Common mode noise current measuring instrument

Abstract

To provide a common mode noise current measuring instrument that has a function of measuring a common mode noise current, and choosing a magnetic material core optimal for noise measures.SOLUTION: A common mode noise current measuring instrument includes: a connection part 7 for connecting to a computer; a storage unit 12 for storing a model number data table including maximum allowable current values of a plurality of magnetic material cores from the computer via the connection part; a clamp type sensor head part 2 for detecting a common mode noise current flowing through a conducting wire; a current measurement unit 10 for preliminarily performing a current measurement of a sensor head part at a preset sample rate to obtain a maximum common mode noise current measurement value as of a period of performing the current measurement thereof; a display unit 5 for numerically displaying the maximum common mode noise current measurement value; a comparison unit for comparing the maximum common mode noise current measurement value with the maximum allowable current values in the model number data table stored in the storage unit; a control unit 13 for controlling the connection part, the storage unit, the sensor head part, the current measurement unit, the display unit, and the comparison unit; and an input unit 4 for inputting data into the control unit.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a common mode noise current measuring instrument that can measure common mode noise current and select a magnetic core to be used as a noise filter based on the current value. [Background technology]

[0002] Noise suppression is important for many electrical devices to ensure stable operation and to prevent interference with other devices, and noise suppression is required when noise levels exceed regulatory limits or malfunctions occur. One type of noise suppression component is a magnetic core. This has the function of reducing noise currents by reflecting and absorbing them, and is often used in power lines where noise currents occur. Reflection is the function of pushing back only the noise components toward the noise source, and allowing only the signal components to pass through. Absorption is the function of absorbing the noise components with the magnetic core and converting them into thermal energy.

[0003] In order to use magnetic cores to suppress noise, it is important to measure the noise current flowing through the conductor and select an appropriate magnetic core. Clamp ammeters are often used as devices to measure current. Clamp ammeters are not only easy to operate, as they can measure current simply by clamping the wire over its insulation, but also have the advantage of being able to safely measure large currents because they are not directly connected to the circuit.

[0004] Noise current measuring instruments have been developed that not only simply measure the current flowing through a conductor using a clamp ammeter, but also add various functions to make noise countermeasures easier, such as selecting the constants of the filter circuit and comparing the reference leakage current value with the actual measured value.

[0005] For example, a clamp current meter has been disclosed that has a function of comparing a measured leakage current value with a reference leakage current value stored in memory and sounds a buzzer when the measured leakage current value exceeds the reference value. Specifically, the device is configured with a memory that stores comparison data, a microcomputer that compares the comparison data with a measured value, and a buzzer that notifies the user of the comparison result of the microcomputer (see, for example, Patent Document 1).

[0006] Furthermore, as a method for easily measuring and evaluating the overall EMC performance of a cable, an evaluation method has been disclosed which includes a transmitter that sends a signal to one end of the cable to drive the cable, a load connected to the other end of the cable, a receiver that receives the signal from the probe, and a control unit that controls the transmitter, load, and receiver, and the control unit selects and controls the sending end conditions of the transmitter and the termination conditions of the load, and scans the probe to measure the characteristics of the cable (see, for example, Patent Document 2).

[0007] Furthermore, a common mode current detector has been disclosed that includes an antenna unit that receives electromagnetic waves radiated from a power line or an AC cable connected to the power line, a detection circuit unit that is connected to the antenna unit and detects a common mode current generated in the antenna unit, and an abnormality determination unit that determines whether the amount of common mode current detected by the detection circuit unit is equal to or greater than a predetermined value (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Utility Model Application Publication No. 6-28745 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-64707 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-172372 Summary of the Invention [Problem to be solved by the invention]

[0009] The invention described in Patent Document 1 realizes an easy-to-use ammeter by enabling the clamp ammeter itself to determine whether the measured current value complies with a predetermined standard. However, this invention measures whether the leakage current due to deterioration of electrical circuits and electrical equipment is below a predetermined value, and does not disclose or suggest measuring noise currents or the like to select a magnetic core taking into account magnetic properties and heat generation characteristics.

