JP4208560B2 - Impedance measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an impedance measuring apparatus that measures the impedance of a measurement object by, for example, a four-terminal method.
[0002]
[Prior art]
As this type of impedance measuring device, for example, an impedance measuring device 51 shown in FIG. 3 is conventionally known. When the impedance of the measuring object M is measured by the impedance measuring device 51, first, a pair of contact probes P1, P2 are brought into contact with both end points (point E and point F) of the measuring object M, and the measuring object is measured. The other pair of contact probes P3 and P4 are brought into contact with two points M (points G and H set between points E and F), respectively. Next, the measurement current I is supplied from the current source 12 through the pair of contact probes P1 and P2. At this time, the measurement unit 13 measures the voltage V between two points (G point and H point) of the measurement object M via the other pair of contact probes P3 and P4, and the voltage of the measured voltage V The impedance Z is calculated based on the value and the current value of the supplied measurement current I. This measurement method is a so-called four-terminal method, and measures the voltage V between two points (G point and H point) of the measurement object M using a high-impedance differential amplifier 13a in the measurement unit 13. In principle, the influence of the resistance of each contact probe P3, P4 and the contact resistance between each contact probe P3, P4 and the measurement object M on the measurement is reduced, and the measurement object M is reduced. Impedance Z can be measured. In this case, the impedance Z is calculated by the arithmetic circuit 13b based on the measured voltage V. Further, when the conductivity σ of the measuring object M is further measured by the impedance measuring device 51, the distance L between two points (G point and H point) of the measuring object M stored in advance in the memory 13c. Based on the cross-sectional area S of the measuring object M between the points G and H and the measured impedance Z, the arithmetic circuit 13b calculates the conductivity σ based on the following equation (1). The calculated impedance Z and conductivity σ are displayed on the display unit 14.
σ = L / (Z × S) (1) equation
[0003]
However, for example, when measuring a measuring object M such as a solid oxide that needs to be in electrical contact with each contact probe by winding a conductive metal such as platinum provided at the tip of each contact probe. The contact resistance between each contact probe and the solid oxide may become so large that it cannot be ignored with respect to the input impedance of the differential amplifier 13a. In this case, the above-described impedance measuring device 51 cannot accurately measure the voltage V between the point G and the point H of the measurement object M, and the impedance Z of the measurement object M, and hence the measurement object. There arises a problem that the conductivity σ of M cannot be accurately calculated. Further, when the contact resistance is large as described above, a potential difference determined by the product of the current value of the measurement current I to be supplied and the contact resistance is generated between the point H of the measurement object M and the ground. The common-mode voltage adversely affects the differential amplifier 13a. For this reason, there arises a problem that the impedance Z and the conductivity σ cannot be accurately measured due to a decrease in calculation accuracy of the differential amplifier 13a.
[0004]
For this reason, in the impedance measuring device disclosed in Japanese Patent Application Laid-Open No. 11-38053, the current supply terminal is set so that the common-mode voltage component at the voltage detection terminal pair (the G point and the H point of the measurement object M) is substantially constant. A control loop for controlling the potential is provided to solve the above-mentioned problem caused by contact resistance.
[0005]
[Patent Document 1]
JP 11-38053 A (2nd page, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, the impedance measuring device disclosed in Japanese Patent Application Laid-Open No. 11-38053 has the following problems. That is, in this impedance measuring apparatus, a large number of electronic circuits such as a differential circuit, a buffer, and a resistor are required to form a control loop. As a result, this impedance measuring apparatus has a problem that the number of parts increases and the apparatus cost increases.
