JP2001153903A - Method and apparatus for measuring resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and certainly exclude influence of thermoelectromotive force, when the resistance value of a resistor to be measured is measured by a four-terminal method. SOLUTION: As the first measurement, constant current I is caused to flow from a constant DC source 10 to the resistor X to be measured from its first lead L1 side toward the second lead L2 side, and voltage Va generated then in the resistor X is measured. Next, as the second measurement, the constant current I is caused to flow reversely to the resistor X this time, from the second lead L2 side toward the first lead L1 side. After voltage Vb generated then in the resistor X is measured, the average voltage Vc of the voltage Va and the voltage Vb is computed, and from this average voltage Vc and the constant current I the resistance value of the resistor X is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring resistance, and more particularly, to the effect of thermoelectromotive force generated at a connection (junction) between dissimilar metals when low resistance is measured by a four-terminal method. The present invention relates to a technology that enables high-precision resistance measurement by eliminating the above.

[0002]

2. Description of the Related Art There are a two-terminal method and a four-terminal method for measuring resistance. A four-terminal method is used for measuring low resistance. The measurement principle of the four-terminal method is that, as shown in FIG. 4, a constant current I is supplied from a DC constant current source CC to a resistor X to be measured via a pair of current probes P1 and P2. This allows
The voltage V generated in the measured resistor X is measured by the voltmeter M via the pair of voltage probes P3 and P4. This constant current I
The resistance value R of the resistor X to be measured is obtained from the equation R = V / I according to Ohm's law based on the following equation:

[0003]

According to the four-terminal method, the resistance value R of the resistance X to be measured can be accurately measured without being affected by the resistances of the current probes P1 and P2. When measuring resistance, the effects of thermoelectromotive force cannot be ignored.

[0004] The thermoelectromotive force is generated when there is a temperature difference between two contacts in a closed circuit made of two kinds of dissimilar metals, and its magnitude depends on the kind of metal at the junction. More specifically, it is about several μV / ° C. to several tens μV / ° C. By the way, a thermocouple known as a temperature sensor applies this phenomenon positively.

[0005] In the four-terminal measurement shown in FIG. 4, the portions where thermal electromotive force may be generated include the leads L 1 and L 2 pulled out from the resistor X to be measured and the voltage probe P.
3 and P4, and the respective junctions between the resistance element of the resistor X to be measured and the leads L1 and L2. Assuming that the thermoelectromotive force at each of these parts is V1, V2, V3, V4,
The voltage V actually measured by the voltmeter M is V = IR +
(V1 + V2 + V3 + V4).

For example, the measurement accuracy of a general 5-digit class digital multimeter (DMM) in the 100 mV range is about ± 10 μV, which is almost the same as the magnitude of the thermoelectromotive force. To eliminate the effect of the thermoelectromotive force, the voltage probes P3 and P4 may be made of the same metal as the leads L1 and L2, but this is not a practical solution.

Therefore, conventionally, as a next best measure, in order to prevent a temperature difference from being generated between the two contacts, the air from the air conditioner is prevented from directly hitting, or the voltage probes P3, P
Although connection of 4 is performed quickly to prevent body temperature from being transmitted, in any case, it is not possible to completely cancel the effect of thermoelectromotive force, since many of the methods rely on the human operator's artificial operation. Met.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to measure the low resistance by the four-terminal method by using the skill of a measurer. Instead, it is an object of the present invention to provide a resistance measuring method and an apparatus thereof that can easily and surely eliminate the influence of thermoelectromotive force.

In order to achieve the above-mentioned object, the present invention provides:
In a state where a pair of current probes and a pair of voltage probes are simultaneously contacted with the first and second leads, respectively, which are drawn out of the resistor to be measured, a DC constant current source passes through the pair of current probes via the pair of current probes. A predetermined constant current I is supplied to the resistance to be measured, and a voltage V generated at the resistance to be measured at that time is measured by voltage measuring means via the pair of voltage probes, and the constant current I and In the resistance measurement method by the four-terminal method for determining the resistance value of the measured resistor from the voltage V, first, the DC constant current source applies the first measured value from the first lead side to the measured resistor. (2) The constant current I is caused to flow toward the lead side, and the voltage Va generated at the resistor to be measured at that time is measured by the voltage measuring means, and then the resistor to be measured is supplied from the DC constant current source. Against The constant current I is passed from the second lead side to the first lead side, and a voltage Vb generated at the resistor to be measured at that time is measured by the voltage measuring means. It is characterized in that an average voltage Vc of Vb is calculated, and a resistance value of the resistor to be measured is obtained from the average voltage Vc and the constant current I.

In this case, the flow direction of the constant current I with respect to the resistor to be measured may be switched by exchanging the positions of the pair of current probes with respect to the respective leads, or the DC constant may be changed. Switching means is provided between each of the current output terminals on the positive and negative sides of the current source and the pair of current probes, and the switching means switches the flow direction of the constant current I to the measured resistor. Either embodiment may be included in the present invention.

When the direction of flow of the constant current I is switched, it is preferable that the DC constant current source is once turned off to discharge the resistor to be measured.

