Fault detection circuit and circuit breaker

Abstract

To provide a connection failure detection circuit and a circuit breaker, capable of detecting a connection failure even with a voltage value of which generated potential difference does not reach an operation voltage of a photo coupler, and not receiving an influence of a cable way current.SOLUTION: A connection failure detection circuit includes: a differential amplifier circuit 21 that amplifies a potential difference generated in a connection terminal 10; a determination part 22 that determines as generation of a connection failure if the amplified potential difference exceeds a predetermined threshold value; a current measurement part 24 that measures a cable way current; and an amplification rate control part 25 that changes and controls an amplification rate of the differential amplifier circuit 21. The amplification rate control part 25 makes the amplification rate of the differential amplifier circuit 21 be in reverse proportion at a predetermined rate to the cable way current, and a disconnection mechanism part of a circuit breaker 1 performs an open operation of a contact part 13 when the determination part 22 determines generation of a connection failure, and the circuit breaker 1 performs a disconnection operation.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a connection failure detection circuit that detects connection failures in connection terminals, and to a circuit breaker that includes the connection failure detection circuit. [Background technology]

[0002] The common connection terminals for connecting the electrical paths of circuit breakers are configured so that the crimp terminal on the wire side is pressed against a washer by a terminal screw to establish mechanical and electrical connections. With this type of terminal, if the terminal screw becomes loose, the contact between the washer and the crimp terminal becomes unstable, causing arc discharge and overheating. To address this issue, there are circuit breakers that detect loose terminal screws and cut off the electrical circuit. For example, in Patent Document 1, when a predetermined potential difference occurs between the terminal screw and the terminal base, it is determined that a poor connection has occurred and the circuit breaker operates to cut off the electrical circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-243666 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology in Patent Document 1 detects a connection failure by turning on a photocoupler using a potential difference generated at a connection terminal and detecting the connection failure based on the output. Therefore, detection is difficult in the early stages because the potential difference at the detection point does not reach the photocoupler's operating voltage. In addition, because the potential difference generated by a connection failure changes depending on the magnitude of the circuit current, there is variation in sensitivity, and a malfunction can occur when the circuit current becomes large.

[0005] In view of these problems, the present invention aims to provide a connection failure detection circuit and a circuit breaker that can detect connection failures even when the generated potential difference is below the operating voltage of the photocoupler, and that are less susceptible to the influence of circuit current. [Means for solving the problem]

[0006] In order to solve the above problem, the invention of claim 1 is a connection failure detection circuit that detects connection failures of connection terminals that connect electric circuits, and includes a potential difference detection circuit that detects a potential difference generated at the connection terminal, and a determination unit that determines that a connection failure has occurred when the detected potential difference exceeds a predetermined threshold, and the potential difference detection circuit amplifies the detected potential difference using a differential amplifier circuit. a current measurement unit that measures a circuit current; and an amplification factor control unit that changes and controls the amplification factor of the differential amplifier circuit, wherein the amplification factor control unit controls the amplification factor of the differential amplifier circuit to be inversely proportional to the circuit current at a predetermined rate; The determining section is characterized by comparing the potential difference amplified by the differential amplifier circuit with a threshold value to make a determination. With this configuration, the detected potential difference is amplified by a differential amplifier circuit and then judged, so that it is possible to detect the potential difference even if it does not reach the voltage that turns on the photocoupler as in the conventional case, and poor connection can be detected at an early stage. In addition, since the amplification factor of the differential amplifier circuit, i.e., the sensitivity for detecting connection defects, is inversely proportional to the circuit current, it is possible to reduce malfunctions caused by voltage drops that increase with an increase in the circuit current.

[0007] The invention of claim 2 is as follows: a terminal temperature measuring unit that measures the temperature of the connection terminal of the potential difference detection target; an ambient temperature measuring unit that measures the ambient temperature; a temperature difference information storage unit that stores the relationship between the temperature difference and the circuit current; and an amplification factor control unit that changes and controls the amplification factor of the differential amplification circuit; the amplification factor control unit determines the temperature difference between the temperature of the connection terminal and the ambient temperature, converts the temperature difference into the circuit current, and controls the amplification factor of the differential amplification circuit to be inversely proportional to the converted circuit current at a predetermined rate; and the determination unit compares the potential difference amplified by the differential amplification circuit with the threshold to make a determination. Let's say. According to this configuration, The detected potential difference is amplified by a differential amplifier circuit and then judged, so it is possible to detect the potential difference even if it does not reach the voltage that turns on the photocoupler, as was the case with conventional technology, and poor connections can be detected at an early stage. In addition, since the circuit current is estimated from the temperature, there is no need to install a current transformer or other device to measure the current.Furthermore, since the sensitivity for detecting connection defects can be made inversely proportional to the circuit current, it is possible to reduce malfunctions caused by voltage drops that increase as the circuit current increases.

