JP2008298459A - Device for measuring impedance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for measuring impedance capable of measuring an impedance with high accuracy, using a comparatively simple measurement. <P>SOLUTION: The device for measuring impedance of an impedance element to be measured by comparing it with a standard impedance element is provided with a measuring energization circuit having the impedance element Zx to be measured, the standard impedance element Zs and a power source PS connected in parallel, for making a current flow into both impedance elements; a signal-forming circuit for detecting a current to be measured flowing in the impedance element to be measured and a standard current flowing in the standard impedance element, and forming a signal to be measured and a standard signal; a deviation detection circuit for taking the difference between the current to be measured and the standard current, and forming a deviation signal; and a processing circuit DP for calculating the impedance of the impedance element to be measured, based on the standard signal and the deviation signal and an impedance measuring device where the current is converted into a voltage is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring the impedance of an unknown impedance element to be measured using a known impedance element.

  A bridge circuit is well known as one method for measuring the impedance of an unknown impedance element using a known impedance element (see FIG. 6).

  This is to connect the power source PS to one span of the bridge circuit constituted by the known impedance elements Z1, Z2, Z3 and the unknown impedance element Zx, and connect the zero detector D to the other span of the bridge circuit. is there. Then, the value of the unknown impedance element Zx is calculated from the values of the known impedance elements Z1, Z2, and Z3 when the values of the impedance elements Z1, Z2, and Z3 are adjusted so that the zero detector D indicates zero or near zero. Is to be calculated.

  However, in this method, since the reference impedances Z1, Z2, and Z3 need to be adjusted on the real and imaginary vector planes, the measurement work is complicated.

  FIG. 7 shows another method for measuring impedance more simply. This is to obtain the impedance to be measured from the ratio of the current flowing through the impedance to be measured and the induced voltage. For this purpose, the impedance to be measured Zx and the known resistance R are directly connected to the power source PS, and the voltages across the respective terminals are supplied to the vector ratio measuring device VRM via the signal conditioners (signal conditioners) C1 and C2. Measurement is performed (see Patent Document 1).

However, since this method is not a comparison with standard impedance, the stability of almost all elements of the circuit directly affects the measurement accuracy.
JP 2002-139528 A

  As described above, the conventional impedance measurement method has a problem that the measurement work is complicated and the measurement accuracy is low, regardless of whether it is a method using a bridge circuit or a method using a vector ratio measurement.

  The present invention has been made in consideration of the above-described points, and an object thereof is to provide an impedance measuring apparatus capable of measuring impedance with high accuracy by relatively simple measurement.

  To achieve the above object, the present application provides the following first and second inventions.

The first invention is
In an apparatus for measuring the impedance of a measured impedance element compared to a standard impedance element,
A current carrying circuit for measurement having a measured impedance element and a standard impedance element connected in parallel to a power supply, and for passing a current through each of the impedance elements;
A signal forming circuit for detecting a measured current flowing in the measured impedance element and a standard current flowing in the standard impedance element, and forming a measured signal and a standard signal;
A deviation detection circuit that extracts a difference between the current to be measured and the standard current and forms a deviation signal;
An impedance measuring device comprising: a processing circuit that calculates an impedance of the impedance element to be measured based on the standard signal and the deviation signal;
It is.

In addition, the second invention,
In an apparatus for measuring the impedance of a measured impedance element compared to a standard impedance element,
A current carrying circuit for measurement having a measured impedance element and a standard impedance element connected in series to a power supply, and for passing a current through each of the impedance elements;
A voltage forming circuit for detecting a voltage to be measured generated in the impedance element to be measured and a standard voltage generated in the standard impedance element and forming a signal to be measured and a standard signal;
A deviation detection circuit that extracts a difference between the measured voltage and the standard voltage and forms a deviation signal;
An impedance measuring device comprising: a processing circuit that calculates an impedance of the measured impedance element based on the standard signal and the deviation signal;
It is.

  Since this invention was comprised as mentioned above, there exist the following effects.

  According to the first aspect of the invention, since the standard impedance is not adjusted in order to compare the impedance to be measured with the standard impedance, the measurement can be performed relatively easily despite obtaining a highly accurate measurement result.

