Current transformer secondary side status detection circuit, fire alarm device, electric energy meter

Abstract

The present invention discloses a current transformer secondary state detection circuit, a fire alarm device, and an electric energy meter, wherein the current transformer secondary state detection circuit comprises a control module, a sampling module, a first filter module, and a second filter module, wherein the control module is used to receive a control signal sent by an external metering judgment module, and is also used to send a detection signal to the sampling module according to the control signal; the sampling module is used to receive the detection signal, and generate a first detection voltage signal and a second detection voltage signal according to the detection signal, the sampling module sends the first detection voltage signal to the external metering judgment module after passing through the first filter module, and sends the second detection voltage signal to the external metering judgment module after passing through the second filter module, and the external metering judgment module judges the state of the secondary winding of the current transformer. The present invention adopts fewer components, is small in size, and has low production and maintenance costs.

Description

Technical Field

[0001] The present invention relates to the field of circuit detection, and in particular to a current transformer secondary side state detection circuit, a fire alarm device, and an electric energy meter. Background Art

[0002] Current transformers are widely used in detection circuits, including current transformers for power supply detection, which are used to provide grid current information to measurement and metering devices within the normal voltage range, and protective current transformers, which are used to provide grid fault current information to relay protection and other devices under grid fault conditions.

[0003] Since the primary winding of the current transformer has few turns, the secondary winding has more turns, and the secondary winding is connected in series in the measuring instrument and protection circuit, when the secondary winding fails, it will cause damage to the current transformer itself and the secondary equipment.

[0004] For example, in the patent application "Current Transformer Secondary Side Open Circuit Protection Early Warning System" with publication number CN106786366A, in order to solve the above technical problems, the existing technology often adopts a complex circuit with an operational amplifier circuit to detect the open circuit and short circuit faults of the secondary winding, which is costly and bulky, so further improvement of the existing technology is needed. Summary of the invention

[0005] The present invention aims at the shortcomings of the prior art and provides a current transformer secondary side state detection circuit, a fire alarm device and an electric energy meter.

[0006] In order to solve the above technical problems, the present invention is solved by the following technical solutions:

[0007] A current transformer secondary side state detection circuit is coupled to the secondary side winding of an external current transformer and a metering judgment module respectively, comprising a control module, a sampling module, a first filter module and a second filter module, wherein the sampling module is coupled to the control module, the first filter module, the second filter module and the secondary side winding of the external current transformer respectively; the control module, the first filter module and the second filter module are coupled to the external metering judgment module;

[0008] The control module is used to receive a control signal sent by an external measurement judgment module, and is also used to send a detection signal to the sampling module according to the control signal;

[0009] The sampling module is used to receive the detection signal and generate a first detection voltage signal and a second detection voltage signal according to the detection signal. The sampling module sends the first detection voltage signal to an external measurement judgment module after passing through a first filtering module, and sends the second detection voltage signal to an external measurement judgment module after passing through a second filtering module. The external measurement judgment module judges the state of the secondary winding of the current transformer.

[0010] As an implementable method:

[0011] The control module includes a control signal input terminal, a voltage input terminal, a voltage output terminal and a switch circuit, wherein the switch circuit is coupled to the control signal input terminal, the voltage input terminal and the voltage output terminal respectively, the control signal input terminal is coupled to an external measurement judgment module, and the voltage output terminal is coupled to a sampling module;

[0012] The control signal input terminal is used to receive a control signal sent by an external measurement judgment module;

[0013] The switch circuit is used to control the voltage input terminal and the voltage output terminal to be connected according to the control signal. When the voltage input terminal and the voltage output terminal are connected, the voltage output terminal outputs a voltage signal to the sampling module as a detection signal.

[0014] As an implementable method:

[0015] The switch circuit comprises a first bias resistor, a second bias resistor and a transistor, and the transistor is a PNP transistor;

[0016] The emitter of the transistor is coupled to the voltage input terminal, and is also coupled to its base via a first bias resistor;

[0017] The base of the transistor is also coupled to the control signal input terminal through a second bias resistor;

[0018] The collector of the transistor is coupled to the voltage output terminal.

