JP2007132806A - Impedance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impedance measuring device capable of reducing manufacturing costs. <P>SOLUTION: The impedance measuring device, which includes an alternating-current feeding section 2 for feeding alternating-current I to a battery 12, an amplifying section 6, which has a different power system insulated mutually to the alternating-current feeding section 2, amplifying signal S1 generated between the two poles of battery 12, a synchronized signal generating section (comparator 2d) synchronizing with alternating-current I to output the synchronized signal St1 referring to a ground of the alternating-current feeding section 2, a synchronous detection section 8 for detecting synchronously the signals S2 output from the amplifying section 6 with the synchronized signal St, an attenuator 3 for attenuating the voltage of synchronized signal St1 into an in-phase input voltage range of a comparator 7, and the comparator 7, while referring to the ground of amplifying section 6, waveform-shaping the attenuated synchronized signal St2 into rectangular waves to generate the synchronized signal St, outputting to a synchronous detection section 8, computes internal impedance R of the battery 12, based on the signal S3 outputted from the synchronous detection section 8 and alternating-current I. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an impedance measuring apparatus suitable for measuring the internal impedance of a battery having a DC electromotive force.

  As this kind of impedance measuring apparatus, the inventor has already proposed an impedance measuring apparatus disclosed in Japanese Patent Laid-Open No. 11-295362. By the way, in this kind of impedance measuring apparatus, an alternating current is supplied to the battery from the alternating current supply unit via the probe, and the battery is based on a signal (voltage) generated between both electrodes of the battery and the alternating current at this time. The internal resistance (internal impedance) is measured. In this case, there is always a contact resistance between the probe and each electrode of the battery. Therefore, the voltage generated when an alternating current flows through the contact resistance becomes in-phase noise with respect to a signal generated between both electrodes of the battery, and as a result, it may be difficult to measure the internal impedance of the battery. For this reason, in the impedance measuring device disclosed in the above publication, this in-phase noise is removed by employing an instrumentation amplifier (a differential amplifier circuit with high input impedance).

  On the other hand, since an instrumentation amplifier is expensive, the inventor has also developed an impedance measurement device 21 using an inexpensive single-ended input type (non-differential input type) amplifier (operational amplifier) as shown in FIG. is doing. As shown in the figure, the impedance measuring device 21 includes an alternating current supply unit 2, a pair of input terminals 4 and 5, a photocoupler 27, an amplification unit 6, a synchronous detection unit 8, an arithmetic control unit 10, and a display unit 11. In addition to the power supply and ground of the alternating current supply unit 2 (shown in black in the figure), other electric circuits including the amplification unit 6 and the synchronous detection unit 8 (other than the alternating current supply unit 2) The power source of the electric circuit) and the ground (shown in white in the figure) are insulated (separated). That is, the alternating current supply unit 2 and other electric circuits including the amplification unit 6 and the like have different power supply systems that are insulated from each other. In this impedance measuring device 21, the alternating current source 2 a of the alternating current supply unit 2 supplies the alternating current I to the battery 12 via the pair of output terminals 2 b and 2 c and is a rectangular wave synchronization signal synchronized with the alternating current I. St1 is output via the comparator 2d. In this case, a signal S1 is generated between the two electrodes of the battery 12 in which the AC component V2 generated due to the AC current I flowing through the internal resistance 12a of the battery 12 is superimposed on the DC electromotive force V1 of the battery 12. To do. In the amplifying unit 6, a single-ended input type operational amplifier 6a receives the signal S1 via the input terminal 4, amplifies it with a gain defined by the resistors 6b and 6c, and outputs it as a signal S2. On the other hand, the photocoupler 27 converts the synchronization signal St1 into a synchronization signal St that is electrically insulated from the synchronization signal St1, and transmits it to the synchronization detector 8. Next, the synchronous detection unit 8 generates the signal S3 by synchronously detecting the signal S2 with the synchronous signal St. Thereafter, the arithmetic control unit 10 measures the internal impedance R of the battery 12 on the basis of the signal S3 and the alternating current I and causes the display unit 11 to display it.

