JP2010107264A - Resistance measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistance measuring apparatus capable of reducing influence of an offset caused by a change in the environmental conditions in use or a change of an electric component with time. <P>SOLUTION: The resistance measuring apparatus includes: a memory for storing an offset current value to a current value of an alternating current I1 flowing a second wiring 23; and a processing part 43 for calculating a current value of a current actually flows the second wiring 23 by subtracting an offset current value from the current value of the alternating current I1, and performing a resistance calculation processing to calculate a resistance value Rx of a measured circuit 5 based on the current value and a voltage value Vx of an alternating current signal Vx for inspection injected to the measured circuit 5. The processing part 43 performs an offset updating processing for storing the current value of the alternating current I1 flowing the second wiring 23 in the memory as a new offset current value when the apparatus is in an offset updatable state in which the resistance value Rx calculated in the resistance calculation processing is equal to or more than a resistance threshold value or is a negative value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a resistance measuring device that measures a resistance value of a circuit to be measured.

As this type of resistance measuring apparatus, a resistance measuring apparatus disclosed in Patent Document 1 below is known. This resistance measuring device is a transformer for injection that injects into the measurement network a current of a second frequency that can be distinguished from the current of the first frequency flowing through the measurement circuit network (measurement object) by clipping the connecting wire of the measurement circuit network. And a detection transformer for detecting the two types of current flowing in the measurement circuit by clipping the connection conductor, and a frequency selection circuit for extracting the second frequency component from the output of the detection transformer (specifically Frequency selection amplification circuit), a rectification amplification circuit that rectifies and amplifies the voltage output from the frequency selection circuit, and display means (specifically, an indicator) that displays the output of the rectification amplification circuit. The injection transformer has an injection coil that receives the output voltage of the oscillator and injects a second frequency current into the measurement circuit network, and a feedback coil, and the voltage induced in the feedback coil is controlled to a constant value. Injection carp It is configured to include a feedback loop so as to vary the voltage supplied to. In this resistance measuring device, the injection voltage obtained by dividing the voltage induced in the feedback coil by the ratio of the number of windings of the feedback coil to the number of connecting conductors (number of clips, one) of the measurement network is also constant. The resistance value of the resistor connected to the detection transformer is detected by detecting the voltage generated in the resistor connected to the detection transformer due to the current flowing through the detection transformer. Based on the voltage generated in this resistor, the voltage generated in the feedback coil, the number of turns of the injection transformer and the number of turns of the detection transformer, the value of the resistance element connected to the measurement network (measured resistance) is measured. It is possible to do.
Japanese Examined Patent Publication No. 2-7031 (page 1-4, Fig. 2)

  However, the above resistance measuring apparatus has the following problems. That is, in this resistance measurement apparatus, the second frequency component of the frequency components included in the output of the detection transformer is selectively amplified using a frequency selection circuit (specifically, a frequency selection amplification circuit). is doing. In this case, an offset is generally generated in an amplifier circuit such as this frequency selection circuit, and this offset causes a measurement error in the resistance measuring apparatus. For this reason, the amplifier circuit is usually configured to include an offset adjustment circuit, and is adjusted (offset cancellation adjustment) so that the offset becomes zero in the adjustment process before shipment of the resistance measuring device. However, in the resistance measuring apparatus, even if the amplifier circuit is once adjusted to such a state with no offset, it is caused by changes in environmental conditions such as temperature and humidity and changes in characteristics of electronic components constituting the amplifier circuit over time. Thus, an offset may occur in the amplifier circuit, and there is a problem that a measurement error occurs due to this offset. The applicant has also developed a resistance measuring device with a function that automatically cancels the offset each time the power is turned on (once every time the power is turned on). There is a problem that an offset caused by a change or a change with time of an electronic component cannot be canceled.

  The present invention has been made to solve such a problem, and a main object of the present invention is to provide a resistance measuring device capable of reducing the influence of offset.

  In order to achieve the above object, the resistance measuring apparatus according to claim 1 includes a voltage injection unit that injects a test AC signal into the circuit to be measured, and an AC that flows through the measurement target circuit due to the injection of the test AC signal. A current detection unit for detecting current with a detection coil; a storage unit for storing an offset current value with respect to a current value of an alternating current flowing through the detection coil; and the offset current value from the current value of the alternating current flowing through the detection coil To calculate the value of the current flowing through the detection coil by subtracting the current value and to calculate the resistance value of the circuit to be measured based on the current value and the voltage value of the injected AC signal for inspection A resistance measuring device, wherein the processing unit determines whether the resistance value calculated in the resistance calculation process is equal to or greater than a predetermined resistance threshold value. When the offset update state to be a negative value, and executes the offset update process to be stored in the storage unit the current value as a new said offset current value of the alternating current flowing in the detection coil.

  The resistance measuring device according to claim 2 is a voltage injecting unit for injecting a test AC signal into the circuit to be measured, and a detection coil for detecting an AC current flowing through the circuit to be measured due to the injection of the test AC signal. A current detection unit that detects the current value of the alternating current that flows through the detection coil, a storage unit that stores an offset current value with respect to the current value of the alternating current that flows through the detection coil, A processing unit that calculates a current value flowing through the detection coil and executes a resistance calculation process that calculates a resistance value of the circuit to be measured based on the current value and the voltage value of the injected AC signal for inspection. The resistance measurement apparatus, wherein the processing unit detects the detection coil when the calculated current value is in an offset updateable state where the current value is equal to or less than a predetermined current threshold value. Wherein executing the offset update process to be stored in the storage unit the current value of the alternating current as a new said offset value of the current flowing through the.

  The resistance measurement device according to claim 3 is the resistance measurement device according to claim 1 or 2, wherein the processing unit executes the offset update processing when the offset updateable state continues for a predetermined time or more. .

  Further, the resistance measuring device according to claim 4 is the resistance measuring device according to any one of claims 1 to 3, further comprising an operation unit that generates an update signal according to the operation content and outputs the update signal to the processing unit. The processing unit executes the offset update process only when the offset update is possible in a state where the update signal is input.

  The resistance measurement device according to claim 5 is the resistance measurement device according to any one of claims 1 to 4, wherein the voltage injection unit generates the inspection AC signal synchronized with a reference signal, and the current The detection unit includes at least a first operational amplifier in which one end of the detection coil is connected to an inverting input terminal and a reference voltage is input to a non-inverting input terminal, and a current flowing through the detection coil is a first voltage signal. A first amplifying unit that converts the output into a non-inverting input terminal and the second operational amplifier having the other end of the detection coil connected to the inverting input terminal and the non-inverting input terminal. A second amplifying unit that converts a current flowing through the detection coil into a second voltage signal having an opposite phase to the first voltage signal and outputs the second voltage signal; and the first voltage signal and the second voltage signal in synchronization with the reference signal Synchronous detection A first extractor for extracting a positive signal composed only of a positive waveform of the first voltage signal and the second voltage signal; and the first voltage signal and the second in synchronization with the reference signal A second extraction unit that performs synchronous detection of the voltage signal to extract a negative signal composed of only the negative waveform of the first voltage signal and the second voltage signal; and the positive signal and the negative signal A differential amplifier that outputs a differential signal of the signal, and detects the alternating current flowing through the circuit to be measured based on the differential signal.

