Measurement cables, measurement systems, and measurement methods

Abstract

This invention provides a highly noise-resistant measurement cable, a highly accurate measurement system using the said measurement cable, and a measurement method. [Solution] A measuring cable for electrically connecting a measuring device and an object to be measured, comprising a triaxial cable 30 having a coaxially arranged internal conductor 31, a first external conductor 35 and a second external conductor 37, and insulators 33 and 36 arranged between the internal conductor and the first external conductor and between the first external conductor and the second external conductor, and a high-side terminal on the measuring device side and a high-side terminal on the object to be measured side electrically connected to each end of the internal conductor, a low-side terminal on the measuring device side electrically connected to one end of the first external conductor and one end of the second external conductor, and a low-side terminal on the object to be measured side electrically connected only to the other end of the first external conductor.

Description

【Technical Field】 【0001】 The present invention relates to a measurement cable, a measurement system, and a measurement method, and particularly to a measurement cable for electrically connecting between a measurement object and a measuring device of a measurement system, a measurement system for measuring electrical characteristics of a measurement object using the measurement cable, and a measurement method. 【Background Art】 【0002】 When measuring the electrical characteristics of a measurement object (hereinafter, also referred to as "DUT: Device Under Test"), a measurement cable for electrically connecting between the DUT and the measuring device is used. Patent Document 1 discloses an example of a measurement cable corresponding to the measurement of electrical characteristics. 【0003】 The measurement cable includes a pair of wirings, a high-side wiring for transmitting a detection signal detected by the DUT and a low-side wiring connected to the ground. For example, there is a twisted pair cable 90 formed by twisting two single-wire cables 91 and 92 as shown in FIG. 9. The single-wire cable 91 is a high-side wiring, and the single-wire cable 92 is a low-side wiring. The twisted pair cable 90 can cancel out currents generated by magnetic fluxes generated by currents flowing through the single-wire cables and magnetic fluxes from the outside world. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Laid-Open No. 8-220135 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, single-wire cables, which have a configuration in which the signal line is surrounded by an insulating or abrasion-resistant layer, have the problem of low noise immunity for the following reasons. Specifically, because there is no shielding for the signal line, it is susceptible to noise from electrostatic coupling from the outside. In addition, if there is a difference in the intersecting magnetic flux between regions where the arrangement of single-wire cables 91 and 92 is reversed (regions A and B shown in Figure 9), it will be susceptible to noise due to the magnetic flux. Furthermore, if the cable is subjected to vibration or bent, the current generated by friction between the conductor constituting the signal line and the insulating layer becomes noise. The effects of noise due to these various factors become greater as the length of the cable increases. 【0006】 Furthermore, using measurement cables with low noise immunity to measure the impedance of low-impedance objects in environments with high external noise can lead to a significant deterioration in measurement accuracy. An example of such measurement is the impedance measurement of water electrolysis cells in a water electrolysis apparatus. A water electrolysis apparatus is a device that supplies direct current to water electrolysis cells to electrolyze water and produce hydrogen. In order to produce a large amount of hydrogen from a single cell, it is equipped with large-area cells, which inevitably makes the water electrolysis apparatus large. Therefore, when measuring the impedance of a water electrolysis cell, the measurement cable connecting the water electrolysis cell and the impedance measuring device must be long. In addition, because a water electrolysis apparatus has a configuration in which many water electrolysis cells are stacked in order to produce a large amount of hydrogen, a high-voltage, high-current direct current is required for driving. For this reason, a water electrolysis apparatus is equipped with a power supply that rectifies AC voltage to generate direct current. The generated direct current has a lot of current ripple, and the power supply itself also generates a lot of noise. Therefore, measurements must be performed in a noisy environment. Furthermore, because the water electrolysis cell, the object being measured, has a low impedance of only a few hundred microohms, the voltage of the detection signal generated by the measurement current is small. Therefore, it is difficult to ensure a high signal-to-noise ratio (SNR). 