JP6778514B2 - Impedance measuring device and impedance measuring method - Google Patents

Description

The present invention relates to an impedance measuring device and an impedance measuring method.

As a method of measuring the internal impedance of an element constituting an electric circuit, there is an AC impedance measuring method in which an AC signal is given to a sample to be measured and the electric response thereof is measured. In this method, the magnitudes of the resistance component, capacitance component, and inductance component of the sample can be investigated.

As such an impedance measurement method, a sinusoidal measurement alternating current is supplied from a constant current source to the sample, and the voltage signal appearing on the sample is referred to as a reference signal (or reference signal) having the same frequency that synchronizes with the supplied measurement alternating current. ), There is an impedance measurement method using synchronous detection that reduces the influence of noise components appearing on the sample.
The following prior art documents are available for impedance measuring devices by synchronous detection.

Impedance measurement by synchronous detection will be described below.
The measured alternating current is supplied from a constant current source to the sample (eg, a battery with internal resistance). A detection resistor (current detection resistor) for detecting the current value of the measured alternating current is inserted in series with the constant current source and the sample. It is provided with a first amplifier that amplifies the detection signal (voltage signal) appearing in the sample according to the measured AC current and a second amplifier that amplifies the voltage signal detected by the current detection resistor, and is amplified by the first amplifier. The voltage detection signal is input to the synchronous detector through a bandpass filter (BPF) that passes the measurement frequency. Further, the reference signal synchronized with the measured alternating current is amplified by the second amplifier and input to the synchronous detector. The synchronous detector synchronously detects the voltage detection signal with the reference signal, and the detection output is input to the low-pass filter (LPF) for removing the AC component, the AC component is removed, and the analog digital converter (ADC) is used. Entered. The analog-to-digital converter converts the synchronous detection output into a digital signal. The converted digital signal is input to the arithmetic unit, the AC impedance value of the sample is calculated, and these values are displayed on a display device or the like, or printed and output.

In this way, the voltage detection signals across the sample are synchronously detected with a reference signal in the same phase as the measured AC current, and the AC component is removed by the low-pass filter, so that only the DC component is extracted, so pure resistance such as a battery The effective impedance of the sample to be measured containing components other than the above can be obtained. Further, since the AC component appearing in the synchronous detection is removed by the low-pass filter, the influence of the noise that is the AC can be removed, and a minute signal buried in the noise can be taken out.

JP-A-2007-132806

Since the sample to be measured is an element constituting an electric circuit, noise may be superimposed on the sample, and the noise affects the impedance measurement. For example, the case where the battery installed in the UPS (uninterruptible power supply) is used as the measurement sample. Since the UPS needs to be constantly operating, an inverter or a converter is operating to charge or discharge the UPS. For this reason, noise generated from the inverter or converter is often applied to the battery. Further, since the load is connected, noise often enters from the load side as well. In this way, when the impedance is measured using the UPS battery as a sample, the noise component is detected from the sample to which the measurement alternating current is applied.

However, noise may not be completely removed even if synchronous detection is performed using a reference signal having the same phase as the measured AC current and the AC component is removed by a low-pass filter.

For example, a low-pass filter having a frequency characteristic as shown in FIG. 10 can remove noise at frequencies above X (Hz), but can hardly remove frequencies below XHz.
As described above, when the noise is a noise having a frequency close to the measurement frequency (for example, X (Hz) in FIG. 10), the low-pass filter having the attenuation characteristic that there is almost no attenuation with respect to the frequency is all the noise. Is difficult to remove.

Therefore, when noise enters the detection signal, a measurement error occurs, and the measured impedance value also varies, which causes a problem that the measured value is not stable.

An object of the present invention is to provide an impedance measuring device and a measuring method capable of acquiring a stable measured value faster and with higher accuracy by suppressing the influence generated from a noise component.