[0010] The invention described in Patent Document 2 measures the common mode current of a cable in order to perform EMC performance evaluation with simple operations, but does not disclose or suggest selecting a magnetic core with optimal characteristics for noise countermeasures for the cable.

[0011] The invention described in Patent Document 3 is used for power line communication, detects common mode current, and stops power line communication when the detected amount exceeds a predetermined value, but does not disclose or suggest any noise countermeasures.

[0012] An object of the present invention is to provide a common mode noise current measuring instrument that has the function of measuring common mode noise current and easily selecting the most suitable magnetic core for noise countermeasures. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems of the related art, the common mode noise current measuring device of the present invention is characterized by including a connection unit for connecting to a computer, a memory unit for storing a model number data table including maximum allowable current values of a plurality of magnetic cores from the computer via the connection unit, a clamp-type sensor head unit for detecting the common mode noise current flowing through the conductor, a current measuring unit that measures current with the sensor head unit at a preset sample rate and determines the maximum common mode noise current measurement value during that time, a display unit that numerically displays the maximum common mode noise current measurement value, a comparison unit that compares the maximum common mode noise current measurement value with the maximum allowable current value in the model number data table stored in the memory unit, a control unit that controls the connection unit, memory unit, sensor head unit, current measuring unit, display unit, and comparison unit, and an input unit that inputs data to the control unit.

[0014] With this configuration, it is easy to detect the common mode noise current flowing through the conductor for noise suppression and compare the maximum common mode noise current measurement value of that common mode noise current with the maximum allowable current value in the pre-stored model number data table.

[0015] The maximum allowable current value refers to the DC current value at which the impedance value decreases significantly. The magnetic core can be any type used as a noise suppression component, such as a ring-shaped toroidal core, an oval core, or a large-sized core with a base that is compatible with thick cables. Materials available include iron oxide, Mn-Zn, or Ni-Zn ferrite cores, dust cores made by mixing magnetic powder with resin, and cores made by winding a sheet. The appropriate core can be selected based on the purpose.

[0016] The above configuration may further include a fixed display instruction unit for fixing and displaying the maximum common-mode noise current measurement value, and when a user instructs the fixed display using the fixed display instruction unit, the control unit may fix and display the maximum common-mode noise current measurement value on the display unit. With this configuration, the maximum common mode noise current measurement value can be fixed and displayed digitally, making it easy for the user to understand.

[0017] In the above configuration, when the user inputs the model number and number of windings of the magnetic core using the input unit, the control unit calculates the effective current value flowing through the magnetic core based on the input number of windings and the maximum common mode noise current measurement value, and reads from the storage unit the maximum allowable current value of the magnetic core corresponding to that model number from the model number data table. The comparison unit compares the effective current value with the maximum allowable current value, and determines whether the effective current value is equal to or greater than the maximum allowable current value. Current value If the effective current value is smaller than the maximum allowable current value, a message indicating that the magnetic saturation is not occurring may be displayed on the display unit, and if the effective current value is greater than the maximum allowable current value, a message indicating that the magnetic saturation is occurring may be displayed on the display unit and / or a sound may be emitted.

[0018] In this case, the user may use the fixed display instruction unit to instruct fixed display, and after the maximum common mode noise current measurement value is displayed on the display unit, the user may use the input unit to input the model number and number of windings of the magnetic core.

[0019] For example, if the number of windings is one turn, the effective current value is the maximum common mode noise current measurement value, but if the number of turns is three, the effective current value is three times the maximum common mode noise current measurement value. In this way, the effective current value is two or three times the maximum common mode noise current measurement value depending on the number of windings.

