Measuring instrument

Abstract

To obtain a measuring instrument with which it is possible to identify the rated value of a current sensor and prevent measurement errors due to incorrect setting without using a dedicated current sensor, and without installing a dedicated electric wire for reading resistance values.SOLUTION: A measuring instrument 2 connects one current sensor 1 among a plurality of current sensors 1 provided with a core 1b and a coil 1a and differing in rating and measures and calculates a current. The measuring instrument 2 comprises: a current input circuit 3 for inputting a signal to the coil 1a of the current sensor 1; a measurement calculation unit 9a for measuring a current flowing in the coil 1a when a signal is inputted; a rating determination unit 9b for determining the rated value of the current sensor 1 on the basis of a rise time of the measured current; and a measurement calculation unit 9a for calculating the current measured by the current sensor 1 on the basis of the determined rated value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a measuring instrument for measuring a current value. [Background technology]

[0002] Current sensors that measure current using a coil like a current transformer require different magnetic flux depending on the magnitude of the current (rated current) flowing through the object being measured. For this reason, there are multiple current sensors for different rated currents. For this reason, measuring instruments that connect these current sensors and measure and calculate current maintain a current transformation ratio between the primary and secondary currents, and calculate the primary current using the measured secondary current and the current transformation ratio. This requires operators to set the current transformation ratio, which can lead to problems with erroneous measurements due to forgetting to set it or setting it incorrectly.

[0003] Therefore, in Patent Document 1, a different resistor is added to the inside of the current sensor for each rating, and the rating of the current sensor is determined by having a measuring instrument read the resistance value of the resistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-87226 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, in order to identify the rated current of a current sensor, it is necessary to prepare a special current sensor in which a resistor with a different resistance value for each rated current is provided inside the current sensor. Also, a connector with a dedicated electric wire for reading the resistance value is required. Therefore, there are problems such as inconvenience and a complicated configuration.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a measuring instrument that can identify the rated value of a current sensor without using a dedicated current sensor or providing a dedicated wire for reading the resistance value, and that can prevent measurement errors due to incorrect settings. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the object, a measuring instrument disclosed herein connects one of a plurality of current sensors each having a core and a coil and different ratings to measure and calculate a current. The measuring instrument includes a signal input circuit that inputs a signal to the coil of the current sensor, a measurement unit that measures the current flowing through the coil when the signal is input, a rating determination unit that determines the rated value of the current sensor based on the rise time of the measured current, and a measurement and calculation unit that calculates the current measured by the current sensor based on the determined rated value. [Effects of the Invention]

[0008] The measuring instrument disclosed herein has the advantage of being able to identify the rated value of a current sensor without using a dedicated current sensor or providing a dedicated wire for reading the resistance value, and is able to prevent measurement errors due to incorrect settings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing a configuration of a measuring instrument according to a first embodiment. [Figure 2] 1 is a flowchart showing a rating determination process of a rating determination unit of a measuring instrument according to a first embodiment; [Figure 3] 1 is a time chart showing the step response of a current sensor with a small rated value in the measuring instrument according to the first embodiment; [Figure 4] 1 is a time chart showing the step response of a current sensor with a large rated value in the measuring instrument according to the first embodiment; [Figure 5] FIG. 10 is a diagram showing the stored contents of a rated value determination table in the measuring instrument according to the first embodiment; [Figure 6] 10 is a time chart showing the response of a current sensor with a small rated value when an AC signal is injected in the measuring instrument according to the second embodiment; [Figure 7] 10 is a time chart showing the response of a current sensor with a large rated value when an AC signal is injected in the measuring instrument according to the second embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a measuring instrument according to an embodiment will be described in detail with reference to the drawings.

[0011] Embodiment 1 FIG. 1 is a block diagram showing the configuration of a measuring instrument 2 according to a first embodiment. The current sensor 1 includes a core 1b and a coil 1a. The current sensor 1 has a core 1b made of a magnetic material (e.g., ferrite or grain-oriented electromagnetic steel sheet) and a coil 1a wound around the core 1b with a number of turns corresponding to the ratio of a primary current (e.g., 5 A or 250 A) to a secondary current (e.g., 20 mA). A conductor of an electric circuit W, which is a conductor to be measured, passes through the core 1b of the current sensor 1. A load 30 is connected to the electric circuit W.

