JP2018017687A - Electric current measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric current measuring device that can detect widening of a gap between joining surfaces by small dust sticking to them.SOLUTION: An electric current measuring device having a magnetic core for detecting magnetic fluxes passing the magnetic core by using Hall effect elements is equipped with two pairs of connecting terminals for the Hall effect elements, a switch circuit that switches over the connection between a source power supply terminal and a sensor signal input terminal, a differential amplifier circuit that supplies feedback coil with a current in the direction of canceling magnetic fluxes attributable to a measured current passing the magnetic core, and a controller that controls the switch circuit so as to switch over the direction of voltage application by the Hall effect elements as to input a measurement voltage and determines a clamping error when the difference between the two measurement voltages is no smaller than a prescribed value. It is made possible to detect widening of a gap between joining surfaces by small dust sticking to them.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current measuring device, and more particularly to a current measuring device that uses a Hall effect element and can detect a clamping failure with high accuracy with a simple configuration.

  Conventionally, various current measuring apparatuses using Hall effect elements have been proposed. For example, Patent Document 1 below discloses a watt-hour meter using a Hall effect element. This watt-hour meter outputs a Hall voltage corresponding to the product of the measurement voltage and the measurement current by the Hall element, and inverts the positive / negative polarity of the Hall voltage at every predetermined period by the switching means SWa1 to SWb2, thereby differential amplification means And the polarity of the differential amplification output is inverted again by the inverting means to the state where the polarity inversion by the switching means has returned, and is integrated by the integrating means. The Hall element has the same polarity as the Hall element. Two Hall elements that output an unbalanced voltage with a polarity different from the voltage are used, and the unbalanced voltage adjusting means adjusts the two Hall elements so that the unbalanced voltages are equal to each other. Thus, the differential amplification outputs of the two Hall elements are added.

JP 2001-159646 A

  In the current sensor circuit using the conventional Hall effect element as described above, a magnetic core having a round or ring shape is used as a whole in order to couple the magnetic field generated by the current to be measured and the Hall effect element. . In use, the core is divided into two parts, attached so that the current cable to be measured passes through the central portion, and clamped so that the core is joined in an annular shape.

  However, if small dust adheres to the joint surface at the time of clamping, there is a problem that the gap of the joint surface becomes wide and current measurement error increases.

An object of the present invention is to solve the above-described conventional problems, and to provide a current measuring device capable of detecting that a small dust adheres to a joint surface during clamping and a gap is widened.

  The current measuring device according to the present invention includes a magnetic core that is divided and magnetically coupled to a conductor through which a current to be measured flows, and detects a magnetic flux passing through the magnetic core using a Hall effect element. , A switch circuit for switching the connection between two sets of connection terminals of the Hall effect element, a power supply terminal and a sensor signal input terminal, and a signal output from the switch circuit is input and measured through the magnetic core An amplifier circuit composed of a differential amplifier circuit for passing a current in a direction to cancel the magnetic flux due to the current to the feedback coil, a feedback coil wound around the magnetic core and through which the output current of the amplifier circuit flows, and the switch circuit When the voltage application direction of the Hall effect element is switched and the measurement voltage is input, and the difference between the two measurement voltages is greater than or equal to a predetermined value, the clamp is not To mainly characterized in that a determining controller and.

  Also, the clamping failure detection method of the present invention is divided, a magnetic core that can be magnetically coupled to a conductor through which a current to be measured flows, a Hall effect element that detects a magnetic flux passing through the magnetic core, and the Hall effect A switch circuit for switching the connection between the two connection terminals of the element, the power supply terminal and the sensor signal input terminal, and a signal output from the switch circuit are input to cancel the magnetic flux caused by the current to be measured passing through the magnetic core. An amplifier circuit composed of a differential amplifier circuit for flowing a current in the direction to the feedback coil, a feedback coil wound around the magnetic core and through which an output current of the amplifier circuit flows, and the switch circuit to control the Hall effect element A current sensor device including a controller that switches a voltage application direction and inputs a measurement voltage. Controlling the switch circuit to switch to one voltage application direction, the controller inputting and storing the measurement voltage, the controller controlling the switch circuit to switch to the other voltage application direction, the controller Inputting and storing a measurement voltage; and calculating a difference between the two measurement voltages by the controller. A main feature is that the controller includes a step of determining a clamp failure when the difference is equal to or greater than a predetermined value.

