Impedance measurement device and method

Abstract

To provide an impedance measuring device with which it is possible to suppress the influence of noise near a measurement frequency and conduct highly accurate measurement.SOLUTION: The above problem can be resolved by an impedance measuring device (1) comprising: a signal generation unit (30) for generating a first reference signal and a second reference signal in which the phase of the first reference signal is inverted on each prescribed inversion cycle; a measurement signal supply unit (10) for generating a measurement signal on the basis of the second reference signal and supplying it to a measurement object; a measurement unit (20) for synchronously detecting the signal generated to the measurement object by the measurement signal with a modulating signal generated on the basis of the first reference signal and further generating a filtered signal having been low-pass filtered; and an arithmetic unit (40) for finding the impedance of the measurement object on the basis of the arithmetic mean of the magnitude of the filtered signal when the first and second reference signals have the same phase and the magnitude of the filtered signal having had its sign inverted when the first and second reference signals have the reverse phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an impedance measuring device and method, and more particularly to a four-terminal impedance measuring device and method that utilizes synchronous detection. [Background technology]

[0002] A four-terminal impedance measuring device is a device used to measure the internal impedance of an object under test. A four-terminal impedance measuring device supplies an AC measurement signal from a current source to the object under test, detects the signal generated in the object by the measurement signal, and calculates the internal impedance of the object under test from the current flowing through the object and the voltage between both terminals of the object.

[0003] At this time, synchronous detection as described in Patent Document 1 may be used to accurately extract the measurement frequency component contained in the detection signal. In four-terminal impedance measurement using synchronous detection, first, the detection signal generated in the measurement object by the measurement signal is detected using two modulation signals that have the same frequency as the measurement signal but are 90 degrees out of phase. Then, the measurement frequency component contained in the detection signal is converted to DC, so the detection signal detected using the in-phase modulation signals contains a DC component proportional to the resistance component of the measurement object. Furthermore, the detection signal detected using the detection signal in a phase orthogonal to the measurement signal contains a DC component proportional to the reactance component of the measurement object. Each detection signal is then filtered using a low-pass filter (L PF ) to extract the DC component, measure its magnitude, and perform numerical processing to determine the internal impedance of the object being measured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5940389 Summary of the Invention [Problem to be solved by the invention]

[0005] Since the detection signal contains a frequency component that is the difference between the frequency of the detection signal and the frequency of the measurement signal, the closer the frequency of the noise contained in the detection signal is to the measurement frequency, the lower the frequency that the noise is modulated to, making it difficult to remove using an LPF. For example, when impedance measurements are performed in parallel using multiple impedance measurement devices, mutual interference occurs between the measurement devices, but if there is no lower limit to the difference between the measurement frequency of one device and the external noise frequency caused by the measurement frequencies of the other devices, it is virtually impossible to remove the effects of the interference using an LPF.

[0006] One way to reduce the effects of this interference is to synchronize the measurement signals from multiple measurement devices. However, synchronization requires accurate communication between the measurement devices, which complicates the hardware and software of the measurement devices and increases the amount of wiring required for the inspection system in which the measurement devices are incorporated.

[0007] Another possible method is to compensate for the effects of interference using signal processing, etc. However, the amount of interference influence varies depending on the loop shape made by the measurement cable, the state of magnetic coupling due to its position relative to surrounding metal, and the state of the measurement signal from the interfering device, and it is not easy to always maintain a constant amount of influence, making it extremely difficult to perform highly accurate compensation.

[0008] The present invention has been made in view of the above-mentioned problems, and has an object to suppress the influence of noise near the measurement frequency and enable highly accurate impedance measurement. [Means for solving the problem]

[0009] The above problem can be solved by an impedance measuring device comprising: a signal generating unit that generates a first reference signal and a second reference signal obtained by inverting the phase of the first reference signal at a predetermined inversion period; a measurement signal supplying unit that generates a measurement signal based on the second reference signal and supplies the measurement signal to an object to be measured; a measurement unit that synchronously detects a signal generated in the object to be measured by the measurement signal using a modulated signal generated based on the first reference signal and generates a filtered signal that is further low-pass filtered; and a calculation unit that calculates the impedance of the object to be measured based on the arithmetic average of the magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and the magnitude of the filtered signal with its sign inverted when the first reference signal and the second reference signal are out of phase.

[0010] In other words, when a measurement signal that inverts at an inversion cycle is synchronously detected using a modulation signal that does not invert, the signal components (original measurement signal components) generated in the measurement object by the measurement signal are inverted at each inversion cycle, but the noise components are not. If the sign of this filtered signal is inverted, the original measurement signal components do not invert at each inversion cycle, and only the noise components are inverted. Therefore, the noise signal can be canceled by averaging before and after inversion at each inversion cycle. Then, by calculating the impedance of the measurement object based on the magnitude of the filtered signal from which the noise signal has been canceled, highly accurate impedance measurement is possible while suppressing the influence of noise near the measurement frequency. Note that, in this application, "arithmetic averaging" includes both the addition and averaging of signal magnitudes (magnitude averaging) and the addition and averaging of magnitude averages over a predetermined period (magnitude and temporal averaging). Furthermore, "synchronous detection" refers to detecting the detection signal generated in the measurement object by the measurement signal using two modulation signals that have the same frequency as the measurement signal but are 90 degrees out of phase with each other.

