JPH06324088A - Current measurement method - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the calculation error of sampling data and the calculation processing time when measuring the current flowing through an electric wire. [Configuration] An alternating current flowing through the electric wire 10 is detected by a current sensor 11
In the current measuring method in which the current is detected by the CPU 16d and the current is calculated by the CPU 16d, the CPU 16d fixes the execution time of the current sampling performed by the sample hold circuit 16a to a constant time regardless of the zero cross of the current. In addition, the execution time is shifted by a predetermined time and a plurality of times are set, the sample and hold circuit 16a samples the current 2 ⁿ (n is an arbitrary integer) times within each execution time, and the CPU 16d processes the sampled data in parallel. Then, the effective value and average value of the current are calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current measuring method for measuring a current flowing through an electric wire which is an object to be measured.

[0002]

2. Description of the Related Art Conventionally, there is a current measuring method of this type which measures an alternating current flowing through an electric wire which is an object to be measured. In the above measuring method, as shown in FIG. 5, a zero-cross point in a waveform of a fluctuating alternating current is detected, current is sampled from the zero-cross point to the next zero-cross point, and the sampling result ( The effective value, average value, etc. of the above-mentioned electric current were calculated | required by carrying out the arithmetic processing of (data). Note that noise and chattering may occur in the electric current flowing through the electric wire due to external influences.

Therefore, in the above measuring method, as shown in FIG. 5, when the noise and chattering occur near the zero cross, the current waveform is repeatedly influenced by these influences before and after the original zero cross. Since the state of zero crossing occurs, it becomes difficult to detect the original zero crossing. Therefore, in the conventional method, when the sampled data is within a certain current range (error range) by using a comparator,
The zero cross is judged, the data sampled from the point of the zero cross that is the result of this judgment to the point of the next zero cross is used as the numerator, and the sampling time is used as the denominator to perform arithmetic processing and output the result. It was

[0004]

However, in the above measuring method, a certain error range is set as an allowable range to detect the zero-cross point, so that there is a deviation between the original zero-cross point and the detected zero-cross point. However, there is a problem that a measurement error occurs due to this. Further, in the above measurement method, the zero crossing interval of the current waveform changes according to the change of the frequency, and the sampling time changes accordingly, so when calculating the effective value or average value of the current, the denominator is calculated. Since the process of determining the number of bytes of must be performed and then the process of comparing the denominator and the numerator must be performed, there is a problem that the calculation process takes time.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a current measuring method capable of reducing a calculation error of sampling data and shortening a calculation processing time when measuring a current. To aim.

[0006]

In order to achieve the above object, according to the present invention, a current flowing through an electric wire which is an object to be measured is detected by a current sensor, and the current is calculated by an arithmetic processing unit. In the method of measuring the current, the CPU of the arithmetic processing unit fixes the execution time of the current sampling to a fixed time, and performs sampling within the execution time performed by the sample hold circuit by 2 ⁿ (n is arbitrary). The current measuring method is provided in which the sampling execution time is shifted by a predetermined time, the sampling is sequentially performed, and the data sampled at each execution time is processed in parallel.

[0007]

The sampling execution time is fixed regardless of the zero cross of the current, the execution times are shifted by a predetermined time, and a plurality of them are set, and the data sampled 2 ⁿ times in each execution time are processed in parallel. Calculate the effective value and average value of the current. Therefore, it is possible to reduce the calculation error and the calculation processing time that occur when measuring the current flowing through the electric wire by sampling and calculating the calculation.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings of FIGS. FIG. 1 is a block diagram showing an embodiment of a measuring device for measuring the electric current of an electric wire by using the electric current measuring method according to the present invention. In the figure, the measuring device includes a CT type current sensor 11 provided near an electric wire 10, a noise filter 12, amplifiers 13 and 15, and the amplifiers 13 and 1 described above.
5, a full-wave rectifier circuit 14 interposed between them, and an arithmetic processing unit 17 for sampling and arithmetically processing the full-wave rectified current.

The CT type current sensor 11 is as shown in FIG.
AC current flowing through the electric wire 10 is detected,
The noise component of the generated current signal is
Removed and further amplified by amplifiers 13 and 15
At the same time, the full-wave rectification circuit 14 performs full-wave rectification for arithmetic processing.
Input to the section 16. The arithmetic processing unit 16 is, for example, a micro
From a computer (hereinafter referred to as "microcomputer")
Therefore, the microcomputer 16 has a fixed sampling execution time.
For example 2 ⁿ(N is an arbitrary integer) Number of times sampling
Sample hold circuit 16a for performing the above sampling
To convert the converted analog data to digital data
Log / digital conversion circuit (hereinafter referred to as “A / D conversion circuit”)
Say. ) 16b and a memory for storing the converted data.
When the memory 16c and the above-mentioned respective parts 16a to 16c are controlled
By reading the data stored in the memory 16c,
It is composed of a CPU 16d that performs arithmetic processing.

As a first embodiment, the CPU 16d has a configuration shown in FIG.
As shown in, the data sampled 2 ⁿ times within a fixed sampling execution time is used as the numerator, and the above execution time is used as the denominator to perform the arithmetic processing within the predetermined arithmetic processing time to obtain the effective value and average value of the current. Is calculated, the result is output to, for example, a host computer, and the next sampling is executed.