In order to solve the above problems, the first aspect of the present invention is an impedance measuring device, in which an AC supply unit that supplies a measurement signal of a predetermined frequency to a sample to be measured and a reference signal synchronized with the measurement signal are provided. A reference signal generator to be generated, a synchronous detection unit that synchronously detects the detection signal appearing in the sample with the reference signal, a plurality of low-pass filters that input the synchronously detected signal by the synchronous detection unit and have different response characteristics and attenuation characteristics. A selection means for switching between a plurality of low-pass filters and selecting one of them, and a selection means for determining whether or not the measured value calculated based on the output data of the low-pass filter is stable, and switching and calculation of the low-pass filter by the selection means. The reference signal generation unit is provided with a means for generating two reference signals having different phases, and the calculation means is a measurement calculated based on the output data of the selected low-pass filter. If the variation of the value is within the predetermined allowable range, it is determined that the measured value is stable, the obtained measured value is retained, and if the variation of the measured value is not within the predetermined allowable range, other means are selected. It is characterized by switching to the low-pass filter of the above and determining whether the variation of the measured value calculated based on the output data of the low-pass filter after switching is within a predetermined allowable range.

It should be noted that the determination of whether the variation of the measured values performed by the calculation means is within the predetermined allowable range is the determination of whether the moving average of the measured values is within the predetermined allowable range, and when the low-pass filter is switched, after the switching. It is preferable to make a judgment by the moving average of the measured values calculated based on the output data of the low-pass filter .

Further, it is preferable that the sample is a battery and the AC supply unit is a constant current source.

Another aspect of the present invention is to supply a measurement signal of a predetermined frequency to a sample to be measured, synchronously detect a detection signal appearing in the sample with a reference signal synchronized with the measurement signal, and extract a DC component of the synchronously detected signal. This is an impedance measurement method for measuring the AC impedance of a sample, in which a step of supplying a measurement signal of a predetermined frequency to the sample to be measured, a step of generating a reference signal synchronized with the measurement signal, and a detection signal appearing on the sample. The step of synchronously detecting with a reference signal, the step of inputting the synchronously detected signal to a plurality of low-pass filters having different response characteristics and attenuation characteristics, and the step of inputting one of a plurality of low-pass filters were selected and selected. The step of calculating the measured value based on the output data of the low-pass filter and determining whether or not the calculated measured value is stable, and the step of generating the reference signal synchronized with the measured signal are two steps having different phases. The determination step , which includes the step of generating one reference signal, determines that the measurement value is stable when the variation of the measurement value calculated based on the output data of the selected low-pass filter is within a predetermined allowable range. If the obtained measured value is retained and the variation of the measured value is not within a predetermined allowable range, the measurement value is switched to another low-pass filter by the selection means, and the calculation is performed based on the output data of the low-pass filter after the switching. It is characterized by including a step of determining whether or not the variation of the measured values is within an allowable range.

The determination of whether the variation of the measured values is within the predetermined allowable range is the determination of whether the moving average of the measured values is within the predetermined allowable range. When the low-pass filter is switched, the output of the low-pass filter after the switching is performed. It can be determined by the moving average of the measured values calculated based on the data .

It is possible to suppress the influence generated by the noise component and obtain a stable measured value faster. In addition, highly accurate measured values can be obtained.

It is a figure which shows the structure of the impedance measuring apparatus by synchronous detection which concerns on one Embodiment of this invention. It is a figure which showed the response characteristic of three kinds of low-pass filters (LPF). It is a figure which showed the attenuation characteristic of three kinds of low-pass filters (LPF). It is a figure which shows the structure of the impedance measuring apparatus which includes the determination means which determines whether the measured value is stable. It is a flowchart explaining the operation of determining whether the measured value is stable by the moving average of the measured value. It is a figure which shows the variation of the output data of LPF1 and LPF2. It is a flowchart explaining the initialization of the moving average when switching between two low-pass filters. It is a figure which shows the structure of the impedance measuring apparatus which uses the synchronous detection by the reference signal of a different phase. It is a figure for demonstrating the effect that the range which is not influenced by noise is widened by a selection process. It is a figure which shows the frequency characteristic example of a low-pass filter.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an impedance measuring device by synchronous detection according to an embodiment of the present invention. The impedance measuring device 1 includes a constant current source 10, amplifiers 15 and 16, a bandpass filter (BPF) 17, a synchronous detector 20, and a plurality of lowpass filters (LPF) 22-1,22-2, ... 22-n. , An analog-to-digital converter (ADC) 23 is provided. The constant current source 10 corresponds to the AC supply unit of claim 1, and the synchronous detector 20 corresponds to the synchronous detector unit of claim 1.

The applicant has applied for the invention of an impedance measuring device and a measuring method in which a plurality of low-pass filters having different characteristics are operated in parallel and one of the low-pass filters is selected to obtain a stable measured value as Japanese Patent Application No. 2015-214019. .. This embodiment uses the configuration of the invention of Japanese Patent Application No. 2015-214019.

