Impedance measurement system and method

Abstract

To suppress the influence of noise near a measurement frequency due to the interference between a plurality of impedance measuring devices and enable highly accurate impedance measurement.SOLUTION: Each of a first impedance measuring device 1 and a second impedance measuring device 2 comprises a measuring signal supply unit, a measurement unit for performing synchronous detection by a modulating signal and generating a filtered signal having been low-pass filtered, and an arithmetic unit for finding the impedance of a measurement object on the basis of the average of the filtered signals. The phase of a measuring signal of the second impedance measuring device 2 changes so that the measuring and modulating signals of the second impedance measuring device 2 alternately have the same phase and the reverse phase on each first inversion cycle which is 1 / 2n (n=natural number) of a measurement period. The arithmetic unit of the second impedance measuring device 2 inverts the sign of the magnitude of the filtered signal that is generated when the measuring and modulating signals have the reverse phase, before calculating the average.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an impedance measurement system and method, and more particularly to an impedance measurement system and method that includes a plurality of impedance measurement devices that utilize 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 signal 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] In this case, synchronous detection, as described in Patent Document 1, is sometimes used to accurately extract the frequency component of the measurement signal contained in the detection signal. In four-terminal impedance measurement using synchronous detection, the detection signal generated in the measurement object by the measurement signal is first detected using two modulation signals: one in phase with the measurement signal and one 90 degrees out of phase with the measurement signal. The measurement frequency component contained in the detection signal is then converted to DC, so the detection signal detected using the in-phase modulation signal contains a DC component proportional to the resistance component of the measurement object. Furthermore, the detection signal detected in quadrature with the detection signal contains a DC component proportional to the reactance component of the measurement object. Each detection signal is filtered using a low-pass filter (LFP) to extract the DC component, measure its magnitude, and perform numerical processing to determine the internal impedance of the measurement object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5941389 Summary of the Invention [Problem to be solved by the invention]

[0005] When impedance measurements are performed in parallel using multiple impedance measuring devices, noise generated by the measurement signals of one impedance measuring device is input to the detection circuits of the other impedance measuring devices, resulting in mutual interference. 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. However, when the frequencies of the measurement signals of the impedance measuring devices are close to each other, particularly when they are the same or nearly the same, the frequency of the noise signal contained in the detection signal is modulated to a low frequency, making it difficult to remove using an LPF.

[0006] One way to reduce the effects of this interference is to compensate for it using signal processing, etc. However, the amount of interference influence fluctuates depending on the loop shape of 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, making it difficult to always maintain a constant amount of influence, making highly accurate compensation extremely difficult.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to suppress the influence of noise near the measurement frequency caused by interference between multiple impedance measuring devices, thereby enabling high-precision impedance measurement. [Means for solving the problem]

[0008] The above problem is solved by an impedance measurement system comprising a first impedance measurement device and a second impedance measurement device, and determining the impedance of an object to be measured that is connected to each of the first impedance measurement device and the second impedance measurement device, wherein each of the first impedance measurement device and the second impedance measurement device comprises a measurement signal supply unit that supplies a measurement signal to the object to be measured over a predetermined measurement period, a measurement unit that synchronously detects, using a modulated signal, a signal generated in the object to be measured by the measurement signal over the measurement period, and further low-pass filters the detected signal to generate a filtered signal, and a calculation unit that determines the impedance of the object to be measured based on the average magnitude of the filtered signal over the measurement period, wherein the measurement signals of the first impedance measurement device and the second impedance measurement device have substantially the same frequency, the measurement signal and modulated signal of the first impedance measurement device have a constant phase angle over the measurement period, the modulated signal of the second impedance measurement device has a constant phase angle over the measurement period, and the measurement signal and modulated signal of the second impedance measurement device are in phase with each other for 1 / 2 of the measurement period. n The phase angle of the measurement signal of the second impedance measuring device changes so that the measurement signal is alternately in phase or out of phase for each first inversion period of (n is a natural number), and the calculation unit of the second impedance measuring device inverts the sign of the magnitude of the filtered signal generated when the measurement signal and the modulating signal are out of phase before calculating the average, which can be solved by the impedance measuring system.

[0009] With this configuration, the measurement signal of the second impedance measuring device is in-phase for half the measurement period and out-of-phase for the other half. Therefore, noise caused by the measurement signal of the second impedance measuring device and input to the detection circuit of the first impedance measuring device is also out-of-phase for half the measurement period. Therefore, by averaging the magnitude of the filtered signal over the measurement period, the noise component contained in the filtered signal can be canceled out. Furthermore, in the second impedance measuring device, the component of the filtered signal caused by the signal generated in the measurement object by the measurement signal is out-of-phase for half the measurement period and out-of-phase for the other half. On the other hand, the component of the filtered signal caused by the noise signal from the first impedance measuring device and input to the detection circuit of the second impedance measuring device is in-phase throughout the measurement period. Therefore, by inverting the sign of the magnitude of the filtered signal generated when the measurement signal and the modulation signal are out-of-phase, and then averaging the magnitude of the filtered signal over the measurement period, the noise component contained in the filtered signal can be canceled out. Then, by determining the impedance of the object to be measured based on the magnitude of the filtered signal in which the noise component has been suppressed, it becomes possible to perform highly accurate impedance measurement while suppressing the influence of noise near the measurement frequency.