【0007】 In environments with high levels of external noise, there has been a need for measurement systems and methods that can accurately measure the impedance of objects with low impedance. The present invention aims to provide a measurement cable with high noise immunity, a highly accurate measurement system using the measurement cable, and a measurement method. [Means for solving the problem] 【0008】 The above problem can be solved by a measuring cable (20) or the like for electrically connecting a measuring device (40, 40', 40") and an object to be measured (10), comprising a triaxial cable (30) having a coaxially arranged internal conductor (31), a first external conductor (35), and a second external conductor (37), and insulators (33, 36) arranged between the internal conductor (31) and the first external conductor (35) and between the first external conductor (35) and the second external conductor (37); a measuring cable (20) or the like having a high-side terminal (24) on the measuring device side and a high-side terminal (22) on the object to be measured side electrically connected to each end of the internal conductor (31), a low-side terminal (25) on the measuring device side electrically connected to one end of the first external conductor (35) and one end of the second external conductor (37), and a low-side terminal (23) on the object to be measured side electrically connected only to the other end of the first external conductor (35). 【0009】 Due to capacitive coupling between the external noise source and the measurement cable, a noise-induced current flows through the second outer conductor, which is located on the outside of the two outer conductors. By electrically connecting the first and second outer conductors at only one end of the cable, it is possible to prevent a potential difference from occurring between both ends of the first outer conductor, thereby suppressing measurement errors caused by this potential difference. Furthermore, by adopting a coaxial shielding structure, it is possible to prevent magnetic field-derived noise (noise originating from the difference between the magnetic fluxes intersecting in region A and region B in Figure 9), which is a problem with twisted pair cables. This makes it possible to provide a measurement cable with high noise immunity. 【0010】 It is desirable to further include conductive layers (32, 34) disposed between the inner conductor (31) and the insulator (33), and between the insulator (33) and the first outer conductor (35). By adding a conductive layer, preferably a flexible conductive film, between the conductor (inner conductor, first outer conductor) and the insulator, friction between the conductor and the insulator can be reduced, and noise caused by friction can be suppressed. This makes it possible to provide a measurement cable with high noise immunity. 【0011】 Furthermore, the above problem is solved by comprising an AC power supply (15) that applies an AC current to the object to be measured (10), a measuring device (40, 40', 40") that measures the electrical characteristics of the object to be measured (10) based on a detection signal when an AC current is applied to the object to be measured (10), and a measuring cable (20) according to claim 1 or 2 that transmits the detection signal from the object to be measured (10) to the measuring device (40, 40', 40"), The high-side terminal (24) of the measuring cable (20) on the measuring device side is electrically connected to the input terminal (41) of the input circuit (44) of the measuring device (40, 40', 40"), and the low-side terminal (25) of the measuring cable (20) on the measuring device side is electrically connected to the ground of the input circuit (44) of the measuring device (40, 40', 40"), and the high-side terminal (22) and low-side terminal (23) of the measuring cable (20) on the object to be measured side are electrically connected to the object to be measured (10) to detect the detection signal, which can be resolved by a measurement system (14). 【0012】 By using the aforementioned noise-resistant measurement cable to transmit detection signals from the object to be measured to the measuring device, and by electrically connecting the first low-side terminal, where the first and second outer conductors are electrically connected, to the ground of the input circuit of the measuring device, the current caused by noise flowing through the second outer conductor is directed to ground, thereby reducing the effects of noise and providing a highly accurate measurement system. In particular, it is possible to provide a measurement system that can accurately measure the impedance of objects with low impedance, even in environments with a lot of external noise. 