JP2009246711A - Signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal processing apparatus, in simple configuration, capable of eliminating a common-mode noise caused by the number of power supply terms by fetching input signals in a fixed sampling term regardless of the number of terms of an AC power source. <P>SOLUTION: In an A/D conversion means, within one operational term set to an arithmetic processing means, a first input signal is sampled iteratively certain times determined in accordance with a power supply frequency, and first and second input signals are carried out digital conversion respectively in a fixed term during which the second input signal can be sampled at least once. In an averaging processing means, an average value of digital conversion values of the first input signal sampled iteratively certain times determined in accordance with the power supply frequency is determined. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention operates with an AC power source as a drive source, and is configured to perform predetermined arithmetic processing on an input signal taken in via an A / D converter, for example, a temperature detection device or temperature control using a thermocouple. The present invention relates to a signal processing device such as a device.

  In a temperature detection device and a temperature control device using a thermocouple, in order to perform cold junction compensation of the thermocouple provided in the temperature detection target, according to a temperature value detected using a temperature sensor for cold junction compensation. It is configured to obtain the temperature of the temperature detection target by compensating the output (electromotive force) of the thermocouple. FIG. 3 is a diagram showing a schematic configuration of this type of temperature detection device, in which 1 is a detection target provided with a thermocouple TC, and 2 is a temperature detection device. This temperature detection device 2 is composed mainly of a microprocessor (CPU) 3, for example, and is detected by temperature information detected by the thermocouple TC and a cold junction compensation temperature sensor CJ incorporated in the temperature detection device 2. Each temperature value is digitally converted via the A / D converter 4 and is taken into the microprocessor (CPU) 3. The temperature control device is configured to control the temperature of the detection target 1 by controlling a control target (such as a heater or a cooler) (not shown) according to the temperature value detected by the temperature detection device 2 described above. [See, for example, Patent Document 1].

By the way, in this type of temperature detection device or temperature control device that operates using a commercial AC power source as a drive source, the input signal taken in via the A / D converter 4 is caused by the frequency of the commercial AC power source. It cannot be denied that common mode noise is superimposed. This common mode noise is a factor that greatly deteriorates the detection accuracy of temperature information detected using the thermocouple TC described above. Therefore, conventionally, the frequency of the commercial AC power source is detected, and the A / D converter is operated in synchronization with the detected frequency to capture (sample) the input signal [see, for example, Patent Document 2]. The common mode noise is removed by averaging digital conversion values over a plurality of samples of the input signal acquired in synchronization with the frequency of the commercial AC power supply.
JP-A-5-53657 JP 2002-286556 A

  However, in order to change the operation cycle (sampling cycle) of the A / D converter according to the frequency of the commercial AC power supply, it is necessary to use an A / D converter capable of switching the operation mode, and the device configuration is complicated. It will be a factor inviting. In addition, when the operation cycle (sampling cycle) of the A / D converter is changed, the filter constant, algorithm, etc. inside the A / D converter change accordingly. For this reason, there arises a problem that response characteristics change when an input signal is taken in via the A / D converter and predetermined signal processing is executed.

  Further, as described above, when the two input signals are taken in and the predetermined signal processing is executed, in order to remove the common mode noise contained in each of these two input signals, the two input signals are input. It is necessary to acquire the signal over a plurality of samples. Accordingly, it takes a considerably long time to obtain two systems of input signals (average values) from which common mode noise is removed while switching the input of one A / D converter, and the signal processing cycle in the temperature detection device 2 is long. It cannot be denied that it will be long. On the contrary, when the cycle of the signal processing in the temperature detection device 2 is defined, it is necessary to capture the above-mentioned two systems of input signals over a plurality of samples within the period of the operation cycle. It is necessary to set the sampling period in the / D converter 4 to be considerably short.

  The present invention has been made in consideration of such circumstances, and the purpose of the present invention is to convert the input signal into a digital signal with a constant sampling period and capture the AC signal regardless of the frequency of the AC power source used as a drive source. An object of the present invention is to provide a signal processing apparatus that can easily execute predetermined signal processing by reducing the influence of common mode noise caused by the frequency of a power supply.