[0010] In this application, "synchronous detection" means detecting a measurement signal using a modulated signal with the same frequency as the measurement signal and a signal with a phase difference of 90 degrees from the modulated signal. Therefore, two detection signals are generated by synchronous detection, and two filtered signals are generated by low-pass filtering each of these signals.

[0011] The impedance measurement system further includes a third impedance measuring device including a measurement signal supply unit that supplies a measurement current to the object to be measured over a measurement period; a measurement unit that performs synchronous detection using a modulated signal to detect a signal generated in the object to be measured by the measurement signal over the measurement period 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 average magnitude of the filtered signal over the measurement period. It is preferable that the measurement signal of the third impedance measuring device has substantially the same frequency as the measurement signals of the first impedance measuring device and the second impedance measuring device, the modulated signal of the third impedance measuring device has a constant phase angle over the measurement period, and the phase angle of the measurement signal of the third impedance measuring device changes so that the measurement signal and the modulated signal of the third impedance measuring device are alternately in phase or out of phase every second inversion period that is 1 / 2 (where 1 / 2 is a natural number) of the first inversion period, and the calculation unit of the third impedance measuring device inverts the sign of the magnitude of the filtered signal that is generated when the measurement signal and the modulated signal are out of phase before calculating the average.

[0012] With this configuration, the measurement signal of the third impedance measuring device is in phase for half of the measurement period and in phase for the other half, and therefore the effects of noise due to interference between the first impedance measuring device and the third impedance measuring device can be suppressed using the same principle as that for the interference between the first impedance measuring device and the second impedance measuring device described above.

[0013] Furthermore, focusing on an arbitrary first inversion period (a period during which the phase angle of the measurement signal of the second impedance measuring device changes), the phase angle of the second impedance measuring device is constant, and the measurement signal of the third impedance measuring device is in-phase for half the period and out-of-phase for the other half. Therefore, it can be seen that, during the period of interest, the interference between the second impedance measuring device and the third impedance measuring device has a relationship similar to that between the first impedance measuring device and the second impedance measuring device described above. Therefore, noise due to interference between the second impedance measuring device and the third impedance measuring device can also be suppressed using the same principle as that for the interference between the first impedance measuring device and the second impedance measuring device described above. Then, by determining the impedance of the object to be measured based on the magnitude of the filtered signal in which the noise component is suppressed, high-precision impedance measurement is possible, suppressing the effects of noise near the measurement frequency.

[0014] Furthermore, the above problem is solved by an impedance measurement method implemented by the above-mentioned impedance measurement device, that is, an impedance measurement method for determining the impedance of an object to be measured connected to each of a first impedance measurement device and a second impedance measurement device, the method comprising the steps of: each of the first impedance measurement device and the second impedance measurement device supplying a measurement signal to the object to be measured over a predetermined measurement period; and each of the first impedance measurement device and the second impedance measurement device synchronously detecting, using a modulated signal, a signal generated in the object to be measured by the measurement signal over the measurement period, and further low-pass filtering the signal to generate a filtered signal. and each of the first impedance measuring device and the second impedance measuring device determining the impedance of the object to be measured based on an average magnitude of the filtered signal over a measurement period, wherein the measurement signals of the first impedance measuring device and the second impedance measuring device have substantially the same frequency, the measurement signal and the modulating signal of the first impedance measuring device have a constant phase angle over the measurement period, and the modulating signal of the second impedance measuring device has a constant phase angle over the measurement period, and the step of generating the low-pass filtered signal includes determining whether the measurement signal and the modulating signal of the second impedance measuring device are equal to or greater than 1 / 2 of the measurement period. n The problem can also be solved by an impedance measurement method including a step of changing the phase angle of the measurement signal of the second impedance measuring device so that the measurement signal and the modulating signal are alternately in phase or out of phase for each first inversion period (n is a natural number), and further including a step in which the second impedance measuring device inverts the sign of the magnitude of the filtered signal generated when the measurement signal and the modulating signal are out of phase before calculating the average. [Effects of the Invention]

[0015] The impedance measurement system and method according to the present invention can suppress the influence of noise near the measurement frequency due to interference between multiple impedance measurement devices, thereby enabling highly accurate impedance measurement. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating a state in which an impedance measurement system according to an embodiment of the present invention is connected to a measurement object. [Figure 2] 1 is a schematic diagram illustrating a state in which a first impedance measuring device constituting an impedance measuring system is connected to an object to be measured. [Figure 3] FIG. 2 is a schematic diagram illustrating the configuration of a second impedance measurement device and a third impedance measurement device that constitute an impedance measurement system, each connected to a measurement target. [Figure 4] 1 is a flowchart of an impedance measurement method according to an embodiment of the present invention. [Figure 5] 5 is a flowchart showing the operation of the first impedance measuring device. [Figure 6] 6 is a flowchart showing the operation of the second impedance measuring device and the third impedance measuring device. [Figure 7] 4 is a signal diagram showing temporal changes in the measurement signal and modulated signal of each impedance measuring device. FIG. 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 an impedance measurement system 4, an example of an embodiment of the present invention, connected to measurement targets 61, 62, and 63. The impedance measurement system 4 includes three impedance measurement devices 1, 2, and 3, each of which is connected to a measurement target 61, 62, or 63, respectively. The impedance measurement device 1 is connected to the other two impedance measurement devices 2 and 3, and controls the operation of the entire impedance measurement system 4. The connection between the impedance measurement devices 1, 2, and 3 may be wired, wireless, or via a network. Because the impedance measurement devices 1, 2, and 3 are arranged close to each other, mutual interference occurs.

