JP2002257868A - Hum noise removal method of electrity measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove power source hum noise with high precision, only by software processings, without requiring modifications of the hardware configuration. SOLUTION: The method includes a first step for A/D-converting a signal to be measured over a data collecting time T integer times larger than a power source cycle Th, and a second step for A/D-converting the signal to be measured by the same data collecting time as the first step, after a time elapse of which is (1/2+N) times (N is zero or larger integer) larger than the power source cycle from a first step start time point. The average value of a first digital conversion value Vi1 obtained after A/D conversion completion of the first step and a second digital conversion value Vi2 obtained after A/D conversion completion of the second step is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing hum noise from an electric measuring instrument, and more particularly, to a method for removing noise (hum noise) generated from a transformer, a fluorescent lamp, a motor or the like driven by a commercial power supply. It is about.

[0002]

2. Description of the Related Art In measuring a DC voltage, a DC current or a DC resistance, a so-called hum noise caused by a commercial power supply often becomes a problem. FIG. 3 shows a basic circuit block diagram of a digital DC voltmeter as an example of an electric measuring instrument that uses a DC voltage as an object to be measured.

The digital DC voltmeter 100 has an input section 102 having a range selecting means for inputting a voltage from a device under test 101, and an A / D converter for digitally converting the voltage under test from the input section 102. 104 and A
There is provided a control means 105 for storing the digital data converted by the / D converter 104 in, for example, a memory 107, processing the digital data in a predetermined manner, and displaying the processed data on a display means 106 such as a display or a printer.

When the digital DC voltmeter 100 is driven by a commercial power supply, for example, when a fluorescent lamp is lit or near an electric motor, noise (hum noise) generated from these devices is superimposed on the signal to be measured. This may cause errors in the measurement.

As one of the methods for removing the hum noise caused by the commercial power supply, an A / D converter 104 is used, for example, of an integral type, and its integration time (data collection time) is used.
A / D conversion is known in which the time is an integral multiple of the power supply cycle of the commercial power supply, and this method will be described with reference to FIG.

[0006] For convenience of explanation, the hum noise Vh included in the signal under measurement is shown as a sine waveform, and in this example, the integration time Ti of the A / D converter 104 is set to one time of the power supply cycle Th. .

When the integration time Ti of the A / D converter 104 and the power supply cycle Th of the commercial power supply coincide with each other, the upper half wave and the lower half wave of the hum noise Vh cancel each other to become zero. . Thereby, the hum noise Vh included in the signal under measurement is obtained.
Is removed, and the measured voltage obtained by A / D conversion of the signal under measurement is displayed on the display means 106.

[0008]

The integration time Ti of the A / D converter 104 is determined by a clock incorporated in the control means (CPU) 105. The clock and the frequency of the commercial power supply are asynchronous. A / D converter 1
It is difficult to completely match the integration time Ti of 04 with an integral multiple of the power supply cycle Th. Further, even if the integration time Ti can be made to match an integral multiple of the power supply cycle Th, the power supply cycle itself may change due to a load change or the like.

As shown in FIG. 4, if a phase difference of .DELTA..theta. Occurs, for example, for one waveform between the integration time Ti and the power supply cycle Th, the hum noise Vh is integrated over a range of 2.pi. +. DELTA..theta. Radians (or 2.pi .-. DELTA..theta. Radians). Therefore, the hum noise corresponding to the phase difference Δθ is not canceled out, and the value Ve1 is included in the measured voltage as an error.

By the way, as described above, the A / D converter 1
In this case, a phase difference of Δθ radian is generated for one waveform between the integration time Ti and the power supply cycle Th in the A / D converter 1.
Assuming that three waveforms (three times as long as the power supply cycle Th) are converted into digital signals by the use of a digital signal 04, a digitally converted value Vi1 of the hum noise Vh is obtained by the following equation (1).
This is an error.

[0011]

(Equation 1)

[0012]

According to the present invention, the hum noise included in the signal to be measured can be removed with higher accuracy by processing exclusively by software, while the hardware configuration is the same as the conventional one. it can.