  The resistance measurement device according to claim 6 is the resistance measurement device according to any one of claims 1 to 4, wherein the voltage injection unit generates the inspection AC signal synchronized with a reference signal, and the current The measurement unit includes at least a first operational amplifier having one end of the detection coil connected to the inverting input terminal and a reference voltage input to the non-inverting input terminal, and the current flowing through the detection coil is a first voltage signal. A first amplifying unit that converts the output into a non-inverting input terminal and the second operational amplifier having the other end of the detection coil connected to the inverting input terminal and the non-inverting input terminal. A second amplifier for converting and outputting a current flowing through the detection coil to a second voltage signal having a phase opposite to that of the first voltage signal; and a third for outputting a difference signal between the first voltage signal and the second voltage signal. An amplification unit; An extraction unit that synchronously detects the differential signal in synchronization with a quasi signal and extracts a unipolar signal composed of only the positive waveform or the negative waveform of the differential signal, and based on the unipolar signal And detecting the alternating current flowing through the circuit to be measured.

  According to the resistance measuring apparatus of the first aspect, when the resistance value calculated in the resistance calculation process is equal to or greater than a predetermined resistance threshold value or is in an offset updateable state where the resistance value is a negative value, the processing unit is As a result of executing the offset update process and storing the current value of the alternating current flowing through the detection coil in the storage unit as a new offset current value, the resistance value is always calculated using the latest offset current value. The resistance value can always be measured with high accuracy even in a situation where an offset occurs due to a change in environmental conditions such as temperature and humidity and a change in electronic components over time.

  According to the resistance measuring apparatus of claim 2, when the current value flowing through the detection coil calculated in the resistance calculation process is in an offset updateable state where the current value is equal to or less than a predetermined current threshold value, the processing unit performs the offset update process. To store the current value of the alternating current flowing through the detection coil as a new offset current value in the storage unit, the resistance value is always calculated using the latest offset current value, resulting in a change in environmental conditions. In addition, the resistance value can always be measured with high accuracy even in a situation where an offset occurs due to a change with time of the electronic component.

  According to the resistance measuring device of claim 3, when the offset updateable state has continued for a predetermined time or more, that is, when the current value of the alternating current flowing through the detection coil is stable, the offset update processing is performed. As a result, it is possible to avoid the update of the offset current value in a state where the current value of the alternating current is not stable. As a result, the reliability of the resistance value of the circuit to be measured to be measured can be sufficiently improved.

  According to the resistance measuring apparatus of the fourth aspect, the offset current value can be updated at a timing desired by the operator by operating the operation unit.

  The resistance measuring apparatus according to claim 5 includes a first operational amplifier having one end of the detection coil connected to the inverting input terminal, and converts the current flowing through the detection coil into a first voltage signal and outputs the first voltage signal. An amplifier and a second operational amplifier having the other end of the detection coil connected to the inverting input terminal, and converts the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal and outputs the second voltage signal; And a second amplifying unit for extracting a positive signal composed of only positive waveforms of the first voltage signal and the second voltage signal by synchronously detecting the first voltage signal and the second voltage signal in synchronization with the reference signal. A first extracting unit that extracts a negative polarity signal composed of only negative waveforms of the first voltage signal and the second voltage signal by synchronously detecting the first voltage signal and the second voltage signal in synchronization with the reference signal; 2 Extraction unit and differential signal between positive polarity signal and negative polarity signal Current detector is constituted by a differential amplifier for force. Therefore, according to this resistance measuring apparatus, it is possible to avoid the use of a detection coil at a single end and the use of a shunt resistor, and therefore it is possible to ensure good frequency characteristics while maintaining a sufficient detection gain. In addition, the first voltage signal and the second voltage signal in which the first amplifying unit and the second amplifying unit connected to each end of the second winding are inverted in phase with each other based on the current flowing through the detection coil. And the differential amplifier outputs a differential signal between the positive polarity signal and the negative polarity signal generated by each extraction unit based on these signals. Even if is superimposed, common mode noise can be canceled in the differential amplifier. In addition, since each extraction unit synchronously detects the first and second voltage signals in synchronization with the reference signal and extracts the positive polarity signal and the negative polarity signal, the current of the detection coil includes normal mode noise. This normal mode noise can be removed even in the case where

  The resistance measuring device according to claim 6 includes a first operational amplifier having one end of the detection coil connected to the inverting input terminal, and converts the current flowing through the detection coil into a first voltage signal for output. An amplifier and a second operational amplifier having the other end of the detection coil connected to the inverting input terminal, and converts the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal and outputs the second voltage signal; 2 amplifying units, a differential amplifying unit that outputs a differential signal between the first voltage signal and the second voltage signal, and synchronous detection of the differential signal in synchronization with the reference signal, and only the positive side waveform or the negative side of the differential signal The current detection unit includes an extraction unit that extracts a unipolar signal including only a waveform. Therefore, according to this resistance measuring device, use of a single-end detection coil and use of a shunt resistor can be avoided, so that good frequency characteristics can be ensured while maintaining a sufficient detection gain. In addition, the first voltage signal and the second voltage signal in which the first amplifying unit and the second amplifying unit connected to each end of the second winding are inverted in phase with each other based on the current flowing through the detection coil. And the differential amplifier outputs the difference between these signals as a differential signal, so even if common mode noise is superimposed on the current flowing through the detection coil, the differential amplifier Noise can be canceled. In addition, since the extraction unit synchronously detects the differential signal in synchronization with the reference signal and extracts a unipolar signal, even if the normal current noise is included in the current of the detection coil, this normal mode noise Can be removed.

  Hereinafter, the best mode of a resistance measuring apparatus according to the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the resistance measuring apparatus 1 according to the present invention will be described with reference to the drawings.

  A resistance measuring device 1 shown in FIG. 1 includes a clamp portion 2 and a device main body portion 4 connected to the clamp portion 2 via a cable 3 and measures a resistance value Rx of a resistance (loop resistance) of a measurement target circuit 5. It is configured to be possible.

  As shown in FIG. 1, the clamp unit 2 includes an injection clamp unit 11, a detection clamp unit 21, and a housing 31. As an example, in this example, the injection clamp unit 11 includes a first annular core 12 divided into two parts, and a first winding 13 (known number of turns) as an injection coil wound around the first annular core 12. : N1). The detection clamp unit 21 includes a second annular core 22 divided into two parts, and a second winding 23 wound around the second annular core 22 (detection coil (known number of turns: N2) in the present invention). )have. The injection clamp part 11 and the detection clamp part 21 are housed together in a clamp-type resin housing 31 whose tip can be freely opened and closed. The two annular cores 22 are configured to open and close simultaneously. With this configuration, each of the first annular core 12 and the second annular core 22 that are in the open state can be obtained by introducing the wiring 5a that constitutes a part of the circuit to be measured 5 inside the housing 31 in the open state. The wiring 5a is also introduced inside, and in this state, the housing 31 is closed, so that the wiring 5a is simultaneously clamped by the closed first annular core 12 and the second annular core 22, that is, the clamp The wiring 2a is clamped by the part 2. In this case, the wiring 5 a functions as a one-turn winding in the first annular core 12 and the second annular core 22.

  As shown in FIG. 1, the apparatus body 4 includes a voltage injection unit 41, a current detection unit 42, a processing unit 43, and an output unit 44. The voltage injection unit 41 includes a D / A conversion unit 51, a power amplification unit 52, and an injection clamp unit 11. In this case, the D / A conversion unit 51, as shown in FIG. 3, based on the AC waveform data output from the processing unit 43 (in this example, sine wave waveform data whose value makes a round at a constant period T) Dv. An AC voltage Va having a period T (frequency f (= 1 / T)) is generated and output. The power amplifying unit 52 amplifies the AC voltage Va with a predetermined amplification factor to generate an AC voltage V1 having a predetermined voltage value (voltage effective value in this example), and the generated AC voltage V1 is injection-clamped. Applied to the first winding 13 of the section 11. As a result, the inspection AC signal Vx having a predetermined current value (current effective value in this example) is injected into the measurement target circuit 5 through the injection clamp unit 11. In this case, since the wiring 5a functions as a one-turn winding in the first annular core 12 as described above, the voltage value of the test AC signal Vx injected into the circuit to be measured 5 turns the AC voltage V1. A voltage value (Vx = V1 / N1) obtained by dividing by the number N1 is obtained. Further, since the inspection AC signal Vx is generated based on the AC voltage Va, it is a signal synchronized with the AC voltage Va, that is, a signal synchronized with a reference signal Sr described later. Since the wiring 5a functions as a one-turn winding in the second annular core 22, the detection clamp unit 21 detects the alternating current Ix flowing through the circuit to be measured 5, and the detection current (the main current is supplied to the second winding 23). In the present invention, the current I1 (= Ix / N2) flowing through the detection coil is output.

  The current detection unit 42 includes a detection clamp unit 21, a first amplification unit 61, a first bandpass filter (hereinafter also referred to as “first BPF”) 62, a first switching unit 63, a second amplification unit 64, and a second bandpass. Filter (hereinafter also referred to as “second BPF”) 65, second switching unit 66, differential amplifier 67, low-pass filter (hereinafter also referred to as “LPF”) 68, DC amplifier 69 and A / D conversion Part 70 is provided. In this case, the first amplifying unit 61 is connected to one end of the second winding 23, converts the detection current I1 generated at the one end into the first voltage signal Vb1, and outputs the first voltage signal Vb1. For example, as shown in FIG. 2, the first amplifying unit 61 includes a first operational amplifier 61a, resistors 61b, 61c, 61d, and a first capacitor 61e. In this case, the first operational amplifier 61a has an inverting input terminal directly connected to one end of the second winding 23, a resistor 61b connected as a feedback resistor between the inverting input terminal and the output terminal, and a non-inverting input terminal. Is grounded through the resistor 61c (an example in which a reference voltage (ground) is input), and the input detection current I1 is converted into a voltage signal Vb (a signal whose amplitude changes in proportion to the current value of the detection current I1). And output. The first capacitor 61e is disposed downstream of the first operational amplifier 61a (in this example, one end thereof is directly connected to the output terminal of the first operational amplifier 61a), and the DC component contained in the voltage signal Vb is reduced. Remove. The other end of the first capacitor 61e is grounded via a resistor 61d. As a result, the voltage signal Vb from which the DC component is removed in the first capacitor 61e is defined as the first voltage signal Vb1, which is an AC signal whose DC level is regulated to the ground potential (zero volts) and changes around zero volts. 1 is output from the amplifying unit 61.

  The first BPF 62 is configured as a band-pass filter as an example, and removes (filters) the harmonic component of the AC voltage Va included in the input first voltage signal Vb1 as the first voltage signal Vb2. Output. Specifically, the first BPF 62 selectively (mainly, the fundamental frequency component of the AC voltage Va included in the first voltage signal Vb1 (the component of the frequency f, which is also the fundamental frequency component of the test AC signal Vx)). ) The first voltage signal Vb2 is output by passing it through.

  The first switching unit 63 is an example of a first extraction unit in the present invention, and includes a positive side waveform of the first voltage signal Vb2 and a positive side waveform of a second voltage signal Vc2 described later output from the second BPF 65. A positive polarity signal Vd, which is a pulsating flow signal, is extracted and output. Specifically, the first switching unit 63 is configured by, for example, an analog switch, and is synchronized with the reference signal Sr output from the processing unit 43 (the AC voltage Va as shown in FIG. As shown in the figure, the first voltage signal Vb2 and the second voltage signal Vc2 are switched by half a cycle and output (synchronous detection operation) to synchronize with the positive signal Vd. Is output.

  The second amplifying unit 64 is connected to the other end of the second winding 23, converts the detection current I1 generated at the other end into the second voltage signal Vc1, and outputs the second voltage signal Vc1. As an example, as shown in FIG. 2, the second amplifying unit 64 includes a second operational amplifier 64a, resistors 64b, 64c, 64d, and a second capacitor 64e, and is configured the same as the first amplifying unit 61. ing. In this case, the second operational amplifier 64a has an inverting input terminal directly connected to the other end of the second winding 23, a resistor 64b connected as a feedback resistor between the inverting input terminal and the output terminal, and a non-inverting input. The terminal is grounded via the resistor 64c (an example in which a reference voltage (ground) is input), and the input detection current I1 is changed to a voltage signal Vc (the amplitude changes in proportion to the current value of the detection current I1 and the voltage Converted to a signal having a polarity opposite to that of the signal Vb). The second capacitor 64e is disposed after the second operational amplifier 64a (in this example, one end thereof is directly connected to the output terminal of the second operational amplifier 64a), and the DC component contained in the voltage signal Vc is reduced. Remove. The other end of the second capacitor 64e is grounded via a resistor 64d. As a result, the voltage signal Vc from which the DC component is removed in the second capacitor 64e is defined as the second voltage signal Vc1 which is an AC signal whose center level is zero volts with the DC level defined as the ground potential (zero volts). 2 is output from the amplifying unit 64. Here, the detection current I1 generated at the other end of the second winding 23 has a phase inverted from that of the detection current I1 generated at one end. Therefore, the second operational amplifier 64a converts the input detection current I1 into a voltage signal Vc whose phase is inverted from that of the voltage signal Vb and outputs the voltage signal Vc. As a result, the second amplifying unit 64 generates and outputs the second voltage signal Vc1, which is an AC signal that changes around zero volts and whose phase is inverted from that of the first voltage signal Vb1.