【0013】 Furthermore, "electrical characteristics" include characteristics that can be measured based on the voltage drop across the object being measured, which are caused by the applied alternating current, such as impedance, amplitude, phase, and their frequency characteristics. 【0014】 The object to be measured (10) is a water electrolysis cell, and the electrical characteristic is preferably the impedance of the water electrolysis cell. The water electrolysis cell of a water electrolysis device has a low impedance, and a water electrolysis device in operation is large and generates a lot of noise. The measurement system according to the present invention makes it possible to accurately measure the impedance of a water electrolysis cell even in environments with a lot of external noise and where the use of long measurement cables is unavoidable. 【0015】 Furthermore, it is desirable that the housing (46) of the measuring device (40, 40', 40") be grounded, and that the input circuit (44) of the measuring device (40, 40', 40") be electrically isolated from the housing (46). A current caused by noise flows through capacitive coupling due to parasitic capacitance between the housing and the input circuit. By preventing this current from flowing to the first external conductor, the effects of noise can be reduced, and a highly accurate measurement system can be provided. 【0016】 Furthermore, the above problem is solved by electrically connecting the object to be measured (10) and the measuring device (40, 40', 40") using the measuring cable (20) described in claim 1 or 2 (80) (84) applying an alternating current to the object to be measured (10) (85) measuring the electrical characteristics of the object to be measured (10) based on a detection signal detected by the measuring cable (20) when the alternating current is applied to the object to be measured (10), wherein the connecting step (80) is performed by connecting the high-side terminal (2) of the measuring device on the measuring cable (20) side. 4) The problem can also be solved by a measurement method that includes the steps of: (81) electrically connecting the input terminal (41) of the input circuit (44) of the measuring device (40, 40', 40"); (82) electrically connecting the low terminal (25) on the measuring device side of the measuring cable (20) to the ground of the input circuit (44) of the measuring device (40, 40', 40"); and (83) electrically connecting the high terminal (22) on the object to be measured side of the measuring cable (20) and the low terminal (23) on the object to be measured side to the object to be measured (10). 【0017】 By using the aforementioned noise-resistant measurement cable to transmit detection signals from the object to be measured to the measuring device, and by electrically connecting the first low-side terminal, where the first and second outer conductors are electrically connected, to the ground of the input circuit of the measuring device, the current caused by noise flowing through the second outer conductor is directed to ground, thereby reducing the effects of noise and providing a highly accurate measurement method. In particular, this method can provide a measurement method that can accurately measure the impedance of objects with low impedance, even in environments with a lot of external noise. [Effects of the Invention] 【0018】 According to the present invention, it is possible to provide a measurement cable with high noise immunity, a highly accurate measurement system using the measurement cable, and a measurement method. [Brief explanation of the drawing] 【0019】 [Figure 1]This is an example of the connection configuration between the measurement system according to the present invention and the measurement object. [Figure 2] This is a schematic configuration diagram of the measurement cable according to the present invention. [Figure 3] This is a schematic cross-sectional view of a triaxial cable. [Figure 4] This is an explanatory diagram showing the electrical connection between the measurement system and the measurement object. [Figure 5] This is an equivalent circuit of the measurement system. [Figure 6] This is a flowchart of the measurement method according to the present invention. [Figure 7] This is another example of the connection configuration between the measurement system according to the present invention and the measurement object. [Figure 8] This is yet another example of the connection configuration between the measurement system according to the present invention and the measurement object. [Figure 9] This is a schematic configuration diagram of a twisted pair cable. 