In order to achieve the above-described object, the signal processing apparatus according to the present invention operates using an AC power source as a drive source,
A / D conversion means for digitally converting the first and second input signals, respectively, and
A digital conversion value of the first input signal taken in via the A / D conversion means is averaged to remove common mode noise caused by the frequency of the AC power source included in the first input signal. Averaging means for
Arithmetic processing means for executing predetermined arithmetic processing using the average value obtained by the averaging processing means of the digital conversion value of the first input signal and the digital conversion value of the second input signal; Prepared,
Particularly, in the A / D conversion means, the first input signal is repeatedly sampled over a number of times determined according to the frequency of the AC power source within one operation cycle set in the arithmetic processing means, and Each of the first and second input signals is digitally converted at a fixed period in which the second input signal can be sampled at least once;
The averaging processing means is configured to obtain an average value of digital conversion values of the first input signal repeatedly sampled over a number of times determined according to the frequency of the AC power supply. .

  Preferably, the A / D conversion means is configured to selectively sample the first and second input signals at a period of [10 / (6n)] m seconds (where n is a natural number), and For the averaging processing means, when the frequency of the AC power source is [50] Hz, the digital conversion value of the first input signal is averaged over the number of consecutive [12n] samples, and the AC power source When the frequency is [60] Hz, it is preferable that the digital conversion value of the first input signal is averaged over the number of consecutive [10n] samples.

  In a preferred embodiment of the present invention, for example, the first input signal is information indicating the temperature of the detection target obtained by a thermocouple, and the second input signal is a calibration obtained by a temperature sensor for cold junction compensation. The calculation processing means corrects an average value of the digital conversion value of the first input signal by using the digital conversion value of the second input signal, and calculates the temperature of the detection target. Configured to seek. Furthermore, it is desirable that the arithmetic processing means is configured to generate a control signal for an external control target according to the temperature of the detection target corrected as described above.

  According to the signal processing apparatus configured as described above, the A / D conversion means is driven at a constant sampling period, and the first input signal is determined according to the frequency of the AC power source within one operation period set in the arithmetic processing means. The second input signal is sampled at least once, and the digital input value of the first input signal repeatedly sampled over the number of times determined according to the frequency of the AC power supply Since only the average value is obtained, the first and the first operation cycles are set in the arithmetic processing means without incurring a complicated configuration of the A / D conversion means and without causing a change in response characteristics thereof. The second input signal can be reliably captured.

  In addition, the A / D conversion means is driven with a sampling period of [10 / (6n)] m seconds (where n is a natural number), and the averaging processing means is continuous when the frequency of the AC power source is [50] Hz. The digital conversion value of the first input signal is averaged over the number of [12n] samples, and when the frequency of the AC power source is [60] Hz, the first over the number of consecutive [10n] samples. Since the digital conversion value of the input signal is averaged, the common mode noise caused by the frequency of the AC power supply can be reliably ensured regardless of whether the frequency of the AC power supply is [50] Hz or [60] Hz. It can be removed (reduced).

  In particular, according to the present invention, the first input signal is information indicating the temperature of a detection target obtained by a thermocouple, and the second input signal is a calibration value obtained by a cold junction compensation temperature sensor. In the case of a temperature value, the first input signal to be measured is detected over a plurality of consecutive samples and averaged to detect the common mode noise included in the first input signal. Therefore, the second input signal that is generally stable and serves as a compensation reference for the first input signal can be detected between the input periods of the first input signal. Thus, since at least one sample is input, the period for capturing the first and second input signals does not become so long. Accordingly, the first and second input signals can be stably captured without setting the sampling period of the A / D conversion means too short within one operation cycle set in the arithmetic processing means. .

Hereinafter, a signal processing device according to an embodiment of the present invention will be described using a temperature detection device using a thermocouple as an example. It should be noted that the present invention is similarly applied to the function of the above-described temperature detection device and also to a temperature control device that controls the operation of an external control target device such as a heater or a refrigerator based on the detected temperature value. be able to.
FIG. 1 is a schematic configuration diagram of a temperature detection device according to an embodiment of the present invention. Reference numeral 1 denotes a thermocouple as a temperature sensor provided at a temperature detection target site. The temperature detection device 10 receives temperature information (first input signal) detected by the thermocouple 1 via a first preamplifier (input buffer) 11 and a second preamplifier ( Temperature information (second input signal) obtained by the cold junction compensation temperature sensor 13 incorporated in the temperature detection device 10 is input via the input buffer) 12. These first and second input signals are sampled at a predetermined cycle via the A / D converter 14, converted into digital signals, and taken into a microprocessor (CPU) 15 constituting the main body of the apparatus. It is configured as follows. The A / D converter 14 may have an A / D conversion function built in the microprocessor (CPU) 15.