[0007]
The present invention has been made in view of such problems, and it is a main object of the present invention to provide an impedance measuring apparatus capable of measuring the impedance of a measurement object at a low cost while eliminating the influence of contact resistance. And
[0008]
[Means for Solving the Problems]
To achieve the above object, the impedance measuring apparatus according to claim 1 is connected to the first and second contact probes connectable to the first and second current supply terminals and to the first and second voltage detection terminals. Possible third and fourth contact probes; Each of the pair of input terminals includes a differential amplifier connected to each of the first and second voltage detection terminals. The third and fourth contact probes respectively brought into contact with the measurement object in a state where a measurement current is supplied from the first contact probe brought into contact with the measurement object to the second contact probe. A voltage generated between the voltage detection terminals via the four-terminal method and measuring the impedance of the measurement object based on the voltage value of the measured voltage and the current value of the measurement current Each of the current supply terminals, the voltage detection terminals, and the contact probes, the current supply terminals, the voltage detection terminals, and the respective current supply terminals. A switching unit capable of switching a connection state with a contact probe is provided, and the measurement unit measures impedance of the measurement object Prior, the by the switching unit 3 and Either one of the fourth contact probes Both In the connection state where the voltage detection terminal is connected, A differential amplifier is connected between the connected voltage detection terminals and the second current supply terminal. The error voltage generated in accordance with the common-mode voltage induced in one of the contact probes is measured by measuring the voltage of the error, and either the error voltage or a parameter value calculated based on the error voltage is measured. And a reference value set in advance corresponding to the one is compared to determine the magnitude of the contact resistance between the second contact probe and the measurement object.
[0009]
The impedance measuring device according to claim 2 is: The impedance measuring device according to claim 1, wherein Prior to the impedance measurement of the measurement object, the measurement unit connects the first current supply terminal and the first voltage detection terminal to the third contact probe by the switching unit and the second contact probe. In a state where the current supply terminal and the second voltage detection terminal are connected to the fourth contact probe, the voltage between the voltage detection terminals is measured, and based on the measured voltage and the measured voltage The magnitude of the contact resistance between the third and fourth contact probes and the measurement object by comparing any one of the calculated parameter values with a reference value set in advance corresponding to the one of the parameter values. Determine.
[0010]
The impedance measuring apparatus according to a third aspect is the impedance measuring apparatus according to the first or second aspect, wherein the measuring unit calculates a conductivity of the measurement object based on the measured impedance.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of an impedance measuring apparatus according to the invention will be described with reference to the accompanying drawings. In addition, about the component same as the conventional impedance measuring apparatus 51, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
[0012]
First, the configuration of the impedance measuring apparatus 1 according to the present invention will be described with reference to FIG.
[0013]
As shown in FIG. 1, the impedance measuring apparatus 1 includes a contact probe P1 (first contact probe), a contact probe P2 (second contact probe), a contact probe P3 (third contact probe), and a contact probe P4 ( A fourth contact probe), a switching box (switching unit) 11, a current source 12, a measuring unit 13, and a display unit 14. The impedance Z of the measuring object M is measured (calculated) by the four-terminal method and measured. The electrical conductivity σ can be measured (calculated) based on the impedance Z.
[0014]
The switching box 11 includes an a terminal, a b terminal, a c terminal, a d terminal, an A terminal, a B terminal, a C terminal, and a D terminal. By changing (switching) the internal connection state, at least the following three combinations Thus, the terminal group from the a terminal to the d terminal and the terminal group from the A terminal to the D terminal can be switched and connected.
(First combination)
a terminal and A terminal, b terminal and C terminal, c terminal and C terminal, d terminal and D terminal
(Second combination)
a terminal and B terminal, b terminal and B terminal, c terminal and C terminal, d terminal and C terminal
(Third combination)
a terminal and A terminal, b terminal and B terminal, c terminal and C terminal, d terminal and D terminal
[0015]
Moreover, in this Embodiment, although the switching box 11 shows and demonstrates the structure which switches the connection of the group of a terminal-d terminal and the group of A terminal-D terminal as an example, for example, a measurement part It is also possible to adopt a configuration in which the combination of connections is automatically switched under the control of 13.
[0016]
The contact probe P1, the contact probe P2, the contact probe P3, and the contact probe P4 (hereinafter also referred to as “contact probe P” when not distinguished from each other) are configured such that each one end to be brought into contact with the measurement object M is made of, for example, platinum wire. The other end side is connected to the A terminal, D terminal, B terminal and C terminal of the switching box 11, respectively.
[0017]
The current source 12 includes a T1 terminal (first current supply terminal) and a T2 terminal (second current supply terminal), and is configured to be able to supply a measurement current I between the T1 terminal and the T2 terminal. The T1 terminal and T2 terminal of the current source 12 are connected to the a terminal and d terminal of the switching box 11, respectively.
[0018]
The measurement unit 13 includes a T3 terminal (first voltage detection terminal), a T4 terminal (second voltage detection terminal), a differential amplifier 13a, an arithmetic circuit 13b, and a memory 13c. In this case, the T3 terminal and the T4 terminal are connected to the b terminal and the c terminal of the switching box 11, respectively. The differential amplifier 13a has a pair of input terminals connected to the T3 terminal and the T4 terminal, respectively, and differentially amplifies and detects the voltage V between the T3 terminal and the T4 terminal. The arithmetic circuit 13 b calculates the impedance Z based on the voltage value of the voltage V and the current value of the measurement current I supplied by the current source 12. The arithmetic circuit 13b determines the magnitude of the contact resistance based on the impedance Z and the reference impedances Zr1 and Zr2, as will be described later. The arithmetic circuit 13b calculates the electrical conductivity σ of the measuring object M based on the impedance Z, the preset cross-sectional area S and the inter-terminal distance L related to the measuring object M. In the memory 13c, the cross-sectional area S, the inter-terminal distance L, and the reference impedances Zr1 and Zr2 are stored in advance.
[0019]
The display unit 14 is configured using, for example, a CRT or LCD, and displays the impedance Z and conductivity σ measured by the measurement unit 13.
[0020]
Next, a measurement method for measuring the electrical conductivity σ of the measurement object M formed in a cylindrical shape by a solid electrolyte (zirconia, beta alumina, etc.) using the impedance measurement device 1 will be described with reference to FIG.
[0021]
First, one end side of the pair of contact probes P1 and P2 is brought into contact with both end points (E point and F point) of the measurement object M, and other two points (G point and H point) of the measurement object M are connected to each other. One end sides of the pair of contact probes P3 and P4 are brought into contact with each other (step 50). Specifically, a platinum wire on one end side of each of the contact probes P1 to P4 is wound around the measurement object M a plurality of times and brought into electrical contact.
[0022]
Next, determination processing for determining the magnitude of the contact resistance for the contact probe P2 is performed (step 51). In this process, first, the internal connection state in the switching box 11 is changed. Specifically, the terminal group of a terminal to d terminal and the terminal group of A terminal to D terminal are connected by the first combination described above. Next, the current source 12 is operated, and the supply of the measurement current I to the measurement object M is started. Subsequently, the measurement unit 13 is operated to measure the impedance Z between the T3 terminal and the T4 terminal. In this case, the b terminal of the switching box 11 is connected to the C terminal, the c terminal is connected to the C terminal, and the T3 terminal and the T4 terminal are short-circuited by the switching box 11. For this reason, in the differential amplifier 13a, the voltage V between the two input terminals (between the T3 terminal and the T4 terminal) becomes zero volts. On the other hand, the differential amplifier 13a measures the impedance between the H point and the F point in the measurement object M, and the combined impedance and measurement of the contact resistance between the contact probe P2 and the measurement object M (contact resistance at the F point). The common mode voltage generated by the working current I is induced (applied) to both input terminals. For this reason, the differential amplifier 13a Wake up Therefore, the arithmetic circuit 13b equivalently calculates the impedance Z (parameter value) based on the error voltage and the current value of the measurement current I.
[0023]
Next, the arithmetic circuit 13b compares the reference impedance Zr1 stored in advance in the memory 13c with the calculated impedance Z. In this case, when the contact resistance between the contact probe P2 and the measurement object M is large, the common-mode voltage increases, so that the error voltage increases and the calculated impedance Z also increases. Therefore, when the impedance Z is equal to or higher than the reference impedance Zr1, it is determined that the contact resistance between the contact probe P2 and the measurement object M is large (the influence of the contact resistance is large), and when the impedance Z is less than the reference impedance Zr1, It is determined that the contact resistance is small (the effect of contact resistance is small).
[0024]
Next, as a result of the above determination processing, when it is determined that the contact resistance is large (the influence of the contact resistance is large), the process proceeds to step 52 and an error is displayed to that effect. On the other hand, when it is determined that the contact resistance is small (the influence of the contact resistance is small), the process proceeds to step 53.
