JP2010096652A - Resistance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent large deterioration of measurement precision even under existence of external noises without raising a product price. <P>SOLUTION: A resistance measuring device includes a saturation monitoring part 45 for starting output of a range switching signal S3 when the amplitude of any one signal (for example, a differential signal Vf) among a positive-polarity signal Vd, a negative-polarity signal Ve which are input to a differential amplifier 67 and a differential signal Vf output from the differential amplifier 67 reaches a predetermined threshold. A processing part 43 defines the amplification factor α of the differential amplifier 67 as a normal predetermined amplification factor when the range switching signal S3 is not output while switched and controlled to the predetermined measurement range. The amplification factor α is made to be lower than a predetermined amplification factor when the range switching signal S3 is output while being swithched and controlled to this predetermined measurement range. <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 clips a connection conductor of a measurement circuit network and injects into the measurement circuit a current of a second frequency that can be distinguished from the current of the first frequency flowing in the measurement circuit network (measurement object). And a detection transformer for detecting the two kinds of currents flowing through the measurement circuit network by clipping them to the connecting conductor, and a frequency selective amplifier circuit for extracting a second frequency component from the output of the detection transformer, And a display means for displaying the output of the frequency selective amplifier circuit, and the injection transformer is supplied with an output voltage of the oscillator and injects a current of the second frequency into the measurement network, and a feedback coil. And a feedback loop configured to vary the voltage supplied to the injection coil so that the voltage induced in the feedback coil is controlled to a constant value. 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 measuring apparatus, only the second frequency component is measured by amplifying only the second frequency component by using the frequency selective amplification circuit. In order to make a configuration that does not pass frequency components other than the components, for example, it is necessary to configure a frequency selective amplifier circuit including a steep band pass filter (a band pass filter having a high Q). In order to realize a selective amplification circuit, high-precision components must be used. In this case, since such highly accurate parts are generally expensive, this resistance measuring apparatus has a problem that the product cost increases. Even if the frequency selective amplifier circuit is configured so as to amplify only the second frequency component in this way, when external noise having the same frequency as the second frequency component is mixed, the signal is thereby generated. As a result, there is a problem that the amplification circuit portion in the frequency selective amplification circuit is saturated, and the measurement accuracy is greatly reduced due to the saturation.

  The present invention has been made to solve such problems, and provides a resistance measuring device capable of preventing a significant decrease in measurement accuracy even in the presence of external noise without increasing the product price. Main purpose.

  In order to achieve the above object, the resistance measuring apparatus according to claim 1 is configured to generate a test AC signal and inject the test AC signal into the measurement target circuit, and to inject the test AC signal into the measurement target circuit. A first amplifying unit that is connected to one end of a detection coil that detects an alternating current flowing through the detection coil and converts the current flowing through the detection coil into a first voltage signal, and is connected to the other end of the detection coil and flows through the detection coil A second amplifying unit that converts a current into a second voltage signal having a phase opposite to that of the first voltage signal, and includes only a positive waveform of the two signals based on the first voltage signal and the second voltage signal; An extractor for extracting a positive polarity signal and a negative polarity signal composed only of a negative waveform, a differential amplifying portion for amplifying and outputting a differential signal between the positive polarity signal and the negative polarity signal at a first amplification factor, The amplified differential signal A low-pass filter that selectively passes the included DC component, a DC amplifier that amplifies the DC component with a second amplification factor, and converts the amplified DC component voltage value into digital data and outputs the digital data A current detection unit having an A / D conversion unit, and a current detection unit defined by a multiplication value of the first amplification factor and the second amplification factor based on the digital data output from the current detection unit. A range that determines whether or not the current measurement range is appropriate, and switches to an appropriate measurement range by changing at least one of the first amplification factor and the second amplification factor when the current measurement range is determined to be inappropriate. Switching processing, the digital data detected in the current detection unit in the appropriate measurement range, the first amplification factor and the first in the appropriate measurement range A resistance value calculation process for calculating the current value of the alternating current based on the amplification factor and calculating the resistance value of the circuit to be measured based on the calculated current value and the voltage value of the AC signal for inspection is executed. And a processing unit that performs the first amplification factor when the range switching signal is not input in a state in which the switching is controlled to a predetermined measurement range. When the range switching signal is input in a state where switching to the predetermined measurement range is controlled, the first amplification factor is made lower than the predetermined amplification factor.

  The resistance measuring device according to claim 2 is the resistance measuring device according to claim 1, wherein an amplitude of any one of the positive signal, the negative signal, and the differential signal is defined in advance. A saturation monitoring unit that starts outputting the range switching signal to the processing unit when the threshold value is reached.

  The resistance measurement device according to claim 3 is the resistance measurement device according to claim 1 or 2, wherein the voltage injection unit generates the AC signal for inspection in synchronization with a reference signal, and the extraction unit includes: A first extraction unit for synchronously detecting the first voltage signal and the second voltage signal in synchronism with the reference signal to extract the positive polarity signal; and the first voltage signal in synchronism with the reference signal and the A second extraction unit that extracts the negative polarity signal by synchronously detecting the second voltage signal is provided.