  The microprocessor (CPU) 15 basically has temperature information (first input signal) detected using the thermocouple 1 as temperature information (first input) obtained by the cold junction compensation temperature sensor 13. 2), the temperature of the temperature detection target portion where the thermocouple 1 is provided is detected with high accuracy. The temperature detected in this way is displayed on a display 16 incorporated in the temperature detection device 10, or is output to an external device or the like as detected temperature information.

  The temperature detection device basically configured as described above operates, for example, using a commercial AC power supply (AC) as a drive source directly or indirectly, and the power supply unit 17 rectifies and smoothes the AC power supply. To generate a predetermined DC power supply voltage Vcc for driving the A / D converter 14 and the microprocessor (CPU) 15 described above. Further, a frequency determination unit 18 for setting the frequency of the AC power supply in the microprocessor (CPU) 15 is provided in association with the power supply unit 17.

  The temperature detection device (signal processing device) according to the present invention is characterized in that the A / D converter 14 is driven at a constant sampling cycle Ts, and one operation cycle T of the microprocessor (CPU) 15 is obtained. The temperature information (first input signal) input from the above-described thermocouple 1 within the period is repeatedly sampled over a number of times determined according to the frequency of the commercial AC power supply as will be described later, and the digital conversion value And the temperature information (second input signal) obtained by the cold junction compensation temperature sensor 13 at least once within the remaining time of one operation cycle T of the microprocessor (CPU) 15. The digital conversion value is obtained by sampling. The selective sampling of the first input signal and the second input signal via the A / D converter 14 is switched under the control of the input control unit 15a in the microprocessor (CPU) 15.

  In the microprocessor (CPU) 15, an average value of the digital conversion values of the first input signal repeatedly sampled over the number of times determined in accordance with the frequency of the commercial AC power in the averaging processing unit 15 b is obtained. As a result, common mode noise caused by the frequency of the commercial AC power supply superimposed on the first input signal is removed (reduced). Then, the microprocessor (CPU) 15 drives the calculation unit 15c, and obtains temperature information (first input signal) indicated by the output of the thermocouple 1 from which common mode noise has been removed by the averaging process described above. Then, cold junction compensation is performed using the temperature value (second input signal) indicated by the output of the cold junction compensation temperature sensor 13, and thereby the temperature of the temperature detection target portion where the thermocouple 1 is provided with high accuracy. It is what we want.

  Here, the sampling period Ts of the A / D converter 14, the operation period T in the microprocessor (CPU) 15, and the number of samplings used for the averaging process will be described. The frequency of the commercial AC power source that drives this temperature detection device (signal processing device) is [50] Hz or [60] Hz, and the common mode noise superimposed on the input signal has a period that depends on the frequency of the commercial AC power source. Presents a substantially constant change. Therefore, if the input signal on which the common mode noise is superimposed is repeatedly sampled at a constant period Ts over, for example, one wavelength of the commercial AC power supply, and the average value of these sampling values is obtained, basically the commercial AC power supply is obtained. It is possible to cancel the change of the common mode noise over one wavelength synchronized with the frequency of the signal, thereby removing the common mode noise from the input signal.

  Therefore, in order to remove the common mode noise depending on the frequency of the commercial AC power supply from the input signal and perform the highly accurate temperature detection, the power supply frequency is [50] Hz in one operation cycle T in the microprocessor (CPU) 15. In this case, it may be [1/50] seconds or more, and may be [1/60] seconds or more when the power supply frequency is [60] Hz. In other words, if one operation cycle T of the microprocessor (CPU) 15 is set to [100] msec or more, basically, common mode noise for one wavelength is detected with good symmetry within the one operation cycle T. Therefore, it is possible to perform highly accurate temperature detection that eliminates the influence of common mode noise regardless of the power supply frequency.