According to the impedance measuring device 21, the power supply and ground of the alternating current supply unit 2 are insulated from the power supply and ground of other electric circuits including the amplification unit 6 and the synchronous detection unit 8, and the photocoupler 27 is used. Since the synchronization signal St1 and the synchronization signal St are insulated, it is possible to reliably prevent a current from flowing between the ground of the alternating current supply unit 2 and the ground of the amplification unit 6. For this reason, even if the contact resistance Rc exists between the input terminal 5 and the electrode of the battery 12, the occurrence of common-mode noise is avoided because no current flows through the contact resistance Rc. In FIG. 2, for convenience, a contact resistance Rc is connected between the input terminal 5 and the ground of the amplifying unit 6. The same applies to FIG. Therefore, according to this impedance measuring apparatus 21, the operational control section 10 accurately determines the internal impedance R of the battery 12 while reducing the apparatus cost by configuring the amplification section 6 with an inexpensive single-ended input operational amplifier 6a. Can be measured.
JP 11-295362 A (page 3, FIG. 1)

  However, even if not as much as an instrumentation amplifier, the photocoupler is also expensive, so that the entire impedance measuring device still requires a high manufacturing cost. For this reason, development of a low-cost impedance measuring apparatus is desired.

  The present invention has been made to meet such demands, and its main object is to reduce the manufacturing cost of an impedance measuring device.

  In order to achieve the above object, the impedance measuring apparatus according to claim 1 includes an alternating current supply unit that supplies an alternating current to a battery, and the alternating current supply unit includes different power supply systems that are insulated from each other, and An amplifying unit for amplifying and outputting a signal generated between the two electrodes of the battery at the time of current supply; and a synchronization for outputting a first synchronization signal based on the ground of the alternating current supply unit in synchronization with the alternating current A signal generation unit; and a synchronous detection unit that synchronously detects the signal output from the amplification unit with a second synchronization signal generated based on the first synchronization signal, and an output signal of the synchronous detection unit and the An impedance measuring device for calculating an internal impedance of the battery based on an alternating current, comprising an attenuator and a comparator, wherein the attenuator is supplied from the synchronization signal generator. The voltage of the applied first synchronization signal is attenuated within the common-mode input voltage range of the comparator, and the comparator has a waveform of the attenuated first synchronization signal in a rectangular waveform with reference to the ground of the amplification unit. The second synchronization signal is generated by shaping and is output to the synchronous detector.

  The impedance measuring apparatus according to claim 2 is the impedance measuring apparatus according to claim 1, wherein the comparator has a hysteresis characteristic.

  The impedance measuring device according to claim 3 is the impedance measuring device according to claim 1 or 2, wherein the potential difference between the ground of the alternating current supply unit and the ground of the attenuator and the amplifying unit is detected. An alarm unit is provided for outputting an alarm signal when the voltage exceeds a predetermined voltage.

  According to the impedance measuring apparatus of claim 1, the alternating current supply unit and the amplifier and the comparator are different power supply systems insulated from each other, the amplification unit is constituted by, for example, a single-end input type operation control unit, and the attenuator is By directly connecting to the comparator and connecting the comparator to the synchronous detection unit, it is possible to configure without using expensive parts such as an instrumentation amplifier and a photocoupler, thereby sufficiently reducing the manufacturing cost of the device. it can. For example, when the potential difference between the ground of the alternating current supply unit and the attenuator and the ground of the amplifier and the comparator is less than a predetermined voltage, the voltage value of the first synchronization signal input to the comparator is always compared by the attenuator. By defining the current to be within the common-mode input voltage range, the AC current supply unit, the attenuator, the power source of the comparator, any electrical element or circuit connected between the power source and the ground, the ground of the comparator And the situation where an electric current flows into the path | route which leads to the ground of an alternating current supply part through the input terminal made to contact the electrode of a battery can be prevented. Accordingly, it is possible to prevent the voltage (common-mode noise) from being generated at the contact resistance existing between the input terminal brought into contact with the electrode of the battery and the electrode, so that the internal impedance of the battery can be accurately measured.

  According to the impedance measuring apparatus according to claim 2, since the comparator is provided with hysteresis characteristics, the potential difference between the ground of the alternating current supply unit and the ground of the comparator varies, and so on. Even if distortion occurs in the first synchronization signal output from the comparator, the comparator can appropriately shape the waveform of the first synchronization signal and output the second synchronization signal with less noise. Therefore, since the synchronous detection unit can normally continue the synchronous detection operation based on the second synchronous signal, a normal signal can be detected stably. Therefore, the calculation unit can accurately and stably measure the internal impedance of the battery based on the output signal of the synchronous detection unit and the alternating current supplied to the battery by the alternating current supply unit.

