A contact resistance online detection device

Abstract

The present invention discloses an online contact resistance detection device, which relates to the technical field of resistance detection and aims to solve the problem of resistance measurement requiring power off in the prior art. The present invention comprises: a power supply, a signal amplification and filtering circuit, a switching circuit, a current testing circuit, and a single-chip microcomputer; a first current testing circuit is connected in parallel with the resistance to be measured R' to shunt current and output a voltage signal V1 representing its own current value; a second current testing circuit is connected in series with both the resistance to be measured R' and the first current testing circuit and outputs a voltage signal V1P representing its own current value; the single-chip microcomputer is connected to the output terminals of the first current testing circuit and the second current testing circuit, and is used to obtain the voltage signals V1 and V1P, calculate, and output the results.

Description

Technical Field

[0001] The present invention relates to the technical field of resistance detection, in particular to an online contact resistance detection device. Background Art

[0002] Currently, contact resistance tests are mostly performed using the four-wire method, which requires disconnecting the component under test and precludes online monitoring. For example, poor contact in a switch can increase resistance at the contact point, causing localized heating when conducting current, posing a risk. However, in homes and factories, disconnecting the power supply is inconvenient. Currently, no product on the market can measure resistance while the component is in use, creating significant inconveniences during electrical inspections. Summary of the Invention

[0003] The present invention proposes an online contact resistance detection device, which includes:

[0004] Power supply, signal amplification and filtering circuit, switching circuit, current test circuit, single chip microcomputer;

[0005] The first current test circuit is connected in parallel with the resistor R' to be tested to split the current and output a voltage signal V1 representing its own current value;

[0006] The second current test circuit is connected in series with the resistor to be tested R' and the first current test circuit, and outputs a voltage signal V1P representing its own current value;

[0007] The single chip microcomputer is connected to the output end of the first current test circuit and the output end of the second current test circuit, and is used to obtain the voltage signal V1 and the voltage signal V1P, calculate and output the results.

[0008] The present invention is further configured as follows: including a signal amplification and filtering circuit and a switching circuit, wherein the output end of the first current testing circuit is connected to the input end of the signal amplification and filtering circuit, the output end of the signal amplification and filtering circuit is connected to the output end of the switching circuit, and the switching circuit controls the conduction and disconnection of the first current testing circuit based on the output result of the signal amplification and filtering circuit.

[0009] The present invention is further configured as follows: the first current testing circuit includes a current transformer U3R, and the two input pins of the current transformer U3R are used to be connected in parallel with the resistor R' to be measured; one output pin of the current transformer U3R is grounded, and the other output pin is connected to the parallel resistor R4 and the resistor R6, the other end of the resistor R4 is connected to the capacitor C6, the other end of the capacitor C6 and the other end of the capacitor R6 are grounded, and one end of the capacitor C6 connected to the resistor R4 is the output end of the first current testing circuit.

[0010] The present invention is further configured as follows: the second current test circuit includes a current transformer U2R, and the two input pins of the current transformer U2R are used to be connected in series with the resistor to be measured R'; one output pin of the current transformer U2R is grounded, and the other output pin is connected to the resistor R3 and the resistor R5 in parallel, the other end of the resistor R3 is connected to the capacitor C5, the other end of the capacitor C5 and the other end of the capacitor R5 are grounded, and one end of the capacitor C5 connected to the resistor R3 is the output end of the second current test circuit.

[0011] The beneficial technical effects of the present invention are:

[0012] 1. Using the principle of parallel shunting, the first current test circuit and the second current test circuit are set to realize online detection of resistance.

[0013] 2. Suitable for large current detection environment, it realizes protection function by feeding back signal V1 to the signal amplification and filtering circuit.

[0014] 3. The first current test circuit and the second current test circuit are suitable for detecting an alternating current environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the schematic diagram of this patent;

[0016] Figure 2 is a circuit diagram of the switching circuit in this patent;

[0017] Figure 3 is a circuit diagram of the first current test circuit and the second current test circuit in this patent;

[0018] Figure 4 This is the circuit diagram of the single chip microcomputer in this patent;

[0019] Figure 5 This is the circuit diagram of the signal amplification and filtering circuit in this patent. DETAILED DESCRIPTION

[0020] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0021] The present invention proposes an online contact resistance detection device, which includes a power supply, a signal amplifying and filtering circuit, a switching circuit, a first current testing circuit, a second current testing circuit, a resistance R' to be tested, a single chip microcomputer and an input 485 communication module.

[0022] The principle of this patent is to obtain the test current I1 of a test resistor R connected in parallel with the resistor to be tested R', and obtain the sum of the current in the test resistor R' and the test current I1, which is named test current I2. Based on the principle of current shunting in parallel circuits, the resistance value of the test resistor R' can be calculated using the formula R'=I1*R / (I2-I1).

