JP3165392B2 - Impedance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impedance measuring device such as a resistor.

[0002]

2. Description of the Related Art FIG. 3 shows a first conventional example. That is,
A 'is an amplifier circuit, B is arithmetic means, C is display means, D is DC current generating means, _RX is a device under test to which a resistor is applied,
P ₁ to P ₄ is the measuring element, C ₁ -C ₄ measuring terminal, A ₁ to A
₃ an operational amplifier, R ₁ to R ₄ is a resistor.

The measuring current I is supplied from a DC current generating means D to a measuring terminal C ₁ → a measuring element P ₁ → a measured element R _X → a measuring element P ₂ →
Flows as measurement terminals C _2, the voltage E _X generated across the measuring element R _X. Further, thermoelectromotive forces Et ₃ and Et ₄ are generated at the connection points of the measuring terminals C ₃ and C ₄ and the measuring elements P ₃ and P ₄ , which are constant because the materials of the measuring elements P ₃ and P ₄ are different depending on the manufacturer. do not do.

[0004] Thus the voltage E _X, measuring terminal C _3, C
₄ and thermoelectromotive force Et ₃ generated at the connection point of the probe P _3, P _4, Et ₄ is added or subtracted value E _X 'is applied to the + input terminal of the operational amplifier A _1, A _2. Here, it is assumed that the resistance values of the resistors R _{1 to} R ₄ are the same, and that the input impedances of the operational amplifiers A _{1 to} A ₃ are sufficiently high and the output impedance is sufficiently low with respect to those values (a general National Semiconductor company). LF35 which is the operational amplifier of
The input impedance of 5A is 10 ¹² Ω, and the output impedance is 0.1 Ω or less), and the amplification factor of the amplifier circuit A ′ is one. Therefore, the output voltage E ₀ = E _X ′
= E _X ~Et ₃ ~Et ₄ next, (~Et ₃ ~Et ₄₎
Becomes an error voltage and is included in the output voltage E ₀ .

The output voltage E ₀ is input to the calculating means B, and is divided by the DC current generating means D by the voltage E ₁ proportional to the measured current I to determine the impedance, and is displayed by the display means C. FIG. 4 shows a second conventional example. In FIG. 3, a constant current circuit is used for the DC current generating means D, and a voltage E ₁ proportional to the measured current I is used.
, And the calculation means B can be provided with a divided value in advance. Other configurations are the same as those in FIG.

[0006]

However, the impedance measured by these conventional examples has a drawback that the measurement accuracy is low because the impedance includes an error due to a thermoelectromotive force.
Therefore, an object of the present invention is to provide an impedance measuring device capable of canceling an error due to an error voltage such as a thermoelectromotive force.

[0007]

According to a first aspect of the present invention, there is provided an impedance measuring apparatus comprising: a power supply for supplying a measuring current to a device under test; Error canceling means for outputting an output voltage obtained by subtracting the voltage of the capacitor from the voltage across the measuring terminal in a state where the measuring current is supplied to the device under test, having a capacitor for charging an error voltage generated in the path of And measuring means for inputting the output voltage of the error canceling means and dividing by the measured current to measure impedance , wherein the error canceling means
Is a pair of voltage holograms whose input terminals are connected to the measurement terminals.
And one non-inverting input terminal of this voltage follower.
A first switch connected to a constant potential through
The output of the pressure follower is input to a pair of input
The output end for outputting a voltage proportional to the voltage of the measuring means
The differential amplifier connected to the
Connected between the non-inverting input terminal of the differential amplifier
When the measurement current is not supplied to the device under test, the first
Appears at the output of the operational amplifier when the switch is on
An integrator having a capacitor for charging an error voltage.
Between the input terminal of the integrator and the output terminal of the operational amplifier.
And a second switch that has been turned on.
Supplying a measuring current and the first switch;
By turning off the second switch, the capacitor
Error voltage input to the operational amplifier with
It's something to cell .

According to the first aspect of the present invention, an error voltage such as a thermoelectromotive force generated in a path from the device under test to the measurement terminal is supplied to the capacitor of the error canceling unit before a measurement current flows through the device under test. By charging and supplying current to the device under test, the voltage appearing at the device under test and the error voltage have been subtracted from the voltage added to the capacitor, so the error voltage can be canceled and the impedance can be measured accurately. Becomes possible. further,
Offset voltage and temperature drift of the differential amplifier
Error can also be canceled at the same time.

[0009]

[0010]

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. That is, the impedance measuring device includes an error canceling unit A, a DC current generating unit D serving as a power supply, and a measuring unit E. Device under test R _X
Applies a resistor. To measure the device under test R _X , current measuring elements P ₁ and P ₂ are connected to both electrodes, and voltage measuring elements P ₃ and P ₄ are connected to both electrodes. C ₁ -C ₄ is a measurement terminal. At this time, as described above, thermoelectromotive forces Et ₃ and Et ₄ are generated at the connection points between the tracing styluses P ₃ and P ₄ and the measuring terminals C ₃ and C ₄ .

The error canceling means A includes a device under test R _X
Measured in a state in which the current I is not supplied, a capacitor Cp to charge the error voltage thermoelectromotive force and the like generated in the path from the measured element R _X to the measurement terminal C _3, C _4, the device under test R measuring terminal C ₃ in a state of supplying a measured current I to _X,
From the voltage across E _X 'of C _4, and outputs an output voltage obtained by subtracting the charge voltage of the capacitor Cp.

The error canceling means A of the embodiment is an amplifier.
A circuit₁~ A_FourAre operational amplifiers, both of which are
The same operational amplifier as that described in the conventional example is used.
R₁~ R_FiveIs a resistance and R₁~ R_FourAre the same resistance value
is there. Cp is a capacitor. That is, this amplification cycle
The path is the measurement terminal C_Three, C_FourComputation with input terminal connected to
Width A₁, A_TwoAnd a pair of voltage followers using
Operational amplifier A, one of the followers_TwoConnected to the non-inverting input terminal of
The first switch connected to the
Chi S_ThreeAnd the outputs of a pair of voltage followers are input to a pair of input terminals.
Output terminal that outputs a voltage proportional to the voltage between the input terminals
A connected to the measuring means E_ThreeDifferential increase using
Width and operational amplifier A_ThreeOutput terminal and operational amplifier A_ThreeNon
Resistor R connected to inverting input_FourConnected between
Device under test R_XIn the state where the measurement current I is not supplied to the first
Switch S_ThreeIs on, the operational amplifier A_ThreeOutput
The error voltage appearing at the end (~ Et_Three~ Et_Four) To charge
Integrator F having a capacitor Cp and an input of the integrator F
End and operational amplifier A_ThreeThe second terminal inserted between the
Switch S_FourAnd the device under test R_XMeasured current I
And the first switch S_ThreeAnd the second
Switch S_FourBy turning off the capacitor Cp
Operational amplifier A with charging voltage of_ThreeThe error voltage (~
Et_Three~ Et _Four) To cancel.

The operational amplifier A is a differential amplifier._ThreeAnd
Anti-R₁~ R_FourAnd an integrator F includes an operational amplifier A
_Four, Capacitor Cp and resistor R_FiveIt consists of.
Measurement terminal C_Three, C_FourProbe P_Three, P_FourIs connected
ing. The DC current generating means D includes a device under test R_XMeasured
A current I is supplied, and a switch S₁,
S_TwoMeasurement terminal C via₁, C_TwoTo the measurement terminal C
₁, C_TwoProbe P₁, P_TwoAre connected.

The measuring means E is to measure the impedance by dividing by with an input terminal connected to the output terminal of the operational amplifier A ₃ receives the output voltage of the cancel means A measurement current I. In the embodiment, the output means comprises an operation means B and a display means C. The operation means B inputs the output voltage E ₀ of the amplifier circuit from the DC current generation means D to a voltage E ₁ proportional to the measured current I of the DC current generation means D. and to measure the impedance of the measuring element R _X by calculating the division of E ₀ / E _1. The display means C displays the value.

The operation of the impedance measuring means will be described.
Will be explained. That is, the measured element R_XIs the measuring element P₁~
P_FourTo switch S₁, S_TwoSwitch off and switch
Chi S _Three, S_FourTurn on. In this case, as described above
Probe P_Three, P_FourAnd measuring terminal C_Three, C_FourAt the connection point
Error voltage due to thermo-electromotive force (~ Et_Three~ Et_Four) Is the operation
Amplifier A₁To the operational amplifier A_ThreeOutput voltage of
Pressure E₀= ~ Et_Three~ Et_FourBecomes This output voltage E₀But
Switch S_FourAnd resistance R_FiveThrough the capacitor Cp
The charging current flows, the capacitor Cp is charged, and the operation is amplified.
Vessel A_FourOutput voltage Ee. This charging is performed at the voltage E
₀Becomes 0V and continues output until charging current stops flowing
Voltage E₀When it becomes 0V, charging stops and the
The voltage for outputting the output voltage Ee when the capacitor is
Cp is charged. This output voltage Ee depends on the thermoelectromotive force.
Error voltage (~ Et_Three~ Et_Four) Is the element to be measured R_XBoth ends of
Voltage E that appears_XOutput voltage E including₀Deducted against
It will be.

That is, the switches S ₁ and S ₂ are turned on immediately before the device under test R _X is measured, and the switches S ₁ and S ₂ are turned on.
_3, turn off the S _4. The measuring current I flows by the DC current generating means D in the order of the switch S ₁ → the measuring terminal C ₁ → the measuring element P ₁ → the measuring element R _X → the measuring element P ₂ → the measuring terminal C ₂ ,
The voltage E _X generated across the measuring element R _X. Measured voltage E _X terminal C _3, C ₄ and the feeler P _3, the thermoelectromotive force Et _3, Et ₄ (yet to be determined polarity of thermoelectric power) is added to or subtracted value generated at the connection point of the P ₄ E _X 'is added to the non-inverting input of the operational amplifier a _1, a _2, further operational amplifier a _1, the output of a ₂ is the inverting input terminal of the operational amplifier a ₃ (-) and the non-inverting input terminal (+) Is added to

Here, it is assumed that the resistance values of the resistors R _{1 to} R ₄ are the same, and the input impedances of the operational amplifiers A _{1 to} A ₃ are sufficiently high and the output impedances are sufficiently low with respect to those values (see the above description). As described above, the input impedance of the LF355A, which is a general operational amplifier manufactured by National Semiconductor, is 10 ¹² Ω and the output impedance is 0.1 Ω or less), and the amplification factor of the amplifier circuit is 1 ×.