[0020] With this configuration, simply measure the maximum common-mode noise current flowing through the conductor and input the model number and number of windings of the magnetic core to be used as a noise filter. The control unit will then operate and display and / or sound a message to indicate whether magnetic saturation will occur when using that magnetic core, making it easy to determine whether it will occur. If the control unit is notified of magnetic saturation, simply input a different model number and number of windings and it will make a new determination. Therefore, it is sufficient to input various model numbers and numbers of windings multiple times until a result indicating no magnetic saturation occurs is obtained. As a result, it is easy to select the optimal magnetic core for a noise filter by simply measuring the common-mode noise current once.

[0021] If there is no magnetic saturation, the magnetic core of that model number can be used, so only a display is sufficient, but if there is magnetic saturation, the magnetic core of that model number cannot be used, so instead of simply displaying the information, it is also possible to display a sound or to transmit only a sound.

[0022] When the user inputs the model number and number of windings, there may be cases where the user inputs a model number that is not in the model number data table, in which case the control unit searches the model number data table stored in the memory unit, confirms that the model number is not in the model number data table, and displays a message on the display unit indicating that the model number is not in the model number data table. This allows the user to input another model number and number of windings again to select the optimal magnetic core.

[0023] In the above configuration, a plurality of preset numbers of windings may be further stored in the memory unit from the computer via the connection unit, and when the maximum common-mode noise current measurement value is determined by the current measurement unit, the control unit may determine the effective current value corresponding to each number of windings based on the plurality of preset numbers of windings and the maximum common-mode noise current measurement value, read out the maximum allowable current value of the magnetic core stored in the memory unit, compare the effective current value with the maximum allowable current value using the comparison unit, and display on the display unit the model number and number of windings of the magnetic core showing an effective current value smaller than the maximum allowable current value.

[0024] With this configuration, the control unit calculates the effective current value based on the preset number of windings and the maximum common-mode noise current measurement value, without the user having to input the model number and number of windings, and then calculates the maximum allowable current value for that magnetic core from a magnetic core model number data table pre-stored in the memory unit.The comparison unit compares the effective current value with the maximum allowable current value, and displays the model number and number of windings of a magnetic core that will not become magnetically saturated.This makes it even easier to select a magnetic core.

[0025] In this case, after the user instructs the fixed display using the fixed display instruction unit, the control unit may start an operation to calculate the effective current value based on the number of windings that was set in advance and the maximum common-mode noise current measurement value.

[0026] The number of windings can be set in advance and stored between 1 and 3 turns. However, it is not necessarily limited to 3 turns. Usually, when using a magnetic core as a noise filter, up to 3 turns is sufficient, but if more windings are required, this can be increased. The display can show the model number of the magnetic core that can be used for each number of windings. In the above configuration, the model number data table stored in the storage unit may be rewritten or added to as desired by a computer via the connection unit.

[0027] In this way, the model number data table of the magnetic core required by the user can be input and stored in the memory unit, and if the user requests more, a new model number data table can be easily added. [Effects of the Invention]

[0028] The common mode noise current measuring device of the present invention has the great advantage that, simply by measuring the common mode noise current flowing through a conductor, it is possible to easily select the optimum magnetic core as a noise filter in accordance with the common mode noise current. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic plan view of a common-mode noise current measuring instrument according to an embodiment of the present invention; [Figure 2] 2A and 2B are schematic perspective views of the common mode noise current measuring device according to the embodiment, in which FIG. 2A is a perspective view seen from the front side, and FIG. 2B is a perspective view seen from the back side. [Figure 3] FIG. 2 is a block diagram showing a circuit configuration of the common-mode noise current measuring device according to the embodiment. [Figure 4] 10 is a diagram showing a state in which the common mode noise current measuring instrument and the computer are connected by a connection part in the embodiment. FIG. [Figure 5] FIG. 1 is a diagram showing impedance characteristics of magnetic cores in the model data table shown in Table 1. [Figure 6] FIG. 1 is a diagram showing the inductance characteristics of the magnetic cores in the model data table shown in Table 1. [Figure 7] FIG. 10 is a block diagram showing the configuration of a common-mode noise current measuring device according to a modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] (First embodiment)

[0031] A common mode noise current measuring device according to a first embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic plan view of the common mode noise current measuring device according to this embodiment. Fig. 2 is a schematic perspective view of the common mode noise current measuring device according to the same embodiment, where (a) is a perspective view seen from the front side and (b) is a perspective view seen from the back side. Fig. 3 is a block diagram showing the circuit configuration of the common mode noise current measuring device according to the same embodiment. The common mode noise current measuring device according to this embodiment will be described in detail below with reference to these figures.

