wherein:

[0051] The 3.3V voltage stabilization circuit includes a linear voltage regulator (LDO) U2, a capacitor C4, and a capacitor C5, which are used to stabilize the battery voltage to 3.3V to supply power to the main control circuit;

[0052] The input end capacitor C6, capacitor C3, and inductor L1 of the boost circuit are connected to the DC-DC power chip U1, and the output end is composed of capacitors C7, C8, resistors R2, and R3. The resistors R2 and R3 are used for output voltage regulation to boost the battery voltage of 3.6V to 5.5V to power the amplifier in the measurement circuit. It has the advantages of high efficiency, low leakage current, and support for shutdown.

[0053] The voltage stabilization circuit includes a linear voltage regulator (LDO) U5, tantalum capacitors C17 and C18, and resistors R7 and R9, which are used to stabilize the 5.5V voltage output by the boost circuit to 5V, to supply power to the positive power supply of the amplifier in the measurement circuit, and to provide conversion between positive and negative power supplies, and has the advantages of small ripple and support for shutdown.

[0054] The negative power supply circuit is electrically connected to the voltage stabilizing circuit, and includes a DC-DC power supply chip U6, tantalum capacitors C19 and C16, inductors L2 and L3, capacitors C13 and C15, resistors R5 and R8, and a Schottky diode D1, which are used to convert the 5V voltage output by the voltage stabilizing circuit to -5V to supply power to the negative power supply of the amplifier in the measuring circuit.

[0055] Specifically, Figure 3 As shown, the main control circuit includes a microcontroller U4, capacitors C9, C10, C11, C12, C14, C20, C21, C22, resistors R1, R4, R6, a magnetic bead L4, a crystal oscillator X1 and pin headers J1, J5. The capacitors C9, C10, C11, and C14 are arranged in parallel and one end is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the resistor R4 is connected to a +3.3V power supply, and the other end is connected to a positive electrode of the capacitor C12, and a negative electrode of the capacitor C12 is connected to a GND end, and a switch SW1 is connected in parallel between the capacitor C12 and the positive and negative electrodes; one end of the resistor R6 is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the capacitor C20 is connected to a GND end, and the other end is connected to an OSC32_IN pin of the microcontroller U4, and one end of the capacitor C22 is connected to GND terminal, and the other end is connected to the OSC32_OUT pin of the microcontroller U4, the crystal oscillator X1 is connected and arranged between the capacitor C20 and the capacitor C22; the positive pole of the magnetic bead L4 is connected to the +3.3V power supply, and the negative pole is respectively connected to the VDDA pin of the microcontroller U4 and the capacitor C21, and the other end of the capacitor C21 is connected to the GND terminal; the pin header J1 includes two interfaces, wherein the first interface is connected to the +3.3V power supply, and the second interface is respectively connected to the BOOTO / PH3 pin of the microcontroller U4 and the resistor R1, and the other end of the resistor R1 is connected to the GND terminal; the pin header J5 includes four interfaces, wherein the first interface is connected to the GND terminal, the second interface is connected to the SWCLK pin of the microcontroller U4, the third interface is connected to the SWDIO pin of the microcontroller U4, and the fourth interface is connected to the GND terminal.

[0056] Specifically, the microcontroller U4 adopts the STM32L431 microcontroller. The STM32L431 microcontroller has multiple sleep modes and a sleep current of only 10uA. Compared with other controllers STM32F103 and STC89C51, it has obvious advantages in low power consumption and pin resources.