  On the other hand, the input signal is repeatedly sampled at a constant period Ts regardless of the power supply frequency, the input signal including common mode noise for one wavelength is detected, and the average value is obtained. The input signal may be sampled at a period Ts of [1 / n] of [1/300] seconds defined by the least common multiple of 50] Hz and [60] Hz. Specifically, the sampling period Ts of the A / D converter 4 may be set as [10 / (3n)] m seconds. Where n is a natural number.

  However, in this case, the number of sampling times of the input signal including common mode noise for one wavelength becomes an odd number, and when there is a deviation in sampling timing, it is impossible to detect common mode noise for one wavelength with good symmetry. There is a fear. Therefore, in practice, the sampling period Ts of the A / D converter 4 is set as [10 / (6n)] m seconds, and the common mode noise for one wavelength can always be set to be positively and negatively sampled. preferable.

  Based on such a viewpoint, in this apparatus, the A / D converter 4 is driven at a constant sampling period Ts of [10 / (6n)] msec. When the frequency of the commercial AC power source is [50] Hz, the first input signal is sampled over [12n] times continuously to obtain the digital conversion value. When the frequency of the commercial AC power source is [60] Hz, the first input signal is sampled over [10n] times continuously to obtain the digital conversion value. The number of consecutive samples of the first input signal is executed under the control of the input control unit 15a based on the power supply frequency set by the frequency determination unit 18 described above.

  Then, in the above-described averaging processing unit 15b, according to the frequency of the commercial AC power detected as described above, specifically, when the power frequency is [50] Hz, the first input signal continues [ 12n] sample, and when the power supply frequency is [60] Hz, the digital conversion value of the [10n] sample of the first input signal is averaged, and the input value obtained by removing common mode noise as the averaged digital value (Temperature detection value) is obtained.

  On the other hand, after controlling the A / D converter 14 to sample the first input signal over [12n] samples or [10n] samples as described above, the input control unit 15a performs the above-described microprocessor. (CPU) The input system is switched to sample the second input signal at least once using the remaining time in one operation cycle T. Then, the digital conversion value of the sampled second input signal is given to the calculation unit 15c and used for a predetermined calculation process.

  Incidentally, the first input signal is temperature information of the temperature detection target portion detected by the thermocouple 1 as described above, and the second input signal is for performing cold junction compensation of the thermocouple 1. It is a temperature value. The first input signal (the output of the thermocouple 1) should be accurately detected without being affected by disturbance, and the second input signal (the output of the cold junction compensation temperature sensor 13). Is a temperature value that can be considered to be relatively stable and substantially constant. For this reason, in this temperature detection device (signal processing device), the first input signal (output of the thermocouple 1) is sampled over [12n] samples or [10n] samples as described above, After removing the influence of the common mode noise by obtaining the average value, using the second input signal (the output of the cold junction compensation temperature sensor 13) that can be considered to be relatively stable and constant as described above, The cold junction compensation is performed.

  Thus, according to the temperature detection device (signal processing device) configured as described above, the first frequency within one operation period T of the microprocessor (CPU) 15 regardless of the frequency of the commercial AC power source that is the drive source. Since the common mode noise included in the input signal (the output of the thermocouple 1) is removed, this is compensated for the cold junction using the second input signal (the output of the temperature sensor 13 for cold junction compensation). The temperature of the temperature detection target part provided with can be detected with high accuracy.

  That is, as shown in FIG. 2, in the temperature detection device (signal processing device) according to the present invention, the common according to the power supply frequency included in the first input signal as shown in FIG. The mode noise is input at the sampling period Ts set as [10 / (6n)] m seconds as shown in FIG. When the power supply frequency is [50] Hz, as shown in FIG. 2C, the first input signal is input over [12n] samples to obtain the average value, and the power supply frequency is [60] Hz. In this case, as shown in FIG. 2 (d), the first input signal is inputted over [10n] samples to obtain the average value. Therefore, the common mode noise depending on the power supply frequency can be accurately and symmetrically detected for one wavelength (n wavelength) regardless of the power supply frequency, and the common mode noise can be removed by the averaging process. In addition, since the second input signal can be sampled using the remaining time within one operation period T of the microprocessor (CPU) 15 shown in FIG. The second input signals can be captured stably and reliably.