[0011] The above problem is solved by the first reference signal and the phase of the first reference signal being inverted at a predetermined period. a signal generating section for generating a second reference signal inverted for each measurement; Generate a constant signal and supply it to the measurement target Measurement signalThis can also be solved by an impedance measuring device comprising a supply unit, a measurement unit that synchronously detects the signal generated in the object to be measured by the measurement signal using a modulated signal generated based on a second reference signal and then generates a filtered signal that is low-pass filtered, and a calculation unit that calculates the impedance of the object to be measured based on the arithmetic average of the magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and the magnitude of the filtered signal when the first reference signal and the second reference signal are out of phase.

[0012] In other words, when a measurement signal that inverts with each inversion cycle is synchronously detected with a modulation signal that inverts with each inversion cycle, the original measurement signal component does not invert, and only the noise component inverts with each inversion cycle. Therefore, by taking an arithmetic average before and after the phase inversion, the noise signal can be canceled out. Then, by calculating the impedance of the measurement target based on the magnitude of the filtered signal from which the noise signal has been canceled out, high-precision impedance measurement is possible, suppressing the effects of noise near the measurement frequency.

[0013] Here, it is desirable that the inversion period is an integer multiple of the period of the measurement signal supplied to the object to be measured, and that the calculation unit calculates the impedance of the object to be measured based on an arithmetic average over a measurement period that is an integer multiple of the inversion period. By taking a temporal average in units of the period of the measurement signal, it is possible to further suppress noise signals having frequencies close to the measurement frequency.

[0014] Furthermore, the above problem can be solved by the above-mentioned signal generating unit, Measurement signal The problem can also be solved by the method of implementing the functions of the supply unit, the measurement unit and the calculation unit. [Effects of the Invention]

[0015] The impedance measuring device according to the present invention can suppress the influence of noise near the measurement frequency, enabling highly accurate impedance measurement. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a schematic diagram illustrating the configuration of an impedance measuring device 1 according to an embodiment of the present invention in a state where the device is connected to an object to be measured. [Figure 2] 2 is a flowchart showing the operation of the impedance measuring device 1 according to the embodiment of the present invention. [Figure 3] 2 is an explanatory diagram of a measurement signal, external noise, and a reference signal supplied to a measurement target in the impedance measuring device 1. FIG. [Figure 4] 1 is a schematic diagram illustrating the configuration of an impedance measuring device 1' according to an embodiment of the present invention in a state where the device is connected to an object to be measured. [Figure 5] 3 is a flowchart showing the operation of an impedance measuring device 1' according to an embodiment of the present invention. [Figure 6] 1 is an explanatory diagram of a measurement signal, external noise, and a reference signal supplied to an object to be measured in an impedance measuring device 1'. FIG. [Figure 7] FIG. 1 is a schematic diagram of a multiple impedance measurement system. [Figure 8] 1 shows the measurement results of multiple impedance measurements. DETAILED DESCRIPTION OF THE INVENTION

[0017] Specific examples of embodiments of the present invention will be described below with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of an impedance measuring device 1, which is an example of an embodiment of the present invention, connected to a measurement target 60. Examples of such impedance measuring devices include a battery tester that measures a storage battery, an LCR meter that measures passive components such as a coil, a capacitor, and a resistor, and a C meter specifically for capacitors.

[0018] Impedance measuring device 1 comprises a measurement signal supply unit 10, a measurement unit 20, a signal generation unit 30, and a calculation unit 40. Impedance measuring device 1 supplies a measurement signal Im from measurement signal supply unit 10 to object to be measured 60 via contact terminals 51, 53 that contact both terminals of object to be measured 60, and measurement unit 20 detects a signal Vm generated by the measurement signal Im between contact terminals 52, 54 that contact both terminals of object to be measured 60. Calculation unit 40 determines the internal impedance Z and phase angle θ of object to be measured 60 based on the magnitude of the measurement signal Im supplied to object to be measured 60 and the magnitude of the detection signal Vm. A reference signal Vr2 that serves as a reference for measurement signal Im, and a reference signal Vr1 that serves as a reference for modulation signals Vmod1 and Vmod2 for detecting detection signal Vm, are generated by signal generation unit 30.

[0019] The measurement signal supplying unit 10 is connected to the signal generating unit 30 and contact terminals 51 and 53, and includes a signal source that generates a measurement signal Im that is in phase with the reference signal Vr2 input from the signal generating unit 30. The generated measurement signal Im is supplied via the contact terminals 51 and 53 to the measurement object 60 that is connected to the contact terminals 51 and 53.