[0008] The invention of claim 3 is as follows: A connection failure detection circuit for detecting a connection failure of a connection terminal for connecting an electric circuit includes a potential difference detection circuit for detecting a potential difference occurring at the connection terminal, and a determination unit for determining that a connection failure has occurred when the detected potential difference exceeds a predetermined threshold value, wherein the potential difference detection circuit includes a differential amplifier circuit for amplifying the detected potential difference, a terminal temperature measurement unit for measuring the temperature of the connection terminal for which the potential difference is to be detected, a temperature correction information storage unit for storing the relationship between temperature and the amplification factor of the differential amplifier circuit, and an amplification factor control unit for changing and controlling the amplification factor of the differential amplifier circuit, wherein the amplification factor control unit refers to the temperature correction information storage unit based on the measured temperature of the connection terminal and controls to lower the amplification factor of the differential amplifier circuit when the temperature rises, and the determination unit compares the potential difference amplified by the differential amplifier circuit with the threshold value to make a determination. Let's say. According to this configuration, The detected potential difference is amplified by a differential amplifier circuit and then judged, so it is possible to detect the potential difference even if it does not reach the voltage that turns on the photocoupler, as was the case with conventional technology, and poor connections can be detected at an early stage. In addition, the gain of the differential amplifier circuit is controlled to be inversely proportional to the temperature of the connection terminals, taking into account the increase in contact resistance, i.e., the increase in potential difference, that accompanies a temperature rise, thereby reducing malfunctions.

[0009] The invention of claim 4 is as follows: A circuit breaker having a primary terminal, a secondary terminal, and a breaker mechanism that breaks an electric circuit disposed between the two terminals, the breaker mechanism performing a breaker operation when an overcurrent flows in the electric circuit, wherein the connection failure detection circuit according to any one of claims 1 to 3 is provided in at least one of the primary terminal and the secondary terminal, and the breaker mechanism performs a breaker operation when the connection failure detection circuit determines that a connection failure has occurred. It is characterized by: According to this configuration, Even if the potential difference between the connection terminals does not reach the voltage that turns on the photocoupler as in the past, the occurrence of a poor connection is detected and a cut-off operation is performed, so the occurrence of a poor connection can be detected at an early stage and a cut-off operation can be performed, preventing deterioration of the circuit breaker. [Effects of the Invention]

[0014] According to the present invention, the detected potential difference is amplified and judged using a differential amplifier circuit or a comparator, so that detection is possible even if the detected potential difference does not reach the voltage that turns on the photocoupler as in the conventional case, and poor connection can be detected at an early stage. Furthermore, since the amplification factor of the differential amplifier circuit or the reference potential of the comparator is changed in response to the current in the electrical path, it is less susceptible to the influence of the current in the electrical path. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram illustrating an example of a circuit breaker equipped with a connection failure detection circuit. [Figure 2] 10A and 10B are explanatory diagrams showing a configuration for detecting a potential difference between connection terminals; [Figure 3] FIG. 10 is a block diagram showing another configuration of the connection failure detection circuit. [Figure 4] FIG. 10 is a block diagram showing another configuration of the connection failure detection circuit. [Figure 5] 10 is a graph showing the relationship between a circuit current and a temperature difference. [Figure 6] FIG. 10 is a block diagram showing another configuration of the connection failure detection circuit. [Figure 7] 1 is a graph showing the relationship between resistance value and temperature. [Figure 8] FIG. 10 is a block diagram showing another configuration of the connection failure detection circuit. [Figure 9] FIG. 10 is a block diagram showing another configuration of the connection failure detection circuit. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments embodying the present invention will be described in detail with reference to the drawings. Figure 1 is an explanatory diagram of a circuit breaker equipped with a connection failure detection circuit according to the present invention, in which 1 is a circuit breaker and 2 is a connection failure detection circuit. The circuit breaker 1 is shown to have a configuration in which the connection failure detection circuit 2 is provided on the secondary terminal of the circuit breaker 1. The circuit breaker 1 shows a configuration used for a three-wire electric circuit, for example, a single-phase three-wire electric circuit. The connection failure detection circuit 2 is mounted on a circuit board (not shown) and incorporated into the housing H of the circuit breaker 1. Although the connection failure detection circuit 2 is provided for all secondary side terminals, for convenience of explanation, only one terminal is shown.