[0018] Next, we will explain the configuration of each of the impedance measuring devices 1, 2, and 3. Fig. 2 is a schematic diagram of the impedance measuring device 1 connected to a measurement object 61, and Fig. 3 is a schematic diagram of the impedance measuring devices 2 and 3 connected to measurement objects 62 and 63, respectively. In Figs. 2 and 3, components having similar functions are assigned the same reference numerals.

[0019] Impedance measuring device 1 comprises measurement signal supply unit 10, measurement unit 20, signal generation unit 35, and calculation unit 41. Over measurement period M, measurement signal supply unit 10 supplies measurement signal Im to object to be measured 61 via contact terminals 51, 53, which contact both terminals of object to be measured 61. Measurement unit 20 detects signal Vm generated between contact terminals 52, 54, which contact both terminals of object to be measured 61, in response to measurement signal Im. Detection signal Vm is synchronously detected using modulation signal Vmod1, and filtered to generate filtered signals Vi and Vq by low-pass filtering. Impedance measuring device 1 determines internal impedance Z and phase angle θ of object to be measured 61 based on the average magnitudes of filtered signals Vi and Vq over measurement period M. Reference signal Vr2, which serves as the basis for measurement signal Im, and reference signal Vr1, which serves as the basis for modulation signal Vmod1 for synchronously detecting detection signal Vm, are generated by signal generation unit 35.

[0020] As mentioned above, synchronous detection means detecting using a modulated signal Vmod1 having the same frequency as the measurement signal Im and a signal Vmod2 that is 90 degrees out of phase with the modulated signal. For ease of explanation, the signal Vmod2 that is 90 degrees out of phase with the modulated signal Vmod1 will be referred to as the modulated signal Vmod2, but in the present invention, the phase angle of the modulated signal of each impedance measuring device means the phase angle of the modulated signal Vmod1 of each impedance measuring device.

[0021] The measurement signal supplying unit 10 is connected to the signal generating unit 35 and the contact terminals 51 and 53, and includes a signal source that generates a measurement signal Im having the same frequency and phase as the reference signal Vr2 input from the signal generating unit 35. The generated measurement signal Im is supplied via the contact terminals 51 and 53 to the measurement object 61 connected to the contact terminals 51 and 53.

[0022] The measuring unit 20 is connected to the signal generating unit 35, the calculating unit 41 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.

[0023] 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 61, in response to the measurement signal Im, and outputs a detection signal Vm.

[0024] The 90-degree phase shifter 26 has an input connected to the signal generating unit 35 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 35 by 90 degrees to generate a modulated signal Vmod2.

[0025] Multipliers 22 and 23 are detectors that perform synchronous detection. The input of multiplier 22 is connected to detection circuit 21 and signal generating unit 35, and the output is connected to LPF 24. Multiplier 22 detects detection signal Vm received from detection circuit 21 with modulated signal Vmod1, which has the same frequency and phase as reference signal Vr1 received from signal generating unit 35, and outputs detected signal Vd1. The input of multiplier 23 is connected to detection circuit 21 and 90-degree phase shifter 26, and the output is connected to LPF 25. Multiplier 23 detects detection signal Vm received from detection circuit 21 with modulated signal Vmod2, which has the same frequency and is in phase with reference signal Vr1 received from 90-degree phase shifter 26, and outputs detected signal Vd2.

[0026] 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 41. LPF 24 performs low-pass filtering on the detection signal Vd1 output from multiplier 22 to extract the DC component and generate a filtered signal Vi. LPF 25 performs low-pass filtering on the detection signal Vd2 output from multiplier 23 to extract the DC component and generate a filtered signal Vq.

[0027] Signal generating unit 35 has an input connected to calculation unit 41 and an output connected to measurement signal supplying unit 10 and measurement unit 20, and is equipped with reference signal generator 33. Reference signal generator 33 has an input connected to calculation unit 41 and an output connected to measurement signal supplying unit 10 and multiplier 22 and 90-degree phase shifter 26 of measurement unit 20. Reference signal generator 33 generates reference signal Vr1 with a period and phase angle specified by a control signal from calculation unit 41.

[0028] The calculation unit 41 records the magnitudes of the filtered signals Vi and Vq input from the measurement unit 20 in memory together with the detection time. The magnitudes of the recorded filtered signals Vi and Vq are averaged over the measurement period M to determine the internal impedance Z and phase angle θ of the object to be measured 61. The calculation unit 41 also generates signals for controlling the period and phase angle of the reference signal Vr1 generated by the reference signal generator 33, control signals for the entire impedance measurement system 4, such as setting the measurement period M of the impedance measurement devices 2 and 3, setting the frequency and phase angle of the measurement signal and modulation signal, setting the inversion period T, and issuing a measurement start command. Which A control signal is generated to perform the above.

