JP2017142068A - Current sensor and filtering method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an unbalanced voltage irrespective of a temperature change and enable highly accurate measurement, and also improve full-scale accuracy.SOLUTION: A current sensor of the present invention comprises: a magnetic core for generating a magnetic flux that corresponds to a measurement current; a pair of hall elements, arranged in a gap formed in the magnetic core, for outputting a voltage that corresponds to a flux density in the gap; switching means for alternately switching a current terminal and an output terminal on the basis of a control signal in each of the pair of hall elements; control signal output means for outputting the control signal so that the control signal inputted to the switching means is mutually inverted in the pair of hall elements; computing means for calculating, for each hall element, the average value of hall voltages successively outputted from the output terminal switched by the switching means; addition means for adding hall voltages calculated for each hall element by the computing means and outputting the added hall voltage; and a closed loop coil provided in the post-stage of the addition means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current sensor and a filtering method therefor, and more particularly to a current sensor that has extremely stable temperature characteristics, is highly accurate, and can improve full-scale sensitivity and a filtering method therefor.

In recent years, there is an increasing demand for direct current power supply in private power generation and data centers. Therefore, there is a need for a DC sensor used in a transaction meter power meter that can handle this.
A Hall element is generally used for a DC sensor that measures DC. However, when a Hall element is used, there are unbalanced voltage (output voltage generated at zero magnetic flux), variation of unbalanced voltage due to temperature characteristics, full-scale sensitivity error, and the like.

Patent Document 1 discloses a method of separating an unbalanced voltage from a Hall voltage by switching an input / output of the Hall element by a switching means and taking an average value of two Hall voltages obtained via the switching means (magnetic field detection). Device).
However, this method has a problem that the unbalanced voltage and sensitivity change due to temperature change.

  In response to such a problem, Patent Document 2 discloses a current measuring device that performs temperature correction by inverting two Hall elements in a gap (in the magnetic field) and canceling out the temperature characteristics of the two Hall elements. ing. According to this method, since temperature correction can be easily performed, there is an advantage that a correction circuit such as a temperature sensor related to offset is not required.

Japanese Unexamined Patent Publication No. 57-42865 JP 7-294561 A

As described above, in the method of switching input / output of the Hall element by the switching means disclosed in Patent Document 1, there is a problem of a change in unbalanced voltage accompanying a temperature change, which is disclosed in Patent Document 2 Can be solved.
However, the method disclosed in Patent Document 1 has another problem that switching noise occurs, and this cannot be solved by the method disclosed in Patent Document 2.
In order to reduce the noise, a low-pass filter or the like is generally used. However, when such a filter is used, there is a problem that a frequency band as a current sensor is narrowed.

  The present invention has been made paying attention to the above points, and in a current sensor for measuring a direct current, it enables high-accuracy measurement by suppressing an unbalanced voltage regardless of a temperature change, and is capable of full scale. An object of the present invention is to provide a current sensor capable of improving sensitivity and a filtering method thereof.

  In order to solve the above-described problem, a current sensor according to the present invention is disposed in a magnetic core that generates a magnetic flux corresponding to a measurement current, and a gap formed in the magnetic core, and a magnetic flux density in the gap. A pair of Hall elements that output a voltage corresponding to the switching element, a switching unit that alternately switches a current terminal and an output terminal based on a control signal in each of the pair of Hall elements, and the control signal that is input to the switching unit Control signal output means for outputting the control signal so as to invert each other in the pair of Hall elements, and for each Hall element, an average value of the Hall voltages sequentially output from the output terminals replaced by the switching means. A calculating means for calculating and an addition for adding and outputting the Hall voltage calculated for each Hall element by the calculating means. And a closed loop winding provided at a stage subsequent to the adding means, and a feedback current proportional to the number of turns of the closed loop winding is applied to the measurement current based on the Hall voltage output from the adding means And switching noise due to the switching means is reduced.