[0025]
In step 53, determination processing for determining the magnitude of the contact resistance for the contact probes P3 and P4 is executed. In this process, first, the internal connection state of the switching box 11 is changed. Specifically, the terminal group of a terminal to d terminal and the terminal group of A terminal to D terminal are connected by the second combination described above. Next, the current source 12 is operated, and the supply of the measurement current I to the measurement object M is started. Subsequently, the measurement unit 13 is operated to measure the impedance Z (parameter value) between the T3 terminal and the T4 terminal. In this case, when the b terminal and the B terminal of the switching box 11 are connected and the c terminal and the C terminal are connected, the a terminal is connected to the B terminal, and the d terminal is connected to the C terminal. Yes. Accordingly, the measurement current I supplied by the current source 12 flows into the point G of the measurement object M via the voltage detection contact probe P3, and from the point H of the measurement object M via the contact probe P4. It flows into the T2 terminal and further flows into the ground. In this case, the contact resistance between the contact probe P3 and the measurement object M, the impedance Z of the measurement object M between the points G and H, and the contact resistance between the contact probe P4 and the measurement object M A voltage V caused by the measurement current I flowing through the combined impedance is generated between the T3 terminal and the T4 terminal.
[0026]
At this time, the differential amplifier 13a detects this voltage V, and the arithmetic circuit 13b calculates the impedance Z based on the voltage V. In this case, if each contact resistance of each contact probe P3, P4 increases, the voltage V detected by the differential amplifier 13a also increases, and accordingly, the impedance Z calculated by the arithmetic circuit 13b also increases. Accordingly, the arithmetic circuit 13b compares the reference impedance Zr2 stored in advance in the memory 13c with the calculated impedance Z, and when the impedance Z is equal to or higher than the reference impedance Zr2, the contact resistance of each contact probe P3, P4 is large. When the impedance Z is less than the reference impedance Zr2, it is determined that the contact resistance is small (the influence due to the contact resistance is small).
[0027]
Next, when it is determined that the contact resistance is large (the influence of the contact resistance is large) as a result of the determination process related to the magnitude of the contact resistance, the process proceeds to step 52 and an error is displayed. On the other hand, when it is determined that the contact resistance is small (the influence of the contact resistance is small), the process proceeds to step 54.
[0028]
In step 54, the impedance measurement process of the measuring object M by the four-terminal method is executed. In this process, first, the internal connection state of the switching box 11 is changed. Specifically, the terminal group of a terminal to d terminal and the terminal group of A terminal to D terminal are connected by the third combination described above. Next, the current source 12 is operated, and the supply of the measurement current I to the measurement object M is started. Subsequently, the measurement unit 13 is operated to measure the impedance Z between the T3 terminal and the T4 terminal. Specifically, the differential amplifier 13a detects the voltage V generated between the T3 terminal and the T4 terminal via the contact probes P3 and P4, and the arithmetic circuit 13b calculates the impedance Z based on the voltage V. In this case, since it is determined that the contact resistance of the contact probes P3 and P4 is small as a result of the determination process related to the contact resistance in Step 53 described above, the voltage V between the T3 terminal and the T4 terminal is mainly applied to the measurement object M. Occurs due to impedance between point G and point H. Moreover, in the determination process regarding the contact resistance in step 51 described above, it is determined that the contact resistance of the contact probes P3 and P4 is small. For this reason, the error generated in the differential amplifier 13a due to the contact resistance of the contact probe P2 is maintained in a sufficiently small state. Therefore, in this impedance measuring apparatus 1, the impedance Z between the point G and the point H of the measurement object M is measured with high accuracy.
[0029]
Subsequently, the arithmetic circuit 13b calculates the conductivity σ according to the above equation (1) based on the measured impedance Z and the cross-sectional area S and the inter-terminal distance L related to the measurement object M stored in advance (Step 1). 55). Next, the arithmetic circuit 13b displays the calculated conductivity σ on the display unit 14 (step 56), and completes the conductivity measurement (calculation) process.
[0030]
As described above, according to the impedance measuring apparatus 1, prior to the impedance measurement of the measurement object M by the four-terminal method, the magnitude of the contact resistance of the contact probes P2 to P4 is determined, and it is determined that these effects are small. By performing the impedance measurement only when it is performed, the influence of the contact resistance of the contact probe P can be eliminated and the impedance can be measured with high accuracy. Therefore, the conductivity of the measuring object M can also be calculated with high accuracy. In addition, since the switch box 11 having a simple structure is simply provided in the conventional impedance measuring device 51, the number of circuit components is sufficiently large as compared with the impedance measuring device described in JP-A-11-38053. Since it can reduce, the raise of product cost can fully be suppressed. Further, when it is determined that the contact resistance of each contact probe P is large, an error is displayed on the display unit 14 so that the operator can be urged to improve the contact failure of each contact probe P. Therefore, as a result of providing an opportunity to readjust the contact state of the contact probe P to the measurement object M, impedance measurement and conductivity measurement in a normal state with low contact resistance can be realized.
[0031]
The present invention is not limited to the configuration shown in the above-described embodiment of the present invention. For example, in the embodiment of the present invention, the example in which the magnitude of the contact resistance for the contact probes P3 and P4 is determined after determining the magnitude of the contact resistance for the contact probe P2 has been described, but in the reverse order It is possible to employ a configuration for determining, or it is possible to employ a configuration for determining only one of them. In the embodiment of the present invention, in the contact resistance magnitude determination process for the contact probe P2, the connection state of the switching box 11 is connected to the C terminal when the c terminal and the C terminal are connected. However, a configuration in which the c terminal is connected to the B terminal in a state where the b terminal and the B terminal are connected may be employed.
[0032]
In addition, the first and second current supply terminals and the first and second voltage detection terminals in the present invention do not necessarily have to be dedicated terminals, and can be formed at arbitrary connection sites. For the first and second current supply terminals, the a terminal and the d terminal of the switching box 11 also serve as the functions, and for the first and second voltage detection terminals, the b terminal and the c terminal of the switching box 11 serve the functions. It can also be used. Furthermore, in the embodiment of the present invention, the impedance Z is used as a parameter value, the impedance Z is compared with reference impedances Zr1 and Zr2 (reference values) set in advance corresponding to the impedance Z, and the contact probes P2 to P2 are compared. Although the example which determines the magnitude of the contact resistance between P4 and the measuring object M was demonstrated, it is not limited to this. For example, the magnitude of the contact resistance between each contact probe P and the measurement object M can be determined by the magnitude of the voltage V itself detected by the differential amplifier 13a. However, according to the configuration in which the impedance Z is a parameter value, even if the current value of the measurement current I changes, the impedance Z itself does not change. Therefore, between each contact probe P and the measurement object M with high accuracy. The magnitude of the contact resistance can be determined. Moreover, in embodiment of this invention, although the solid electrolyte was mentioned as an example as the measuring object body M, what was formed with materials other than a solid electrolyte can be used as a measuring object body. In particular, by measuring the impedance Z and the conductivity σ of the measurement object M made of a substance such as a solid electrolyte that is likely to have a large contact resistance with the contact probe, the contact is obtained by applying the present invention. The effect of resistance can be effectively eliminated.
[0033]
【The invention's effect】
As described above, according to the impedance measuring apparatus of claim 1, the switching unit capable of switching the connection state between each current supply terminal and each voltage detection terminal and each contact probe is provided with each current supply terminal and each voltage detection terminal. The voltage measuring terminal is connected to either the third or fourth contact probe by the switching unit prior to the impedance measurement of the measurement object. In the state, by measuring the voltage between the voltage detection terminals, the error voltage generated according to the common-mode voltage induced in one of the contact probes is measured, and the error voltage and the error voltage are calculated based on the error voltage. The second contact probe by comparing one of the parameter values to be compared with a reference value set in advance corresponding to one of the parameter values. By determining the magnitude of the contact resistance between the measured object, only when it is determined that the contact resistance is small, it is possible to perform measurements of impedance. For this reason, as a result of avoiding impedance measurement when the contact resistance is large, highly accurate impedance measurement can be performed. In addition, since the configuration is simple by simply providing a switching unit with a simple structure, an increase in the number of circuit components can be suppressed to a minimum, so that an increase in product cost can be suppressed.