The constant current source 10 is connected to the sample (DUT) 11 to be measured via a pair of output terminals (not shown). In this embodiment, the sample 11 is a battery and has R _x as an internal resistance. A current detection resistor R _s is inserted (connected) between the constant current source 10 and the sample 11, and the detection signal of the sample 11 is input to a bandpass filter (BPF) 17 that passes the measurement frequency via the amplifier 15. Will be done. The current detection resistor R _s corresponds to the reference signal generation unit of claim 1.

The amplifier 15 amplifies the detection signal (voltage signal) appearing in the sample 11 according to the measured AC current i supplied from the constant current source 10, and the amplifier 16 amplifies the voltage signal detected by the current detection resistor Rs. .. Voltage detection signal v ₁ which is amplified by the amplifier 15 is input to a synchronous detector 20 via band-pass filter (BPF) 17 for passing the measurement frequency. The reference signal v ₂ to synchronize the measuring alternating current i is input to the synchronous detector 20 is amplified by the amplifier 16.

The output unit of the bandpass filter (BPF) 17 is connected to the input unit of the synchronous detector 20, and the output of the bandpass filter (BPF) 17 is input to the synchronous detector 20. The current detection resistors Rs are connected to the amplifier 16, the output unit of the amplifier 16 is connected to the input unit of the synchronous detector 20, and the output of the amplifier 16 is input to the synchronous detector 20.

The output section of the synchronous detector 20 is connected to the input section of the low-pass filter (LPF) 22-1,22-2, ... 22-n. Synchronous detector 20, the voltage detection signal _{v 1} synchronous detection by the reference signal _{v 2} a, the detection output, a low pass filter for removing an AC component (LPF) 22-1,22-2, ··· 22 Input to -n.

The output section of the low-pass filter 22-1,22-2, ... 22-n is connected to the analog-to-digital converter (ADC) 23 via SW1, and the low-pass filter 22-1,22-2, ... 22 The -n outputs V _AD1 , V _AD2 , ... V _ADn are input to the analog-to-digital converter (ADC) 23 via SW1. The low-pass filters 22-1,22-2, ... 22-n are connected in parallel with each other. SW1 corresponds to the selection means of claim 1.

Filter processing (AC component removal) is performed in parallel in each low-pass filter (LPF) 22-1,22-2, ... 22-n, and the output is selected and output based on a predetermined rule described later. The output is input to the analog-to-digital converter (ADC) 23. The analog-digital converter 23 converts the synchronous detection output into a digital signal. The converted digital signal is input to an arithmetic unit (not shown), the AC impedance value of the sample 11 is calculated, and these values are displayed or printed on a display device (not shown) or output.

Here, the low-pass filters (LPF) 22-1,22-2, ... 22-n have different response characteristics and attenuation characteristics, respectively. The response characteristic refers to the property that when an input is given to the low-pass filter (LPF) 22-1,22-2, ... 22-n, the output changes with time according to the time change. For example, good response characteristics mean that the response time until the output reaches 100% is short. Attenuation characteristics refer to the property of passing frequencies lower than the cutoff frequency and not passing frequencies higher than that. As shown in FIG. 3 described later, the damping gradient represents the damping characteristic.

Next, the impedance measurement operation in the impedance measurement device of FIG. 1 will be described. From the constant current source 10, a sine wave of i = Isin (ω ₁ t) is applied to the sample 11 as the measured alternating current. A voltage corresponding to the internal resistance R _{x of the} battery is generated at both ends of the sample 11, and the voltage is amplified by the amplifier 15 and output as v ₁ = iR _x . Further, v ₂ = iRs corresponding to the current detection resistor R _s is output from the amplifier 16 and synchronously detected by the synchronous detector 20. Here, v ₁ and v ₂ are
_{v 1 = Vsin (ω 1 t} ) = IR x sin (ω 1 t)
v ₂ = iRs = IR _s sin (ω ₁ t) = k sin (ω ₁ t)
Is. In addition, k is a constant (I and Rs are constant).

Synchronous detection output is
v ₁ x v ₂ = kIR _x sin (ω ₁ t) sin (ω ₁ t)
= 1/2 · kIR _x [cos (0) -cos (2ω ₁ t)]
Will be.