According to such a configuration, the switching operation is performed by alternately switching the current terminal and the output terminal of the Hall element, and the unbalanced voltage is separated from the Hall voltage by obtaining the average value of the Hall voltage obtained in each case. Is done.
Further, since the two Hall elements are inverted in the magnetic field, the unbalanced voltage can be canceled regardless of the temperature change by adding both outputs, and a double output Hall voltage can be obtained.
Furthermore, unlike conventional filtering that narrows the frequency band, closed-loop filtering reduces the switching noise while extending the frequency band range of the sensor and significantly improving the full-scale sensitivity error. it can.

  In order to solve the above-described problem, a current sensor filtering method according to the present invention includes a pair of Hall elements disposed in a gap formed in a magnetic core, and a voltage corresponding to the magnetic flux density in the gap. A filtering method for a current sensor that outputs a signal, wherein in each of the pair of Hall elements, a step of performing switching by alternately switching a current terminal and an output terminal based on a control signal, and a control signal used for the switching include A step of outputting the control signal so as to invert each other in a pair of Hall elements; a step of calculating an average value of Hall voltages sequentially output from the output terminals switched by the switching for each Hall element; Adds the average value of the Hall voltage calculated for the Hall element and outputs it. And applying a feedback current proportional to the number of turns of the closed loop winding through which the measurement current flows to the measurement current based on the Hall voltage obtained by the addition, and reducing noise due to the switching. It has the characteristics in having.

  According to such a filtering method, unlike the conventional filtering that narrows the frequency band by closed loop type filtering, the range of the sensor frequency band is expanded while reducing the switching noise, and the full-scale sensitivity error is reduced. It can be remarkably improved.

  In a current sensor that measures a direct current, it is possible to obtain a current sensor capable of suppressing an unbalanced voltage regardless of a temperature change, enabling highly accurate measurement, and improving full-scale sensitivity.

FIG. 1 is a circuit diagram of a current sensor according to the present invention. FIG. 2 is a circuit diagram showing an internal configuration of the Hall IC included in the circuit of FIG. FIG. 3A and FIG. 3B are graphs showing current measurement results as a comparative example. FIG. 4A and FIG. 4B are graphs showing current measurement results as examples.

Hereinafter, embodiments of a current sensor according to the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram (block diagram) of a current sensor according to the present invention. FIG. 2 is a circuit diagram showing an internal configuration of the Hall IC included in the circuit of FIG.

The circuit of the current sensor 1 shown in FIG. 1 is supplied with a power supply circuit 2, a hall element portion 3 disposed in a gap of a magnetic core (not shown), and an output (hall voltage) of the hall element portion 3. An adder 4 (adding means), and a filter unit 5 that performs a filtering process on the output of the adder 4.
For example, in the power supply circuit 2 including a constant voltage circuit, a resistor R1 and a Zener diode 12 are connected in series to a battery power supply 11. That is, the cathode of the Zener diode 12 is connected to the resistor R 1, and the output of this cathode is applied to the Hall element portion 3.
If the Hall element unit 3 is designed to operate at a constant current, the power supply circuit 2 may be configured as a constant current circuit.

In addition, as shown in FIG. 1, the Hall element unit 3 is configured by a pair of Hall ICs 13 and 14 connected in parallel. The Hall ICs 13 and 14 are inverted from each other in the magnetic field formed in the gap of the magnetic core (not shown), and output the Hall voltage corresponding to the magnetic flux density.
As shown in FIG. 2, each of the Hall ICs 13 and 14 includes a cross-shaped Hall element 21, a multiplexer 23 (switching means) connected to the electrodes a, b, c, and d of the Hall element 21, and the multiplexer 23. And a differential amplifier 24 to which the output of the Hall element 21 obtained in this way is input. Furthermore, the Hall ICs 13 and 14 are the first and second peak hold circuits 25 and 26 for peak-holding the Hall voltage output from the differential amplifier 24, and the holes held by the first and second peak hold circuits 25 and 26. And an arithmetic unit 27 (calculation means) for calculating the average of the voltages.

