JP4384281B2 - Current measuring apparatus and current measuring method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method suitable for measuring alternating current.
[0002]
[Prior art]
2. Description of the Related Art A non-contact type current measuring device is known in which a power cable is sandwiched between clamp type CT sensors and current is measured via a magnetic field generated in the power cable. This non-contact type current measuring device does not require wiring work and can realize a handy measuring device that operates on a battery. For this reason, it is used for various purposes such as measuring and monitoring the power consumption of individual power lines in factories, offices, and homes. Furthermore, some clamp-type current measuring devices in recent years are capable of displaying not only the current itself but also integrated power or instantaneous power by converting it into a power value by a calculation process.
[0003]
[Problems to be solved by the invention]
Measuring power consumption using such a current measuring device is important for taking power saving measures and confirming the results. On the other hand, leakage monitoring is also very important in order to reduce power consumption and to safely operate an electric device connected to a power line. Continuing electric leakage can be confirmed by a method such as comparative examination of the power consumption of each device and the power consumption of each power line. However, since instantaneous current fluctuations do not appear in the process of being integrated into electric power, it is impossible to detect instantaneous electric leakage that occurs due to various causes. There is a need for a special device that can record the instantaneous current for checking an earth leakage breaker, but a device that can be used easily has not been developed.
[0004]
Therefore, an object of the present invention is to provide a current measuring device that can monitor or record a load current and can also monitor or record an instantaneous electric leakage.
[0005]
[Means for Solving the Problems]
For this reason, the current measuring device of the present invention is a current measuring device capable of measuring the current values of a plurality of alternating currents having different frequencies, and is obtained from a plurality of instantaneous current values obtained periodically, with a short number of units of several waves . Means for calculating an effective value of the alternating current at every one time interval, and first recording means for obtaining and recording an average value of the effective values at every second time interval longer than the first time interval ; the maximum value of these effective values, have a second recording means for recording asking the same or shorter every third time interval and the second time interval longer than the first time interval, the first The time interval is an integral multiple of the period of a plurality of alternating currents having different frequencies to be measured . The current measuring method of the present invention is a current measuring method capable of measuring the current values of a plurality of alternating currents having different frequencies, and is a first short unit of several waves from a plurality of instantaneous current values obtained periodically. A step of calculating an effective value of the alternating current at each time interval, and a first recording step of obtaining and recording an average value of the effective values for each second time interval longer than the first time interval ; the maximum value of these effective values, have a second recording process of recording asking the same or shorter every third time interval and the second time interval longer than the first time interval, the first time The interval is an integral multiple of the period of a plurality of alternating currents having different frequencies to be measured .
[0006]
In the current measuring apparatus and the measuring method of the present invention, the effective value is calculated from the instantaneous current value of the alternating current periodically measured at every short first time interval of several tens or several hundreds msec, and the measurement is performed. The load current can be determined by averaging the values every second time interval that is somewhat longer than the first time interval. Therefore, power consumption can be monitored or recorded. On the other hand, a third time interval longer than the first time interval and equal to or shorter than the second time interval is set, and an instantaneous increase / decrease in the current value is obtained by obtaining the maximum value of the effective value therebetween. Can be recorded. Therefore, instantaneous leakage can be monitored or recorded. For this reason, the current measuring apparatus and measuring method of the present invention can record or monitor the leakage current as well as the load current.
[0007]
In the current measuring apparatus and current measuring method of the present invention, it is important to obtain the effective value of the alternating current in a short time. When the first time interval is set to a positive multiple of the period of the alternating current to be measured, an effective value can be obtained simply by averaging the instantaneous current values periodically measured during that period. Therefore, the effective value of instantaneous current can be calculated with a simple digital circuit. The first time interval may be 20 msec if it is an AC current of one cycle, for example 50 Hz, but it is desirable to measure at intervals of about three waves in consideration of the measurement cycle or the tolerance of the AC frequency.
[0008]
For this reason, it is necessary to be able to set the first time interval according to the frequency of the alternating current. However, when the AC power source is a measurement target, the first time interval is set to 100 msec, It is not necessary to change the first time interval in the 60 Hz region. Therefore, measurement errors can be prevented.
[0009]
The average value and the maximum value are recorded together with the time at which they are obtained, so that temporal variations can be found. However, as the measurement time increases, the memory capacity for recording data increases. Therefore, in the first recording means and the recording process, the memory capacity is saved by sequentially recording the average value obtained every second time interval. Even if the time is not recorded, if the average value is recorded in order, the time when the average value is obtained based on the second time interval can be obtained later.