[0029] 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 41, 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 41 described above is stored in the memory, and the functions of the elements of the measuring unit 20 and the calculating unit 41 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 41 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 above refers to electrical and mechanical connections for the hardware configuration and processing flows for the software configuration.

[0030] Next, the configuration of the impedance measuring devices 2 and 3 will be described with reference to Fig. 3. The impedance measuring devices 2 and 3 include a measurement signal supplying section 10, a measuring section 20, a signal generating section 30, and a calculating section 40. Impedance measuring devices 2 and 3 supply measurement signal Im from measurement signal supply unit 10 to objects of measurement 62 and 63 over measurement period M via contact terminals 51 and 53, which contact both terminals of objects of measurement 62 and 63, respectively. Measurement unit 20 detects signal Vm generated between contact terminals 52 and 54, which contact both terminals of objects of measurement 62 and 63, in response to measurement signal Im. Detected signal Vm is synchronously detected using modulation signal Vmod1, and low-pass filtered to generate filtered signals Vi and Vq. The signs of the filtered signals Vi and Vq, generated when measurement signal Im and modulation signal Vmod1 are out of phase, are inverted, and the internal impedance Z and phase angle θ of objects of measurement 62 and 63 are calculated based on the average magnitude of filtered signals Vi and Vq over measurement period M. Reference signal Vr2, which serves as the basis for measurement signal Im, and reference signal Vr1, which serves as the basis for modulation signal Vmod1, are generated by signal generating unit 30.

[0031] Of the configurations of the impedance measuring devices 2 and 3, the configurations of the measurement signal supplying unit 10 and the measurement unit 20 are the same as those of the impedance measuring device 1. The signal generating unit 30 has an input connected to the calculation unit 40 and an output connected to the measurement signal supplying unit 10 and the measurement unit 20, and includes a reference signal generator 33, a phase inverter 31, and a switch 32.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The calculation unit 40 records the magnitudes of the filtered signals Vi and Vq input from the measurement unit 20 in memory along with the detection time. Then, over the measurement period M, the calculation unit 40 calculates the average of the magnitudes of the filtered signals Vi and Vq when the reference signals Vr1 and Vr2 are in positive phase and the magnitudes of the filtered signals Vi and Vq with their signs inverted when the reference signals Vr1 and Vr2 are in negative phase, to determine the internal impedance Z and phase angle θ of the object to be measured 61. The calculation unit 40 also generates a signal to control the period and phase angle of the reference signal Vr1 generated by the reference signal generator 33, and generates a control signal Vs that switches the switch 32 every inversion period T. Furthermore, the calculation unit 40 of the impedance measuring devices 2 and 3 is connected to the calculation unit 41 of the impedance measuring device 1, and sets the measurement period M of each of the impedance measuring devices 2 and 3, the frequency and phase angle of the measurement signal and modulation signal, the inversion period T, and starts measurement, in response to the control signal received from the impedance measuring device 1. Similar to the calculation unit 41 described above, the calculation unit 40 in this embodiment is configured as a computer equipped with a processor and memory.

[0036] Next, before describing the operation of the impedance measurement system 4, the principle of suppressing the influence of noise near the measurement frequency due to mutual interference between a plurality of impedance measurement devices using the impedance measurement system and method of the present invention will be described.

[0037] When a measurement signal Im = I sin2πft (I is a constant, f is the measurement frequency, and t is time) is passed through the objects under test 61, 62, and 63, a signal Vm = ZI sin(2πft + θ) corresponding to the impedance Z and phase angle θ of the object under test 61 is generated between the two terminals of each of the objects under test 61, 62, and 63. When this signal is detected as a detection signal Vm and modulated by a modulation signal Vmod1 = sin2πft that has the same frequency and phase as the measurement signal Im, a detection signal Vd1 is obtained in which a DC component corresponding to the resistance component R = Z cosθ of the impedance Z of the objects under test 61, 62, and 63 and an AC component of frequency 2f are superimposed, as shown in equation (1).

[0038]

number

[0039] Furthermore, when the detection signal Vm is modulated by a modulation signal Vmod2=cos2πft that is 90 degrees out of phase with the measurement signal Im, a detection signal Vd2 is obtained in which a DC component corresponding to the reactance component X=Zsinθ of the impedance Z of the measurement objects 61, 62, and 63 and an AC component of frequency 2f are superimposed, as shown in equation (2).

[0040]

number

[0041] The detection signals Vd1 and Vd2 are low-pass filtered to generate filtered signals Vi and Vq, from which the DC component has been extracted, as shown in equation (3). 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 61 can be determined from the instantaneous voltage values of the filtered signals Vi and Vq. Note that 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]

number

[0043] 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 signal component shown in equation (4).

[0044]

number

[0045] 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 multiple impedance measuring devices 1, 2, and 3 are used in parallel to perform impedance measurements at similar measurement frequencies, particularly the same or nearly the same measurement frequencies, mutual interference between the measuring devices can occur. Because the frequency fn of the external noise Vn is close to the modulating signal Vmod1, it is difficult to sufficiently remove the external noise Vn by low-pass filtering. Therefore, the filtered signals of each impedance measuring device 1, 2, and 3 contain 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 measurement targets 61, 62, and 63 from the measured values of such filtered signals Vi and Vq results in large measurement errors.