[0032] The common mode noise current measuring instrument 1 according to this embodiment comprises a connection unit 7 for connecting to a computer, a memory unit 12 for storing a model number data table including the maximum allowable current values of multiple magnetic cores, which is received from the computer via the connection unit 7, a clamp-type sensor head unit 2 for detecting the common mode noise current flowing through the conductor, a current measuring unit 10 for measuring current with the sensor head unit 2 at a preset sample rate and determining the maximum common mode noise current measured during that measurement, a display unit 5 for displaying the maximum common mode noise current measurement value as a numerical value, a comparison unit 11 for comparing the maximum common mode noise current measurement value with the maximum allowable current value in the model number data table stored in the memory unit 12, a control unit 13 for controlling the connection unit 7, the memory unit 12, the sensor head unit 2, the current measuring unit 10, the display unit 5, and the comparison unit 11, and an input unit 4 for inputting data to the control unit 13.

[0033] The input unit 4 and the display unit 5 are attached to the main body 6. The sensor head unit 2 is also attached to the main body 6, and the entire system has a shape that allows it to be operated with one hand. The comparison unit 11, the storage unit 12, and the control unit 13 may each be composed of separate components, or a microcomputer may be used so that the microcomputer has these functions.

[0034] The sensor head 2 is a clamp type, with the fixed head 2a fixed to the main body 6 and the pivoting head 2b opening and closing by the user operating the opening / closing lever 3, allowing it to clamp the conductor to be measured. The fixed head 2a and pivoting head 2b come into contact at the contact part 2c, allowing the current flowing through the conductor to be measured. Current detection uses a transformer core to detect the magnetic field generated by the flow of current, and extracts an output proportional to the measured current. Note that current detection methods include not only the transformer core method, but also Rogowski coil methods, Hall element methods, and fluxgate methods, but the transformer core method is easy to use and inexpensive for measuring common mode noise currents.

[0035] In the common mode noise current measuring instrument 1 of this embodiment, the input section 4 is made up of multiple buttons 4a to 4h, and the model number, number of windings, etc. can be input by operating the buttons. Note that these buttons 4a to 4h do not have a single function, but if they are configured to have multiple functions when operated, even complex input can be easily performed.

[0036] The display unit 5 is made up of, for example, a liquid crystal display element, and can display not only numbers but also letters. In the common mode noise current measuring instrument 1 of this embodiment, the input unit 4 and the display unit 5 are each made up of separate components, but it is also possible to use an integrated display unit with a touch panel, in which the input unit and display unit are integrated. A display unit with such a configuration allows for more complex input and display.

[0037] A method for storing a core model number data table containing the maximum allowable current values of multiple magnetic cores in the memory unit 12 of the common-mode noise current measuring instrument 1 will be described. FIG. 4 shows the common-mode noise current measuring instrument 1 and computer 14 connected via the connection unit 7. After connecting the computer 14, the computer 14 is operated to store a core model number data table in the memory unit 12, which lists the model numbers and maximum allowable current values as shown in Table 1. The computer 14 may be a personal computer (PC) or a tablet terminal. The model number data table may be stored in the PC or tablet terminal and then stored in the memory unit 12. Alternatively, the PC or tablet terminal may be connected to the common-mode noise current measuring instrument 1 and connected to a server via the Internet, and the model number data table stored on the server may be stored in the memory unit 12.

