JPH04370769A - Correction method of voltage and current signal by using a/d converter - Google Patents

Abstract

PURPOSE:To enable highly accurate correction by determining errors of a circuit beforehand based on a reference signal with limited errors to correct an input signal by a correction value determined from an approximate curve of errors. CONSTITUTION:A voltage signal V and a current signal I as reference with limited errors are inputted 1 and 2 to be converted 3 and 4 into voltages with specified levels suited to a circuit voltage and undergo an A/D conversion 7 through a multiplexer 5 to measure and store 9 a voltage value containing error component of a circuit with a CPU8A. Then, the CPU8A subtracts a true value programmed previously for an input signal to be forecast from measured values to determine errors. A specified approximate curve is calculated from the errors and an average error per section is obtained from the approximate curve with respect to an input signal to be a correction value. Then, signals with undefined errors are inputted 1 and 2, the CPU8A judges which section the value corresponds to. Thus, the correction value of the section involved is read out to be added to the value of the input signal or subtracted therefrom thereby outputting the signal corrected outside.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for correcting voltage and current signals using an A/D converter, and in particular, a method for correcting voltage and current signals of a measuring instrument or a measuring instrument.
The present invention relates to a method of correcting voltage/current signals using an A/D converter.

0002

2. Description of the Related Art FIG. 3 is a block diagram showing a circuit to which a conventional voltage/current signal correction method using an A/D converter is applied. In the figure, 1 is an input terminal to which a voltage signal V is applied, 2 is an input terminal to which a current signal I is applied, and 3 is an input terminal to which the input voltage signal V is adjusted to a predetermined level voltage VV that is compatible with a predetermined circuit voltage. 4 is a current-to-voltage converter that converts the input current signal I into a current of a predetermined level and then converts it into a voltage VI suitable for a predetermined circuit voltage;
5 has switches 5a and 5b, and switches between voltages VV and VI to output a reference voltage V as a correction signal from the correction circuit 6.
A multiplexer, 8, which supplies R to the A/D converter 7;
is a central processing unit (
CPU).

Next, the operation of the circuit to which the conventional voltage/current signal correction method using the A/D converter shown in FIG. 3 is applied will be described. When correcting the voltage signal V applied to the input terminal 1, both switches 5a and 5b are connected to the contact a side, and the voltage VV converted by the voltage converter 3 is
is applied to the A/D converter 7 together with the reference voltage VR from the correction circuit 6.
supplied to The reference voltage VR can be manually varied based on the output of the A/D converter 7, and is set to a value that minimizes the error in the amount of change from the minimum value to the maximum value of the input signal. It is set. The A/D converter 7 converts the input voltage VV and reference voltage VR from analog signals to digital signals, and supplies the digital signals to the CPU 8. CPU8
A pre-programmed true value V1 is set for the predicted voltage signal V, and the CPU 8 determines that if the voltage VV from the A/D converter 7 is higher than the true value V1, the voltage V
A corrected value is obtained by subtracting the reference voltage VR from the A/D converter 7 from V. Conversely, if the voltage VV from the A/D converter 7 is lower than the true value V1, the Then, the reference voltage VR from the A/D converter 7 is added to obtain a corrected value. Further, when correcting the current signal I applied to the input terminal 1, both switches 5a and 5b are connected to the contact b side, and the voltage VI converted by the current-voltage converter 4 is output from the correction circuit 6. It is supplied to the A/D converter 7 together with the reference voltage VR. The A/D converter 7 receives the input voltage VI and the reference voltage V.
Convert R from analog signal to digital signal, CPU8
supply to. A true value V2 programmed in advance for the predicted current signal I is set in the CPU 8, and the CPU 8 has a true value V2 programmed in advance for the predicted current signal I.
If the voltage VI from the A/D converter 7 is higher than the true value V2, U8 subtracts the reference voltage VR from the A/D converter 7 from the voltage VI to obtain a corrected value, and vice versa. True value V1
On the other hand, if the voltage VI from the A/D converter 7 is low, the reference voltage VR from the A/D converter 7 is added to the voltage VI to obtain a corrected value. 4 and 5 are reference voltage V
This shows the voltage relationship when R is a voltage in the direction of subtraction from voltages VV and VI, and ΔVV, ΔV
I is a voltage value after each correction.

0004

[Problems to be Solved by the Invention] As described above, the conventional method of correcting voltage and current signals using an A/D converter is to simply add or subtract a constant reference voltage to reduce errors. Therefore, as can be seen from FIGS. 4 and 5, the error can only be kept within a certain range, and the error is not necessarily constant with respect to the true value, making it impossible to perform accurate correction. This invention was made in order to solve the above-mentioned problems, and it is possible to perform highly accurate correction.
The purpose of this invention is to obtain a method for correcting voltage and current signals using a /D converter.

[0005]

[Means for Solving the Problems] A voltage/current signal correction method using an A/D converter according to the present invention measures a reference signal and calculates the error at each point from a predetermined true value of the measured value. calculating an approximate curve from the error at each point, and calculating a correction value for each interval for the input signal from the approximate curve; and determining which of the above intervals the input signal corresponds to. a step of selecting the correction value for the corresponding section; and a step of subtracting or adding the correction value to the input signal depending on whether the value of the input signal is higher or lower than the predetermined true value. This includes:

[0006]

[Operation] In the present invention, the circuit error is determined in advance based on a reference signal with a small error. After obtaining this error by changing the magnitude of the reference signal at several points, an approximate curve of the error is calculated. The sections are determined in advance, and the average value for each section is determined from the approximate curve, and this is used as the correction value. Then, when the value of the input signal is higher than a predetermined true value, the correction value is subtracted from the input signal, and when it is lower, the correction value is added to the input signal to obtain a corrected signal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing an embodiment of the present invention, and FIG. 2 is a block diagram of a circuit to which the present invention is applied. In FIG. 2, 1 to 4 and 7 are the same as described above. In FIG. 2, 5A is a multiplexer that switches each voltage from the voltage converter 3 and the current-voltage converter 4 and supplies it to the A/D converter 7, and 8A is a multiplexer that switches the voltages from the voltage converter 3 and the current-voltage converter 4 and supplies them to the A/D converter 7. a central processing unit (CPU) that performs arithmetic processing, 9
is a memory using, for example, RAM or E2PROM, which stores errors, correction values, etc. determined by the CPU 8A.

Next, the operation of an embodiment of the present invention will be explained. First, preparation for correction will be explained with reference to FIGS. 1(a) and 2. In step 1, a reference voltage signal V and a reference current signal I are applied to input terminals 1 and 2, respectively. This reference voltage signal V
and the current signal I are made to be as error-free as possible. In step 12, the voltage signal V is converted by the voltage converter 3 into a voltage at a predetermined level suitable for the circuit voltage, and is supplied to the A/D converter 7 via the multiplexer 5A to provide the A/D converter 7.
The signal is converted into D and further supplied to the CPU 8A for measurement, and the measured value is temporarily stored in the memory 9. Similarly, the current signal I is converted by the current-voltage converter 4 to a voltage at a predetermined level suitable for the circuit voltage, and is supplied to the A/D converter 7 via the multiplexer 5A for A/D conversion. , is further supplied to the CPU 8A and measured, and the measured value is temporarily stored in the memory 9. For example, set the reference voltage signal to 3 points from 0 to 15V (for example, 0V
, 7V, 15V), each (0+E0
)V, (7+E7)V, (15+E15)V are CPU8
A and stored in the memory 9. Here, E0,
E7 and E15 are errors mainly determined by the circuits before the A/D converter 7 when each reference voltage signal is applied. In step 13, the CPU 8A reads out each measurement value stored in the memory 9, and sets the true value (for example, 0V, 7V, 15V) programmed in advance for the input signal predicted from each measurement value. Each error is determined by subtraction, and in step 14, each error is stored in the memory 9. That is, in step 13, the CPU
8A reads out the measured value (0+E0)V from, for example, the memory 9, subtracts the true value 0V from it to obtain its error E0, and stores this error E0 in the memory 9 in step 14. The same applies to other measured values. In step 15, the CPU 8A reads each error stored in the memory 9, performs approximation using an n-th order curve from these errors, and calculates a predetermined approximate curve. In step 16, the CPU 8A determines a correction value for each section for the input signal from the calculated approximate curve. That is, CPU8A
Since the error for each section can be found from the approximate curve, for example, assuming 4 sections, 0 to 3V, 4 to 7V, 8 to 11
V, 12 to 15 V, calculate the average error for each of these sections, and use this as the correction value. In step 17,
The CPU 8A stores the determined correction value for each section in the memory 9, and completes the preparation for correction.

Next, the operation during actual correction will be explained with reference to FIGS. 1(b) and 2. In step 21, an input signal with an undefined error is input to the A/D from input terminal 1 or 2.
When inputted via the converter 7 or the like, the CPU 8A determines in step 22 which of the sections the value of the input signal corresponds to, and in step 23 stores the correction value of the corresponding section in the memory 9. Read more, step 24
Depending on whether the value of the input signal is higher or lower than the predetermined true value, the correction value of the corresponding section is subtracted or added to the value of the input signal to obtain a corrected value. That is,
In step 24, the CPU 8A subtracts the correction value of the corresponding section from the value of the input signal if the value of the input signal is higher than the true value, and if it is lower than the true value, adds the correction value of the section corresponding to the value of the input signal to obtain the desired value. Obtain the corrected signal. and,
In step 25, the desired corrected signal is output to the outside.

0010

[Effects of the Invention] As described above, according to the present invention, there are the steps of measuring a reference signal, calculating the error at each point from a predetermined true value of the measured value, and calculating an approximate curve from the error at each point. , a step of determining a correction value for each section of the input signal from the approximate curve, and a step of determining which of the above-mentioned sections the input signal corresponds to and selecting the above-mentioned correction value for the corresponding section. , subtracting or adding the correction value to the input signal depending on whether the value of the input signal is higher or lower than the predetermined true value, and performing the correction for each section of the input signal. Therefore, it is possible to obtain highly accurate voltage and current signals over a wide range as if they were being continuously corrected, and the effect is that the accuracy can be improved as the resolution of the A/D converter increases. be.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a circuit to which the present invention is applied.

FIG. 3 is a configuration diagram showing a circuit to which a conventional voltage/current signal correction method using an A/D converter is applied.

FIG. 4 is a diagram for explaining the operation of FIG. 3;

FIG. 5 is a diagram for explaining the operation of FIG. 3;

[Explanation of symbols]

3 Voltage converter 4 Current-voltage converter 5A Multiplexer 7 A/D converter 8A Central processing unit (CPU) 9. Memory

Claims (1)

[Claims] Claim 1: A step of measuring a reference signal, calculating an error at each point from the measured value to a predetermined true value, calculating an approximate curve from the error at each point, and calculating an approximate curve from the approximate curve to the input signal. a step of obtaining a correction value for each section; a step of determining which of the above-mentioned sections the input signal corresponds to; and a step of selecting the above-mentioned correction value for the corresponding section; A method for correcting a voltage/current signal using an A/D converter, comprising the step of subtracting or adding the correction value to the input signal depending on whether the input signal is higher or lower than the true value.