Further, the present invention provides a DC constant current source for supplying a predetermined constant current I to a resistor to be measured via a pair of current probes, and a pair of voltage probes for applying a voltage V generated in the resistor to be measured. And a control means for monitoring the DC constant current source and the voltage measuring means and calculating a resistance value of the measured resistor from the constant current I and the voltage V. In the resistance measuring apparatus according to the four-terminal method, one of the current probes is connected to a positive-side current output terminal of the DC constant current source, and the other of the current probes is connected to a negative-side current output terminal of the DC constant current source. A first switching stage connected to the DC constant current source and one of the current probes connected to the negative current output terminal of the DC constant current source, and the other of the current probes connected to the positive current output of the DC constant current source. A switching means and a second switching stage to be connected to the terminal, when determining the resistance value of the measuring resistor, the control means, said switching means said first switching stage (or the second switch stage)
To obtain the voltage Va measured at that time from the voltage measuring means, and then switch the switching means to the second switching stage (or the first switching stage), and After obtaining the measured voltage Vb, an average voltage Vc of the voltage Va and the voltage Vb is calculated, and the resistance value of the measured resistor is obtained from the average voltage Vc and the constant current I. I have.

According to this, the influence of the thermoelectromotive force can be canceled by a simple method. In the measuring device of the present invention, the switching means is preferably automatically switched by the control means, but the present invention also includes manual switching.

[0014]

Next, the present invention will be described specifically with reference to examples. FIG. 1 is a circuit configuration diagram of the resistance measuring apparatus according to this embodiment.

This resistance measuring device includes a DC constant current source 10 for supplying a predetermined constant current I to a resistance X to be measured, and a voltage measurement unit 2 for measuring a voltage V generated in the resistance X to be measured.
0. The current is supplied to the measured resistor X through a pair of current probes P1 and P2.
In this case, the DC constant current source 10 and the current probes P1, P2
The switch 11 is connected between the two.

The switch 11 is provided with first and second two switches 12 and 13 which operate in conjunction with each other. The first switch 12 includes a switching contact 12a connected to the first current probe P1, a switching contact 12b connected to the second current probe P2, and these switching contacts 12a, 12
b, which is connected to the negative electrode 10b of the DC constant current source 10 in this case.

The second switch 13 is connected to a second current probe P
Switching contact 13a connected to the first current probe P
1 and the switching contacts 13b
movable contact 1 that can be switched to one of a and 13b
3c, and the movable contact 13c is connected to the positive electrode 10a side of the DC constant current source 10.

A pair of voltage probes P3 and P4 for detecting the voltage V of the resistor X to be measured are connected to the voltage measuring section 20. In this embodiment, the voltage measuring unit 20
Is supplied to the CPU 30 as control means via the A / D converter 21.

An input unit 31 for setting various measurement conditions and the like, a display unit 32 such as a display or a printer, a memory 33, and the like are connected to the CPU 30.
The CPU 30 has a switching control function for switching the current output range of the DC constant current source 10 and the switch 11 in addition to various arithmetic functions.

In measuring the resistance value of the measured object X, for example, the first current probe P1 is connected to the measured object X
And the second current probe P2 is brought into contact with the other lead L2. Also,
A pair of voltage probes P3 and P4 are brought into contact with the leads L1 and L2, respectively.

First, as a first measurement, the movable contacts 12c, 1 of the switches 12, 13 of the switch 11 are set.
3c is switched to the switching contacts 12b and 13b, and a constant current is supplied from the DC constant current source 10 to the resistor X to be measured. As a result, as shown in FIG. 4 described above, the constant current I flows from the one lead L1 to the other lead L2 in the resistor X to be measured.

At this time, the voltage Va generated in the resistor X to be measured is measured by the voltage measuring unit 20 and the voltage is measured by the A / D converter 21.
Via the CPU 30. The CPU 30 stores the voltage Va in the memory 33. After the measurement of the voltage Va, the DC constant current source 10 is once turned off, and the measured resistor X
Is discharged (discharged). This discharge is performed by short-circuiting between the leads L1 and L2 by a short circuit (not shown).

Here, the resistance value of the resistor X to be measured is R, the thermoelectromotive force generated at each contact point between the voltage probes P3 and P4 and the leads L1 and L2 is V1 and V4, and the leads L1 and L2 are The thermoelectromotive force generated at the junction with the resistor X is V2,
Let V3 be the voltage Va measured by the voltage measurement unit 20.
Is Va = IR + (V1 + V2 + V3 + V4).

Next, the switch 11 is switched to perform a second measurement. That is, each of the switches 12, 13
Are switched to the switching contacts 12a and 13a, and a constant current is supplied from the DC constant current source 10 to the resistor X to be measured. As a result, as shown in FIG. 2, the constant current I flows from the other lead L2 to the one lead L1 with respect to the resistor X to be measured.

At this time, the voltage Vb generated in the resistor X to be measured is measured by the voltage measuring section 20 and the voltage is measured by the A / D converter 21.
Via the CPU 30. Since the flow direction of the current at the time of the second measurement is opposite to that of the first measurement, the voltage Vb measured by the voltage measurement unit 20 is Vb = IR−
(V1 + V2 + V3 + V4).

After the second measurement, the CPU 30
The average voltage Vc is obtained by performing the calculation of (Va + Vb) / 2, and the resistance value R of the measured resistor X is calculated from the average voltage Vc and the constant current I and displayed on the display unit 32. For reference, an operation flowchart of the above embodiment is shown in FIG.

As described above, the influence of the thermoelectromotive force can be canceled by measuring twice with respect to the resistor X to be measured while changing the current direction and obtaining the average voltage.
Further, the offset in the measurement circuit can be removed. The average voltage may be obtained by performing the measurement while changing the current direction two or more times, that is, 2 × n times (n is an integer of 2 or more).

In order to automate the measurement, it is desirable to control the switch 11 and the like by the CPU 30 as in the above embodiment. However, in some cases, the switch 11 may be switched manually. Also, the switch 11
Current probe P for leads L1 and L2
The direction of the current flowing through the measured resistor X may be changed by exchanging the positions of 1 and P2.

[0029]

As described above, according to the present invention,
When measuring the resistance value of the measured resistor by the four-terminal method, the direction of the current flowing through the measured resistor is changed and the voltage generated in the measured resistor is measured at least twice, and the average value of the measured voltages is measured. Since the resistance value of the measured resistor is calculated from the average value and the measured current, the influence of the thermoelectromotive force can be easily and reliably eliminated without depending on the skill of the measurer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a resistance measuring device according to the present invention.

FIG. 2 is an explanatory diagram for explaining a direction of a current flowing through a resistor to be measured.

FIG. 3 is an operation flowchart of the present invention.

FIG. 4 is an explanatory diagram for explaining a resistance measuring method by a four-terminal method.

[Explanation of symbols]

 Reference Signs List 10 DC constant current source 11 Switching device 20 Voltage measurement unit 21 A / D converter 30 CPU P1, P2 Current probe P3, P4 Voltage probe X Resistance to be measured L1, L2 Lead

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Satoshi Uehara 81 Sakuracho, Oizumi, Ueda-shi, Nagano F-term (reference) 2F056 PA01 PA09 2G028 AA01 AA04 BB03 CG02 DH03 DH13 FK01 GL07 GL11 HM07 HN11 HN13 LR02

Claims (5)

[Claims] A first resistor drawn out of the resistance to be measured;
And a pair of current probes and a pair of voltage probes are simultaneously contacted with the respective second leads,
A predetermined constant current I is supplied from the DC constant current source to the resistor to be measured via the pair of current probes, and a voltage V generated at the resistor to be measured at that time is supplied to the resistor via the pair of voltage probes. In a resistance measurement method by a four-terminal method for measuring the resistance value of the resistor to be measured from the constant current I and the voltage V, the resistance is measured by the DC constant current source. The constant current I is passed from the first lead side to the second lead side to the body, and a voltage Va generated in the resistor to be measured at that time is measured by the voltage measuring means. In addition, the constant current I from the DC constant current source to the resistor to be measured from the second lead side to the first lead side.
And the voltage V generated at the resistor to be measured at that time
b is measured by the voltage measuring means, and an average voltage Vc of the voltage Va and the voltage Vb is calculated.
c) determining a resistance value of the measured resistor from the constant current I and c. 2. The resistance measuring method according to claim 1, wherein the flow direction of the constant current I with respect to the measured resistor is switched by exchanging positions of the pair of current probes with respect to each of the leads. 3. A switching means is provided between each of the current output terminals on the positive electrode side and the negative electrode side of the DC constant current source and the pair of current probes, and the switching means supplies the constant current to the resistor to be measured. 2. The resistance measuring method according to claim 1, wherein the flow direction of I is switched. 4. When the direction of flow of the constant current I is switched, the DC constant current source is once turned off,
4. The resistance measuring method according to claim 1, wherein the resistance of the measured resistor is discharged. 5. A DC constant current source for supplying a predetermined constant current I to a measured resistor through a pair of current probes, and a voltage V generated in the measured resistor is measured via the pair of voltage probes. The constant current I and the voltage V are monitored by monitoring the DC constant current source and the voltage measuring means.
And a control means for calculating a resistance value of the resistance to be measured from the four-terminal method, wherein one of the current probes is connected to a positive side current output terminal of the DC constant current source. A first switching stage for connecting the other of the current probes to the negative current output terminal of the DC constant current source, and connecting one of the current probes to the negative current output terminal of the DC constant current source;
A switching unit having a second switching stage for connecting the other of the current probes to a positive-side current output terminal of the DC constant current source. In obtaining a resistance value of the measured resistor, the control unit includes: The switching means is switched to the first switching stage (or the second switching stage) to obtain the voltage Va measured at that time from the voltage measuring means, and then the switching means is switched to the second switching stage (or the second switching stage). After switching to the first switching stage and obtaining the voltage Vb measured at that time from the voltage measuring means, an average voltage Vc of the voltage Va and the voltage Vb is calculated, and the average voltage Vc and the constant current Ic are calculated. A resistance value of the resistor to be measured.