[0038] Note that the model number data table shown in Table 1 is an example; in an actual common mode noise current meter, several dozen pieces of data will be stored in the memory depending on whether it is for low frequency, high frequency, or dual use. The connector 7 has a terminal that can be connected to a USB cable, making it easy to use and connect to a computer. Also, while Table 1 only lists the model number and maximum allowable current value, it is possible to add other information such as the external dimensions of the magnetic core and the allowable heat generation temperature rise value.

[0039] [Table 1]

[0040] By storing the model number data table in memory unit 12 in this way, the comparison unit 11 can compare the maximum common mode noise current measurement value with the maximum allowable current value listed in the model number data table. Figures 5 and 6 are impedance and inductance characteristic diagrams of the magnetic core in the model number data table shown in Table 1. The maximum allowable current value was calculated based on these characteristic diagrams.

[0041] In this embodiment, a fixed display instruction unit 4a is provided for fixing and displaying the maximum common mode noise current measurement value. When the user instructs fixed display using the fixed display instruction unit 4a, the control unit 15 causes the maximum common mode noise current measurement value to be fixed and displayed on the display unit 5. In this embodiment, the fixed display instruction unit 4a is a button in the input unit 4, but the present invention is not limited to this and may be configured as a button separate from the input unit 4. This allows the user to easily visually confirm the maximum common mode noise current measurement value. Next, a procedure for selecting a magnetic core using the common mode noise current measuring instrument 1 according to this embodiment will be described.

[0042] First, press the power button 4b of the common mode noise current measuring instrument 1 to turn the power on. The power button 4b may also be configured as a button separate from the input section 4. Next, press the open / close lever 3 to open the rotating head section 2b of the sensor head section 2, and insert the conductors for measuring the common mode noise current, such as the PN2 wire and the three wires of the UVW phases, into the sensor head section 2, then close and clamp the conductors.

[0043] In this state, the common mode noise current flowing through the conductor (not shown) is measured. The sensor head unit 2 measures the current at a preset sample rate, and the current measurement unit 10 determines the maximum common mode noise current measurement value during that period. The sample rate is, for example, 3 times per second for 5 seconds, and the maximum value measured during that period is taken as the maximum common mode noise current measurement value. Note that the sample rate is not limited to the above and can be selected as appropriate.

[0044] When the button on the fixed display indicator 4a is pressed, the maximum common mode noise current measurement value is fixed and displayed numerically on the display 5. After that, the opening / closing lever 3 is operated to open the rotating head 2b, and the conducting wire (not shown) is removed from the sensor head 2.

[0045] Next, the user operates operation buttons 4c to 4h of the input unit 4 to input the model number and number of windings of the magnetic core to be used. Note that, although the number of operation buttons on the input unit 4 is eight in this embodiment, this is just an example and the number may be increased. Furthermore, the operation buttons are configured to allow input of not only numbers but also alphabets, so simple sentences can also be input.

[0046] When the model number and number of windings are input, control unit 13 calculates the effective current value based on the input number of windings and the maximum common-mode noise current measurement value. Control unit 13 also reads from memory unit 12 the maximum allowable current value of the magnetic core corresponding to that model number from the model number data table. Comparison unit 11 then compares the effective current value with the maximum allowable current value.

[0047] As a result, if the effective current value is smaller than the maximum allowable current value, a message indicating that magnetic saturation has not occurred is displayed on the display unit 5. On the other hand, if the effective current value is larger than the maximum allowable current value, a message indicating that magnetic saturation has occurred is displayed on the display unit 5 and / or a sound is emitted. Since magnetic saturation means that the magnetic core cannot be used, the message is not only displayed but also sounded, or sounded only, to enable the user to recognize the message more clearly.