[0010]
On the other hand, for the purpose of monitoring leakage, the second recording means and the recording process do not require data with small fluctuations. Therefore, when the maximum value obtained every third time interval is equal to or higher than a predetermined detection level, the maximum value and time are recorded. As a result, the maximum number of times of recording can be reduced, so that the memory capacity can be saved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be further described below with reference to the drawings. FIG. 1 shows a current measuring device according to the present invention and a system for measuring current using this current measuring device. The current measuring apparatus 1 of this example is a measuring apparatus that connects a clamp type CT sensor 2 and measures the current flowing through the measured line with the clamped CT sensor 2 sandwiching the measured line such as the power cable 9. The current can be measured in a contact state. The measured current value is once stored in the measuring device and transmitted to the personal computer 4 via the communication cable 3 at an appropriate timing for analysis. As described above, by using the measuring apparatus 1 of this example, it is possible to construct a data logger system for current that performs processing such as display and analysis of measured current data on a personal computer.
[0012]
The measuring apparatus 1 of this example is provided with two connectors 11 to which a clamp-type CT sensor can be connected, and the data obtained from each clamp-type CT sensor can be uniquely processed even in the measurement and recording functions described later. It is like that. Therefore, one unit can measure and record for two channels, and the single measuring apparatus 1 can measure and monitor the currents of different lines to be measured. However, for the sake of simplicity, the function for one channel will be described below.
[0013]
The measurement apparatus 1 of this example is provided with an LCD panel 12 at the center that can monitor measurement data, measurement conditions, and the like. Moreover, the battery is built in and the whole apparatus is gathered up in the handy size. For this reason, it is also possible for the user to monitor the current value at an appropriate location by carrying it for a patrol inspection or the like. Then, the measured data can be collectively transferred to a personal computer via a communication cable or the like and analyzed. On the other hand, the clamp-type CT sensor 2 can be set on a predetermined power cable 9 and the current value can be monitored over a long period. When measuring over such a long period, the AC adapter 5 is used for home use. It is desirable to operate with a power source. It is of course possible to transmit the measurement data by other transmission means such as a telephone line or radio instead of the communication cable.
[0014]
FIG. 2 shows a schematic function of the current measuring apparatus 1 of this example in a block diagram. The measuring apparatus 1 of this example includes a data acquisition unit 14 that acquires an instantaneous current value by the clamp-type CT sensor 2, an effective value calculation unit 16 that calculates an effective value from the instantaneous data, and an average current value from the effective value. An average value recording unit 18 for obtaining and recording, and a peak value recording unit 19 for obtaining and storing the maximum value from the effective value are provided.
[0015]
The data acquisition unit 14 digitally converts the current value detected by the clamp-type CT sensor 2 at every predetermined measurement interval To, and temporarily stores it as instantaneous data φ1 in the memory 15 for instantaneous data. In addition, the effective value calculation unit 16 calculates the effective value φ2 from the instantaneous data φ1 obtained during an appropriate sampling interval (first time interval) Ts in accordance with the AC current cycle longer than the measurement interval To. And stored in the effective value memory 17. Further, the average value recording unit 18 calculates the average current value φ3 by averaging the effective value φ2 calculated during the recording interval (second time interval) Tr longer than the sampling interval, and stores the average value in the RAM 20. Record in area 21. Then, the peak value recording unit 19 obtains the maximum value φ4 of the effective value φ2 calculated during the specific time (third time interval) Tp different from the recording interval and stores it in the peak value storage area 22 of the RAM 20. Remember.
[0016]
Further, the measuring apparatus 1 communicates with a control unit 25 that instructs the timing of processing in each of these processing units 14, 16, 18, and 19 and performs overall control, and a host machine such as a personal computer, A communication unit 26 capable of transmitting data stored in the RAM 20 and a display unit 27 capable of displaying data obtained in the RAM 20 on the monitor 12 are provided.
[0017]
FIG. 3 is a flowchart showing a processing procedure in the measuring apparatus 1 of this example. Below, the function of each processing unit will be further described with reference to this flowchart. The measurement apparatus 1 of this example first acquires the instantaneous data (instantaneous current value) φ1 by the data acquisition unit 14 at step 32 when the timing is the measurement interval To at step 31. The measurement interval To is desirably a sufficiently short interval in order to improve data accuracy. In the measuring apparatus of this example, for example, instantaneous data φ1 is acquired and output to the memory 15 by analog-digital conversion of the output of the clamp-type CT sensor 2 every 1 msec.