[0017] The circuit breaker 1 has a connection terminal 10 that constitutes a primary terminal 11 and a secondary terminal 12 that electrically connect the electric circuit 4, each of which has three terminals: voltage poles L1 and L2, and a neutral pole N. The housing H of the circuit breaker 1 contains a contact 13 that opens and closes the electrical circuit spanning between the primary terminal 11 and the secondary terminal 12, and a breaker mechanism (not shown) that breaks the contact 13. A handle (not shown) that turns the contact 13 on and off is provided on the top of the housing H. For the sake of explanation, FIG. 1 shows the inside of the housing H in a see-through manner.

[0018] The connection failure detection circuit 2 includes a differential amplifier circuit 21, which is a potential difference detection circuit that detects a potential difference based on the contact resistance generated at the connection terminal 10, a determination unit 22 that determines a connection failure, an output unit 23 that receives the determination result and outputs a predetermined signal, and a threshold value storage unit 26 that stores a threshold value. 21a denotes an operational amplifier that constitutes the differential amplifier circuit 21. The determination unit 22, the output unit 23, and the threshold value storage unit 26 are configured by an MCU (Micro Controller Unit) 3. Then, the breaking mechanism opens the contact portion 13 in response to a signal output from the output portion 23, and the circuit breaker 1 performs a breaking operation.

[0019] 2 shows the configuration of the connection terminal 10 of the secondary terminal 12 to which the connection failure detection circuit 2 is connected. The configuration of the connection terminal 10 itself is common to the individual connection terminals 10 of the primary terminal 11 and the secondary terminal 12. The connection terminal 10 has a washer 61, a terminal screw 62, and a nut 63, and a crimp terminal 65 fixed to the end of an electric wire 60, which is an electric circuit 4, is pressed against the washer 61 by the terminal screw 62 and the nut 63 so as to be in close contact with the washer 61. The operational amplifier 21a constituting the differential amplifier circuit 21 has a positive input terminal 20a and a negative input terminal 20b, with the positive input terminal 20a connected to a washer 61 and the negative input terminal 20b connected to a crimp terminal 65. In this way, the potential difference between the washer 61 and the crimp terminal 65 of the connection terminal 10 is input. The voltage may be detected between the washer 61 and the nut 63 or between the washer 61 and the terminal screw 62.

[0020] The connection failure detection circuit 2 configured as described above operates as follows: The potential difference generated at the connection terminal 10 is input to the differential amplifier circuit 21, amplified by, for example, 10 times with the amplification factor (gain) set by the ratio of the resistance elements R1 and R2, and output to the determination unit 22. The amplification factor G of the differential amplifier circuit 21 is set to R2 / R1 or 1+R2 / R1, and depends on the connection of the resistance elements R1 and R2 to the operational amplifier 21a.

[0021] The threshold memory unit 26 stores a threshold value for determining whether a connection failure has occurred, and when the voltage information output from the differential amplifier circuit 21 exceeds the threshold value stored in the threshold memory unit 26, the judgment unit 22 determines that a connection failure has occurred and causes the output unit 23 to output a predetermined signal. Upon receiving this signal, the circuit breaking mechanism performs a circuit breaking operation, opening the contact point 13 and breaking the electrical circuit 4 .

[0022] In this way, the detected potential difference is amplified and judged by the differential amplifier circuit 21, so that it is possible to detect the potential difference even if it does not reach the voltage that turns on the photocoupler as in the conventional case, and it is possible to detect a connection failure at an early stage and cut off the electrical circuit, thereby preventing deterioration of the circuit breaker 1. It is preferable that the threshold value stored in the threshold memory unit 26 is not a fixed value but is set based on the actual measured value of the contact resistance of the monitored connection terminal 10. Since the voltage drop amount differs by an order of magnitude even with the same circuit current when the initial contact resistance is 1 mΩ and 10 mΩ, it is desirable to set a relatively large threshold value for connection terminals 10 with a large initial contact resistance. This can reduce malfunctions even if the contact resistance increases due to deterioration over time.