[0023] The power supply is used to power the entire device. The first current test circuit is connected in parallel with the resistor to be measured R' to shunt the current, and outputs a voltage signal V1 representing its own current value. The second current test circuit is connected in series with the resistor to be measured R' and the first current test circuit at the same time, and outputs a voltage signal V1P representing its own current value. The single-chip microcomputer is connected to the output end of the first current test circuit and the output end of the second current test circuit, and is used to obtain the voltage signal V1 and the voltage signal V1P, calculate and output the results. The output end of the single-chip microcomputer is connected to the 485 communication module. The output end of the first current test circuit is connected to the input end of the signal amplification and filtering circuit, and the output end of the signal amplification and filtering circuit is connected to the output end of the switching circuit. The switching circuit controls the conduction and disconnection of the first current test circuit based on the output result of the signal amplification and filtering circuit.

[0024] The switching circuit includes driver U7, optocouplers U6 and U10, and transistors Q2 and Q3. The optocoupler model is PC817S, driver U7 is TC4426BPA, and the transistor model is FQPF6N90C. Pin 1 of the two optocouplers U6 and U10 is connected to a 5V power supply, pin 2 is connected to resistors R15 and R20, respectively, pin 3 is connected to DGND, and pin 4 is connected to resistors R12 and R19, respectively. The other ends of resistors R15 and R20 are connected to the output of the signal amplification and filtering circuit. The other ends of resistors R12 and R19 are connected to a 12V power supply.

[0025] Pin 1 of driver U7 is floating, pin 2 is connected to resistor R12 connected to one end of photocoupler U6, pin 3 is connected to DGND, pin 4 is connected to resistor R19 connected to one end of photocoupler U10, pin 5 is connected to the base of transistor Q4, pin 6 is connected to 12V power supply, pin 7 is connected to the base of transistor Q1, and pin 8 is floating.

[0026] The base and collector of transistor Q1 are connected in parallel with resistor R10. The collector of transistor Q1 is connected to a 12V power supply and capacitor C38, with the other end of capacitor C38 grounded. The emitter of transistor Q1 is connected in parallel with capacitor C9 and resistor R11. The other ends of capacitor C9 and resistor R11 are connected to the gate of transistor Q2. Resistor R14 is connected in parallel with the gate and source of transistor Q2, and the source of transistor Q2 is connected to DGND. The drain of transistor Q2 serves as an output terminal of the switching circuit, outputting a voltage signal UA.

[0027] The base and collector of transistor Q4 are connected in parallel with resistor R18. The collector of transistor Q4 is connected to a 12V power supply and capacitor C39, with the other end of capacitor C39 grounded. The emitter of transistor Q4 is connected in parallel with capacitor C16 and resistor R22. The other ends of capacitor C16 and resistor R22 are connected to the gate of transistor Q2. Resistor R17 is connected in parallel with the gate and source of transistor Q3, with the source of transistor Q3 connected to DGND. The drain of transistor Q2 serves as the other output terminal of the switching circuit, outputting a voltage signal UB.

[0028] The operating principle of the switching circuit is as follows: the input end of the switching circuit receives a 5V or 0V voltage signal from the signal amplification and filtering circuit. When the switching circuit input is 0V, optocouplers U6 and U10 are turned on, and pins 2 and 4 of driver U7 are at a low level, and pins 5 and 7 of driver U7 are at a high level, and transistors Q2 and Q3 are turned on. When the switching circuit input is 5V, optocouplers U6 and U10 are turned off, and pins 2 and 4 of driver U7 are at a high level, and pins 5 and 7 of driver U7 are at a low level, and transistors Q2 and Q3 are turned off. Logically speaking, driver U7 acts as an inverter in the switching circuit, and its purpose is to improve the response speed of the switching circuit.

[0029] The first current test circuit includes a current transformer U3R and terminal JP2. Current transformer U2R is model JCT5254GZ. Pin 1 of terminal JP2 is connected to the drain of transistor Q2 in the switching circuit, pin 2 is connected to current transformer U3R, and pins 3 and 4 are used to connect to the second current test circuit. Pin 1 of current transformer U3R is connected to the drain of transistor Q3 in the switching circuit, pin 3 is connected to ground, and pin 4 is connected to resistors R4 and R6 in parallel. The other end of resistor R6 is grounded. The other end of resistor R4 is connected to capacitor C6, which in turn is grounded. One end of resistor R4 connected to capacitor C6 serves as the output of the first current test circuit, connected to the input of the microcontroller and the signal amplification and filtering circuit, and outputs a voltage signal V1. Voltage signal V1 can be used to infer the current flowing between pins 1 and 2 of current transformer U3R.

[0030] The second current test circuit includes a current transformer U2R, model JCT5254GZ. Pin 1 of current transformer U2R is connected to pin 3 of terminal JP2, pin 2 is connected to pin 4 of terminal JP2, and pin 3 is grounded. Pin 4 is connected to resistors R3 and R5 in parallel, with the other end of resistor R5 grounded. The other end of resistor R3 is connected to capacitor C5, with the other end of capacitor C5 grounded. One end of resistor R3 connected to capacitor C5 serves as the output of the second current test circuit, connected to a microcontroller and outputting a voltage signal V1P. Voltage signal V1P can be used to infer the current flowing between pins 1 and 2 of current transformer U2R.

[0031] The principle behind the coordinated operation of the first and second current test circuits and the switch circuit is as follows: Connecting the two ends of the resistor under test, R', to pins 1 and 2 of terminal JP2 creates a parallel connection between the resistor under test, R', and current transformer U3R. Based on the principle of parallel current shunt, the resistance of the resistor under test, R', affects the current flowing through U3R, which in turn affects the output of V1. The current between pins 1 and 2 of current transformer U2R represents the aforementioned current I1. The output of V1 is fed back to the signal amplification and filtering circuit, forming negative feedback, which in turn controls the on and off state of the switch circuit. When V1 exceeds a set threshold, indicating that the resistance of the resistor under test, R', is too high, the switch circuit is triggered by this feedback and switches to the off state, protecting the first current test circuit. When V1 falls below the set threshold, the switch circuit switches to the on state. Pins 3 and 4 of terminal JP2 are connected to the same side of the resistor under test, R'. The current between pins 1 and 2 of current transformer U2R represents the aforementioned current I2. Depending on the actual situation, a current transformer may be added between pins 3 and 4 of terminal JP2.

[0032] Take the measurement of the contact resistance of the air switch as an example. The contact resistance of the air switch is the resistance R' to be measured. Pins 3 and 4 of terminal JP2 are connected to the live wire of the mains, and are located on the side of the air switch connected to the mains. Pins 1 and 2 of terminal JP2 are also connected to the live wire of the mains, but the two pins are respectively connected to the end of the air switch connected to the mains and the end connected to the room. Measurements can be made when the air switch is in a closed state. The current of the current transformer U3R is affected by the contact resistance of the air switch. The contact resistance of the air switch can be calculated based on the values ​​of V1 and V1P. The air switch does not need to be disconnected during the entire process, which does not affect the normal use of electrical appliances and can also be used to troubleshoot faults. In addition, the technical solution of this patent can be applied to civilian AC environments. Once the contact resistance of the air switch exceeds a certain value, the switch short circuit is feedback-disconnected and the device can be protected.

[0033] The microcontroller model is HT5019. The output of the first current test circuit is connected to resistor R38, the other end of which is connected to pin 7 of the microcontroller. The output of the second current test circuit is connected to pin 9 of the microcontroller. The microcontroller calculates and outputs the analog signals received by pins 7 and 9. The output of the microcontroller is connected to a 485 communication module. The microcontroller output and 485 communication module are prior art. Alarm or notification circuits can also be configured based on changes in V1 as needed. This prior art will not be discussed here.

[0034] Although the present invention has been described with reference to preferred embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various technical features described in the various embodiments may be combined in any manner as long as no structural conflicts exist. The present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

[0035] In the description of the present invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. These are intended solely for ease of description and are not intended to indicate or imply that the device or component described must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0036] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0037] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, article, or apparatus / device.

[0038] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A contact resistance online detection device, characterized in that: include: Power supply, signal amplification and filtering circuit, switching circuit, current test circuit, single chip microcomputer; The first current test circuit is connected in parallel with the resistor R' to be tested to split the current and output a voltage signal V1 representing its own current value; The second current test circuit is connected in series with the resistor to be tested R' and the first current test circuit, and outputs a voltage signal V1P representing its own current value; The single chip microcomputer is connected to the output end of the first current test circuit and the output end of the second current test circuit, and is used to obtain the voltage signal V1 and the voltage signal V1P, calculate and output the result; The first current test circuit comprises a signal amplifying and filtering circuit and a switching circuit, wherein the output end of the first current test circuit is connected to the input end of the signal amplifying and filtering circuit, the output end of the signal amplifying and filtering circuit is connected to the output end of the switching circuit, and the switching circuit controls the conduction and disconnection of the first current test circuit based on the output result of the signal amplifying and filtering circuit; The first current testing circuit includes a current transformer U3R, and the two input pins of the current transformer U3R are used to be connected in parallel with the resistor R' to be measured; one output pin of the current transformer U3R is grounded, and the other output pin is connected to the parallel resistors R4 and R6, the other end of the resistor R4 is connected to the capacitor C6, the other end of the capacitor C6 and the other end of the capacitor R6 are grounded, and one end of the capacitor C6 connected to the resistor R4 is the output end of the first current testing circuit.

2. The contact resistance online detection device according to claim 1, characterized in that: The second current test circuit includes a current transformer U2R, and the two input pins of the current transformer U2R are used to be connected in series with the resistor R' to be measured; one output pin of the current transformer U2R is grounded, and the other output pin is connected to the resistor R3 and the resistor R5 in parallel, the other end of the resistor R3 is connected to the capacitor C5, the other end of the capacitor C5 and the other end of the capacitor R5 are grounded, and the end of the capacitor C5 connected to the resistor R3 is the output end of the second current test circuit.

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