  The second BPF 65 is configured as a band pass filter similar to the first BPF 62 as an example, and removes the harmonic component of the AC voltage Va included in the input second voltage signal Vc1 (filtering process) A two-voltage signal Vc2 is output. The second switching unit 66 is an example of a second extraction unit in the present invention, and has the same configuration as the first switching unit 63, and includes a negative-side waveform of the first voltage signal Vb2 and a negative voltage of the second voltage signal Vc2. A negative polarity signal Ve, which is a pulsating flow signal composed of a side waveform, is extracted and output. Specifically, the second switching unit 66 is configured by, for example, an analog switch, and in synchronization with the reference signal Sr, the first voltage signal Vb2 and the second voltage signal Vc2 are half-cycled as shown in FIG. By switching and outputting each time (synchronous detection operation), the negative polarity signal Ve is output.

  The differential amplifier 67 receives the positive signal Vd and the negative signal Ve, calculates the difference between these signals Vd and Ve, amplifies the difference with a predetermined amplification factor, and outputs the difference signal Vf. To do. In this example, as shown in FIG. 2, the differential amplifier 67 includes, as an example, an operational amplifier 67a, a resistor 67b connected between the first switching unit 63 and the non-inverting input terminal of the operational amplifier 67a, a first A resistor 67c connected between the switching unit 66 and the inverting input terminal of the operational amplifier 67a, a resistor 67d connected between the non-inverting input terminal of the operational amplifier 67a and the reference voltage (ground in this example), and A resistor 67e is provided between the inverting input terminal and the output terminal of the operational amplifier 67a. Further, since the difference signal Vf is obtained by amplifying the difference between the positive polarity signal Vd and the negative polarity signal Ve, as shown in FIG. 3, the pulsating flow signal (in this example, synchronized with the polarity signals Vd and Ve). As an example, it is a pulsating signal composed of a positive waveform, but it may be a pulsating signal composed of a negative waveform). Therefore, the differential amplifying unit 67 that calculates and amplifies the difference between the signals Vd and Ve has the above-described configuration and functions as a wideband amplifier. In this case, since the difference signal Vf is generated as described above based on the voltage signals Vb and Vc whose amplitude is proportional to the current value of the detection current I1, the amplitude of the difference signal Vf is also set to the current value of the detection current I1. It is proportional.

  The LPF 68 removes most of the AC component contained in the differential signal Vf and selectively passes the DC component Vdc (see FIG. 3). The direct current amplifier 69 amplifies the direct current component Vdc with a predetermined amplification factor and outputs it as a direct current voltage Vdc1. Further, since the signal amplified by the DC amplifying unit 69 is the DC component Vdc, the DC amplifying unit 69 is not configured as a wideband amplifier unlike the differential amplifying unit 67, and is a narrow band that mainly amplifies the DC component. It is configured as an amplifier. The A / D converter 70 converts the DC voltage Vdc1 into digital data and outputs it as current data Di. Therefore, the current data Di output from the A / D conversion unit 70 becomes data proportional to the current value of the detection current I1, and this current data Di is multiplied by the number of turns (N2) of the second winding 23, and this By dividing the multiplication value by the respective amplification factors of the differential amplifier 67 and the DC amplifier 69, the current value of the AC current Ix flowing through the circuit to be measured 5 is calculated.

  The processing unit 43 includes a CPU and a memory, and executes an offset update process and a resistance measurement process. The memory is composed of a RAM or the like and corresponds to the storage unit in the present invention. The memory has an initial value of the offset current value Ioff used in the resistance measurement process and a resistance threshold value Rth used in the offset update process in advance. It is remembered. Note that the initial value of the offset current value Ioff may be stored in a memory at the manufacturing stage of the resistance measuring device 1, or may not be stored in the memory at the manufacturing stage of the resistance measuring device 1, The processing unit 43 may store the current data Di output from the A / D conversion unit 70 in the memory as an initial value of the offset current value Ioff. The memory is configured to be able to store the latest plurality (5 in this example) of the resistance values Rx calculated by the processing unit 43 in the resistance measurement process.

  The resistance threshold value Rth is a condition for executing the update of the offset current value Ioff in the offset update process. The update of the offset current value Ioff is performed when the clamp unit 2 is closed and the clamp current value Ioff is updated. Even if the part 2 is in a state where nothing is clamped, or even if any wiring is clamped, the wiring is in an open state (a state where it is not in a closed circuit). It should also be executed. Therefore, in order to update the offset current value Ioff when the state is close to the open state, the resistance threshold value Rth is larger than the resistance value Rx calculated by the processing unit 43 when the state is open. A value that is small and exceeds the upper limit value Rmax (for example, 1600Ω when the measurement range is 0Ω or more and 1600Ω or less) (preferably a value that greatly exceeds, twice the upper limit value Rmax) A value of about or more (in this example, 3000Ω). The reason why the value is significantly greater than the upper limit value Rmax is to cause the offset current value Ioff to be updated in a state closer to the open state (a state approximate to the open state). The output unit 44 includes a monitor device as an example, and displays the result of the resistance measurement process.

  Next, the resistance measurement process 100 by the resistance measurement apparatus 1 will be described with reference to FIG. The processing unit 43 repeatedly executes the resistance measurement process 100 at a predetermined cycle (for example, a cycle of several seconds to several tens of seconds).

  In the resistance measurement process 100, the processing unit 43 first starts an application process of the alternating voltage V1 having a predetermined frequency f to the injection clamp unit 11 (step 101). Specifically, in this application process, the processing unit 43 starts outputting the AC waveform data Dv for generating the AC voltage Va having the frequency f to the voltage injection unit 41. As a result, in the voltage injection unit 41, the D / A conversion unit 51 converts the AC waveform data Dv into an AC voltage (analog signal) Va and outputs it, and the power amplification unit 52 converts the AC voltage Va into the AC voltage. Amplified to V 1 and applied to the first winding 13 of the injection clamp unit 11.

