JPH05264604A - Digital multimeter - Google Patents

Abstract

PURPOSE:To measure high resistance highly precisely and at high speed by providing a constant current electric power source consisting of a high voltage circuit, etc., an electric power source to be connected to a resistance measuring object, a high voltage and a low voltage side terminals in the electric power side and the measuring side, a priamplifier, and three switches. CONSTITUTION:A stray capacitor Cstray is charged with terminal Lse voltage when a switch SW1 is turned on and measures the output voltage of a priamplifier 4 based on the terminal Lse. When the SW1 is turned off and a switch SW3 is turned on, the capacitor Cstray is discharged through the switch SW3 and the voltage becomes 0V. Further the switch SW3 is turned off and a switch SW2 is turned on, the output voltage of the priamplifier 4 is measured based on the measuring terminal Hse. In this way, resistance is measured at high speed even if a four-way resistance measuring method is applied to measure high resistance wherein the charged electric charge of the capacitor Cstray is discharged to an earth by turning the switch SW3 on during the on-off period of the switches SW1 and SW2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital multimeter, and more particularly to a digital multimeter which enables 4-wire resistance measurement even in a high resistance range.

[0002]

2. Description of the Related Art Digital multimeters are
It is a digital display measuring instrument that can measure resistance etc. in various ranges. In this multimeter, there is a circuit configuration shown in FIG. 3 as a circuit configuration for measuring resistance by a four-wire system.

In the figure, reference numeral 1 is a constant voltage circuit for supplying a constant voltage power source to the circuit. Amplifier A2, standard resistance R
_{The ref} , the amplifier B3 and the constant voltage circuit 1 form a constant current circuit for supplying a constant current I _ref to the circuit under test.

R _x is the resistance to be measured whose resistance value is to be measured, and is the power supply side terminals H _so and L _so and the measurement side terminals H _se and L _se .
connected to _se . r ₁ and r ₂ are lead resistances in which the resistances of wirings are integrated.

Reference numeral 4 is a preamplifier for amplifying a voltage which is a measured value, SW ₁ is a switch inserted between the measurement terminal L _se and the preamplifier 4, and SW ₂ is a measurement terminal H _se and the preamplifier 4.
It is a switch inserted between and. C _stray is a stray capacitance existing in this circuit.

In order to measure the resistance in this way, a constant current I
_{The ref} voltage is applied to the resistance R _x to be measured, and the voltage I across the R _x is generated.
although the measuring _ref R _x, turning on the switch SW ₁ as the measurement method, the voltage at the L _se terminals was measured through a preamplifier 4 to turn off the switch SW _2, then turns off the switch SW _1, the switch SW ₂ The voltage at the H _se terminal is turned on and measured through the preamplifier 4, and the resistance R _x to be measured is obtained by the calculation of the following equation.

R_x= (V_Hse-V_Lse) / I_ref The timing for switching the above switches is as shown in FIG.
It is Ri. In the figure, (a) is a switch SW₁On
Off timing diagram, (b) is switch SW ₂On
It is a figure of an off timing. Switch SW₁And switch
Ji SW₂Is turned on and off at the same timing, and one is turned on
If so, the other is off. Resistance measurement like this
Switch SW at the same timing₁And switch SW₂
By changing the value of the lead resistance r
A 4-wire measurement that can eliminate the error is performed.

In the 4-wire measurement, in the conventional circuit of FIG. 3, the stray capacitance C _{stray is generated} when the switch SW ₁ is turned on.
The electric charge charged in is discharged through the measured resistance R _x when the switch SW ₂ is on.

[0009]

By the way, in the high resistance range (1 MΩ range or more), the H side has a high impedance of 1 MΩ or more when viewed from the ground, and when the switch SW ₁ is switched to the switch SW ₂ for measurement, the switch S
Since the electric charge charged in the _stray capacitance C _stray when W ₁ is on is discharged through the measured resistance R _x of 1 MΩ or more, the discharge time constant is large and the discharge time is long. Therefore, high precision measurement of 6 to 7 digits at high speed cannot be expected.

Therefore, in the conventional multimeter, in the case of measurement in the high resistance range, the 4-wire measurement is not performed, but only the L _se terminal is measured, _{so that} the lead resistance on the H _so side has an error.

The present invention has been made in view of the above points, and an object thereof is to realize a digital multimeter capable of performing high-precision 4-wire measurement at high speed in high resistance measurement. It is in.

[0012]

DISCLOSURE OF THE INVENTION The present invention which solves the above-mentioned problems includes a constant voltage circuit, a standard resistor, a first amplifier and a second amplifier.
A constant current source consisting of an amplifier, a high-voltage measurement terminal and a low-voltage measurement terminal on the power supply side for connecting the resistance to be measured, and a high-voltage measurement terminal and a low-voltage measurement terminal on the measurement side for connecting the resistance to be measured, A preamplifier for amplifying the measurement voltage to increase the measurement sensitivity, a first switch inserted between the measurement-side low-voltage measurement terminal and the preamplifier, and a first switch inserted between the measurement-side high-voltage measurement terminal and the preamplifier And a third switch inserted between the output side of the first switch and the second switch and the ground.