This synchronous detection output is input to a low-pass filter (LPF) 22-1,22-2, ... 22-n having different attenuation characteristics (cutoff frequency, attenuation amount) and response characteristics (response time). Initially, the switch SW1 selects the low pass filter (LPF) 22-1. That is, the output V _AD1 of the low-pass filter (LPF) 22-1 is selected by the switch SW1, and the output from which the predetermined AC component is cut off is input to the analog-digital converter 23.

The input of the analog-to-digital converter 23 is
V _AD = 1/2 · kIR _x cos (0) = 1/2 · kIR _x
As a result, the resistance value Rx of the internal resistance of the sample, which is the measured value, becomes
R _x = 2 / k · ( _VAD / I)
Can be obtained by.

Here, if the obtained measured value is not stable due to the influence of noise, the switch SW1 switches to the low-pass filter (LPF) 22-2. If the measured value is still unstable due to the influence of noise, switch to the low-pass filter (LPF) 22-3 with switch SW1. In this way, the low-pass filter (LPF) is sequentially switched by the switch SW1 until the measured value becomes stable.

Next, the switching operation of the low-pass filter (LPF) will be described in detail with reference to FIGS. 2 and 3. Refer to FIGS. 2 and 3 for how to select (switch) the above-mentioned low-pass filter (LPF) in order to stabilize the output of the measured value and shorten the measurement time in the calculation of the measured value. This will be described in detail. FIG. 2 is a diagram showing the response characteristics of three types of low-pass filters (LPF). FIG. 3 is a diagram showing the attenuation characteristics of three types of low-pass filters (LPF).

Regarding the response characteristics of the low-pass filters (1), (2), and (3), as shown in FIG. 2, the response time of the low-pass filter (1) is the fastest, and the response time of the low-pass filter (3) is the slowest. .. Regarding the attenuation characteristics of the low-pass filters (1), (2), and (3), as shown in FIG. 3, the attenuation of the low-pass filter (1) is the smallest and the attenuation of the low-pass filter (3) is the largest. .. In this embodiment, three types of low-pass filters having such characteristics are prepared.

First, a predetermined measurement frequency is selected, and the low-pass filter (1) is selected with the switch SW1. As shown in FIGS. 2 and 3, the low-pass filter (1) is a low-pass filter having the fastest response speed and the smallest attenuation. If the obtained measured value is stable, the impedance measurement at that measurement frequency ends here.

However, when the obtained measured value is not stable, the low-pass filter (2) is selected (switched) by the switch SW1. As shown in FIGS. 2 and 3, the low-pass filter (2) has a slower response speed than the low-pass filter (1) and a larger attenuation than the low-pass filter (1). If the obtained measured value is stable, the impedance measurement at that measurement frequency ends here.
However, when the obtained measured value is not stable, the low-pass filter (3) is selected (switched) by the switch SW1. As shown in FIGS. 2 and 3, the low-pass filter (3) has a slower response speed than the low-pass filter (2) and a larger attenuation than the low-pass filter (2). If the obtained measured value is stable, the impedance measurement at that measurement frequency ends here.

In the above example, three types of low-pass filters are used, but if low-pass filters with different characteristics are prepared, more stable measured values can be calculated as quickly as possible compared to the three types. be able to. The number of low-pass filters is preferably determined in consideration of the balance between stability and measurement time.

Regarding the selection (switching) of the low-pass filter, in the above-described embodiment, the low-pass filters (1), (2), and (3) were switched in this order, but in the order stored in the memory (not shown in FIG. 1). Therefore, it may be performed, or it may be switched according to the measured value displayed on the display unit (not shown).

Next, FIG. 4 shows and describes a configuration of an impedance measuring device including a determining means for determining whether or not the measured value is stable. The configuration of FIG. 4 further shows the configuration of the analog-to-digital converter (ADC) 23 or later of FIG. The alternating current of the constant current source 10 of the impedance measuring device shown in FIG. 1 is applied to the sample 11. The detection output appearing in the sample 11 is input to the voltage detection unit 30. The voltage detection unit 30 includes the current detection resistors Rs, amplifiers 15 and 16, bandpass filter (BPF) 17, synchronous detector 20, lowpass filter (LPF) 22, switch SW1, and analog digital converter (ADC) 23 shown in FIG. The voltage detection output thereof is input to the calculation unit 32 including the CPU. Further, the current detection unit 31 includes the current detection resistor Rs, detects the current i for impedance calculation, and inputs the output to the calculation unit 32. The calculation unit 32 includes a CPU, and the outputs of the voltage detection unit 30 and the current detection unit 31 are input, and are connected to the display unit 33, the operation unit 34, and the storage unit 35. The calculation unit 32 determines whether or not the measured value of the voltage detection unit 30 is stable, or performs measurement control such as low-pass filter switching control, sample impedance calculation, and hold control of the measured impedance value. The display unit 33 displays the measured value and the operation screen, and the operation unit 34 operates the impedance measuring device. The storage unit 35 stores the output data of the analog-to-digital converter (ADC) 23, calculated resistance values, parameters such as measurement conditions, and the like.