Therefore, in this embodiment, the zero crossing of the current is performed.
Sampling within a certain execution time,
Since the arithmetic processing is performed after the above sampling, zero cross
The measurement error due to detection is reduced, and noise and
It is less affected by terring and reduces calculation error
it can. Furthermore, in this embodiment, the support is performed within a certain execution time.
2 in the sample hold circuit 16a ⁿSampling times
Therefore, the sampled data is used as the numerator and the execution time
When performing arithmetic processing of division with denominator as the denominator, the CPU 16
The shift register (not shown) in d
The processing time can be shortened. That is, in the above arithmetic processing
The CPU 16d, for example, operates in binary numbers.
The number is 2¹When multiplying, the cash register in the CPU 16d
You only have to shift 1 bit by the shift operation of the star,
Some number (2¹+2⁰) Times, that is, 3 times,
The data to be tripled is stored in the memory 16c or the like.
The value after shifting the above register by 1 bit and the above memo
Add the data stored in memory 16c, and add 3 times the original value.
Must be a value. As a result, the performance performed by the CPU 16d
Arithmetic processing is 2ⁿDouble the number of calculation processing steps
The sampled data can be calculated in a short time.
It

Further, according to the current measuring method of the present invention,
As a second embodiment, for example, as shown in FIG. 3, a plurality of sampling execution times set to be constant are shifted by a predetermined time (for example, arithmetic processing time) and set, and the sample hold circuit 16a is set within each execution time. Data sampling is performed 2 ⁿ times with the CPU 16 after each execution time described above.
It is also possible to configure the microcomputer 16 so that d processes the sampling data in parallel and outputs the calculation result.

In this case, since the next sampling time is started in the middle of the previous sampling time, the calculation of the sampled data can be performed in a shorter time as compared with the above embodiment. In addition, FIG. 4 is a configuration diagram showing an embodiment of a measuring device for measuring the current of a three-phase four-wire type electric wire by using the current measuring method according to the present invention.
In FIG. 4, the same components as those in FIG. 1 are designated by the same reference numerals for convenience of description.

In the figure, current sensors 11a to 11d are shown.
Are provided near the four electric wires not shown,
U-phase, V-phase, W-phase, and N-phase alternating currents flowing through the respective electric wires are detected. The detected current signals have noise components removed by noise filters 12a to 12d, and further amplifiers 13a to 13d. Is amplified by, and full-wave rectified by the full-wave rectifier circuits 14a to 14d, and input to the multiplexer 19 configured by analog switches. Further, the respective current signals amplified by the amplifiers 13a to 13c are added by the adding circuit 17a, and the U phase +
It becomes a V-phase + W-phase current signal, full-wave rectified by the full-wave rectification circuit 14e, and input to the multiplexer 19. The current signal amplified by the amplifier 13d and the current signal from the adder circuit 17a are added by the adder circuit 17b into a U-phase + V-phase + W-phase + N-phase current signal, which is full-wave rectified by the full-wave rectifier circuit 14f. It is then input to the multiplexer 19.

The multiplexer 19 sequentially selects the above-mentioned six types of input signals, and an amplifier 15 provided in the subsequent stage.
Is output to the microcomputer 16 via. Microcomputer 16
In the same manner as in the case of FIG. 3, for each input current signal, a plurality of execution times of sampling set to be constant are shifted by a predetermined time, and a plurality of times are set. Data sampling is performed 2 ⁿ times, the CPU 16d performs parallel arithmetic processing on the sampling data after each execution time, and outputs the arithmetic result corresponding to each current signal through the digital output circuit 19. In addition, the DIP switches 20a to 20
c sets various judgment values, and these judgment values are stored in the CPU 1
It outputs to 6a.

Therefore, also in this embodiment, sampling is performed within a fixed execution time regardless of the zero crossing of the current,
Since the arithmetic processing is performed after the sampling, the measurement error due to the zero-cross detection is reduced, the measurement error is less likely to be influenced by noise and chattering, and the calculation error can be reduced. In addition, in the present embodiment, sampling of the data of the detected current and calculation processing are performed with a certain time delay,
Since a plurality of parallel processes are performed, the output interval of the calculation result can be shortened.

[0017]

As described above, according to the present invention, in the current measuring method for detecting the current flowing through the object to be measured and performing the arithmetic processing to measure the current, the execution time of the current sampling Is fixed to a fixed time, and sampling is performed 2 ⁿ (n is an arbitrary integer) times within the execution time, and the data sampled during the execution time is arithmetically processed. Therefore, when measuring the current, The calculation error of the sampling data can be reduced and the calculation processing time can be shortened.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a measuring device for measuring a current of an electric wire by using a current measuring method according to the present invention.

FIG. 2 is a current waveform diagram for explaining the first embodiment of the current measuring method according to the present invention shown in FIG.

3 is a current waveform diagram for explaining a second embodiment of the current measuring method according to the present invention shown in FIG. 1. FIG.

FIG. 4 is a configuration diagram showing an embodiment of a measuring device for measuring the current of a three-phase four-wire type electric wire using the current measuring method according to the present invention.

FIG. 5 is a current waveform diagram for explaining a conventional current measuring method.

[Explanation of symbols]

 10 wire 11, 11a-11d current sensor 12, 12a-12d noise filter 13, 13a-13d, 15 amplifier 14, 14a-14f full-wave rectifier circuit 16 arithmetic processing unit (microcomputer) 16a sample hold circuit 16b analog / digital conversion circuit 16c memory 16d CPU

Claims (2)

[Claims] 1. A current measuring method for detecting a current flowing through an object to be measured and performing arithmetic processing to measure the current, wherein an execution time of sampling the current is fixed to a fixed time, and Sampling within run time is 2 ⁿ
(N is an arbitrary integer) times, and the data sampled at the execution time is arithmetically processed. 2. A current measuring method for detecting a current flowing through an object to be measured and performing arithmetic processing to measure the current, wherein an execution time of sampling the current is fixed to a fixed time, and Sampling within run time is 2 ⁿ
(N is an arbitrary integer) times, the sampling execution time is shifted by a predetermined time, the sampling is sequentially performed, and the data sampled at each execution time is processed in parallel. Measuring method.