JPH0613899A - Input correcting method for analog/digital converter - Google Patents

Abstract

PURPOSE:To provide an input correction method for an A/D converter with which correction is facilitated with high performance by preparing a correction relation based on the input data value of the A/D converter and the reference value of input data. CONSTITUTION:At the time of correction, a microcomputer supplies an instruction through an interface 19 to a reference value generator 9 and supplies several values to be inputted to an analog input channel 11. The imparted values pass through an operation amplifier part 12, are converted to digital data at the A/D converter 7 and are inputted to the microcomputer 15. The microcomputer 15 stores the value generated by the reference value generator 9 and the digital data at a memory device 16. When measurement at all scheduled points is completed, the microcomputer 15 forms functions to be corrected based on the data stored in the memory device 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input calibration method for an analog / digital converter.

[0002]

2. Description of the Related Art Some devices require calibration of an analog input portion when converting an analog amount into an appropriate digital amount. Generally, in the case of converting an analog amount into a digital amount, analog input data is arithmetically amplified in a desired form by an operational amplifier and input to an analog / digital converter (A / D converter). This operational amplifier requires calibration work using a variable resistor (offset adjustment, span adjustment, etc.).

FIG. 5 shows an example of a conventional input calibration method for an A / D converter, which is an example of a current / voltage conversion circuit composed of operational amplifiers 3, 4, and 6.

According to the calibration method of FIG. 5, the current flowing through the analog input channel 1 is converted into current / voltage by the span adjusting variable resistor 2. The span adjustment variable resistor 2 also serves as the adjustment of the current / voltage conversion rate (span adjustment). The current / voltage converted analog data is passed through the buffer amplifiers of the operational amplifiers 3 and 4 to the operational amplifier 6
Is amplified by and output to the A / D converter 7. The offset adjustment variable resistor 5 performs adjustment so that the voltage at the input terminal 8 of the A / D converter 7 becomes 0 when the current flowing through the analog input channel 1 is 0.

FIG. 6 shows the relationship between the current flowing in the analog input channel 1 of the circuit of FIG. 5 and the voltage output to the input terminal 8 of the A / D converter 7. In FIG. 6, a straight line C indicates a case where the span adjustment and the offset adjustment are in the ideal state. The straight line A shows the case where the offset adjustment is good but the span adjustment is bad (the span amount is large).
Shows the case where the offset adjustment is good but the span adjustment is bad (the offset amount is small), and the straight line B shows the case where the span adjustment is good but the offset adjustment is bad (the offset amount is large).
The straight line D shows the case where the span adjustment is good but the offset adjustment is bad (the offset amount is small).

[0006]

In a device having many analog input channels, since there are many calibration points, there have been problems such as complicated calibration work and deterioration of calibration quality. Further, since it is necessary to dispose the variable resistor at a position where calibration is easy, there are restrictions in designing the printed board and modularizing it.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an input calibration method for an A / D converter which solves the above problems and has a high performance and is easy to calibrate. is there.

[0008]

In order to achieve the above-mentioned object, the present invention provides an input data value of an A / D converter and the A / D converter.
A correction function is created based on the reference value of the input data of the D converter, and the input data of the A / D converter is calibrated based on the correction function.

[0009]

The variable resistors for span adjustment and offset adjustment need to be changed to fixed resistors. However, if fixed resistors are used, it becomes impossible to deal with offset and span deviations. However, if the offset and the shift of the span can be grasped, the data after the A / D converter can be corrected by the microcomputer.

[0010]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a system configuration diagram for automatically calibrating an analog input. In FIG. 1, 9 is a reference value generator, 10 is a switch, 11 is an analog input channel, 12 is an operational amplifier, and 13 is A fixed resistor for offset adjustment, and a fixed resistor 14 for span adjustment. 15 is A
A microcomputer that is an arithmetic processing unit (CPU) that receives digital data from the / D converter 7, 16 is a memory device, 17 is an output device, 18 is an input device such as a keyboard, and 19 is an interface.

In the system of FIG. 1, the reference value generator 9
Is used only at the time of calibration and is usually a device that processes analog data input to the analog input channel 11 with a system configuration excluding the reference value generator 9.
When calibrating this device, the reference value generator 9 is connected to the analog input channel 11, and the microcomputer 15 and the reference value generator 9 are connected by the interface 19. After the connection is completed, calibration is performed by giving an instruction from the input device 17 to execute automatic calibration.

For the calibration, the microcomputer 15 gives an instruction to the reference value generator 9 through the interface 19 and gives a value to be inputted to the analog input channel 11 at several points in the range from O to D in FIG. The given value passes through the operational amplifier 12 and is converted into digital data by the A / D converter 7 and input to the microcomputer 15. The microcomputer 15 stores the value generated by the reference value generator 9 and the digital data in the memory device 16. When the measurement at all the scheduled points is completed, the microcomputer 15 creates a correction function based on the data stored in the memory device 16.