[0057] Specifically, Figure 4As shown, the wireless communication circuit includes a Lora module U3, capacitors C1 and C2, and pins J2, J3, and J4, wherein: the GND pin of the Lora module U3 is grounded, the VCC pin is connected to the positive electrode of the battery, and the capacitors C1 and C2 are arranged in parallel between the GND pin and the VCC pin of the Lora module U3; the first interface of the pin J2 is grounded, the second interface is connected to the M1 pin of the Lora module U3, and the third interface is connected to the M1_IO pin of the microcontroller U4; the first interface of the pin J3 is grounded, the second interface is connected to the M0 pin of the Lora module U3, and the third interface is connected to the M0_IO pin of the microcontroller U4; the first interface of the pin J4 is connected to the positive electrode of the battery, the second interface is grounded, the second interface is connected to the M0 pin of the Lora module U3, the third interface is respectively connected to the TXD_1 pin of the microcontroller U4 and the RXD pin of the Lora module U3, and the fourth interface is respectively connected to the RXD_1 pin of the microcontroller U4 and the TXD pin of the Lora module U3.

[0058] In this embodiment, the pins J2 and J3 are used to adjust the working state of the module. The current in the sleep state is only 2uA. When the resistance measurement is completed, the wireless communication is sent to the software platform or the central control unit, which is convenient for the staff to monitor the equipment, thereby greatly reducing the wiring workload and failure rate.

[0059] Specifically, Figure 5 As shown, the measuring circuit comprises:

[0060] The first-stage amplifier circuit is used to amplify the collected ground resistance signal. Since the measurement range of resistance is 0.01Ω-100Ω, the returned signal is closely related to the resistance value, so the span of the signal may be on the order of 104. The first-stage amplification of the signal can ensure the integrity of the signal.

[0061] The first band-pass filter is used to remove high and low frequency interference in the primary amplifier circuit, only allow signals of specific frequencies to pass through, reduce environmental interference, and send the output signal to the secondary amplifier circuit. The first band-pass filter in this embodiment can remove high and low frequency interference in the primary amplifier circuit, only allow signals of specific frequencies to pass through, reduce environmental interference, and send the output signal to the secondary amplifier circuit, thereby reducing signal noise and ensuring signal quality;

[0062] The secondary amplifier circuit amplifies the signal output by the first bandpass filter to a set ideal range value to prevent the signal from being too large or too small from affecting the measurement accuracy. The secondary amplifier circuit of this embodiment amplifies the signal near a certain ideal value to prevent the signal from being too large or too small from affecting the measurement accuracy, thereby eliminating the influence of the signal amplitude on the measurement and improving the measurement accuracy.

[0063] The second band-pass filter is used to remove the high and low frequency interference that is not removed by the first band-pass filter, reduce the ripple interference, and send the output signal to the signal conversion circuit. The second band-pass filter of this embodiment can remove the high and low frequency interference that is not removed by the first band-pass filter, reduce the ripple interference, and send the output signal to the signal conversion circuit, thereby reducing signal noise and ensuring signal quality;

[0064] The signal conversion circuit is used to convert the AC analog signal output by the second bandpass filter into a DC signal. The advantages of converting the AC analog signal into a DC signal in this embodiment include: DC signals are easier to measure than AC signals, the AC signal ripple has a larger peak value on the signal, and the DC signal can reduce the impact and improve measurement accuracy. Compared with traditional AC-DC conversion circuits, it is less affected by signal frequency, has a faster conversion rate, and is not affected by the on-state voltage.

[0065] Specifically, the first-stage amplifier circuit includes a resistor R13, diodes D2 and D3, and a variable gain amplifier U8. The variable gain amplifier U8 includes a dual-channel amplifier circuit, and the amplification factor is adjusted by a program, wherein the positive electrodes of the resistor R13 and the diode D2 are connected to the collected ground resistance signal and the INA pin of the variable gain amplifier U8, the negative electrode of the resistor R13 and the positive electrode of the diode D3 are grounded, the negative electrode of the diode D3 is connected to the negative electrode of the diode D2, and the OUTA pin of the variable gain amplifier U8 is connected to the first bandpass filter;

[0066] The secondary amplification circuit is formed by an internal circuit between the INB pin and the OUTB pin of the variable gain amplifier U8, wherein the INB pin is connected to the output end of the first bandpass filter, and the OUTB pin is connected to the input end of the second bandpass filter.