【Embodiments for Carrying Out the Invention】 【0020】 The measurement system 14, which is an embodiment of the measurement system according to the present invention, will be described while referring to FIG. 1. The measurement system 14 is a measurement system that measures the impedance, which is one of the electrical characteristics of the water electrolysis cell 10 of a water electrolysis device. FIG. 1 shows a schematic configuration diagram of the state in which the measurement system 14 is connected to the water electrolysis cell 10 of a water electrolysis device, which is the device under test (DUT), and an analyzer 16. The water electrolysis device includes a large number of water electrolysis cells 10 and a DC power supply 12 electrically connected to the water electrolysis cells 10, and is a device that supplies a driving DC current from the DC power supply 12 to the water electrolysis cells 10 to electrolyze water and generate hydrogen. 【0021】 The measurement system 14 measures the impedance of the water electrolysis cell 10 in its operating state, that is, in the state where a DC current is supplied to the water electrolysis cell 10 and electrolysis of water is being performed. To this end, the measurement system 14 applies a measurement AC current to the water electrolysis cell 10 by applying a measurement AC current to the drive circuit 17 to which the water electrolysis cell 10 and the DC power supply 12 are connected. The voltage generated between both terminals of the water electrolysis cell 10 when an AC current is applied to the water electrolysis cell 10 is detected as a detection signal by the measurement cable 20. Based on the detection signal and the amount of AC current flowing through the water electrolysis cell 10 detected by the current sensor 11, the impedance of the water electrolysis cell 10 is measured. The measured impedance of the water electrolysis cell 10 is transmitted to the measurement device 40 of the measurement system 14 and / or to the analysis device 16, where numerical processing and analysis processing are performed. The analysis device 16 consists of a computer with a processor, and performs numerical processing and analysis processing by executing processing applications on the processor. Furthermore, the analyzer 16 may be configured to transmit signals to the measurement system 14 for setting and controlling the frequency, voltage, current amount, waveform, and application timing of the AC current to be measured, as well as for setting and controlling the detection timing and sampling frequency of the detection signal. 【0022】 The measurement system 14 comprises an AC power supply 15, a source cable 13, a current sensor 11, a measurement cable 20, and a measurement device 40. The AC power supply 15 generates an AC current to be applied to the DUT 10 for impedance measurement. The source cable 13 electrically connects the AC power supply 15 to the drive circuit 17, supplying the AC current for measurement to the drive circuit 17, and applying the AC current for measurement to the DUT 10 via the drive circuit 17. The frequency, voltage, current amount, waveform, and application timing of the AC current applied to the DUT 10 may be determined using settings pre-stored in the AC power supply 15, or they may be controlled according to a signal from the analysis device 16. 【0023】 The current sensor 11 detects the amount of AC current flowing through the drive circuit 17, i.e., the amount of AC current flowing through the DUT 10, and transmits a signal indicating the detected amount of AC current to the measuring device 40. The current sensor 11 is preferably a non-contact type current sensor, such as a magnetic current sensor, but may also be a contact type current sensor. The measuring cable 20 contacts both terminals of the DUT 10 and is electrically connected to the measuring device 40. It detects the voltage between the two terminals of the DUT 10 as a detection signal and transmits the detection signal from the DUT 10 to the measuring device 40. The measuring device 40 measures the impedance, one of the electrical characteristics of the DUT 10, based on the detection signal and the amount of AC current. The detection timing and sampling frequency of the detection signal may be set using settings pre-stored in the measuring device 40, or they may be set according to the signal from the analysis device 16. 【0024】 Next, the measuring cable 20, which is one of the components of the measurement system 14 and is an embodiment according to the present invention, will be described with reference to Figures 2 and 3. Figure 2 is a schematic diagram of the measuring cable 20, and Figure 3 is a schematic cross-sectional view of the triaxial cable 30 that constitutes the measuring cable 20. 【0025】 The measurement cable 20 comprises a triaxial cable 30, a high-side terminal 24 and a low-side terminal 25 electrically connected to one end of the triaxial cable 30 on the measuring device 40 side, and a high-side terminal 22 and a low-side terminal 23 electrically connected to the other end of the triaxial cable 30 on the DUT 10 side. The high-side terminal 22 and the low-side terminal 23 on the DUT 10 side need to be in contact with both ends of the DUT 10 in order to detect the detection signal, and therefore need to have a structure that allows them to be positioned independently. For this reason, the high-side terminal 22 and the low-side terminal 23 on the DUT 10 side are connected to the triaxial cable 30 via corresponding straight cables 21a and 21b, respectively. The straight cables 21a and 21b are single-wire cables, i.e., signal lines made of conductors, with an insulating layer or abrasion layer covering the perimeter. To prevent deterioration of noise immunity, it is desirable that the lengths of the straight cables 21a and 21b be short. 