The present invention has the following effects.
(1) Since it is possible to detect even if a small amount of dust adheres to the joint surface without using mechanical means, it is possible to improve the accuracy of detecting a clamping failure.
(2) If the gap between the joint surfaces is equal to or greater than a predetermined value, for example, a state in which the core is completely separated can be detected, which can be used for confirming the clamped state.

FIG. 1 is a block diagram showing a configuration of a current measuring apparatus according to the present invention. FIG. 2 is a circuit diagram showing a configuration of a current sensor circuit according to the present invention. FIG. 3 is a circuit diagram showing the configuration of the switch circuit in the present invention. FIG. 4 is an explanatory diagram showing an example of current measurement values in the present invention. FIG. 5 is a flowchart showing the processing contents of the controller of the present invention.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a current measuring apparatus according to the present invention. The current measuring device of the present invention includes a magnetic coupling device and a current sensor circuit 40. The magnetic coupling device includes magnetic cores 43 and 44 that are magnetically coupled to an electric cable 45 that is a conductor through which a current to be measured flows, a Hall effect element 41 that is disposed in a gap between the magnetic cores 43, and the magnetic cores 43 and 44. And a feedback coil 42 wound around.

  The B-shaped magnetic core is divided into halves. One of the U-shaped magnetic cores 44 is removed, the electric cable 45 is passed through the internal space, and the magnetic cores 44 are mounted. The magnetic core can be magnetically coupled to the electric cable 45 by fixing the joint surfaces 46 of the two magnetic cores 43 and 44 in a joined state by a locking mechanism using a hinge or the like.

  A well-known Hall effect element 41 that is commercially available has two sets of terminals. When a constant voltage is applied to one terminal and a current flows, a voltage proportional to the magnetic field penetrating the element is applied between the other terminals. Occur. Note that even if the connection destination of the two terminals of the Hall effect element 41 is exchanged to switch the voltage application direction of the Hall effect element and a voltage is applied to the other terminal, the one terminal is proportional to the magnetic field. Generated.

  As will be described later, the current sensor circuit 40 is magnetically coupled to the electric wire 45, measures the current value flowing through the electric wire using the Hall effect element 41, and outputs data proportional to the electric current value of the electric wire.

  FIG. 2 is a circuit diagram showing the configuration of the current sensor circuit 40 in the present invention. The controller 56 is a well-known one-chip microcomputer circuit that is commercially available. The controller 56 includes a CPU, a ROM, a RAM, a digital input / output circuit, an analog input circuit (A / D conversion circuit), a hardware timer circuit, and the like. The ROM stores programs and data for executing processing to be described later.

  The switch circuit 50 is an analog switch circuit using a semiconductor switching element that is switch-controlled by an output signal of the controller 56, and includes two sets of connection terminals of the Hall effect element 41 and a power supply terminal (for example, a + 3V power source and a ground) ) And sensor signal input terminals (+ output and −output to the amplifier circuit 51) are switched.

  The amplifier circuit 51 to which a signal is input from the switch circuit 50 is composed of a differential amplifier circuit having a predetermined amplification factor composed of an operational amplifier. The output of the amplifier circuit 51 is connected to one end of a resistor 54 via a feedback coil 42, and the other end of the resistor 54 is grounded. The resistor 54 is a load resistor of the amplifier circuit 51, and the voltage generated at the resistor 54 is proportional to the current flowing through the electric cable 45. This voltage value is read from the analog input terminal of the controller 56 (A / D converted) and stored.