[0048] For example, if the maximum common-mode noise current measurement value is 7A, suppose the user inputs T-003 as the model number and 2 turns as the number of windings via input unit 4. Control unit 13 calculates the effective current value based on the 2 turns of windings and the maximum common-mode noise current measurement value of 7A. In this case, it is 14A. Next, it reads the maximum allowable current value for T-003 stored in memory unit 12. Then, comparison unit 11 compares the effective current value of 14A with the maximum allowable current value of 10A. Since the maximum allowable current value is 10A and the effective current value is 14A, it is clear that magnetic saturation will occur if this magnetic core is used. Therefore, in this case, a message indicating magnetic saturation is generated and / or a buzzer sounds.

[0049] If magnetic saturation is detected by a buzzer sound or other means, the next step is to input, for example, the same model number T-003 with one turn of winding. In this case, the effective current value is 7A, the same as the maximum common mode noise current measurement value, and the maximum allowable current value is 10A, so it is clear that magnetic saturation is not occurring. As a result, the display 5 will indicate that magnetic saturation is not occurring. In this way, a magnetic core that will not become magnetically saturated can be easily selected based on the model number and number of windings.

[0050] In this embodiment, the user issues an instruction to display the maximum common-mode noise current measurement value in a fixed manner using the buttons on fixed display indicator 4a, and then operates operation buttons 4c to 4h on input unit 4 to input the model number and number of windings of the magnetic core to be used, but the present invention is not limited to this. It is also possible to immediately operate operation buttons 4c to 4h on input unit 4 to input the model number and number of windings of the magnetic core to be used, without operating fixed display indicator 4a to display the value in a fixed manner. (Modification of the first embodiment)

[0051] A common mode noise current measuring device 16 according to a modified example of this embodiment will be described with reference to the drawings. FIG. 7 is a block diagram showing the configuration of the common mode noise current measuring device 16 according to this modified example. This modified common mode noise current measuring device 16 is characterized in that it further includes a non-contact temperature sensor 15 in addition to the components of the common mode noise current measuring device 1 according to the first embodiment. From an operational standpoint, it is preferable that the non-contact temperature sensor 15 be attached to the rear surface shown in FIG. 2(b). An operation button for activating the non-contact temperature sensor 15 may be newly provided on the input unit 4, or one of the operation buttons of the input unit 4 shown in FIG. 1 may be shared and used.

[0052] When the magnetic core heats up due to the current flowing through the conductor, the characteristics of the magnetic core deteriorate, and the magnetic core may even be damaged by overheating. For this reason, it is preferable to measure the temperature generated during actual use using this non-contact temperature sensor 15 to determine whether the magnetic core can be used stably. By providing this temperature sensor 15, it is possible to quickly determine the possibility of deterioration or damage due to heat, and to select the optimal magnetic core. (Second embodiment)

[0053] In the common mode noise current measuring instrument 1 according to the first embodiment, the user inputs the model number and number of windings to select a magnetic core that will not become magnetically saturated. The common mode noise current measuring instrument according to this embodiment is characterized in that after measuring the maximum common mode noise current of the conductor and the user instructs the display unit to display a fixed value, the control unit automatically displays the model number and number of windings of a magnetic core that will not become magnetically saturated on the display unit.

[0054] The configuration and block diagram of the measuring device are the same as those of the common mode noise current measuring device 1 according to the first embodiment, so a description of the configuration will be omitted. In this embodiment, the function of the control unit is slightly different from that of the control unit in the first embodiment, but the same reference numerals as in Figures 1 to 3 are used, including the control unit, to explain a method for displaying the model number and number of windings of a magnetic core that does not become magnetically saturated in the common mode noise current measuring device according to this embodiment.

[0055] This embodiment also has a fixed display instruction unit 4a for fixing and displaying the maximum common mode noise current measurement value, and the user uses the fixed display instruction unit 4a to instruct fixed display. In response, the control unit 13 fixes and displays the maximum common mode noise current measurement value on the display unit 5. In this embodiment, the fixed display instruction unit 4a is a button in the input unit 4, but the present invention is not limited to this and may be configured as a button separate from the input unit 4. This allows the user to easily visually confirm the maximum common mode noise current measurement value. Next, a procedure for selecting a magnetic core using the common mode noise current measuring instrument 1 according to this embodiment will be described.

