JP2000278128A - Multi-channel a/d converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a noise in a commercial power supply with both 50 Hz and 60 Hz frequencies in multi-channel A/D conversion independently of the area using either of the 50 Hz or 60 Hz and to allow an A/D converter at a low cost with a comparatively long AD conversion time to be used for the multi-channel A/D conversion at less sacrifice of input response and an input value period. SOLUTION: A multiplexer 3 selects an analog signal from channels CH1, CH2 for a scanning period of 25 ms in an anomalous scanning sequence such as CH1→CH2→CH1→CH2→CH2→CH1→CH2→CH1→CH1→CH2→CH1→CH2.... Number of use of digital signals for calculating a moving mean by moving mean calculation sections 9-1, 9-2 is selected to be 4 or a multiple of 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel A which converts an analog signal from multiple channels into a digital signal and obtains an input value for each channel from the digital signal.
The present invention relates to a D conversion device.

[0002]

2. Description of the Related Art An industrial instrument using a microcomputer often converts an analog signal from multiple channels into a digital signal by an AD converter. In this case, it is conceivable that the analog signal is electrically affected by the wiring of the commercial power supply or the device depending on the installation environment. In industrial instruments, it is desirable to remove the effects of these commercial noises (50 Hz, 60 Hz) as much as possible without sacrificing product performance (input accuracy and responsiveness at the time of input fluctuation).

Therefore, conventionally, the following method has been considered as a method for removing commercial noise contained in an analog signal. [Removal method by analog filter] An analog filter is provided at the input section of the analog signal. That is, an analog signal is passed through an analog filter such as an RC filter,
Commercial noise is removed from an analog signal before being converted to a digital signal.

[Removal Method by Digital Filter] Analog signals from multiple channels are sequentially scanned at a predetermined period, the scanned analog signals are converted into digital signals, and a moving average of the latest N digital signals is provided for each channel. , The commercial noise is removed from the digital signal (input value) after AD conversion.

For example, when analog signals are input from two channels, the analog signals from these two channels are alternately scanned. Here, the commercial noise is, for example, 5
If the frequency is 0 Hz, the cycle is 20 ms, so that scanning is performed twice in the cycle, that is, in a 10 ms cycle, and the moving average of the two data is set as a digital signal (input value). Good.

[0006]

However, according to the above-described removal method using an analog filter, input responsiveness often deteriorates when it is attempted to increase the ability to remove commercial noise.

Further, according to the above-described removal method using a digital filter, it is necessary to AD-convert each channel at a period of 10 ms. Therefore, for example, in order to calculate input values of two channels, the AD conversion time is set to 5 ms or less. There is a need.

In the above-described removal method using a digital filter, it is necessary to switch the scan cycle between the case where the commercial noise is 50 Hz and the case where the commercial noise is 60 Hz. That is, when the commercial noise is 50 Hz, as described above, analog signals from two channels are alternately scanned at a period of 10 ms, and the scanned analog signals are converted into digital signals. The moving average of the digital signals may be obtained. On the other hand, when the commercial noise is 60 Hz, the period is 16.6.
ms, the analog signals from two channels are alternately scanned at a period of 8.3 ms, the scanned analog signals are converted into digital signals, and the moving average of the latest two digital signals must be obtained for each channel. Must. Therefore, it is necessary to switch the scan cycle depending on whether the frequency of the main power supply in the installation environment is 50 Hz or 60 Hz.

Further, as a method of eliminating the switching of the scan period, an integrating AD converter or a charge balanced AD converter is used.
Using a converter, the noise period (in this case, 50 Hz, 60 Hz)
This is a method in which the AD converter is continuously operated during the period of 10 Hz, which is the least common multiple of Hz = 100 ms). There is a problem.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a lower cost AD converter having a relatively long AD conversion time without significantly sacrificing input responsiveness. A converter can be used and 50
It is an object of the present invention to provide a multi-channel A / D converter capable of removing both commercial noises regardless of whether it is in a 60 Hz region or a 60 Hz region.