[0019] As an implementable method:

[0020] The sampling module includes a first sampling resistor and a second sampling resistor connected in series;

[0021] The second sampling resistor is connected in parallel with the secondary winding of the external current transformer to form a parallel branch;

[0022] One end of the parallel branch is coupled to the control module through a first sampling resistor, and is also coupled to an external metering judgment module through a second filter module. The other end of the parallel branch is coupled to an external metering judgment module through a first filter module.

[0023] As an implementable method:

[0024] The first filter module and the second filter module both use a resistor-capacitor filter circuit.

[0025] As an implementable method:

[0026] It also includes an input signal protection module, which is connected in parallel to both ends of the secondary winding of the external current transformer and is composed of two reverse-parallel diodes.

[0027] The present invention also proposes a fire alarm device, comprising a residual current transformer, a metering and judgment module and an alarm module, wherein the metering and judgment module and the alarm module are coupled, the primary winding of the residual current transformer is used to collect the residual current, and the secondary winding is used to generate the corresponding induced current; and also includes a state detection circuit as described in any one of the above items, and the state detection circuit is coupled to the secondary winding and the metering and judgment module respectively.

[0028] As an implementable method:

[0029] The metering judgment module is used to control the state detection circuit to output the induced voltage signal of the induced current, or output a detection voltage signal for detecting the state of the secondary winding;

[0030] The metering judgment module is also used to generate a residual current value according to the induced voltage signal, and control the alarm module to alarm according to the residual current value;

[0031] The metering judgment module is also used to determine the state of the secondary winding according to the detection voltage signal, and control the alarm module to alarm according to the state.

[0032] As an implementable method:

[0033] The metering judgment module includes a single-chip microcomputer and a metering chip, wherein the single-chip microcomputer is coupled to the metering chip, the control state detection circuit and the alarm module respectively, and the metering chip is also coupled to the control state detection circuit;

[0034] The single chip microcomputer is used to collect the induced voltage signal or the detection voltage signal output by the state detection circuit through the metering chip, and generate the residual current value according to the induced voltage signal, and judge the state of the secondary winding according to the detection voltage signal;

[0035] The single chip microcomputer is also used to control the alarm module to alarm according to the residual current value or the state of the secondary winding.

[0036] The present invention also proposes an electric energy meter, comprising an alarm module, a single-chip microcomputer and a metering chip, wherein the single-chip microcomputer is coupled to the alarm module and the metering chip respectively, and also comprises a residual current transformer and a state detection circuit described in any one of the above items, wherein the state detection circuit is coupled to the residual current transformer, the single-chip microcomputer and the metering chip respectively.

[0037] As an implementable method:

[0038] The primary winding of the residual current transformer is used to collect the residual current, and the secondary winding is used to generate the corresponding induced current;

[0039] The single chip microcomputer is used to collect the induced voltage signal or the detection voltage signal output by the state detection circuit through the metering chip, and generate the residual current value according to the induced voltage signal, and judge the state of the secondary winding according to the detection voltage signal;

[0040] The single chip microcomputer is also used to control the alarm module to alarm according to the residual current value or the state of the secondary winding.

[0041] The present invention has significant technical effects due to the adoption of the above technical solution:

[0042] 1. The design of the status detection circuit of the present invention can realize the status detection of the secondary winding with fewer components, which can effectively reduce the detection cost and maintenance cost; and compared with the existing status detection circuit, it is smaller in size and easy to be integrated into the existing device that needs to detect the status of the secondary winding.

[0043] 2. The present invention designs the first filter module and the second filter module so that they cooperate with the measurement judgment module for detection, and the detection accuracy reaches 200mA. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 It is a module connection diagram of a current transformer secondary side state detection circuit of the present invention;

[0046] Figure 2 is a circuit connection diagram of the control module 110 in Example 1;

[0047] Figure 3is a circuit diagram of a current transformer secondary side state detection circuit in Example 1;

[0048] Figure 4 The present invention is a schematic diagram of the connection of modules used for fire alarm in a fire alarm device (or electric energy meter).

