Detection circuit for electrification of metal shell of electrical equipment

Abstract

The utility model discloses a detection circuit for electrification of a metal shell of electrical equipment, which comprises a first sampling circuit, a second sampling circuit and a sampling differential biasing circuit, the first sampling circuit is used for sampling voltage on a live wire, the second sampling circuit is used for sampling voltage on the metal shell of the electrical equipment, and the sampling differential biasing circuit is used for biasing the sampling differential biasing circuit. The first sampling circuit and the second sampling circuit are respectively connected with the sampling differential bias circuit, the sampling differential bias circuit is used for carrying out differential and forward bias on a sampled voltage signal to obtain a sampling waveform, and by analyzing the sampling waveform, when the waveform is abnormal, the condition that the power supply live wire of the electrical equipment is lapped on the shell can be known. The detection circuit can detect and judge whether the metal shell of the electrical equipment is lapped with the live wire to generate dangerous voltage in real time, thereby effectively avoiding the electric shock risk possibly caused by electrification of the metal shell of the electrical equipment, protecting the personal safety, and is simple in judgment mode, safe and reliable.

Description

Technical Field

[0001] This utility model relates to the field of electrical equipment technology, and more specifically, to a detection circuit for an electrical equipment with a live metal casing. Background Technology

[0002] Electrical equipment with metal casings typically uses grounding as a leakage current protection measure. Grounding connects the metal casing to the earth, diverting current to the ground and maintaining zero potential between the metal casing and the earth, thereby reducing the risk of electric shock. However, during operation, aging or abnormal wear of power supply lines can lead to damaged cable insulation, broken wires, and other issues. When the casing ground wire breaks or falls off, the equipment loses its leakage current protection function. If the insulation of the live wire is also damaged at this time, the exposed metal wire can short-circuit with the casing, causing the metal casing of the electrical equipment to carry a dangerous voltage, posing a serious threat to personal safety. Utility Model Content

[0003] In order to overcome the shortcomings of the existing technology, this utility model provides a detection circuit for live metal casing of electrical equipment. It can quickly identify the abnormal situation and issue an alarm signal the moment the live wire touches the casing or the live and neutral wires are reversed, thereby effectively avoiding the risk of electric shock that may be caused by live metal casing of electrical equipment and protecting personal safety.

[0004] The technical solution of this utility model is as follows: a detection circuit for the liveness of the metal casing of electrical equipment, comprising a first sampling circuit, a second sampling circuit, and a sampling differential bias circuit. The first sampling circuit is used to sample the voltage on the live wire, and the second sampling circuit is used to sample the voltage on the metal casing of the electrical equipment. The first sampling circuit and the second sampling circuit are respectively connected to the sampling differential bias circuit. The sampling differential bias circuit is used to differentially and positively bias the sampled voltage signal to obtain the sampled waveform.

[0005] Furthermore, it also includes capacitor C1 and capacitor C2. One end of capacitor C1 is connected to the live wire, and the other end of capacitor C1 is connected to the metal casing of the electrical equipment. One end of capacitor C2 is connected to the metal casing of the electrical equipment, and the other end of capacitor C2 is connected to the neutral wire.

[0006] Furthermore, it also includes a waveform analysis circuit and an alarm output circuit. The waveform analysis circuit is connected to the differential bias circuit. The waveform analysis circuit is used to analyze the sampled waveform. When the live wire and neutral wire are connected normally and the sampled waveform tends to be flat, the alarm output circuit issues an alarm signal. When the live wire and neutral wire are reversed and the sampled waveform is an AC sine wave, the alarm output circuit issues an alarm signal.

[0007] Furthermore, the first sampling circuit includes resistors R1 and R3 and operational amplifier U1. The non-inverting input terminal of operational amplifier U1 is connected to the live wire through resistor R1. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U1 and outputs a first sampling voltage signal. One end of resistor R3 is connected to the non-inverting input terminal of operational amplifier U1, and the other end of resistor R3 is grounded.

[0008] Furthermore, the second sampling circuit includes resistor R2, resistor R4, and operational amplifier U2. The non-inverting input terminal of operational amplifier U2 is connected to the metal casing of the electrical equipment through resistor R2. The output terminal of operational amplifier U2 is connected to the inverting input terminal of operational amplifier U2 and outputs a second sampling voltage signal. One end of resistor R4 is connected to the non-inverting input terminal of operational amplifier U2, and the other end of resistor R4 is grounded.