  According to the second aspect of the present invention, since the voltage division ratio has only to be substantially equal to the ratio between the impedance to be measured and the standard impedance, it is possible to easily perform measurement even though a highly accurate measurement result is obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. As shown in FIG. 1, a known standard impedance Zs and a measured impedance Zx are connected in parallel to a power source PS, and an energization current of these standard impedances Zs is converted into a voltage signal by a current-voltage converter E1 to generate a signal. On the other hand, the deviation current Id of both currents flowing through the standard impedance Zs and the impedance to be measured Zx taken out by the current comparator CC is converted into a voltage by the current-voltage converter E2 and supplied to the signal processing unit DP.

  FIG. 2 is a circuit diagram showing the configuration shown in FIG. 1 in more detail. The current-voltage converter E1 includes a current transformer CT1 and an operational amplifier OP1 having a feedback resistor R1 to form a reference voltage Vs, and the other current-voltage converter E2 is fed back to the current comparator CC. The deviation voltage ΔV is formed by an operational amplifier OP2 having a resistor R2. The reference voltage Vs and the deviation voltage ΔV are given to a digital calculation unit DP having an A / D converter.

  FIG. 3 shows the internal configuration of the digital operation unit DP. Inputs Vs and ΔVs given to the two AD converters ADC1 and ADC2 are respectively digitally converted, and then Vs is converted to jVs by the 90 ° phase shift memory M to form three digital signals Vs, jVs and ΔVs. Is done. These three digital signals are given to multipliers MP1, MP2, and MP3, and an operation shown in the following equation (2) is performed to obtain A, B, and C.

  First, when the turns ratio is n11 = n12 = n21a = n21b = n22, the resistance is R1 = R2 = R, and the error and input impedance of the current transformers CT1 and CT2 are sufficiently small, the reference voltage Vs and the deviation voltage ΔV is expressed as follows.

In the following equation (1), the standard impedance Zs is represented by its reciprocal admittance Ys, and the measured impedance Zx is represented by its reciprocal admittance Yx.

が行われる（ただし、［ｊＶｓ］は、Ｖｓをディジタル演算部ＤＰで＋９０度移相したもの。）。 The reference voltage Vs and the deviation voltage ΔV are digitally converted by the A / D converters ADC1 and ADC2 and given to the multipliers MP1, MP2, MP3 and the 90 ° phase shift memory M, and an operation represented by the following equation (2):

(However, [jVs] is obtained by shifting Vs by +90 degrees in the digital operation unit DP).

A, B, and C obtained by the operations in the multipliers MP1, MP2, and MP3 are given to the digital operation unit DP, and the operation according to the following equation (3) is performed to obtain the ratio error ε and the phase angle θ. .

  Next, a case where capacitance, resistance, and inductance are connected as the admittance elements Ys and Yx to the circuit shown in FIGS. 2A and 2B will be described.

と表わされる。ただし、Ｃｓは、標準コンデンサのキャパシタンス、ＣｘおよびＧｘは、被測定コンデンサのキャパシタンスおよび等価並列コンダクタンス、である。 In the case of the measured capacitance, when considering the standard capacitor Cs as the admittance element Ys and the measured capacitor Cx as Yx, the following equation (4) is obtained.

It is expressed as Where Cs is the capacitance of the standard capacitor, and Cx and Gx are the capacitance of the capacitor to be measured and the equivalent parallel conductance.

となる。これを上記式（２）に代入すると、

が得られる。これを上記式（３）に代入すると、

となる。よって、未知のキャパシタンス値Ｃｘ、ならびに損失角Ｄｘおよび損失角Ｄｘ＝Ｇｘ／ωＣｘは、

として求められる。 Substituting the above equation (4) into the above equation (1),

It becomes. Substituting this into equation (2) above,

Is obtained. Substituting this into equation (3) above,

It becomes. Therefore, the unknown capacitance value Cx and the loss angle Dx and loss angle Dx = Gx / ωCx are

As required.

と表わせる。ただし、Ｒｓは、標準抵抗器の抵抗値、ＲｘおよびＣｘは、被測定抵抗器の抵抗値および等価並列キャパシタンス、である。 In the case of resistance measurement resistance, connecting a standard resistor to Ys and a resistor to be measured to Yx,

It can be expressed as Where Rs is the resistance value of the standard resistor, and Rx and Cx are the resistance value of the resistor under measurement and the equivalent parallel capacitance.