Next, the hold function will be described. The hold function is a function that performs impedance measurement and stops the measurement when the measured value becomes stable. During the measurement, the detection signal (here, the voltage signal) appearing in the sample supplied with the measurement AC current is sampled, and this sampling is performed at a predetermined cycle, for example, every 100 msec. By obtaining the resistance value Rx of the sample for each sampling, the resistance value of the sample can be obtained at predetermined time intervals.
The measured value for each sampling varies, and the resistance value of the sample can be obtained by the user monitoring that the output of the analog-to-digital converter (ADC) 23 becomes stable. In order to save the user from monitoring the displayed value, the impedance measuring device is equipped with a hold function that determines that the calculated resistance value or voltage detection signal is stable and automatically stops the measurement.
The calculation unit 32 determines whether the resistance value or the detection signal of the calculated sample is stable, and holds the sample. Whether or not the resistance value and the detection signal are stable can be determined by taking the moving average of the resistance value and the detection signal (voltage).

FIG. 5 shows and describes a flowchart for determining whether or not the measured resistance value and the voltage are stable by taking a moving average. Here, an example is shown in which whether or not the measured value is stable is determined based on whether or not the difference between the resistance value of the previous time, the time before the previous time, and the resistance value of this time is within a predetermined allowable range.

First, it is determined whether or not the difference between the current resistance value R _n acquired by sampling and the previous two times (two times previous resistance value) R _n-2 is within the first allowable range (step S11). Then, if it is within the first allowable range, it is determined whether or not the difference between the previous resistance value R _n-1 and the current resistance value R _n is within the second allowable range (step S12). .. When the difference between the two is within the allowable range, it is determined that the measured value is stable (step S13), and the measurement is held. If either of the two differences is not within the permissible range, it is determined that the measured value is unstable, sampling is continued, and the next moving averaging process is performed.
Whether or not this measured value is stable is determined by taking the moving average of the three samplings of the previous time, the previous time, and the current time, but it is possible to judge by sampling a larger number of times. Judging by the moving average of 5 samplings, if the sampling cycle is 100 msec, it takes at least 0.5 sec to hold.

Here, returning to FIG. 1, the output of the synchronous detector 20 is given in parallel to the low-pass filter 22-1, the low-pass filter 22-2, ... The low-pass filter 22-n. The low-pass filter 22-1 has a high response speed but a small amount of attenuation, and the low-pass filter 22-2 has a slower response speed but a larger amount of attenuation than the low-pass filter 22-1.

As shown in FIG. 5, the determination means of the calculation unit 32 determines whether or not the measured value is stable by taking the moving average of the output of any one of the plurality of low-pass filters.
Here, when it is determined that the measured value is not stable by taking a moving average for the output of the low-pass filter 22-1 (hereinafter referred to as LPF1), the output side of the low-pass filter 22-2 (hereinafter referred to as LPF2). The switch SW1 is switched to, and the moving average of the output is taken to determine whether or not the measured value is stable.
At this time, the measured value due to the output of LPF1 varies due to the influence of noise, and when switching to LPF2, the variation in the measured value of the output is naturally different between LPF1 and LPF2.

FIG. 6 shows the situation. If a noise component close to the measurement frequency is present, the LPF1 cannot remove the noise and the measured value varies. When switching to LPF2, which has characteristics that are resistant to noise, stable measured values may be obtained. At this time, if the moving average of the measured values of the low-pass filter is continuously used as the output data of LPF1 and the moving average is taken, it is determined that the measured values are stable at the measured values outside the guaranteed accuracy range due to being dragged by the measured values of LPF1. There is a possibility of holding it. Therefore, when the low-pass filter is switched from one having a fast response speed to one having a slow response speed, it is necessary to initialize the moving average as well.

