JP7146558B2 - Impedance measuring device and adjustment method of negative feedback circuit in impedance measuring device - Google Patents

Description

The present invention relates to an impedance measuring device and a method of adjusting a negative feedback circuit in the impedance measuring device.

For example, there is known a technique disclosed as a prior art in Patent Document 1 below, regarding this type of impedance measuring device and a feedback loop stabilization method (negative feedback circuit adjustment method) in this type of impedance measuring device. there is This feedback loop stabilization method adjusts the null amplifying means 51 constituting the feedback loop (null loop) of the impedance measuring device 50 shown in FIG. 3 to stabilize this feedback loop. First, this impedance measuring device 50 will be described.

In this impedance measuring device 50 , a first sine wave signal V 1 (AC voltage signal with a constant frequency and constant amplitude) output from a first signal source 10 passes through a switch 11 to a protective resistor 12 . , the measurement current I is supplied from the first signal source 10 to one terminal 92 of the object 91 to be measured via the switch 11 , the protective resistor 12 , the measurement cable 6 and the Hc measurement terminal 2 . Further, in the impedance measuring device 50, when the feedback loop (the feedback loop consisting of the measuring cable 8, the null amplifying means 51, the current measuring section 25, the measuring cable 9, and the other terminal 93 of the measuring object 91) is stabilized, , the null amplifying means 51 draws in all the measured current I from the other terminal 93 via the Lc measuring terminal 5, the measuring cable 9 and the current measuring section 25 (specifically, the detection resistor 25a of the current measuring section 25). , the other terminal 93 is virtual grounded (equivalently connected to the internal ground G) to perform a negative feedback operation.

In this state, the voltmeter 25b, which constitutes the current measuring section 25 together with the detecting resistor 25a, measures the voltage across the detecting resistor 25a, whereby the measured current I is measured by the current measuring section 25. FIG. Also, the voltage at one terminal 92 of the measurement object 91 is measured by the voltage measurement section (voltmeter) 13 from the Hp measurement terminal 3 via the measurement cable 7 . As described above, since the other terminal 93 is connected to the internal ground G, the voltage measuring section 13 measures the voltage applied across the object 91 to be measured (voltage between both ends). Therefore, the impedance measurement device 50 can obtain the impedance measurement value of the measurement object 91 from the ratio of the measurement value of the voltage measurement section 13 and the measurement value of the current measurement section 25 .

Next, the null amplifying means 51 will be specifically described. The null amplifying means 51 comprises an input amplifier 61, a narrow band high gain amplifier 62 and an output amplifier 63 connected in series, as shown in FIGS. Further, the null amplifying means 51 is provided with a synchronizing signal source 64, a switch 65 and a vector voltmeter 66. FIG. The synchronizing signal source 64 outputs a second sine wave signal V2 (synchronizing signal) having the same frequency as the first sine wave signal V1 output from the first signal source 10 and synchronizing with it and having a constant amplitude. The switch 65 is interposed in the preceding stage of the output amplifier 63 and switches between the AC signal Vac output from the narrow-band high-gain amplifier 62 and the second sine wave signal V2 output from the synchronization signal source 64 to output to the output amplifier 63. Output.

As an example, the input amplifier 61 is configured as a current-voltage converter using an operational amplifier whose non-inverting input terminal is connected to the internal ground G, as shown in FIG. The current flowing into the null amplifying means 51 through the Via is converted into a voltage Vi and output. In this case, when the current flowing into the null amplifying means 51 in this way is zero amperes (that is, when the voltage Vi is zero volts), the voltage at the Lp measuring terminal 4 becomes the potential of the internal ground G (that is, The other terminal 93 is virtually grounded).

