JP3566124B2 - Multi-channel AD converter - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-channel AD converter for converting analog signals from multiple channels into digital signals and obtaining input values for each channel from the digital signals.
[0002]
[Prior art]
Industrial instruments using microcomputers often convert analog signals from multiple channels into digital signals using 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 influence of these commercial noises (50 Hz, 60 Hz) as much as possible without sacrificing product performance (input accuracy and responsiveness when input changes).
[0003]
Therefore, conventionally, the following method has been considered as a method of removing commercial noise included in an analog signal.
[(1) Removal method by analog filter]
An analog filter is provided at the input section of the analog signal. That is, the analog signal is passed through an analog filter such as an RC filter, and commercial noise is removed from the analog signal before being converted into a digital signal.
[0004]
[(2) Removal method by digital filter]
By sequentially scanning analog signals from multiple channels at a predetermined cycle, converting the scanned analog signals into digital signals, and taking a moving average of the latest N digital signals for each channel to obtain an input value, Commercial noise is removed from the digital signal (input value) after AD conversion.
[0005]
For example, when analog signals are input from two channels, the analog signals from these two channels are alternately scanned. Here, if the commercial noise is, for example, 50 Hz, the cycle is 20 ms. Therefore, scanning is performed twice in the cycle, that is, in a 10 ms cycle, and the moving average of the two data is converted into a digital signal. (Input value).
[0006]
[Problems to be solved by the invention]
However, according to the above-described removal method using an analog filter, input responsiveness often deteriorates in an attempt to enhance the ability to remove commercial noise.
[0007]
In addition, according to the above-described removal method using a digital filter, it is necessary to AD-convert each channel at a cycle of 10 ms. Therefore, for example, to calculate an input value of two channels, the AD conversion time needs to be 5 ms or less. .
[0008]
In addition, 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. A moving average of the digital signals may be obtained. On the other hand, when the commercial noise is 60 Hz, the cycle is 16.6 ms. Therefore, analog signals from two channels are alternately scanned at a cycle of 8.3 ms, and this scanned analog signal is converted into a digital signal. Conversion and a moving average of the two latest digital signals for each channel. 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.
[0009]
Further, as a method of eliminating the switching of the scan period, an integration type AD converter or a charge balance type AD converter is used for a noise period (in this case, a period of 10 Hz which is the greatest common divisor of 50 Hz and 60 Hz = 100 ms). , The AD converter is kept operating, but there is a problem in that the channel switching period and the input value updating period become as long as 100 ms × the number of channels (200 ms in the case of two channels).
[0010]
The present invention has been made to solve such a problem, and an object of the present invention is to provide a low-cost AD converter having a relatively long AD conversion time without significantly sacrificing input responsiveness. It is an object of the present invention to provide a multi-channel AD converter that can be used and can remove both commercial noises regardless of whether the area is 50 Hz or 60 Hz.
[0011]
[Means for Solving the Problems]
To achieve the above object, the present invention provides an analog signal from the multi-channel scans, converts the analog signal this scan digital signal, the moving average of the most recent N digital signals for each channel In the multi-channel A / D converter that takes the input values and calculates the input values for each channel , the scan period is set so that any of the 50 Hz and 60 Hz commercial noise included in the N digital signals is canceled. Is set to 25 ms, and the number N of digital signals used is set to 4 .
According to the present invention, when calculating the input value of each channel , both of the 50 Hz and 60 Hz commercial noise included in the four digital signals are canceled.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
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 section (analog signal input means), 3 is a first multiplexer (analog signal selection means), 4 is an AD converter (AD conversion means), and 5 is a second , A RAM (AD conversion result storing means), 7 a ROM, 8 a CPU (control means), and 9 an input value calculating section (inputting section) comprising moving average calculating sections 9-1 and 9-2. Value calculation means).
[0013]
The analog signal input unit 2 includes signal conversion units 2-1 and 2-2, analog filters 2-3 and 2-4, and the like. 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. The signal conversion unit 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 converts the analog signal as necessary. Is converted into a voltage signal that can be directly handled.
[0014]
The analog filter 2-3 removes general noise included in the analog signal from CH1 converted into a voltage signal by the signal converter 2-1. The analog filter 2-4 removes general noise included in the analog signal from CH2 converted into a voltage signal by the signal conversion unit 2-2.
[0015]
The CPU 8 controls the first multiplexer 3, the AD converter 4, the second multiplexer 5, and the moving average calculators 9-1 and 9-2 in accordance with a program stored in the ROM 7. 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 in the present embodiment will be described while exchanging the functions of the respective units.