FIG. 7 is a flowchart illustrating the operation of initializing the moving average processing when the low-pass filter is switched. First, the measurement is started in LPF1 (step S21), the output of LPF1 is sampled (step S22), the moving average processing is performed (step S23), and if the number of samples of the moving average is satisfied, the measured value is stable. If it is stable, if the hold function is effective, the measurement is stopped and the measured value is held (steps S25 and S26). If the measured value is not stable after performing the moving average processing, the number of measurements (number of samplings) is counted up (step S27), and the product of the number of measurements and the sampling cycle (number of measurements x sampling cycle) is the response of LPF2. It is determined whether the time has come (step S28). If the number of measurements x sampling period does not meet the response time of LPF2, the process proceeds to the next sampling, and if the number of measurements x sampling cycle satisfies the response time of LPF2 and the measured value is not stable, switch SW1 In, the LPF1 is switched to the LPF2, the moving average processing is initialized, the LPF2 is switched to, and the sampling of the output of the LPF2 is performed (steps S30 and S31). When the number of measurements x the sampling cycle satisfies the response time of LPF2 and the measured value is stable, the switch SW1 switches from LPF1 to LPF2 with the switch SW1 to sample the output of LPF2 without performing the moving average initialization. Transition (steps S29, S31).

If there are more low-pass filters and the LPF2 is not stable, the response time of the next low-pass filter 22-3 is reached, the low-pass filter 22-3 is switched to, the output is sampled, and the moving average is initialized.

In the above example, the determination of whether or not the measured value is stable has been described by using a moving average, but in addition to this, for example, whether or not the measured value is stable due to the dispersion of the measured value is statistically determined. It can be judged, or it can be judged whether or not it is stable by the inclination of the measured value, and even in that case, when the low-pass filter is switched, the initialization for the stability judgment of the measured value is performed.

FIG. 1 has described an example in which one synchronous detector 20 is used as the synchronous detector 20 for synchronous detection with one reference signal synchronized with the measured AC current, but different phases such as 45 ° or 90 are used as the reference signal. It is also possible to generate reference signals having different phases and synchronously detect the detection signals appearing in the sample 11.
In FIG. 8, the detection signals appearing in the sample 11 are synchronously detected by reference signals having different phases by 45 °, and each detection signal is input to a plurality of low-pass filters having different characteristics and input to an analog-to-digital converter (ADC). It shows the configuration of the impedance measuring device.
When synchronous detection is performed using a reference signal of one phase, the phase of noise is unknown, and the noise level may be reduced depending on the phase of noise. By performing synchronous detection with reference signals of different phases, accurate noise level can be measured and the influence of noise appearing in the detection signal can be reduced. In addition, by detecting gain fluctuations due to bandpass filters and peripheral devices and phase fluctuations due to phase rotation and performing impedance measurement, measurement errors can be reduced and stable measurement can be performed.

(Effect of the present invention)
In the present invention, a low-pass filter having a plurality of different characteristics (response characteristics, attenuation characteristics) is operated in parallel, and then the low-pass filter is switched, which is the least affected by noise and has the fastest response speed. Since we continue until we find, we can quickly obtain stable measurements that are least affected by noise. For example, in the case where the influence of noise is small like a battery in which no load current or charging current is flowing, the low-pass filter (1) in the above examples of FIGS. 2 and 3 is selected and performed after measurement. Impedance measurement at the measurement frequency ends.

That is, even if the measurement is performed on a sample having a small influence of noise or a sample having a large influence of noise, for example, a sample in which noise is superimposed on a detection signal such as a UPS battery, the response speed is the fastest. Moreover, since the low-pass filter with the least amount of attenuation is selected, a stable impedance measurement value that is less affected by noise can be obtained more quickly.

In addition, other effects according to the present invention will be described with reference to FIG. When the predetermined measurement frequency is, for example, Y (Hz) and noise as shown in FIG. 9 appears, and the impedance is measured at the measurement frequency of Y (Hz), the range affected by the noise is the measurement frequency. It is a range from left and right a (Hz). In this case, since the noise in the range up to the left and right a (Hz) is attenuated by the selection (switching) process described above, the range not affected by the noise can be expanded (the range not affected by the noise is expanded).
Then, when the low-pass filter is switched, whether the measured value is stable is also determined by initializing each time the low-pass filter is switched, so that the output is temporarily affected by noise in the previous low-pass filter. Even if there is a variation, it does not affect the determination of whether or not the output of the next low-pass filter is stable, so that it is possible to hold the measured value more accurately.