[0012] The measuring instrument 2 has a current input circuit 3 as a signal input circuit, a voltage input circuit 4, a processing unit 7, a display unit 5, a setting unit 6, and a memory 10. A current signal detected by the current sensor 1 is input to the current input circuit 3. The voltage of the electric circuit W is input to the voltage input circuit 4. The processing unit 7 performs rating determination processing for the current sensor 1 and measurement processing for the current, voltage, and power. The display unit 5 displays the current, voltage, power, etc. measured and processed by the processing unit 7. The setting unit 6 sets the phase and wire system of the electric circuit W, the display content of the display unit 5, etc. The memory 10 stores a phase and wire system setting value 10c, a current sensor setting value 10b, a rated value determination table 10a as a determination table, etc.

[0013] The current input circuit 3 includes a switch 3a, a resistor 3c, a switch 3b, a resistor 3d, a switch 3e, and a power supply 3f. One end of the switch 3a is connected to one end of the current sensor 1. One end of the resistor 3c is connected to the other end of the switch 3a, and the other end of the resistor 3c is connected to the other end of the current sensor 1. One end of the switch 3b is connected to one end of the current sensor 1. One end of the resistor 3d is connected to the other end of the switch 3b. One end of the switch 3e is connected to the other end of the resistor 3d. One end of the power supply 3f is connected to the other end of the switch 3e, and the other end of the power supply 3f is connected to the other end of the current sensor 1. The circuit portion including the switch 3a and the resistor 3c functions as a normal measurement circuit that converts the current output from the current sensor 1 into a current using the resistor 3c and inputs it to the processing unit 7. The circuit portion including the switch 3b, the resistor 3d, the switch 3e, and the power supply 3f functions as a signal injection circuit that performs a step input to the current sensor 1.

[0014] The processing unit 7 includes an analog-to-digital converter (hereinafter referred to as the A / D converter) 8, a software (S / W) processing unit 9, and a memory 10. The A / D converter 8 converts the analog current signal from the current input circuit 3 and the analog voltage signal from the voltage input circuit 4 into a digital current signal and a digital voltage signal. The S / W processing unit 9 receives the digital current signal and digital voltage signal from the A / D converter 8 and performs processes such as rating determination for the current sensor 1 and measuring current, voltage, and power. The memory 10 stores a phase / wire setting value 10c set by the setting unit 6 and a current sensor setting value 10b including information on the determined rating value of the current sensor 1. The memory 10 also stores a rating value determination table 10a for determining the rating value of the connected current sensor 1. A first output 11 is output from the rating determination unit 9b and drives switches 3a and 3b. A second output 12 is output from the rating determination unit 9b and drives switch 3e.

[0015] The S / W processing unit 9 has a measurement calculation unit 9a as a measurement unit, a rating determination unit 9b, and a set value setting unit 9c. The measurement calculation unit 9a performs measurement processing of current, voltage, and power based on the digital current signal and digital voltage signal from the A / D converter 8. The rating determination unit 9b determines the rated current of the current sensor 1 using a rating value determination table 10a. The set value setting unit 9c stores the rated current and phase and wire type information of the current sensor 1 determined by the rating determination unit 9b in the memory 10 as a current sensor set value 10b and a phase and wire type set value 10c.

[0016] The display unit 5 is installed to display current values, voltage values, power amounts, etc., and the operator can change the settings of the measuring instrument 2, such as the voltage rating and phase and wire type information, while referring to the display screen.

[0017] Next, the rating determination process performed by the rating determination unit 9b will be described with reference to Fig. 2. Fig. 2 is a flowchart showing the rating determination process performed by the rating determination unit 9b of the measuring instrument 2 according to the first embodiment. In this rating determination process, a step input is made to the current sensor 1, and the rated value of the current sensor 1 is determined based on the rise time, which is the response time.