[0067] The original design is built with discrete chips such as operational amplifiers, analog switches or operational amplifiers, and digital potentiometers. Since the analog switches or digital potentiometers are only powered by power, there will be waveform loss when facing small signals, resulting in measurement deviations. When amplifying, the analog switches and digital potentiometers are not pure impedance devices, and there will be capacitance and inductance, which will cause signal waveform distortion, thus affecting the measurement accuracy.

[0068] This embodiment uses a PGA programmable gain amplifier to build a circuit with an adjustable gain range, so that the signal reaches the optimal amplification range, eliminates the influence of the signal amplitude on the measurement, improves the measurement accuracy, reduces the influence of the capacitance and inductance values ​​of the device on amplification and measurement, and at the same time, there is no signal loss when facing small signals, thereby improving the measurement accuracy.

[0069] Specifically, the first bandpass filter includes resistors R10 and R11, capacitors C23, C24, C26, C27, an operational amplifier U7.1 and an adjustable potentiometer R12, wherein:

[0070] The positive electrode of the capacitor C23 is connected to the OUTA pin of the variable gain amplifier U8 through the resistor R10, and the negative electrode is connected to the output end of the operational amplifier U7.1. The positive electrode of the capacitor C26 is connected to one end of the adjustable potentiometer R12, and the negative electrode is connected to the negative input end of the operational amplifier U7.1. The other end of the adjustable potentiometer R12 is grounded, the positive input end of the operational amplifier U7.1 is grounded, the negative input end of the power supply of the operational amplifier U7.1 is connected to a -5V voltage and is grounded through a capacitor C27, the positive input end of the power supply of the operational amplifier U7.1 is connected to a +5V voltage and is grounded through a capacitor C24, the resistor R11 is connected between the negative electrode of the capacitor C23 and the negative electrode of the capacitor C26, the resistor R11 is connected between the positive electrode of the capacitor C23 and the positive electrode of the capacitor C26 through a line conduction, and the output end of the operational amplifier U7.1 is connected to the INB pin of the variable gain amplifier U8.

[0071] Specifically, the second bandpass filter includes resistors R18 and R21, capacitors C31 and C35, an operational amplifier U7.2 and an adjustable potentiometer R23, wherein: the positive electrode of the capacitor C31 is connected to the OUTB pin of the variable gain amplifier U8 through the resistor R18, and the negative electrode is connected to the negative input terminal of the operational amplifier U7.2, the positive input terminal of the operational amplifier U7.2 is grounded, and the output terminal of the operational amplifier U7.2 is connected to the input terminal of the signal conversion circuit; the positive electrode of the capacitor C35 is connected to one end of the adjustable potentiometer R23, the negative electrode is connected to the output terminal of the operational amplifier U7.2, and the other end of the adjustable potentiometer R23 is grounded; the resistor R21 is connected and arranged between the negative input terminal and the output terminal of the operational amplifier U7.2.

[0072] Specifically, the signal conversion circuit includes capacitors C29, C30, C32, C33, C34, resistors R14-R17, R19, R20, R22, PNP transistors Q1 and Q2, operational amplifiers U9.1 and U9.2, wherein:

[0073] The positive electrode of the capacitor C30 is connected to the output end of the second bandpass filter, and the negative electrode is connected to the resistor R17 and the negative input end of the operational amplifier U9.1 in sequence. The positive input end of the operational amplifier U9.1 is grounded through the resistor R20, and the positive and negative power supply input ends of the operational amplifier U9.1 are respectively connected to the +5V voltage and the -5V voltage; one end of the resistor R16 is respectively connected to the collector and base of the PNP transistor Q1 and the negative input end of the operational amplifier U9.1, and the other end is connected to the emitter of the PNP transistor Q2; the emitter of the PNP transistor Q1 is connected to the base of the PNP transistor Q2, and the collector of the PNP transistor Q2 is respectively connected to the output end of the operational amplifier U9.1 and the emitter of the PNP transistor Q1; the resistor R19 One end is connected to the emitter of the PNP transistor Q2, and the other end is connected to the negative input terminal of the operational amplifier U9.2. The positive input terminal of the operational amplifier U9.2 is grounded, and the output terminal of the operational amplifier U9.2 is respectively connected to the positive electrodes of capacitors C32, C33, and C34 and the ADC pin of the microcontroller U4, and the negative electrodes of the capacitors C32, C33, and C34 are grounded; the positive electrode of the capacitor C29 is connected to the negative input terminal of the operational amplifier U9.2, and the negative electrode is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R15 is connected to the negative input terminal of the operational amplifier U9.2, and the other end is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R14 is connected to the circuit between the capacitor C30 and the resistor R17, and the other end is connected to the negative input terminal of the operational amplifier U9.2.

[0074] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A low-power wireless ground resistance precision monitoring device, characterized in that: It includes power supply circuit, wireless communication circuit, measurement circuit and main control circuit, among which: The power supply circuit is used to stabilize, boost and stabilize the battery voltage, and then perform positive and negative conversion to supply power; The wireless communication circuit is used to wirelessly send the calculated ground resistance value to the upper platform or central control unit for the staff to monitor the equipment; The measuring circuit is used to amplify, filter and convert the collected grounding resistance signal into AC / DC and then transmit it to the main control circuit to calculate the grounding resistance value; The main control circuit is electrically connected to the wireless communication circuit and the measuring circuit, and is used to control the transmission and reception of signals of the wireless communication circuit, calculate the grounding resistance value, switch the working state of the wireless communication circuit and the measuring circuit, and automatically wake up.

2. The low-power wireless ground resistance precision monitoring device according to claim 1 is characterized in that: The power supply circuit includes a 3.3V voltage stabilizing circuit, a voltage boosting circuit, a voltage stabilizing circuit, and a negative power supply circuit, wherein: The 3.3V voltage stabilizing circuit is used to stabilize the battery voltage to 3.3V to supply power to the main control circuit; The boost circuit is used to boost the battery voltage to 5.5V as a regulated power supply; to supply power to the amplifier in the measurement circuit; The voltage stabilizing circuit is used to stabilize the 5.5V voltage output by the boost circuit to 5V, and is used to supply power to the positive power supply of the amplifier in the measuring circuit, and to provide conversion between positive and negative power supplies; The negative power supply circuit is electrically connected to the voltage stabilizing circuit and is used to convert the 5V voltage output by the voltage stabilizing circuit into -5V to supply the negative power supply of the amplifier in the measuring circuit.

3. The low-power wireless ground resistance precision monitoring device according to claim 1 is characterized in that: The main control circuit includes a microcontroller U4, capacitors C9, C10, C11, C12, C14, C20, C21, C22, resistors R1, R4, R6, a magnetic bead L4, a crystal oscillator X1 and pin headers J1, J5. The capacitors C9, C10, C11, and C14 are arranged in parallel and one end is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the resistor R4 is connected to a +3.3V power supply, and the other end is connected to a positive electrode of the capacitor C12, and a negative electrode of the capacitor C12 is connected to a GND end, and a switch SW1 is connected in parallel between the capacitor C12 and the positive and negative electrodes; one end of the resistor R6 is connected to a +3.3V power supply, and the other end is connected to a GND end; one end of the capacitor C20 is connected to a GND end, and the other end is connected to an OSC32_IN pin of the microcontroller U4, and one end of the capacitor C22 is connected to a GN D terminal, and the other end is connected to the OSC32_OUT pin of the microcontroller U4, the crystal oscillator X1 is connected and arranged between the capacitor C20 and the capacitor C22; the positive pole of the magnetic bead L4 is connected to the +3.3V power supply, and the negative pole is respectively connected to the VDDA pin of the microcontroller U4 and the capacitor C21, and the other end of the capacitor C21 is connected to the GND terminal; the pin header J1 includes two interfaces, wherein the first interface is connected to the +3.3V power supply, and the second interface is respectively connected to the BOOTO / PH3 pin of the microcontroller U4 and the resistor R1, and the other end of the resistor R1 is connected to the GND terminal; the pin header J5 includes four interfaces, wherein the first interface is connected to the GND terminal, the second interface is connected to the SWCLK pin of the microcontroller U4, the third interface is connected to the SWDIO pin of the microcontroller U4, and the fourth interface is connected to the GND terminal.