[0009] Furthermore, the sampling differential bias circuit includes resistors R5 and R9 and operational amplifier U3. The non-inverting input of operational amplifier U3 is connected to the output of operational amplifier U1 through resistor R7, and the inverting input of operational amplifier U3 is connected to the output of operational amplifier U2 through resistor R8. One end of resistor R5 is connected to the voltage source VCC, and the other end of resistor R5 is connected to the non-inverting input of operational amplifier U3. The output of operational amplifier U3 is connected to the inverting input of operational amplifier U3 through resistor R9, and the output of operational amplifier U3 outputs a sampling waveform signal.

[0010] Furthermore, the alarm output circuit includes a resistor R6 and a transistor Q1. The base of the transistor Q1 is connected to the output terminal of the waveform analysis circuit through the resistor R6. The emitter of the transistor Q1 is grounded, and the collector of the transistor Q1 is used to send an alarm signal.

[0011] Furthermore, the transistor Q1 is an NPN transistor.

[0012] The advantages of this utility model according to the above solution are as follows: The utility model provides a detection circuit for live metal casing of electrical equipment, including a first sampling circuit, a second sampling circuit, and a sampling differential bias circuit. The first sampling circuit is used to sample the voltage on the live wire, and the second sampling circuit is used to sample the voltage on the metal casing of the electrical equipment. The first and second sampling circuits are respectively connected to the sampling differential bias circuit. The sampling differential bias circuit is used to differentially and forward bias the sampled voltage signal to obtain the sampled waveform. By analyzing the sampled waveform, when the waveform is abnormal, it can be known that the live wire of the electrical equipment is connected to the casing. This design can detect and judge in real time whether the metal casing of the electrical equipment is connected to the live wire and generates a dangerous voltage, thereby effectively avoiding the risk of electric shock that may be caused by the live metal casing of the electrical equipment and protecting personal safety. Secondly, the judgment method of this detection circuit is simple and safe and reliable. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a structural block diagram of the detection circuit in an embodiment of the present utility model;

[0015] Figure 2 This is an exemplary circuit diagram of the detection circuit in an embodiment of the present utility model;

[0016] Figure 3 This is a sampled waveform obtained under normal conditions after processing by the sampling differential bias circuit;

[0017] Figure 4 This is a sampled waveform obtained after the ground wire is disconnected and processed by the sampling differential bias circuit;

[0018] Figure 5 The sampled waveform is obtained after L and PE are short-circuited and processed by the sampling differential bias circuit.

[0019] Figure 6 This is a schematic diagram of the alarm judgment logic of the sampling alarm circuit.

[0020] In the diagram: 1. First sampling circuit; 2. Second sampling circuit; 3. Sampling differential bias circuit; 4. Waveform analysis circuit; 5. Alarm output circuit; 6. Metal casing; 7. Short circuit point where the exposed metal wire core meets the metal casing. Detailed Implementation

[0021] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments.

[0022] To better understand this utility model, the following description, in conjunction with the accompanying drawings and embodiments, will further illustrate the present utility model:

[0023] See Figure 1 As shown in the figure, the present invention provides a detection circuit for the liveness detection of the metal casing 6 of an electrical device, including a first sampling circuit 1, a second sampling circuit 2, and a sampling differential bias circuit 3. The first sampling circuit 1 is used to sample the voltage on the live wire, and the second sampling circuit 2 is used to sample the voltage on the metal casing 6 of the electrical device. The first sampling circuit 1 and the second sampling circuit 2 are respectively connected to the sampling differential bias circuit 3. The sampling differential bias circuit 3 is used to differentially and positively bias the sampled voltage signal to obtain the sampled waveform. By analyzing the sampled waveform, when the waveform is abnormal, it can be known that the live wire of the electrical device is connected to the casing. This design can detect and judge in real time whether the metal casing 6 of the electrical device is connected to the live wire and generates a dangerous voltage, thereby effectively avoiding the risk of electric shock that may be caused by the liveness of the metal casing 6 of the electrical device, protecting personal safety. Furthermore, the judgment method of this detection circuit is simple and safe and reliable.

[0024] In this embodiment, the detection circuit further includes capacitors C1 and C2. The two ends of capacitor C1 are a first node and a second node, respectively. The first node is connected to the live wire and the first sampling circuit 1, respectively, and the second node is connected to the ground wire and the second sampling circuit 2, respectively. One end of capacitor C2 is connected to the second node, and the other end of capacitor C2 is connected to the neutral wire.

[0025] In this embodiment, the detection circuit also includes a waveform analysis circuit 4 and an alarm output circuit 5. The waveform analysis circuit 4 is connected to the differential bias circuit. The waveform analysis circuit 4 is used to analyze the sampled waveform. When the live wire and neutral wire are connected normally and the sampled waveform tends to be flat, the alarm output circuit 5 issues an alarm signal. When the live wire and neutral wire are reversed and the sampled waveform is an AC sine wave, the alarm output circuit 5 issues an alarm signal.