Narrow band high gain amplifier 62 includes detectors 71 and 72, integrators 73 and 74, modulators 75 and 76, adder 77, phase shifters 78 and 79, and variable phase shifter 80, as shown in FIG. It has In the narrow-band high-gain amplifier 62, the detectors 71 and 72 are supplied with the voltage Vi, the detector 71 is supplied with the second sine wave signal V2, and the detector 72 is supplied with a phase shifter 78. A second sinusoidal signal V2 phase-shifted by 90° is input. With this configuration, the detectors 71 and 72 function as quadrature detectors that divide the voltage Vi into two quadrature components and perform synchronous detection. Detector 72 outputs a second DC signal representing a component (orthogonal component) of voltage Vi which is orthogonal to second sine wave signal V2. The integrator 73 integrates the first DC signal and outputs it to the modulator 75 as a third DC signal, and the integrator 74 integrates the second DC signal and outputs it to the modulator 76 as a fourth DC signal. do.

In the narrow-band high-gain amplifier 62, the variable phase shifter 80 phase-shifts the input second sine wave signal V2 by a preset phase, and outputs it as a carrier wave V2a. This carrier wave V2a is input as it is to one of the modulators 75 and 76, and is also input to the other modulator 76 after being phase-shifted by 90° by the phase shifter 79 as the carrier wave V2b. With this configuration, the modulators 75 and 76 form a quadrature modulator, and the modulator 75 amplitude-modulates the carrier wave V2a with the third DC signal output from the integrator 73 and outputs it as the first AC signal. , the modulator 76 amplitude-modulates the carrier wave V2b with the fourth DC signal output from the integrator 74, and outputs it as a second AC signal. Adder 77 combines the first and second AC signals output from modulators 75 and 76 and outputs the result to switch 65 as AC signal Vac.

Thus, the narrow-band high-gain amplifier 62 quadrature-synchronously detects the voltage Vi, converts it to a DC signal, integrates it, and quadrature-modulates it back to the AC signal Vac. Amplification is possible. In the narrow-band high-gain amplifier 62, the phase between the quadrature detector composed of the detectors 71 and 72 and the quadrature modulator composed of the modulators 75 and 76 is shifted by the variable phase shifter 80. phase), narrow-band high-gain amplifier 62 can function as a narrow-band high-gain amplifier with an arbitrary phase difference.

Moreover, the stability condition of the feedback loop in the impedance measuring device 50 is to prevent 0° phase from existing within the gain band of this feedback loop (null loop). This impedance measuring device 50 is designed to flexibly stabilize the feedback loop even when the phase state of the feedback loop changes, such as when the measurement cables 8 and 9 are extended. , a function of finding the necessary phase shift amount (phase correction amount) to be set in the variable phase shifter 80 in order to satisfy this stability condition is incorporated. Hereinafter, a method of finding the necessary phase shift amount using this function, and a feedback loop stabilization method of setting the found phase shift amount in the variable phase shifter 80 to stabilize the feedback loop (null amplifying means 51 adjustment method) will be explained.

First, the switch 11 is switched to the ground side to disconnect the first signal source 10 from the protective resistor 12 . Also, the switch 65 is switched to the synchronous signal source 64 side to disconnect the feedback loop and input the second sine wave signal V2 to the output amplifier 63 . In this state, the vector voltmeter 66 measures the voltage Vi output from the input amplifier 61 . The phase difference between the voltage Vi and the second sine wave signal V2 measured by the vector voltmeter 66 in this way is the phase shift amount in one round of the feedback loop excluding the narrow-band high-gain amplifier 62. FIG. Based on this phase shift amount, the phase shift amount that makes the total phase shift amount of the feedback loop 180° (the state with the greatest margin for 0°) is obtained and set in the variable phase shifter 80 . This completes the procedure of finding the phase shift amount in the variable phase shifter 80 necessary to satisfy the above stability condition and setting it in the variable phase shifter 80. Therefore, switching is performed in preparation for subsequent impedance measurement. 11 is switched to the first signal source 10 side, and the switch 65 is switched to the narrow band high gain amplifier 62 side.