[0020] The measuring unit 20 is connected to the signal generating unit 30, the calculating unit 40 and the contact terminals 52, 54, and includes a detecting circuit 21, a 90-degree phase shifter 26, two low-pass filters (LPFs) 24, 25, and two multipliers 22, 23.

[0021] The detection circuit 21 has inputs connected to the contact terminals 52 and 54 and outputs connected to the multipliers 22 and 23. The detection circuit 21 detects a signal generated between the contact terminals 52 and 54, which are in contact with both terminals of the object to be measured 60, in response to the measurement signal Im, and outputs a detection signal Vm.

[0022] The 90-degree phase shifter 26 has an input connected to the signal generating unit 30 and an output connected to the multiplier 23. The 90-degree phase shifter 26 shifts the phase of the reference signal Vr1 received from the signal generating unit 30 by 90 degrees to generate a modulated signal Vmod2.

[0023] The inputs of the multiplier 22 are connected to the detection circuit 21 and the signal generating unit 30, and the output is connected to the LPF 24. The multiplier 22 detects the detection signal Vm received from the detection circuit 21 with the modulation signal Vmod1 that is in phase with the reference signal Vr1 received from the signal generating unit 30, and outputs a detection signal Vd1. The inputs of the multiplier 23 are connected to the detection circuit 21 and the 90-degree phase shifter 26, and the output is connected to the LPF 25. The multiplier 23 detects the detection signal Vm received from the detection circuit 21 with the modulation signal Vmod2 that is received from the 90-degree phase shifter 26 and has a phase that is quadrature with the reference signal Vr1, and outputs a detection signal Vd2.

[0024] The inputs of LPFs 24 and 25 are connected to the corresponding multipliers 22 and 23, respectively, and the outputs are connected to the calculation unit 40. LPF 24 low-pass filters the detection signal Vd1 output from multiplier 22 to extract the DC component and generates a filtered signal Vi. LPF 25 low-pass filters the detection signal Vd2 output from multiplier 23 to extract the DC component and generates a filtered signal Vq.

[0025] The signal generating section 30 has an input connected to the calculating section 40 and an output connected to the measurement signal supplying section 10 and the measuring section 20 , and includes a reference signal generator 33 , a phase inverter 31 , and a switch 32 .

[0026] The reference signal generator 33 has an input connected to the calculation unit 40 and an output connected to the phase inverter 31, the switch 32, and the multiplier 22 and 90-degree phase shifter 26 of the measurement unit 20. The reference signal generator 33 generates a reference signal Vr1 having a period and a phase angle specified by a control signal from the calculation unit 40.

[0027] The phase inverter 31 has an input connected to the reference signal generator 33 and an output connected to the switch 32. The phase inverter 31 generates a reference signal by shifting (inverting) the phase of the reference signal Vr1 received from the reference signal generator 33 by 180 degrees.

[0028] One input terminal of the switch 32 is connected to the reference signal generator 33, the other terminal is connected to the phase inverter 31, a control terminal is connected to the calculation unit 40, and an output is connected to the measurement signal supply unit 10. Based on the control signal Vs generated by the calculation unit 40, the switch 32 selects between a signal in phase with the reference signal Vr1 (positive phase) and a signal out of phase with the reference signal Vr1 generated by the phase inverter 31, and outputs the selected signal as the reference signal Vr2.

[0029] Calculation unit 40 records in memory the magnitudes of filtered signals Vi and Vq input from measurement unit 20. It also calculates the internal impedance Z and phase angle θ of object to be measured 60 based on the arithmetic average of the magnitudes of filtered signals Vi and Vq (positive-phase filtered signals) when reference signals Vr1 and Vr2 are in positive phase and the magnitudes of the filtered signals Vi and Vq (negative-phase filtered signals) with their signs inverted when reference signals Vr1 and Vr2 are in negative phase. Calculation unit 40 also generates a signal that controls the period and phase angle of reference signal Vr1 generated by reference signal generator 33, and a control signal Vs that switches switch 32 every predetermined inversion period T.

[0030] The inversion period T is set to be an integer multiple of the period of the reference signal Vr1 (i.e., the period of the measurement signal). This makes it possible to obtain the magnitudes of the positive-phase filtered signal and the negative-phase filtered signal corresponding to each phase of the reference signal Vr1. The measurement period is also set to be an integer multiple of the inversion period T. Furthermore, by setting the measurement period to an even multiple of the inversion period T, the measurement period for obtaining the magnitude of the positive-phase filtered signal and the measurement period for obtaining the magnitude of the negative-phase filtered signal can be made equal.

[0031] In the impedance measuring device 1 of this embodiment, the multipliers 22 and 23, LPFs 24 and 25, and 90-degree phase shifter 26 of the measuring unit 20, as well as the calculating unit 40, are configured as a computer having a processor and memory. That is, a program containing instructions that, when executed by the processor, realize the functions of the elements of the measuring unit 20 and the calculating unit 40 described above is stored in the memory, and the functions of the elements of the measuring unit 20 and the calculating unit 40 are realized by executing each program on the processor. However, some or all of the elements of the measuring unit 20 and the calculating unit 40 described above may also be realized by hardware such as electronic circuits or devices. The description of the connections between the elements of the impedance measuring device 1 described above refers to electrical and mechanical connections for the hardware configuration and processing flows for the software configuration.

