JP2020026959A - Clamp meter - Google Patents

Abstract

To provide a clamp meter that can notify a measurement state even when a display of a measured value cannot be seen, and can efficiently perform a work and the like for searching a leakage current location.SOLUTION: A clamp meter is provided with means for notifying by sound or light in addition to displaying a measured value when an effective value and a peak value of a leakage current detected in a current of a measurement target wire are stable within a predetermined fluctuation range and exceed a preset threshold value, so as to inform an operator that there is a phenomenon to be measured even if the display is not visible.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a clamp meter.

  2. Description of the Related Art A clamp meter is used to search for a leak current location on a distribution board or the like when a leak current occurs. To measure the leakage current, clamp the current sensor to the live wire under measurement to acquire the current signal of the wire under measurement, and calculate the current measurement value from the signal acquired by the sensor in the measuring device itself Output and measure, and output the measured value.

The operation of detecting a leakage current using a clamp meter will be described.
When a leakage current occurs, the leakage monitoring device and the leakage breaker are activated, and it is known that a leakage has occurred, and the location of the leakage is searched.
In the search for a leak location, for example, in a distribution board, a search is performed by sequentially detecting a leak from a master to a terminal. In the search for leakage, clamp the round-trip line of the wiring to check for leakage. In the normal case, the measured value becomes zero due to the current reciprocation. On the other hand, since the earth leakage is a ground fault and there is no reciprocation of the current, if an earth leakage occurs, the amount of the earth leakage can be measured with a clamp meter. First, the clamp meter is clamped to the main wiring, and the measured value is displayed on the display section of the clamp meter to determine whether or not leakage has occurred.The operator can check this displayed value to determine whether or not leakage has occurred. Confirm. The current is measured by clamping the reciprocating line from the master to the lower hierarchy.
Since the amount of leaked current is known from the leakage monitoring device, the leakage breaker, and the leakage check at the main unit, the search is narrowed down to terminals where the amount of leaked current is flowing.
Such a leak location search operation is performed while clamping the wiring of each layer in a distribution board in which a large number of wirings are formed and checking the measured value displayed on the clamp meter.

  However, since a large number of wirings are provided on the distribution board, even if the wiring is clamped, the display of the clamp meter does not face the operator depending on the location of the clamp, and the displayed measured value is read by the operator. May not always be able to confirm. For example, when wiring above or below a distribution board is clamped, it is not easy to visually observe the measured values. Also, in general, the wiring is horizontal to the operator, so when clamped to the electric wire to be measured, the display of the clamp meter is usually directed sideways to the operator. In some cases, the clamp meter is not suitable for the operator and the clamp meter needs to be directed to the operator in order to visually check the display of the measured values. Further, it is also difficult to clamp the display unit to the wiring at a place where a large number of wirings are collected so that the operator can see the display unit.

  Patent Literature 1 discloses that a threshold value is set in advance in such a leakage current measurement with a clamp meter, a measured current value is compared with the threshold value, and when the measured value exceeds the threshold value, The invention describes driving a vibration motor, outputting a warning sound, blinking a measured value to be displayed, and the like.

JP 2009-068883 A

However, when measuring the leakage current, the measured value fluctuates due to external noise or the opening and closing of the clamp sensor. There is a risk that the part will be recognized.
In addition, there is a possibility that an operator may make a measurement without noticing that the clamp sensor is not closed, and in such a case, the measured value itself is not accurate and the measured value is not correct. It is stable, and the search operation is redone without being able to detect the leakage current, so that it takes a long time to search for a leakage point.

  An object of the present invention is to provide a clamp meter for measuring the leakage current, which facilitates the work of searching for a leakage current portion and can improve the efficiency.

  According to a first aspect of the present invention, there is provided a clamp meter including a signal processing unit including a signal processing unit that receives a signal of a measurement target wire acquired by a sensor that clamps the measurement target wire and calculates a measurement value. The unit has a display unit for displaying the measured value of the current of the electric wire to be measured, and the signal processing unit is configured to display the measured value when the fluctuation range between the effective value and the peak value of the measured current is within a predetermined range. Is determined to be stable, and when the measured value at the time of stabilization exceeds the set threshold value, means for notifying that the measured value has exceeded the threshold value by sound or light It is characterized by having.