Therefore, the present invention provides an input unit to which a DC signal under test is inputted, an A / D converter for digitally converting the signal under test from the input unit, and a control unit for controlling the A / D converter. And a control means for processing the digital data in a predetermined manner and displaying the digital data on a display means. By making the data collection time of the digital data an integral multiple of the power supply cycle of the commercial power supply, In removing the hum noise caused by the included commercial power supply, a first step of performing A / D conversion of the signal under measurement over a data collection time that is an integral multiple of the power supply cycle, and Power cycle 1
/ 2 + N times (N is an integer of 0 or more) time, and the first
The signal to be measured is A
/ D conversion of the first digital conversion value obtained after completion of the A / D conversion of the first step and the second digital conversion value obtained after completion of the A / D conversion of the second step. It is characterized by finding the average value.

In this case, the second step is performed by the first step.
After the end of the step, 1/2 + N times of the power supply cycle (N is 0
The processing may be started after the elapse of the above (integer) time, which also achieves the above object.

Also, two A / D converters are provided, one of the A / D converters executes the first step, and the other A / D converter executes the second step. However, this also achieves the above object.

Assuming that there is a phase difference of Δθ per waveform between the data collection time of the A / D converter and the power supply cycle, the first digital conversion value obtained in the first step includes For example, an error of + Ve1 is included due to the phase difference Δθ.

Next, as the second step, data is collected for the same time as the first step. In this case,
There is a time difference between the first step and the second step that is at least half the power supply cycle.

According to this, in terms of waveforms, the data collection in the second step is started from a point shifted by a half waveform (π radians) from the first step. This means that for the waveforms collected in the first step,
The waveform for which data is collected in the second step means an inverted waveform.

The second digital conversion value in the second step also includes an error Ve1 due to the above-mentioned phase difference Δθ radian, but the polarity of the error Ve1 is negative as opposed to the first error. Therefore, by adding the first digital conversion value in the first step and the second digital conversion value in the second step, + Ve1 and -Ve1 are almost canceled, hum noise is removed, and the average value is obtained. Thus, the measured value of the signal under measurement is obtained.

[0020]

Next, an embodiment of the present invention will be described with reference to a waveform diagram of hum noise shown in FIG.

The basic hardware configuration is the same as that of FIG.
In this embodiment, the A / D converter 104 is a kind of integral type.
Although a Δ-type A / D converter is used, an A / D converter such as a successive approximation type may be used. The control means 105
, A CPU, a microprocessor, a microcomputer, or the like is used.

The control means 105 controls the A / D converter 10
4, the sampling rate and A / D conversion start / end timing are controlled. These control items may be input to the control unit 105 from an operation unit (not shown), or may be written in a control program of the control unit 105 in advance.

In order to remove power supply hum noise from the signal under measurement, the control means 105 collects A / D conversion data of the signal under measurement (for example, DC voltage) at least two times at predetermined time intervals, The average value of the digital conversion values is obtained.

That is, the control means 105 converts the signal under measurement into an A / D signal over a data acquisition time that is an integral multiple of the power supply cycle.
A first step of converting to obtain a first digitally converted value;
A second step of starting A / D conversion at the same data collection time as the first step after a lapse of 1/2 + N times (N is an integer of 0 or more) of the power supply cycle from the start of the first step; An average value of the first digital conversion value obtained after the A / D conversion in the first step and the second digital conversion value obtained after the A / D conversion in the second step is obtained.

In order to collect data from the signal under measurement in each of the first and second steps, the A / D converter 104
The operation time (start / end timing of A / D conversion) itself may be controlled, or the A / D converter 10
4 is set, for example, in a self-propelled state, and on the control unit 105 side,
The data collection time may be controlled (managed). Either case is included in the present invention.

Referring to FIG. 1, each step will be described. Also in this example, as described with reference to FIG. 4 above, between the integration time (data collection time) Ti of the A / D converter 104 and the power supply cycle Th, Δ
It is assumed that a phase difference of θ radians has occurred. It is also assumed that the hum noise Vh has a sine waveform.