  The resistance measuring device according to claim 4 is a voltage injection unit that generates an AC signal for inspection and injects the AC signal into the measurement target circuit, and an AC current that flows through the measurement target circuit due to the injection of the AC signal for inspection. A first amplifying unit which is connected to one end of a detection coil for detecting the current and converts the current flowing through the detection coil into a first voltage signal; and the current which is connected to the other end of the detection coil and flows through the detection coil A second amplifying unit that converts the first voltage signal into a second voltage signal having a phase opposite to that of the first voltage signal; An extraction unit that inputs the amplified differential signal and extracts a unipolar signal composed of only the positive waveform or the negative waveform of the differential signal, and selectively passes a DC component included in the unipolar signal Low-pass filter, this A current detection unit having a DC amplification unit that amplifies the DC component at a second amplification factor, and an A / D conversion unit that converts the voltage value of the amplified DC component into digital data and outputs the digital data; and the current detection unit The current measurement range is determined based on the digital data output from the current measurement range determined by the multiplication value of the first amplification factor and the second amplification factor. Is detected by the current detection unit in the appropriate measurement range, and a range switching process for changing at least one of the first amplification factor and the second amplification factor to switch to an appropriate measurement range when it is determined that And calculating the current value of the alternating current based on the digital data and the first amplification factor and the second amplification factor in the appropriate measurement range. A resistance measuring device comprising: a processing unit that executes a resistance value calculation process for calculating a resistance value of the circuit to be measured based on a current value that is output and a voltage value of the AC signal for inspection, wherein the processing unit When the range switching signal is not input in the state where the switching to the predetermined measurement range is performed, the first amplification factor is defined as a normal predetermined amplification factor, and the switching control is performed to the predetermined measurement range. When the range switching signal is input in a state in which the first amplification factor is input, the first amplification factor is lowered below the predetermined amplification factor.

  The resistance measuring device according to claim 5 is the resistance measuring device according to claim 4, wherein when the amplitude of the unipolar signal reaches a predetermined threshold value, the processing unit of the range switching signal is sent to the processing unit. Is provided with a saturation monitoring unit for starting the output.

  The resistance measuring device according to claim 6 is the resistance measuring device according to claim 4 or 5, wherein the voltage injection unit generates the inspection AC signal in synchronization with a reference signal, and the extraction unit includes: The unipolar signal is extracted by synchronously detecting the amplified differential signal in synchronization with the reference signal.

  According to a seventh aspect of the present invention, there is provided the resistance measuring device according to the first or fourth aspect, further comprising an operation unit that starts outputting the range switching signal to the processing unit in accordance with an operation content.

  The resistance measurement device according to claim 8 is the resistance measurement device according to any one of claims 1 to 7, wherein the first amplifying unit is connected to an end of the detection coil with an inverting input terminal. A reference voltage is input to the inverting input terminal, and at least a first operational amplifier that converts the current flowing through the detection coil into the first voltage signal and outputs the first voltage signal, and the second amplifying unit includes the detection coil An inverting input terminal is connected to the other end, the reference voltage is input to the non-inverting input terminal, and at least a second operational amplifier that converts the current flowing through the detection coil into the second voltage signal and outputs the second voltage signal is provided. is doing.

  The resistance measuring device according to claim 9 is the resistance measuring device according to claim 8, wherein the resistance measuring device is provided at a stage subsequent to the first operational amplifier and removes a direct current component included in the first voltage signal. And a second capacitive element that is disposed after the second operational amplifier and removes a DC component contained in the second voltage signal.

  A resistance measuring device according to a tenth aspect is the resistance measuring device according to any one of the first to ninth aspects, wherein a first harmonic component is removed from the inspection AC signal included in the first voltage signal. A filter unit; and a second filter unit that removes a harmonic component of the inspection AC signal included in the second voltage signal.

  In the resistance measurement apparatus according to claim 1, when the processing unit is not input the range switching signal in a state where the processing unit is controlled to switch to the predetermined measurement range, the first amplification factor of the differential amplification unit is used as the predetermined predetermined value. When the range switching signal is input in a state where the amplification factor is defined and the switching control is performed to the predetermined measurement range, the first amplification factor is made lower than the predetermined amplification factor.

  Therefore, according to this resistance measurement apparatus, the first amplification factor of the differential amplification unit is set to the predetermined amplification factor by inputting the range switching signal in the predetermined measurement range even in the presence of the external noise. It is possible to avoid the saturation of the differential amplifier due to the extraneous noise being superposed, so that the current detector as a whole can be detected while avoiding a significant decrease in detection accuracy due to the influence of the extraneous noise. The current can be detected, and as a result, a significant decrease in detection accuracy of the resistance value of the circuit to be measured can be avoided. In addition, a steep band-pass filter (high-Q band-pass filter) that requires expensive, high-precision parts can be eliminated, so that the detection accuracy of the resistance value of the circuit under measurement is greatly increased without increasing the product price. Can be prevented.