[0046] To suppress the effects of external noise as described above, it is sufficient to obtain a filtered signal that is opposite in phase to the first term on the right-hand side of equation (4) and average it to cancel it out. To obtain such an opposite-phase filtered signal, the measurement signal Im from another measurement device that is the source of external noise can be made opposite in phase, or the phase angle of the measurement signal Im itself can be inverted and the signs of the filtered signals Vi and Vq can be inverted. In the present invention, the measurement signals Im from the impedance measuring devices 2 and 3 are changed to a positive phase for half of the measurement period M and to a negative phase for the other half, thereby inverting the phase of the external noise Vn input to the impedance measuring device 1 during the measurement period M. Then, the impedance measuring device 1 averages the filtered signals Vi and Vq over the measurement period M to cancel out the low-frequency components of equation (4) and suppress the effects of the external noise Vn.

[0047] Furthermore, the impedance measuring devices 2 and 3 change the phase of their own measurement signals Im so that they are in phase with modulated signal Vmod1 for half of the measurement period M and out of phase with modulated signal Vmod1 for the remaining half. Then, components of filtered signals Vi and Vq resulting from signals generated in the objects of measurement 62 and 63 by measurement signal Im are out of phase when the measurement current Im and modulated signal Vmod1 are in phase and out of phase. Meanwhile, components of filtered signals Vi and Vq resulting from noise signals from other impedance measuring devices are in phase when the measurement current Im and modulated signal Vmod1 of the second impedance measuring device are in phase and out of phase. Therefore, by inverting the signs of filtered signals Vi and Vq during the period when the phase of measurement signal Im and modulated signal Vmod1 are out of phase and averaging filtered signals Vi and Vq over measurement period M, the noise components contained in the filtered signals can be canceled out. Then, by determining the impedance and phase angle of the object to be measured based on the magnitude of the filtered signal with the noise components suppressed, it becomes possible to perform highly accurate impedance measurement while suppressing the effects of noise near the measurement frequency caused by mutual interference.

[0048] Next, the operation of the impedance measurement system 4 of this embodiment, that is, one example of an embodiment of the impedance measurement method of the present invention, will be described with reference to the flowcharts of Figures 4 to 6 and the signal diagram of Figure 7. Figure 4 is a flowchart showing the operation of the entire impedance measurement system 4. In the impedance measurement system 4 of this embodiment, the calculation unit 41 of the impedance measurement device 1 also controls the entire impedance measurement system 4, and therefore all operations except for the individual impedance measurements of the impedance measurement devices 1, 2, and 3 (step 205) are carried out by the computer of the calculation unit 41 of the impedance measurement device 1.

[0049] Fig. 5 is a flowchart of the operation of impedance measuring device 1 to measure the impedance of object to be measured 61, and Fig. 6 is a flowchart of the operation of impedance measuring devices 2 and 3 to measure the impedance of objects to be measured 62 and 63. In Figs. 5 and 6, steps that perform similar functions are given the same reference numerals. Fig. 7 is a signal diagram showing the temporal changes in the measurement signal Im and modulation signal Vmod1 of each of the impedance measuring devices 1, 2, and 3.

[0050] First, the calculation unit 41 of the impedance measuring device 1 communicates with the calculation units 40 of the impedance measuring devices 2 and 3 to set the measurement period of each of the impedance measuring devices 1, 2, and 3 to the same measurement period M (step 201). The calculation unit 41 of the impedance measuring device 1 also communicates with the calculation units 40 of the impedance measuring devices 2 and 3 to set the reference signal generators 33 of each of the impedance measuring devices 1, 2, and 3 to generate reference signals Vr1 of the same frequency f. Because the reference signal Vr1 is a signal that serves as the basis for the reference signal Vr2, the measurement signal Im, and the modulation signals Vmod1 and Vmod2, the above setting sets the measurement signal Im and modulation signal Vmod1 of each of the impedance measuring devices 1, 2, and 3 to the same frequency (step 202). Note that the measurement signals Im and modulation signals Vmod1 of each of the impedance measuring devices 1, 2, and 3 do not all need to be the same; they only need to be approximately the same.

[0051] Next, the calculation unit 41 of the impedance measuring device 1 communicates with the calculation unit 40 of the impedance measuring device 2 to set the inversion period T1 of the impedance measuring device 2 to 1 / 2 of the measurement period M. n (n is a natural number) (step 203). As a result, the phase angle of the reference signal Vr2 of the impedance measuring device 2 is inverted every inversion period T1. Then, the phase angle of the measurement signal Im, which is in phase with the reference signal Vr2, is also inverted every inversion period T1. As a result, during the measurement period M, the total period during which the measurement signal Im of the impedance measuring device 2 is in positive phase and the total period during which it is in negative phase are both half the measurement period M. In this embodiment, n=1, that is, the inversion period T1 is set to 1 / 2 of the measurement period M.