First, as shown in FIG.
As a first step, the data acquisition time (A / D conversion time) Ti of the A / D converter 104 is set to one time the power supply cycle Th, and the A / D conversion of the signal under measurement is performed. In addition,
The power supply cycle Th here is a cycle calculated from 50 Hz or 60 Hz for a commercial power supply.

Assuming that the start point of the A / D conversion in the first step is, for example, 0 radians, the hum noise Vh is A / D converted over a range of 0 radians to 2π + Δθ radians, and a first digital conversion value Vi1 is obtained. It is stored in the memory 107. Therefore, the first digital conversion value Vi1 in the first step includes an error Ve1 caused by the phase difference Δθ radian.

Next, as shown in FIG.
After the start of the A / D conversion in the first step, the A / D conversion (integration) in the second step is started after an elapsed time of 1/2 + N times (N is an integer of 0 or more) of the data collection time Ti. However, in this example, since the elapsed time is Ti / 2 (N = 0), the elapsed time Ti / 2 corresponds to a half wave in terms of waveform.

Since the phase difference occurring during the elapsed time Ti / 2 is (1/2) Δθ radians, the start point of the second step is π + (1/2) Δθ radians. The data collection time Ti in the second step is also one time of the power supply cycle Th, as in the first step.

The data collection time Ti in the second step
, The hum noise Vh is π + (の 間 に) Δθ radian to 3π +
A / D conversion is performed over the range of (3/2) Δθ radians, and the second digital conversion value Vi2 is stored in the memory 107. Note that π + (1/2) Δθ radian to 2π
+ Δθ data in the range of radian
Shared by both steps.

After the completion of the second step, the control means 10
5 calculates an average value from the first digital conversion value Vi1 and the second digital conversion value Vi2 stored in the memory 107. Here, the digital conversion value Vi in the second step
Assuming that the error included in the control unit 10 is Ve2, the control unit 10
By the average value calculation at 5, the error Ve1 of the first step and the error Ve2 of the second step are relatively subtracted.

In the above embodiment, the first step and the second step are executed only once as one unit.
It may be repeatedly executed plural times. Although the error calculation is performed on the assumption that the hum noise is a sine wave, the result is the same even when the hum noise is assumed to be a cosine wave. Also,
In the above embodiment, the phase difference between the data collection time and the power supply cycle is + Δθ radian. However, even if the phase difference is −Δθ radian, hum noise can be similarly reduced.

As another embodiment (an embodiment of claim 2), as shown in FIG. 2, the second step is performed at a rate of 1/2 + N times (N is 0 or more) the power supply cycle after the end of the first step. (Integer) It may be controlled to start after the elapse of time.

Next, another embodiment will be described for each step. In this example, the integration time (data collection time) Ti of the A / D converter 104 is also the same as that described with reference to FIG. Between the power supply cycle Th and Δθ per waveform
It is assumed that a radian phase difference has occurred. It is also assumed that the hum noise Vh has a sine waveform.

Also in this example, first, as a first step, the data acquisition time Ti of the A / D converter 104 is set to one time the power supply cycle Th, and A / D conversion of the signal under measurement is performed. As a result, assuming that the start time of the A / D conversion is, for example, 0 radians, the hum noise Vh is A / D converted (integrated) over the range of 0 radians to 2π + Δθ radians, and the first digital converted value Vi1 is obtained. 107 is stored.

The first digital conversion value Vi1 in the first step also includes an error Ve1 caused by the phase difference Δθ. This first digital conversion value Vi1 is
The following equation (2) is represented by the first term in the first row.

[0038]

(Equation 2)

Next, after the A / D conversion in the first step, an elapsed time of 1/2 + N times (N is an integer of 0 or more) of the data collection time Ti is provided, and then the A / D conversion in the second step is performed. (Integration) is started. In this example, the elapsed time is set to Ti / 2 (N = 0). In terms of waveform, this elapsed time Ti / 2 corresponds to a half wave.

The data collection time Ti of the first step
The phase difference of (1/2) Δθ radian is accumulated during the elapsed time Ti / 2 with respect to the phase difference of Δθ due to the following equation, so the start time of the second step is 3π + (3/2) Δθ
Radians. The data collection time Ti in the second step is one time of the power supply cycle Th, as in the first step.