  According to the resistance measuring apparatus of the second aspect, the saturation monitoring unit is any one of the positive signal and the negative signal input to the differential amplifier and the differential signal output from the differential amplifier. When the external noise is superimposed on any one of the above signals by starting output of the range switching signal to the processing unit when the amplitude of the one signal reaches the threshold value, that is, the external noise In the presence of, it is possible to automatically avoid saturation of the differential amplifying unit and to automatically avoid a significant decrease in detection accuracy.

  According to the resistance measuring apparatus of the third aspect, the voltage injection unit generates the AC signal for inspection in synchronization with the reference signal, and the extraction unit generates the first voltage signal and the second voltage in synchronization with the reference signal. A first extractor for synchronously detecting a voltage signal to extract a positive polarity signal; and a second extractor for extracting a negative polarity signal by synchronously detecting the first voltage signal and the second voltage signal in synchronization with a reference signal. In order to detect the first and second voltage signals in synchronization with the reference signal and extract the positive polarity signal and the negative polarity signal, even when normal mode noise is included in the current of the detection coil, This normal mode noise can be removed.

  In the resistance measurement apparatus according to claim 4, when the processing unit is not input the range switching signal in the state where the processing unit is controlled to switch to the predetermined measurement range, the first amplification factor of the differential amplification unit is used as the predetermined predetermined value. When the range switching signal is input in a state where the amplification factor is defined and the switching control is performed to the predetermined measurement range, the first amplification factor is made lower than the predetermined amplification factor.

  Therefore, according to this resistance measurement apparatus, the first amplification factor of the differential amplification unit is set to the predetermined amplification factor by inputting the range switching signal in the predetermined measurement range even in the presence of the external noise. It is possible to avoid the saturation of the differential amplifier due to the extraneous noise being superposed, so that the current detector as a whole can be detected while avoiding a significant decrease in detection accuracy due to the influence of the extraneous noise. The current can be detected, and as a result, a significant decrease in detection accuracy of the resistance value of the circuit to be measured can be avoided. In addition, a steep band-pass filter (high-Q band-pass filter) that requires expensive, high-precision parts can be eliminated, so that the detection accuracy of the resistance value of the circuit under measurement is greatly increased without increasing the product price. Can be prevented.

  According to the resistance measuring apparatus of claim 5, the saturation monitoring unit starts outputting the range switching signal to the processing unit when the amplitude of the unipolar signal reaches a predetermined threshold value. Therefore, when the external noise is superimposed on the unipolar signal, that is, in the presence of the external noise, the saturation of the differential amplifier is automatically avoided, and the significant decrease in detection accuracy is automatically avoided. Can do.

  According to the resistance measuring apparatus of the sixth aspect, the voltage injection unit generates the AC signal for inspection in synchronization with the reference signal, and the extraction unit generates the amplified difference signal in synchronization with the reference signal. Since the unipolar signal is extracted by synchronous detection, the normal mode noise can be removed even if the current of the detection coil includes normal mode noise.

  Moreover, according to the resistance measuring apparatus of Claim 7, when it was judged that the operator received the influence of an external noise by providing the operation part which outputs a range switching signal to a process part according to operation content. By operating the operation unit, the output of the range switching signal to the processing unit can be started, and resistance measurement is performed while manually avoiding the saturation of the differential amplification unit and, consequently, a significant decrease in detection accuracy. Can do.

  According to the resistance measurement device of the eighth aspect, the first amplifying unit includes a current that flows through the detection coil when the inverting input terminal is connected to one end of the detection coil and the reference voltage is input to the non-inverting input terminal. At least a first operational amplifier that converts and outputs the first voltage signal to the first voltage signal, and the second amplifying unit has an inverting input terminal connected to the other end of the detection coil and a reference voltage input to the non-inverting input terminal. And at least a second operational amplifier that converts the current flowing through the detection coil into a second voltage signal and outputs it, so that the use of a single-end detection coil and the use of a shunt resistor can be avoided. A good frequency characteristic can be ensured while maintaining a good detection gain.

  Further, according to the resistance measuring apparatus of the ninth aspect, even if the offset voltage of each operational amplifier varies due to the capacitive element being arranged at the subsequent stage of each operational amplifier, this offset voltage (DC voltage) ) Can be removed, so that the measurement accuracy of the resistance value of the circuit to be measured can be improved.

  In addition, according to the resistance measuring apparatus of the tenth aspect, since the first and second filter units are disposed, the harmonic components contained in the first voltage signal and the second voltage signal can be removed, and therefore the measurement target The measurement accuracy of the resistance value of the circuit can be further improved.