  Further, the present invention provides two paths for a signal to be input to the signal processing unit, a path for inputting the signal to the signal processing unit via a filter, and a path for inputting the signal to the signal processing unit without passing through the filter. And a signal that does not pass through a filter, and a signal that passes through a filter are input in parallel to a signal processing unit, and the signal processing unit passes a measurement value from the signal that does not pass through a filter and a signal that passes through a filter. There may be comparison means for comparing the measured value from the signal.

  Determine whether the measured value is stable, compare it with the threshold value, and output sound and light when it exceeds the threshold value, so that accurate measurements can be made and leakage current of workers It is possible to improve the efficiency of the exploration work of the location.

It is a figure showing an example of composition of a clamp meter which is an embodiment of the invention. It is a flowchart explaining the work of earth leakage detection. 5 is a flowchart illustrating an operation of the clamp meter according to the embodiment of the present invention. 5 is a flowchart illustrating an operation of the embodiment of the present invention for determining whether a measured value is stable.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of a configuration of a clamp meter according to an embodiment of the present invention.

  This clamp meter includes a current sensor 10 and a measuring device main body 20, and the current sensor 10 is selected and connected to the measuring device main body 20 according to a measurement application. As the current sensor 10, there is a current sensor that includes a magnetic core that forms a closed magnetic path that is annularly arranged around the electric wire to be measured, and a magnetic sensor that includes a Hall element and a detection coil that detects the magnetism of the magnetic core. There is also a cable type flexible current sensor.

  The measuring device main body 20 includes an amplifier 21 to which the output of the current sensor 10 is input, a low-pass filter (LPF) 22 for removing a signal having a frequency higher than the commercial frequency from the signal of the amplifier 21, and an analog conversion of the output of the amplifier 21. Analog-to-digital converter 24, an analog-to-digital converter 25 for converting the output of the low-pass filter 22 to analog, and a CPU (Central Processing Unit) 26 to which the output of the analog-to-digital converter 24 and the output of the analog-to-digital converter 25 are input. , A memory 27, an operation unit 31 connected to the CPU 26 via an interface (I / O) 28, a communication unit 32, a display unit (LCD) 33, a sound output unit 34, and an LED 35. ing.

The operation of the measuring device shown in FIG. 1 will be described.
The signal output from the current sensor 10 is amplified by the amplifier 21, and one branched signal is input to the analog / digital converter 24, converted into a digital signal, and output to the CPU 26. The other branched signal is input to the analog-to-digital converter 25 via the low-pass filter 22, converted into a digital signal, and output to the CPU 26. The low-pass filter 22 has a cutoff frequency of, for example, 150 Hz or 180 Hz, and is a filter that passes a commercial frequency component and removes a high frequency component mixed in the commercial frequency. Note that a low-pass filter indicated by reference numeral 22 below may be simply abbreviated as a filter.

  The CPU 26 calculates a signal input as a digital signal based on a program stored in the memory 27 to calculate a current value of the electric wire to be measured. This output is displayed on the display unit 33 via the interface 28, and the calculated measurement value is also stored in the memory 27. The input measurement signal is stored in the memory 27 in order to calculate a measurement value. The operation unit 31 inputs various settings and operations. The communication unit 32 can output information such as measured values to the outside by, for example, Bluetooth (registered trademark). The sound output unit 34 can output sounds such as various operations. The LED 35 emits light or is extinguished by operation or the like.

The flow of the work of searching for a leak location using the clamp meter according to the present embodiment will be described with reference to the flowchart of FIG.
When a leak is detected by a leak monitoring device or the like and a leak is detected, it is necessary to search for a leak location.
First, it moves to the "main trunk" line which is the highest layer where the leakage is detected, and starts to search for a leakage point using the clamp meter (steps S11 and S12). The clamp meter is clamped to the target electric wire to be measured (step S13). This clamping is performed by clamping two reciprocating lines of the wiring with the current sensor 10. In the two reciprocating lines, the single-phase alternating current cancels the magnetic field generated by the forward and return currents, so that the detected current becomes almost zero. On the other hand, since the same current does not return due to the ground fault, a magnetic field corresponding to the leakage current is generated, and the leakage current can be measured by detecting the magnetic field by the current sensor 10 which clamps the electric wire.

