JPH0599961A - Measurement device - Google Patents

Abstract

PURPOSE:To automatically correct the offset value or a measurement device. CONSTITUTION:Provided in a measurement device including a constant current circuit 2 to supply a constant current I to a measured body 1 and a measurement circuit 3 to calculate a measurement value of the measured body 1 using the voltage generated in the measured body 1 by the constant current i, are a second basic voltage generation circuit 13 generating a second basic voltage much, lower than the source voltage of the constant current circuit 2 and a comparator 14 to compare the terminal voltage of the constant current circuit 2 and the second basic voltage and detect the open state of the constant current i. Also provided are a switch circuit 16 to short-circuit the input of an amplifier 15 in the measurement circuit 3 or enable the input to connect with the measured body 1 and a CPU 17 to switch the above switch circuit 16 following the detection signal from the comparator 14, obtain the offset value of the measurement circuit 3 in the case the constant current i is in open state, update and store the previous offset value, measure the above measured body 1 in the case the current i is not in open state, correct the measured value using the offset value and obtain the true value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device which is used in a measuring device such as an ohmmeter and which automatically corrects an offset temperature drift of a measuring circuit according to a change in ambient temperature.

[0002]

2. Description of the Related Art Conventionally, a measuring apparatus of this type has, for example, the configuration shown in FIG. The measuring circuit 3 detects the voltage (Vx) generated in the device under test 1 by the supply of i and calculates the resistance value of the device under test 1.

The constant current circuit 2 uses a reference voltage generator 4 for generating a reference voltage, and a constant current i for generating the reference voltage.
Amplifier 5 for converting to and supplying it to the device under test 1
And npn-type transistor 6, and a reference resistance (Rref) 7 for determining the value of the constant current i supplied to the device under test 1.
It consists of and.

Further, the constant current i flows through the device under test 1 and the reference resistor 7, but the voltage generated in the reference resistor 7 is fed back to the amplifier 5 so that the constant current i becomes constant. The constant current circuit 2 operates.

The measuring circuit 3 detects the voltage (Vx) generated in the device under test 1 by the constant current i and adjusts the gain, and the A / D for digitally converting the detected voltage. The conversion unit 9 and C for calculating the resistance value of the DUT 1 based on the digitally converted DUT data.
And PU10.

Further, the amplifier 8 is provided with a variable volume 8a for adjusting the offset, and the input of the amplifier 8 is set to the state of "0" (short-circuited), and the variable volume 8a is adjusted to adjust the above. The offset error of the amplifier 8 can be adjusted.

The measuring device uses the CPU 10 for displaying the measurement result and the like by the CPU 10 and the measuring range switching instruction (reference resistance switching instruction).
A key portion 12 for outputting to 10 can be provided, various resistances can be measured, and this measurement result can be displayed.

[0008]

In the measuring device, the offset temperature drift (offset amount) of the amplifier 8 can be adjusted by changing the variable volume 8a. The input has to be short-circuited and adjustments have to be made, which is not only annoying but also unfavorable to the user.

Further, if the ambient temperature of the measuring device changes, an error occurs due to the offset amount of the A / D conversion section 9 as well as the amplifier 8 when measuring the object to be measured.

The present invention has been made in view of the above problems, and an object thereof is to be able to automatically correct an offset temperature drift according to a change in ambient temperature and obtain an accurate measured value of an object to be measured. Therefore, it is an object of the present invention to provide a measuring device capable of improving the measurement accuracy.

[0011]

In order to achieve the above-mentioned object, the measuring apparatus of the present invention generates a constant current circuit for supplying a constant current to an object to be measured, and an identifying current to generate the same in the object to be measured. A measurement circuit that calculates the measured value of the DUT by voltage, and to detect whether or not the DUT is connected to the measurement terminal, the terminal voltage of the constant current circuit and the power supply voltage of the identification current circuit are used. It is provided with a comparator for comparing with a slightly lower reference voltage and a switch circuit for short-circuiting the input of the measuring circuit or for inputting the voltage generated in the device under test, and the CPU of the measuring circuit described above. The switch circuit is controlled according to the comparison result of the comparator, and when it is determined that the DUT is not connected to the measurement terminal, the input of the measurement circuit is short-circuited to obtain the offset temperature drift of the measurement circuit. The offset temperature drift obtained last time is updated and stored, and when the DUT is connected to the measurement terminal, the offset temperature drift is subtracted by the voltage generated in the DUT, and the measured value of the DUT is subtracted. The point is to get

[0012]

With the above configuration, when the device under test is not connected to the measuring device, that is, when the constant current is in the open state, the terminal voltage of the constant current circuit becomes equal to or higher than the reference voltage, and Outputs a detection signal indicating that the constant current is in the open state.

