JPS613076A - Measuring apparatus - Google Patents

Abstract

PURPOSE:To enable the maintaining of a high accuracy for a long time, by correcting a high resistance using a reference resistor with a low resistance value to allow the value of the reference resistor to maintain the initial value with a proper stability. CONSTITUTION:Switches S1-S9 are turned ON or OFF with a controller 3 to perform a calibration. Here, an output voltage V0 of an operational amplifier 1 is converted digitally with an A/D converter 4 and brought into the controller 3 to show a measured value on a display 5. Then, when the calibration is done, the switch S8 is turned ON and the switch S9 OFF while the switch S1 is turned ON and the switches S2 and S3 OFF and the switch S5 is connected to a contact (b). On the other hand, when the value of output voltage V0 after T time is represented by AT1, the value of voltage VC after the removal of an off-set voltage CT1 and the value of the voltage VC with the aging of zero C01, the values AT1, CT1 and the like are measured and memorized into the controller 3 in case aging occurs in resistances R1 and R2. After the computation thereof, the measured value is divided by the results and is shown on the display 5 as cleared of aging in the resistances R1 and R2.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a measuring device for measuring weak current or high resistance.

``Prior art'' A digital display shadow measuring device equipped with current measurement mode and resistance measurement mode. In this measuring device, in the current measurement mode, a current-to-voltage converter is disposed in the input circuit to convert the current to be measured into a voltage, and the voltage is all AD converted to digitally display the value of the current to be measured.

In the resistance measurement mode, a resistance-voltage converter is arranged in the input circuit to convert the resistance value of the resistor to be measured into a voltage, and this voltage is converted into iAD and digitally displayed.

FIG. 11 shows a conventional current-voltage converter, and FIG. 12 shows a conventional resistance-voltage converter. The output voltage V in the current-voltage converter shown in FIG. becomes Vo=-IxR. Output voltage V when the current to be measured Ix is a weak current. A
In order to obtain a voltage value at an appropriate level suitable for D conversion, the value of resistor R must be selected to a large value. For example, when measuring a current of 1 microampere, the output voltage V
.

In order to obtain 1 port, R,=IQ''Ω.

On the other hand, in the resistance-voltage converter shown in FIG.

The resistance value of the resistor must be a large resistance value close to the RxO value of the resistor to be measured.

"Problem to be Solved by the Invention" As described above, depending on the measurement conditions, it is necessary to use a resistor with a large resistance value, but in the current measurement mode and resistance measurement mode, as is clear from the above formula, the resistor R used is , directly affects the measured value. %, a resistor with a high resistance value is easily affected by changes in temperature, humidity, etc., and tends to show relatively large changes over time. Therefore, it is difficult to maintain the accuracy of the measurement mode using high resistance at the initial state.

For this reason, it is conceivable to provide a reference voltage source and a reference resistor in the measuring instrument and calibrate the measured value using the reference voltage source and reference resistor, but setting the resistance value of the reference resistor to a large value is not stable. This is obviously a disadvantage if you take gender into account. The limit of the resistance value that can be adopted as a reference resistor is about IMΩ.

When a circuit using a high resistance of several hundred MΩ or more is calibrated using a reference resistor of IMΩ, the calibration accuracy will be low.

[Means for Solving the Problems] This invention focuses on the fact that both the current measurement mode and the resistance measurement mode are equipped with a range switching circuit. The resistor used in the calibrated range is used to calibrate a range using a higher resistor.

FIG. 1 shows the connection state during calibration of the current-voltage converter.

This connection state shows that the resistance value (equivalent to the gain of the operational amplifier 1) of the resistor R, which has a relatively low resistance value, for example, about IOMΩ, is being calibrated by the reference resistor Rr.

FIG. 2 shows a state in which calibration is performed using the resistor R calibrated in FIG. 1 and a resistor Rz' having a larger resistance value.

In this way, in this invention, the first resistor R1 having a relatively small resistance value is calibrated using the reference resistor R,, and the second resistor R2 having an even higher resistance value is calibrated using the first resistor R1. It is characterized by being calibrated.

A concrete example thereof is shown in FIGS. 8 and 9.

"Function" In FIG. 1, switch S. is connected to the contact a, and the reference voltage source ■r is connected to one end of the reference resistor R1. This connection constitutes a reference current source, and the reference current is supplied to operational amplifier 1.
, is given. Reference current■.

The output voltage when is given is ∆ol. Connect the switch So to the contact point and connect it to the common potential point 2, which is one end of the reference resistor. The output voltage at this time is v. Set it to 2. This VC2 is off celler of operational amplifier 1) Voltage 11 [
Then, VOI - VO2 is calculated to obtain a value VC with the offset voltage removed. The value of vc at zero time is Co
, , 'CT the value of VC after r time.