[0032] Next, the operation of the impedance measuring device 1 of this embodiment, that is, an example of an embodiment of the impedance measuring method of the present invention, will be described with reference to the flowchart of FIG.

[0033] First, the signal generating unit 30 generates in-phase reference signals Vr1 and Vr2 (step 101). More specifically, based on a control signal from the calculation unit 40, the reference signal generator 33 generates a reference signal Vr1=sin2πft (t is time) of frequency f, and the switch 32 selectively outputs the positive-phase input. As a result, the switch 32 outputs a reference signal Vr2=sin2πft that is in-phase with the reference signal Vr1.

[0034] Next, the measurement signal supplying unit 10 generates a measurement signal Im=I sin2πft that is in phase with the reference signal Vr2 received from the signal generating unit 30 and supplies it to the object under test 60 (step 102). The measurement signal Im generates a voltage between both terminals of the object under test 60 that corresponds to the impedance Z and phase angle θ of the object under test 60. The detection circuit 21 detects a detection signal Vm=ZI sin(2πft+θ) generated between contact terminals 52, 54 that are in contact with both terminals of the object under test 60, respectively (step 103).

[0035] Next, the detection signal Vm is modulated by the multiplier 22 with a modulation signal Vmod1=sin2πft that is in phase with the reference signal Vr1, and as a result, a detection signal Vd1 is obtained in which a DC component corresponding to the resistance component R=Zcosθ of the impedance Z of the object to be measured 60 and an AC component of frequency 2f are superimposed, as shown in equation (1) (step 104).

[0036]

number

[0037] Furthermore, when the detection signal Vm is modulated by the multiplier 23 with the modulation signal Vmod2=cos2πft, which is generated by the 90-degree phase shifter 26 and has a phase difference of 90 degrees from that of the reference signal Vr1, a detection signal Vd2 is obtained in which a DC component corresponding to the reactance component X=Zsinθ of the impedance Z of the object to be measured 60 is superimposed on an AC component of frequency 2f, as shown in equation (2) (step 104).

[0038]

number

[0039] Next, the detection signals Vd1 and Vd2 are low-pass filtered by the LPFs 24 and 25 to generate filtered signals Vi and Vq from which the DC component has been extracted, as shown in equation (3) (step 105). Next, the calculation unit 40 stores the magnitudes of the generated filtered signals Vi and Vq in memory together with the detection times (step 106).

[0040]

number

[0041] When there is no noise from outside the impedance measuring device 1, the impedance Z (R and X) and phase angle θ of the object to be measured 60 can be determined from the instantaneous voltage values of the filtered signals Vi and Vq. Even if the value of the measurement signal Im is not known, if the amplitude and phase of the measurement signal are measured using a synchronous detection method, the impedance Z (R and X) and phase angle θ can be determined based on the respective voltage and current values.

[0042] Here, if the detection signal Vm contains external noise Vnsin(2πfnt+φ) of frequency fn, the detection signal of the external noise Vn contains a component signal shown in equation (4).

[0043]

number

[0044] As is clear from the first term on the right side of equation (4), the detection signal contains a frequency component that is the difference between the frequency fn of the external noise and the frequency f of the modulating signal Vmod1. When impedance measurements are performed using multiple impedance measurement devices in parallel, such as when the frequency fn of the external noise Vn is close to the modulating signal Vmod1, it becomes difficult for the LPFs 24 and 25 to sufficiently remove the external noise Vn. As a result, the filtered signal contains the low-frequency component of the first term on the right side of equation (4). Calculating the impedance Z (R and X) and phase angle θ of the object to be measured 60 from the measured values of such filtered signals Vi and Vq results in significant measurement errors. Therefore, the impedance measurement device 1 generates a low-frequency component with a phase opposite to that of the low-frequency component of the first term on the right side of equation (4) and averages it to cancel out the low-frequency component and suppress the influence of the external noise Vn.

[0045] Specifically, first, the operations from step 102 to step 106 described above are repeatedly performed over an inversion period T at each predetermined sampling period (step 107). The inversion period T is preferably set to an integer multiple of the period of the reference signals Vr1 and Vr2. This makes it possible to record in memory the temporal changes in the voltages of the filtered signals Vi and Vq corresponding to each phase of the reference signal Vr1. In the impedance measuring device 1 of this embodiment, the inversion period T is set to twice the period of the reference signals Vr1 and Vr2. The inversion period T can be set as appropriate, such as 10 or 100 periods of the reference signals Vr1 and Vr2.