[0023] Fig. 3 shows another embodiment of the connection failure detection circuit 2. It differs from the embodiment shown in Fig. 1 in that the amplification factor of the differential amplifier circuit 21 changes based on information about the current flowing through the electrical path. Specifically, it includes a current measurement unit 24 that obtains current information from a current transformer 7 provided in the electric circuit 4 and measures the circuit current, and an amplification factor control unit 25 that controls the amplification factor of the differential amplifier circuit 21, and the resistance elements R1 and R2 that set the amplification factor of the differential amplifier circuit 21 are configured with a digital potentiometer 9, and the amplification factor of the differential amplifier circuit 21 can be controlled by changing the resistance value. 26a is a current information storage unit that stores the correspondence between the current value and the amplification factor, and stores information that makes the circuit current and the amplification factor of the differential amplifier circuit 21 inversely proportional to a predetermined rate. The gain control unit 25 reads the corresponding gain based on the measured circuit current information, and when the circuit current increases, controls R1 and R2 to reduce the gain.

[0024] In this way, when the circuit current increases, the amplification factor of the differential amplifier circuit 21 is reduced. In other words, the sensitivity for detecting poor connections is inversely proportional to the circuit current. Therefore, it is possible to reduce malfunctions caused by voltage drops that increase with an increase in the circuit current.

[0025] Fig. 4 shows another embodiment of the poor connection detection circuit 2. This embodiment differs from the embodiment shown in Fig. 3 in that the amplification factor of the differential amplifier circuit 21 is controlled based on temperature information rather than on circuit current information. Specifically, it is equipped with a first temperature sensor 8a that obtains temperature information of the connection terminal 10, a second temperature sensor 8b that obtains information on the ambient temperature of the circuit breaker 1, a temperature measurement unit 27 that calculates the temperature of the connection terminal 10 and the ambient temperature (environmental temperature), a current information memory unit 26a that stores the relationship between the current value and the amplification factor, a temperature difference information memory unit 26b that stores the relationship between the temperature and the circuit current, and an amplification factor control unit 25a that controls the amplification factor of the differential amplifier circuit 21. The gain control unit 25a calculates the difference between the temperature of the connection terminal 10 and the ambient temperature, converts the circuit current based on the calculated temperature difference information by referring to the temperature difference information storage unit 26b, and determines the gain from the converted current value by referring to the current information storage unit 26a.Then, the resistance elements R1 and R2 formed by the digital potentiometer 9 are controlled to achieve the determined gain.

[0026] FIG. 5 shows the relationship between the circuit current (estimated circuit current value) and the temperature difference stored in the temperature difference information storage unit 26b, which is set based on the actual measurement value. In this way, since the circuit current is estimated from the temperature, there is no need to install a current transformer or other device for measuring current. Furthermore, since the sensitivity for detecting connection defects can be made inversely proportional to the circuit current, malfunctions caused by voltage drops that increase as the circuit current increases can be reduced.

[0027] Fig. 6 shows another embodiment of the connection failure detection circuit 2. It differs from the embodiment in Fig. 4 in that the amplification factor of the amplifier circuit is controlled based on temperature information from one location. Specifically, it is equipped with a temperature sensor 8c that obtains temperature information of the connection terminal 10, a temperature measurement unit 27a that calculates the temperature from the information from the temperature sensor 8c, an amplification factor control unit 25b that controls the amplification factor of the differential amplifier circuit 21, and a temperature correction information storage unit 26c that stores the relationship between temperature and amplification factor. The amplification factor control unit 25b controls the amplification factor based on the detected temperature information of the connection terminal 10 and by referring to the information in the temperature correction information storage unit 26c.

[0028] Figure 7 shows the relationship between resistance and temperature, where Rt is the resistance at reference temperature t and RT is the resistance at measurement temperature T. As shown in Figure 7, as the temperature rises, the contact resistance (resistance) also rises (the detected potential difference also rises). The temperature correction information storage unit 26c stores the relationship between the gain and temperature of the differential amplifier circuit 21 in order to correct for the change in resistance value that accompanies this temperature change. The gain control unit 25b references the information in the temperature correction information storage unit 26c and performs control to lower the gain of the differential amplifier circuit 21 so as to prevent erroneous detection due to a temperature rise. As a result, the determination threshold is raised to perform control to prevent malfunction.