  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, an output unit 44, and a saturation monitoring unit 45. 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 an example of the first capacitive element according to the present invention, and is disposed at the subsequent stage 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. The DC component included in the voltage signal Vb is removed. 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 a first filter unit in the present invention, and is configured as a band-pass filter as an example, and removes a harmonic component of the AC voltage Va included in the input first voltage signal Vb1 (filtering). Processed) and output as the first voltage signal Vb2. 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. In this case, the first BPF 62 is preferably configured as a band-pass filter having a steep characteristic (a band-pass filter having a very high Q) so that unnecessary bands other than the fundamental frequency component of the AC voltage Va can be removed. However, in order to realize this configuration, it is essential to use high-precision and expensive parts, and the cost of the first BPF 62 increases. For this reason, in the first BPF 62 of this example, since the use of high-precision and expensive parts is unnecessary, as an example, Q is not so high, and the band of a predetermined width having the basic frequency of the AC voltage Va as the center frequency is used. It is configured to allow passage of included signals (passage of not only the fundamental frequency component of the AC voltage Va but also frequency components other than the fundamental frequency component).

  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 an example of the second capacitive element according to the present invention, and is disposed at the subsequent stage of the second operational amplifier 64a (in this example, one end thereof is directly connected to the output terminal of the second operational amplifier 64a. The DC component included in the voltage signal Vc is removed. 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 a second filter unit in the present invention, and is configured as a band-pass filter similar to the first BPF 62 as an example, and the harmonic component of the AC voltage Va included in the input second voltage signal Vc1 is obtained. It is removed (filtered) and output as the second voltage signal Vc2. 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, and uses the set amplification factor (first amplification factor in the present invention) α. This difference is amplified and output as a difference signal Vf. 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 2 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), A resistor 67e and a switch 67f connected in series and connected between the inverting input terminal and the output terminal of the operational amplifier 67a, and a series circuit composed of the resistor 67e and the switch 67f connected in series to each other. A resistor 67g (resistance value lower than the resistance value of the resistor 67e) and a switch 67h are provided in parallel. In addition, one of the switches 67f and 67h selected by the control signal S1 output from the processing unit 43 is turned on, and the other is controlled to be switched off. Therefore, as an example, the differential amplifier 67 of this example functions as a differential amplifier that can change the amplification factor α in two stages by the control signal S1. 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 DC amplifying unit 69 amplifies the DC component Vdc with one amplification factor (second amplification factor in the present invention) β selected from among a plurality of amplification factors, and outputs it as a DC voltage Vdc1. In this case, the DC amplification unit 69 is controlled to switch the amplification factor β by the control signal S2 output from the processing unit 43. 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 amplification factors α and β 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 (both not shown), and executes a resistance measurement process. The output unit 44 includes a monitor device as an example, and displays the result of the resistance measurement process. The saturation monitoring unit 45 predefines the amplitude (voltage value) of any one of the positive signal Vd, the negative signal Ve, and the differential signal Vf (in this example, the differential signal Vf) as shown in FIG. When the threshold value Vth is reached, the output of the range switching signal S3 is started and the output state of the range switching signal S3 is maintained for a predetermined period Ta. Therefore, when the state in which the amplitude of the difference signal Vf reaches the threshold value Vth repeatedly occurs at a time interval shorter than the predetermined period Ta, the saturation monitoring unit 45 continuously outputs the range switching signal S3. become. On the other hand, when the state where the amplitude of the difference signal Vf is less than the threshold value Vth continues for a predetermined period Ta, the saturation monitoring unit 45 stops outputting the range switching signal S3. As an example, the saturation monitoring unit 45 detects that the amplitude of the difference signal Vf has reached the threshold value Vth and outputs a pulse signal, and a pulse signal for a predetermined period using the pulse signal as a trigger. A monostable multivibrator for output (none of which is shown) can be configured, and a pulse signal output from the monostable multivibrator functions as the range switching signal S3. In this case, the threshold value Vth is defined as a voltage value slightly before reaching this voltage value with reference to the voltage value of the differential signal Vf when the differential amplifier 67 is saturated. For example, as shown in FIG. 3, when the difference signal Vf is a positive signal, the threshold value Vth is defined to be a voltage value slightly lower than the maximum voltage value Vmax of the output of the differential amplifier 67.

  Next, the resistance measurement process 100 by the resistance measurement apparatus 1 will be described with reference to FIG. As an example, the differential amplifying unit 67 has an amplification factor α of 3 times (“× 3”: magnification when the resistor 67e is used) and 1/2 times (“× 1/2”: when the resistor 67g is used). The DC amplification unit 69 has a gain β of 2 times (“× 2”), 20 times (“× 20”), and 200 times (“× 200”). It is assumed that switching control is possible in three stages (see FIG. 5). As a result, the amplification factor of the entire current detection unit 42 is set to any one of six types from 1 × (“× 1”) to 600 × (“× 600”) as shown in FIG. It can be set selectively. In this example, when the range switching signal S3 is not output from the saturation monitoring unit 45, the processing unit 43 “600 times (low range), 60 times (first middle range), 6 times (second middle range)”. The detection current I1 is detected while automatically switching the four measurement ranges (first measurement range system) defined by each amplification factor of “1 times (high range)”. Therefore, in the resistance measuring apparatus 1, the first measurement range system is regularly used in preference to the emergency second measurement range system described later. On the other hand, when the range switching signal S3 is output from the saturation monitoring unit 45 (an example when the “range switching signal S3 is output” in the present invention), the low range of 600 times and the high range of 1 time are provided. Sometimes it is the same measurement range, and when it is 60 times (the first middle range, one of the predetermined measurement ranges in the present invention), the amplification factor α is increased from three times (the normal predetermined amplification factor) to ½ times. By reducing the measurement range, the amplification factor α is set to 3 when the measurement range is 100 times (the first middle range) or 6 times (the second middle range, another one of the predetermined measurement ranges in the present invention). By using a 10x (second middle range) instead of the measurement range by reducing the frequency from the normal (predetermined normal amplification factor) to 1 / 2x, "600x, 100x, 10x, 1x" 4 measurement ranges defined by each gain The detection current I1 is detected while automatically switching (second measurement range system).