4. The low-power wireless ground resistance precision monitoring device according to claim 3 is characterized in that: The microcontroller U4 adopts an STM32L431 microcontroller.

5. The low-power wireless ground resistance precision monitoring device according to claim 1 is characterized in that: The wireless communication circuit includes a Lora module U3, capacitors C1 and C2, and pins J2, J3, and J4, wherein: the GND pin of the Lora module U3 is grounded, the VCC pin is connected to the positive electrode of the battery, and the capacitors C1 and C2 are arranged in parallel between the GND pin and the VCC pin of the Lora module U3; the first interface of the pin J2 is grounded, the second interface is connected to the M1 pin of the Lora module U3, and the third interface is connected to the M1_IO pin of the microcontroller U4; the first interface of the pin J3 is grounded, the second interface is connected to the M0 pin of the Lora module U3, and the third interface is connected to the M0_IO pin of the microcontroller U4; the first interface of the pin J4 is connected to the positive electrode of the battery, the second interface is grounded, the second interface is connected to the M0 pin of the Lora module U3, the third interface is respectively connected to the TXD_1 pin of the microcontroller U4 and the RXD pin of the Lora module U3, and the fourth interface is respectively connected to the RXD_1 pin of the microcontroller U4 and the TXD pin of the Lora module U3.

6. The low-power wireless ground resistance precision monitoring device according to claim 1 is characterized in that: The measuring circuit comprises: A first-stage amplifier circuit is used to amplify the collected ground resistance signal; The first bandpass filter is used to remove high and low frequency interference in the first-stage amplification circuit, allowing only signals of specific frequencies to pass through, reducing environmental interference, and sending the output signal to the second-stage amplification circuit; The secondary amplifier circuit amplifies the signal output by the first bandpass filter to a set ideal range value to prevent the signal from being too large or too small from affecting the measurement accuracy; The second band-pass filter is used to remove the high and low frequency interference that is not removed by the first band-pass filter, reduce the ripple interference, and send the output signal to the signal conversion circuit; The signal conversion circuit is used to convert the AC analog signal output by the second bandpass filter into a DC signal.

7. The low-power wireless ground resistance precision monitoring device according to claim 6 is characterized in that: The first-stage amplifier circuit includes a resistor R13, diodes D2 and D3, and a variable gain amplifier U8. The variable gain amplifier U8 includes a dual-channel amplifier circuit, and the amplification factor is adjusted by a program, wherein the positive electrodes of the resistor R13 and the diode D2 are connected to the collected ground resistance signal and the INA pin of the variable gain amplifier U8, the negative electrode of the resistor R13 and the positive electrode of the diode D3 are grounded, the negative electrode of the diode D3 is connected to the negative electrode of the diode D2, and the OUTA pin of the variable gain amplifier U8 is connected to the first bandpass filter; The secondary amplification circuit is formed by an internal circuit between the INB pin and the OUTB pin of the variable gain amplifier U8, wherein the INB pin is connected to the output end of the first bandpass filter, and the OUTB pin is connected to the input end of the second bandpass filter.

8. The low-power wireless ground resistance precision monitoring device according to claim 7 is characterized in that: The first bandpass filter includes resistors R10 and R11, capacitors C23, C24, C26, C27, operational amplifier U7.1 and adjustable potentiometer R12, wherein: The positive electrode of the capacitor C23 is connected to the OUTA pin of the variable gain amplifier U8 through the resistor R10, and the negative electrode is connected to the output end of the operational amplifier U7.