として求められる。 As in the case of capacitance measurement, substituting the above equation (6) into the following equation (1) and rearranging by the above method, the unknown resistance value Rx and phase angle θx (= ωCxRx) are

As required.

と表わせる。ただし、Ｌｓは、標準インダクタのインダクタンス値、ＬｘおよびＧｘは、被測定インダクタのインダクタンス値および等価並列コンダクタンス値、である。 In the case of inductance measurement, connecting a standard inductor to Ys and an inductor to be measured to Yx,

It can be expressed as Where Ls is the inductance value of the standard inductor, and Lx and Gx are the inductance value and equivalent parallel conductance value of the inductor to be measured.

として求められる。 Using the above equation (3), the measured inductor Lx and the quality factor Qx = 1 / ωLxGx are

As required.

Measurement of inductance with a standard capacitor Generally, a standard inductor is less accurate than a standard capacitor. Therefore, if inductance measurement can be performed using a standard capacitor, more accurate inductance measurement can be performed.

と表わされる。これらを、ＡＤ変換器Ａ／Ｄおよびディジタル演算部ＤＰに与えて、まず下式（１１） に示す、

の演算を行う（ただし、［ｊＶｓ］は、Ｖｓをディジタル演算部ＤＰで＋９０°移相した値。）。これを基に、ディジタル演算部ＤＰでは、下式（１２）に示した演算、

を行う。そして、図４において、Ｙｓに標準コンデンサ、Ｙｘに被測定インダクタを接続すると、

と表わすことができる。ただし、Ｃｓは標準コンデンサのコンダクタンス、ＬｘおよびＧｘは被測定インダクタのインダクタンス値および等価コンダクタンス値、である。この上記式（１３）を用いて、インダクタンス値Ｌｘおよびクォリティ・ファクタＱｘ（＝１／ωＬｘＧｘ）は、下式（１４）の通り、

である。 FIG. 4 is a connection diagram for inductance measurement using this standard capacitor, and it is assumed that the polarity of the n12a winding which is one of the two secondary windings of the current transformer CT2 is reversed. In this circuit, when the winding ratio is n11 = n12 = n21a = n21b = n22, the resistance ratio is R1 = R2 = R, and the error and input impedance of the current transformers CT1 and CT2 are sufficiently small, the reference voltage Vs and the difference voltage ΔV are expressed by the following equation (10):

It is expressed as These are given to the AD converter A / D and the digital operation unit DP, and first shown in the following equation (11):

(Where [jVs] is a value obtained by shifting Vs by + 90 ° by the digital operation unit DP). On the basis of this, in the digital calculation unit DP, the calculation shown in the following formula (12),

I do. In FIG. 4, when a standard capacitor is connected to Ys and a measured inductor is connected to Yx,

Can be expressed as Where Cs is the conductance of the standard capacitor, and Lx and Gx are the inductance value and equivalent conductance value of the inductor to be measured. Using the above equation (13), the inductance value Lx and the quality factor Qx (= 1 / ωLxGx) are expressed by the following equation (14):

It is.

  In the description using FIG. 2 and FIG. 4, the winding ratio is n11 = n12 = n21a = n21b = n22 and the resistance ratio is R1 = R2. However, these values should be selected appropriately. Therefore, it is possible to deal with various values of standard impedance and measured impedance.

  FIG. 5 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, impedance measurement is performed by voltage comparison, and the power supply PS is configured as a bridge circuit that connects an inductive voltage divider VD, a standard impedance Zs, and a series circuit of measured impedance Zx.

  Then, the output Vs of the transformer VT and the voltage ΔV at the interconnection point between the standard impedance Zs and the measured impedance Zx are applied to the digital computing unit DP, and the voltage is compared by the digital computing unit DP to measure the measured impedance Zx. I do.

  In this case, the potential at the output point of the induction voltage divider VD is set to the ground potential, and the voltage dividing ratio n1 / n2 is set so as to substantially match the ratio between the standard impedance Zs and the impedance to be measured Zx. .