  According to the impedance measuring apparatus according to claim 3, for example, when the potential difference between the ground of the alternating current supply unit and the ground of the amplifier and the comparator becomes equal to or higher than a predetermined voltage, for example, an alarm output from the alarm unit Based on the signal, this can be displayed on the display unit for notification. Therefore, when the potential difference between the grounds exceeds a predetermined voltage and the voltage value of the second synchronization signal output from the attenuator exceeds the common-mode input voltage range of the comparator, the comparator normally continues the waveform shaping operation. As a result of the occurrence of an unacceptable situation or a further increase in the potential difference between the grounds, the AC current supply unit, the power supply of the attenuator, the comparator, any electrical element or electrical device connected between the power supply and the ground As a result of the situation where current flows through the circuit, the ground of the comparator, and the input terminal in contact with the electrode of the battery to the path leading to the ground of the AC current supply unit, the synchronous detection unit When a signal that accurately indicates the effective value of the voltage generated in the internal resistance of the battery cannot be generated by synchronous detection Also, the internal impedance measured it is possible to reliably informed that there may not be accurate, as a result, it is possible to avoid erroneous measurements.

  The best mode of an impedance measuring apparatus according to the present invention will be described below with reference to the accompanying drawings.

  First, the configuration of the impedance measuring apparatus 1 will be described.

  As shown in FIG. 1, the impedance measuring apparatus 1 includes an alternating current supply unit 2, an attenuator 3, a pair of input terminals 4 and 5, an amplification unit 6, a comparator 7, a synchronous detection unit 8, an alarm unit 9, and an arithmetic control unit 10. And a display unit 11. In this case, the power supply and ground (shown in black in the figure) of the AC current supply unit 2 and the attenuator 3 are other electric circuits (amplification unit 6 and comparator 7) than the AC current supply unit 2 and the attenuator 3. Etc.) is isolated from the power source and ground (shown in white in the figure). That is, the alternating current supply unit 2 and the attenuator 3 and other electrical circuits have different power supply systems that are insulated from each other.

  The AC current supply unit 2 corresponds to the AC current supply unit and the synchronization signal generation unit in the present invention, and includes an AC current source 2a, a pair of output terminals 2b and 2c, and a comparator 2d as shown in FIG. Then, the alternating current I generated by the alternating current source 2a is supplied to the battery 12 via the pair of output terminals 2b and 2c. In this case, the output terminal 2 c is connected to the ground of the alternating current supply unit 2. The alternating current supply unit 2 generates a synchronization signal St0 synchronized with the alternating current I, and shapes the waveform of the synchronization signal St0 into a rectangular waveform synchronization signal St1 (first synchronization signal in the present invention) by the comparator 2d. Output. The attenuator 3 divides the synchronization signal St1 and outputs it as the synchronization signal St2. In this example, the attenuator 3 includes, as an example, two resistors 3a and 3b connected in series between the output terminal of the comparator 2d and the ground. The attenuation amount of the attenuator 3 (attenuation amount defined by the resistance values of the resistors 3a and 3b) is determined by the potential difference between the ground of the comparator 7 and the ground of the attenuator 3 (AC current supply unit 2) being a predetermined voltage. When the value is less than the predetermined value, the voltage value of the synchronization signal St2 is defined to be always within the common-mode input voltage range of the comparator 7. Here, the common-mode input voltage range means an allowable range of input voltage in which the comparator 7 operates normally (voltage range of the synchronization signal St2).

  As shown in FIG. 1, the amplifying unit 6 includes an operational amplifier 6a and resistors 6b and 6c, and is configured as a single-ended input type non-inverting amplifier circuit. In this case, the input terminal 4 is connected to the non-inverting input terminal of the operational amplifier 6 a, and the input terminal 5 is connected to the ground of the amplifying unit 6. With this configuration, the amplifying unit 6 amplifies the signal S1 generated between the two poles of the battery 12 input via the input terminal 4 and outputs the amplified signal S2 (signal output from the amplifying unit in the present invention).