[0034]
Moreover, according to the impedance measuring apparatus of claim 2, , Measure Prior to the impedance measurement of the measurement object, the fixed unit connects the first current supply terminal and the first voltage detection terminal to the third contact probe by the switching unit, and the second current supply terminal and the second current supply terminal. In a state where the voltage detection terminal is connected to the fourth contact probe, the voltage between the voltage detection terminals is measured, and either one of the measured voltage and a parameter value calculated based on the measured voltage, The contact resistance is determined to be small by comparing the reference value set in advance corresponding to one of them and determining the contact resistance between the third and fourth contact probes and the measurement object. Only when impedance measurements can be performed. For this reason, as a result of avoiding impedance measurement when the contact resistance is large, highly accurate impedance measurement can be performed. In addition, since the configuration is simple by simply providing a switching unit with a simple structure, an increase in the number of circuit components can be suppressed to a minimum, so that an increase in product cost can be suppressed.
[0035]
Furthermore, according to the impedance measuring apparatus of claim 3, by calculating the conductivity of the measurement object based on the impedance measured with high accuracy in a state where the contact resistance causing the measurement error is small, with high accuracy. The conductivity can be calculated.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an impedance measuring apparatus 1 according to an embodiment of the present invention.
FIG. 2 is a flowchart for explaining conductivity measurement processing by the impedance measuring apparatus 1;
FIG. 3 is a block diagram showing a configuration of a conventional impedance measuring device 51. FIG.
[Explanation of symbols]
1 Impedance measuring device
11 Switching box
12 Current source
13 Measurement unit
I Current for measurement I
M Measuring object
P1, P2, P3, P4 Contact probe
T1, T2 terminals (current supply terminals)
T3 and T4 terminals (voltage detection terminals)
V voltage
Z impedance
Zr1, Zr2 reference impedance

Claims (3)

First and second contact probes connectable to the first and second current supply terminals, third and fourth contact probes connectable to the first and second voltage detection terminals, and a pair of inputs thereof Each of the terminals is configured to include a differential amplifier connected to the first and second voltage detection terminals, respectively, and the first contact probe is brought into contact with the measurement object, and then the second contact probe. In the state in which the measurement current is supplied, the voltage generated between the voltage detection terminals is measured by the four-terminal method via the third and fourth contact probes respectively brought into contact with the measurement object. An impedance unit comprising: a measurement unit that measures an impedance of the measurement object based on a voltage value of the measured voltage and a current value of the measurement current; A measuring device,
A switching unit disposed between each current supply terminal and each voltage detection terminal and each contact probe and capable of switching a connection state between each current supply terminal and each voltage detection terminal and each contact probe. With
The measuring unit, prior to the impedance measurement of the measured object, in the connected state of the two voltage detection terminal is connected to one of said third and fourth contact probe by the switching unit, the differential amplifier Measuring an error voltage generated according to a common-mode voltage induced in one of the contact probes by measuring a voltage between the connected two voltage detection terminals and the second current supply terminal , The second contact probe and the measurement object are compared by comparing either the error voltage or a parameter value calculated based on the error voltage with a reference value set in advance corresponding to the error voltage. Impedance measuring device that determines the magnitude of contact resistance. Before SL measuring unit, prior to the impedance measurement of the measured object, wherein the second with the by switching unit first current supply terminal and the first voltage detection terminal is connected to the third contact probe In the state where the current supply terminal and the second voltage detection terminal are connected to the fourth contact probe, the voltage between the voltage detection terminals is measured, and based on the measured voltage and the measured voltage The contact resistance between the third and fourth contact probes and the measurement object is determined by comparing any one of the calculated parameter values with a reference value set in advance corresponding to the one parameter value. The impedance measuring apparatus according to claim 1, wherein the impedance is determined.   The impedance measurement apparatus according to claim 1, wherein the measurement unit calculates a conductivity of the measurement object based on the measured impedance.

Images