[0018]
If it is the timing of the sampling interval Ts in step 33, the effective value φ2 is calculated by the effective value calculator 16 in step 34. In order to easily calculate the effective value of the alternating current digitally, it is desirable to set a time that is an integral multiple of the period of the alternating current as the sampling time Ts. Furthermore, it is desirable to use instantaneous data for several waves in order to calculate an effective value with high accuracy in consideration of tolerances such as period tolerance and sampling time Ts. For example, considering the responsiveness of a breaker and the like, the initial current of the starting current, etc., about three waves are desirable. Therefore, if an alternating current of 50 Hz is measured, a sampling interval (first time interval) Ts of 60 msec is appropriate if instantaneous data for three waves is used, and if an alternating current of 60 Hz is measured. A sampling interval Ts of 50 msec is appropriate. When a sampling time Ts that is an integral multiple of the AC current period Tc is set, the instantaneous data φ1 changes as shown in FIG. Accordingly, the value of each instantaneous data φ1 is squared and added to obtain the square root of the average value, that is, the effective value φ2 of the current at the sampling interval Ts can be calculated by taking the square average.
[0019]
The sampling interval Ts is not limited to the above value, but it is desirable that the sampling interval Ts be short in consideration of monitoring instantaneous electric leakage. In this example, it is important to select the sampling interval Ts in accordance with the AC frequency. If the sampling interval Ts deviates from an integral multiple of the AC cycle Tc, the accuracy of the effective value deteriorates. Considering measuring the current value of a power supply system using a commercial power supply, 50 and 60 Hz are used in each region in Japan, so it is necessary to change the setting for each region.
[0020]
On the other hand, when 100 msec, which is the least common multiple of the 50 and 60 Hz periods, is set as the sampling interval Ts, the sampling time is slightly longer than the above, but it is not necessary to change the setting for each region, and an effective effective value can always be obtained. Can do. Therefore, it is desirable that the user can set the sampling interval Ts to any one of 50, 60 and 100 msec.
[0021]
Thus, in the current measuring apparatus 1 of this example, an effective value can be obtained at a short sampling interval of about several tens of msec by averaging the instantaneous data in accordance with the timing of the alternating current cycle. Therefore, the average current value can be calculated based on the effective value, and the peak current can be monitored based on the effective value. In addition, since the measuring apparatus 1 of this example uses a direct current amplifier as an input amplifier that amplifies the signal from the clamp type CT sensor 2, it is not limited to alternating current, and is a case where an alternating current component is mounted on direct current or direct current. The effective value can be calculated in the same procedure.
[0022]
Further, in the measuring apparatus 1 of this example, if the timing of the recording interval Tr is in step 35, in step 36, the average value φ2 between the recording intervals Tr is averaged by the average value recording unit 18 to obtain the average current φ3. Ask. Then, the average current φ3 obtained in the recording area 21 of the RAM 20 is recorded in order. Therefore, as shown in FIG. 5, even if the effective value fluctuates during the recording interval Tr, the average current value φ3 during that time can be recorded, and the power consumption can be easily reduced using this value. Can be sought. Of course, it is also possible to input a voltage and a power factor and record it in terms of power consumption. However, in many cases, such processing is performed when data is analyzed by a personal computer.
[0023]
In the measuring apparatus 1 of this example, the user can set an appropriate time with the recording interval Tr between 1 minute and 60 minutes. In the memory area 21 for storing the average value φ3, 8000 pieces of data can be recorded. Further, by recording the average current value φ3 obtained at every recording interval Tr in order, the average current value φ3 can be changed from the recorded order without recording the time at which each average current value φ3 was obtained. The obtained time can be obtained. For this reason, the memory area 21 which is an average value storage area can be fully used to record the average current value φ3, and the average current value for 133 hours at the shortest and 333 days at the longest is recorded in the memory. Can do.
[0024]
In the measuring apparatus 1 of this example, if it is the timing of the specific time Tp in step 37, the maximum value φ4 of the effective value φ2 obtained during the specific time Tp in step 38 and the time at that time are recorded in the RAM 20. Record in area 22. In the measuring apparatus 1 of this example, as shown in FIG. 6, only when the maximum value φ4 is equal to or higher than the detection level DL, the value φ4 and the time are recorded. Since the effective value φ2 always varies, there is always a maximum value during the specific time Tp. However, the maximum value φ4 obtained in this step is mainly intended to detect instantaneous leakage, and therefore it is not necessary to record the maximum value in the range where the normal current value fluctuates. Therefore, by setting the detection level DL, the peak value can be more easily discriminated, and the memory capacity required for recording the peak value φ4 can be reduced.
[0025]
In the measurement apparatus 1 of this example, the user can select an optimum value for the detection level DL. On the other hand, the specific time Tp is preset to 1 minute, and fluctuations in peak current can be monitored and recorded in minutes. The time recorded together with the peak value φ4 may be the time when the peak value φ4 is obtained, or may be the time when the maximum value is recorded every specific time Tp. In this example, since a time resolution of 1 minute can be obtained, even in the latter case, sufficient accuracy is provided as information for specifying the cause of leakage.
[0026]
In the measuring apparatus of this example, 2000 peak values φ4 can be recorded in the peak value memory 22 together with time data.