[0011]

In order to achieve the above object, the present invention scans analog signals from multiple channels in a predetermined order, converts the scanned analog signals into digital signals, and converts the analog signals into digital signals. The latest N for each
In a multi-channel A / D converter that calculates a moving average of digital signals and uses them as input values, when calculating the input values of each channel, both the 50 Hz and 60 Hz commercial noises contained in the N digital signals cancel each other out. Thus, the scan period, the scan order, and the number N of digital signals used are determined. According to the present invention, by appropriately determining the scan period, the scan order, and the number N of digital signals to be used, when calculating the input value of each channel, 50 bits included in the N digital signals are calculated.
Both Hz and 60 Hz commercial noise cancel each other out.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a block diagram showing a main part of a two-channel AD converter according to an embodiment of the present invention. In the figure, 1 is a terminal block, 2 is an analog signal input unit (analog signal input means), 3 is a first multiplexer (analog signal selection means), and 4 is an AD converter (AD converter).
Conversion means), 5 is a second multiplexer, 6 is a RAM
(AD conversion result storage means), 7 is a ROM, 8 is a CPU
(Control means) 9 is an input value calculation section (input value calculation means) composed of moving average calculation sections 9-1 and 9-2.

The analog signal input unit 2 is a signal conversion unit 2-
1 and 2-2 and analog filters 2-3 and 2-4. The signal conversion unit 2-1 takes in an analog signal (for example, a 4 to 20 mA DC current input signal) from a channel 1 (hereinafter, CH1) input via the terminal block 1, and the AD converter 4 outputs the signal as necessary. It is converted into a voltage signal that can be handled directly. Signal converter 2-
2 receives an analog signal (for example, an electromotive force signal from a thermocouple) from a channel 2 (hereinafter, CH2) input via the terminal block 1 and, if necessary, an AD converter 4
Is converted to a voltage signal that can be directly handled.

The analog filter 2-3 includes a signal conversion unit 2-
1 removes general noise included in the analog signal from CH1 converted into a voltage signal. The analog filter 2-4 removes general noise included in the analog signal from CH2 converted into a voltage signal by the signal converter 2-2.

The CPU 8 operates in accordance with a program stored in the ROM 7 to control the first multiplexer 3, the AD converter 4,
Second multiplexer 5, moving average calculation units 9-1 and 9-
2 is controlled. FIG. 2 is a flowchart showing a control situation by the CPU 8. FIG. 3 is a diagram showing a data collection schedule by the CPU 8. Hereinafter, based on this flowchart and the data collection schedule, the characteristic operation of the present embodiment will be described while exchanging the functions of the respective units.

The analog signal from the channel CH1 is supplied to a signal converter 2-1 of an analog signal input unit 2 via a terminal block 1, converted into a voltage signal, and general noise is removed by an analog filter 2-3. Then, it is supplied to the multiplexer 3. Here, the analog signal from CH1 supplied to the multiplexer 3 still contains commercial noise. On the other hand, the analog signal from CH2 is transmitted via the terminal block 1 to the signal conversion unit 2- of the analog signal input unit 2.
2, the signal is converted into a voltage signal, general noise is removed by an analog filter 2-4, and then supplied to a multiplexer 3. Here, the multiplexer 3
The analog signal from CH2 supplied to the circuit still contains commercial noise.

Upon receiving an instruction from the CPU 8, the multiplexer 3 selects analog signals from CH 1 and CH 2 in accordance with a specified scan cycle and a specified scan order, and outputs the analog signals to the AD converter 4. In this case, the CPU
8, the scan cycle is set to 25 ms, and CH1 → CH2 →
CH1 → CH2 → CH2 → CH1 → CH2 → CH1 → C
The analog signals from CH1 and CH2 are selected in an irregular scan order such as H1 → CH2 → CH1 → CH2.

That is, the CPU 8 first switches the multiplexer 3 to the CH1 side in the first cycle (steps 201 and 202), supplies an analog signal from the CH1 to the AD converter 4, and performs AD conversion (step 20).
3) Obtain a digital signal AD1 (1). Then, the multiplexer 5 is switched to the CH1 side, and the digital signal AD1 (1) from the AD converter 4 is stored in the storage area 6-1 for the CH1 in the RAM 6 (step 204).