[0052] Next, the calculation unit 41 of the impedance measuring device 1 communicates with the calculation unit 40 of the impedance measuring device 3 to set the inversion period T2 of the impedance measuring device 3 to 1 / 2 of the inversion period T1 of the impedance measuring device 3. m (m is a natural number) (step 204). As a result, the phase angle of the reference signal Vr2 of the impedance measuring device 3 is inverted every inversion period T2. Then, the phase angle of the measurement signal Im, which is in phase with the reference signal Vr2, is also inverted every inversion period T2. As a result, during the inversion period T1, during which the measurement signal Im of the impedance measuring device 2 is in either positive or negative phase, the total period during which the measurement signal Im of the impedance measuring device 3 is in positive phase and the total period during which it is in negative phase are both half the inversion period T1. In this embodiment, m=1, i.e., the inversion period T2 is set to 1 / 2 of the inversion period T1, i.e., 1 / 4 of the measurement period M.

[0053] FIG. 7 shows the temporal changes in the measurement signal Im and modulation signal Vmod1 of each of the impedance measuring devices 1, 2, and 3 with the above settings. The phase angle of the modulation signal Vmod1 of each of the impedance measuring devices 1, 2, and 3 and the measurement signal Im of the impedance measuring device 1 is constant over the measurement period M. The phase angle of the measurement signal Im of the impedance measuring device 2 changes between the first half of the measurement period M (time 0 to T1) and the second half of the measurement period M (time T1 to 2T1). In other words, the measurement signal Im of the impedance measuring device 2 and modulation signal Vmod1 change over half of the measurement period M. n The phase angle of the measurement signal Im of the impedance measuring device 2 changes so that it alternates between being in phase and being out of phase every inversion period T1 (n is a natural number).

[0054] The measurement signal Im of the impedance measuring device 3 changes phase angle between the first half (time 0 to T2, 2T2 to 3T2) of the inversion period T1 (time 0 to T1, T1 to 2T1) and the second half (time T2 to 2T2, 3T2 to 4T2) of the inversion period T1. That is, the measurement signal Im of the impedance measuring device 3 and the modulation signal Vmod1 are in phase with each other for 1 / 2 of the inversion period T1. m The phase angle of the measurement signal Im of the impedance measuring device 3 changes so that it alternates between being in phase and being out of phase every inversion period T2 (m is a natural number).

[0055] Returning to the explanation of the flowchart in Fig. 4, based on the above-mentioned settings, the impedance measuring devices 1, 2, and 3 perform impedance measurements in parallel (step 205).

[0056] Next, the impedance measurement (step 205) in each of the impedance measuring devices 1, 2, and 3 will be described in detail. FIG. 5 shows the operation of the impedance measuring device 1 of this embodiment. First, the signal generating unit 35 generates in-phase reference signals Vr1 and Vr2 (step 101). More specifically, based on a control signal from the calculation unit 41, the reference signal generator 33 generates a reference signal Vr1 of frequency f. The generated reference signal Vr1 is supplied to the measurement signal supplying unit 10 as the reference signal Vr2. As is clear from FIG. 2, the reference signals Vr1 and Vr2 of the impedance measuring device 1 are always in-phase.

[0057] The measurement signal supply unit 10 generates a measurement signal Im having the same frequency and phase as the reference signal Vr2 received from the signal generation unit 35 and supplies it to the object under test 61 (step 102). Because the phase angle of the reference signal Vr2 is always constant, the measurement signal Im has a constant phase angle over the measurement period M. The measurement signal Im generates a voltage between both terminals of the object under test 61 that corresponds to the impedance Z and phase angle θ of the object under test 61. The detection circuit 21 detects the detection signal Vm generated between the contact terminals 52, 54 that are in contact with both terminals of the object under test 61 (step 103).

[0058] Next, multipliers 22 and 23 synchronously detect detection signal Vm with modulation signal Vmod1 (step 104). More specifically, multiplier 22 detects detection signal Vm with modulation signal Vmod1 that is in phase with reference signal Vr1. Because the phase angle of reference signal Vr1 is always constant, modulation signal Vmod1 has a constant phase angle over measurement period M. Furthermore, measurement signal Im and modulation signal Vmod1 are in phase over measurement period M. By modulating detection signal Vm with modulation signal Vmod1, detection signal Vd1 is obtained, in which a DC component corresponding to resistance component R of impedance Z of object to be measured 61 and an AC component of frequency 2f are superimposed. Furthermore, when the multiplier 23 modulates the detection signal Vm with a signal Vmod2 generated by the 90-degree phase shifter 26 and having 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 of the impedance Z of the object to be measured 61 and an AC component of frequency 2f are superimposed.

[0059] Next, the LPFs 24 and 25 low-pass filter the detection signals Vd1 and Vd2 to extract the DC components and generate filtered signals Vi and Vq (step 105). Next, the calculation unit 41 stores the magnitudes of the filtered signals Vi and Vq together with the detection times in memory (step 106). This completes the measurement of the instantaneous values of the filtered signals Vi and Vq at the detection times.

[0060] As described above, in the present invention, the magnitude of the filtered signals Vi and Vq is measured over the measurement period M, and the average is calculated to determine the magnitude of the filtered signal with the noise component suppressed. Specifically, first, the operations from step 102 to step 106 described above are repeated every predetermined sampling period over the measurement period M (step 109). When the measurement period M ends, the temporal changes in the magnitude of the filtered signals Vi and Vq over the measurement period M are recorded in memory.