    The amplifier circuit 51 is connected so that a current in a direction to cancel the magnetic flux due to the current to be measured passing through the magnetic cores 43 and 44 flows through the feedback coil 42. Therefore, a current that is proportional to the current flowing through the conductor 45 and inversely proportional to the turn ratio of the feedback coil with the number of turns of the conductor 45 being 1 flows through the feedback coil 42. However, since negative feedback is applied, the magnetic flux density inside the magnetic cores 43 and 44 is considerably smaller than the magnetic flux density due to the current flowing through the conductor 45. As a result, since the magnetic flux density inside the magnetic cores 43 and 44 does not become a large value, the magnetic cores 43 and 44 are not magnetized, and the occurrence of measurement errors due to magnetization can be prevented.

  The power supply circuit 55 is a power supply circuit that generates a bipolar power supply for the amplifier circuit and a unipolar power supply for the Hall effect element and the controller.

  FIG. 3 is a circuit diagram showing the configuration of the switch circuit in the present invention. Even if the connection destinations of the two terminals of the Hall effect element 41 are exchanged and a voltage is applied to the other terminal, a voltage proportional to the applied magnetic field is generated at one terminal. At this time, the unbalanced voltage value of the voltage output from the Hall effect element 41 has a reverse polarity before and after replacing the terminal set.

  The switch circuit 50 includes two sets of connection terminals (a set of + A and −A and a set of + B and −B) of the Hall effect element 41, a power supply terminal (for example, a + 3V power supply and a ground), and a sensor signal input terminal (amplification). The connection with the + output and the -output) to the circuit 51 is switched.

  For example, when the control signal of the switch circuit is 0, the switch circuit 50 is in a state as shown in FIG. 3, the power supply is connected to the A set terminals, and the B set terminals are connected to the sensor signal input terminals. When the control signal of the switch circuit is 1, each switch of the switch circuit 50 is switched, the power source is connected to the B set terminals, and the A set terminals are connected to the sensor signal input terminals. As a result, the A group and B group output signals are alternately output to the sensor signal input terminals (+ output and -output) with the same polarity.

  FIG. 4 is an explanatory diagram showing an example of current measurement values in the present invention. FIG. 4A shows an example of a measured voltage value when clamped normally, and the absolute value of the difference between the value V1 before switching of the switch circuit and the value V2 after switching becomes a small value. Yes.

  On the other hand, FIG. 4B shows a clamp voltage failure, that is, a measured voltage value when dust or the like is present on the core joint surface 46 and the gap of the joint surface 46 is wider than a predetermined value or the clamp is not closed. The absolute value of the difference between the value V3 before the switching of the switch circuit and the value V4 after the switching is large.

  The present inventor has found from the experiment simulating the clamping failure that the difference between the two measured voltage values increases as the gap is widened. The present invention uses this relationship to detect a clamping failure.

  FIG. 5 is a flowchart showing the processing contents of the controller 56. When attempting to measure current, the user first clamps the magnetic coupling device without passing an electrical cable, and then presses a setup button on the device panel (not shown). In S10, it is determined whether or not the setup is started depending on whether or not the setup button is pressed. If the determination result is negative, the process returns to S10, but if the determination is positive, the process proceeds to S11.

  In S11, a control signal for switching the switch circuit 50 to one state is output. In S12, the voltage Va is read (A / D converted) from the analog input terminal connected to one end of the resistor 54 and stored. In S13, a control signal for switching the switch circuit 50 to the other state is output. In S14, the voltage Vb is read from the analog input terminal and stored.

  In S15, d1 = Va−Vb is calculated. In S16, the calculated value d1 is compared with the normal stored value d0. d0 is measured and calculated in the same manner as d1 at the time of manufacture of the current measuring device, and is written in the ROM in the controller 56. In S17, it is determined whether or not the difference (absolute value of d1) is equal to or smaller than a predetermined value. If the determination result is negative, the process proceeds to error stop processing, but if the determination is positive, the process proceeds to S18.