In the next cycle, the CPU 8 switches the multiplexer 3 to the CH2 side (steps 201 and 207),
The analog signal from CH2 is supplied to the AD converter 4,
The conversion is performed (step 208), and the digital signal AD
2 (1) is obtained. Then, the multiplexer 5 is switched to the CH2 side, and the digital signal AD2 from the AD converter 4 is switched.
(1) is stored in the storage area 6-2 for CH2 in the RAM 6 (step 209).

Hereinafter, similarly, the CPU 8 operates for 25 ms.
Selection of an analog signal in the multiplexer 3 for each
The execution of the AD conversion in the D converter 4 is repeated,
(2) → AD2 (2) → AD2 (3) → AD1 (3) →
AD2 (4) → AD1 (4) → AD1 (5) → AD2
(5) → AD1 (6) → AD2 (6)... A digital signal is obtained in this order, and the digital signal
The digital signal AD2 is stored in the storage area 6-1 for CH1.
Are sequentially stored in the storage area 6-2.

The CPU 8 includes a moving average calculation section 9-1.
To the storage area 6-1 for the CH1 in the RAM 6
Every time the digital signal AD1 is stored in the memory, the moving average of the latest four digital signals AD1 is calculated as PV1 = (AD1 (n
-3) + AD1 (n-2) + AD1 (n-1) + AD1
(N)) / 4 (step 205), and the moving average PV1 is stored in the RAM 6 as an input value of CH1 (step 206).

That is, in FIG. 3, the digital signal A
When D1 (4) is obtained, this digital signal AD1
(4) and the previously stored AD1 (1), AD1 (2),
The average of the four digital signals including AD1 (3) is set as PV1 (1) and stored in the RAM 6 as the input value of CH1. When the digital signal AD1 (5) is obtained, the digital signal AD1 (5) and the previously stored AD1 (5)
The average of four digital signals including (2), AD1 (3), and AD1 (4) is set as PV2 (2) and stored in the RAM 6 as the input value of CH1.

Similarly, the CPU 8 includes a moving average calculator 9-
To the storage area 6 for the CH2 in the RAM 6
2 each time the digital signal AD2 is stored, the moving average of the latest four digital signals AD2 is calculated as PV2 = (AD2
(N-3) + AD2 (n-2) + AD2 (n-1) + A
D2 (n)) / 4 (step 210).
The moving average PV2 is stored in the RAM 6 as an input value of CH2 (step 211).

That is, in FIG. 3, the digital signal A
When D2 (4) is obtained, this digital signal AD2
(4) and the previously stored AD2 (1), AD2 (2),
The average of the four digital signals including AD2 (3) is set as PV2 (1) and stored in the RAM 6 as the input value of CH2. When the digital signal AD2 (5) is obtained, the digital signal AD2 (5) and the previously stored AD2 (5)
The average of the four digital signals including (2), AD2 (3) and AD2 (4) is defined as PV2 (2) and stored in the RAM 6 as the input value of CH2.

Here, in the present embodiment, the scan cycle in the multiplexer 3 is 25 ms, the scan order is the above-mentioned irregular order, and the digital values used for calculating the moving average in the moving average calculating sections 9-1 and 9-2 are described. By setting the number of used signals AD1 and AD2 to four (N = 4), the moving average calculators 9-1 and 9-2 include the four digital signals when calculating the input values of CH1 and CH2. Both of the 50 Hz and 60 Hz commercial noise cancel each other out. As a result, regardless of whether the area is 50Hz or 60Hz,
Both commercial noises can be removed.
The input value is updated to a new value every 25 ms to 75 ms (average 50 ms).

[Reason for removing both 50 Hz and 60 Hz commercial noise] FIGS. 4A and 4B show 50 Hz commercial noise and 60 Hz commercial noise. The period of the commercial noise of 50 Hz is 20 ms, and the period of the commercial noise of 60 Hz is 1
6.6 ms.

Here, in the present embodiment, the scan cycle is set to 25 ms. By setting the scan cycle to 25 ms, with commercial noise of 50 Hz, the phase at the scan timing is shifted from 0 ° → 90 ° → 180 ° → 270 ° → 360 °, and the phase component is −1 → −.
1 → −2 → −2 is repeated. In the case of 60 Hz commercial noise, the phase at the scan timing is 0.
゜ → 180 ゜ → 0 ゜ → 180 ゜ → 0 ゜ and the phase component is '-1 →' -1 → '-1 →' -1
Is repeated.

In this case, the phase components -1 and -2 of the 50 Hz commercial noise have an opposite phase relationship, and the phase components -1 and -2 also have an opposite phase relationship. Therefore, the moving average of the digital signal AD1 is calculated as PV1 = (AD
1 (n-3) + AD1 (n-2) + AD1 (n-1) +
AD1 (n)) / 4 cancels phase components -1 and -2, cancels phase components -1 and -2, and removes 50 Hz commercial noise from input value PV1 of CH1. You. Similarly, the digital signal AD2
Is calculated as PV2 = (AD2 (n−3) + AD2 (n
-2) + AD2 (n-1) + AD2 (n)) / 4, the phase components -1 and -2 cancel each other, and the phase components -1 and -2 cancel each other.
The commercial noise of 50 Hz is removed from the input value PV2.

That is, when the digital signal AD1 (4) is obtained, four digital signals including the digital signal AD1 (4) and the previously stored AD1 (1), AD1 (2), AD1 (3) are combined. The moving average PV1 (1) is obtained from the signal. In this case, the phase component-
1, AD1 (2) contains the phase component -2, AD1 (3) contains the phase component -1 and AD1 (3)
(4) includes a phase component -2. in this case,
The phase component -1 and AD1 included in AD1 (1)
The phase component-2 included in (2) is canceled, and A
Phase component -1 and AD1 included in D1 (3)
The phase component-2 included in (4) is canceled, and C
The commercial noise of 50 Hz is removed from the input value PV1 (1) of H1. Similarly, commercial noise of 50 Hz is removed from PV1 (2), PV1 (3),....

When the digital signal AD2 (4) is obtained,
This digital signal AD2 (4) and the previously stored AD2
A moving average PV2 (1) is obtained from four digital signals including (1), AD2 (2) and AD2 (3). In this case, AD2 (1) includes a phase component -1 and AD2 (2) includes a phase component -2.
(3) includes a phase component -1 and AD2 (4) includes a phase component -2. In this case, AD2
The phase component -1 included in (1) and the phase component -2 included in AD2 (2) cancel each other, and AD2
The phase component -1 included in (3) and the phase component -2 included in AD2 (4) are canceled, and 50 Hz commercial noise is removed from the input value PV2 (1) of CH2. Similarly, the commercial noise of 50 Hz is removed from PV2 (2), PV2 (3),....

On the other hand, the phase components' -1 'and' -2 in the 60 Hz commercial noise have an opposite phase relationship. Therefore, the moving average of the digital signal AD1 is calculated as PV1 = (AD
1 (n-3) + AD1 (n-2) + AD1 (n-1) +
AD1 (n)) / 4, the phase components' -1 'and' -1 are canceled, and the input value PV of CH1
Commercial noise from 1 to 60 Hz is removed. Similarly, the moving average of the digital signal AD2 is calculated as PV2 = (AD2 (n−
3) + AD2 (n-2) + AD2 (n-1) + AD2
(N)) / 4, the phase component '−
1 and '-1 are canceled, and 60 Hz commercial noise is removed from the input value PV2 of CH2.

That is, when the digital signal AD1 (4) is obtained, four digital signals including the digital signal AD1 (4) and the previously stored AD1 (1), AD1 (2), and AD1 (3) are combined. The moving average PV1 (1) is obtained from the signal. In this case, the phase component '
-1 is included, AD1 (2) includes the phase component '-1, AD1 (3) includes the phase component' -1,
D1 (4) includes the phase component '-1. In this case, the phase component '-1 included in AD1 (1) and the phase component' -1 included in AD1 (3) are canceled, and the phase component '-included in AD1 (2) is canceled. 1 and the phase component '-1 included in AD1 (4) are canceled, and 60 Hz commercial noise is removed from the input value PV1 (1) of CH1. PV1 (2), PV1 (3) ...
Similarly, the commercial noise of 60 Hz is removed.