[0016]
The analog signal from CH1 is supplied to the signal conversion unit 2-1 of the analog signal input unit 2 via the terminal block 1, converted into a voltage signal, and subjected to general noise removal by the analog filter 2-3. , 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 supplied to the signal converter 2-2 of the analog signal input unit 2 via the terminal block 1, converted into a voltage signal, and general noise is removed by the analog filter 2-4. In addition, it is provided to the multiplexer 3. Here, the analog signal from CH2 supplied to multiplexer 3 still contains commercial noise.
[0017]
The multiplexer 3 receives an instruction from the CPU 8, 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 sets the scan cycle to 25 ms and sets CH1 in the irregular scan order such as CH1 → CH2 → CH1 → CH2 → CH2 → CH1 → CH2 → CH1 → CH1 → CH2 → CH1 → CH2. , CH2.
[0018]
That is, the CPU 8 first switches the multiplexer 3 to the CH1 side in the first cycle (steps 201 and 202), supplies the analog signal from the CH1 to the AD converter 4, and performs the AD conversion (step 203). AD1 (1) is obtained. 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).
[0019]
In the next cycle, the CPU 8 switches the multiplexer 3 to the CH2 side (steps 201 and 207), supplies an analog signal from the CH2 to the AD converter 4 to perform AD conversion (step 208), and performs a digital signal AD2 (1 Get) Then, the multiplexer 5 is switched to the CH2 side, and the digital signal AD2 (1) from the AD converter 4 is stored in the storage area 6-2 for the CH2 in the RAM 6 (step 209).
[0020]
Thereafter, similarly, the CPU 8 repeats the selection of the analog signal in the multiplexer 3 and the execution of the AD conversion in the AD converter 4 every 25 ms, and AD1 (2) → AD2 (2) → AD2 (3) → AD1 (3 ) → AD2 (4) → AD1 (4) → AD1 (5) → AD2 (5) → AD1 (6) → AD2 (6)... The digital signal AD2 is sequentially stored in the storage area 6-1 for CH2 in the storage area 6-1 for CH2.
[0021]
Further, the CPU 8 sends a command to the moving average calculating unit 9-1, and every time the digital signal AD1 is stored in the storage area 6-1 for CH1 in the RAM 6, the moving average of the latest four digital signals AD1 is sent. Is calculated as PV1 = (AD1 (n−3) + AD1 (n−2) + AD1 (n−1) + AD1 (n)) / 4 (step 205), and this moving average PV1 is input into the RAM 6 as the input value of CH1. It is stored (step 206).
[0022]
That is, in FIG. 3, when the digital signal AD1 (4) is obtained, the digital signal AD1 (4) and four previously stored AD1 (1), AD1 (2), and AD1 (3) are combined. The average of the digital signals is set to PV1 (1) and stored in the RAM 6 as the input value of CH1. When the digital signal AD1 (5) is obtained, the average of four digital signals obtained by combining the digital signal AD1 (5) and the previously stored AD1 (2), AD1 (3), and AD1 (4) is calculated as PV1. (2) is stored in the RAM 6 as the input value of CH1.
[0023]
Similarly, the CPU 8 sends a command to the moving average calculation unit 9-2, and every time the digital signal AD2 is stored in the storage area 6-2 for CH2 in the RAM 6, the movement of the latest four digital signals AD2 is performed. The average is calculated as PV2 = (AD2 (n−3) + AD2 (n−2) + AD2 (n−1) + AD2 (n)) / 4 (step 210), and this moving average PV2 is input to the RAM 6 as the input value of CH2 (Step 211).
[0024]
That is, in FIG. 3, when the digital signal AD2 (4) is obtained, the digital signal AD2 (4) and the previously stored AD2 (1), AD2 (2), and AD2 (3) are combined into four signals. The average of the digital signals 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 average of four digital signals obtained by combining the digital signal AD2 (5) with the previously stored AD2 (2), AD2 (3), and AD2 (4) is calculated as PV2. (2) is stored in the RAM 6 as the input value of CH2.
[0025]
Here, in the present embodiment, the scan cycle in the multiplexer 3 is 25 ms, the scan order is the irregular order described above, and the digital signals AD1 and AD1 in the moving average calculation sections 9-1 and 9-2 when calculating the moving average. By setting the number of AD2 used to four (N = 4), when the moving average calculators 9-1 and 9-2 calculate the input values of CH1 and CH2, 50 Hz included in the four digital signals and Any of the 60 Hz commercial noise cancels each other. This makes it possible to remove both commercial noises irrespective of the region of 50 Hz or the region of 60 Hz. The input value is updated to a new value every 25 ms to 75 ms (average 50 ms).