[0018] First, the rating determination unit 9b turns on the first output 11 (step S101), which opens the switch 3a of the current input circuit 3 and closes the switch 3b.

[0019] Next, the rating determination unit 9b turns on the second output 12 (step S102). This closes the switch 3e of the current input circuit 3, and the DC voltage of the power supply 3f is applied to the resistor 3d. When the DC voltage of the power supply 3f is applied to the resistor 3d, a current flows through the following path: power supply 3f → switch 3e → resistor 3d → switch 3b → coil 1a → power supply 3f. At this time, the voltage measured by the A / D converter 8 rises due to a time constant determined by the inductance of the coil 1a in the current sensor 1 and the resistance value of the resistor 3d.

[0020] Because the number of turns of coil 1a of current sensor 1 varies depending on the rated value, the inductance of coil 1a also varies depending on the rated value. Therefore, if the rated value of current sensor 1 varies, the rise time of the voltage measured by A / D converter 8 will also vary. Therefore, by measuring the rise time of the voltage measured by A / D converter 8, it is possible to determine the rated value of current sensor 1.

[0021] The rating determination unit 9b measures the rise time required for the voltage measured by the A / D converter 8 to rise to a first set value (e.g., 90%), and determines the rated value of the current sensor 1 based on the measured rise time and the rated value determination table 10a (step S103).

[0022] Next, the rating determination unit 9b writes the determined rating value of the current sensor 1 into the current sensor setting value 10b in the memory 10, and sets the rating value of the current sensor 1 (step S104).

[0023] FIG. 3 is a time chart showing the step response of current sensor 1 with a small rated value in measuring instrument 2 according to the first embodiment. The rated value of current sensor 1 with a small rated value is, for example, 5 A. FIG. 4 is a time chart showing the step response of current sensor 1 with a large rated value in measuring instrument 2 according to the first embodiment. The rated value of current sensor 1 with a large rated value is, for example, 250 A. A method for determining the rated value of current sensor 1 according to the first embodiment will be described using FIGS. 3 and 4.

[0024] First, in the case of current sensor 1 with a small rated value, first output 11 turns ON at time t1, as shown in Figure 3. Then, at time t2, second output 12 turns ON, and the DC voltage of power supply 3f is applied as a step input to resistor 3d and coil 1a. Due to a time constant determined by the inductance of coil 1a and the resistance value of resistor 3d, the voltage measured by A / D converter 8 gradually rises and reaches a first set value that has a certain percentage (e.g., 90%) of the DC voltage of power supply 3f at time t3.

[0025] Next, in the case of current sensor 1 with a large rated value, first output 11 turns ON at time t1, as shown in Figure 4. After that, at time t2, second output 12 turns ON, and the DC voltage of power supply 3f is applied as a step input to resistor 3d and coil 1a. Due to a time constant determined by the inductance of coil 1a and the resistance value of resistor 3d, the voltage measured by A / D converter 8 gradually rises and reaches a first set value that has a certain percentage (e.g., 90%) of the DC voltage of power supply 3f at time t4.

[0026] Here, when comparing the rise time from time t2 to time t3 with the rise time from time t2 to time t4, t3-t2 <t4-t2 Thus, the current sensor 1 with a larger number of turns of the coil 1a and a larger rated value (for example, 250A) has a longer rise time.

[0027] The rating determination unit 9b determines the rating value using the measured rise time t3-t2 or rise time t4-t2 and the rating value determination table 10a.

[0028] 5 is a diagram showing the contents stored in the rated value determination table 10a in the measuring instrument 2 according to the first embodiment. The rated value of the current sensor 1 is determined as follows. For example, the rise time of the step response is measured in advance for each of a plurality of current sensors 1 having a plurality of different rated values that can be connected to the measuring instrument 2, and the measured rise times of the step response for the plurality of current sensors 1 are stored in the rated value determination table 10a in the memory 10. As shown in FIG. 5, in the rated value determination table 10a, the rise time of the step response for each current sensor 1 is stored in association with the rated value (rated current) of each current sensor 1.