  In the resistance measurement process 100, the processing unit 43 first executes an injection process for injecting an inspection AC signal Vx having a predetermined frequency f into the measurement target circuit 5 (step 101). Specifically, in this injection 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, 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 saturation monitoring unit 45 determines whether the amplitude of the difference signal Vf generated in the current detection unit 42 has reached the threshold value Vth. Perform detection of no. Further, the current detection unit 42 detects the alternating current Ix in the current measurement range, 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 the difference between the positive signal Vd and the negative signal Ve, and amplifies the difference with an amplification factor α corresponding to the current measurement range and outputs the difference signal Vf. . Next, the LPF 68 selectively passes the DC component Vdc included in the difference signal Vf, and the DC amplifier 69 amplifies the DC component Vdc with an amplification factor β corresponding to the current measurement range, and the DC voltage Vdc1. Output as. 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.

  Next, the processing unit 43 executes a calculation process for calculating a current value (current effective value in this example) of the detected current I1 based on the current data Di (step 102). In this current value calculation process, the processing unit 43 calculates the current value of the detected current I1 based on the current data Di and the current measurement range of the current detection unit 42 (specifically, the amplification factors α and β). To do. Subsequently, the processing unit 43 executes a range switching process (step 103). In this range switching process, the processing unit 43 determines the current value of the calculated detection current I1 and the upper limit threshold and lower limit for range switching that are defined in advance for the measurement range currently set for the current detection unit 42. When the calculated current value of the detected current I1 is equal to or greater than the upper threshold value, the switching control for switching the current measurement range of the current detection unit 42 to the next higher measurement range is also calculated. When the current value of the detected current I1 is smaller than the upper threshold value and larger than the lower threshold value, switching control for maintaining the current measurement range is performed for the current detector 42, and the calculated current value of the detected current I1 is lower limit. When the current value is less than the threshold value, the switching control for switching the current measurement range of the current detection unit 42 to the next measurement range is output to the current detection unit 42 with the control signals S1 and S2. To run each by.

  Specifically, as in the period T1 shown in FIG. 3, when the differential amplifier 67 configured as a wideband amplifier is operating normally in the non-saturated region with almost no influence of external noise, Since the external noise is hardly superimposed on the difference signal Vf and as a result, the difference signal Vf does not reach the threshold value Vth, the saturation monitoring unit 45 does not output the range switching signal S3. In this case, as described above, the processing unit 43 changes the detection current I1 while automatically switching the four measurement ranges defined by the amplification factors of “600 times, 60 times, 6 times, and 1 time”. To detect.

  On the other hand, when the differential amplifier 67 is affected by the external noise and this external noise is superimposed on the differential signal Vf as in the period T2 shown in FIG. The signal Vf may reach the threshold value Vth. In this case, the saturation monitoring unit 45 outputs the range switching signal S3 because the differential amplifier 67 may be saturated. In this state, the processing unit 43 detects the detection current I1 while automatically switching the four measurement ranges defined by the respective amplification factors of “600 times, 100 times, 10 times, and 1 time” as described above. . In this configuration, in the two middle measurement ranges excluding the high range and the low range “100 times, 10 times”, the amplification factor β of the DC amplification unit 69 that is not easily affected by external noise is set to “100 times”. From the magnification of x20 at “60 times” of the corresponding first middle range to the magnification of × 200, and for “10 times”, from the magnification of x2 at “6 times” of the corresponding second middle range to x20 By increasing the magnification, the influence of the offset of the operational amplifier constituting the DC amplification unit 69 increases, and although the detection accuracy is slightly reduced at this point, it is configured as a broadband amplifier and is affected by external noise. The amplification factor α of the easy differential amplifier 67 corresponds to “60 times” of the first middle range corresponding to both “100 times” of the first middle range and “10 times” of the second middle range. And × was reduced to 1/2 magnification from the magnification of × 3 in the "six times" during the second range, it is possible to avoid saturation of the differential amplifier 67 on for larger impact detection accuracy. Therefore, the detection current I1 can be detected while avoiding a significant decrease in detection accuracy due to the saturation of the differential amplifier 67 due to external noise as a whole of the current detection unit 42.