Null amplifying means 51 including narrow-band high-gain amplifier 62 having variable phase shifter 80 with the phase shift amount set in this manner performs stable negative feedback operation to The amplitude and phase of AC signal Vac output from narrow-band high-gain amplifier 62 (and thus the amplitude of the AC signal output from output amplifier 63) are adjusted so that the potential of is equal to the ground potential (voltage of internal ground G: zero volts). and phase) control the amplitude and phase of the current drawn through the detection resistor 25a. As a result, the voltage measured by the voltage measuring section 13 from the Hp measuring terminal 3 via the measuring cable 7 is the voltage applied between the terminals 92 and 93 of the measuring object 91 (voltage between both ends). In addition, due to this control, the measurement current I flowing through the measurement object 91 does not flow from the Lp measurement terminal 5 to the measurement cable 8 side, but passes through the Lc measurement terminal 5, the measurement cable 9 and the detection resistor 25a and is null-amplified. All are drawn into the means 51 (specifically, the output amplifier 63). Therefore, the current measured by the current measuring unit 25 is the measured current I. Thereby, the impedance measuring device 50 can accurately measure the impedance of the object 91 to be measured based on the voltage across the ends measured by the voltage measuring section 13 and the measured current I measured by the current measuring section 25. It's becoming

Japanese Patent No. 3930586 (pages 4-5, Figures 2, 3 and 6)

However, the adjustment method for the narrow-band high-gain amplifier 62 (negative feedback circuit adjustment method) in the impedance measuring apparatus disclosed in the above-mentioned Patent Document 1 requires an expensive vector voltmeter 66, which is a problem to be solved. exists.

The present invention has been made in view of such problems to be solved, and provides an impedance measuring device capable of adjusting a negative feedback circuit without using a vector voltmeter, and a method of adjusting the negative feedback circuit in the impedance measuring device. The main purpose is to

In order to achieve the above object, an impedance measuring apparatus according to claim 1 comprises: a first signal source for applying a first sine wave signal having a constant frequency and a predetermined amplitude to one terminal of an object to be measured; a negative feedback circuit for prescribing the other terminal of the object to be measured to be a reference potential in a state where the first sine wave signal is applied to the terminal of the negative feedback circuit, wherein the other terminal is set to the reference potential by the negative feedback circuit An impedance measuring device for measuring the impedance of the object to be measured based on the voltage of the one terminal and the current flowing in the negative feedback circuit when specified in and a scalar voltmeter for measuring the voltage output from the current-voltage converter with reference to the reference potential. and a second signal source that outputs a second sine wave signal having the same frequency as that of the first sine wave signal and having a set amplitude with a set phase shifted with respect to the first sine wave signal; and an amplifier that amplifies the second sine wave signal to an amplified sine wave signal and outputs the signal from an output terminal to the other terminal of the object to be measured, and is interposed between the other terminal and the output terminal of the amplifier. , a current measuring unit that measures a current flowing between the other terminal and the output terminal; and the second signal source that is set so that the voltage measured by the scalar voltmeter approaches zero volts. and a processing unit that adjusts the amplitude and the phase, wherein the processing unit adjusts the amplitude to be set to the second signal source in a state in which the first sine wave signal is applied to the one terminal. and sweeping the set phase, a phase detection process for detecting a target phase that minimizes the voltage measured by the scalar voltmeter; and an amplitude adjustment process of adjusting the amplitude set to the second signal source in a state where the phase is set to the second signal source so that the voltage measured by the scalar voltmeter approaches zero volts. to set the other terminal to the reference potential.

A method for adjusting a negative feedback circuit in an impedance measuring apparatus according to claim 2 includes a first signal source that applies a first sine wave signal having a constant frequency and a predetermined amplitude to one terminal of a measurement object; , a current-voltage converter connected to the other terminal of the object to be measured to convert the inflow current from the other terminal into a voltage and output the voltage, the voltage output from the current-voltage converter being referenced to a reference potential; and outputs a second sine wave signal having the same frequency as the first sine wave signal and having a set amplitude, shifted by a set phase with respect to the first sine wave signal. 2 signal sources, an amplifier for amplifying said second sinusoidal signal to an amplified sinusoidal signal for output from an output terminal to the other terminal of said object to be measured, and between said other terminal and said output terminal of said amplifier. a negative feedback circuit configured to include a current measuring section interposed to measure a current flowing between the other terminal and the output terminal, and prescribing the other terminal to be measured at the reference potential; and based on the voltage of the one terminal and the current measured by the current measuring unit in a state where the other terminal is regulated to the reference potential by the negative feedback circuit, A method for adjusting the negative feedback circuit in an impedance measuring device for measuring impedance, wherein the first sinusoidal wave signal is applied to the one terminal of the first signal source and set to the second signal source. While sweeping the phase set in the second signal source with the amplitude kept constant, a target phase that minimizes the voltage measured by the scalar voltmeter is detected, and On the other hand, in a state where the target phase is set as the phase, the amplitude set in the second signal source is adjusted so that the voltage measured by the scalar voltmeter approaches zero volts.

According to the impedance measuring device of claim 1 and the method of adjusting a negative feedback circuit in the impedance measuring device of claim 2, an inexpensive scalar voltmeter is used instead of an expensive vector voltmeter to perform measurement. Since the other terminal of the target can be equivalently defined as the reference potential, device costs and adjustment costs can be reduced compared to a configuration using an expensive vector voltmeter.

1 is a configuration diagram showing the configuration of an impedance measuring device 1; FIG. 2 is a configuration diagram of a current-voltage converter 21 in FIG. 1. FIG. 1 is a configuration diagram showing a configuration of a conventional impedance measuring device 50; FIG. 4 is a configuration diagram of a null amplifying means 51 in FIG. 3; FIG.

Embodiments of an impedance measuring device and a method of adjusting a negative feedback circuit in this device will be described below with reference to the accompanying drawings.

First, the configuration of an impedance measuring device 1 as this impedance measuring device will be described with reference to FIGS.

The impedance measuring device 1 includes an Hc measuring terminal 2, an Hp measuring terminal 3, an Lp measuring terminal 4, an Lc measuring terminal 5, measuring cables 6, 7, 8, 9, a first signal source 10, a protective resistor 12, and a voltage measuring section 13. , a negative feedback circuit 14, and a processing unit 15 so that the impedance of the measurement object 91 can be measured.

The first signal source 10 outputs a first sine wave signal V1 having a constant frequency and a predetermined amplitude with reference to a reference potential (the potential of the internal ground G of the impedance measuring device 1, zero volts). This first sine wave signal V1 passes through the protective resistor 12, the measuring cable 6 (the core wire of the measuring cable 6 made of a coaxial cable or a shielded cable, not shown), and the Hc measuring terminal 2 to one side of the measuring object 91. Applied to terminal 92 . When the first sine wave signal V 1 is applied to one terminal 92 , a measurement current I 1 that is a sine wave signal flows from the first signal source 10 to the object 91 to be measured. In addition, the first signal source 10 is controlled by the processing unit 15 as an example in this example to perform the output operation of the first sine wave signal V1. Of course, a configuration that does not use the protective resistor 12 may be used.

One measuring terminal of a pair of measuring terminals (not shown) of the voltage measuring section 13 is connected to the Hp measuring terminal 3 via a measuring cable 7 (core wire not shown of the same cable as the measuring cable 6). , the other measuring terminal is connected to the internal ground G. With this configuration, the voltage measurement unit 13 measures the voltage generated at the Hp measurement terminal 3 with the internal ground G as a reference, and the negative feedback circuit 14 causes the other terminal 93 of the measurement object 91 to be connected to the internal ground as will be described later. In the state defined by the potential of G, the voltage between both terminals 92 and 93 of the object 91 to be measured (voltage between both ends) is measured and output to the processing section 15 .

The negative feedback circuit 14 includes, for example, a current-voltage converter 21 , a scalar voltmeter 22 , a second signal source 23 , an amplifier 24 and a current measuring section 25 . As will be described later, the processing unit 15 also controls the amplitude set for the second signal source 23 based on the scalar voltage value Vsc output from the scalar voltmeter 22 (the amplitude of the second sine wave signal V2, which in turn is amplified). Amplitude of the sine wave signal V3) is adjusted to constitute a part of the negative feedback circuit 14. FIG. The input terminal 14a of the negative feedback circuit 14 is connected to the Lp measurement terminal 4 via the measurement cable 8 (the core wire of the same cable as the measurement cable 6, not shown), and the output terminal 14b is connected to the measurement cable 9 ( It is connected to the Lc measurement terminal 5 via a core wire (not shown) of the same type of cable as the measurement cable 6 .

Each measuring cable 6, 7, 8, 9 has an outer conductor (braided wire) at one end to which the corresponding measuring terminals 2, 3, 4, 5 are connected, They are connected via wirings L1, L2, and L3, and their outer conductors (braided wires) are connected to the internal ground G at the other end.

For example, as shown in FIG. 2, the current-voltage converter 21 includes an operational amplifier 21a having a non-inverting input terminal connected to the internal ground G, one end connected to the input terminal 14a and the other end connected to the operational amplifier 21a. It comprises an input resistor 21b connected to the inverting input terminal, and a feedback resistor 21c having one end connected to the inverting input terminal of the operational amplifier 21a and the other end connected to the output terminal of the operational amplifier 21a. With this configuration, when the current-voltage converter 21 is connected to the other terminal 93 of the measurement object 91 via the measurement cable 8 and the Lp measurement terminal 4, the inflow from the other terminal 93 to the negative feedback circuit 14 It converts the current into a voltage Vi and outputs it. The scalar voltmeter 22 measures a scalar voltage value Vsc (for example, effective value) of the voltage Vi output from the current-voltage converter 21 with reference to the potential of the internal ground G, and outputs it to the processing unit 15 .

The second signal source 23 shifts the second sine wave signal V2 having the same frequency as the first sine wave signal V1 and the set amplitude A by the set phase φ with respect to the first sine wave signal V1. Output to amplifier 24 . The amplifier 24 amplifies the second sine wave signal V2 to an amplified sine wave signal V3 and outputs the amplified sine wave signal V3 to the output terminal 14b of the negative feedback circuit 14 from its output terminal (not shown). In this example, the current measuring section 25 is interposed between the output terminal of the amplifier 24 and the output terminal 14b of the negative feedback circuit 14. FIG. Therefore, the amplified sine wave signal V3 is output to the other terminal 93 of the object 91 to be measured via the current measuring section 25, the output terminal 14b, the measuring cable 9 and the Lp measuring terminal 4.

As an example, the current measurement unit 25 includes a detection resistor 25a interposed between the output terminal of the amplifier 24 and the output terminal 14b of the negative feedback circuit 14, and a voltage across the detection resistor 25a (flowing through the detection resistor 25a). A voltage that varies in proportion to the current I2) is measured and output to the processing unit 15 by a voltmeter 25b.

The processing unit 15 includes a CPU, a memory, and the like, and executes control processing, phase detection processing, amplitude adjustment processing, and impedance measurement processing for the first signal source 10 .

In this phase detection process, as shown in FIG. 1, the processing unit 15 connects the Hc measurement terminal 2 and the Hp measurement terminal 3 to one terminal 92 of the measurement object 91, and connects the other terminal 93 to the Lp measurement terminal. 4 and Lc measurement terminals 5 are connected (that is, the impedance measurement device 1 is connected to the measurement object 91), the first sinusoidal signal V1 from the first signal source 10 is applied to one terminal 92, and the amplifier 24 is applied to the other terminal 93, the amplitude A set in the second signal source 23 is kept constant (that is, the second sine wave signal V2, and thus the amplified sine wave while keeping the amplitude of the signal V3 constant), sweeping the phase φ set in the second signal source 23 (eg increasing from 0° to 180° or vice versa from 180° to 0° in predefined steps). ) to detect the target phase φt that minimizes the scalar voltage value Vsc measured by the scalar voltmeter 22 . Further, the processing unit 15 sets the detected target phase φt to the second signal source 23 as the phase φ. As a result, the phase of the amplified sine wave signal V3 propagating to the other terminal 93 is shifted from the phase of the first sine wave signal V1 propagating to the other terminal 93 by 180°. In this phase detection process, the processing unit 15 can directly detect the target phase φt at which the scalar voltage value Vsc is the minimum, or detect the phase at which the scalar voltage value Vsc is the maximum, and detect the detected phase. By subtracting 180° from , it is possible to indirectly detect the target phase φt that minimizes the scalar voltage value Vsc. Further, if the amplitude of the first sine wave signal V1 output by the first signal source 10 is constant, it can be set to any amplitude.

In the amplitude adjustment process, the processing unit 15 controls the scalar voltmeter while the first signal source 10 is outputting the first sine wave signal V1 with a normal amplitude (amplitude when performing the impedance measurement process). The amplitude A of the second sinusoidal signal V2 set to the second signal source 23 is adjusted so that the scalar voltage value Vsc measured at 22 approaches zero volts. In the above phase detection process, the target phase φt at which the phase of the first sine wave signal V1 and the amplified sine wave signal V3 at the other terminal 93 of the measurement object 91 are shifted by 180° is set by the second signal source 23 is set as the phase φ, the amplitude of the first sine wave signal V1 at the other terminal 93 (amplitude attenuated from the amplitude when output from the first signal source 10) and the amplitude of the amplified sine wave signal V3 The scalar voltage value Vsc becomes zero volts when the amplitude (amplitude attenuated from the amplitude when output from the amplifier 24) matches. Even after the scalar voltage value Vsc becomes zero volts, the processing unit 15 continues to execute the amplitude adjustment process, thereby adjusting the amplitude of the second sine wave signal V2 so that the scalar voltage value Vsc is maintained at zero volts. Adjust A.

Further, in the impedance measurement process, the processing unit 15 causes the voltage between both terminals 92 and 93 of the measurement object 91 measured by the voltage measurement unit 13 to be measured by the voltage measurement unit 13 in a state where the scalar voltage value Vsc is maintained at zero volts by executing the amplitude adjustment process. and the current I2 measured by the current measuring unit 25, the impedance of the measurement object 91 is calculated. When the scalar voltage value Vsc is maintained at zero volts, the current flowing into the current-voltage converter 21, that is, the current flowing from the Lp measurement terminal 4 to the negative feedback circuit 14 via the measurement cable 8 is zero amperes. Therefore, the measurement current I1 flowing from the first signal source 10 to the measurement object 91 all flows to the current measuring section 25 as the current I2. Therefore, the current measurement unit 25 measures the measurement current I1 flowing through the measurement target 91 as the current I2 and outputs the current I2 to the processing unit 15 . Thereby, the processing unit 15 accurately measures (calculates) the impedance of the measurement object 91 . In the impedance measurement process, the processing unit 15 also outputs the measured impedance to an output unit (not shown) (for example, a display device such as an LCD).

Next, the operation of the impedance measuring device 1 will be described together with the adjusting operation (adjusting method) of the negative feedback circuit 14 in the impedance measuring device 1 with reference to the drawings. It is assumed that the impedance measuring device 1 is normally connected to the object 91 to be measured.

In this state, in the impedance measuring device 1, the processing unit 15 first executes control processing for the first signal source 10 to output the first sine wave signal V1 having a constant frequency and a constant amplitude.

Next, the processing unit 15 executes the phase detection process described above. In this phase detection process, the processing unit 15 maintains the amplitude A set in the second signal source 23 constant (that is, while maintaining the amplitude of the amplified sine wave signal V3 constant), the second signal source 23 is swept to detect the target phase φt that minimizes the scalar voltage value Vsc measured by the scalar voltmeter 22 . The processing unit 15 also sets the detected target phase φt as the phase φ for the second signal source 23 . As a result, the phase of the amplified sine wave signal V3 propagating to the other terminal 93 is set (adjusted) to be 180° out of phase with respect to the phase of the first sine wave signal V1 propagating to the other terminal 93 .