It is determined whether or not there is a leakage current, and it is determined whether or not the wiring is a leaked wiring (step S14). If there is a leakage, the process proceeds to the next step. If there is no leakage, the next round trip line is clamped to measure the leakage current. At this time, in the present embodiment, when the leakage current exceeds a predetermined set value, not only the measured value is displayed but also sound and light are emitted as the leakage current is present, so that the operator can confirm.
If there is no leakage current, the next round trip line is clamped (step S13), and if there is a leakage current, it is determined whether there is a branch (step S15). If there is a branch and there is a next hierarchy, the system moves downstream to measure leakage current (step S16). If there is no branch, a leakage has occurred in the reciprocating line, and the leakage point of the electric wire is specified (step S17).

  Next, the measured value is compared with the set threshold value, which is a feature of the present embodiment, and when the measured value exceeds the threshold value, not only the measured value is displayed, but also the sound is displayed. The operation of the comparison function for outputting a light pattern will be described with reference to the flowchart in FIG.

The threshold is set by the operator before the measurement (step S21). The amount of leakage current can be confirmed by the leakage monitoring device, the leakage breaker, or the leakage confirmation by the master, so the threshold value is set based on the confirmed leakage current amount. The setting is performed by operating the operation unit 31.
The comparison between the threshold value and the measured value is performed by the CPU 26. When the sampled measurement value is acquired from the current sensor 10 (Step S22), the measurement value is displayed on the display unit 33 (Step S23). Here, it is determined whether the measured value is stable (step S24). If the measured value is not stable, the acquisition of the measured value is continued until the measured value is stabilized without comparing with the threshold value. When the measured value is not stable, the sound, light, and the like are not changed (step S25).
If it is determined that the measured value is stable, it is compared with a set threshold value (step S26). If the measured value exceeds the set threshold value, the sound / light of pattern 1 is changed. At this time, the sound / light of pattern 1 is output by the sound output unit 34 and the LED 35 (step S27). If the measured value does not exceed the set threshold value, the sound / light of pattern 2 is output (step S28).

  Until the measured value stabilizes, there is no output that changes sound and light, so you can see that the measured value is not stable, and if the measured value is stable, it will not exceed when the threshold value is exceeded Since different patterns of sound and light are output, the operator can determine whether or not there is a predetermined leakage current even if the measurement value displayed on the display unit 33 is not visible. Know which task to move on.

Here, the determination as to whether or not the measured value has stabilized will be described with reference to the flowchart in FIG.
External noise may be mixed into the wiring or the like, resulting in an inaccurate measured value. Further, even if the clamp of the current sensor 10 is not closed, the measured value may be inaccurate, and an erroneous determination may occur. Therefore, in the present embodiment, the stability of the measured value is monitored, and when it is determined that the measured value is stabilized, the measured value is compared with the set threshold value.

As an example of determining that the measured value has been stabilized, an example will be described in which the determination is made based on the fluctuation width between the effective value and the peak value.
The peak value and the effective value of the obtained current data are obtained, and an arbitrary number of data is stored in the memory 27. Then, the maximum value and the minimum value of the peak values of the past M pieces of current data are acquired (step S31). Then, it is determined whether or not the value obtained by subtracting the minimum value from the maximum value is less than 10% of the range (step S32). If it is less than 10%, the maximum value and the minimum value of the effective values of the past N data are acquired (step S33). Then, it is determined whether the value obtained by subtracting the minimum value from the maximum value is less than 10% of the range (step S34). If it is less than 10%, it is determined that the measured value is stable (step S35), and the measured value is compared with the set threshold value (step S25 in FIG. 3). When the difference between the maximum value and the minimum value of the peak value and the effective value does not become less than 10% of the range, it is determined that the measured value is not stable (step S36), and the acquisition of the measured value is repeated (step S22 in FIG. 3). ~ S25). Note that M and N are arbitrary constants.