[0029] In this way, the gain of the differential amplifier circuit 21 is controlled to be inversely proportional to the temperature of the connection terminal 10, taking into account the increase in contact resistance, i.e., the increase in potential difference, that accompanies a temperature rise, and therefore malfunctions can be reduced. 4 and 6, which change and control the amplification factor of the differential amplifier circuit 21, the resistance values ​​of the two resistance elements R1 and R2 are variable, but only one of them may be variable as a digital potentiometer, and the other may be a fixed value.

[0030] 8 shows another embodiment of the connection failure detection circuit 2, which differs from the above series of embodiments in that a comparator circuit 31 is used in the potential difference detection circuit. Note that the configuration of the circuit breaker 1 is the same as that of the above embodiments, and therefore description thereof will be omitted. Specifically, the connection failure detection circuit 2 includes a comparator circuit 31 as a potential difference detection circuit that detects the potential difference of the connection terminal 10, a determination unit 22 that determines a connection failure from the H / L signal output by the comparator circuit 31, and an output unit 23 that outputs a predetermined signal in response to the determination result. 31a is an operational amplifier that forms the comparator circuit 31, and R3 and R4 are resistance elements that set the threshold value (reference potential) of the H / L output of the comparator circuit.

[0031] When the comparator circuit 31 outputs an H signal, the determination unit 22 determines that a connection failure has occurred and outputs a signal to cause the breaking mechanism unit to perform a breaking operation from the output unit 23. As a result, the contact unit 13 performs an opening operation and the circuit breaker 1 performs a breaking operation. As in the above embodiment, the determination unit 22 and the output unit 23 are configured by an MCU (Micro Controller Unit) 3.

[0032] In this way, the detected potential difference may be amplified by the comparator circuit 31, and the amplified value may be compared with a reference potential for judgment. As with the differential amplifier circuit 21, it is possible to detect a connection fault even with a slight potential difference, and it is possible to easily detect a connection fault even if the detected potential difference does not reach the voltage that turns on the photocoupler, as in the conventional case. Therefore, it is possible to detect a connection fault at an early stage and cut off the electric circuit 4, thereby preventing deterioration of the circuit breaker 1.

[0033] FIG. 9 shows another embodiment of a connection failure detection circuit using a comparator circuit 31, which differs from the configuration of FIG. 8 in that the reference potential is variable. Specifically, in addition to the comparator circuit 31, the determination unit 22, and the output unit 23, the device is equipped with a current transformer 7 that detects the circuit current, a current measurement unit 24 that calculates the circuit current from information about the current detected by the current transformer 7, a reference potential control unit 28 that changes the reference potential, and a reference potential information storage unit 26d that stores the correspondence relationship between the current and the reference potential, and is configured as a digital potentiometer 9a that can change the resistance value of the resistance element R3, one of the two resistance elements R3 and R4 that set the reference potential. A predetermined relationship in which the reference potential changes in proportion to the circuit current is stored in the reference potential information storage unit 26d.

[0034] The reference potential control unit 28 reads the corresponding reference potential from the reference potential information storage unit 26d based on the measured circuit current information, and controls the resistance element R3. For example, the value of the resistance element R3 is controlled to be inversely proportional to an increase in the circuit current, thereby controlling the reference potential to increase. As a result, an increase in the path current causes the reference potential to increase.

[0035] In this way, since the reference potential is proportional to the circuit current, the sensitivity for detecting poor connections can be made inversely proportional to the circuit current, thereby reducing malfunctions due to increased voltage drop caused by increased circuit current.

[0036] In FIG. 9, the resistor element R3 is variable to change the reference potential. However, to prevent malfunction due to an increase in the circuit current, the resistor element R3 may be configured as a negative temperature coefficient thermistor, and this negative temperature coefficient thermistor may be placed near the connection terminal 10 for detecting the potential difference. In this way, the value of the resistor element R3 decreases as the temperature rises, allowing the reference potential to increase. As a result, malfunction due to temperature rise can be prevented. Furthermore, there is no need to provide the current measurement unit 24 or the reference potential control unit 28. In addition, in all of the above embodiments, the case where the poor connection detection circuit 2 is provided at the secondary terminal 12 of the circuit breaker 1 has been described, but the poor connection detection circuit 2 may also be provided at the primary terminal 11 or at both. Furthermore, the above-mentioned connection failure detection circuit 2 can be applied not only to the circuit breaker 1 but also to a terminal block having multiple connection terminals, and by adding a function such as issuing an alarm when a connection failure occurs, it can be made to function well even in devices other than circuit breakers. [Explanation of symbols]