  In the error stop process, the clamp is not completely closed (dust is present on the core joining surface 46 and the gap between the joining surfaces 46 is wider than a predetermined value) or the clamp is not closed. Is displayed and the startup process is terminated.

  Here, the user closes the clamp while passing the electric cable 45 through the magnetic coupling device, and then presses a measurement start button on a panel (not shown). In S18, it is determined whether or not the current measurement is started depending on whether or not the measurement start button is pressed. If the determination result is negative, the process returns to S18, but if the determination is positive, the process proceeds to S19.

  In S19, a control signal for switching the switch circuit 50 to one state is output. In S20, the voltage Va is read from the analog input terminal connected to one end of the resistor 54 and stored. In S21, a control signal for switching the switch circuit 50 to the other state is output. In S22, the voltage Vb is read from the analog input terminal and stored. In S23, d2 = Va−Vb is calculated.

  In S24, the calculated value d2 is compared with the previously calculated d1. In S25, it is determined whether or not the absolute value of the difference (| d1-d2 |) is equal to or smaller than a predetermined value. If the determination result is negative, the process proceeds to an error stop process. Migrate to In the error stop process, the clamp is not completely closed (dust is present on the core joining surface 46 and the gap between the joining surfaces 46 is wider than a predetermined value) or the clamp is not closed. Is displayed and the current measurement process is terminated.

  In S26, the current value is measured and stored. For example, the average value of the measured values V1 and V2 before and after switching in FIG. 4A is taken as the current value, and a digital value of this average value is output or recorded. Thereafter, S19 to S26 are repeated at a predetermined cycle.

  The present invention is applicable to any device that needs to measure current.

DESCRIPTION OF SYMBOLS 40 ... Current sensor circuit 41 ... Hall effect element 42 ... Feedback coil 43, 44 ... Magnetic core 45 ... Electric cable 46 ... Joining surface

Claims (2)

In a current measuring device that is divided and includes a magnetic core that can be magnetically coupled to a conductor through which a current to be measured flows, and that detects magnetic flux passing through the magnetic core using a Hall effect element,
A switch circuit that switches connection between the two sets of connection terminals of the Hall effect element, a power supply terminal, and a sensor signal input terminal;
An amplifier circuit comprising a differential amplifier circuit that receives a signal output from the switch circuit and flows a current in a direction to cancel the magnetic flux due to the current to be measured passing through the magnetic core to the feedback coil;
A feedback coil wound around the magnetic core and through which an output current of the amplifier circuit flows;
A controller for controlling the switch circuit, switching a voltage application direction of the Hall effect element, inputting a measurement voltage, and determining a clamp failure when a difference between the two measurement voltages is a predetermined value or more. A characteristic current measuring device. A magnetic core that is divided and can be magnetically coupled to a conductor through which a current to be measured flows;
A Hall effect element for detecting magnetic flux passing through the magnetic core;
A switch circuit that switches connection between the two sets of connection terminals of the Hall effect element, a power supply terminal, and a sensor signal input terminal;
An amplifier circuit comprising a differential amplifier circuit that receives a signal output from the switch circuit and flows a current in a direction to cancel the magnetic flux due to the current to be measured passing through the magnetic core to the feedback coil;
A feedback coil wound around the magnetic core and through which an output current of the amplifier circuit flows;
In a current sensor device comprising a controller for controlling the switch circuit and switching a voltage application direction of the Hall effect element to input a measurement voltage,
The controller controlling the switch circuit to switch to one voltage application direction;
The controller inputs and stores the measured voltage;
The controller controlling the switch circuit to switch to the other voltage application direction;
The controller inputs and stores the measured voltage;
The controller calculating a difference between two measured voltages;
A clamp failure detection method comprising the step of determining that the controller has a clamp failure when the difference is greater than or equal to a predetermined value.

Images