  Therefore, according to the temperature detection device (signal processing device) according to the present invention, the sampling frequency Ts of the A / D converter 14 is not changed according to the power supply frequency, so that the configuration can be simplified. There is no need to prepare a special A / D converter capable of changing the sampling frequency Ts. In addition, since there is no change in the response characteristic of the A / D converter accompanying the change of the sampling frequency Ts, the first and second input signals are stably digitally converted and fetched in accordance with preset specifications, It can be used for signal processing. In particular, even when one operation cycle T of the microprocessor 15 is set to be as short as 25 milliseconds, the first input signal can be captured in 20 milliseconds under the above-described conditions. In practice, a great effect can be obtained, such as being able to effectively cope with the high-speed processing operation of the temperature detection device (signal processing device).

  The present invention is not limited to the embodiment described above. Here, a case where the present invention is applied to a temperature detection device or a temperature control device using a thermocouple has been described as an example, but the present invention can be similarly applied to other signal processing devices driven by a commercial AC power supply. The setting of the power supply frequency by the frequency determination unit 18 may be automatic detection or manual operation. Furthermore, although the apparatus using a commercial AC power supply directly as a drive source has been described here, the commercial power supply is indirectly used such that the commercial AC power supply is once converted into DC and then the DC converted power is used as the drive source. The present invention can be similarly applied to a device to be used or a device that boosts and uses a commercial power supply via an inverter.

  The present invention can also be implemented in the same manner when an AC power supply other than a commercial AC power supply is used as a drive source, or when a DC power supply is converted into an AC and used as a drive source. In particular, even if spike noise associated with high-frequency switching in the inverter affects the common mode noise, the influence can be removed by the same method. In short, the present invention eliminates the influence of common mode noise caused by the frequency of the AC power supply as described above, and can be implemented with various modifications without departing from the scope of the present invention.

The figure which shows schematic structure of the temperature detection apparatus which is a signal processing apparatus which concerns on one Embodiment of this invention. The figure which shows the relationship between the sample timing with respect to the 1st and 2nd input signal and common mode noise in the temperature detection apparatus which concerns on this invention. The figure which shows the structural example generally of a temperature detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermocouple 13 Temperature sensor for cold junction compensation 14 A / D converter 15 Microprocessor (CPU)
15a Input control unit 15b Averaging processing unit 15c Calculation unit 17 Power supply unit 18 Frequency detection unit

Claims (4)

A signal processing device that operates using an AC power source as a drive source,
A / D conversion means for digitally converting the first and second input signals, respectively, and
A digital conversion value of the first input signal taken in via the A / D conversion means is averaged to remove common mode noise caused by the frequency of the AC power source included in the first input signal. Averaging means for
Arithmetic processing means for executing predetermined arithmetic processing using the average value obtained by the averaging processing means of the digital conversion value of the first input signal and the digital conversion value of the second input signal; Prepared,
The A / D conversion means repeatedly samples the first input signal for a number of times determined according to the frequency of the AC power source within one operation cycle set in the arithmetic processing means, and Each of the first input signal and the second input signal is converted into a digital signal at a constant period at which two input signals can be sampled at least once;
The signal processing apparatus, wherein the averaging processing means obtains an average value of digital conversion values of the first input signal repeatedly sampled over a number of times determined according to the frequency of the AC power supply. The A / D conversion means selectively samples the first and second input signals at a period of [10 / (6n)] m seconds (where n is a natural number),
The averaging processing means averages the digital conversion value of the first input signal over the number of consecutive [12n] samples when the frequency of the AC power source is [50] Hz, and the AC power source 2. The signal processing device according to claim 1, wherein when the frequency is [60] Hz, the digital conversion value of the first input signal is averaged over the number of consecutive [10n] samples. The first input signal is information indicating the temperature of a detection target obtained by a thermocouple, and the second input signal is a calibration temperature value obtained by a cold junction compensation temperature sensor,
2. The arithmetic processing unit obtains the temperature of the detection target by correcting an average value of digital conversion values of the first input signal using a digital conversion value of the second input signal. A signal processing device according to 1.   The signal processing apparatus according to claim 3, wherein the arithmetic processing unit generates a control signal for an external control target in accordance with the corrected temperature of the detection target.

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