[0029] 2, the rating determination unit 9b compares the actually measured rise time of the step response of the current sensor 1 with the stored data in the rated value determination table 10a, selects the rise time closest to the actually measured rise time of the step response from the stored data in the rated value determination table 10a, and determines the rated value associated with the selected rise time as the currently measured rated value of the current sensor 1. In step S104 in FIG. 2, the set value setting unit 9c sets the determined rated value in the current sensor set value 10b in the memory 10 as the rated value of the connected current sensor 1.

[0030] Once the rated value of the connected current sensor 1 is known, the specifications of the current sensor 1, including the inductance of the coil 1a of the connected current sensor 1, are determined. Therefore, when measuring the current flowing through the electrical circuit W using the current sensor 1, the rating determination unit 9b turns off switches 3b and 3e and turns on switch 3a using the first output 11 and the second output 12. The measurement calculation unit 9a calculates the current flowing through the electrical circuit W using the voltage measured by the A / D converter 8, the inductance of coil 1a, and the resistance value of resistor 3c.

[0031] According to the first embodiment, a measuring instrument 2 connects one of multiple current sensors 1 having different ratings, each equipped with a core 1b and a coil 1a, to measure and calculate current. The measuring instrument 2 automatically determines the rated value of the current sensor 1 by utilizing the fact that the inductance of the current sensor 1 varies depending on the rated value of the current sensor 1. Specifically, a step waveform is input to the coil 1a of the current sensor 1, the current flowing through the coil 1a when the step waveform is input is measured, the rated value of the current sensor 1 is determined based on the rise time of the measured current, and the current measured by the current sensor 1 is calculated based on the determined rated value. This eliminates the need for additional dedicated components or wiring for the current sensor 1, allowing existing current sensors to be used as is. Furthermore, because the rated value of the current sensor 1 is automatically determined without the need for inputting the rated value, measurement errors due to incorrect settings can be prevented.

[0032] Embodiment 2 In embodiment 1, a step response in the transient response was used as the signal to be injected into the coil 1a of the current sensor 1, but in embodiment 2, a high-frequency signal is injected into the coil 1a of the current sensor 1 and the transient response is measured to determine the rated current of the connected current sensor 1.

[0033] The configuration of the measuring instrument 2 according to the second embodiment is the same as that shown in Fig. 1, and therefore a duplicated description will be omitted. However, whereas the power supply 3f in the first embodiment is a DC power supply, the power supply 3f in the second embodiment is an AC power supply, and its frequency is, for example, about 180 Hz.

[0034] FIG. 6 is a time chart showing the response of the current sensor 1 with a small rated value when an AC signal is injected in the measuring instrument 2 according to the second embodiment. The rated value of the current sensor 1 with a small rated value is, for example, 5 A. FIG. 7 is a time chart showing the response of the current sensor 1 with a large rated value when an AC signal is injected in the measuring instrument 2 according to the second embodiment. The rated value of the current sensor 1 with a large rated value is, for example, 250 A. A method for determining the rated value of the current sensor 1 according to the second embodiment will be described using FIGS. 6 and 7.

[0035] First, in the case of current sensor 1 with a small rated value, first output 11 turns ON at time t1, as shown in Figure 6. Then, at time t2, second output 12 turns ON, and a signal of the AC voltage of power supply 3f is applied to resistor 3d and coil 1a. Due to a time constant determined by the inductance of coil 1a and the resistance value of resistor 3d, the voltage measured by A / D converter 8 gradually rises, and at time t5, it reaches a second set value that has a certain percentage (e.g., 90%) of the peak value of the AC voltage of power supply 3f.

[0036] On the other hand, in the case of current sensor 1 with a large rated value, first output 11 turns ON at time t1, as shown in Figure 7. Then, at time t2, second output 12 turns ON, and a signal of the AC voltage of power supply 3f is applied to resistor 3d and coil 1a. Due to a time constant determined by the inductance of coil 1a and the resistance value of resistor 3d, the voltage measured by A / D converter 8 gradually rises and, at time t6, reaches a second set value that is a certain percentage (e.g., 90%) of the peak value of the AC voltage of power supply 3f.

[0037] Here, when comparing the rise time from time t2 to time t5 with the rise time from time t2 to time t6, t5-t2 <t6-t2 Thus, a current sensor 1 having a larger number of turns of the coil 1a and a larger rated value (for example, 250A) has a longer rise time.

[0038] The rating determination unit 9b determines the rating value using the measured rise time t5-t2 or rise time t6-t2 and the rating value determination table 10a.

[0039] For example, the rise time of the AC signal input is measured in advance for each of a plurality of current sensors 1 having a plurality of different rated values that can be connected to the measuring instrument 2, and the measured rise times of the AC signal input for the plurality of current sensors 1 are stored in the rated value determination table 10a of the memory 10. In the rated value determination table 10a, the rise time of the AC signal input for each current sensor 1 is stored in association with the rated value (rated current) of each current sensor 1, as in Fig. 5 .

[0040] The rating determination unit 9b compares the actually measured rise time of the AC signal input to the current sensor 1 with the stored data in the rating value determination table 10a, selects the rise time that is closest to the actually measured rise time of the AC signal input from the stored data in the rating value determination table 10a, and determines the rated value associated with the selected rise time as the currently measured rated value of the current sensor 1. The set value setting unit 9c sets the determined rated value in the current sensor set value 10b in the memory 10 as the rated value of the connected current sensor 1.

[0041] Once the rated value of the connected current sensor 1 is known, the specifications of the current sensor 1, including the inductance of the coil 1a of the connected current sensor 1, are determined. Therefore, when measuring the current flowing through the electrical circuit W using the current sensor 1, the rating determination unit 9b turns off switches 3b and 3e and turns on switch 3a using the first output 11 and the second output 12, as in the first embodiment. The measurement calculation unit 9a calculates the current flowing through the electrical circuit W using the voltage measured by the A / D converter 8, the inductance of coil 1a, and the resistance value of resistor 3c.

[0042] According to the second embodiment, a high-frequency AC waveform is input to the coil 1a of the current sensor 1, the current flowing through the coil 1a when the high-frequency AC waveform is input is measured, the rated value of the current sensor 1 is determined based on the rise time of the measured current, and the current measured by the current sensor 1 is calculated based on the determined rated value. As a result, no additional dedicated parts or wiring are required for the current sensor 1, and existing current sensors can be used as is. Furthermore, since there is no need to input the rated value and the rated value of the current sensor 1 is automatically determined, measurement errors due to incorrect settings can be prevented.

[0043] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, the configurations of each embodiment may be combined as appropriate, and some of the configurations may be omitted or modified within the scope of the gist of the present disclosure. [Explanation of symbols]

[0044] 1 current sensor, 1a coil, 1b core, 2 measuring instrument, 3 current input circuit, 3a, 3b, 3e switch, 3c, 3d resistor, 3f power supply, 4 voltage input circuit, 5 display unit, 6 setting unit, 7 processing unit, 8 analog / digital converter, 9 S / W processing unit, 9a measurement calculation unit, 9b rating determination unit, 9c setting value setting unit, 10 memory, 10a rating value determination table, 10b current sensor setting value, 10c phase and wire setting value, 11 first output, 12 second output, 30 load, W electric circuit.

Claims

1. A measuring instrument that measures and calculates a current by connecting one of a plurality of current sensors having a core and a coil and different ratings, a signal input circuit for inputting a signal to the coil of the current sensor; a measurement unit that measures the current flowing through the coil when the signal is input; a rating determination unit that determines a rating value of the current sensor based on the measured current rise time; a measurement calculation unit that calculates a current measured by the current sensor based on the determined rated value; A measuring instrument comprising:

2. a determination table storing correspondence between rated values of a plurality of current sensors having different ratings and a plurality of different rise times; The rating determination unit obtains a rating value corresponding to the rise time of the measured current from the determination table, and determines the obtained rating value as the rating value of the connected current sensor.

2. The measuring instrument according to claim 1 .

3. The signal input circuit inputs a step waveform to the coil.

3. The measuring instrument according to claim 1 or 2.

4. The signal input circuit inputs a high-frequency AC waveform to the coil.

3. The measuring instrument according to claim 1 or 2.

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