[0056] In this embodiment, multiple preset numbers of windings are further stored in the memory unit via the connection unit. When the user issues a fixed display command using the fixed display command unit 4a, the control unit 13 calculates the effective current value corresponding to each number of windings based on the multiple preset numbers of windings and the maximum common-mode noise current measurement value. Next, the control unit 13 reads the maximum allowable current value of the magnetic core stored in the memory unit 12.

[0057] The comparison unit 11 then compares the effective current value corresponding to the number of windings with the maximum allowable current value for the model number. The model number and number of windings of magnetic cores with an effective current value smaller than the maximum allowable current value are then displayed on the display unit 5. There may be multiple model numbers and numbers of windings of magnetic cores with an effective current value smaller than the maximum allowable current value, and these are displayed all at once or sequentially on the display unit 5. The user checks the display and selects the most suitable magnetic core. This will be further explained using the following example.

[0058] The preset number of windings is, for example, one to three turns. This number of windings is stored in advance in the memory unit via a computer. Then, after measuring the maximum common-mode noise current flowing through the conductor, when the button on the fixed display indicator 4a is pressed, the control unit 13 calculates the effective current value. For example, if the maximum common-mode noise current measurement is 8 A, the effective current value will be the same as the maximum common-mode noise current measurement with one turn, 16 A with two turns, or twice the maximum common-mode noise current measurement, and 24 A with three turns, or three times the maximum common-mode noise current measurement.

[0059] Next, control unit 13 sequentially reads out the maximum allowable current values for the model numbers stored in memory unit 12. Then, comparison unit 11 compares the effective current value corresponding to the number of windings with the maximum allowable current value read from the model number. For model number T-003, the maximum allowable current value is 10 A. Therefore, comparison unit 11 compares the maximum allowable current value of 10 A with the effective current values of 8 A, 16 A, and 24 A corresponding to the number of windings. As a result, it is found that magnetic saturation does not occur only when the number of windings is one turn.

[0060] Next, the control unit 13 reads out the maximum allowable current value for model number T-004 and compares it using the comparison unit 11. In this case, the maximum allowable current value is 50 A, and when compared with the effective current values of 8 A, 16 A, and 24 A corresponding to the number of windings, it is found that magnetic saturation does not occur for any of the numbers of windings.

[0061] The same process is performed for all other model numbers. In this example, T-001 and T-002 become magnetically saturated under all conditions and are therefore unusable. T-003 does not become magnetically saturated only when the number of windings is one turn. On the other hand, T-004, T-005, and T-006 do not become magnetically saturated under any conditions. As a result, the control unit 13 displays on the display unit 5 that model number T-003 can only be used with one turn of winding, while T-004, T-005, and T-006 can be used with windings from one turn to three turns. This allows the user to easily determine which magnetic core should be used as a noise filter for the conductor based on the measurement result of the maximum common current. In this embodiment, a non-contact temperature sensor may be provided in the same manner as in the modified example of the first embodiment.

[0062] In this embodiment, after the user issues an instruction to display the maximum common mode noise current measurement value in a fixed manner using the buttons on fixed display instruction unit 4a, control unit 13 calculates the effective current value corresponding to each number of turns based on a plurality of preset numbers of turns and the maximum common mode noise current measurement value, but the present invention is not limited to this. If the maximum common mode noise current value is measured without the user operating fixed display instruction unit 4a to issue an instruction to display a fixed display, control unit 13 may calculate the effective current value corresponding to each number of turns based on a plurality of preset numbers of turns and the maximum common mode noise current measurement value, compare them in comparison unit 11, and display unit 5 with the model number that does not become magnetically saturated and the number of turns.