[0046] When a predetermined inversion period T has elapsed, the calculation unit 40 transmits a control signal Vs that switches the switch 32. Then, the switch 32 selectively outputs the negative-phase input. As a result, the switch 32 outputs a reference signal Vr2=-sin2πft that is negative in phase with the reference signal Vr1 (step 108).

[0047] Thereafter, it is determined whether the predetermined measurement period has ended (step 109). The measurement period is desirably set to an integer multiple of the inversion period T. In particular, in order to obtain a temporal arithmetic average of the magnitudes of the filtered signals Vi and Vq when the reference signals Vr1 and Vr2 are in phase and the magnitudes of the filtered signals Vi and Vq with their signs inverted when the reference signals Vr1 and Vr2 are in phase, it is desirable to record the magnitudes of the in-phase and out-of-phase filtered signals Vi and Vq with equal measurement periods. Therefore, it is desirably set to an even multiple of the inversion period T. In the impedance measuring device 1 of this embodiment, the measurement period is set to twice the inversion period T, and therefore to a period equivalent to four periods of the reference signals Vr1 and Vr2.

[0048] At the point when the first processing of steps 102 to 108 is completed, measurements have only been performed for one inversion period, so the process returns to step 102 and repeats the operations of steps 102 to 108. However, in the second processing, the two reference signals Vr1 and Vr2 are in opposite phases.

[0049] FIG. 3 shows the temporal changes of the measurement signal Im, external noise Vn, and modulation signal Vmod1 supplied to the system under test 60. Time 0 to T corresponds to the first processing run, and time T to 2T corresponds to the second processing run. Because modulation signal Vmod1 is based on reference signal Vr1, there is no phase change between the first and second processing runs. However, because measurement signal Im is based on reference signal Vr2, its phase is reversed between the first and second processing runs. Therefore, the components proportional to the impedance Z of system under test 60 contained in filtered signals Vi and Vq are out of phase between the first and second processing runs. In contrast, the components due to external noise Vn contained in the detection signal are not affected by the phase of measurement signal Im, and are therefore in phase between the first and second processing runs.

[0050]

number

[0051] When the second processing of steps 102 to 108 is completed, the measurement time twice the inversion period T has elapsed, and the measurement period ends (step 109). As a result, the memory records the temporal changes in the voltages of the filtered signals Vi and Vq for two reference signal periods when the two reference signals Vr1 and Vr2 are in phase, and the temporal changes in the voltages of the filtered signals Vi and Vq for two reference signal periods when the two reference signals Vr1 and Vr2 are out of phase.

[0052] Next, the processor of the calculation unit 40 reads the voltages of the filtered signals Vi and Vq from the memory, inverts the signs of the voltages of the filtered signals Vi and Vq when the two reference signals Vr1 and Vr2 are in opposite phases, and calculates the average (step 110). By calculating the average of the magnitudes of the filtered signals Vi and Vq when the two reference signals Vr1 and Vr2 are in phase and the magnitudes of the filtered signals Vi and Vq with their signs inverted when the two reference signals Vr1 and Vr2 are in opposite phases, the component corresponding to the first term on the right-hand side of equations (4) and (4') can be canceled out, and the magnitudes of the filtered signals Vi and Vq with the influence of the external noise Vn suppressed can be obtained.

[0053] Although the impedance measuring device 1 of this embodiment calculates the arithmetic average of the magnitudes of the filtered signals Vi and Vq over the entire measurement period stored in memory, it is also possible to obtain one or more sets of in-phase and out-of-phase filtered signals when the reference signal Vr1 is in phase during the measurement period and calculate the arithmetic average of each filtered signal Vi and Vq. For example, a total of four filtered signal magnitudes, consisting of the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 is π / 4 in the first processing of steps 102 to 108 and the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 is π / 4 in the second processing of steps 102 to 108, are obtained from memory, and the magnitude of the filtered signal Vi in the first processing and the magnitude of the filtered signal Vi with its sign inverted in the second processing, are averaged to determine the magnitude of the filtered signal Vi with the influence of external noise Vn suppressed. Furthermore, the magnitude of the filtered signal Vq obtained by the first processing and the magnitude of the filtered signal Vq obtained by the second processing with its sign inverted are averaged to obtain the magnitude of the filtered signal Vq with the influence of the external noise Vn suppressed.

[0054] As another example, a total of eight filtered signal magnitudes are read from memory: a first set consisting of the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 in the first processing is π / 4 and the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 in the second processing is π / 4; and a second set consisting of the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 in the first processing is π / 2 and the magnitudes of the filtered signals Vi and Vq when the phase of the reference signal Vr1 in the second processing is π / 2. The magnitudes of the four filtered signals Vi included in the acquired filtered signal magnitudes are averaged (magnitude and time average) with only the filtered signals Vi and Vq in the second processing sign-inverted to determine the magnitude of the filtered signal Vi with the influence of external noise Vn suppressed. Furthermore, the magnitudes of the four filtered signals Vq are averaged (magnitude and time average) with only the filtered signals Vi and Vq in the second processing sign-inverted to determine the magnitude of the filtered signal Vq with the influence of external noise Vn suppressed.