  As shown in FIG. 1, the comparator 7 includes a comparator body 7a and resistors 7b and 7c (resistance values: R1 and R2) that define the hysteresis characteristics of the comparator body 7a. The comparator 7 shapes the synchronization signal St2 output from the attenuator 3 into a rectangular waveform (upper and lower limit voltages: + Vc, −Vc), and uses the ground of the amplifier 6 as a reference (St 2 in the present invention). (Synchronization signal). Therefore, the comparator 7 outputs an output voltage of −Vc when the synchronization signal St2 exceeds the upper limit comparator voltage (+ (Vc × R2) / (R1 + R2)), and the synchronization signal St2 becomes the lower limit comparator voltage (− ( It has a hysteresis characteristic that the output voltage becomes + Vc when Vc × R2) / (R1 + R2)). In the impedance measuring apparatus 1 of this example, the ground of the attenuator 3 and the power source and ground of the comparator 7 are insulated as described above. For this reason, when the ground of the comparator 7 is used as a reference, the ground potential of the attenuator 3 (alternating current supply unit 2) fluctuates, and the synchronization signal St2 output from the attenuator 3 is caused by the fluctuation of the potential. The voltage waveform may be distorted. However, as long as the comparator 7 is in the in-phase input voltage range even when the synchronization signal St2 is distorted, the comparator 7 calculates the waveform of the synchronization signal St2 based on the hysteresis characteristic defined by the above upper and lower limit comparator voltages. Waveform shaping to a rectangular wave synchronization signal St without distortion and output.

  As shown in FIG. 1, the synchronous detection unit 8 performs synchronous detection on the signal S <b> 2 with the synchronous signal St generated based on the synchronous signal St <b> 2, so that the alternating current I flows through the battery 12. A signal S3 (output signal of synchronous detection in the present invention) indicating the effective value of the voltage generated in the internal resistor 12a is generated and output. As shown in the figure, the alarm unit 9 includes two comparators 9a and 9b, two reference power supplies 9c and 9d for an output voltage V3, two diodes 9e and 9f, and a termination resistor 9g. With this configuration, the alarm unit 9 has a potential difference between the ground of the alternating current supply unit 2 and the ground of the amplifier unit 6 (which is also the alarm unit 9) equal to or higher than a predetermined voltage (−V3 or higher and + V3 or lower). The alarm signal S4 is output to the arithmetic control unit 10 when it is off. The arithmetic control unit 10 corresponds to the arithmetic unit in the present invention, and includes an A / D converter, a CPU, a memory, and the like (all not shown). In the memory, the current value (effective value) of the alternating current I supplied by the alternating current supply unit 2 is stored in advance. The arithmetic control unit 10 calculates the resistance value (internal impedance of the battery 12) R of the internal resistance 12a of the battery 12 based on the voltage value of the signal S3 output from the synchronous detection unit 8 and the current value of the alternating current I. The impedance calculation process is executed. Moreover, the arithmetic control part 10 performs an alarm process, when the alarm signal S4 is input. The display unit 11 is configured by, for example, a liquid crystal display.

  Next, the measurement operation of the internal impedance R of the battery 12 by the impedance measuring device 1 will be described.

  First, as shown in FIG. 1, the output terminal 2b is connected to the positive electrode of the battery 12, and the output terminal 2c is connected to the negative electrode of the battery 12. In this state, the supply of the alternating current I to the alternating current supply unit 2 is performed. To start. Next, the input terminal 4 is connected to the positive electrode of the battery 12, and the input terminal 5 is connected to the negative electrode of the battery 12. At this time, the amplifying unit 6 receives a signal S1 in which an AC component V2 generated due to the AC current I flowing through the internal resistance 12a of the battery 12 is superimposed on the DC electromotive force V1 of the battery 12. 4 is input. The amplifying unit 6 amplifies the signal S1 with a predetermined amplification factor and outputs the amplified signal S1 to the synchronous detection unit 8 as the signal S2.