Subsequently, the processing unit 15 executes the above amplitude adjustment processing. In this amplitude adjustment process, the processing unit 15 first executes a control process for the first signal source 10 to set the amplitude of the first sine wave signal V1 to the amplitude used when performing the impedance measurement process. When the amplitude of the first sine wave signal V1 when executing the phase detection process is set to the amplitude when executing the impedance measurement process, the control process for the first signal source 10 can be omitted. Next, the processing unit 15 controls the scalar voltage value Vsc measured by the scalar voltmeter 22 to approach zero volts in a state in which the amplitude of the first sine wave signal V1 is set to the amplitude used when performing the impedance measurement process. Then, the amplitude A of the second sine wave signal V2 set for the second signal source 23 is adjusted. Further, even after the scalar voltage value Vsc becomes zero volt as a result of adjusting the amplitude A of the second sine wave signal V2, the processing unit 15 continues to execute this amplitude adjustment process, so that the scalar voltage value Adjust the amplitude A of the second sinusoidal signal V2 so that Vsc is maintained at zero volts.

In this way, when the scalar voltage value Vsc is maintained at zero volts, the current flowing into the current-voltage converter 21, that is, the current flowing from the Lp measurement terminal 4 to the negative feedback circuit 14 via the measurement cable 8 is is zero amperes, the measurement current I1 flowing from the first signal source 10 to the measurement object 91 all flows to the current measuring section 25 as the current I2. Therefore, the current measurement unit 25 measures the current I2, which is the measurement current I1 flowing through the measurement target 91, and outputs the current I2 to the processing unit 15. FIG. Also, since the scalar voltage value Vsc is maintained at zero volts, the other terminal 93 of the measurement target 91 is equivalently connected to the internal ground G. Therefore, the voltage measurement unit 13 measures the voltage generated at the Hp measurement terminal 3 with reference to the internal ground G, thereby measuring the voltage (the voltage across the terminals) between the terminals 92 and 93 of the object 91 to be measured. Output to the processing unit 15 .

Next, the processing unit 15 executes impedance measurement processing in this state, and the voltage across the terminals 92 and 93 of the measurement object 91 measured by the voltage measurement unit 13 and the voltage across the terminals 92 and 93 measured by the current measurement unit 25 are measured. The impedance of the object 91 to be measured is accurately calculated based on the current I2 that is applied. Also, the calculated impedance is output to the output section.

Thus, in the impedance measuring device 1, the processing section 15 causes the first signal source 10 to output the first sine wave signal V1 and the second signal source 23 to output the second sine wave signal V2. A phase detection process is performed based on the scalar voltage value Vsc measured by the scalar voltmeter 22 in the state (where the amplifier 24 is outputting the amplified sine wave signal V3), and the phase A target phase φt to be set as φ is detected, and in a state where the target phase φt is set as the phase φ for the second signal source 23, amplitude adjustment processing is executed based on the scalar voltage value Vsc to obtain a scalar voltage value The amplitude A of the second sine wave signal V2 output from the second signal source 23 is adjusted (set) so that Vsc is maintained at zero volts. Further, in the adjustment method of the negative feedback circuit 14 in this impedance measuring device 1, the first sine wave signal V1 is applied to one terminal 92 of the first signal source 10, and the amplitude set in the second signal source 23 is In a constant state, while sweeping the phase φ set in the second signal source 23, the target phase φt that minimizes the scalar voltage value Vsc measured by the scalar voltmeter 22 is detected. On the other hand, with the target phase φt set as the phase φ, the amplitude A set in the second signal source 23 is adjusted so that the scalar voltage value Vsc measured by the scalar voltmeter 22 approaches zero volts.