[0049] In the figure, 110 is a control module, 120 is a sampling module, 130 is a first filtering module, 140 is a second filtering module, 150 is an input signal protection module, 200 is a metering judgment module, 210 is a single chip microcomputer, 220 is a metering chip, 300 is a current transformer, and 400 is an alarm module. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below in conjunction with embodiments. The following embodiments are for explanation of the present invention but the present invention is not limited to the following embodiments.

[0051] Embodiment 1: A current transformer secondary side state detection circuit, such as Figure 1 As shown, it is composed of a control module 110, a sampling module 120, a first filter module 130, a second filter module 140 and an input signal protection module 150. The sampling module 120 is respectively coupled to the control module 110, the first filter module 130, the second filter module 140, the input signal protection module 150 and the secondary winding of the external current transformer 300, wherein the input signal protection module 150 is connected in parallel at both ends of the secondary winding, and the control module 110, the first filter module 130 and the second filter module 140 are all coupled to the external measurement judgment module 200.

[0052] The control module 110 is used to receive a control signal sent by the external measurement judgment module 200, and is also used to send a detection signal to the sampling module 120 according to the control signal;

[0053] Reference Figure 2 , the control module 110 includes a control signal input terminal, a voltage input terminal, a voltage output terminal and a switch circuit, wherein the switch circuit is coupled to the control signal input terminal, the voltage input terminal and the voltage output terminal respectively, the control signal input terminal is coupled to the external measurement judgment module 200, and the voltage output terminal is coupled to the sampling module 120;

[0054] The control signal input terminal is used to receive the control signal sent by the external measurement judgment module 200;

[0055] The switch circuit is used to control the voltage input terminal and the voltage output terminal to be connected according to the control signal. When the voltage input terminal and the voltage output terminal are connected, the voltage output terminal outputs a voltage signal to the sampling module 120 as a detection signal.

[0056] When the voltage input terminal and the voltage output terminal are not connected, the voltage output terminal cannot form a current loop with the sampling module 120 through the switch circuit, and will not affect the normal AC signal.

[0057] The switch circuit is composed of a first bias resistor RN6, a second bias resistor RN7 and a transistor QN1, wherein the transistor QN1 is a PNP transistor;

[0058] The emitter of the transistor QN1 is coupled to the voltage input terminal, and is also coupled to its base via a first bias resistor RN6;

[0059] The base of the transistor QN1 is also coupled to the control signal input terminal through the second bias resistor RN7;

[0060] The collector of the transistor QN1 is coupled to the voltage output terminal.

[0061] The first bias resistor RN6 and the second bias resistor RN7 form a bias circuit of the transistor QN1, providing a stable static operating voltage for the transistor QN1, so that the transistor QN1 is in a stable state;

[0062] In this embodiment, when the external metering judgment module 200 outputs a control signal (such as Figure 2 When the control signal pulls down the high level at the base of the transistor QN1, the transistor QN1 is turned on, and the voltage input terminal outputs a voltage signal as a detection signal to the voltage output terminal through the transistor QN1.

[0063] The sampling module 120 is used to receive the detection signal and generate a first detection voltage signal and a second detection voltage signal according to the detection signal. The sampling module 120 sends the first detection voltage signal to the external measurement and judgment module 200 after passing through the first filtering module 130, and sends the second detection voltage signal to the external measurement and judgment module 200 after passing through the second filtering module 140. The external measurement and judgment module 200 judges the state of the secondary winding of the current transformer 300.

[0064] Reference Figure 3 , the sampling module 120 includes a first sampling resistor RN3 and a second sampling resistor RN4 connected in series, the first sampling resistor RN3 and the second sampling resistor RN4 constitute a proportional voltage divider circuit to divide the detection signal;

[0065] The second sampling resistor RN4 is connected in parallel with the secondary winding of the external current transformer 300 to form a parallel branch;

[0066] One end of the parallel branch is coupled to the voltage output end through the first sampling resistor RN3, and is also coupled to the external measurement judgment module 200 through the second filter module 140, and the other end of the parallel branch is coupled to the external measurement judgment module 200 through the first filter module 130.