[0055] Finally, the processor of the calculation unit 40 calculates the impedance Z (R and X) and phase angle θ of the object to be measured 60 from the average obtained in step 110, i.e., the magnitudes of the filtered signals Vi and Vq from which the external noise Vn has been canceled out (step 111).

[0056] 4 and 5 show a schematic configuration diagram and an operational flowchart of an impedance measuring device 1' according to another embodiment of the present invention, connected to a measurement target 60. The impedance measuring device 1' differs from the impedance measuring device 1 in the positions of the phase inverter 31 and switch 32 of the signal generating section 30' and the operation of step 110 in Fig. 2 by the calculating section 40', but the other configurations are the same as those of the impedance measuring device 1. For this reason, the configurations and operations that show the same functions and operations as those of the impedance measuring device 1 are given the same reference numerals and will not be described again.

[0057] The signal generating section 30 ′ has an input connected to the calculating section 40 ′ and an output connected to the measurement signal supplying section 10 and the measuring section 20 , and includes a reference signal generator 33 , a phase inverter 31 , and a switch 32 .

[0058] The input of the reference signal generator 33 is connected to the calculation unit 40′, and the output is connected to the phase inverter 31 and the switch 32. The reference signal generator 33 generates a reference signal Vr1 having a period and a phase angle specified by a control signal from the calculation unit 40′.

[0059] The phase inverter 31 has an input connected to the reference signal generator 33 and an output connected to the switch 32. The phase inverter 31 generates a reference signal by shifting (inverting) the phase of the reference signal Vr1 received from the reference signal generator 33 by 180 degrees.

[0060] One input terminal of switch 32 is connected to reference signal generator 33, the other terminal to phase inverter 31, a control terminal to calculation unit 40', and an output connected to measurement signal supply unit 10 and multiplier 22 and 90-degree phase shifter 26 of measurement unit 20. Based on a control signal Vs generated by calculation unit 40', switch 32 selects between a signal in phase with reference signal Vr1 (positive phase) and a signal out of phase with reference signal Vr1 generated by phase inverter 31, and outputs the selected signal as reference signal Vr2.

[0061] Calculation unit 40' determines the magnitudes of filtered signals Vi and Vq input from measurement unit 20 and records them in memory. It also determines the internal impedance Z and phase angle θ of object to be measured 60 based on the arithmetic average of the magnitudes of filtered signals Vi and Vq (positive-phase filtered signals) when reference signals Vr1 and Vr2 are in positive phase and the magnitudes of filtered signals Vi and Vq (negative-phase filtered signals) when reference signals Vr1 and Vr2 are in negative phase. Calculation unit 40' also generates a signal that controls the period and phase angle of reference signal Vr1 generated by reference signal generator 33, and a control signal Vs that switches switch 32 every predetermined inversion period T.

[0062] In the impedance measuring device 1' of this embodiment, the multipliers 22, 23, LPFs 24, 25 and 90-degree phase shifter 26 of the measuring unit 20, and the calculation unit 40 ’ is configured with a computer having a processor and memory. That is, a program containing instructions that, when executed by the processor, realize the functions of each element of the measuring unit 20 and each of the calculation unit 40' described above is stored in the memory, and the functions of each element of the measuring unit 20 and each of the calculation unit 40' described above are realized by executing each program on the processor. However, some or all of the elements of the measuring unit 20 and the calculation unit 40' described above may be realized by hardware such as electronic circuits or devices. The description of the connection relationships between each element of the impedance measuring device 1' above refers to electrical and mechanical connections for the hardware configuration and the processing flow for the software configuration.

[0063] Next, the operation of the impedance measuring device 1' of this embodiment will be described with reference to the flowchart of FIG.

[0064] First, the signal generating unit 30' generates in-phase reference signals Vr1 and Vr2 (step 101). More specifically, based on a control signal from the calculation unit 40', the reference signal generator 33 generates a reference signal Vr1=sin2πft (t is time) of frequency f, and the switch 32 selectively outputs the positive-phase input. As a result, the switch 32 outputs a reference signal Vr2=sin2πft that is in-phase with the reference signal Vr1.

[0065] Next, the measurement signal supplying unit 10 generates a measurement signal Im=I sin2πft that is in phase with the reference signal Vr2 received from the signal generating unit 30' and supplies it to the object under test 60 (step 102). The measurement signal Im generates a voltage between both terminals of the object under test 60 that corresponds to the impedance Z and phase angle θ of the object under test 60. The detection circuit 21 detects a detection signal Vm=ZI sin(2πft+θ) generated between contact terminals 52, 54 that are in contact with both terminals of the object under test 60, respectively (step 103).

[0066] Next, the multiplier 22 modulates the detection signal Vm with a modulation signal Vmod1=sin2πft that is in phase with the reference signal Vr2, thereby obtaining a detection signal Vd1 in which a DC component corresponding to the resistance component R=Zcosθ of the impedance Z of the object to be measured 60 and an AC component of frequency 2f are superimposed (step 104).

[0067] Furthermore, when the multiplier 23 modulates the detection signal Vm with a modulation signal Vmod2=cos2πft, which is generated by the 90-degree phase shifter 26 and has a phase difference of 90 degrees from that of the reference signal Vr2, a detection signal Vd2 is obtained in which a DC component corresponding to the reactance component X=Zsinθ of the impedance Z of the object to be measured 60 and an AC component of frequency 2f are superimposed (step 104).

[0068] Next, the detection signals Vd1 and Vd2 are low-pass filtered by the LPFs 24 and 25 to generate filtered signals Vi and Vq from which the DC components have been extracted (step 105). Next, the calculation unit 40' stores the magnitudes of the generated filtered signals Vi and Vq in memory together with the detection times (step 106).

[0069] The operations from step 102 to step 106 described above are repeatedly performed over an inversion period T at each predetermined sampling period (step 107). In the impedance measuring device 1' of this embodiment, the inversion period T is also set to twice the period of the reference signals Vr1 and Vr2.

[0070] After a predetermined inversion period T has elapsed, the calculation unit 40' transmits a control signal Vs that switches the switch 32. The switch 32 then selectively outputs the negative-phase input. As a result, the switch 32 outputs a reference signal Vr2=-sin2πft that is negative in phase with the reference signal Vr1 (step 108).

[0071] Thereafter, it is determined whether or not the predetermined measurement period has ended (step 109). In the impedance measuring device 1' of this embodiment, the measurement period is also set to twice the inversion period T, and therefore to a period equivalent to four periods of the reference signals Vr1 and Vr2.

[0072] At the point when the first processing of steps 102 to 108 is completed, measurements have only been performed for one inversion period, so the process returns to step 102 and repeats the operations of steps 102 to 108. However, in the second processing, the two reference signals Vr1 and Vr2 are in opposite phases.

[0073] FIG. 6 shows the temporal changes in the measurement signal Im, external noise Vn, and modulation signal Vmod1 supplied to the object under test. Time 0 to T corresponds to the first processing run, and time T to 2T corresponds to the second processing run. Because both measurement signal Im and modulation signal Vmod1 are based on reference signal Vr2, their phases are opposite between the first and second processing runs. However, the relationship between measurement signal Im and modulation signal Vmod1 remains in phase. Therefore, the components proportional to the impedance Z of object under test 60 contained in filtered signals Vi and Vq are in phase between the first and second processing runs. In contrast, the components due to external noise Vn contained in the detection signal are out of phase because modulation signal Vmod1 is out of phase between the first and second processing runs.

[0074] When the second processing of steps 102 to 108 is completed, the measurement time twice the inversion period T has elapsed, and the measurement period ends (step 109). As a result, the memory records the temporal changes in the voltages of the filtered signals Vi and Vq for two reference signal periods when the two reference signals Vr1 and Vr2 are in phase (measurement signal Im and modulation signal Vmod1 are both in positive phase), and the temporal changes in the voltages of the filtered signals Vi and Vq for two reference signal periods when the two reference signals Vr1 and Vr2 are out of phase (measurement signal Im and modulation signal Vmod1 are both out of phase).

[0075] Next, the processor of the calculation unit 40' reads the voltages of the filtered signals Vi and Vq from the memory and calculates the average of the filtered signals Vi and Vq (step 110'). The component caused by the external noise Vn contained in the filtered signal is out of phase when the two reference signals Vr1 and Vr2 are in phase and out of phase with each other. Therefore, by calculating the average of the two, the components are cancelled out, and it is possible to obtain the magnitudes of the filtered signals Vi and Vq with the influence of the external noise Vn suppressed.

[0076] Finally, the processor of the calculation unit 40′ calculates the impedance Z (R and X) and phase angle θ of the object to be measured 60 from the average obtained in step 110′, i.e., the magnitudes of the filtered signals Vi and Vq from which the external noise Vn has been canceled out (step 111).

[0077] FIG. 7 shows a configuration for simultaneously performing impedance measurements using two of the impedance measuring devices described in the above embodiment, and FIG. 8 shows simulation results for filtered signals. Impedance measuring device 2 measures the impedance Z and phase angle θ of object to be measured 61 at a measurement frequency f of 1 kHz. Impedance measuring device 3 measures the impedance Z and phase angle θ of object to be measured 62 at a measurement frequency f of 999 Hz. Because the two impedance measuring devices 2 and 3 are located close to each other, they interfere with each other. Specifically, external noise caused by the 999 Hz measurement signal Im from impedance measuring device 3 is input to detection circuit 21 of impedance measuring device 2. Furthermore, external noise caused by the 1 kHz measurement signal Im from impedance measuring device 2 is input to detection circuit 21 of impedance measuring device 3.

[0078] FIG. 8 shows the measurement results of the impedance measuring device 2 (measurement frequency: 1 kHz, external noise: 999 Hz). FIG. 8(a) shows the filtered signal before averaging in step 110, and FIG. 8(b) shows the filtered signal after averaging. In the filtered signal before averaging, an AC component corresponding to the frequency difference between the reference signal and the external noise (1 Hz = 1000 Hz - 999 Hz) is superimposed on the DC component. In contrast, the filtered signal after averaging has the AC component suppressed. This indicates that the influence of external noise Vn can be suppressed by averaging the filtered signals Vi and Vq when the two reference signals Vr1 and Vr2 are in phase with each other and the filtered signals Vi and Vq when they are out of phase. By calculating the impedance Z and phase angle θ of the object to be measured 61 based on the magnitude of the filtered signal with the external noise suppressed, high-precision impedance measurement is possible, suppressing the influence of noise near the measurement frequency.

[0079] The invention made by the inventors of the present application has been specifically described above based on the embodiments, but the present invention is not limited thereto and can be modified in various ways without departing from the gist of the invention. RukoIt goes without saying. For example, in the impedance measuring devices 1, 1' described in the above-described embodiments, the signal generating unit 30 generates a reference signal based on the frequency and phase angle of the reference signal specified by the calculating unit 40, 40'. However, it is also possible to configure the signal generating unit 30 to generate digital data of a reference signal waveform that switches between positive and negative phases within the calculating unit 40, and generate the reference signal. Also, the measurement signal Im of the impedance measuring devices 1, 1' is in phase with the reference signal Vr2, and the modulation signal Vmod1 is in phase with the reference signal Vr1 or Vr2, but there may be the same amount of phase offset based on each reference signal. However, even if there is a phase offset, the measurement signal Im and the modulation signal Vmod1 must maintain an in-phase or anti-phase relationship. [Explanation of symbols]

[0080] 1, 1', 2, 3 Impedance measuring device 10. Measurement signal supply unit 20 Measuring part 21 Detection circuit 22, 23 Multiplier 24, 25 Low-pass filter (LPF) 26 90 degree phase shifter 30, 30' Signal generating section 31 Phase inverter 32 Switch 33 Reference Signal Generator 40, 40' calculation section 51, 52, 53, 54 contact terminal 60, 61, 62 Measurement target

Claims

1. a signal generating unit that generates a first reference signal and a second reference signal obtained by inverting the phase of the first reference signal at predetermined inversion periods; a measurement signal supply unit that generates a measurement signal based on the second reference signal and supplies the measurement signal to an object to be measured; a measurement unit that performs synchronous detection of a signal generated in the object to be measured by the measurement signal using a modulation signal generated based on the first reference signal, and generates a filtered signal by performing low-pass filtering on the signal; a calculation unit that calculates the impedance of the object to be measured based on an arithmetic average of a magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and a magnitude of the filtered signal with a sign inverted when the first reference signal and the second reference signal are out of phase; An impedance measuring device comprising:

2. a signal generating unit that generates a first reference signal and a second reference signal obtained by inverting the phase of the first reference signal at predetermined inversion periods; a measurement signal supply unit that generates a measurement signal based on the second reference signal and supplies the measurement signal to an object to be measured; a measurement unit that performs synchronous detection of a signal generated in the object to be measured by the measurement signal using a modulation signal generated based on the second reference signal, and generates a filtered signal by performing low-pass filtering on the signal; a calculation unit that calculates the impedance of the object to be measured based on an arithmetic average of the magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and the magnitude of the filtered signal when the first reference signal and the second reference signal are out of phase; An impedance measuring device comprising:

3. the inversion period is an integer multiple of the period of the measurement signal, the calculation unit calculates the impedance of the object to be measured based on an arithmetic average over a measurement period that is an integer multiple of the inversion period.

3. The impedance measuring device according to claim 1 or 2.

4. generating a first reference signal and a second reference signal obtained by inverting the phase of the first reference signal at predetermined inversion periods; generating a measurement signal based on the second reference signal and supplying the measurement signal to a measurement target; a step of synchronously detecting a signal generated in the object to be measured by the measurement signal using a modulation signal generated based on the first reference signal, and generating a filtered signal by low-pass filtering the signal; determining the impedance of the object to be measured based on an arithmetic average of a magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and a magnitude of the filtered signal with a sign inverted when the first reference signal and the second reference signal are out of phase; A method comprising:

5. generating a first reference signal and a second reference signal obtained by inverting the phase of the first reference signal at predetermined inversion periods; generating a measurement signal based on the second reference signal and supplying the measurement signal to a measurement target; a step of synchronously detecting a signal generated in the object to be measured by the measurement signal using a modulation signal generated based on the second reference signal, and generating a filtered signal by low-pass filtering the signal; determining the impedance of the object to be measured based on an arithmetic average of the magnitude of the filtered signal when the first reference signal and the second reference signal are in phase and the magnitude of the filtered signal when the first reference signal and the second reference signal are out of phase; A method comprising:

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