[0026]
[Reason for removing both 50Hz and 60Hz 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 16.6 ms.
[0027]
Here, in the present embodiment, the scan cycle is 25 ms. By setting the scan cycle to 25 ms, with commercial noise of 50 Hz, the phase at the scan timing shifts from 0 ° → 90 ° → 180 ° → 270 ° → 360 °, and the phase component is (1) -1. → (2) -1 → (1) -2 → (2) -2 is repeated. In the case of 60 Hz commercial noise, the phase at the scan timing shifts from 0 ° → 180 ° → 0 ° → 180 ° → 0 °, and the phase component is (1) '-1 → (2)'-. 1 → ▲ 1 ▼ '-1 → ▲ 2 ▼' -1 is repeated.
[0028]
In this case, the phase components (1) -1 and (1) -2 in the 50 Hz commercial noise have an opposite phase relationship, and the phase components (2) -1 and (2) -2 also have an opposite phase relationship. is there. Accordingly, by calculating the moving average of the digital signal AD1 as PV1 = (AD1 (n−3) + AD1 (n−2) + AD1 (n−1) + AD1 (n)) / 4, the phase components {1} −1 and (1) -2 is canceled out, and the phase components (2) -1 and (2) -2 are canceled out, and 50 Hz commercial noise is removed from the input value PV1 of CH1. Similarly, by calculating the moving average of the digital signal AD2 as PV2 = (AD2 (n-3) + AD2 (n-2) + AD2 (n-1) + AD2 (n)) / 4, the phase component (1) -1 And (1) -2 are canceled out, and the phase components (2) -1 and (2) -2 are canceled out, and 50 Hz commercial noise is removed from the input value PV2 of CH2.
[0029]
That is, when the digital signal AD1 (4) is obtained, the digital signal AD1 (4) is shifted from four digital signals obtained by combining the previously stored AD1 (1), AD1 (2), and AD1 (3). An average PV1 (1) is determined. In this case, AD1 (1) includes a phase component (1) -1, AD1 (2) includes a phase component (1) -2, and AD1 (3) includes a phase component (2) -1. , And AD1 (4) includes the phase component {circle around (2)}-2. In this case, the phase component (1) -1 included in AD1 (1) and the phase component (1) -2 included in AD1 (2) cancel each other out and are included in AD1 (3). The phase component {circle around (2)}-1 and the phase component {circle around (2)}-2 included in AD1 (4) are canceled out, and 50 Hz commercial noise is removed from the input value PV1 (1) of CH1. Similarly, commercial noise of 50 Hz is removed from PV1 (2), PV1 (3),....
[0030]
When the digital signal AD2 (4) is obtained, a moving average PV2 is calculated from four digital signals obtained by combining the digital signal AD2 (4) and the previously stored AD2 (1), AD2 (2), and AD2 (3). (1) is required. In this case, AD2 (1) includes the phase component (2) -1; AD2 (2) includes the phase component (2) -2; and AD2 (3) includes the phase component (1) -1. , And the phase component (1) -2 is included in AD2 (4). In this case, the phase component (2) -1 included in AD2 (1) and the phase component (2) -2 included in AD2 (2) cancel each other out and are included in AD2 (3). The phase component (1) -1 and the phase component (1) -2 included in the AD2 (4) are canceled, and 50 Hz commercial noise is removed from the input value PV2 (1) of the CH2. Similarly, the commercial noise of 50 Hz is removed from PV2 (2), PV2 (3),...
[0031]
On the other hand, the phase components (1) '-1 and ( 2) '-1 in the 60 Hz commercial noise have an opposite phase relationship. Therefore, by calculating the moving average of the digital signal AD1 as PV1 = (AD1 (n-3) + AD1 (n-2) + AD1 (n-1) + AD1 (n)) / 4, the phase component (1) '-1 is obtained. And (2) '-1 are canceled, and the commercial noise of 60 Hz is removed from the input value PV1 of CH1. Similarly, by calculating the moving average of the digital signal AD2 as PV2 = (AD2 (n-3) + AD2 (n-2) + AD2 (n-1) + AD2 (n)) / 4, the phase component {1} '- 1 and (2) '-1 are canceled, and 60 Hz commercial noise is removed from the input value PV2 of CH2.