Since the phase difference of Δθ radian is accumulated during the data collection time Ti, the hum noise Vh is 3
A / D conversion is performed over a range from π + (3/2) Δθ radian to 5π + (5/2) Δθ radian, and a second digital conversion value Vi2 is obtained and stored in the memory 107.
The second digital conversion value Vi obtained in the second step
2 is given by the second term in the first row of equation (2) above.

After the completion of the second step, the control means 10
5 obtains an average value of the first digital conversion value Vi1 and the second digital conversion value Vi2 stored in the memory 107. That is, the calculation of (Vi1 + Vi2) / 2 is performed, but when adding Vi1 + Vi2, the error included in each digital conversion value Vi1, Vi2 is relatively subtracted.

An example of the calculation is the above equation (2). In this example, the error is approximately zero due to data collection of at most three waveforms of the hum noise. As can be seen by comparing this with Expression (1) in the conventional example described above, according to the present invention, hum noise can be significantly reduced.

As still another embodiment (third embodiment), two A / D converters are provided and one A / D converter is provided.
Control may be performed such that the first step is executed by the D converter and the second step is executed by the other A / D converter.

The present invention relates to a commercial power supply (50H in Japan).
This is effective not only for hum noise caused by z or 60 Hz) but also for hum noise caused by a special power supply at or around 400 Hz used in ships and the like. It is also effective against hum noise caused by a signal source other than the power source, and in interpreting the scope of the present invention, the commercial power source and the other signal sources should be treated equally.

[0046]

As described above, according to the present invention,
A first step of A / D-converting the signal under test over a data acquisition time that is an integral multiple of the power supply cycle; A second step of A / D converting the signal under measurement in the same data collection time as one step,
The hardware configuration is changed by calculating the average of the first digital conversion value obtained after the A / D conversion in the first step and the second digital conversion value obtained after the A / D conversion in the second step. The hum noise included in the signal under measurement can be removed with higher accuracy without the need for the following.

[Brief description of the drawings]

FIG. 1 is a hum noise waveform diagram for explaining an embodiment of the present invention.

FIG. 2 is a hum noise waveform diagram for explaining another embodiment of the present invention.

FIG. 3 is a block diagram of a general DC electric measurement device.

FIG. 4 is a hum noise waveform diagram for explaining a problem of the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Electricity measuring device 101 DUT 102 Input unit 104 A / D converter 105 Control means 106 Display means 107 Memory Th Power cycle Ti Data collection time

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G035 AA01 AA08 AB01 AC01 AD28 AD65 5J022 AA01 AA07 BA02 CA09 CB06 CE01

Claims (3)

[The claims] 1. An input section to which a DC signal under test is input, an A / D converter for digitally converting the signal under test from the input section, and an A / D converter. Control means for processing the digital data in a predetermined manner and displaying the digital data on a display means, wherein the data collection time of the digital data is set to an integral multiple of the power supply cycle of the commercial power supply, so that the commercial A hum noise removing method for an electric measuring instrument for removing hum noise caused by a power supply, wherein a first step of A / D-converting the signal under measurement over a data collection time that is an integral multiple of the power supply cycle;
A second step of A / D converting the signal under measurement with the same data collection time as the first step after a lapse of 1/2 + N times (N is an integer of 0 or more) of the power supply period from the start of the step. An average value of a first digital conversion value obtained after the A / D conversion in the first step is completed and a second digital conversion value obtained after the A / D conversion in the second step is completed. How to remove hum noise from electric measuring instruments. 2. The method according to claim 1, wherein the second step is started after a lapse of １ ／ + N times (N is an integer of 0 or more) times of the power supply cycle after the end of the first step. The hum noise removing method of the electric measuring instrument according to the above. 3. The method according to claim 1, wherein two A / D converters are provided, one of the A / D converters performs the first step, and the other A / D converter performs the second step. The method for removing hum noise of an electric measuring instrument according to claim 1, wherein: