Device for detecting insulation resistivity of anticorrosive coating outside steel cylinder concrete pipe

Abstract

The utility model belongs to the technical field of detection, and particularly relates to a device for detecting the insulation resistivity of an anticorrosive coating outside a steel cylinder concrete pipe, which comprises a current acquisition module, a voltage acquisition module, an analog-to-digital conversion module, a microcontroller and a display module, the voltage acquisition module is connected with the microcontroller through the analog-to-digital conversion module, the current acquisition module comprises a current metering circuit and a voltage stabilizing circuit, a current signal flowing through a measured anticorrosive coating is metered through the current metering circuit, and a digital current signal is directly measured through the current metering circuit, so that analog-to-digital conversion is avoided; cost is saved, accuracy is high, stable voltage is provided for the current metering circuit through the voltage stabilizing circuit, and the accuracy of current acquisition of the current acquisition module is improved.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of detection, concretely relates to a kind of steel cylinder concrete pipe outer anticorrosive coating insulation resistivity detection device. BACKGROUND

[0002] In the industrial field, anticorrosive layer is an important barrier to protect equipment from corrosion. In order to ensure the effectiveness of the anticorrosive layer, resistivity testing has become an indispensable link. Anticorrosive layer resistivity testing, as the name implies, is a measurement of the resistivity of the anticorrosive material layer. Resistivity, as an important parameter for measuring the electrical conductivity of materials, plays a key role in evaluating the protective effect of the anticorrosive layer. Through testing, we can understand whether the anticorrosive layer is uniform, dense, and whether there are potential defects or damage

[0003] The existing steel cylinder concrete pipe outer anticorrosive coating insulation resistivity detection device generally calculates the resistivity by collecting current signals and voltage difference signals. However, during current collection, the current collection module may not collect accurate current signals due to the power supply of the current collection module not being stable or being affected by other interference signals, resulting in inaccurate resistivity and other problems. SUMMARY

[0004] The utility model provides a kind of steel cylinder concrete pipe outer anticorrosive coating insulation resistivity detection device for the above problems, it is helpful to provide stable voltage for current sampling module, to ensure the accuracy of current collection module to collect current.

[0005] To achieve the above technical solutions, the utility model provides a kind of steel cylinder concrete pipe outer anticorrosive coating insulation resistivity detection device, including current collection module, voltage collection module, analog-digital conversion module, microcontroller and display module;

[0006] The current collection module is connected with the first current detection electrode and the second current detection electrode;

[0007] The current collection module is connected with the microcontroller to send the current signal flowing through the measured anticorrosive coating collected by the first current detection electrode and the second current detection electrode to the microcontroller;

[0008] The current collection module includes a current metering circuit for metering the current flowing through the measured anticorrosive coating to obtain a digital current signal, and a voltage stabilizing circuit for providing stable voltage to the current metering circuit;

[0009] The voltage collection module is connected with the first voltage detection electrode and the second voltage detection electrode;

[0010] The voltage acquisition module is connected with the analog-digital conversion module to send the measured analog voltage difference signal between the two ends of the anticorrosive coating measured by the first voltage detection electrode and the second voltage detection electrode to the analog-digital conversion module for conversion to obtain a digital voltage difference signal;

[0011] The analog-digital conversion module is connected with the microcontroller to send the obtained digital voltage difference signal to the microcontroller, so that the microcontroller calculates the resistivity based on the digital current signal and the digital voltage difference signal;

[0012] The display module is connected with the microcontroller to display the current signal, the digital voltage difference signal and the resistivity.

[0013] Further, the voltage stabilizing circuit comprises a fifth capacitor C5, a fourth capacitor C4, a third capacitor C3 and a third inductor L3; the output end VCC1_OUT of the voltage stabilizing circuit is connected with the first end of the fifth capacitor C5, the first end of the fourth capacitor C4, the first end of the third capacitor C3 and the first end of the third inductor L3; the second end of the fifth capacitor C5, the second end of the fourth capacitor C4 and the second end of the third capacitor C3 are grounded; the second end of the third inductor L3 is connected with the first end of the first resistor R1; the second end of the first resistor R1 is connected with the first end of the sixth capacitor C6, the first end of the seventh capacitor C7, the first end of the second voltage-dependent resistor MR2 and the first end of the first voltage-dependent resistor MR1, and the first end of the first resistor R1 is connected with the first power supply VCC1; the first end of the fourth inductor L4 is grounded; the second end of the fourth inductor L4 is connected with the second end of the sixth capacitor C6, the second end of the eighth capacitor C8 and the first end of the third voltage-dependent resistor MR3, and then grounded; the second end of the seventh resistor R7 and the first end of the eighth capacitor C8 are grounded; the second end of the third voltage-dependent resistor MR3 and the second end of the second voltage-dependent resistor MR2 are grounded through the second ceramic gas discharge tube D2; the second end of the first voltage-dependent resistor MR1 is grounded through the second ceramic gas discharge tube D2.

[0014] Further, the current metering circuit comprises: a current metering chip U2, an I OUT pin of the current metering chip U2 is connected with a first wiring terminal J1 for connecting with the first current detection electrode; an I IN pin of the current metering chip U2 is connected with a second wiring terminal J2 for connecting with the second current detection electrode; a V+ pin of the current metering chip U2 is connected with a first end of a second capacitor C2; a V- pin of the current metering chip U2 is connected with a second end of the second capacitor C2 and a first end of a second inductor L2; the first end of the second capacitor C2 is also connected with a 4 pin of an electrical isolation chip U1; a second end of the second inductor L2 is connected with a 3 pin of the electrical isolation chip U1, a 1 pin of the electrical isolation chip U1 is grounded through a first inductor L1; a 2 pin of the electrical isolation chip U1 is connected with a first end of a first capacitor C1 and an output end VCC1 OUT of the voltage stabilizing circuit; a second end of the first capacitor C1 is grounded; a Tx pin of the current metering chip U2 is connected with a TX pin of the microcontroller, and a Rx pin of the current metering chip U2 is connected with a RX pin of the microcontroller, so as to send the collected current to the microcontroller.

[0015] Further, the voltage acquisition module comprises a signal conditioning circuit and an operational amplification circuit.

[0016] Further, the signal conditioning circuit comprises: a third wiring terminal J3 and a fourth wiring terminal J4; the third wiring terminal J3 is connected with a first end of a fifth resistor R5; a second end of the fifth resistor R5 is connected with a 3 pin of a third dual diode D3 and an -IN pin of an amplification chip U3; a 1 pin of the third dual diode is connected with a second power supply VCC2, and a 2 pin of the third dual diode is grounded; a second end of a second resistor R2 is connected with a 3 pin of a fourth dual diode D4 and a +IN pin of the amplification chip U3; a 1 pin of the fourth dual diode is connected with the second power supply VCC2, and a 2 pin of the fourth dual diode is grounded; an RG pin 1 of the amplification chip U3 is connected to an RG pin 8 of the amplification chip U3 through a potentiometer BP1; a -VS pin of the amplification chip U3 is connected with a negative electrode of a ninth polarized capacitor C9 and a first end of a tenth capacitor C10; a positive electrode of the ninth polarized capacitor C9 and a second end of the tenth capacitor C10 are grounded; a REF pin of the amplification chip U3 is grounded; a +VS pin of the amplification chip U3 is connected with a first end of an eleventh capacitor C11 and a positive electrode of a twelfth polarized capacitor C12; a second end of the eleventh capacitor C11 and a negative electrode of the twelfth polarized capacitor C12 are grounded; an OUT pin of the amplification chip U3 is connected with an input end of the operational amplification circuit.

[0017] Further, the operational amplifier circuit comprises a third resistor R3, a first end of the third resistor R3 is connected with an OUT pin of the amplification chip U3, a second end of the third resistor R3 is connected with a first end of a fourth resistor R4 and a +IN pin of an operational amplifier U4, a second end of the fourth resistor R4 is grounded, and the -IN pin and the OUT pin of the operational amplifier U4 are connected with an output end VO of the voltage sampling module.

[0018] Further, the device further comprises an RS485 conversion module, and the RS485 conversion module is connected with the microcontroller.

[0019] Further, the RS485 conversion module comprises an RS485 transceiver U5, a RO pin of the RS485 transceiver is connected with a first end of a tenth resistor R10, a second end of the tenth resistor R10 is connected with a first end of a ninth resistor R9 and an output end connected with an RXD end of the microcontroller, a second end of the ninth resistor R9 and a first end of an eighth resistor R8 are connected with a first power supply VCC1, a second end of the eighth resistor R8 is connected with an RE pin and a DE pin of the RS485 transceiver U5 and a collector of a first triode Q1, a base of the first triode Q1 is connected with a first end of a thirteenth capacitor C13 and a first end of a seventh resistor R7, a second end of the thirteenth capacitor C13 is grounded, a second end of the seventh resistor R7 and a first end of a sixth resistor R6 and an output end connected with a TXD end of the microcontroller are connected, and a second end of the sixth resistor R6 is connected with the first power supply VCC1.

[0020] a DI pin of the RS485 transceiver U5 is connected with the output end connected with the TXD end of the microcontroller through an eleventh resistor R11, a +5 pin of the RS485 transceiver U5 is connected with a third power supply VCC3, a B pin of the RS485 transceiver U5 is connected with a first end of a twelfth resistor R12, a first end of a thirteenth resistor R13, a first end of a fifteenth resistor R15 and a first end of a fifth bidirectional transient suppression diode D5, a second end of the twelfth resistor R12 is connected with a second end of the fifth bidirectional transient suppression diode D5, an A pin of the RS485 transceiver U5 is connected with a second end of the thirteenth resistor R13, a first end of a fourteenth resistor R14, a first end of a sixth bidirectional transient suppression diode D6 and a first end of a sixth resistor R16, a second end of the fourteenth resistor R14 is connected with the third power supply VCC3, a second end of the sixth bidirectional transient suppression diode D6 is grounded, and a second end of the sixteenth resistor R16 is connected with an A pin of the RS485 plug.

[0021] The utility model discloses the beneficial effect is:

[0022] (1) The utility model discloses, current acquisition module includes current measurement circuit and voltage stabilizing circuit, and the current signal of flowing through the anticorrosive coating of being measured is measured through current measurement circuit, and the digital current signal is directly measured through current measurement circuit, avoids the analog-digital conversion, not only saves the cost and high accuracy, and provides stable voltage for current measurement circuit through voltage stabilizing circuit, helps to improve the accuracy of current acquisition module current acquisition.

[0023] (2) The host computer PC reads data from the microcontroller through the RS485 conversion module, which helps to improve the transmission distance and effectively suppresses common mode interference.

[0024] The advantages of the additional aspects of the utility model will be partially given in the following description, some will become obvious from the following description, or be understood through the practice of the utility model. BRIEF DESCRIPTION OF DRAWINGS

[0025] The drawings accompanying the specification of the utility model form part of the utility model and are used to provide further understanding of the utility model, and the illustrative embodiments of the utility model and the description thereof are used to explain the utility model, and do not constitute improper limitation on the utility model.

[0026] Figure 1 It is the electric schematic diagram of the steel cylinder concrete pipe outer anticorrosive coating insulation resistivity detection device of the utility model;

[0027] Figure 2 It is the circuit diagram of the current acquisition module of the utility model;

[0028] Figure 3 It is the circuit diagram of the voltage acquisition module of the utility model embodiment;

[0029] Figure 4 It is the circuit diagram of the RS485 conversion module of the utility model embodiment. DETAILED DESCRIPTION

[0030] The utility model will be further described below in combination with the drawings and embodiments.

[0031] It should be pointed out that the following detailed description is all exemplary, and aims at providing further description to the utility model. Unless otherwise specified, each technical and scientific term used in the embodiment has the same meaning as that generally understood by ordinary maintenance personnel in the technical field to which the utility model belongs.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] In this utility model, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of the structural relationship between the various components or elements of this utility model and do not specifically refer to any component or element in this utility model. They should not be construed as limiting this utility model.

[0034] In this utility model, terms such as "fixed connection," "connected," and "joined" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. For researchers or maintenance personnel in this field, the specific meaning of the above terms in this utility model can be determined according to the specific circumstances, and should not be construed as a limitation of this utility model.

[0035] Example 1:

[0036] like Figure 1 As shown, this embodiment provides a device for detecting the insulation resistivity of the external anti-corrosion coating of a steel cylinder concrete pipe, comprising:

[0037] (a) Current acquisition module 3, which is connected to a first current detection electrode and a second current detection electrode to acquire the current signal flowing through the measured anti-corrosion coating through the first current detection electrode and the second current detection electrode.

[0038] Specifically, such as Figure 2 As shown, the current acquisition module 3 includes: a current metering circuit 3-1 and a voltage stabilizing circuit 3-2.

[0039] The current measurement circuit 3-1 comprises: a current measurement chip U2, an I_OUT pin of the current measurement chip U2 is connected with a first wiring terminal J1 for connecting with a first current detection electrode; an I_IN pin of the current measurement chip U2 is connected with a second wiring terminal J2 for connecting with a second current detection electrode; a V+ pin of the current measurement chip U2 is connected with a first end of a second capacitor C2; a V- pin of the current measurement chip U2 is connected with a second end of the second capacitor C2 and a first end of a second inductor L2; the first end of the second capacitor C2 is also connected with a 4 pin of an electrical isolation chip U1; a second end of the second inductor L2 is connected with a 3 pin of the electrical isolation chip U1, a 1 pin of the electrical isolation chip U1 is grounded through a first inductor L1; a 2 pin of the electrical isolation chip U1 is connected with a first end of a first capacitor C1 and an output end VCC1_OUT of a voltage stabilizing circuit; a second end of the first capacitor C1 is grounded; a Tx pin of the current measurement chip U2 is connected with a TX pin of a microcontroller, and an Rx pin of the current measurement chip U2 is connected with an RX pin of the microcontroller, so as to send the collected current to the microcontroller.

[0040] The voltage stabilizing circuit 3-2 comprises: a fifth capacitor C5, a fourth capacitor C4, a third capacitor C3 and a third inductor L3; an output end VCC1_OUT of the voltage stabilizing circuit is connected with a first end of the fifth capacitor C5, a first end of the fourth capacitor C4, a first end of the third capacitor C3 and a first end of the third inductor L3; a second end of the fifth capacitor C5, a second end of the fourth capacitor C4 and a second end of the third capacitor C3 are grounded; a second end of the third inductor L3 is connected with a first end of a first resistor R1; a second end of the first resistor R1 is connected with a first end of a sixth capacitor C6, a first end of a seventh capacitor C7, a first end of a second pressure sensitive resistor MR2 and a first end of a first pressure sensitive resistor MR1; a first end of a fourth inductor L4 is grounded; a second end of the fourth inductor L4 is connected with a second end of the sixth capacitor C6, a second end of an eighth capacitor C8 and a first end of a third pressure sensitive resistor MR3, and then grounded; a second end of a seventh resistor R7 and a first end of the eighth capacitor C8 are grounded; a second end of the third pressure sensitive resistor MR3 and a second end of the second pressure sensitive resistor MR2 are grounded through a second ceramic gas discharge tube D2; a second end of the first pressure sensitive resistor MR1 is grounded through the second ceramic gas discharge tube D2.

[0041] In the embodiment, MR2, MR3 and D4 together realize surge common mode protection, MR1 and D1 realize surge differential mode protection, the capacitors C7 and C8 provide a quick return path for high-frequency signals, the inductors L3 and L4 form a pair of common mode inductors to reduce interference generated when common mode current is conducted in the circuit, and the capacitor and the common mode inductor are used in cooperation to improve the ability to filter common mode interference in the circuit, so that the voltage provided by the first power supply VCC1 is more stable after being stabilized by the voltage stabilizing circuit, and the stabilized voltage is output to supply voltage to the current measurement circuit.

[0042] (ii) Voltage acquisition module 2, which is connected to a first voltage detection electrode and a second voltage detection electrode to measure the voltage difference across the anti-corrosion coating.