It is necessary to change the variable resistors for span adjustment and offset adjustment to fixed resistors, but if fixed resistors are used, it becomes impossible to deal with offset or span deviation. However, if the offset and the shift of the span can be grasped, the data after the A / D converter can be corrected by the microcomputer.

FIG. 2 is a flowchart showing the operation of the microcomputer 15 in the system of FIG. 1. First, automatic calibration is performed in step S1 and a reference value is generated via the interface 19 in step S2. Step S
The value from the A / D converter 7 is read in step 3, and step S4
Proceed to. In step S4, the value indicated by the A / D converter 7 and the reference value are stored in the memory device 16. Then step S5
Then, it is determined whether all the reference values have been generated. If all the reference values have been generated, the process proceeds to step S6 and the correction function is obtained. If all the correction functions have not been generated, the operations of steps S2 to S4 are repeated.

When the correction function is obtained in step S6, the process proceeds to step S7, and it is determined whether the correction amount is larger than a specified value. If the correction amount is not larger than the specified value, the process proceeds to step S8 and the correction function is stored in the memory device 16. If the correction amount is larger than the specified value in step S7, the process proceeds to step S10 and it is determined that the correction is impossible. In this case, the offset resistance 13 and the span resistance 14 are selected to have optimum resistance values.

The correction function in the above operation flow is created and an example of correction is executed as shown in FIG. Figure 4
In, the straight line L1 shows the correction target (y ′ = αx + β), and the curve L2 shows the actual measurement value (A / D converter output when the reference values x ₀ to x ₈ are input). The correction target value of L1 can be set freely, and the actually measured value of L2 is stored in the memory device 16. The correction is performed for each section, and the correction function is also prepared for each section.

The section on the y-axis is y _n -y _{n + 1} (n = 0, 1,
2, 3, ...). The correction function in the interval from y _{n to} y _{n + 1} is
'When the = αx + β, y' corrected target y = α · {[(y -y n) · (x n + 1 -y n) / (y n + 1 -y n)] + x n} + β ... (1) However, y _n <y <y _{n + 1} and y ≠ y ₀ .

As an example, when point A in FIG. 4 is corrected to point A ', point A is the output value of the A / D converter 7 and y = 14, y.
_{5 to} y ₆ are sections including point A, y ₅ = 12, y ₆ = 16
And x _{5 to} x ₆ are values on the x axis corresponding to the y axis, and x ₅
= 15, x ₆ = 18, point A ′ is the corrected value of point A, and y ′ = A ′. In this case, y ′ = αx + β is a function of the correction target, and if α = 0.5 and β = 0, then y ₅ ~
The correction function in the interval of y ₆ is y ′ = α · {[(y−y ₅ ) · (x ₆ −x ₅ ) / (y ₆ −y ₅ )] + β (2), and the above values , Y ′ = {0.5 × [(14-12) × (18-15) / (16-12)] + 1 5} + 0 = 0.5 × [(6/4) × 15] = 8.25 = A '... (3) Therefore, the corrected value of A point = 14 is A ′ point = 8.
25.

[0020]

The present invention is as described above, and since the calibration is automatically performed, even in an apparatus having a large number of calibration points, the calibration work can be performed only by connecting the reference value generator. Can be shortened.

Further, since the knowledge about the calibration work is not required, the training of the calibration staff is also unnecessary. Further, since the variable resistor for calibration can be omitted, it is easy to downsize and modularize the equipment, and at the time of maintenance, it is only necessary to connect the reference generator and maintenance is easy.

[Brief description of drawings]

FIG. 1 is a system diagram for performing an input calibration method for an analog / digital converter according to an embodiment of the present invention.

2 is an operation flowchart of the system of FIG.

FIG. 3 is an input / output characteristic diagram of an A / D converter.

FIG. 4 is a calibration characteristic diagram of input data and output data of the A / D converter.

FIG. 5 is a circuit diagram of a system showing an input calibration method for a conventional A / D converter.

FIG. 6 is a characteristic diagram of the system of FIG.

[Explanation of symbols]

7 ... A / D converter, 9 ... Reference value generator, 10 ... Switch, 11 ... Analog input channel, 12 ... Operation amplification part, 13 ... Fixed resistor for offset, 14 ... Fixed resistor for span adjustment, 15 ... Microcomputer , 16 ... Memory device, 17 ... Output device, 18 ... Input / output device, 19 ... Interface.

Claims (1)

[Claims] 1. An input data value of an A / D converter and the A / D
Create a correction function based on the reference value of the input data of the converter,
An input calibration method for an analog / digital converter, characterized in that the input data of the A / D converter is calibrated based on the correction function.