1. The positive electrode of the capacitor C26 is connected to one end of the adjustable potentiometer R12, and the negative electrode is connected to the negative input end of the operational amplifier U7.

1. The other end of the adjustable potentiometer R12 is grounded, the positive input end of the operational amplifier U7.1 is grounded, the negative input end of the power supply of the operational amplifier U7.1 is connected to a -5V voltage and is grounded through a capacitor C27, the positive input end of the power supply of the operational amplifier U7.1 is connected to a +5V voltage and is grounded through a capacitor C24, the resistor R11 is connected between the negative electrode of the capacitor C23 and the negative electrode of the capacitor C26, the resistor R11 is connected between the positive electrode of the capacitor C23 and the positive electrode of the capacitor C26 through a line conduction, and the output end of the operational amplifier U7.1 is connected to the INB pin of the variable gain amplifier U8.

9. The low-power wireless ground resistance precision monitoring device according to claim 8, characterized in that: The second bandpass filter includes resistors R18 and R21, capacitors C31 and C35, an operational amplifier U7.2 and an adjustable potentiometer R23, wherein: the positive electrode of the capacitor C31 is connected to the OUTB pin of the variable gain amplifier U8 through the resistor R18, and the negative electrode is connected to the negative input terminal of the operational amplifier U7.2, the positive input terminal of the operational amplifier U7.2 is grounded, and the output terminal of the operational amplifier U7.2 is connected to the input terminal of the signal conversion circuit; the positive electrode of the capacitor C35 is connected to one end of the adjustable potentiometer R23, the negative electrode is connected to the output terminal of the operational amplifier U7.2, and the other end of the adjustable potentiometer R23 is grounded; the resistor R21 is connected and arranged between the negative input terminal and the output terminal of the operational amplifier U7.

2.

10. The low-power wireless ground resistance precision monitoring device according to claim 9, characterized in that: The signal conversion circuit includes capacitors C29, C30, C32, C33, C34, resistors R14-R17, R19, R20, R22, PNP transistors Q1 and Q2, operational amplifiers U9.1 and U9.2, wherein: The positive electrode of the capacitor C30 is connected to the output end of the second bandpass filter, and the negative electrode is connected to the resistor R17 and the negative input end of the operational amplifier U9.1 in sequence. The positive input end of the operational amplifier U9.1 is grounded through the resistor R20, and the positive and negative power supply input ends of the operational amplifier U9.1 are respectively connected to the +5V voltage and the -5V voltage; one end of the resistor R16 is respectively connected to the collector and base of the PNP transistor Q1 and the negative input end of the operational amplifier U9.1, and the other end is connected to the emitter of the PNP transistor Q2; the emitter of the PNP transistor Q1 is connected to the base of the PNP transistor Q2, and the collector of the PNP transistor Q2 is respectively connected to the output end of the operational amplifier U9.1 and the emitter of the PNP transistor Q1; the resistor R19 One end is connected to the emitter of the PNP transistor Q2, and the other end is connected to the negative input terminal of the operational amplifier U9.

2. The positive input terminal of the operational amplifier U9.2 is grounded, and the output terminal of the operational amplifier U9.2 is respectively connected to the positive electrodes of capacitors C32, C33, and C34 and the ADC pin of the microcontroller U4, and the negative electrodes of the capacitors C32, C33, and C34 are grounded; the positive electrode of the capacitor C29 is connected to the negative input terminal of the operational amplifier U9.2, and the negative electrode is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R15 is connected to the negative input terminal of the operational amplifier U9.2, and the other end is connected to the output terminal of the operational amplifier U9.2; one end of the resistor R14 is connected to the circuit between the capacitor C30 and the resistor R17, and the other end is connected to the negative input terminal of the operational amplifier U9.2.

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