  The processing unit 43 performs switching control for maintaining the current measurement range for the current detection unit 42 after the above-described range switching processing is performed, whether or not the current detection unit 42 is controlled to be switched to an appropriate measurement range. If it is determined that it is not appropriate (step 104), the above steps 102 to 104 are repeatedly executed to switch the measurement range of the current detector 42 to an appropriate measurement range.

  Next, the processing unit 43 executes a calculation process of the resistance value Rx of the measurement target circuit 5 (step 105). In this calculation process, the processing unit 43 first calculates the voltage effective value 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 step 102. The current value (current effective value in this example) of the alternating current Ix is calculated based on the current value (current effective value) of the detected current I1 calculated in step S2 and the number of turns (N2) of the second winding 23. Next, the processing unit 43 calculates the resistance value Rx of the measurement target circuit 5 when the frequency of the AC voltage V1 is f based on the calculated effective values of the AC signal Vx for inspection and the AC current Ix. The resistance value Rx is stored in the memory in correspondence with the frequency f. In this example, as an example, when calculating the resistance value Rx, the processing unit 43 calculates the resistance value Rx a plurality of times, calculates an average of these values (moving average as an example), and calculates the final resistance value Rx. To do. Thereby, the calculation process of the resistance value Rx is completed. Finally, the processing unit 43 causes the output unit 44 to output the calculated resistance value Rx (step 106). Thereby, the resistance measurement process is completed.

  Thus, according to the resistance measuring apparatus 1, when the processing unit 43 is not switched to the predetermined measurement range (two middle ranges) and does not input the range switching signal S3, the amplification factor ( When the range switching signal S3 is input in a state where the first amplification factor α is defined as a regular predetermined amplification factor (three times in the above example) and is switched to a predetermined measurement range (two middle ranges). In this predetermined measurement range, external noise is superimposed on the differential signal Vf by reducing the amplification factor α to a predetermined amplification factor (three times in the above example). In other words, since saturation of the differential amplification unit 67 can be avoided in the presence of external noise, the current detection unit 42 as a whole detects a detection current while avoiding a significant decrease in detection accuracy due to the influence of external noise. I1 can be detected, and as a result, a significant decrease in detection accuracy of the resistance value Rx of the measurement target circuit 5 can be avoided. In addition, a steep band-pass filter (a high-Q band-pass filter) that requires expensive high-precision components can be eliminated, so that the resistance value of the measurement target circuit 5 can be detected significantly without increasing the product price. A reduction in accuracy can be prevented.

  Further, according to the resistance measuring apparatus 1, since the saturation monitoring unit 45 starts outputting the range switching signal S3 to the processing unit 43 when the amplitude of the difference signal Vf reaches the threshold value Vth, the difference signal Vf When the external noise is superimposed on the external noise, that is, in the presence of the external noise, the saturation of the differential amplifying unit 67 can be automatically avoided, and a significant decrease in detection accuracy can be automatically avoided.

  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.

  Further, according to this resistance measuring apparatus 1, even if the offset voltages of the respective operational amplifiers 61a and 64a vary due to the capacitors 61e and 64e being arranged at the subsequent stage of the respective operational amplifiers 61a and 64a, this offset Since the voltage (DC voltage) can be removed, it is possible to improve the measurement accuracy of the effective current value of the alternating current Ix and consequently the resistance value Rx.

  Further, according to the resistance measuring apparatus 1, the harmonic components contained in the first voltage signal Vb1 and the second voltage signal Vc1 can be removed by arranging the BPFs 62 and 65 in the subsequent stages of the capacitors 61e and 64e, respectively. Therefore, the measurement accuracy of the effective current value of the alternating current Ix, and hence the resistance value Rx, can be further improved.

  In addition, this invention is not limited to said structure. For example, in the above configuration, the current detection unit 42 has two switching units 63 and 66, but has one switching unit 71 like the current detection unit 42A of the resistance measuring apparatus 1A shown in FIG. A configuration can also be adopted. 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 an amplification factor β 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.

  Therefore, also in this resistance measuring apparatus 1A, similarly to the resistance measuring apparatus 1, the processing unit 43 calculates the current value (current effective value in this example) of the detected current I1 based on the current data Di, Based on the voltage effective value of the AC voltage V1 and the number of turns (N1) of the first winding 13, the voltage effective value of the AC signal Vx for inspection is calculated, and the calculated current effective value of the detected current I1 and the second winding are calculated. The current value of the alternating current Ix (current effective value in this example) is calculated based on the number of turns (N2) of 23, and finally, the measurement target based on the effective values of the alternating current signal Vx for inspection and the alternating current Ix. The resistance value Rx of the circuit 5 can be calculated.