Then, αIVi represents the change over time in the resistance R1, β represents the change over time in the reference resistor Rr, and γ represents the change over time in the reference voltage source Vr.

The ratio of changes in this circuit is CTI/Col. If the time elapsed is zero, CT+/Co1=1.

Here, in the state shown in Fig. 3, if the value of the output voltage vo when the input current I is applied and the elapsed time is zero is AOi, and the value of the output voltage vo when the current is applied after T time is AT+, then A01= -RI I ・・・・・・・・・・・・・・・
...(3) ATt=-几t(1+α1)1...
...(4).

When a value X1 is obtained by dividing A T I by CTI/Cot, X1 becomes a calibrated value with time-dependent changes removed.

ζ-R1・Ir・(1+β-γ). Change over time β of reference resistor Rr and reference voltage source vr
If the time-dependent change γ is assumed to be very small, β and γ can be ignored. Therefore, XI obtained by calculation of equation (5) becomes a value that does not account for the change over time α1 of the resistor R1, and the change over time α1 of the resistor R1 is calibrated.

Next, the state is changed to the state shown in FIG. 2, and the second resistor R2 is calibrated by the first resistor R1. The output voltage VO at zero time is A(+z, the output voltage after T time Vo k AT
2. The actual measured value after removing the offset voltage at zero time is Co2. If the actual value after T time is cT2, then Ao2 = R2·I In this case, since the first resistor R also has a high resistance, this is calculated. As a result, the change over time β of the reference resistor Rr and the reference voltage source V
The change over time of r is only 2γ, and the first. Second resistor R1・
The aging of R2 is removed.

Highly accurate calibration can be performed by calibrating the resistances from low to high using the calculations described above. Although the two-stage case has been proven above, n-stage calibration can be performed.

The error ρ in the case of n-step calibration is ρ−β+nγ.

Next, the case of a resistance-voltage converter will be explained.

First, as shown in FIG. 4, when the standard resistor RX is connected, the value of the output voltage vO at zero over time is Ao, and V after T time. If the value of is AT, then the state is switched to the state shown in FIG. At this time, it is assumed that a voltage higher than the voltage of the reference voltage source ■r2 times VrI is generated. Turn on the switch So, measure the offset voltage of the operational amplifier, and after removing the offset voltage, the value when VC reaches zero over time is Co.
, , If the value after T time is CT+, then it is calculated as in the case of the current-voltage converter. That is, il (1+α1)(1+, &)(1+γ2)γ1.
γ2 is the change over time of the reference voltage sources vr, , Vr2, which becomes zero if γl=γ2. Further, β is the change over time of the reference resistor ur, and since this is also sufficiently small, it is determined by Xl substantially VCRx·V r 1/R1.

Therefore, by calculating the sixth equation, the change over time α1 of the resistor R1 can be removed.

To calibrate the next higher resistor R2, see Figures 5 and 6.
As shown in the figure, connect R2 to the position of R1, and connect 几1 to the position of the reference resistor ■r. In this state, measure and calculate. In other words, the cause of error due to changes in R, , R2 is eliminated.

When this calibration is performed sequentially starting from the lowest resistance, the n-th error ρ becomes ρ=γ1−β−nγ2 γl; when r2, ρ−−β−(r−1) r2.

"Example" A specific example is shown in FIG. 8 and FIG. 9. FIG. 8 shows the case of a current-voltage converter, and FIG. 9 shows the case of a resistance-voltage converter.

In FIGS. 8 and 9, reference numeral 3 indicates a controller configured by a microcomputer. The controller 3 turns on and off the switches 81 to S9 to perform the above-described calibration. At this time, the output voltage VO of the operational amplifier 1 is AD converted by the AD converter 4 and input to the controller 3, and the display 5
In addition to displaying the measured value, in the case of calibration operation, the COI *
cT, l Aol + ATI, CO2, cT2
．． AO2, AT2k are stored and calculations are performed for calibration.

In the current-voltage converter shown in FIG. 8, when performing calibration, first turn on switch S8, turn off switch S9, turn on switch 31, turn off S2, Sak, and turn off switch S
By connecting to the SE contact, the state shown in FIG. 3 can be achieved. In this state, connect the reference current source ■o to the input terminal, and apply the reference current I, A, 01* or A T 1
Determine. A01 is stored in the controller 3 at the time of initial shipment, and then when the user performs calibration, A01 is stored in the controller 3 at the time of initial shipment.
This means measuring T+.

Next, switch Sat off, S9 on/S, S3 all on, Szk off, switch S, contact bVC.