[0061] Next, the processor of the calculation unit 41 reads out from memory the magnitudes of all filtered signals Vi during measurement period M and calculates the average. Similarly, the processor of the calculation unit 41 reads out from memory the magnitudes of all filtered signals Vq during measurement period M and calculates the average (step 110). Because the measurement signals Im of the impedance measuring devices 2 and 3 are positive in phase for half of measurement period M and negative in phase for the other half, the noise signal input to the detection circuit 21 of the impedance measuring device 1 is also positive in phase for half of measurement period M and negative in phase for the other half. Therefore, by averaging the filtered signals Vi and Vq over measurement period M, the effects of external noise Vn can be suppressed.

[0062] Finally, the processor of the calculation unit 41 calculates the impedance Z (R and X) and phase angle θ of the object to be measured 61 using equation (3) 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).

[0063] Next, the impedance measurement (step 205) of the impedance measuring devices 2 and 3 will be described in detail with reference to Fig. 6. First, the signal generating unit 30 generates in-phase reference signals Vr1 and Vr2 (step 101). In the impedance measuring devices 2 and 3, the signal generating unit 30 includes a reference signal generator 33, a phase inverter 31, and a switch 32. First, based on a control signal from the calculation unit 40, the reference signal generator 33 generates a reference signal Vr1 of frequency f, and the switch 32 selectively outputs a positive-phase input. As a result, the switch 32 outputs a reference signal Vr2 that is in-phase with the reference signal Vr1.

[0064] Thereafter, operations similar to steps 102 to 106 of the impedance measuring device 1 are repeatedly performed for each predetermined sampling period over inversion periods T1 and T2 (step 107). As is clear from Fig. 3, the reference signal Vr1 that serves as the basis for the modulated signal Vmod1 of the impedance measuring devices 2 and 3 always has a constant phase angle, and therefore the modulated signal Vmod1 of the impedance measuring devices 2 and 3 has a constant phase angle over the measurement period M.

[0065] After the inversion periods T1 and T2 have elapsed, the calculation unit 40 transmits a control signal Vs that switches the switch 32. The switch 32 then selectively outputs the opposite-phase input. As a result, the switch 32 outputs a reference signal Vr2 that is opposite in phase to the reference signal Vr1 (step 108). Thereafter, steps 102 to 108 are repeated until the predetermined measurement period M ends (step 109).

[0066] As a result, the measurement signal Im of the impedance measuring device 2 and the modulation signal Vmod1 are inverted at an inversion period T1, i.e., 1 / 2 of the measurement period M. n The phase angle of the measurement signal Im changes so that it is alternately in phase or out of phase every inversion period T2 (n is a natural number). m The phase angle of the measurement signal Im changes so that it is alternately in phase or out of phase every m (m is a natural number).

[0067] After the measurement period M ends, the memory records the temporal changes in the voltages of the filtered signals Vi and Vq over the measurement period M. However, half of the recorded filtered signals Vi and Vq are the voltages of the filtered signals Vi and Vq when the measurement signal Im and the modulation signal Vmod1 are in phase, and the other half are the voltages of the filtered signals Vi and Vq when the measurement signal Im and the modulation signal Vmod1 are out of phase.

[0068] Next, the processor of the calculation unit 41 reads from memory the magnitudes of all filtered signals Vi during the measurement period M, inverts the sign of the magnitude of the filtered signal Vi generated when the measurement signal Im and the modulation signal Vmod1 are out of phase, and then averages them. Similarly, the processor of the calculation unit 41 reads from memory the magnitudes of all filtered signals Vq during the measurement period M, inverts the sign of the magnitude of the filtered signal Vq generated when the measurement signal Im and the modulation signal Vmod1 are out of phase, and then averages them (step 110). Because the noise signal caused by the measurement signal Im of the impedance measuring device 1 has a constant phase angle over the measurement period M, and the modulation signal Vmod1 of the impedance measuring devices 2 and 3 also has a constant phase angle over the measurement period M, the components of the external noise Vn included in the filtered signals Vi and Vq are in phase over the measurement period M. On the other hand, the measurement signal Im of the impedance measuring devices 2 and 3 is in phase with the modulating signal Vmod1 for half of the measurement period M and is out of phase with the modulating signal Vmod1 for the remaining half, so the components contained in the filtered signals Vi and Vq that are attributable to the signals generated in the objects of measurement 62 and 63 by the measurement signal Im are out of phase with each other for half and the remaining half of the measurement period M. Therefore, by inverting the signs of the magnitudes of the filtered signals Vi and Vq generated when the measurement signal Im and the modulating signal Vmod1 are out of phase, and then averaging the filtered signals Vi and Vq over the measurement period M, the effects of external noise Vn can be suppressed.

[0069] Finally, the processor of the calculation unit 40 calculates the impedance Z (R and X) and phase angle θ of the objects to be measured 62, 63 from the average obtained in step 110, i.e., the magnitude of the filtered signals Vi, Vq from which the external noise Vn has been canceled (step 111).