【0026】 The triaxial cable 30 consists of an inner conductor 31, an inner conductive layer 32, an insulator 33, a second conductive layer 34, an inner outer conductor 35, an insulating primary sheath 36, an outer outer conductor 37, and an insulating secondary sheath 38, all arranged coaxially from the inside outwards. The inner conductor 31 is made of copper wire, and the inner outer conductor 35 and outer outer conductor 37 are made of braided copper wire. The inner conductive layer 32, located between the inner conductor 31 and the insulator 33, and the outer conductive layer 34, located between the insulator 33 and the inner outer conductor 35, are made of flexible conductive films to reduce friction between the inner conductor 31 and the insulator 33, and between the insulator 33 and the inner outer conductor 35, when the cable 30 is subjected to vibration or bending. In other words, the inner conductive layer 32 is made of a more flexible material and / or structure than one or both of the inner conductor 31 and the insulator 33. Furthermore, the outer conductive layer 34 is made of a more flexible material and / or structure than one or both of the insulator 33 and the inner outer conductor 35. Note that since the conductive layers 32 and 34 are layers intended for friction reduction rather than signal transmission or shielding, they may be made of a material and / or structure with lower conductivity than the inner conductor 31 and the outer conductors 35 and 37. 【0027】 One end of the inner conductor 31 on the measuring device 40 side is electrically connected to the high-side terminal 24 on the measuring device 40 side. The other end of the inner conductor 31 on the DUT10 side is electrically connected to the high-side terminal 22 on the DUT10 side. Also, one end of the inner outer conductor 35 on the measuring device 40 side is electrically connected to the low-side terminal 25 on the measuring device 40 side. The other end of the inner outer conductor 35 on the DUT10 side is electrically connected to the low-side terminal 23 on the DUT10 side. One end of the outer outer conductor 37 on the measuring device 40 side is electrically connected to the low-side terminal 25 on the measuring device 40 side, but the other end on the DUT10 side is open. In other words, the low-side terminal 23 on the DUT10 side is electrically connected only to the DUT10 side end of the inner outer conductor 35. 【0028】 The detection signal detected at the high-side terminal 22 and low-side terminal 23 on the DUT10 side is transmitted to the measuring device 40 through the inner conductor 31 and the inner outer conductor 35. Although a current due to noise flows through the outer outer conductor 37, since the inner outer conductor 35 and the outer outer conductor 37 are electrically connected at only one end, no potential difference is generated between the two ends of the inner outer conductor 35 through which the detection signal is transmitted, thereby suppressing measurement errors caused by potential differences. Furthermore, since the triaxial cable 30 has a coaxial shield structure, it can prevent magnetic field-derived noise (noise originating from the difference between the magnetic fluxes that intersect in region A and region B in Figure 9), which is a problem with twisted pair cables. This makes it possible to provide a measurement cable 20 with high noise immunity. 【0029】 Next, the electrical connections of the measurement system 14 will be explained based on Figures 4 and 5. Figure 4 is an explanatory diagram showing the electrical connections of an example connection configuration between the measurement system 14 and the DUT 10 shown in Figure 1, and Figure 5 is the equivalent circuit of the measurement system 14, including parasitic capacitance and coupling capacitance. 【0030】 The measuring device 40 of the measuring system 14 comprises a housing 46 that is grounded E, an input circuit 44 that is electrically connected to the measuring cable 20 and electrically isolated from the housing 46, and a measuring circuit 45 that is electrically connected to the input circuit 44 and the current sensor 11. 【0031】 The input circuit 44 includes a high-side input terminal 41, a low-side input terminal 42, and a buffer circuit 43. The high-side input terminal 41 is electrically connected to the high-side terminal 24 on the measuring device side of the triaxial cable 30. The low-side input terminal 42 is electrically connected to the low-side terminal 25 on the measuring device side of the triaxial cable 30. The input circuit 44 receives a detection signal indicating the voltage between both terminals of the DUT 10, transmitted via the measurement cable 20, at the high-side input terminal 41 and the low-side input terminal 42. At this time, the low-side input terminal 42 is connected to ground G as a reference voltage. Since the input circuit 44 is isolated from the housing 46, ground G is not grounded. The received detection signal is buffered by the buffer circuit 43 and output to the measurement circuit 45. The buffer circuit 43 is composed of an inverting amplifier circuit using an operational amplifier. The measurement circuit 45 determines the impedance, one of the electrical characteristics of the DUT10, based on the signal received from the input circuit 44, i.e., the detection signal indicating the voltage between both terminals of the DUT10 when a measurement AC current is applied to the DUT10, and the signal received from the current sensor 11, i.e., the signal indicating the amount of AC current flowing through the DUT10 when a measurement AC current is applied to the DUT10. 【0032】 The high-side terminal 22 of the measurement cable 20 on the DUT10 side is in contact with one end of the DUT10, and the low-side terminal 23 on the DUT10 side is in contact with the other end of the DUT10. As a result, the measurement cable 20 detects the voltage generated between both terminals of the DUT10 as a detection signal and transmits the detection signal to the measuring device 40. Specifically, the signal detected at the high-side terminal 22 on the DUT10 side is transmitted to the high-side input terminal 41 of the measuring device 40 via the straight cable 21a, the inner conductor 31, and the high-side terminal 24 on the measuring device 40 side. The signal detected at the low-side terminal 23 on the DUT10 side is transmitted to the low-side input terminal 42 of the measuring device 40 via the straight cable 21b, the inner outer conductor 35, and the low-side terminal 25 on the measuring device 40 side. 【0033】 If a noise source 50 that generates a large amount of noise, such as the DC power supply 12 used to drive the water electrolysis device, is located near the measurement system 14, noise enters the outer conductor 37 of the triaxial cable 30 due to capacitive coupling between the external noise source 50 and the outer conductor 37. In the equivalent circuit of Figure 5, this state is shown as the coupling capacitance 51 due to capacitive coupling. Since the magnitude of the noise entering the outer conductor 37 from the noise source 50 varies depending on the location, a potential difference is generated in the outer conductor 37. 【0034】 The outer conductor 37 is electrically connected to the ground G of the input circuit 44 via the low-side terminal 25 and low-side input terminal 42 on the measuring device 40 side. Although the input circuit 44 of the measuring device 40 and the housing 46 are electrically insulated, a parasitic capacitance 52 exists between them. Current caused by noise containing a large AC component is grounded E via the parasitic capacitance 52. That is, a closed circuit 53 is formed as shown by the dashed line in Figure 5. Current caused by noise entering the outer conductor 37 from the external noise source 50 flows through this closed circuit 53. 【0035】 On the other hand, the inner outer conductor 35 and the outer outer conductor 37 are electrically connected at only one end, and the other end of the outer outer conductor 37 is open. Therefore, current caused by noise flowing through the outer outer conductor 37 does not flow into the inner outer conductor 35. As a result, the potential difference generated in the outer outer conductor 37 due to external noise does not affect the inner outer conductor 35 through which the detection signal is transmitted, and no potential difference occurs between the potential on the DUT 10 side of the measurement cable 20 (potential at point A in Figure 5) and the potential on the measurement device 40 side (potential at point B). As a result, measurement errors caused by potential differences are prevented, and a highly accurate measurement system can be provided. 【0036】 Next, the operation of the measurement system 14, which is an embodiment of the measurement method according to the present invention, will be explained with reference to the flowchart in Figure 6. 【0037】 First, the DUT10 and the measuring device 40 are electrically connected using the measuring cable 20 (step 80). More specifically, the high-side terminal 24 of the measuring cable 20 on the measuring device 40 side is electrically connected to the high-side input terminal 41 of the input circuit 44 on the measuring device 40 side (step 81). Also, the low-side terminal 25 of the measuring cable 20 on the measuring device 40 side is electrically connected to the low-side input terminal 42 of the input circuit 44 on the measuring device 40 side. This electrically connects the low-side input terminal 42 of the input circuit 44 on the measuring device 40 side to the ground G of the input circuit 44 (step 82), forming the closed circuit 53 shown in Figure 5. Furthermore, the high-side terminal 22 of the measuring cable 20 on the DUT10 side is electrically connected to one end of the DUT10, and the low-side terminal 23 on the DUT10 side is electrically connected to the other end of the DUT10 (step 83). Furthermore, the AC power supply 15 and the drive circuit 17 are electrically connected by a source cable 13 so that the AC current for measurement flows through the DUT 10. In addition, a current sensor 11 is installed in the drive circuit 17 near the DUT 10 to detect the amount of AC current flowing through the DUT 10. 【0038】 Next, an AC current for measurement is applied to the DUT10 from the AC power supply 15 via the drive circuit 17 (step 84). Then, based on the detection signal detected by the measurement cable 20 when the AC current is applied to the DUT10, the impedance, one of the electrical characteristics of the DUT10, is measured (step 85). More specifically, the voltage between both terminals of the DUT10 when the AC current for measurement is applied to the DUT10 is detected as a detection voltage by the measurement cable 20 and transmitted to the measuring device 40. The measuring device 40 acquires the detection signal via the measurement cable 20. At the same time, the measuring device 40 acquires the amount of AC current flowing through the DUT10 when the AC current for measurement is applied to the DUT10 from the current sensor 11. The measurement circuit 45 of the measuring device 40 determines the impedance of the DUT10 based on the acquired detection signal and the amount of AC current. The measured impedance is transmitted to the processing unit of the measuring device 40 and / or to the analysis device 16, where numerical processing and analysis are performed by the processing application. 【0039】 In this way, to transmit the detection signal from the DUT 10 to the measuring device 40, the above-mentioned noise-resistant measuring cable 20 is used, and the low-side terminal 25 on the measuring device 40 side, where the inner outer conductor 35 and the outer outer conductor 37 are electrically connected, is electrically connected to the ground G of the input circuit 44 of the measuring device 40. By allowing the current caused by noise flowing through the outer outer conductor 37 to flow to the ground G, the effects of noise are reduced, and a highly accurate measurement system and method can be provided. 【0040】 The measurement cable, measurement system, and measurement method according to the present invention have been described above, but the present invention is not limited to the above embodiments and includes all aspects included in the concept and claims of the present invention. For example, the configuration and functions of the analyzer 16 may be integrated into the measurement device. In the measurement system 14' shown in Figure 7, the measurement device 40' combines the configuration and functions of the measurement device 40 and the analyzer 16 shown in the measurement system 14 in Figure 1. That is, the measurement device 40' has the configuration and function of measuring the impedance of the water electrolysis cell 10, as well as the configuration and function of performing numerical processing and analysis processing of the measured impedance of the water electrolysis cell 10, and controlling the measurement system 14'. The measurement device 40' is electrically connected to the AC power supply 15 and has the function of transmitting signals to the AC power supply 15 for setting and controlling the frequency, voltage, current amount, waveform, application timing, etc. of the AC current for measurement. 【0041】 Furthermore, the configuration and functions of the AC power supply 15 and the analyzer 16 may be integrated into the measuring device. In the measuring system 14” shown in Figure 8, the measuring device 40” combines the configuration and functions of the AC power supply 15, analyzer 16, and measuring device 40 of the measuring system 14 shown in Figure 1. That is, the measuring device 40” has the configuration and function to measure the impedance of the water electrolysis cell 10, as well as the configuration and function to generate an AC current for impedance measurement and apply it to the DUT 10, the configuration and function to perform numerical processing and analysis processing of the measured impedance of the water electrolysis cell 10, and the configuration and function to control the operation of the entire measuring system 14”. 