Then, in the CPU of the measuring circuit, the switch circuit is operated by the detection signal,
The input of the input stage circuit (amplifier) of the measuring circuit is short-circuited. In this state, the same offset temperature drift is obtained by the output data of the A / D conversion unit of the measurement circuit, that is, the output data of the amplifier and the A / D conversion unit. For example, the previously obtained offset temperature drift is updated and stored.

When the device under test is connected to the measuring device, that is, when the constant current is not in the open state, the terminal voltage of the constant current circuit falls below the reference value,
The comparator outputs a detection that the constant current is not in the open state.

Then, in the CPU, the normal measurement operation is performed and the measured value of the measured object is calculated, but the offset temperature drift already stored is subtracted from this measured value, and this subtraction is performed. The measured value is used as the measured value of the measured object.

The offset temperature drift of the measuring circuit is updated and stored every time the device under test is replaced.
Since the offset temperature drift is canceled each time the measurement object is measured, an error due to the offset temperature drift does not occur even if the ambient temperature changes.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figure, the same parts as those in FIG.

In FIG. 1, this measuring apparatus is provided with a second reference voltage generator 13 for generating a second reference voltage, a terminal voltage (V0) of the constant current circuit 2 and its second reference value. By comparison, a comparator 14 that outputs a detection signal indicating whether or not the constant current i is in an open state, that is, whether or not the device under test 1 is connected, and the constant current i is generated in the device under test 1 by the constant current i. An amplifier 15 that detects the voltage (Vx) and adjusts the gain, a switch circuit (relay circuit) 16 that short-circuits the input of the amplifier 15 when the constant current i is open, and other functions of the CPU 10 shown in FIG. In addition, the switch circuit 16 is controlled by the detection signal from the comparator 14, and the offset temperature drift value (offset amount) of the amplifier 15 and the A / D converter 9 is calculated when the constant current i is open. Updating the offset amount of the previously calculated, stored, and a CPU17 calculating true measure by subtracting the already offset amount which stores the measured values of the measuring body 1 (for example, resistance).

The second reference voltage generated by the second reference voltage generator 13 is set to be slightly lower than the power supply voltage (V) of the measuring circuit 3.

The operation of the measuring apparatus having the above configuration will be described with reference to the flow chart of FIG. 2. First, when the DUT 1 is not connected to the measuring apparatus, the constant voltage circuit 2 is used.
The terminal voltage (V0) becomes close to the power supply voltage (V) and becomes higher than the second reference value.

Then, the comparator 14 outputs a detection signal indicating that the constant current i is in the open state. As a result, the CPU 17 determines that the constant current i is in the open state (step ST1), and the switch circuit 1
6 is switched to the B terminal side, and the input of the amplifier 15 is short-circuited, that is, the state of the input "0".

In this state, the output voltage of the amplifier 15 is converted into a digital value by the A / D converter 9, and this digital value is taken into the CPU 17, so that the offset of the amplifier 15 and the A / D converter 9 is offset. The amount is calculated (step ST3).

The measured offset amount is stored in the internal memory of the CPU 17 (step ST4), and the previously stored offset amount is updated with the offset amount measured this time, for example. When the measurement of the offset temperature drift is completed, the switch circuit 16 is switched to the A terminal side (step ST5).

Subsequently, when the device under test 1 is not yet connected to the measuring device (step ST1), the steps are repeated, so that, for example, when the ambient temperature changes, the measuring circuit 3 Since the offset amount is calculated and the previously stored offset amount is updated, for example, the above steps are repeated every predetermined time until the DUT 1 is connected to the measurement device, and at each predetermined time. The offset amount is updated and stored.

That is, when the ambient temperature of the measuring device is fluctuating, the offset amount of the measuring circuit 3 is automatically corrected.

Subsequently, when the device under test 1 is connected to the measuring device, that is, when the constant current i is not in the open state, the terminal voltage (V0) of the constant current circuit 2 is higher than the second reference voltage. It becomes low, and the constant current i
A detection signal indicating that is not open is output.

As a result, the CPU 17 causes the constant current i
Is determined not to be in the open state (step ST1),
The process proceeds from step ST1 to step ST6. In this case, since the switch circuit 16 is switched to the B terminal side only when the offset amount is calculated and is always switched to the A terminal side when the measurement of the offset amount is completed, the switch circuit 16 is switched. I can't.