[0013]

[Function] A constant current is applied to the resistance to be measured, the first switch is turned on, the voltage of the low-voltage measurement terminal on the measurement side is measured via the preamplifier, and then the third switch is turned on to charge the stray capacitance. Discharged electric charge to ground. Next, the third switch is turned off and the second switch is turned on, the voltage of the high-voltage measurement terminal on the measurement side is measured through the preamplifier, and the difference between the two voltages is obtained to perform high-precision measurement.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals. In the figure, SW ₃ is a switch SW ₁ and a switch S
It is a switch inserted between the output side to which W ₂ is connected and the ground.

Next, the operation of the embodiment configured as described above
Will be described with an example. That is, the resistance in the 10MΩ range
The case of measurement will be described. Now, measuring terminal H_soTo
Voltage to V_ref, I_ref= 1 μA, R_x= 10 MΩ,
Let r = 100Ω. At this time, H_seTerminal, L_seTo the terminal
Output voltage V of the preamplifier 4 based on the voltage in the₁, V ₂
Is given by the following formula.

V ₂ = V _ref −I _ref r ₁ = V _ref −10
^-6 A x 100 Ω = V _ref -0.0001 V V ₁ = V _ref -I _ref (R _x + r ₁ ) = V _ref -10 ^-6 A (10 ⁷ Ω +10 ² Ω) = V _ref -10.0001 V where 2 shows the operation timings of the switches SW ₁ , SW ₂ , SW ₃ . (A) is a timing chart of the operation of the switch SW ₁ , (B) is a timing chart of the operation of the switch SW ₂ , and (C) is a timing chart of the operation of the switch SW ₃ . As is apparent from the figure, when the switch SW ₁ is turned on, the switch SW ₃ is turned on for a short time, and then the switch SW ₂ is turned on. The circuit operation by the operation of this switch is as follows.

Switch SW ₁ : ON → stray capacitance C _stray
Is charged by the voltage of L _se to -10V. The output voltage V ₁ of the preamplifier 4 based on the measurement terminal L _se is measured.

Switch SW ₁ : off, switch SW ₃ :
The ON → stray capacitance C _stray is discharged through the switch SW ₃ and becomes 0V.

Switch SW ₃ : off, switch SW ₂ :
ON → Output voltage V of preamplifier 4 based on measurement terminal H _se
Measure ₂ .

From the above, the measured resistance R _x is calculated by the following equation. R _x = (V ₂ −V ₁ ) / I _ref = (− 0.0001V + 10.0001V) / 1 μA = 10 MΩ In the high resistance measurement as described above, the resistance value of the lead resistance r ₁ is canceled and an accurate resistance value is obtained. Is obtained.

As described above, in this embodiment, the switch S ₁ and the switch SW ₂ are switched between on and off.
By turning on W ₃ , the electric charge charged by the stray capacitance C _stray is dropped to the ground for discharging, so that high-precision 4-wire resistance measurement can be performed at high speed even when used for high resistance measurement. become able to.

[0022]

As described in detail above, according to the present invention, the 4-wire resistance measurement capable of high precision measurement can be performed at high speed even for the high resistance measurement, which is a practical effect. Is big.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an apparatus according to an embodiment of the present invention.

2 is a time chart of the operation of the switches of the device of FIG.

FIG. 3 is a circuit diagram of a conventional digital multimeter.

FIG. 4 is a time chart of the operation of the conventional device of FIG.

[Explanation of symbols]

1 constant voltage circuit 2, 3 amplifier 4 preamplifier H _so , L _so power supply side measurement terminal H _se , L _se measurement side measurement terminal R _x measured terminal SW ₁ , SW ₂ , SW ₃ switch

Claims (1)

[Claims] 1. A constant current source comprising a constant voltage circuit (1), a standard resistance (R _ref ), a first amplifier (2) and a second amplifier (3) and a resistance to be measured (R _x ) are connected. a power supply side of the high-pressure measuring terminal to (H _so) and a low-pressure measuring terminal (Lso), the measurement side of the high-voltage measuring terminal for connecting the measured resistance (R _x) (H _se) and low pressure measuring terminal ( L _se ), a preamplifier (4) for amplifying the measurement voltage to increase the measurement sensitivity, and a first switch (inserted between the measurement-side low-voltage measurement terminal (L _se ) and the preamplifier (4). SW ₁ ), a second switch (SW ₂ ) inserted between the measurement-side high-voltage measuring terminal (H _se ) and the preamplifier (4), the first switch (SW ₁ ) and the second switch (SW ₂ ). third and a switch (SW ₃₎ that is inserted in between the output side and the ground of the switch (SW ₂₎ Digital multimeter, characterized in Rukoto.