Therefore, according to the impedance measuring device 1 and the adjustment method of the negative feedback circuit 14 in the impedance measuring device 1, the low-cost scalar voltmeter 22 is used instead of the high-priced vector voltmeter. Since the other terminal 93 can be equivalently connected to the internal ground G (the potential of the other terminal 93 can be defined equivalently to the potential of the internal ground G), the configuration using an expensive vector voltmeter can be avoided. In comparison, equipment costs and adjustment costs can be reduced. Moreover, according to this impedance measuring apparatus 1, compared with a configuration using an expensive vector voltmeter, the narrow-band high-gain amplifier 62 having a complicated circuit configuration can be eliminated, and the first signal source 10 Since the switch 11 on the side can also be eliminated, the device cost can be further reduced.

1 impedance measuring device 10 first signal source 14 negative feedback circuit 21 current-voltage converter 22 scalar voltmeter 23 second signal source 24 amplifier 25 current measuring section 91 measurement object 92 one terminal 93 the other terminal
A amplitude
G Internal ground V1 First sine wave signal V2 Second sine wave signal V3 Amplified sine wave signal Vi Voltage
φ phase

Claims (2)

a first signal source that applies a first sinusoidal signal of constant frequency and predefined amplitude to one terminal of the measurement object;
a negative feedback circuit that defines the other terminal of the object to be measured as a reference potential in a state where the first sine wave signal is applied to the one terminal, wherein the negative feedback circuit causes the other terminal to An impedance measuring device for measuring the impedance of the object to be measured based on the voltage of the one terminal when defined as a reference potential and the current flowing in the negative feedback circuit,
The negative feedback circuit is
a current-voltage converter connected to the other terminal and configured to convert the inflow current from the other terminal into a voltage and output the voltage;
a scalar voltmeter for measuring the voltage output from the current-voltage converter with reference to the reference potential;
a second signal source that outputs a second sine wave signal having the same frequency as that of the first sine wave signal and having a set amplitude with a set phase shifted from the first sine wave signal;
an amplifier that amplifies the second sine wave signal to an amplified sine wave signal and outputs the amplified sine wave signal from an output terminal to the other terminal of the object to be measured;
a current measuring unit interposed between the other terminal and the output terminal of the amplifier and measuring a current flowing between the other terminal and the output terminal;
a processing unit that adjusts the amplitude and the phase set for the second signal source so that the voltage measured by the scalar voltmeter approaches zero volts,
In a state in which the first sine wave signal is applied to the one terminal, the processing unit keeps the amplitude set to the second signal source constant and sweeps the set phase, while the scalar Phase detection processing for detecting a target phase that minimizes the voltage measured by a voltmeter; and an impedance measuring device that adjusts the amplitude set in the signal source so that the voltage measured by the scalar voltmeter approaches zero volts, thereby prescribing the other terminal at the reference potential. . a first signal source that applies a first sinusoidal signal of constant frequency and predefined amplitude to one terminal of the measurement object;
a current-voltage converter that is connected to the other terminal of the object to be measured and converts the inflow current from the other terminal into a voltage and outputs the voltage; A second scalar voltmeter to be measured, which outputs a second sine wave signal having the same frequency as the first sine wave signal and having a set amplitude, shifted by a set phase with respect to the first sine wave signal a signal source, an amplifier for amplifying the second sine wave signal to an amplified sine wave signal for output from an output terminal to the other terminal of the object to be measured, and an interface between the other terminal and the output terminal of the amplifier. a negative feedback circuit configured to include a current measuring unit configured to measure a current flowing between the other terminal and the output terminal, and prescribing the other terminal to be measured at the reference potential; and based on the current measured by the current measuring unit and the voltage of the one terminal in a state where the other terminal is regulated to the reference potential by the negative feedback circuit, the impedance of the object to be measured A method for adjusting the negative feedback circuit in an impedance measuring device that measures
causing the first signal source to apply the first sine wave signal to the one terminal;
Detecting a target phase that minimizes the voltage measured by the scalar voltmeter while sweeping the phase set to the second signal source while the amplitude set to the second signal source is kept constant. death,
With the target phase set as the phase for the second signal source, the amplitude set for the second signal source is adjusted so that the voltage measured by the scalar voltmeter approaches zero volts. A method for adjusting a negative feedback circuit in an impedance measuring device.

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