[0067] Note that the parallel branch is also connected in parallel with the input signal protection phase.

[0068] When the external metering judgment module 200 outputs a control signal to the control signal input terminal, the transistor QN1 is turned on, and the voltage input terminal, the first sampling resistor RN3 and the second sampling resistor RN4 form a current loop. At this time, the voltage signal input from the voltage input terminal is divided proportionally, and the external metering judgment module 200 samples the voltage across the second sampling resistor RN4 through the first filter module 130 and the second filter module 140, and uses the obtained voltage signal as a detection voltage signal, and judges the state of the secondary winding based on the detection voltage signal. The state includes short circuit, open circuit and normal.

[0069] When the external metering judgment module 200 is prohibited from outputting a control signal to the control signal input terminal, the transistor QN1 is turned off. At this time, the voltage input terminal, the first sampling resistor RN3 and the second sampling resistor RN4 cannot form a current loop. At this time, the induced current generated by the secondary winding is converted into a voltage signal by the second sampling resistor RN4. The external metering judgment module 200 samples the voltage across the second sampling resistor RN4 through the first filtering module 130 and the second filtering module 140, uses the obtained voltage signal as the induced voltage signal, and calculates the residual current value based on the induced voltage signal.

[0070] The induced voltage signal includes a first detection voltage signal (such as Figure 3 ) and the second detection voltage signal filtered by the second filtering module 140 (as shown in FIG. Figure 3 As shown in FIG. 1 , the external measurement judgment module 200 can obtain the amplitude of the voltage divided by the second sampling resistor RN4 through the first detection voltage signal and the second detection voltage signal, thereby determining the state of the secondary winding according to the amplitude.

[0071] The measurement determination module 200 determines the state of the secondary winding as:

[0072] According to the voltage inputted by the voltage input terminal and the resistance values ​​of the first sampling resistor RN3 and the second sampling resistor RN4, the maximum threshold value and the minimum threshold value are set, and the state detection is performed when the secondary winding does not generate the induced current, that is, the measurement judgment module 200 sends a control signal;

[0073] When it is detected that the voltage value across the second sampling resistor RN4 exceeds the maximum threshold value, it is determined that the state of the secondary winding is open circuit;

[0074] When it is detected that the voltage value across the second sampling resistor RN4 is less than the minimum threshold value, it is determined that the state of the secondary winding is short-circuited;

[0075] When it is detected that the voltage value across the second sampling resistor RN4 is between the maximum threshold value and the minimum threshold value (including the maximum threshold value and the minimum threshold value), it is determined that the state of the secondary winding is normal.

[0076] The design of the sampling module 120 in this embodiment avoids the problem of damage to the external measurement and judgment module 200 caused by a large current generated by a short circuit of the secondary winding during the state detection process.

[0077] Reference Figure 3 , the input signal protection module 150 is composed of two reverse parallel diodes, such as Figure 3 The diodes DN1 and DN2 are used to ensure that the signal amplitude does not exceed the maximum input range of the external metering judgment module 200 when the interference signal is abnormally large, so as to avoid damage to the external metering judgment module 200.

[0078] Reference Figure 3 The first filter module 130 and the second filter module 140 both use a resistor-capacitor filter circuit to filter out useless noise high-frequency signals to improve measurement accuracy.

[0079] Note, Figure 3 The resistor RN1 and the capacitor CN1 constitute a first filtering module 130 , and the resistor RN2 and the capacitor CN2 constitute a second filtering module 140 .

[0080] The state detection circuit disclosed in the present embodiment can realize the state detection of the secondary winding only by using the above-mentioned components. Compared with the existing state detection circuit, it uses fewer components, is easy to manufacture, and can effectively reduce the detection cost and maintenance cost; and compared with the existing state detection circuit, it is smaller in size and is easy to integrate into the existing device that needs to detect the state of the secondary winding; due to noise reasons, the accuracy of the prior art can only reach 300mA. If it wants to improve the accuracy, it needs to use a higher precision operational amplifier chip. This solution is expensive and not practical. The state detection circuit proposed in this embodiment, through the cooperation of the first filter module 130, the second filter module 140 and the measurement judgment module 200, does not need to use a high-precision operational amplifier chip, and its detection accuracy can reach 200mA.