  As a result, when the injection clamp unit 11 is in a state of clamping the wiring 5a of the measurement target circuit 5, the inspection AC signal Vx (frequency f) is injected from the injection clamp unit 11 into the measurement target circuit 5. For this reason, the alternating current Ix of the frequency f flows through the measurement target circuit 5 due to the injection of the inspection alternating signal Vx. The processing unit 43 outputs the reference signal Sr whose frequency is defined as f to each of the switching units 63 and 66 at the same time as the cycle of the AC waveform data Dv at the same time as the output of the AC waveform data Dv starts. Also start.

  In a state where the inspection AC signal Vx having the frequency f is injected into the measurement target circuit 5, the current detection unit 42 detects the AC current Ix and generates current data Di. Specifically, in the current detection unit 42, the detection clamp unit 21 detects the alternating current Ix flowing through the circuit 5 to be measured, outputs the detection current I1 from the second winding 23, and the first and second The amplifying units 61 and 64 convert the detected current I1 into first and second voltage signals Vb1 and Vc1 and output them. In this case, the current detection unit 42 differs from the conventional configuration (the configuration in which the second winding 23 as a detection coil is used at a single end and a resistor for current detection is connected in series) in the second winding. Since each end of the line 23 is connected to the inverting input terminals of the operational amplifiers 61a and 64a, there is no need for a current detection resistor (shunt resistor) that may cause a decrease in gain or a deterioration in frequency characteristics. Therefore, good frequency characteristics are ensured while maintaining a sufficient detection gain.

  Next, the first and second BPFs 62 and 65 remove the harmonic components contained in the corresponding voltage signals Vb1 and Vc1, and output them as the first and second voltage signals Vb2 and Vc2, respectively. 66 generates and outputs a positive polarity signal Vd and a negative polarity signal Ve by switching the first and second voltage signals Vb2 and Vc2 in synchronization with the reference signal Sr. In this case, even if normal mode noise is included in the detection current I1, the normal mode noise is removed by the switching operation for the signals Vb2 and Vc2 synchronized with the reference signal Sr by the switching units 63 and 66. The

  Subsequently, the differential amplifier 67 calculates and amplifies the difference between the positive signal Vd and the negative signal Ve and outputs it as a differential signal Vf. Next, the LPF 68 selectively passes the DC component Vdc contained in the difference signal Vf, and the DC amplifier 69 amplifies the DC component Vdc and outputs it as a DC voltage Vdc1. Finally, the A / D conversion unit 70 converts the DC voltage Vdc1 into digital data and outputs it as current data Di to the processing unit 43. In this case, in the current detection unit 42, the first amplifying unit 61 and the second amplifying unit 64 connected to each end of the second winding 23 are connected to the end of the second winding 23 to which each is connected. Based on the generated detection current I1, the first voltage signal Vb1 and the second voltage signal Vc1 whose phases are inverted are output, and the differential amplifying unit 67 selects each switching unit based on the signals Vb1 and Vc1. The difference signal Vf is generated by calculating the difference between the positive polarity signal Vd and the negative polarity signal Ve generated at 63 and 66. For this reason, even if the common mode noise is superimposed on the detection current I1, the noise is canceled by the differential amplifier 67 performing the difference calculation. Therefore, the current data Di includes only the amplified detection current I1 data and the offset current value Ioff generated by the current detection unit 42.

  Next, the processing unit 43 performs a calculation / storage process of the resistance value Rx of the measurement target circuit 5 (step 102). In this calculation / storage process, the processing unit 43 first determines the true current value of the detected current I1 based on the current data Di (the current value that actually flows through the second winding 23; in this example, the current effective value). ) A calculation process for calculating I1re is executed. Specifically, the processing unit 43 first calculates the current value (effective value) I1e of the detection current I1 based on the current data Di and the amplification factors of the differential amplification unit 67 and the DC amplification unit 69. . Next, the processing unit 43 calculates a current value I1re (= I1e−Ioff) for the detected current I1 by subtracting the offset current value Ioff stored in the memory from the current value I1e of the detected current I1.

  Subsequently, the processing unit 43 calculates the voltage effective value Vxe of the AC signal Vx for inspection based on the voltage effective value of the AC voltage V1 and the number of turns (N1) of the first winding 13, and calculates the detected current I1. Current value I1re and the number of turns of the second winding 23 (N2), the current value of the alternating current Ix (current effective value Ixe (= N2 × I1re) in this example) is calculated. Next, the processing unit 43 determines the resistance value Rx (= Vxe) of the measurement target circuit 5 when the frequency of the AC voltage V1 is f based on the calculated effective values Vxe and Ixe of the test AC signal Vx and the AC current Ix. / Ixe) and the calculated resistance value Rx is stored in the memory together with the parameter (current value I1e of the detection current I1) used in calculating the resistance value Rx. As described above, the processing unit 43 repeatedly executes the resistance measurement process 100 at a predetermined cycle, and stores the latest plurality (5 in this example) of the calculated resistance values Rx in the memory. Thereby, the calculation / storage processing of the resistance value Rx is completed.

  Finally, the processing unit 43 causes the output unit 44 to output the calculated latest resistance value Rx (step 103). In this case, when the latest resistance value Rx is within the measurement range, the processing unit 43 causes the output unit 44 to display the resistance value Rx. On the other hand, when the resistance value Rx exceeds the measurement range, the processing unit 43 displays “OF” instead of the calculated resistance value Rx. Further, when the resistance value Rx is below the measurement range (a negative value), the processing unit 43 displays the numerical value “0” instead of the calculated resistance value Rx. Thereby, the resistance measurement process 100 is completed. Note that when the injection clamp unit 11 does not clamp the wiring 5a of the measurement target circuit 5 or when the measurement target circuit 5 is open, the alternating current Ix does not flow through the wiring 5a and is detected. The detection current I1 output from the second winding 23 of the clamp part 21 is substantially zero. Therefore, since the current data Di output from the current detection unit 42 is only data corresponding to the offset current value Ioff in the current detection unit 42, the calculated resistance value Rx is an infinite value.

  Next, the offset update process 110 will be described. In this example, as an example, the processing unit 43 executes the offset update processing 110 every time a new resistance value Rx is calculated.

  In the offset update process 110, the processing unit 43 first reads a plurality of resistance values Rx stored in the memory (step 111), and then executes a comparison process for each resistance value Rx (step 112). In this comparison process, the processing unit 43 reads the resistance threshold value Rth, which is also stored in the memory, and compares it with all the resistance values Rx read out earlier. The processing unit 43 also compares each resistance value Rx with the numerical value “0” (determines whether each resistance value Rx is a negative value).