[0043] Specifically, such as Figure 3 As shown, the voltage sampling module 2 includes a signal conditioning circuit 2-1 and an operational amplifier circuit 2-2. The signal conditioning circuit 2-1 includes a third terminal J3 for connection to the first voltage detection electrode and a fourth terminal J4 for connection to the second voltage detection electrode; the third terminal J3 is connected to the first end of a fifth resistor R5; the second end of the fifth resistor R5 is connected to pin 3 (control terminal) of a third dual diode D3 (e.g., a BAV199 dual diode) and the -IN pin of an amplifier chip U3 (e.g., an AD620 instrumentation amplifier chip); pin 1 (cathode) of the third dual diode is connected to the second power supply VCC2, and pin 2 of the third dual diode is grounded; the second end of the second resistor R2 is connected to pin 3 (control terminal) of a fourth dual diode D4 (e.g., a BAV199 dual diode) and the -IN pin of an amplifier chip U3 (e.g., an AD620 instrumentation amplifier chip). The +IN pin is connected; pin 1 (cathode) of the fourth dual diode is connected to the second power supply VCC2, and pin 2 of the fourth dual diode is grounded; pin 1 of amplifier chip U3 is connected to pin 8 of amplifier chip U3 through potentiometer BP1; the -VS pin of amplifier chip U3 is connected to the negative terminal of the ninth polarized capacitor C9 and the first terminal of the tenth capacitor C10; the positive terminal of the ninth polarized capacitor C9 and the second terminal of the tenth capacitor C10 are grounded; the REF pin of amplifier chip U3 is grounded; the +VS pin of amplifier chip U3 is connected to the first terminal of the eleventh capacitor C11 and the positive terminal of the twelfth polarized capacitor C12; the second terminal of the eleventh capacitor C11 and the negative terminal of the twelfth polarized capacitor C12 are grounded; the OUT pin of amplifier chip U3 is connected to the input terminal of the operational amplifier circuit.

[0044] The operational amplifier circuit 2-2 includes: a third resistor R3, the first end of which is connected to the OUT pin of the amplifier chip U3; the second end of the third resistor R3 is connected to the first end of the fourth resistor R4 and the +IN pin of the operational amplifier U4 (e.g., the OPA177 operational amplifier); the second end of the fourth resistor R4 is grounded; and both the -IN pin and the OUT pin of the operational amplifier U4 are connected to the output terminal VO of the voltage sampling module.

[0045] (iv) Analog-to-digital conversion module 4, used to connect to the voltage sampling module (specifically, to connect to the output terminal VO of the voltage sampling module) to convert the acquired analog voltage signal into a digital voltage signal.

[0046] (v) Microcontroller 1, used to connect with analog-to-digital conversion module and current acquisition module to calculate the resistivity of the measured anti-corrosion coating based on the received digital voltage difference signal and current signal.

[0047] (vi) Display module 6, used to display the resistivity calculated by the microcontroller, as well as the acquired current value and voltage difference signal.

[0048] In this embodiment, by displaying the collected current signal and voltage difference signal, the operator can calculate the resistivity of the measured anti-corrosion coating based on the current signal and voltage signal.

[0049] (vii) RS485 conversion module 5, used to connect to microcontroller 1 to connect microcontroller to external PC and read data in microcontroller through PC.

[0050] Specifically, such as Figure 4 As shown, the RS485 conversion module includes: an RS485 transceiver U5 (e.g., MAX485); the RO pin of the RS485 transceiver is connected to the first end of the tenth resistor R10; the second end of the tenth resistor R10 is connected to the first end of the ninth resistor R9 and the output terminal for connection to the RXD terminal of the microcontroller; the second end of the ninth resistor R9 and the first end of the eighth resistor R8 are connected to the first power supply VCC1; the second end of the eighth resistor R8 is connected to the RE and DE pins of the RS485 transceiver U5 and the collector of the first transistor Q1; the base of the first transistor Q1 is connected to the first end of the thirteenth capacitor C13 and the first end of the seventh resistor R7; the second end of the thirteenth capacitor C13 is grounded; the second end of the seventh resistor R7 and the first end of the sixth resistor R6 are connected to the output terminal connected to the TXD terminal of the microcontroller; the second end of the sixth resistor R6 is connected to the first power supply VCC1.

[0051] The DI pin of RS485 transceiver U5 is connected to the output terminal of the microcontroller's TXD pin via the eleventh resistor R11; the +5 pin of RS485 transceiver U5 is connected to the third power supply VCC3; the B pin of RS485 transceiver U5 is connected to the first terminal of the twelfth resistor R12, the first terminal of the thirteenth resistor R13, the first terminal of the fifteenth resistor R15, and the first terminal of the fifth bidirectional transient suppressor diode D5; the second terminal of the twelfth resistor R12 is connected to the second terminal of the fifth bidirectional transient suppressor diode D5; the A pin of RS485 transceiver U5 is connected to the second terminal of the thirteenth resistor R13, the first terminal of the fourteenth resistor R14, the first terminal of the sixth bidirectional transient suppressor diode D6, and the first terminal of the sixth resistor R16; the second terminal of the fourteenth resistor R14 is connected to the third power supply VCC3; the second terminal of the sixth bidirectional transient suppressor diode D6 is grounded; and the second terminal of the sixteenth resistor R16 is connected to the A pin of the RS485 connector.