[0063] Furthermore, while Table 1 only lists the model number and maximum allowable current value, it is also possible to add the outer dimensions of the magnetic core and the allowable heat temperature rise value. For example, if the outer dimensions are included in the model number and it is found that multiple magnetic cores do not saturate magnetically, then by displaying these outer dimensions as well, the user can easily select a magnetic core with the optimal outer dimensions from among the magnetic cores that do not saturate magnetically.

[0064] Although the present invention is a current measuring instrument primarily for measuring common mode noise currents, the present invention is not limited to the name of the invention and can be widely used when measuring currents to suppress noise using a magnetic core, including normal mode noise currents.

[0065] Furthermore, there are no small current measuring devices that integrate the display and sensor units and are capable of measuring minute current values of around 1 mA in the frequency range of several kHz, but the common mode noise current measuring device of the present invention can measure minute currents in this range. [Industrial Applicability]

[0066] The common mode noise current measuring instrument of the present invention not only measures the common mode noise current flowing through a conductor, but also makes it easy to select a magnetic core that will not magnetically saturate based on the current value, making it useful in the field of noise countermeasures. [Explanation of symbols]

[0067] 1, 16 Common mode noise current measuring instrument 2 Sensor head 2a Fixed head part 2b Rotating head 2c Contact part 3 Opening / closing lever 4 Input section 4a Fixed display instruction section 4b Power button 4c, 4d, 4e, 4f, 4g, 4h operation buttons 5 Display section 6 Main body 7 Connection 10 Current measurement section 12 Storage section 13 Control Unit 14 Computer 15 Non-contact temperature sensor

Claims

1. a connection portion for connecting to a computer; a storage unit for storing a model number data table including maximum allowable current values of a plurality of magnetic cores, the ... a clamp-type sensor head for detecting common mode noise current flowing through a conductor; a current measurement unit that measures the current of the sensor head unit at a preset sample rate and obtains the maximum common mode noise current measurement value during that time; a display unit that displays the maximum common mode noise current measurement value as a numerical value; a comparison unit that compares the maximum common mode noise current measurement value with the maximum allowable current value in the model number data table stored in the storage unit; a control unit that controls the connection unit, the storage unit, the sensor head unit, the current measurement unit, the display unit, and the comparison unit; an input unit for inputting data to the control unit.

2. a fixed display indicator for displaying the maximum common mode noise current measurement value in a fixed manner; 2. The common mode noise current measuring instrument according to claim 1, wherein when a user instructs the fixed display using the fixed display instruction unit, the control unit fixes and displays the maximum common mode noise current measurement value on the display unit.

3. When the user inputs the model number and number of windings of the magnetic core using the input unit, the control unit calculates an effective current value flowing through the magnetic core based on the input number of windings and the maximum common-mode noise current measurement value, reads from the storage unit the maximum allowable current value of the magnetic core corresponding to the model number in the model number data table, and compares the effective current value with the maximum allowable current value using the comparison unit; 3. The common mode noise current measuring instrument according to claim 1, wherein the display unit displays a message indicating that magnetic saturation has not occurred when the effective current value is smaller than the maximum allowable current value, and the display unit displays a message indicating that magnetic saturation has occurred when the effective current value is larger than the maximum allowable current value, and / or emits a sound.

4. a plurality of preset numbers of windings are further stored in a storage unit from the computer via the connection unit; When the maximum common mode noise current measurement value is obtained by the current measurement unit, 3. The common mode noise current measuring instrument according to claim 1, wherein the control unit calculates an effective current value corresponding to each number of windings based on a plurality of preset numbers of windings and the maximum common mode noise current measurement value, reads out the maximum allowable current value of the magnetic core stored in the memory unit, compares the effective current value with the maximum allowable current value using the comparison unit, and displays on the display unit the model number and number of windings of a magnetic core showing an effective current value smaller than the maximum allowable current value.

5. 5. The common mode noise current measuring instrument according to claim 1, wherein the model number data table stored in the memory unit can be arbitrarily rewritten or added to by the computer via the connection unit.

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