  On the other hand, when the alternating current supply unit 2 starts supplying the alternating current I, the alternating current supply unit 2 also outputs a synchronization signal St1 synchronized with the alternating current I to the attenuator 3 via the comparator 2d. Next, the attenuator 3 divides the synchronization signal St1 and outputs it as the synchronization signal St2. Subsequently, the comparator 7 shapes the synchronization signal St2 into a rectangular waveform and outputs the waveform to the synchronization detection unit 8 as the synchronization signal St. In this case, when the potential difference between the ground of the comparator 7 and the ground of the alternating current supply unit 2 is less than a predetermined voltage, the attenuator 3 causes the voltage value of the synchronization signal St2 to be within the common-mode input voltage range of the comparator 7. The sync signal St2 is attenuated. For this reason, in this state, the situation where the synchronization signal St2 exceeding the common-mode input voltage range is input to the comparator 7 is reliably avoided. Therefore, from the comparator 2d, the attenuator 3, the power source of the comparator 7, the electrical element or circuit connected between the power source and the ground, the ground of the comparator 7, and the input terminal 5, the alternating current supply unit As a result of preventing the current from flowing through the path leading to the ground 2, the generation of voltage (common-mode noise) at the contact resistance Rc existing between the input terminal 5 and the electrode of the battery 12 is prevented. Further, since the comparator 7 has the above hysteresis characteristic, a noise signal (common-mode voltage) is generated as the synchronization signal St2 due to a potential difference between the ground of the alternating current supply unit 2 and the ground of the comparator 7. Even when is superimposed, the synchronization signal St2 is shaped well and the synchronization signal St is output.

  Next, the synchronous detection unit 8 generates and outputs a signal S3 indicating the effective value of the voltage generated in the internal resistance 12a of the battery 12 by synchronously detecting the signal S2 with the synchronous signal St. The arithmetic control unit 10 executes an impedance calculation process based on the signal S3 output from the synchronous detection unit 8, and calculates the internal impedance R of the internal resistance 12a of the battery 12. Specifically, the arithmetic control unit 10 divides the effective value of the voltage indicated by the signal S3 by the current value of the alternating current I read from the memory, thereby obtaining the internal impedance R of the battery 12 (the resistance of the internal resistor 12a). Value). Further, the arithmetic control unit 10 causes the display unit 11 to display the calculated internal impedance R.

  On the other hand, the alarm unit 9 constantly monitors the potential difference between the ground of the alternating current supply unit 2 and the ground of the amplifier unit 6 (also the alarm unit 9), and when this potential difference is equal to or higher than a predetermined voltage (−V3). The alarm signal S4 is output when the value exceeds the range of + V3 or less. The arithmetic control unit 10 constantly monitors the input of the alarm signal S4, and displays the calculated internal impedance R on the display unit 11 as described above when the alarm signal S4 is not input. On the other hand, the arithmetic control unit 10 executes an alarm process when the alarm signal S4 is input. In this processing, the arithmetic control unit 10 causes the synchronous detection unit 8 to synchronize because the potential difference between the ground of the alternating current supply unit 2 and the ground of the amplification unit 6 (also the alarm unit 9) is equal to or higher than a predetermined voltage. It is determined that the signal S2 cannot be normally synchronously detected by the signal St, and that effect (for example, “measurement impossible”) is displayed on the display unit 11. As a result, erroneous measurement can be avoided.

  As described above, according to the impedance measuring apparatus 1, the AC current supply unit 2, the amplifier 6 and the comparator 7 are configured as different power supply systems that are insulated from each other, and the amplification unit 6 is configured as a single-end input type operation control unit. In addition, since the attenuator 3 is directly connected to the comparator 7 and the comparator 7 is connected to the synchronous detection unit 8, no expensive parts such as an instrumentation amplifier or a photocoupler are used, thereby sufficiently reducing the manufacturing cost of the apparatus. be able to. When the potential difference between the grounds of the alternating current supply unit 2 and the attenuator 3 and the grounds of the amplifier unit 6 and the comparator 7 is less than a predetermined voltage, the voltage value of the synchronization signal St2 input to the comparator 7 is the attenuator 3. Therefore, while the waveform shaping operation in the comparator 7 is normally continued, the attenuator 3, the power supply of the comparator 7, the power supply of the comparator 7, the power supply and the ground It is possible to prevent a situation in which a current flows through a path leading to the ground of the alternating current supply unit 2 via any of the electrical elements or electrical circuits connected therebetween, the ground of the comparator 7, and the input terminal 5. Therefore, according to this impedance measuring apparatus 1, since the generation of voltage (common-mode noise) at the contact resistance Rc existing between the input terminal 5 and the electrode of the battery 12 can be prevented, the internal impedance R of the battery 12 can be accurately determined. Can be measured.