[0037] 1 Circuit breaker, 2 Connection failure detection circuit, 4 Electrical circuit, 9, 9a Digital potentiometer, 10 Connection terminal, 11 Primary terminal, 12 Secondary terminal, 13 Contact section, 21 Differential amplifier circuit, 21a Operational amplifier, 22 Judgment section, 23 Output section, 24 Current measurement section, 25, 25a, 25b Amplification factor control section, 26 Threshold memory section, 26a Current information memory section, 26b Temperature difference information memory section, 26c Temperature correction information memory section, 26d Reference potential information memory section, 27 Temperature measurement section (terminal temperature measurement section, ambient temperature measurement section), 27a Temperature measurement section, 31 Comparator, 31a Operational amplifier, H Housing.

Claims

1. A connection failure detection circuit for detecting a connection failure of a connection terminal for connecting an electric circuit, a potential difference detection circuit for detecting a potential difference occurring at the connection terminal; a determination unit that determines that a connection failure has occurred when the detected potential difference exceeds a predetermined threshold value; a differential amplifier circuit that amplifies the potential difference detected by the potential difference detection circuit; a current measurement unit that measures a circuit current; an amplification factor control unit that changes and controls the amplification factor of the differential amplifier circuit; the amplification factor control unit performs control to make the amplification factor of the differential amplifier circuit inversely proportional to the path current at a predetermined factor; The connection failure detection circuit is characterized in that the determination unit compares the potential difference amplified by the differential amplifier circuit with the threshold value to make a determination.

2. A connection failure detection circuit for detecting a connection failure of a connection terminal for connecting an electric circuit, comprising: a potential difference detection circuit for detecting a potential difference occurring at the connection terminal; a determination unit that determines that a connection failure has occurred when the detected potential difference exceeds a predetermined threshold value; a differential amplifier circuit that amplifies the potential difference detected by the potential difference detection circuit; a terminal temperature measurement unit that measures the temperature of a connection terminal that is a potential difference detection target; an ambient temperature measuring unit that measures the ambient temperature; a temperature difference information storage unit that stores the relationship between the temperature difference and the circuit current; an amplification factor control unit that changes and controls the amplification factor of the differential amplifier circuit; the amplification factor control unit calculates a temperature difference between the temperature of the connection terminal and the ambient temperature, converts a circuit current from the temperature difference, and performs control such that the amplification factor of the differential amplifier circuit is inversely proportional to the converted circuit current at a predetermined rate; The connection failure detection circuit is characterized in that the determination unit compares the potential difference amplified by the differential amplifier circuit with the threshold value to make a determination.

3. A connection failure detection circuit for detecting a connection failure of a connection terminal for connecting an electric circuit, a potential difference detection circuit for detecting a potential difference occurring at the connection terminal; a determination unit that determines that a connection failure has occurred when the detected potential difference exceeds a predetermined threshold value; a differential amplifier circuit that amplifies the potential difference detected by the potential difference detection circuit; a terminal temperature measurement unit that measures the temperature of a connection terminal that is a potential difference detection target; a temperature correction information storage unit that stores a relationship between temperature and the amplification factor of the differential amplifier circuit; an amplification factor control unit that changes and controls the amplification factor of the differential amplifier circuit; the amplification factor control unit refers to the temperature correction information storage unit based on the measured temperature of the connection terminal, and performs control to reduce the amplification factor of the differential amplifier circuit when the temperature rises; The connection failure detection circuit is characterized in that the determination unit compares the potential difference amplified by the differential amplifier circuit with the threshold value to make a determination.

4. A circuit breaker having a primary terminal, a secondary terminal, and a cutoff mechanism that cuts off an electric circuit arranged between the two terminals, wherein the cutoff mechanism performs a cutoff operation when an overcurrent flows in the electric circuit, the connection failure detection circuit according to any one of claims 1 to 3 is provided on at least one of the primary side terminal and the secondary side terminal, When the connection failure detection circuit determines that a connection failure has occurred, the breaking mechanism performs a break operation.

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