The above example is an example of determining whether the measured value is stable.In addition, for a predetermined period, a moving average is obtained for the obtained measured value, and it is determined that the measured value is stable from the fluctuation range. There are ways.
Leakage current must be measured in the field.If the clamp of the current sensor is not closed, the measured value will not be stable, and in that case, the sound and light will not change from the measuring device body. It is possible to prevent an erroneous determination due to the fact that it is not closed.

  In the clamp sensor according to the embodiment shown in FIG. 1, a signal not passing through the low-pass filter 22 and a signal passing through the low-pass filter 22 are converted into digital signals by analog / digital converters 24 and 25, respectively, and input to the CPU 26 in parallel. It is configured to be.

The function of the low-pass filter 22 will be described.
In recent years, the power supply unit of various electric machines includes an inverter, and a frequency component higher than a commercial frequency due to harmonics generated by the inverter may be mixed in the power supply line. Also, the use of a UPS or the like in a power supply causes high-frequency harmonic components to be mixed into a power supply line.
In the leakage current measurement, if the current value including the high frequency component in addition to the commercial frequency component is detected, the measured current value becomes larger than the original value of the leakage current. On the other hand, the leakage current is a phenomenon in which a ground fault occurs in the commercial frequency component. Therefore, if a high frequency component is also detected, the value detected as the leakage current value becomes too large to obtain an accurate current value. For this reason, a high-frequency component is cut by a low-pass filter having a cutoff frequency of 150 Hz or 180 Hz to obtain a more accurate leakage current value.

  Therefore, when the signal filtered by the low-pass filter 22 and the unfiltered signal are input simultaneously in parallel, the CPU 26 can calculate two current measurement values from the two signals, and compare the two measured values. can do. As a result, when the difference is large, it can be understood that a large external noise is mixed or that the clamp is not closed. Thus, by inputting the signal passing through the low-pass filter 22 and the signal not passing through in parallel, calculating and comparing the signals, the influence of external noise is reduced, and the time until the measured value is stabilized is shortened. This will increase the efficiency of the work of searching for a leak location.

  The output of the sound and light of the patterns 1 and 2 can be the output of an intermittent sound by the sound output unit 34, the emission of red light on the screen of the display unit 33, and the like. Further, an LED 35 that is not provided on the display screen side of the display unit 33 may blink. When the clamp meter is mounted at a position where the screen cannot be seen, the sound output unit 34 and the LED 35 allow the operator to confirm that the measured value has exceeded the threshold value.

(Other embodiments)
In the above embodiment, an example in which two analog-to-digital converters are provided has been described. However, the number of analog-to-digital converters may be one by performing time-division sampling. In this case, the CPU calculates two measured values from the digital signal of the signal through the filter that has been time-divisionally sampled and the digital signal of the signal that has not passed through the filter to determine the stability of the measured value. And compare them.

DESCRIPTION OF SYMBOLS 10 Current sensor 20 Measuring device main body 21 Amplifier (AMP)
22 Low-pass filter (LPF)
23 switch 24, 25 analog / digital converter (A / D)
26 CPU
27 Memory 28 Interface (I / O)
31 operation unit 32 communication unit 33 display unit (LCD)
34 Sound output unit 35 LED

Claims (2)

A clamp meter having a signal processing unit including a calculation unit that receives a signal of the measurement target wire acquired by a sensor that clamps the measurement target wire and calculates a measured value,
The signal processing unit includes a display unit that displays a measured value of the current of the measurement target electric wire,
The signal processing unit,
When the fluctuation range between the effective value and the peak value of the measured current is within a predetermined range, it is determined that the measurement value is stable,
When the measured value at the time of the stabilization exceeds the set threshold value, a means for notifying that the measured value has exceeded the threshold value by sound or light is provided. Clamp meter. The clamp meter according to claim 1, wherein
The signal input to the signal processing unit has two paths, a path input to the signal processing unit via the filter, and a path input to the signal processing unit without a filter. Having a route and
The signal not passing through the filter and the signal passing through the filter are input to the signal processing unit in parallel,
The said signal processing part has the comparison means which compares the measured value from the signal which does not pass a filter, and the measured value from the signal which passed a filter, The clamp meter characterized by the above-mentioned.

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