  As a result of this comparison processing, when all the resistance values Rx are in an offset updateable state, that is, all the resistance values Rx are equal to or greater than the resistance threshold value Rth, the offset updateable state is set, or each resistance When the value Rx is a negative value and the offset update is possible, the processing unit 43 updates the offset value (step 113). Specifically, the processing unit 43 reads the current value I1e of the detected current I1 stored in the memory corresponding to the latest resistance value Rx, and this current value I1e is stored in the memory as a new offset current value Ioff. The offset current value Ioff is updated (overwritten and stored), and the offset update processing 110 is completed. On the other hand, as a result of the comparison processing in step 112, the processing unit 43 is not in the above-described offset updateable state (all resistance values Rx read from the memory are positive values, and at least one of the resistance values is in resistance. If it is less than the threshold value Rth), the offset update processing 110 is completed without proceeding to step 113.

  As described above, the processing unit 43 executes the offset update processing 110 each time a new resistance value Rx is measured, and when all the resistance values Rx stored in the memory are in the above-described offset updateable state. That is, when each resistance value Rx is stable in one of the two offset updateable states described above over a period of calculating a plurality of resistance values Rx, that is, the source of calculation of the resistance value Rx When the current value I1e of the detected current I1 is stable, the current value I1e is updated and stored as a new offset current value Ioff. For this reason, the resistance measuring device 1 always calculates the correct resistance value Rx using the latest offset current value Ioff.

  As described above, according to the resistance measuring apparatus 1, when the calculated resistance value Rx is equal to or greater than the resistance threshold value Rth or is in an offset updateable state where the resistance value Rx is a negative value, the processing unit 43 performs the offset update process. The current value I1e of the detection current I1 flowing through the second winding 23 of the detection clamp unit 21 is updated and stored in the memory as the new offset current value Ioff. Therefore, the latest offset current value Ioff is always used. As a result of the calculation of the resistance value Rx, an offset occurs due to a change in environmental conditions such as temperature and humidity (a change in use environment) and a change over time of the electronic components constituting the amplification unit of the current detection unit 42. Even under such circumstances, the resistance value Rx can always be measured with high accuracy.

  Further, according to the resistance measuring apparatus 1, when all the resistance values Rx stored in the memory are in the above-described offset updateable state, that is, over the period for calculating the plurality of resistance values Rx, the respective resistance values Rx. Is stable in one of the two offset updatable states (when the offset updatable state continues for a predetermined time or more), that is, the detection current I1 that is the basis for calculating the resistance value Rx. Since the offset current value Ioff can be updated with the current value I1e when the current value I1e is stable, the update of the offset current value Ioff when the current value I1e is not stable can be avoided. The reliability of the measured resistance value Rx can be sufficiently improved.

  In addition, according to the resistance measuring apparatus 1, the second winding 23 has the first operational amplifier 61a having one end connected to the inverting input terminal, and the current I1 flowing through the second winding 23 is converted into the first voltage signal Vb1. The first amplifying unit 61 that converts and outputs the current I1 that flows through the second winding 23 with the second operational amplifier 64a having the other end of the second winding 23 connected to the inverting input terminal. A second amplifying unit 64 that converts and outputs the second voltage signal Vc1 whose phase is inverted from that of the voltage signal Vb1 (opposite phase with the first voltage signal Vb1); and the first voltage signal Vb2 in synchronization with the reference signal Sr; A first switching unit 63 for synchronously detecting the second voltage signal Vc2 (switching every half cycle) and outputting a positive signal Vd composed only of the first voltage signal Vb2 and the positive side waveform of the second voltage signal Vc2; The first voltage signal Vb2 is synchronized with the reference signal Sr. And a second switching unit 66 for synchronously detecting the second voltage signal Vc2 (switching every half cycle) and outputting a negative polarity signal Ve composed only of the negative waveform of the first voltage signal Vb2 and the second voltage signal Vc2. And a differential amplifying unit 67 that calculates a difference between the positive signal Vd and the negative signal Ve and outputs the difference signal Vf, thereby forming a current detection unit 42.

  On the other hand, in the conventional resistance measuring apparatus, the detection coil formed in the detection transformer is configured to be grounded at one end (single end), and it is necessary to connect a shunt resistor in parallel to the detection coil. At the same time, it is easily affected by an induced current flowing into the ground due to external induction. In order to reduce this influence, it is necessary to provide a shield for the detection transformer and to ground this shield. However, when such a configuration in which the shield is grounded is employed, there is a problem that it is disadvantageous in terms of safety standards (for example, safety standards such as IEC61010 international safety standards). Therefore, compared with this conventional resistance measuring device, according to this resistance measuring device 1, the use of the second winding 23 at the single end and the use of the shunt resistor can be avoided, so that the safety standard is cleared. Therefore, it is possible to ensure a good frequency characteristic while maintaining a sufficient detection gain.

  In addition, the first amplifying unit 61 and the second amplifying unit 64 connected to each end of the second winding 23 invert the phases of each other based on the detected current I1 generated in the second winding 23. The first voltage signal Vb1 and the second voltage signal Vc1 are output, and the differential amplifier 67 generates the positive signal Vd and the negative signal generated by the switching units 63 and 66 based on the signals Vb1 and Vc1. Since the difference signal Vf is generated by calculating the difference of Ve, the common mode noise is canceled in the difference calculation in the differential amplifier 67 even if the common mode noise is superimposed on the detection current I1. Can do. Further, the switching units 63 and 66 switch the first and second voltage signals Vb2 and Vc2 in synchronization with the reference signal Sr (synchronous detection) to generate the positive signal Vd and the negative signal Ve. Due to the output configuration, even when normal mode noise is included in the detection current I1, this normal mode noise can be removed.

  In addition, this invention is not limited to said structure. For example, in the above configuration, the resistance threshold value Rth with respect to the resistance value Rx is provided to determine whether or not the offset update is possible. Since the current value (effective value) I1e of the flowing detection current I1 and the resistance value Rx are in a corresponding relationship (inversely proportional relationship), it is determined whether or not the offset can be updated based on the current value I1e of the detection current I1. It is also possible to adopt a configuration that performs the determination, that is, a configuration that is equivalent to the above configuration.

  Specifically, the current value I1e when the resistance value Rx calculated based on the current value I1e of the detected current I1 matches the resistance threshold value Rth is stored in the memory as the current threshold value Ith, and the processing is performed. The unit 43 reads the current value I1e of the detected current I1 instead of reading the resistance value Rx from the memory in step 111 of the offset update processing 110 shown in FIG. 5, and in step 112, the read current value I1e It is determined whether or not the threshold value is equal to or smaller than the threshold value Ith, and when the current value I1e is equal to or smaller than the current threshold value Ith (when the offset can be updated), the offset value is updated in step 113.

  Also in this configuration, the resistance value Rx can always be calculated using the latest offset current value Ioff in the same manner as in the configuration using the resistance threshold value Rth. The resistance value Rx can always be measured with high accuracy even in a situation where the temperature changes with time.