[0026] It should be noted that this application does not involve the specific circuit design of waveform analysis circuit 4. Therefore, this application will not elaborate on waveform analysis circuit 4. Those skilled in the art can obtain it from the prior art and apply it to this embodiment to analyze the sampled waveform.

[0027] See Figure 2As shown, the first sampling circuit 1 includes resistor R1, resistor R3 and operational amplifier U1. The non-inverting input terminal of operational amplifier U1 is connected to the live wire through resistor R1. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U1 and outputs the first sampling voltage signal. One end of resistor R3 is connected to the non-inverting input terminal of operational amplifier U1, and the other end of resistor R3 is grounded.

[0028] Specifically, the second sampling circuit 2 includes resistor R2, resistor R4 and operational amplifier U2. The non-inverting input terminal of operational amplifier U2 is connected to the metal casing 6 of the electrical equipment through resistor R2. The output terminal of operational amplifier U2 is connected to the inverting input terminal of operational amplifier U2 and outputs the second sampling voltage signal. One end of resistor R4 is connected to the non-inverting input terminal of operational amplifier U2, and the other end of resistor R4 is grounded.

[0029] In this embodiment, the sampling differential bias circuit 3 includes resistors R5 and R9 and operational amplifier U3. The non-inverting input of operational amplifier U3 is connected to the output of operational amplifier U1 through resistor R7, and the inverting input of operational amplifier U3 is connected to the output of operational amplifier U2 through resistor R8. One end of resistor R5 is connected to the voltage source VCC, and the other end of resistor R5 is connected to the non-inverting input of operational amplifier U3. The output of operational amplifier U3 is connected to the inverting input of operational amplifier U3 through resistor R9, and the output of operational amplifier U3 outputs a sampling waveform signal.

[0030] The alarm output circuit 5 includes a resistor R6 and a transistor Q1. The base of transistor Q1 is connected to the output terminal of waveform analysis circuit 4 through resistor R6, the emitter of transistor Q1 is grounded, and the collector of transistor Q1 is used to send an alarm signal. Specifically, transistor Q1 is an NPN transistor.

[0031] To further explain, this embodiment also provides the working principle of the detection circuit for the liveness of the metal casing 6 of the electrical equipment, as detailed below:

[0032] In a normal power supply system, the ground wire and the neutral wire (hereinafter referred to as N) are basically equal. The voltage waveform between the live wire (hereinafter referred to as L) and the ground wire (metal casing 6, hereinafter referred to as PE) is an AC sine wave. When L and PE are short-circuited, the voltage between L and PE is 0V and there is no voltage waveform. Therefore, by judging the waveform change between L and PE, it can be determined whether L and PE are short-circuited.

[0033] See Figure 1As shown, the first sampling circuit 1 samples the voltage on the live wire, and the second sampling circuit 2 samples the voltage on the metal casing 6 of the electrical equipment. The first sampling circuit 1 and the second sampling circuit 2 are respectively connected to the sampling differential bias circuit 3. The sampling differential bias circuit 3 differentially and forward biases the sampled voltage signal to obtain the sampled waveform. By analyzing the sampled waveform, when the waveform is abnormal, it can be known that the live wire of the electrical equipment is connected to the metal casing 6, and thus an alarm signal is issued through the alarm output circuit 5.

[0034] Under normal circumstances, PE and N are basically equal, and the sampled waveform after sampling differential bias circuit 3 is as follows: Figure 3 The sampling waveform between L and PE is an AC sine wave (hereinafter referred to as waveform one). At this time, the waveform is normal and the detection circuit does not alarm.

[0035] After the ground wire is disconnected, PE (metal casing 6) is in a floating state. Due to the influence of capacitors C1 and C2, PE is approximately equal to 1 / 2 of the input voltage. The sampling waveform after the sampling differential bias circuit 3 is as follows: Figure 4 The sampling waveform between L and PE becomes an asymmetrical sine wave (hereinafter referred to as waveform two). At this time, the leakage current of capacitors C1 and C2 is very small and will not cause harm to the person. The detection circuit does not alarm.

[0036] When L and PE are short-circuited, PE and L are equal, and the voltage between L and PE is approximately 0V. The sampled waveform after passing through the sampling differential bias circuit 3 is as follows: Figure 5 When the sampling waveform between L and PE tends to flatten (hereinafter referred to as waveform three), the casing becomes charged, which can cause personal injury, and the detection circuit will issue an alarm.

[0037] It is worth mentioning that in practical applications, there is also a situation where the L and N lines are reversed. In this scenario, the sampling waveform will be the opposite of the normal wiring scenario. That is, when the sampling waveform is waveform three, it indicates that it is normal. When the sampling waveform is waveform one, it indicates that L and PE are short-circuited. At this time, the circuit will issue an alarm.