By connecting S6 to contact a, the state shown in FIG. 1 can be achieved. In this state, Co+' is measured at the time of shipment and stored in the controller 3. Further, the state shown in FIG. 2 can be achieved by turning off the switch S3, turning on S,, S2, and bringing the switch S4 into contact with the contact bK and the switch Sst'' with the contact a.

Therefore, CO2 can be measured in this state.

These Cot and Co2h are stored in the controller 3 at the time of shipment.At the time of shipment, CT+ and cT2 are Co1-CT1. Co
Since it is 2-CTz, the calculation for calibration is to divide the measured value by 1.

When time passes and a change occurs in R2, the user's AT, , AT2 and cT, , cT
2 and store it in the controller 3. Using this stored value, calculate CTI/Cot and CT2/CO2.

By dividing the measured value by the calculation result, it is possible to display the measured value on the display 5 with the time-dependent change of R, R2 removed.

In the case of the resistance-voltage converter shown in FIG. 9, switch S8 is turned on, S is turned off, switch Sl is turned on, S2, S3
, switch S5 is brought into contact with contact bK, and switch S5 is turned off.
By bringing 7 into contact with contact a, the state shown in FIG. 4 can be achieved. In this state, measure the external standard resistor Rx to find the AOI. This Ao+Vi is stored in the controller 3 at the time of shipment.

Next, switch S8 is turned off, and switch S1 is turned off.

The state shown in FIG. 5 can be achieved by turning on S3, turning off S2, bringing switch S5 into contact, bringing switch S6 into contact with contact a, and bringing switch S7 into contact with contact . In this state, the switch S9 is turned on and off to obtain Co1 from which the offset voltage has been removed, and this is stored in the controller 3 at the time of shipment. In this way, COI at the time of shipment,
CO2 is measured and stored in the controller 3. Calibration work is carried out based on the passage of time after shipment. Through this calibration work, CT1
1 Measure cT2, CT+/Co1 and CT2/CO
2, and the reciprocal of this calculated value is the total measured value AT+, A
By multiplying by 'r2, it is possible to display the correct resistance value that eliminates the change over time of the resistors R1 and R2.

The state of control in the controller 3 is shown in a flowchart in FIG.

In step (2), it is determined whether external calibration is required. In the case of external calibration, the process branches to external calibration routine L.

In the external calibration routine L, in step ■, switch to the state shown in Figure 3 or the state shown in Figures 4 and 6, and set A, 01°AC+2.
seek. In step (2), find co, l 002 and store them.

When the external calibration is completed, it is determined in step (2) whether or not the mode for calibrating changes over time is selected. When the mode is to calibrate changes over time, the process branches to routine L2.

In routine L2, calculate cT, , CT2 in step ■,
Step ■Co+/CT+also Fi”02 ・Cot/
CT2 ' Performs CT+ calculation and stores the calculation result.

If it is determined that it is the measurement mode in step ■, step 2 calculates the measured value AT1 and AT2, and calculates the measured value ATI,
The value X calibrated by calculation in step ■ to ATz
,, find X2. The calibrated value X1 in step ■
is displayed on the Xzk display 5.

"Effects of the Invention" As described above, according to the present invention, high resistance can be calibrated using the reference resistor Rr having a low resistance value. As a result, the reference resistor RrO value can be maintained at its initial value with good stability, and high accuracy can be maintained over a long period of time.

"Modified Embodiment" FIG. 13 shows a modified embodiment of the present invention. In this example, by switching to switches 84, Ss, and 86, the 14th
Switch to the state shown in Fig. 15 and resistors R1 and R2.
This shows the case where the change over time is calibrated.

In the above description, the current-voltage converter and the resistance-voltage converter are shown separately, but in practice, the operational amplifier 1 is shared by both by switching a switch, and is configured as an integrated measuring device.

[Brief explanation of the drawing]

1 to 7 are connection diagrams for explaining the present invention in detail, FIGS. 8 and 9 are connection diagrams for explaining the invention in detail, and FIG. 10 is the connection diagram for explaining the invention in detail. A flowchart for explaining the operation of the embodiment shown in the figure, FIGS. 11 and 12 are connection diagrams for explaining the conventional measuring device,
FIGS. 13 to 15 are connection diagrams for explaining modified embodiments of the present invention. 1: operational amplifier, 2: common potential point, 3: controller. 4: AD converter, 5: Display, J, R, 2: High resistor for range switching, Rr two reference resistors, Vr: Reference voltage source. Patent applicant Kugagu Riken Kogyo Co., Ltd. Agent
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Claims (1)

[Claims] (1) It has a reference resistor with a relatively small resistance value and a highly stable reference voltage source, and uses this reference resistor and reference voltage source to calibrate the first range switching resistor. The above first range switching resistor and reference voltage source are used.
A measuring device characterized in that it calibrates a second range switching resistor whose resistance value is larger than that of the range switching resistor.