[0027]
In this way, the measuring apparatus 1 of this example records the values of the average current and the peak current in the RAM 20 and transfers the data in the RAM 20 to the host via the communication cable 3 at a preset timing or a request from the host side. To the personal computer 4. As described above, the measurement apparatus 1 of this example has a sufficient memory capacity for normal measurement, but the memory capacity may be insufficient depending on the measurement situation. For this reason, the measuring apparatus 1 has two one-time and two endless measurement modes. In the one-time mode, when the memory capacity is full, recording of the average current and the peak current is stopped at that time. On the other hand, in the endless mode, when the memory capacity is full, the recording returns to the beginning of the memory address while overwriting the average current and the peak current. The user can select which mode is used for measurement.
[0028]
In the above, the present invention has been described based on a current detection device that detects current with a clamp-type CT sensor. However, the present invention is not limited to a measurement device using a non-contact type sensor such as a clamp-type CT sensor. Of course, the present invention can also be applied to a system that directly detects current using the above. However, a clamp-type current detection device that can measure without affecting the power supply circuit and the like, and can be easily attached and detached, is suitable for configuring a data logger system for current measurement as shown in FIG. ing.
[0029]
【The invention's effect】
As described above, in the current measuring apparatus of the present invention, since the effective value can be calculated by about three power supply frequencies, the responsiveness is very good. On the other hand, since the main purpose of conventional clamp meters is to obtain electric power, a dedicated IC is used to convert measured data into effective values, and the data is processed in an analog manner so that it can handle AC frequencies. However, the time constant for obtaining the effective value is long. On the other hand, the measuring apparatus 1 of the present example aims to obtain a peak value so that leakage monitoring can be performed together with the average current. For this reason, the sampling time is set to several waves based on the period of the alternating current. The effective value of the alternating current is obtained at short intervals by digitally processing the instantaneous data. Since effective values are obtained at short intervals, it is possible to capture instantaneous current fluctuations along with the average value. By recording both the average current and peak current, the leakage current to load current can be recorded together. Can be measured, monitored, recorded and analyzed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a current measuring device according to the present invention and a system for measuring current using the same.
2 is a block diagram showing a schematic configuration of the current measuring device shown in FIG. 1; FIG.
FIG. 3 is a flowchart showing a process for measuring an average current and a peak current in the current measuring apparatus shown in FIG. 1;
FIG. 4 is a diagram showing how an effective value is obtained from instantaneous data.
FIG. 5 is a diagram showing how an average current is obtained from an effective value.
FIG. 6 is a diagram illustrating a state in which a peak current (maximum value) is obtained from an effective value.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Current measuring device 2 Clamp type CT sensor 3 Communication cable 4 Personal computer 9 Power cable 12 Display part (LCD panel)
14 Data acquisition unit 16 RMS value calculation unit 18 Average value recording unit 19 Peak value recording unit 20 RAM
25 Control unit 26 Communication unit

Claims (6)

A current measuring device capable of measuring a plurality of alternating current values having different frequencies,
Means for calculating an effective value of the alternating current for each short first time interval of several wave units from a plurality of instantaneous current values obtained periodically;
A first recording means for obtaining and recording an average value of a plurality of effective values for each second time interval longer than the first time interval;
A second recording means for obtaining and recording a plurality of maximum values of the effective values for each third time interval longer than the first time interval and equal to or shorter than the second time interval;
The current measurement device, wherein the first time interval is an integral multiple of a period of a plurality of alternating currents having different frequencies to be measured.   2. The current measuring device according to claim 1, wherein an alternating current of 50 Hz and an alternating current of 60 Hz can be measured, and the first time interval is 100 msec.   3. The first recording means according to claim 1, wherein the first recording means sequentially records an average value obtained every second time interval, and the second recording means obtains every third time interval. A current measuring device that records the maximum value and time when the maximum value obtained is equal to or greater than a predetermined detection level. A current measurement method capable of measuring the current values of a plurality of alternating currents having different frequencies,
Calculating an effective value of the alternating current for each short first time interval of several wave units from a plurality of instantaneous current values obtained periodically;
A first recording step of obtaining and recording an average value of a plurality of effective values for each second time interval longer than the first time interval;
A second recording step of obtaining and recording a plurality of maximum values of the effective values for each third time interval longer than the first time interval and equal to or shorter than the second time interval;
The current measurement method, wherein the first time interval is an integral multiple of a period of a plurality of alternating currents having different frequencies to be measured.   5. The current measuring method according to claim 4, wherein an alternating current of 50 Hz and an alternating current of 60 Hz can be measured, and the first time interval is 100 msec.   6. The average value obtained for each of the second time intervals in the first recording step is recorded in order in the first recording step, and is obtained for each of the third time intervals in the second recording step. A method for measuring current, wherein the maximum value and time are recorded when the maximum value obtained is equal to or greater than a predetermined detection level.

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