When the digital signal AD2 (4) is obtained,
This digital signal AD2 (4) and the previously stored AD2
A moving average PV2 (1) is obtained from four digital signals including (1), AD2 (2) and AD2 (3). In this case, AD2 (1) contains the phase component '-1; AD2 (2) contains the phase component'-1;
D2 (3) contains the phase component '-1 and AD2 (3)
(4) includes the phase component '-1. In this case, the phase component '-1 included in AD2 (1) and A
The phase component '-1 included in D2 (3) is canceled, and the phase component' -1 included in AD2 (2) and A
The phase component '-1 included in D2 (4) is canceled, and 60 Hz commercial noise is removed from the input value PV2 (1) of CH2. PV2 (2), PV2 (3) ...
Similarly, the commercial noise of 60 Hz is removed.

As described above, according to the present embodiment, 50
Since both commercial noises can be removed irrespective of the region of Hz or the region of 60 Hz, it is not necessary to switch the scan cycle depending on whether the frequency of the main power supply of the installation environment is 50 Hz or 60 Hz.

In the embodiment described above, the scan cycle is 25 ms, and the scan order is CH1 → CH2 →
CH1 → CH2 → CH2 → CH1 → CH2 → CH1 → C
H1 → CH2 → CH1 → CH2... And the number of digital signals AD1 and AD2 used for calculating the moving average is set to N = 4. It is sufficient that the phase components can be canceled, and any combination may be used as long as the combination satisfies this condition. That is, the scan cycle is not limited to 25 ms, the scan order is not limited to the above-described scan order, and the number N of digital signals used in calculating the moving average is not limited to four.

Further, in the present embodiment, the case of two channels has been described, but application to an AD converter of two or more channels is also possible. Further, as the AD converter 4, various AD converters can be used in addition to the integral AD converter.

[0037]

As is apparent from the above description, according to the present invention, by appropriately setting the scan period, the scan order, and the number N of digital signals to be used, the input value of each channel can be calculated by N Both of the 50 Hz and 60 Hz commercial noises included in the digital signal are canceled out from each other, so that both commercial noises can be removed regardless of the 50 Hz region or the 60 Hz region. Further, it is possible to use a low-cost AD converter having a relatively long AD conversion time without sacrificing the input responsiveness and the input value update cycle.

[Brief description of the drawings]

FIG. 1 shows two channels A showing an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a main part of the D conversion device.

FIG. 2 shows a CP in the two-channel AD converter.
6 is a flowchart showing a control situation by U.

FIG. 3 is a diagram showing a data collection schedule by the CPU.

FIG. 4 shows a diagram of a two-channel A / D converter;
It is a figure for explaining the reason why commercial noise of both 60Hz and 60Hz is removed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Terminal block, 2 ... Analog signal input part, 3 ... First multiplexer, 4 ... AD converter, 5 ... Second multiplexer, 6 ... RAM, 6-1 ... Storage area for CH1, 6-2
... Storage area for CH2, 7 ... ROM, 8 ... CPU, 9 ...
Input value calculators, 9-1, 9-2... Moving average calculators.

Claims (3)

[Claims] 1. An analog signal from multiple channels is scanned in a predetermined order, the scanned analog signal is converted into a digital signal, and a moving average of the latest N digital signals is calculated for each channel to obtain an input value and In the multi-channel A / D conversion apparatus, when calculating the input value of each channel, the scan cycle, the scan order, and the scan order are set such that both of the 50 Hz and 60 Hz commercial noise included in the N digital signals cancel each other. A multi-channel AD converter, wherein the number N of digital signals used is determined. 2. An analog signal selecting means for selecting and outputting analog signals from multiple channels according to a specified scan cycle and a specified scan order, and converting the analog signals from the analog signal selecting means into digital signals. AD conversion means, AD conversion result storage means for storing the digital signal converted by the AD conversion means for each channel, and movement of the latest N digital signals of each channel stored in the AD conversion result storage means An input value calculating means for obtaining an input value for each channel by taking an average; and calculating the input value of each channel by the input value calculating means, wherein any of 50 Hz and 60 Hz commercial noise included in the N digital signals is used. Scan cycle and scan order to the analog signal selecting means so that Constant, the multi-channel AD converter, characterized in that a control means for setting a use number N of digital signal at said input value-calculating means. 3. The multi-channel A / D converter according to claim 1, wherein the scan cycle is set to 25 ms.