  Further, for example, in the above configuration, the current detection unit 42 includes the two switching units 63 and 66. However, like the current detection unit 42A of the resistance measurement apparatus 1A illustrated in FIG. It is also possible to adopt a configuration having Hereinafter, the resistance measuring apparatus 1 </ b> A will be described with reference to FIGS. 6 to 8. The resistance measuring device 1A is configured in the same manner as the resistance measuring device 1 except for the configuration of the current detecting unit 42A other than the switching unit 71. For this reason, the same code | symbol is attached | subjected about the same structure, the overlapping description is abbreviate | omitted, and only the structure of 42 A of different electric current detection parts is demonstrated.

  The current detection unit 42A includes a detection clamp unit 21, a first amplification unit 61, a first BPF 62, a second amplification unit 64, a second BPF 65, a differential amplification unit 67, a switching unit 71, an LPF 68, a DC amplification unit 69, and an A / D conversion. Part 70 is provided. The differential amplifier 67 receives the first voltage signal Vb2 output from the first BPF 62 and the second voltage signal Vc2 output from the second BPF 65, and outputs a differential signal Vg between these signals Vb2 and Vc2. In this example, as an example, the differential amplifier 67 is configured as the same differential amplifier as the resistance measuring device 1 as shown in FIG. With this configuration, the differential amplifier 67 detects the difference between the first voltage signal Vb2 and the second voltage signal Vc2 and outputs the difference signal Vg as shown in FIG. The difference signal Vg is an AC signal whose amplitude is proportional to the current value of the detection current I1.

  The switching unit 71 is an example of the extraction unit in the present invention, and synchronously detects the differential signal Vg in synchronization with the reference signal Sr, and only the positive waveform or only the negative waveform of the differential signal Vg (in this example, As shown in FIG. 8, a unipolar signal Vh composed of only the positive side waveform as an example is extracted and output. Specifically, the switching unit 71 is configured by an analog switch, for example, and in synchronization with the reference signal Sr output from the processing unit 43, as shown in the figure, the difference signal Vg and the reference voltage (ground potential). Are switched by half a cycle and output (synchronous detection operation), thereby outputting a unipolar signal Vh that is a positive polarity signal. The LPF 68 removes most of the AC component contained in the unipolar signal Vh and selectively passes the DC component Vdc (see FIG. 8). As shown in FIG. 6, the direct current amplifier 69 amplifies the direct current component Vdc with a predetermined amplification factor and outputs it as a direct current voltage Vdc1. The A / D converter 70 converts the DC voltage Vdc1 into digital data and outputs it as current data Di. In this case, the current data Di is data representing the detection current I1.

  In the resistance measuring apparatus 1A, similarly to the resistance measuring apparatus 1, the processing unit 43 first calculates the current value I1e of the detected current I1 based on the current data Di and the like, and the offset current value from the current value I1e. The current value I1re for the detection current I1 is calculated by subtracting Ioff, and then the voltage effective value of the test AC signal Vx based on the voltage effective value of the AC voltage V1 and the number of turns (N1) of the first winding 13 Vxe is calculated, and the current value of the alternating current Ix (current effective value Ixe (= N2 × I1re in this example)) based on the calculated current value I1re of the detected current I1 and the number of turns (N2) of the second winding 23. ), And finally, the resistance value Rx (= Vxe / Ixe) of the circuit to be measured 5 based on the calculated effective values Vxe and Ix of the alternating current signal Vx for inspection and the alternating current Ix. It can be calculated. Therefore, also in this resistance measurement apparatus 1A, the configuration of the current detection unit 42A is only different from the current detection unit 42 of the resistance measurement apparatus 1, and the other configuration is the same as that of the resistance measurement apparatus 1. By using the resistance threshold value Rth and the current threshold value Ith, the offset current value Ioff can be updated with the current value I1e of the detection current I1, and the resistance value is always used by using the latest offset current value Ioff. As a result of calculating the value Rx, it is possible to always measure the resistance value Rx with high accuracy even in a situation where the usage environment changes or the electronic component changes over time.

  In addition, the resistance measuring apparatus 1A can be used in the same manner as the resistance measuring apparatus 1 because the use of the second winding 23 at a single end and the use of a shunt resistor can be avoided, so that the resistance measuring apparatus 1A is satisfactory while maintaining sufficient detection gain. Frequency characteristics can be ensured. In addition, since the differential amplifier 67 calculates and outputs the difference signal Vg between the first voltage signal Vb2 output from the first BPF 62 and the second voltage signal Vc2 output from the second BPF 65, the detection current I1 is output. Even if the common mode noise is superimposed, the common mode noise can be canceled in the difference calculation in the differential amplifier 67. Further, since the switching unit 71 detects the difference signal Vg synchronously, the normal mode noise can be removed even when the normal mode noise is included in the detection current I1.

  Further, for example, in the resistance measuring devices 1 and 1A described above, the capacitors 61e and 64e are respectively arranged after the operational amplifiers 61a and 64a, but when the offset voltages of the operational amplifiers 61a and 64a are extremely small, A configuration in which the capacitors 61e and 64e are not provided may be employed. In this configuration, the resistors 61d and 64d can be made unnecessary. Further, the first and second BPFs 62 and 65 are used for improving the measurement accuracy of the resistance value Rx. However, when the required measurement accuracy can be ensured, the first and second BPFs 62 and 65 are provided. It is also possible to adopt a configuration that does not. In addition, as an example of the extraction unit in the present invention, the example using the switching units 63 and 66 and the switching unit 71 has been described above, but a configuration in which synchronous detection is performed using a multiplier may be employed. In addition, the example in which the resistance value Rx is calculated based on the voltage effective value as the voltage value of the test AC signal Vx and the current effective value as the current value of the AC current Ix has been described above. The current value is not limited to the effective current value. Specifically, a configuration in which the resistance value Rx is calculated based on the voltage average value as the voltage value of the AC signal Vx for inspection and the current average value as the current value of the AC current Ix, or the voltage of the AC signal Vx for inspection A configuration for calculating the resistance value Rx based on the peak-to-peak value (voltage amplitude) as the value and the peak-to-peak value (current amplitude) as the current value of the alternating current Ix, and the voltage value of the inspection AC signal Vx It is also possible to adopt a configuration in which the resistance value Rx is calculated on the basis of the voltage peak value and the current peak value as the current value of the alternating current Ix.

  Further, for example, in the resistance measuring devices 1 and 1A, it is determined whether or not the processing unit 43 is in an offset updateable state (each resistance value Rx is greater than or equal to the resistance threshold value Rth or a negative value). It is determined that the offset value is always updated when the offset update is possible. However, as shown in FIGS. 1 and 6, the update signal S1 is generated according to the operation content and the processing unit 43 is updated. As a configuration including the operation unit 45 that outputs the information, the operator can operate the operation unit 45 to update the offset value at a desired timing. The offset update process 120 in this configuration will be described with reference to FIG. The offset update process 120 is different from the offset update process 110 of FIG. 5 only in that it includes step 121. Therefore, the same steps as the offset update process 110 are denoted by the same reference numerals and detailed. The detailed explanation is omitted.