と表せる（ただし、Ｎ＝１＋ｎ２／ｎ１）。これらをＡＤ変換器及びディジタル演算器ＤＰに入力し、次の演算を行う。

In this configuration, the reference voltage Vs and the difference voltage ΔV are expressed by the following equation (15):

(Where N = 1 + n2 / n1). These are input to the AD converter and the digital arithmetic unit DP, and the next calculation is performed.

  However, [jVs] is data obtained by shifting Vs by + 90 ° in the digital operation unit DP.

を求める。 Based on these, the following calculation is performed. Then, the digital operation unit DP performs the following operation using A, B, and C obtained by the above equation (16),

Ask for.

と置くと、上記式（１６）は、

と表わせる。したがって、上記式（１７）は、

here,

Then, the above equation (16) is

It can be expressed as Therefore, the above equation (17) is

である。各インピーダンスを、

と置き、上記式（１８）に代入すると、

となる。この式（１９）を実数部、虚数部ごとに纏めると、
実数部：

虚数部：

となる。ここで、上記式（２０）をＲｘについて纏めると、

となり、同様に上記式（２１）をＸｘについて纏めると、

となる。上記式（２２），（２３）より、

が得られる。 From the above formulas (15 ′), (16 ′), (17 ′)

It is. Each impedance

And substituting it into equation (18) above,

It becomes. When this equation (19) is summarized for each real part and imaginary part,
Real part:

Imaginary part:

It becomes. Here, when the above equation (20) is summarized for Rx,

Similarly, when the above equation (21) is summarized for Xx,

It becomes. From the above equations (22) and (23),

Is obtained.

  Here, ΔV is a voltage due to the difference between the set value of the voltage division ratio of the induction voltage divider VD and the ratio of the standard impedance Zs and the impedance to be measured Zx. Since the ratio of the induction transformer VD is set so as to substantially match the ratio of the standard impedance Zs and the impedance to be measured Zx, ε and θ are sufficiently smaller than 1 / N, and the squares of ε and θ are greater than or equal to This term can be ignored.

ただし、

と表わせる。 Therefore, the above equation (24) is

However,

It can be expressed as

と表せる。ただし、ＣｓおよびＲｓは、標準コンデンサのキャパシタンスおよび等価直列抵抗、ＣｘおよびＲｘは、被測定コンデンサのキャパシタンスおよび等価直列抵抗、である。 Measurement of capacitance In FIG. 5, when a standard capacitor is connected as Zs and a measured capacitor is connected as Zx,

It can be expressed. Where Cs and Rs are the capacitance and equivalent series resistance of the standard capacitor, and Cx and Rx are the capacitance and equivalent series resistance of the capacitor to be measured.

と表わせるので、上記式（２５）に上記式（２７）を代入して

となる。したがって、

Here, reactances Xs and Xx are

Therefore, the above equation (27) is substituted into the above equation (25).

It becomes. Therefore,

であり、また、被測定コンデンサの損失角Ｄｘ＝ωＣｘＲｘは、上記式（２５）を用いて

と求められる。とくにＤｓが十分小さい場合、Ｄｘは次のように近似できる。

However, Ds is the loss angle of the standard capacitor. In particular, when Ds is sufficiently small, Cx can be approximated as follows.

In addition, the loss angle Dx = ωCxRx of the capacitor to be measured is expressed by the above equation (25).

Is required. In particular, when Ds is sufficiently small, Dx can be approximated as follows.

と表せる。ただし、ＲｓおよびＣｓは、標準抵抗器の抵抗値および等価直列インダクタンス、ＲｘおよびＬｘは、被測定抵抗器の抵抗値および等価直列インダクタンス、である。 In FIG. 5, when a standard capacitor is connected to Zs and a capacitor to be measured is connected to Zx,

It can be expressed. Where Rs and Cs are the resistance value and equivalent series inductance of the standard resistor, and Rx and Lx are the resistance value and equivalent series inductance of the resistor under measurement.

と表わされるので、上記式（２５）に上記式（３４）を代入して

となる。ただし、φｓは、標準抵抗器の位相角であり、とくにφｓが十分小さい場合、Ｒｘは次のように近似できる。

Here, reactances Xs and Xx are

Therefore, substituting the above equation (34) into the above equation (25)

It becomes. However, φs is the phase angle of the standard resistor, and particularly when φs is sufficiently small, Rx can be approximated as follows.

と求められる。とくに、φｓが十分小さい場合、φｘは次のように近似できる。

Further, the phase angle φx = ωLx / Rx of the resistor to be measured is calculated using the above equation (25).

Is required. In particular, when φs is sufficiently small, φx can be approximated as follows.

と表せる。ただし、ＲｓおよびＬｓは、標準抵抗器の抵抗値および等価直列インダクタンス、ＲｘおよびＬｘは被測定抵抗器の抵抗値および等価直列インダクタンス、である。 Inductance Measurement In FIG. 5, when the standard inductance is connected to Zs and the inductance to be measured is connected to Zx,

It can be expressed. Where Rs and Ls are the resistance value and equivalent series inductance of the standard resistor, and Rx and Lx are the resistance value and equivalent series inductance of the resistor under measurement.

と表わされるので、上記式（２５）に上記式（４０）を代入して

となる。したがって、

Here, reactances Xs and Xx are

Therefore, substituting the above equation (40) into the above equation (25)

It becomes. Therefore,

However, Qs is a quality factor of the standard inductor, and particularly when Qs is sufficiently large, Lx can be approximated as follows.

として求められる。とくにＱｓが十分小さい場合、Ｑｘは次のように近似できる。

Further, the quality factor Qx = ωLxRx is calculated using the above equation (25).

As required. In particular, when Qs is sufficiently small, Qx can be approximated as follows.

The block diagram which shows the structure of one Example of this invention comprised as a current comparison type | mold. FIG. 2 is an overall circuit diagram showing a circuit configuration of the embodiment shown in FIG. FIG. 3 is a circuit diagram showing an internal configuration of a digital arithmetic unit DP used in the circuit of FIG. FIG. 3 is a circuit diagram in which the circuit shown in FIG. 2 is configured to measure inductance using a standard capacitor. The circuit diagram which shows the structure of one Example of this invention comprised as a voltage comparison type. The circuit diagram which shows the impedance measurement circuit comprised as a conventional bridge circuit. The circuit diagram which shows the impedance measurement circuit by the conventional voltage-current ratio.

Explanation of symbols

PS power supply Zs standard impedance Zx ratio measurement impedance Y admittance E current voltage converter DP digital operation part M 90 ° phase shift memory MP multiplier ADC AD converter CT current transformer VT transformer VD induction voltage divider C signal regulator VRM vector Ratio measuring device

Claims (3)

In an apparatus for measuring the impedance of a measured impedance element compared to a standard impedance element,
A current carrying circuit for measurement having a measured impedance element and a standard impedance element connected in parallel to a power supply, and for passing a current through each of the impedance elements;
A signal forming circuit for detecting a measured current flowing in the measured impedance element and a standard current flowing in the standard impedance element, and forming a measured signal and a standard signal;
A deviation detection circuit that extracts a difference between the current to be measured and the standard current and forms a deviation signal;
An impedance measuring device comprising: a processing circuit that calculates an impedance of the impedance element to be measured based on the standard signal and the deviation signal. The impedance measuring device according to claim 1,
The deviation detection circuit extracts the deviation signal by electromagnetically coupling with a first winding for passing the current to be measured, a second winding for passing the standard current, and the first and second windings. An impedance measuring device configured as a current transformer having three windings. In an apparatus for measuring the impedance of a measured impedance element compared to a standard impedance element,
A current carrying circuit for measurement having a measured impedance element and a standard impedance element connected in series to a power supply, and for passing a current through each of the impedance elements;
A potential adjusting circuit having an inductive voltage divider connected to the power source and forming an arbitrary potential between both ends of the power source;
A standard signal circuit having an isolation transformer having a primary winding connected to the power supply and a secondary winding connected to the potential adjustment circuit, and forming a standard signal adjusted in potential by the potential adjustment circuit;
A deviation signal circuit connected to the power source and forming a deviation signal at an interconnection point of the two impedance elements;
An impedance measuring apparatus, comprising: a processing circuit that receives the standard signal and the deviation signal and calculates an impedance of the impedance element to be measured.

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