[0038] In another embodiment, the detection circuit also includes a sampling alarm circuit. The judgment logic of the sampling alarm circuit is different depending on the power supply wiring method. This detection logic can automatically determine the wiring method of the input power supply and then detect according to the judgment logic corresponding to the wiring method.

[0039] Among them, the alarm judgment logic refers to Figure 6 As shown, the specifics are as follows:

[0040] When the device is powered on, it first reads the internally stored alarm status. If there is no alarm record, it is assumed that the current power supply line of the device is normal. At this time, the sampling alarm circuit determines the input power supply wiring method according to the sampling waveform and performs detection according to the corresponding judgment logic. If the previously saved alarm record is read after power-on, the circuit will determine the input power supply wiring method according to the alarm flag and perform detection according to the corresponding judgment logic to see if the fault has disappeared. If the fault has not disappeared, the alarm status will be maintained.

[0041] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

[0042] The present utility model patent has been described above with reference to the accompanying drawings. Obviously, the implementation of the present utility model patent is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present utility model patent, or the direct application of the inventive concept and technical solution of the present utility model patent to other occasions without modification, are all within the protection scope of the present utility model.

Claims

1. A detection circuit for detecting live metal casing of electrical equipment, characterized in that, It includes a first sampling circuit, a second sampling circuit, and a sampling differential bias circuit. The first sampling circuit is used to sample the voltage on the live wire, and the second sampling circuit is used to sample the voltage on the metal casing of the electrical equipment. The first sampling circuit and the second sampling circuit are respectively connected to the sampling differential bias circuit. The sampling differential bias circuit is used to differentially and positively bias the sampled voltage signal to obtain the sampled waveform.

2. The detection circuit for energizing the metal casing of electrical equipment as described in claim 1, characterized in that: It also includes capacitors C1 and C2. One end of capacitor C1 is connected to the live wire, and the other end of capacitor C1 is connected to the metal casing of the electrical equipment. One end of capacitor C2 is connected to the metal casing of the electrical equipment, and the other end of capacitor C2 is connected to the neutral wire.

3. The detection circuit for energizing the metal casing of electrical equipment as described in claim 1, characterized in that: It also includes a waveform analysis circuit and an alarm output circuit. The waveform analysis circuit is connected to the differential bias circuit. The waveform analysis circuit is used to analyze the sampled waveform. When the live wire and neutral wire are connected normally and the sampled waveform tends to be flat, the alarm output circuit issues an alarm signal. When the live wire and neutral wire are reversed and the sampled waveform is an AC sine wave, the alarm output circuit issues an alarm signal.

4. The detection circuit for energizing the metal casing of electrical equipment as described in claim 3, characterized in that: The first sampling circuit includes resistors R1 and R3 and operational amplifier U1. The non-inverting input of operational amplifier U1 is connected to the live wire through resistor R1. The output of operational amplifier U1 is connected to the inverting input of operational amplifier U1 and outputs a first sampling voltage signal. One end of resistor R3 is connected to the non-inverting input of operational amplifier U1, and the other end of resistor R3 is grounded.

5. The detection circuit for energizing the metal casing of electrical equipment as described in claim 4, characterized in that: The second sampling circuit includes resistors R2 and R4 and operational amplifier U2. The non-inverting input of operational amplifier U2 is connected to the metal casing of the electrical equipment through resistor R2. The output of operational amplifier U2 is connected to the inverting input and outputs a second sampling voltage signal. One end of resistor R4 is connected to the non-inverting input of operational amplifier U2, and the other end of resistor R4 is grounded.

6. The detection circuit for energizing the metal casing of electrical equipment as described in claim 5, characterized in that: The sampling differential bias circuit includes resistors R5 and R9 and operational amplifier U3. The non-inverting input of operational amplifier U3 is connected to the output of operational amplifier U1 through resistor R7, and the inverting input of operational amplifier U3 is connected to the output of operational amplifier U2 through resistor R8. One end of resistor R5 is connected to the voltage source VCC, and the other end of resistor R5 is connected to the non-inverting input of operational amplifier U3. The output of operational amplifier U3 is connected to the inverting input of operational amplifier U3 through resistor R9, and the output of operational amplifier U3 outputs a sampling waveform signal.

7. The detection circuit for energizing the metal casing of electrical equipment as described in claim 6, characterized in that: The alarm output circuit includes a resistor R6 and a transistor Q1. The base of the transistor Q1 is connected to the output terminal of the waveform analysis circuit through the resistor R6. The emitter of the transistor Q1 is grounded, and the collector of the transistor Q1 is used to send an alarm signal.

8. The detection circuit for energizing the metal casing of electrical equipment as described in claim 7, characterized in that: The transistor Q1 is an NPN transistor.

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