[0081] Embodiment 2: A fire alarm device, such as Figure 4As shown, it includes a current transformer 300, a metering judgment module 200, an alarm module 400 and the state detection circuit described in Example 1, wherein the metering judgment module 200 and the alarm module 400 are coupled;

[0082] In this embodiment, the current transformer 300 adopts a residual current mutual inductance, the primary winding of the residual current mutual inductance is used to collect the residual current, and the secondary winding is used to generate the corresponding induced current. The state detection circuit is coupled to the secondary winding and the measurement judgment module 200 respectively.

[0083] The metering judgment module 200 is used to control the state detection circuit to output the induced voltage signal of the induced current, or output the detection voltage signal for detecting the state of the secondary winding;

[0084] The measurement determination module 200 is also used to generate a residual current value according to the induced voltage signal;

[0085] The metering judgment module 200 is further used to determine the state of the secondary winding according to the detection voltage signal, and control the alarm module 400 to alarm according to the state.

[0086] Note:

[0087] The induced voltage signal is the voltage signal across the second sampling resistor RN4 (the voltage signal after the induced current is converted) when the measurement judgment module 200 prohibits issuing the control signal;

[0088] The detection voltage signal is the voltage value across the second sampling resistor RN4 when the measurement determination module 200 sends a control signal (the voltage signal after the detection signal is divided);

[0089] The metering and judging module 200 may be, for example, a central controller in an existing fire alarm device, and the alarm module 400 may be, for example, a fire alarm module 400 in an existing fire alarm device.

[0090] Furthermore, the metering judgment module 200 includes a single chip microcomputer 210 and a metering chip 220. Figure 4 , wherein the single-chip microcomputer 210 is coupled to the metering chip 220, the control state detection circuit and the alarm module 400 respectively, and the metering chip 220 is also coupled to the control state detection circuit, specifically, the single-chip microcomputer 210 is coupled to the control signal input terminal, and the metering chip 220 is coupled to the first filter module 130 and the second filter module 140 respectively;

[0091] The single chip microcomputer 210 is used to collect the induced voltage signal or the detection voltage signal output by the state detection circuit through the metering chip 220, and generate the residual current value according to the induced voltage signal, and determine the state of the secondary winding according to the detection voltage signal;

[0092] The single chip microcomputer 210 is further used to control the alarm module 400 to alarm according to the residual current value or the state of the secondary winding, specifically:

[0093] When the residual current value exceeds the preset alarm current threshold, the single chip microcomputer 210 controls the alarm module 400 to alarm;

[0094] When the secondary winding is in an open circuit or a short circuit state, the single chip microcomputer 210 controls the alarm module 400 to sound an alarm.

[0095] The metering chip 220 can also be used to monitor the power supply conditions of the power supply network, such as overvoltage, undervoltage, overcurrent, power load, etc. This application is a prior art and will not be introduced in detail.

[0096] Embodiment 3, an electric energy meter comprises an alarm module 400, a single-chip microcomputer 210, a metering chip 220, a current transformer 300 and the status detection circuit described in Embodiment 1, wherein the single-chip microcomputer 210 is coupled to the alarm module 400 and the metering chip 220 respectively, and the status detection circuit is coupled to the current transformer 300, the single-chip microcomputer 210 and the metering chip 220 respectively.

[0097] Note that the alarm module 400, the single-chip computer 210, and the metering chip 220 are all modules / chips possessed by existing electric energy meters, and the current transformer 300 is a residual current transformer.

[0098] The primary winding of the residual current mutual inductance is used to collect the residual current, and the secondary winding is used to generate the corresponding induced current;

[0099] The single chip microcomputer 210 is used to collect the induced voltage signal or the detection voltage signal output by the state detection circuit through the metering chip 220, and generate the residual current value according to the induced voltage signal, and determine the state of the secondary winding according to the detection voltage signal;

[0100] The single chip microcomputer 210 is further configured to control the alarm module 400 to generate an alarm according to the state of the secondary winding.

