JP2001091552A - Method for correcting phase difference in circuit element measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a phase difference during synchronization and rectification in a device for measuring circuit element constant such as a digital LCR meter. SOLUTION: A reference sample whose phase is well-known is measured to obtain a phase difference θREF producing in a detection circuit, etc., and when a detected waveform is synchronized and rectified, a fundamental wave whose phase is displaced by phase difference θREF is applied to a current waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a phase error in a circuit element measuring instrument, and more particularly, to a method for correcting a phase error when extracting 0-degree and 90-degree components of a voltage waveform and a current waveform by synchronous rectification. It is about the method.

[0002]

2. Description of the Related Art A circuit element measuring device (for example, a digital L
In a CR meter), while a measurement voltage is applied to an object to be measured, a voltage appearing between terminals of the object to be measured and a current flowing therethrough are detected by a detection circuit, and digitally processed by an A / D converter. Various circuit constants are obtained by control means such as a CPU.

By the way, since the detection circuit is provided with a filter or the like, when detecting a voltage or a current, an error peculiar to the circuit (equipment) occurs in the phase information of the voltage or the current depending on the characteristics of the detection circuit. There are cases. Since this phase error affects the calculation result, it needs to be corrected. The following method is generally known as a method for correcting this error.

One of them is a method of correcting by software (first conventional example). In this method, first, a reference sample whose impedance Z ₀ and phase angle θ ₀ are known is measured, and an actually measured value θ ₁ of the phase angle is obtained. Then, the difference θ ₂ (= θ ₀₎ between the known phase angle θ ₀ and the actually measured value θ ₁
−θ ₁ ) is calculated and stored in the memory.

[0005] Next, when measuring an unknown sample, its After obtaining the measured values theta phase angle is added to the measured value theta from the memory reads the phase difference theta _2. As a result, an error inherent in the detection circuit can be removed from the measured value.

As another method, there is a method of performing hardware correction (second conventional example). In this method, an adjustment circuit including, for example, a trimmer capacitor is provided in the detection circuit,
While confirming the phase information by observing the actual detected waveform with an oscilloscope, the trimmer capacitor is manually adjusted to eliminate the phase error.

[0007]

In the case of the first conventional example in which correction is performed by software, an error relating to the phase angle can be relatively easily obtained by using a sample whose phase angle is known. However, when calculating various circuit constants, the CPU must always perform a phase angle correction operation to remove the error component and then obtain the circuit constants. There were challenges.

On the other hand, according to the second conventional example using an adjustment circuit, software processing is not required, so that it can be applied to an apparatus that does not use a CPU. In this case,
It is not preferable because the trimmer or the like may be inadvertently moved due to an external factor such as vibration and the adjustment may be shifted. In addition, since the adjustment is performed manually, there is a problem in terms of reliability.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to perform a synchronous rectification process on a voltage / current detection waveform to obtain a zero-degree component and a zero-degree component. Provided is a phase error correction method for a circuit element measuring instrument that can correct a phase error based on characteristics unique to a device such as a detection circuit without imposing an extra burden on a CPU in obtaining a 90-degree component. It is in.

In order to achieve the above object, the present invention provides a measuring method for detecting a voltage between terminals of a sample (circuit element to be measured) to which a predetermined measuring voltage is applied from a measuring signal source and a current flowing through the sample. A signal detection circuit, an A / D converter for converting the voltage and current detected by the measurement signal detection circuit into digital signals at predetermined sampling intervals, and a circuit for the sample from the digitally converted voltage data and current data. A control means for calculating a constant; and a memory for storing data necessary for the calculation, a calculation result, and the like. In the phase error correction method of the circuit element measuring device for extracting the 0-degree component and the 90-degree component of the voltage waveform and the detected current waveform, respectively, at least the phase angle is already determined. Measuring the reference sample is a (theta _ST), a first step of obtaining the measured value of the phase angle (theta _M) by the control means, the known phase angle (theta _ST) and the measured value (theta _M) (Θ _ST −θ _M ) = θ _ref
And for the synchronous rectification of the detected voltage waveform, one cycle of data is extracted from the sin θ waveform and the cos θ waveform, which are the fundamental waves, at the same interval as the sampling interval, and the first data table is extracted. 3rd to create
A step, for the synchronous rectification of the detected current waveform, sin each phase of sinθ waveform and cosθ waveform is fundamental wave by shifting the phase difference theta _{r ef} fraction (theta-
_θref ) and cos (θ− _θref ), a fourth step of extracting one cycle of data at the same interval as the sampling interval and creating a second data table at the same interval as the sampling interval, is executed in advance. Thereafter, measurement is performed on the actual sample to be measured to obtain the voltage data and the current data. The fundamental wave data of the sin θ waveform and the cos θ waveform are read from the first data table, and the product sum calculation is performed with the voltage data. In addition to extracting the 0-degree component and the 90-degree component of the voltage data, sin (θ-θ _ref ) and cos (θ-θ
_ref ) is read out, and a product-sum operation is performed with the current data to calculate the 0-degree component and 90
It is characterized by extracting a degree component.

According to the present invention, it is only necessary to adjust the phase of the fundamental wave in advance in comparison with the method of calculating the phase and then correcting the phase as in the first conventional example, and it is necessary to adjust the phase in the actual measurement stage. Since there is no need to change the calculation procedure of
There is no loss of calculation time in the PU. That is, according to the present invention, the phase error can be corrected during the synchronous rectification processing. Further, unlike the second conventional example, the correction data does not change due to external vibration or the like.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention;

As schematically shown in FIG. 1, the circuit element measuring device according to this embodiment has the following main components.
Measurement signal detection circuit 1, A / D converter 2, CPU (central processing) as arithmetic processing means
(unit) 3 and a memory 4 for storing data necessary for the operation, an operation result, and the like.

The measurement signal detection circuit 1 is applied with a predetermined measurement voltage from a measurement signal source (not shown), and has a voltage between terminals of a sample (circuit element to be measured) not shown and is flowing through the sample. Detect the current.

The A / D converter 2 includes the measurement signal detection circuit 1
Converts the detected voltage and current into digital data at a predetermined sampling interval. Further, the CPU 3 executes A /
The circuit constant of the sample is calculated from the D-converted voltage data and current data.

FIG. 2 shows a voltage waveform Vv and a current waveform Vi detected from the sample by the measurement signal detection circuit 1. In this embodiment, the current waveform Vi is the voltage waveform Vv
Phase is delayed by 30 degrees.

FIG. 2 shows that the A / D converter 2 operates as follows.
The voltage waveform Vv and the current waveform Vv sampled at equal intervals of n points per cycle, in this embodiment, 12 points.
i are data points Vv (0) to Vv (1
1), Vi (0) to Vi (11).

FIG. 3 shows a sin waveform S and a cos waveform C as fundamental waves used for synchronous rectification.
By performing a product-sum operation on the fundamental wave and the detected waveform detected from the sample, a 0-degree component and a 90-degree component of the detected waveform are extracted. In the present invention, the phase information of the fundamental wave is manipulated. To correct the phase error of the detected waveform generated in the measurement signal detection circuit 1 and the like, and the procedure will be described below.

First, the phase is known (true value) θ._STIs a group
Measure the quasi sample and measure its actual value θ_MAsk for. And that
Measured value θ_MAnd true value θ_STFrom the phase error θ
_REF(= Θ _ST−θ_M) Is calculated.

Next, a first data table of a fundamental wave for synchronously rectifying the voltage waveform Vv and a second data table of a fundamental wave for synchronously rectifying the current waveform Vi are created.
These data tables are prepared in the memory 4.

The first data table contains a sin waveform S (sin θ) and a cos waveform C (cos
θ) as it is, fundamental wave data Sa (0) to S (S) sampled at equal intervals of 12 points per cycle.
a (11), Ca (0) to Ca (11) are written.

On the other hand, when creating the second data table, the phases of the sin waveform S and the cos waveform C are shifted by θ _{REF to} obtain sin (θ−θ _REF ),
cos (θ−θ _REF ). Then, the fundamental wave data Sb (0) to Sb (11), Cb sampled at equal intervals of 12 points per cycle for each of them.
Write (0) to Cb (11) in the second data table.

After the first and second data tables are prepared in this way, an actual measurement is performed on an unknown sample (measured object). The voltage waveform Vv detected from the sample is as follows. From the first data table, fundamental data Sa (0) to Sa (11), Ca (0) to
Ca (11) is read out and synchronously rectified. That is, C
The product-sum operation of the following equations (1) and (2) is executed in PU3, and the 0-degree component VVS and the 90-degree component Vvc of the voltage waveform Vv are obtained.
Is required.

[0024]

(Equation 1)

(Equation 2)

Next, as for the current waveform Vi, the fundamental wave data Sb (0) to Sb (11) and Cb (0) to Cb (1) whose phases are shifted by θ _REF from the second data table.
1) is read out and synchronously rectified. That is, the CPU 3 executes the product-sum operation of the following equations (3) and (4), and obtains the 0-degree component Vis and the 90-degree component Vic of the current waveform Vi.

[0026]

(Equation 3)

(Equation 4) In addition, in each of the above formulas (1) to (4), n is 12.

As described above, when synchronous rectification is performed, the phase error can be corrected in the synchronous rectification processing by multiplying the current waveform Vi by the fundamental wave whose phase is shifted by the phase error θ _REF .

A resistance Rx, a reactance Xx, a conductance Gx, and a susceptance Bx are obtained from the components Vvs, Vvc, Vis, and Vic of the voltage waveform Vv and the current waveform Vi according to a predetermined calculation formula. Circuit constants such as Z |, capacitance C, inductance L, and resistance R are determined.

[0029]

As described above, according to the present invention,
When a reference sample with a known phase is measured to determine a phase error θ _REF generated in a detection circuit or the like, and synchronously rectifying a detection waveform,
By applying a fundamental wave whose phase is shifted by the phase error θ _REF to the current waveform, the phase error can be corrected during the synchronous rectification process.

That is, as compared with the method in which the phase is obtained by calculation and then corrected as in the first conventional example, it is only necessary to adjust the phase of the fundamental wave in advance. Does not require any change, so there is no loss of calculation time in the CPU. Further, unlike the second conventional example, the correction data does not change due to external vibration or the like.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a circuit element measuring device to which a phase error correction method of the present invention is applied.

FIG. 2 is a waveform chart showing an example of a detection waveform.

FIG. 3 is a waveform diagram showing a fundamental wave.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement signal detection circuit 2 A / D converter 3 Operation processing means (CPU) 4 Memory

Claims (1)

[Claims] A predetermined measurement voltage is applied from a measurement signal source.
Voltage between terminals of the sample (circuit element under test)
A measurement signal detection circuit for detecting a current flowing through the sample,
The voltage and current detected by the measurement signal detection circuit are
A / D that converts to digital at a predetermined sampling interval
Converter and its digitally converted voltage data and current
Control means for calculating the circuit constant of the sample from the data
And the data necessary for the operation and the operation result are stored.
A memory, and the voltage data and the current data
Synchronous rectification, which calculates the sum of products of
The detected voltage waveform, the 0-degree component of the detected current waveform and 90
Phase error compensation of the circuit element measuring instrument to extract the degree component
In the positive method, at least the phase angle is known (θ_ST) Is measured.
And the control unit measures the actual value of the phase angle (θ_M)
And the known phase angle (θ_ST) And the measured value (θ_M) With
Difference (θ_ST−θ_M) = Θ_refSecond step for finding
And s, which is a fundamental wave, for synchronous rectification of the detection voltage waveform.
From the inθ waveform and cosθ waveform to the above sampling
One cycle of data is extracted at the same interval as the
A third step of creating a data table, and s which is a fundamental wave for synchronous rectification of the detected current waveform.
The phase of the inθ waveform and the phase of the cos θ waveform
_refLet me know sin (θ-θ_ref), Cos (θ
−θ_ref) Is the same as the sampling interval above.
At one interval, the data for one cycle is extracted and the second data
Execute the fourth step of creating a data table in advance
After that, measure the actual sample to be measured,
From the first data table, the sin θ waveform and the cos
Read each fundamental wave data of θ waveform and
Multiply and accumulate with data, 0 degree component and 90 degree of the same voltage data
Extract the components and from the second data table
sin (θ−θ _ref) And cos (θ−θ_ref)
And read the fundamental data of
And the 0-degree and 90-degree components of the current data
Phase error compensation of circuit element measuring device characterized by extracting
Right way.