  Thus, according to this resistance measuring apparatus 1A, when the amplitude of the unipolar signal Vh reaches the threshold value Vth, the saturation monitoring unit 45 starts outputting the range switching signal S3 as shown in FIG. When the range switching signal S3 is output and the range switching signal S3 is not output in the state where the range switching signal S3 is output and the range switching signal S3 is not being output in the state where the range switching signal S3 is output. (1 amplification factor) α is defined as a regular predetermined amplification factor (three times in the above example), and when the range switching signal S3 is output in a state where the switching is controlled to a predetermined measurement range (two middle ranges) In this predetermined measurement range, external noise is superimposed on the unipolar signal Vh by lowering the amplification factor α from the predetermined amplification factor (3 times in the above example) (by 1/2). When you are That is, since the saturation of the differential amplifier 67 can be avoided in the presence of external noise, the detection current I1 can be detected while avoiding a significant decrease in detection accuracy due to the influence of external noise as the entire current detection unit 42A. As a result, a significant decrease in the detection accuracy of the resistance value Rx of the circuit to be measured 5 can be avoided.

  The resistance measuring apparatus 1A also has a unipolar signal Vh because the saturation monitoring unit 45 starts outputting the range switching signal S3 to the processing unit 43 when the amplitude of the unipolar signal Vh reaches the threshold value Vth. When the external noise is superimposed on the external noise, that is, in the presence of the external noise, the saturation of the differential amplifying unit 67 can be automatically avoided, and a significant decrease in detection accuracy can be automatically avoided.

  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.

  In addition, the example in which the amplification factor α is switched to two stages and the amplification factor β is switched to three stages has been described above, but the number of switching stages of the amplification factors α and β is not limited thereto, and the amplification factor α is 3 or 4 Of course, the number of stages may be further increased, and the amplification factor β may be decreased to two stages, or the number of stages may be increased, such as 4, 5,. Further, for 600 times (low range) and 1 time (high range), a configuration that is commonly used both when the range switching signal S3 is not output and when it is output is employed. Each of the amplification factors α, β by switching the amplification factor α, such as a set of medium ranges (a set of measurement ranges of 60 times and 6 times and a set of measurement ranges of 100 times and 10 times corresponding thereto). Of course, the magnification of the measurement range defined by the multiplication value may be switched. In the resistance measuring apparatus 1, the saturation monitoring unit 45 compares the threshold value Vth with the difference signal Vf. However, instead of the difference signal Vf, any one of the positive signal Vd and the negative signal Ve is used. It is also possible to adopt a configuration that compares with one.

  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, the resistance measuring devices 1 and 1A include the saturation monitoring unit 45, and automatically avoids saturation of the differential amplification unit 67 in the presence of external noise, thereby automatically reducing the detection accuracy significantly. However, instead of the saturation monitoring unit 45, an operation unit 46 that generates a range switching signal S3 according to the operation content and outputs it to the processing unit 43, as shown in FIGS. It is also possible to adopt a configuration provided. According to the resistance measuring apparatuses 1 and 1A having this configuration, when an operator is affected by external noise due to, for example, the variation state of the resistance value Rx output to the output unit 44 or the usage environment of the resistance measuring apparatuses 1 and 1A. When the determination is made, it is possible to manually switch from the normal first measurement range system to the emergency second measurement range system by operating the operation unit 46, and the saturation of the differential amplifying unit 67, and hence the great detection accuracy. The resistance measurement can be performed while avoiding the decrease in the resistance.

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. 6 is a waveform diagram for explaining operations of a current detection unit and a saturation monitoring unit 45. FIG. 4 is a flowchart for explaining resistance measurement processing by the resistance measuring apparatus 1; It is explanatory drawing for demonstrating the relationship between each amplification factor (alpha) and (beta) of the resistance measuring apparatus 1, and a measurement range. 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 current detection part 42A and the saturation monitoring part 45. FIG.

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 45 Saturation monitoring unit 46 Operation unit 61 First amplification unit 62 First BPF
63 1st switching part 64 2nd amplification part 65 2nd BPF
66 Second switching unit 67 Differential amplification unit 71 Switching unit Ix AC current Rx Resistance S3 Range switching signal Sr Reference signal Vb1, Vb2 First voltage signal Vc1, Vc2 Second voltage signal Vd Positive polarity signal Ve Negative polarity signal Vf, Vg Differential signal Vh Unipolar signal Vth threshold Vx AC signal for inspection

Claims (10)