[0032]
That is, when the digital signal AD1 (4) is obtained, the digital signal AD1 (4) is shifted from four digital signals obtained by combining the previously stored AD1 (1), AD1 (2), and AD1 (3). An average PV1 (1) is determined. In this case, AD1 (1) includes the phase component (1) ′-1, AD1 (2) includes the phase component (1) ′-1, and AD1 (3) includes the phase component (2). '-1 is included, and the phase component (2)'-1 is included in AD1 (4). In this case, the phase component (1) '-1 included in AD1 (1) and the phase component (2)'-1 included in AD1 (3) are canceled and included in AD1 (2). The phase component (1) '-1 included in AD1 (4) and the phase component (2)'-1 included in AD1 (4) are canceled, and 60 Hz commercial noise is removed from the input value PV1 (1) of CH1. . The commercial noise of 60 Hz is similarly removed from PV1 (2), PV1 (3),.
[0033]
When the digital signal AD2 (4) is obtained, a moving average PV2 is calculated from four digital signals obtained by combining the digital signal AD2 (4) and the previously stored AD2 (1), AD2 (2), and AD2 (3). (1) is required. In this case, AD2 (1) contains the phase component (2) '-1, AD2 (2) contains the phase component (2)'-1, and AD2 (3) contains the phase component (1). '-1 and AD2 (4) includes the phase component (1)'-1. In this case, the phase component (2) '-1 included in AD2 (1) and the phase component (1)'-1 included in AD2 (3) are canceled out and included in AD2 (2). The phase component {circle around (1)} ′ − 1 included in the AD2 (4) and the phase component {circle around (1) ″ ′} included in the AD2 (4) are canceled, and 60 Hz commercial noise is removed from the input value PV2 (1) of the CH2. . Similarly, the commercial noise of 60 Hz is removed from PV2 (2), PV2 (3),...
[0034]
As described above, according to the present embodiment, both the commercial noise can be removed regardless of the region of 50 Hz or the region of 60 Hz. Therefore, the frequency of the main power supply of the installation environment is 50 Hz or 60 Hz. It is not necessary to switch the scan cycle depending on the situation.
[0035]
In the above-described embodiment, the scan order is CH1 → CH2 → CH1 → CH2 → CH2 → CH1 → CH2 → CH1 → CH1 → CH2 → CH1 → CH2... In this case, it is sufficient that the phase components of the commercial noise at both 50 Hz and 60 Hz can be cancelled, and any combination that satisfies this condition may be used.
[0036]
Further, in the present embodiment, the case of two channels has been described, but application to an AD converter having 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]
【The invention's effect】
As is apparent from the above description, according to the present invention, when calculating the input value of each channel , both of the 50 Hz and 60 Hz commercial noise included in the four digital signals are offset, Regardless of whether the area is 50 Hz or 60 Hz, both commercial noises can be removed. Also, it is possible to use a lower-priced AD converter having a relatively long AD conversion time without sacrificing the input responsiveness and the input value updating cycle.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a main part of a two-channel AD converter according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a control situation by a CPU in the two-channel AD converter.
FIG. 3 is a diagram showing a data collection schedule by the CPU.
FIG. 4 is a diagram for explaining the reason why commercial noise of both 50 Hz and 60 Hz is removed in the two-channel AD converter.
[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 ... CH2 storage area, 7 ROM, 8 CPU, 9 input value calculator, 9-1, 9-2 moving average calculator.

Claims (2)

The analog signals from the multi-channel scans, converts the analog signal this scan into digital signals in the multi-channel AD converter according to the input value by taking the moving average of the most recent N digital signals for each channel,
In calculating the input value of each channel, the scan cycle is 25 ms and the number N of the digital signals used is such that any of the 50 Hz and 60 Hz commercial noises contained in the N digital signals is canceled. 4. A multi-channel A / D converter, wherein the number is set to 4 . A multi-channel AD converter that scans analog signals from two channels at a period of 25 ms, converts the scanned analog signals into digital signals, calculates the moving average of the latest four digital signals for each channel, and uses the moving average as an input value. At
In calculating the input value of each channel, the 50 Hz commercial noise included in the four digital signals is canceled out of opposite phases in each two combinations of the four digital signals, and The scan order of the analog signals is determined so that 60 Hz commercial noise included in the four digital signals is canceled out of phase with each other in a combination of two of the four digital signals. multi-channel AD converter according to claim <br/> Being.

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