[0070] 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. RukoFor example, in the impedance measurement system 4 described in the above embodiment, the calculation unit 41 of the impedance measurement device 1 serves as a control device for the entire system, but a central control device connected to the impedance measurement devices 1, 2, and 3 may be provided, and the central control device may control the entire system shown in steps 201 to 204 in Fig. 4.

[0071] In the above-described embodiment, the inversion period is set before each of the impedance measuring devices 2 and 3 starts impedance measurement (steps 203 and 204). However, instead of setting the period in advance, the phase angle may be changed by the impedance measuring device 1 or a central control device at the timing of changing the phase angle (step 108). Furthermore, in the impedance measuring devices 2 and 3, the signal generating unit 35 generates a reference signal based on the frequency and phase angle specified by the calculation unit 41. Alternatively, the calculation unit 41 may generate digital data of a reference signal waveform that changes between positive and negative phases and generate the reference signal. Furthermore, the measurement signal Im of the above-described impedance measuring devices 1, 2, and 3 is in phase with the reference signal Vr2, and the modulation signal Vmod1 is in phase with the reference signal Vr1. However, there may be the same amount of phase offset relative to 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]

[0072] 1, 2, 3 Impedance measuring device 4. Impedance measurement system 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, 35 Signal generating unit 31 Phase inverter 32 Switch 33 Reference Signal Generator 40 41 Arithmetic unit 51, 52, 53, 54 contact terminal 61, 62, 63 Measurement target

Claims

1. An impedance measurement system comprising a first impedance measurement device and a second impedance measurement device, and determining the impedance of a measurement object connected to the first impedance measurement device and the second impedance measurement device, Each of the first impedance measuring device and the second impedance measuring device comprises: a measurement signal supply unit that supplies a measurement signal to the measurement object over a predetermined measurement period; a measurement unit that, over the measurement period, synchronously detects a signal generated in the object to be measured by the measurement signal using a modulated signal, and generates a filtered signal by low-pass filtering the detected signal; a calculation unit that calculates the impedance of the object to be measured based on an average magnitude of the filtered signal over the measurement period; Equipped with the measurement signals of the first impedance measuring device and the second impedance measuring device have substantially the same frequency; the measurement signal and the modulation signal of the first impedance measuring device have a constant phase angle over the measurement period; the modulated signal of the second impedance measuring device has a constant phase angle over the measurement period; The measurement signal and the modulation signal of the second impedance measuring device are ｎ the phase angle of the measurement signal of the second impedance measuring device is changed so as to be alternately in phase or out of phase for each first inversion period of n (n is a natural number); the calculation unit of the second impedance measuring device inverts the sign of the magnitude of the filtered signal generated when the measurement signal and the modulation signal are in opposite phase before calculating the average. Impedance measurement system.

2. a measurement signal supply unit that supplies a measurement signal to the measurement object over the measurement period; a measurement unit that, over the measurement period, synchronously detects a signal generated in the object to be measured by the measurement signal using a modulated signal, and generates a filtered signal by low-pass filtering the detected signal; a calculation unit that calculates the impedance of the object to be measured based on an average magnitude of the filtered signal over the measurement period; a third impedance measuring device comprising: the measurement signal of the third impedance measuring device has substantially the same frequency as the measurement signals of the first impedance measuring device and the second impedance measuring device; the modulated signal of the third impedance measuring device has a constant phase angle over the measurement period; The measurement signal and the modulation signal of the third impedance measuring device are inverted at half the frequency of the first inversion period. ｍ the phase angle of the measurement signal of the third impedance measuring device is changed so as to be alternately in phase or out of phase for each second inversion period of m (m is a natural number); the calculation unit of the third impedance measuring device inverts the sign of the magnitude of the filtered signal generated when the measurement signal and the modulation signal are in opposite phase before calculating the average. The impedance measurement system of claim 1 .

3. An impedance measurement method for determining impedances of objects to be measured that are connected to a first impedance measurement device and a second impedance measurement device, the method comprising: each of the first impedance measuring device and the second impedance measuring device supplying a measurement signal to the measurement target for a predetermined measurement period; each of the first impedance measuring device and the second impedance measuring device synchronously detecting, over the measurement period, a signal generated in the object to be measured by the measurement signal using a modulated signal, and generating a filtered signal by low-pass filtering the signal; each of the first impedance measuring device and the second impedance measuring device determining the impedance of the object to be measured based on an average magnitude of the filtered signal over the measurement period; Including, the measurement signals of the first impedance measuring device and the second impedance measuring device have substantially the same frequency; the measurement signal and the modulation signal of the first impedance measuring device have a constant phase angle over the measurement period; the modulated signal of the second impedance measuring device has a constant phase angle over the measurement period; The step of generating the low-pass filtered signal includes the step of generating the low-pass filtered signal by adjusting the frequency of the measurement signal of the second impedance measuring device and the modulation signal for half the measurement period. ｎ (n is a natural number) first inversion periods, the phase angle of the measurement signal of the second impedance measuring device is changed so that the measurement signal is alternately in phase or out of phase, the second impedance measuring device further includes the step of inverting the sign of the magnitude of the filtered signal produced when the measurement signal and the modulation signal are in antiphase before calculating the average. Impedance measurement method.

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