[0101] The specific working contents of the fire alarm performed by the electric energy meter in this embodiment are as follows:

[0102] 1. The single chip microcomputer 210 is prohibited from sending control signals to the status detection circuit;

[0103] The primary winding of the residual current mutual inductance collects the residual current, and the secondary winding generates the corresponding induced current;

[0104] The transistor QN1 in the state detection circuit is in the cut-off state, the induced current and the second sampling resistor RN4 form a current loop, and the second sampling resistor RN4 converts the induced current into a voltage signal;

[0105] The metering chip 220 collects the voltage signal across the second sampling resistor RN4 through the first filter module 130 and the second filter module 140 to obtain an induced voltage signal, and sends the induced voltage signal to the single chip microcomputer 210. The single chip microcomputer 210 calculates the residual current value according to the induced voltage signal.

[0106] The single chip microcomputer 210 determines whether the residual current value is greater than a preset alarm current threshold value. If so, the alarm module 400 is controlled to generate a fire alarm.

[0107] The single chip microcomputer 210 determines whether the residual current value is 0. If it is not 0, the single chip microcomputer 210 keeps detecting the residual current value.

[0108] 2. The single-chip microcomputer 210 determines whether the residual current value is 0. If it is not 0, the single-chip microcomputer 210 keeps detecting the residual current value. Otherwise, the single-chip microcomputer 210 detects the working state of the secondary winding.

[0109] When the residual current value is 0, the single chip microcomputer 210 sends a control signal to the state detection circuit. At this time, the transistor QN1 in the state detection circuit is in the on state, and the input voltage terminal outputs a detection signal to the sampling module 120 through the output voltage terminal;

[0110] Since the residual current value is 0 at this time, that is, the secondary winding does not generate an induced current, the detection signal is divided by the first sampling resistor RN3 and the second sampling resistor RN4 in the sampling module 120;

[0111] The metering chip 220 collects the voltage signal across the second sampling resistor RN4 through the first filter module 130 and the second filter module 140 to obtain a detection voltage signal, and sends the detection voltage signal to the single chip microcomputer 210. The single chip microcomputer 210 calculates the voltage amplitude according to the detection voltage signal.

[0112] The single chip microcomputer 210 compares the obtained voltage amplitude with the preset maximum threshold value and minimum threshold value:

[0113] When the voltage amplitude exceeds the maximum threshold value, the state of the secondary winding is determined to be open circuit, and the control alarm module 400 alarms;

[0114] When the voltage amplitude is less than the minimum threshold value, the secondary winding is determined to be open circuit, and the alarm module 400 is controlled to alarm;

[0115] When the voltage amplitude is between the maximum threshold value and the minimum threshold value (including the maximum threshold value and the minimum threshold value), the state of the secondary winding is determined to be normal, and the single chip microcomputer 210 stops sending control signals to the state detection circuit and continues to detect the residual current value.

[0116] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0117] It should be noted that:

[0118] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0119] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0120] In addition, it should be noted that the names of the components of the specific embodiments described in this specification may be different. Any equivalent or simple changes made based on the structure, features and principles described in the patent concept of the present invention are included in the protection scope of the patent of the present invention. The technicians in the technical field of the present invention can make various modifications or supplements to the specific embodiments described or replace them in a similar manner, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A current transformer secondary side state detection circuit, coupled to the secondary side winding of an external current transformer and a measurement judgment module, characterized in that: The detection accuracy of the current transformer secondary side state detection circuit is 200mA, and it includes a control module, a sampling module, a first filter module and a second filter module, wherein the sampling module is respectively coupled to the control module, the first filter module, the second filter module and the secondary side winding of the external current transformer; the control module, the first filter module and the second filter module are all coupled to the external measurement judgment module; The control module is used to receive a control signal sent by an external measurement judgment module, and is also used to send a detection signal to the sampling module according to the control signal; The sampling module is used to receive the detection signal, and generate a first detection voltage signal and a second detection voltage signal according to the detection signal. The sampling module sends the first detection voltage signal to an external measurement judgment module after passing through the first filtering module, and sends the second detection voltage signal to an external measurement judgment module after passing through the second filtering module, and the external measurement judgment module judges the state of the secondary winding of the external current transformer; Among them, the control module includes a control signal input terminal, a voltage input terminal, a voltage output terminal and a switching circuit, wherein the switching circuit is coupled to the control signal input terminal, the voltage input terminal and the voltage output terminal respectively, the control signal input terminal is coupled to an external measurement and judgment module, and the voltage output terminal is coupled to a sampling module; the control signal input terminal is used to receive a control signal sent by an external measurement and judgment module; the switching circuit is used to control the voltage input terminal and the voltage output terminal to be conductive according to the control signal, and when the voltage input terminal and the voltage output terminal are conductive, the voltage output terminal outputs a voltage signal to the sampling module as a detection signal, and the switching circuit includes a first bias resistor, a second bias resistor and a transistor.