The above-described embodiment has been described with an example in which an AC constant current is supplied from the constant current source 10 to the sample 11 to measure the impedance, but impedance measurement by voltage is also possible. For example, the impedance may be measured by supplying a constant AC voltage from a voltage source to the sample and performing synchronous detection. When the measurement target is a battery, it is preferable to measure the impedance with a constant current, but for example, in the case of a capacitor incorporated in an electric circuit where noise may appear, the impedance measurement with an AC constant voltage may be used. ..

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment and can be modified in various ways.

10 constant current source
11 Sample (DUT)
15, 16 Amplifier 17 Bandpass Filter (BPF)
20 Synchronous detector 22-1, 22-2, ..., 22-n low-pass filter (LPF)
23 Analog-to-digital converter (ADC)
30 Voltage detection unit 31 Current detection unit 32 Calculation unit 33 Display unit 34 Operation unit 35 Storage unit Rs Current detection resistor SW1 switch

Claims (5)

An AC supply unit that supplies a measurement signal of a predetermined frequency to the sample to be measured,
A reference signal generator that generates a reference signal synchronized with the measurement signal,
A synchronous detection unit that synchronously detects the detection signal appearing in the sample with the reference signal,
A plurality of low-pass filters in which signals synchronously detected by the synchronous detection unit are input and have different response characteristics and attenuation characteristics,
A selection means for switching the plurality of low-pass filters and selecting one of them, and
It is provided with a calculation means for determining whether or not the measured value calculated based on the output data of the low-pass filter is stable, switching the low-pass filter by the selection means, and holding the calculated measured value.
The reference signal generation unit includes means for generating two reference signals having different phases.
The calculation means is
When the variation of the measured value calculated based on the output data of the selected low-pass filter is within a predetermined allowable range, it is determined that the measured value is stable, the obtained measured value is held, and the measurement is performed. When the variation of the value is not within the predetermined allowable range, the variation of the measured value calculated based on the output data of the low-pass filter after switching to another low-pass filter by the selection means is the predetermined allowable range. An impedance measuring device characterized by determining whether or not. The impedance measuring device according to claim 1.
The determination of whether or not the variation of the measured values performed by the calculation means is within a predetermined allowable range is a determination of whether or not the moving average of the measured values is within a predetermined allowable range.
An impedance measuring device characterized in that when the low-pass filter is switched, it is determined by a moving average of the measured values calculated based on the output data of the low-pass filter after switching. The impedance measuring device according to claim 1 or 2 .
An impedance measuring device, wherein the sample is a battery, and the AC supply unit is a constant current source. A measurement signal of a predetermined frequency is supplied to the sample to be measured, the detection signal appearing in the sample is synchronously detected by a reference signal synchronized with the measurement signal, and the DC component of the synchronously detected signal is extracted to convert the sample. It is an impedance measurement method that measures impedance.
A step of supplying a measurement signal of a predetermined frequency to a sample to be measured, and
A step of generating a reference signal synchronized with the measurement signal, and
A step of synchronously detecting the detection signal appearing in the sample with the reference signal, and
The step of inputting the synchronously detected signal to multiple low-pass filters with different response characteristics and attenuation characteristics,
It has a step of selecting any one of the plurality of low-pass filters, calculating a measured value based on the output data of the selected low-pass filter, and determining whether or not the calculated measured value is stable.
The step of generating a reference signal synchronized with the measurement signal includes a step of generating two reference signals having different phases.
The determination step is
When the variation of the measured value calculated based on the output data of the selected low-pass filter is within a predetermined allowable range, it is determined that the measured value is stable, the obtained measured value is retained, and the measured value is retained. If the variation of is not a predetermined allowable range is switched to the other of the low-pass filter selected means, whether the variation allowable range of the measurement value calculated on the basis of the output data of the low-pass filter after the switching An impedance measurement method comprising a determination step. The impedance measuring method according to claim 4.
The determination of whether the variation of the measured values is within the predetermined allowable range is the determination of whether the moving average of the measured values is within the predetermined allowable range.
When the low-pass filter is switched, it is determined by the moving average of the measured values calculated based on the output data of the low-pass filter after switching.
An impedance measurement method characterized by this .

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