  Further, according to the impedance measuring apparatus 1, since the comparator 7 is configured with hysteresis characteristics, the potential difference between the ground of the alternating current supply unit 2 and the ground of the comparator 7 varies, and so on. Even if distortion occurs in St2, the synchronization signal St2 can be shaped well and the synchronization signal St with less noise can be output. Therefore, since the synchronous detector 8 can stably detect the normal signal S3, the internal impedance R of the battery 12 can be accurately and stably measured.

  Furthermore, according to the impedance measuring apparatus 1, when the alarm unit 9 is provided, the potential difference between the ground of the alternating current supply unit 2 and the ground of the amplifier unit 6 and the comparator 7 becomes equal to or higher than a predetermined voltage. In addition, for example, based on the alarm signal S4 output from the alarm unit 9, the calculation control unit 10 can notify the display unit 11 of that fact. Therefore, when the potential difference between the grounds becomes a predetermined voltage or more and the voltage value of the synchronization signal St2 output from the attenuator 3 exceeds the common-mode input voltage range of the comparator 7, the comparator 7 normally performs the waveform shaping operation. Any of the electrical elements connected between the power source of the attenuator 3 and the comparator 7 and the power source of the attenuator 3 and the comparator 7 due to the occurrence of a situation where it cannot be continued or the potential difference between the grounds further increasing. Or the electric circuit, the ground of the comparator 7, and the input terminal 5, a situation in which current flows through the path leading to the ground of the alternating current supply unit 2 occurs. As a result, the synchronous detection unit 8 performs synchronous detection. Cannot generate a signal S3 that accurately indicates the effective value of the voltage generated in the internal resistance 12a of the battery 12 Even when the error occurs, it is possible to reliably notify that the internal impedance R (internal impedance displayed on the display unit 11) measured by the arithmetic control unit 10 may not be accurate. Measurement can be avoided.

  In addition, this invention is not limited to said structure. For example, in the impedance measuring apparatus 1, the comparator 7 is configured with hysteresis characteristics, but when noise is superimposed on the synchronization signal St <b> 2, a configuration without hysteresis characteristics may be employed. Further, the potential difference between the ground of the alternating current supply unit 2 and the grounds of the amplifier 6 and the comparator 7 can be suppressed to a low level, and when the synchronous detector 8 can always perform normal synchronous detection, the alarm unit 9 The arrangement can be made unnecessary.

1 is a block diagram showing a configuration of an impedance measuring device 1. FIG. 3 is a block diagram showing a configuration of an impedance measuring device 21. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Impedance measuring apparatus 2 AC current supply part 3 Attenuator 4,5 Input terminal 6 Amplification part 7 Comparator 8 Synchronous detection part 9 Alarm part 10 Arithmetic control part 12 Battery I AC current R Internal impedance St1 Synchronization signal S1, S2, S3 signal

Claims (3)

An alternating current supply for supplying alternating current to the battery;
The alternating current supply unit has different power supply systems that are insulated from each other, and amplifies a unit that amplifies and outputs a signal generated between both electrodes of the battery when the alternating current is supplied;
A synchronization signal generation unit that outputs a first synchronization signal based on the ground of the AC current supply unit in synchronization with the AC current;
A synchronous detection unit that synchronously detects the signal output from the amplification unit with a second synchronization signal generated based on the first synchronization signal;
An impedance measuring device that calculates an internal impedance of the battery based on an output signal of the synchronous detection unit and the alternating current,
An attenuator and a comparator, wherein the attenuator attenuates the voltage of the first synchronization signal output from the synchronization signal generator within the common-mode input voltage range of the comparator, and the comparator An impedance measuring device that generates a second synchronization signal by outputting a waveform of the synchronization signal with reference to the ground of the amplification unit and a rectangular waveform, and outputs the second synchronization signal to the synchronization detection unit.   The impedance measuring apparatus according to claim 1, wherein the comparator has a hysteresis characteristic.   The alarm unit which detects a potential difference between the ground of the alternating current supply unit and the ground of the attenuator and the amplifying unit and outputs an alarm signal when the potential difference is equal to or higher than a predetermined voltage. Impedance measuring device.

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