【0042】 Furthermore, while the above-described embodiment explained a measurement system and method for measuring the impedance of a water electrolysis cell in a water electrolysis apparatus as an example, it can also be applied to measuring the impedance of other DUTs with low impedance, such as fuel cells, during operation. Moreover, the electrical characteristics to be measured are not limited to impedance; they may also be other electrical characteristics that can be measured based on the voltage drop across the DUT caused by the applied AC current, such as amplitude, phase, and their frequency characteristics. It will be obvious to those skilled in the art that measuring other electrical characteristics can be done by changing the measuring device of the above-described measurement system to a measuring device capable of measuring the desired electrical characteristics. [Explanation of Symbols] 【0043】 10 Measured object (DUT), water electrolysis cell 11 Current Sensor 12 DC power supply 13 Source Cable 14, 14', 14” measurement system 15 AC power supply 16 Analyzer 17 Drive Circuit 20 Measuring Cables 21, 21a, 21b straight cable 22 DUT side high terminal 23 Low-side terminal on the DUT side 24 High-side terminal on the measuring device side 25 Low-side terminal on the measuring device side 30 Triaxial Cables 31 Inner conductor 32 Conductive layer 33 Insulator 34 Conductive layer 35 Inner outer conductor, first outer conductor 36. Primary sheath, insulator 37 Outer outer conductor, second outer conductor 38 Secondary sheath 40, 40', 40” measuring device 41 High-side input terminal 42 Low-side input terminal 43 Buffer Circuit 44 Input Circuits 45 Measurement circuit 46 cabinets 50 External noise sources 51 Coupling capacitance with noise source 52 Parasitic capacitance 53 Closed circuit 90 Twisted Pair Cable 91, 92 Single-wire cable

Claims

[Claim 1] A measuring cable for electrically connecting a measuring device and an object to be measured, An inner conductor, a first outer conductor, and a second outer conductor arranged coaxially, An insulator disposed between the inner conductor and the first outer conductor and between the first outer conductor and the second outer conductor, A triaxial cable equipped with, The high-side terminal on the measuring device side and the high-side terminal on the object to be measured side are electrically connected to each end of the internal conductor, The low-side terminal on the measuring device side is electrically connected to one end of the first outer conductor and one end of the second outer conductor, The low-side terminal on the object to be measured is electrically connected only to the other end of the first outer conductor, A measuring cable equipped with the necessary features. [Claim 2] The measuring cable according to claim 1, further comprising conductive layers disposed between the inner conductor and the insulator and between the insulator and the first outer conductor. [Claim 3] An AC power supply that applies alternating current to the object to be measured, A measuring device that measures the electrical characteristics of an object based on a detection signal when the alternating current is applied to the object to be measured, A measuring cable according to claim 1 or 2, which transmits the detection signal from the object to be measured to the measuring device, Equipped with, The high-side terminal of the measurement cable on the measuring device side is electrically connected to the input terminal of the input circuit of the measuring device. The low-side terminal of the measurement cable on the measuring device side is electrically connected to the ground of the input circuit of the measuring device. The high-side terminal and the low-side terminal of the measurement cable on the object to be measured side are electrically connected to the object to be measured to detect the detection signal. Measurement system. [Claim 4] The object to be measured is a water electrolysis cell, The aforementioned electrical characteristic is the impedance of the water electrolysis cell. The measurement system according to claim 3. [Claim 5] The housing of the measuring device is grounded. The input circuit of the measuring device is electrically isolated from the housing. The measurement system according to claim 3. [Claim 6] The steps of electrically connecting the object to be measured and the measuring device using the measuring cable described in claim 1 or 2, The steps include applying an alternating current to the object to be measured, The steps include: measuring the electrical characteristics of the object to be measured based on a detection signal detected by the measuring cable when the alternating current is applied to the object to be measured; Includes, The aforementioned connection step is, The steps include electrically connecting the high-side terminal of the measuring cable on the measuring device side to the input terminal of the input circuit of the measuring device, The steps include electrically connecting the low-side terminal of the measuring cable on the measuring device side to the ground of the input circuit of the measuring device, The steps include electrically connecting the high-side terminal and the low-side terminal of the measurement cable on the side of the object to be measured to the object to be measured, including, Measurement method.

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