Subsequently, when the constant current i is supplied to the device under test 1, a voltage (Vx) is generated in the device under test 1, and this voltage (Vx) is input to the measuring circuit 3. Then, the normal measurement operation is performed, and the voltage (Vx) is A
The digital value is converted into a digital value by the / D conversion unit 9 and taken into the CPU 17, and the measurement value of the DUT 1 is calculated. At this time, the previously stored offset amount is canceled from the measured value of the measured object 1, and the true measured value of the measured object 1 is obtained (step ST7).

The A / D converted digital value of the offset amount is updated and stored, and when the measured value is calculated, for example, the digital value of the offset amount is calculated from the A / D converted digital value of the DUT 1. May be subtracted, and the true measured value may be calculated from the subtracted data.

Subsequently, the true measured value calculated above is the CPU.
It is stored in the internal memory 17 and displayed on the display unit 11 (step ST8).

By the way, immediately before the measurement of the object 1 to be measured,
Since the same offset amount is obtained, that is, the measurement of the offset amount is performed every time the device under test 1 is replaced, an error due to the offset temperature drift may occur at the time of the measured value of the device under test 1 in step ST7. Nor.

Therefore, the user can obtain an accurate measured value of the device under test 1 without requiring an operation such as an error measurement of the offset temperature drift due to the temperature change in advance.

The offset amount of the measuring circuit 3 is not automatically corrected, or the amplifier 15 of the measuring circuit 3 is not corrected.
Since it may not be possible to short the input of
The key portion 12 may be provided with a switch for automatic offset adjustment, and the offset amount may be obtained, updated, and stored only when the switch is operated.

[0034]

As described above, according to the present invention, in the measuring device provided with the constant current circuit for supplying the constant current to the object to be measured and the measuring circuit for obtaining the measured value of the object to be measured, From the detecting means, a detecting means for detecting whether or not the constant current is in an open state, a switching means for short-circuiting an input of an input stage (amplifier) of the measuring circuit, or a device to be measured can be connected, When the constant current is in the open state, the switching means is switched by the detection signal of the offset temperature drift (offset amount) of the measuring circuit.
And the offset amount obtained last time is updated and stored, and when the constant current is not in the open state, the measured value of the measured object is calculated, and the measured value is corrected by the offset amount. Therefore, the offset amount is automatically obtained immediately before the measurement of the object to be measured, that is, the offset amount can be automatically corrected, and even when the ambient temperature changes, when measuring the object to be measured, An accurate measurement result of the object to be measured can be obtained without causing an error due to the offset temperature drift of the measurement circuit, and without the user's trouble, and thus the measurement accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a measuring apparatus showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the measuring device shown in FIG.

FIG. 3 is a schematic block diagram of a conventional measuring device.

[Explanation of symbols]

 1 device under test (Rx) 2 constant current circuit 3 measurement circuit 4 first reference voltage generation circuit 5, 15 amplifier 6 npn type transistor 9 A / D conversion unit 11 display unit 12 key unit 13 second reference voltage generation unit 14 comparator 16 switch circuit (relay circuit) 17 CPU (control means)

Claims (2)

[Claims] 1. A measuring device including a constant current circuit for supplying a constant current to an object to be measured, and a measuring circuit for calculating a measured value of the object to be measured by a voltage generated in the object to be measured by an identification current. In, a detection unit that detects whether the DUT is connected to a measurement terminal, and a switching unit that short-circuits the input of the measurement circuit, or allows the voltage generated in the DUT to be input. The switching means is controlled by the detection signal from the detection means, and when the DUT is not connected to the measurement terminal, the input of the measurement circuit is short-circuited to obtain the offset temperature drift of the measurement circuit and the previous time. The offset temperature drift is updated and stored, and when the measured object is connected to the measurement terminal, the offset temperature drift amount is calculated from the measured value by the voltage generated in the measured object. And a control means for subtracting the measured value of the object to be measured. 2. The reference voltage generation circuit, wherein the detection means generates a reference voltage lower than a power supply voltage of the constant current circuit,
It is composed of a comparator for comparing the terminal voltage of the identification current circuit and the reference voltage, and outputs the comparison result by the comparator to the control means, the control means depending on the comparison result from the comparator. The measuring apparatus according to claim 1, wherein an offset temperature drift of the measuring circuit is obtained at predetermined time intervals when it is determined that the device under test is not connected to the measuring terminal.