2. The current transformer secondary side state detection circuit according to claim 1, characterized in that: The transistor is a PNP transistor; The emitter of the transistor is coupled to the voltage input terminal, and is also coupled to the base via a first bias resistor; The base of the transistor is also coupled to the control signal input terminal through a second bias resistor; The collector of the transistor is coupled to the voltage output terminal.

3. The current transformer secondary side state detection circuit according to claim 1, characterized in that: The sampling module includes a first sampling resistor and a second sampling resistor connected in series; The second sampling resistor is connected in parallel with the secondary winding of the external current transformer to form a parallel branch; One end of the parallel branch is coupled to the control module through a first sampling resistor, and is also coupled to an external metering judgment module through a second filter module. The other end of the parallel branch is coupled to an external metering judgment module through a first filter module.

4. The current transformer secondary side state detection circuit according to claim 1, characterized in that: The first filter module and the second filter module both use a resistor-capacitor filter circuit.

5. The current transformer secondary side state detection circuit according to claim 1, characterized in that: It also includes an input signal protection module, which is connected in parallel to both ends of the secondary winding of the external current transformer and is composed of two reverse-parallel diodes.

6. A fire alarm device, comprising a residual current transformer, a metering and judging module and an alarm module, wherein the metering and judging module and the alarm module are coupled, the primary winding of the residual current transformer is used to collect the residual current, and the secondary winding of the residual current transformer is used to generate the corresponding induced current; characterized in that: It also includes a current transformer secondary side state detection circuit as described in any one of claims 1 to 5, and the current transformer secondary side state detection circuit is coupled to the secondary side winding of the residual current transformer and the metering judgment module respectively.

7. The fire alarm device according to claim 6, characterized in that: The metering judgment module is used to control the current transformer secondary side state detection circuit to output the induced voltage signal of the induced current, or output a detection voltage signal for detecting the state of the secondary side winding of the residual current transformer; The metering judgment module is also used to generate a residual current value according to the induced voltage signal, and control the alarm module to alarm according to the residual current value; The metering judgment module is also used to determine the state of the secondary winding of the residual current transformer according to the detection voltage signal, and control the alarm module to alarm according to the state.

8. An electric energy meter, comprising an alarm module, a single-chip microcomputer and a metering chip, wherein the single-chip microcomputer is coupled to the alarm module and the metering chip respectively, characterized in that: It also includes a residual current transformer and a current transformer secondary side state detection circuit as claimed in any one of claims 1 to 5, wherein the current transformer secondary side state detection circuit is coupled to the residual current transformer, the single chip microcomputer and the metering chip respectively.

9. The electric energy meter according to claim 8, characterized in that: The primary winding of the residual current transformer is used to collect the residual current, and the secondary winding of the residual current transformer is used to generate the corresponding induced current; The single chip microcomputer is used to collect the induced voltage signal or the detection voltage signal output by the secondary side state detection circuit of the current transformer through the metering chip, and generate the residual current value according to the induced voltage signal, and judge the state of the secondary side winding of the residual current transformer according to the detection voltage signal; The single chip microcomputer is also used to control the alarm module to alarm according to the residual current value or the state of the secondary winding of the residual current transformer.

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