[0052] The embodiment adopts balanced transmission and differential reception through RS-485, so that the transmission distance is longer than RS-232, and common mode interference can be effectively suppressed.

[0053] In the embodiment, the microcontroller adopts an STM32 series single-chip microcomputer.

[0054] The above merely describes preferred embodiments of the present application and is not intended to limit the present application. The present application can be changed and modified in various ways by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A device for detecting the insulation resistivity of an external anticorrosive coating of a steel cylinder concrete pipe, characterized by comprising: The current acquisition module, the voltage acquisition module, the analog-digital conversion module, the microcontroller and the display module are included. The first current detection electrode and the second current detection electrode are connected to the current acquisition module. The current acquisition module is connected to the microcontroller to send the current signal flowing through the measured anticorrosive coating to the microcontroller through the first current detection electrode and the second current detection electrode. The current acquisition module includes a current metering circuit for metering the current flowing through the measured anticorrosive coating to obtain a digital current signal, and a voltage stabilizing circuit for providing a stable voltage for the current metering circuit. The first voltage detection electrode and the second voltage detection electrode are connected to the voltage acquisition module. The voltage acquisition module is connected to the analog-digital conversion module to send the analog voltage difference signal measured by the first voltage detection electrode and the second voltage detection electrode to the analog-digital conversion module for conversion to obtain a digital voltage difference signal. The analog-digital conversion module is connected to the microcontroller to send the obtained digital voltage difference signal to the microcontroller, so that the microcontroller calculates the resistivity based on the digital current signal and the digital voltage difference signal. The display module is connected to the microcontroller to display the current signal, the digital voltage difference signal and the resistivity.

2. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 1, characterized by The voltage stabilizing circuit includes a fifth capacitor C5, a fourth capacitor C4, a third capacitor C3 and a third inductor L3; the output end VCC1_OUT of the voltage stabilizing circuit is connected to the first end of the fifth capacitor C5, the first end of the fourth capacitor C4, the first end of the third capacitor C3 and the first end of the third inductor L3; the second end of the fifth capacitor C5, the second end of the fourth capacitor C4 and the second end of the third capacitor C3 are grounded; the second end of the third inductor L3 is connected to the first end of the first resistor R1; the second end of the first resistor R1 is connected to the first end of the sixth capacitor C6, the first end of the seventh capacitor C7, the first end of the second voltage-dependent resistor MR2 and the first end of the first voltage-dependent resistor MR1, and the first power supply VCC1 is connected; the first end of the fourth inductor L4 is grounded; the second end of the fourth inductor L4 is connected to the second end of the sixth capacitor C6, the second end of the eighth capacitor C8 and the first end of the third voltage-dependent resistor MR3, and then grounded; the second end of the seventh resistor R7 and the first end of the eighth capacitor C8 are grounded; the second end of the third voltage-dependent resistor MR3 and the second end of the second voltage-dependent resistor MR2 are grounded through the second ceramic gas discharge tube D2; the second end of the first voltage-dependent resistor MR1 is grounded through the second ceramic gas discharge tube D2.

3. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 2, characterized by The current metering circuit comprises a current metering chip U2, an I_OUT pin of the current metering chip U2 is connected with a first wiring terminal J1 for connecting with a first current detection electrode; an I_IN pin of the current metering chip U2 is connected with a second wiring terminal J2 for connecting with a second current detection electrode; a V+ pin of the current metering chip U2 is connected with a first end of a second capacitor C2; a V- pin of the current metering chip U2 is connected with a second end of the second capacitor C2 and a first end of a second inductor L2; the first end of the second capacitor C2 is also connected with a 4 pin of an electrical isolation chip U1; a second end of the second inductor L2 is connected with a 3 pin of the electrical isolation chip U1, a 1 pin of the electrical isolation chip U1 is grounded through a first inductor L1; a 2 pin of the electrical isolation chip U1 is connected with a first end of a first capacitor C1 and an output end VCC1_OUT of a voltage stabilizing circuit; a second end of the first capacitor C1 is grounded; a Tx pin of the current metering chip U2 is connected with a TX pin of a microcontroller, and a Rx pin of the current metering chip U2 is connected with a RX pin of the microcontroller, so as to send the collected current to the microcontroller.

4. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 1, characterized by The voltage acquisition module comprises a signal conditioning circuit and an operational amplification circuit.

5. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 4, characterized by The signal conditioning circuit comprises a third wiring terminal J3 and a fourth wiring terminal J4; the third wiring terminal J3 is connected with a first end of a fifth resistor R5; a second end of the fifth resistor R5 is connected with a 3 pin of a third dual diode D3 and an -IN pin of an amplification chip U3; a 1 pin of the third dual diode is connected with a second power supply VCC2, and a 2 pin of the third dual diode is grounded; a second end of a second resistor R2 is connected with a 3 pin of a fourth dual diode D4 and a +IN pin of the amplification chip U3; a 1 pin of the fourth dual diode is connected with the second power supply VCC2, and a 2 pin of the fourth dual diode is grounded; an RG pin 1 of the amplification chip U3 is connected to an RG pin 8 of the amplification chip U3 through a potentiometer BP1; a -VS pin of the amplification chip U3 is connected with a negative electrode of a ninth polarized capacitor C9 and a first end of a tenth capacitor C10; a positive electrode of the ninth polarized capacitor C9 and a second end of the tenth capacitor C10 are grounded; a REF pin of the amplification chip U3 is grounded; a +VS pin of the amplification chip U3 is connected with a first end of an eleventh capacitor C11 and a positive electrode of a twelfth polarized capacitor C12; a second end of the eleventh capacitor C11 and a negative electrode of the twelfth polarized capacitor C12 are grounded; an OUT pin of the amplification chip U3 is connected with an input end of the operational amplification circuit.

6. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 5, characterized by The operational amplification circuit comprises a third resistor R3, a first end of the third resistor R3 is connected with an OUT pin of the amplification chip U3; a second end of the third resistor R3 is connected with a first end of a fourth resistor R4 and a +IN pin of an operational amplifier U4; a second end of the fourth resistor R4 is grounded; -IN and OUT pins of the operational amplifier U4 are both connected with an output end VO of the voltage sampling module.

7. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 1, characterized by The device further comprises an RS485 conversion module connected with the microcontroller.

8. The apparatus for detecting the insulation resistivity of the external anticorrosive coating of a steel cylinder concrete pipe according to claim 7, characterized by The RS485 conversion module comprises an RS485 transceiver U5; a RO pin of the RS485 transceiver is connected with a first end of a tenth resistor R10; a second end of the tenth resistor R10 is connected with a first end of a ninth resistor R9 and an output end for connecting with an RXD end of a microcontroller; a second end of the ninth resistor R9 and a first end of an eighth resistor R8 are connected with a first power supply VCC1; a second end of the eighth resistor R8 is connected with an RE pin and a DE pin of the RS485 transceiver U5 and a collector of a first triode Q1; a base of the first triode Q1 is connected with a first end of a thirteenth capacitor C13 and a first end of a seventh resistor R7; a second end of the thirteenth capacitor C13 is grounded; a second end of the seventh resistor R7 and a first end of a sixth resistor R6 and an output end for connecting with a TXD end of the microcontroller are connected; a second end of the sixth resistor R6 is connected with the first power supply VCC1; a DI pin of the RS485 transceiver U5 is connected with an output end for connecting with a TXD end of the microcontroller through an eleventh resistor R11; a +5 pin of the RS485 transceiver U5 is connected with a third power supply VCC3; a B pin of the RS485 transceiver U5 is connected with a first end of a twelfth resistor R12, a first end of a thirteenth resistor R13, a first end of a fifteenth resistor R15 and a first end of a fifth bidirectional transient suppression diode D5; a second end of the twelfth resistor R12 is connected with a second end of the fifth bidirectional transient suppression diode D5; an A pin of the RS485 transceiver U5 is connected with a second end of the thirteenth resistor R13, a first end of a fourteenth resistor R14, a first end of a sixth bidirectional transient suppression diode D6 and a first end of a sixteenth resistor R16; a second end of the fourteenth resistor R14 is connected with the third power supply VCC3; a second end of the sixth bidirectional transient suppression diode D6 is grounded; a second end of the sixteenth resistor R16 is connected with an A pin of an RS485 connector.

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