A voltage injection unit that generates an AC signal for inspection and injects it into a circuit to be measured;
A first amplifying unit connected to one end of a detection coil for detecting an alternating current flowing in the circuit to be measured due to the injection of the alternating current signal for inspection and converting the current flowing in the detection coil into a first voltage signal; A second amplifier connected to the other end of the detection coil and converting the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal; the first voltage signal; and the second voltage signal. Based on the positive signal composed only of the positive waveform and the negative signal composed only of the negative waveform based on the both signals, the difference signal between the positive signal and the negative signal is extracted. A differential amplification unit that amplifies and outputs with a first amplification factor, a low-pass filter that selectively passes a DC component included in the amplified differential signal, and amplifies the DC component with a second amplification factor A direct current amplifier, and A current detection unit and a A / D converter for converting the voltage value of the DC component which is the amplified digital data,
Based on the digital data output from the current detection unit, it is determined whether or not the current measurement range of the current detection unit is defined by a multiplication value of the first amplification factor and the second amplification factor, and Range switching processing for switching to an appropriate measurement range by changing at least one of the first amplification factor and the second amplification factor when it is determined that the current measurement range is not appropriate, and the current detection in the appropriate measurement range A current value of the alternating current is calculated based on the digital data detected in the unit and the first amplification factor and the second amplification factor in the appropriate measurement range, and the calculated current value and the inspection A resistance measuring device including a processing unit that executes a resistance value calculation process for calculating a resistance value of the circuit to be measured based on a voltage value of an AC signal,
When the processing unit is controlled to switch to a predetermined measurement range and does not input a range switching signal, the processing unit defines the first amplification factor as a normal predetermined amplification factor and switches to the predetermined measurement range. A resistance measurement device that reduces the first amplification factor below the predetermined amplification factor when the range switching signal is input in a controlled state.   When the amplitude of any one of the positive signal, the negative signal, and the differential signal reaches a predetermined threshold value, the output of the range switching signal to the processing unit is started. The resistance measuring device according to claim 1, further comprising a saturation monitoring unit. The voltage injection unit generates the AC signal for inspection in synchronization with a reference signal,
The extraction unit is configured to detect the positive polarity signal by synchronously detecting the first voltage signal and the second voltage signal in synchronization with the reference signal, and the first extraction unit to synchronize with the reference signal. The resistance measuring apparatus according to claim 1, further comprising a second extraction unit configured to synchronously detect one voltage signal and the second voltage signal and extract the negative polarity signal. A voltage injection unit that generates an AC signal for inspection and injects it into a circuit to be measured;
A first amplifying unit connected to one end of a detection coil for detecting an alternating current flowing in the circuit to be measured due to the injection of the alternating current signal for inspection and converting the current flowing in the detection coil into a first voltage signal; A second amplifier connected to the other end of the detection coil and converting the current flowing through the detection coil into a second voltage signal having a phase opposite to that of the first voltage signal; the first voltage signal; and the second voltage signal A differential amplifier that amplifies the differential signal with a first amplification factor and outputs it, and inputs the amplified differential signal to extract a unipolar signal composed of only the positive waveform or the negative waveform of the differential signal Extracting part, a low-pass filter that selectively passes a direct current component included in the unipolar signal, a direct current amplification part that amplifies the direct current component with a second amplification factor, and a voltage value of the amplified direct current component The digital data A current detection unit and a A / D converter for converting and outputting,
Based on the digital data output from the current detection unit, it is determined whether or not the current measurement range of the current detection unit is defined by a multiplication value of the first amplification factor and the second amplification factor, and Range switching processing for switching to an appropriate measurement range by changing at least one of the first amplification factor and the second amplification factor when it is determined that the current measurement range is not appropriate, and the current detection in the appropriate measurement range A current value of the alternating current is calculated based on the digital data detected in the unit and the first amplification factor and the second amplification factor in the appropriate measurement range, and the calculated current value and the inspection A resistance measuring device including a processing unit that executes a resistance value calculation process for calculating a resistance value of the circuit to be measured based on a voltage value of an AC signal,
When the processing unit is controlled to switch to a predetermined measurement range and does not input a range switching signal, the processing unit defines the first amplification factor as a normal predetermined amplification factor and switches to the predetermined measurement range. A resistance measurement device that reduces the first amplification factor below the predetermined amplification factor when the range switching signal is input in a controlled state.   The resistance measuring apparatus according to claim 4, further comprising a saturation monitoring unit that starts outputting the range switching signal to the processing unit when the amplitude of the unipolar signal reaches a predetermined threshold value. The voltage injection unit generates the AC signal for inspection in synchronization with a reference signal,
The resistance measuring apparatus according to claim 4, wherein the extraction unit extracts the unipolar signal by synchronously detecting the amplified differential signal in synchronization with the reference signal.   The resistance measuring apparatus according to claim 1, further comprising an operation unit that starts outputting the range switching signal to the processing unit in accordance with an operation content. The first amplifying unit converts the current flowing through the detection coil into the first voltage signal when an inverting input terminal is connected to one end of the detection coil and a reference voltage is input to the non-inverting input terminal. Having at least a first operational amplifier for output;
The second amplifying unit has an inverting input terminal connected to the other end of the detection coil, and the reference voltage is input to a non-inverting input terminal to convert the current flowing through the detection coil into the second voltage signal. The resistance measuring device according to claim 1, further comprising at least a second operational amplifier that outputs the same. A first capacitive element disposed downstream of the first operational amplifier to remove a direct current component contained in the first voltage signal;
The resistance measuring apparatus according to claim 8, further comprising: a second capacitive element that is disposed downstream of the second operational amplifier and removes a DC component included in the second voltage signal. A first filter section for removing harmonic components of the inspection AC signal included in the first voltage signal;
The resistance measuring apparatus according to claim 1, further comprising: a second filter unit that removes a harmonic component of the AC signal for inspection contained in the second voltage signal.

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