  In the offset update process 120, the processing unit 43 first determines whether or not the update signal S1 is input from the operation unit 45 (step 121), and if not input, the offset update process 120 is completed. On the other hand, when the update signal S1 is input from the operation unit 45 in step 121, all the resistance values Rx can be offset-updated by executing steps 111 to 113 in the same manner as the offset update processing 110. The current value I1e of the detected current I1 stored in the memory corresponding to the latest resistance value Rx is read out, and the current value I1e is stored in the memory as a new offset current value Ioff. The current value Ioff is updated, and this offset update processing 110 is completed. According to the resistance measuring apparatuses 1 and 1A having this configuration, the offset current value Ioff can be updated only when the operator operates the operation unit 45 to output the update signal S1. The offset current value Ioff can be updated at a desired timing.

1 is a configuration diagram showing a configuration of a resistance measuring device 1. FIG. 3 is a circuit diagram of a current detection unit 42 excluding an LPF 68, a DC amplification unit 69, and an A / D conversion unit 70. FIG. FIG. 6 is a waveform diagram for explaining the operation of the current detection unit. 4 is a flowchart for explaining resistance measurement processing by the resistance measuring apparatus 1; It is a flowchart for demonstrating the offset update process by the resistance measuring apparatus. It is a block diagram which shows the structure of 1 A of resistance measuring apparatuses. 4 is a circuit diagram of a current detection unit 42A excluding an LPF 68, a DC amplification unit 69, and an A / D conversion unit 70. FIG. It is a wave form diagram for demonstrating operation | movement of the electric current detection part 42A. It is a flow chart for explaining other offset update processing by resistance measuring devices 1 and 1A.

Explanation of symbols

1,1A Resistance measurement device 5 Circuit to be measured 23 Second winding (detection coil)
41 Voltage injection unit 42, 42A Current detection unit 43 Processing unit 61 First amplification unit 62 First BPF
63 1st switching part 64 2nd amplification part 65 2nd BPF
66 Second switching section 67 Differential amplification section 71 Switching section Ith Current threshold Ix AC current Rth Resistance threshold Rx Resistance S1 Update signal Sr Reference signal Vb1, Vb2 First voltage signal Vc1, Vc2 Second voltage signal Vd Positive Sex signal Ve Negative polarity signal Vf, Vg Differential signal Vh Unipolar signal Vth threshold Vx AC signal for inspection

Claims (6)

A voltage injection unit for injecting an inspection AC signal into the measurement target circuit, a current detection unit for detecting an AC current flowing in the measurement target circuit due to the injection of the inspection AC signal, and a detection coil; A storage unit that stores an offset current value with respect to a current value of the flowing AC current, and calculates a current value that flows through the detection coil by subtracting the offset current value from the current value of the AC current that flows through the detection coil. A resistance measuring device including a processing unit that executes a resistance calculation process for calculating a resistance value of the measurement target circuit based on a current value and a voltage value of the injected AC signal for inspection,
The processing unit includes the alternating current that flows through the detection coil when the resistance value calculated in the resistance calculation process is equal to or greater than a predetermined resistance threshold value or is in an offset updateable state where the resistance value is a negative value. A resistance measurement device that executes an offset update process for storing the current value of the current value in the storage unit as the new offset current value. A voltage injection unit for injecting an inspection AC signal into the measurement target circuit, a current detection unit for detecting an AC current flowing in the measurement target circuit due to the injection of the inspection AC signal, and a detection coil; A storage unit that stores an offset current value with respect to a current value of the flowing AC current, and calculates a current value that flows through the detection coil by subtracting the offset current value from the current value of the AC current that flows through the detection coil. A resistance measuring device including a processing unit that executes a resistance calculation process for calculating a resistance value of the measurement target circuit based on a current value and a voltage value of the injected AC signal for inspection,
The processing unit sets the current value of the alternating current flowing in the detection coil as a new offset current value when the calculated current value is in an offset updateable state in which the current value is equal to or less than a predetermined current threshold value. A resistance measurement device that executes an offset update process stored in the storage unit.   The resistance measurement apparatus according to claim 1, wherein the processing unit executes the offset update process when the offset updateable state continues for a predetermined time or more. An operation unit that generates an update signal according to the operation content and outputs the update signal to the processing unit,
4. The resistance measurement device according to claim 1, wherein the processing unit executes the offset update processing only when the offset update is possible in a state where the update signal is input. 5. The voltage injection unit generates the inspection AC signal synchronized with a reference signal,
The current detection unit includes at least a first operational amplifier in which one end of the detection coil is connected to an inverting input terminal and a reference voltage is input to a non-inverting input terminal, and a current flowing through the detection coil is first A first amplifying unit that converts the voltage into a voltage signal and outputs it; and at least a second operational amplifier in which the other end of the detection coil is connected to the inverting input terminal and the reference voltage is input to the non-inverting input terminal. A second amplifier that converts the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal and outputs the second voltage signal; and the first voltage signal and the second voltage in synchronization with the reference signal A first extraction unit for detecting a signal synchronously and extracting a positive signal composed only of a positive waveform of the first voltage signal and the second voltage signal; and the first extraction unit in synchronization with the reference signal 1 voltage signal and the first A second extraction unit that performs synchronous detection of the voltage signal to extract a negative signal composed of only the negative waveform of the first voltage signal and the second voltage signal; and the positive signal and the negative signal The resistance measuring apparatus according to claim 1, further comprising: a differential amplifier that outputs a differential signal of the signal, and detecting the alternating current flowing through the measurement target circuit based on the differential signal. The voltage injection unit generates the inspection AC signal synchronized with a reference signal,
The current measuring unit includes at least a first operational amplifier in which one end of the detection coil is connected to an inverting input terminal and a reference voltage is input to a non-inverting input terminal, and a current flowing through the detection coil is first A first amplifying unit that converts the voltage into a voltage signal and outputs it; and at least a second operational amplifier in which the other end of the detection coil is connected to the inverting input terminal and the reference voltage is input to the non-inverting input terminal. A second amplifying unit that converts the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal and outputs the second voltage signal; and outputs a difference signal between the first voltage signal and the second voltage signal. A third amplifying unit; and an extracting unit that synchronously detects the differential signal in synchronization with the reference signal and extracts a unipolar signal including only a positive waveform or a negative waveform of the differential signal. The unipolar signal Resistance measuring apparatus according to claim 1 for detecting the alternating current flowing in the measurement target circuit Zui 4.

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