On the other hand, since the voltage for generating the voltage Ee for canceling the error voltage (ＥEt _{3 to} Et ₄ ) remains charged in the capacitor Cp and is applied to the non-inverting input terminal of the operational amplifier A ₃ . , the input voltage of the error voltage component from the voltage E _X 'is subtracted. As a result, the output voltage E ₀ =
E _X next to, can cancel the effect of the error voltage due to thermal electromotive force.

The output voltage E ₀ is calculated by the calculating means B of the measuring means.
The impedance is calculated by dividing by a voltage E ₁ proportional to the measured current I, and the value is displayed by the display means C. According to this embodiment, the device under test R
The error voltage of thermoelectric power, etc. appearing in the gauge head P _3, P ₄ or the like before flowing the measurement current I to _X to charge the capacitor Cp of the error canceling means A, by supplying a current to the device under test R _X Since the charging voltage of the capacitor Cp is subtracted from the voltage obtained by adding the error voltage to the voltage appearing at the device under test R _X , the error voltage due to electromotive force such as thermal electromotive force can be canceled, and accurate impedance measurement can be performed. Becomes

Errors due to offset voltages and temperature drifts of the operational amplifiers A _{1 to} A ₄ such as differential amplifiers can be canceled together. FIG. 2 shows a second embodiment of the present invention. That is, in this embodiment, a constant current circuit is used for the DC current generating means D of the first embodiment, and the calculation by the voltage E ₁ proportional to the measured current I is eliminated, and the calculation means B is provided with a divided value in advance. Can be kept. Others are the same as in the first embodiment.

In the present invention, the switches S ₁ ,
S ₂ may be eliminated by using both the probes P ₁ and P ₂ , or may be provided in the DC current generating means itself.

[0023]

According to the first aspect of the present invention, an error voltage such as a thermo-electromotive force generated in a path from the device under test to the measurement terminal before the measurement current flows through the device under test is measured by the error canceling means. By charging the capacitor and supplying current to the device under test, the error voltage was subtracted from the voltage obtained by adding the error voltage to the voltage appearing at the device under test, thereby canceling the error voltage.
Accurate impedance measurement becomes possible. Further
In addition, offset voltage and temperature drift of differential amplifier etc.
Can also be canceled at the same time.

[0024]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a circuit diagram according to a second embodiment.

FIG. 3 is a circuit diagram of a first conventional example.

FIG. 4 is a circuit diagram of a second conventional example.

[Explanation of symbols]

A error canceling means A _1, A ₂ voltage follower of the operational amplifier A ₃ differential amplifier of the operational amplifier A ₄ integrator operational amplifier Cp capacitor D power become DC current generating means E measuring means F integrator R _X element to be measured P _3, P ₄ feeler S ₃ first switch S ₄ second switch

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-10-123189 (JP, A) JP-A-3-148072 (JP, A) JP-A-3-97673 (JP, U) JP-A-63 90172 (JP, U) JP-B-53-9538 (JP, B2) JP-B-49-22475 (JP, B1) Registered utility model 3003659 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G01R 27/02

Claims (1)

(57) [Claims] 1. A power supply for supplying a measurement current to a device under test, and a capacitor for charging an error voltage generated in a path from the device under test to a measurement terminal when the measurement current is not supplied to the device under test. An error canceling unit that outputs an output voltage obtained by subtracting the voltage of the capacitor from the voltage across the measuring terminal in a state where the measuring current is supplied to the device under test, and the output voltage of the error canceling unit is input. Measuring means for measuring the impedance by dividing by the measurement current , wherein the error canceling means
Is a pair of voltage holograms whose input terminals are connected to the measurement terminals.
And one non-inverting input terminal of this voltage follower.
A first switch connected to a constant potential through
The output of the pressure follower is input to a pair of input
The output end for outputting a voltage proportional to the voltage of the measuring means
The differential amplifier connected to the
Connected between the non-inverting input terminal of the differential amplifier
When the measurement current is not supplied to the device under test, the first
Appears at the output of the operational amplifier when the switch is on
An integrator having a capacitor for charging an error voltage.
Between the input terminal of the integrator and the output terminal of the operational amplifier.
And a second switch that has been turned on.
Supplying a measuring current and the first switch;
By turning off the second switch, the capacitor
Error voltage input to the operational amplifier with
Cell impedance measuring device.