In response to the control signal to the select switch, the multiplexer 23 connects the electrodes a and b of the Hall element 21 to the power supply circuit 2 and connects the electrodes c and d of the Hall element 21 to the differential amplifier 24 in the first operation mode. Connect to.
Further, in the second operation mode, the electrodes c and d of the Hall element 21 are connected to the power supply circuit 2 and the electrodes a and b of the Hall element 21 are connected to the differential amplifier 24.
The differential amplifier 24 takes a differential output from the Hall element 21 and outputs a Hall voltage.

  As shown in FIGS. 1 and 2, the Hall ICs 13 and 14 are supplied with a control signal Ct from the control circuit 30 (control signal output means). For example, the control signal Ct is input to the select switch of the multiplexer 23 of the Hall IC 13. Is input at the same timing, an inverted signal of the control signal Ct is input to the select switch of the multiplexer 23 of the Hall IC 14.

That is, in the Hall ICs 13 and 14, when one is in the first operation mode, the other is in the second operation mode, and the connection destination of the electrodes a and b of the Hall element 21 and the connection destination of the electrodes c and d are It is controlled to be different from each other.
As a result, the Hall elements 21 of the Hall ICs 13 and 14 having the same temperature drift tendency simultaneously perform normal operation and inversion operation, respectively.

  Further, the control signal Ct to the multiplexer 23 is alternately switched at a predetermined timing, whereby the current terminals and the output terminals of the Hall elements are alternately switched in each of the Hall ICs 13 and 14 (the first operation mode and the first operation mode). 2 operation modes are switched). For this reason, the average value of the Hall voltage obtained in each operation mode is obtained by the calculator 27, whereby the unbalanced voltage is separated from the Hall voltage.

The adder 4 adds the Hall voltage VH input from the Hall ICs 13 and 14, amplifies it, and outputs it.
The temperature drift characteristics of the Hall elements 21 of the Hall ICs 13 and 14 are the same, and the Hall ICs and 14 simultaneously perform normal operation and inversion operation, respectively. Therefore, the sign of the unbalanced voltage VH0 is inverted.
Therefore, by obtaining the sum of the outputs of the Hall ICs 13 and 14, the unbalanced voltage VH0 is canceled regardless of the temperature change as shown in the equation (1), and the Hall ICs 13 and 14 output is the Hall voltage of the double output. VH can be obtained.
(Equation 1)
(VH + VH0) + (VH−VH0) = 2VH (1)

In addition, since the switching noise is generated in the Hall ICs 13 and 14 having the multiplexer 23, it is desirable to suppress the noise by using a strong filter for lowering the cutoff frequency.
Therefore, the current sensor according to the present invention includes a closed loop type filter unit 5 that functions as a filter as shown in FIG.

  The filter unit 5 includes a closed loop winding 28 and a resistor R2, and applies a feedback current proportional to the number of turns of the closed loop winding 28 to the measurement current based on the Hall voltage output from the adder 4. To output the measurement current. This makes it possible to obtain a filter effect that makes the generated magnetic flux zero and reduces the influence of the temperature characteristics of the sensitivity of the Hall element. In addition, while suppressing noise by the filter effect, the range of the frequency band of the sensor can be extended, and the full-scale sensitivity error can be remarkably improved.

  In the current sensor 1 configured as described above, the control signal Ct (or its inverted signal) is input from the control circuit 30 to the multiplexer 23 of the Hall ICs 13 and 14 in the Hall element unit 3 in the Hall element unit 3, and the Hall element 21 of the Hall IC 13. And the Hall element 21 of the Hall IC 14 are normally operated and reversed (for example, the first operation mode).

Further, a predetermined constant voltage is applied from the power supply circuit 2 to the Hall element 21 of the Hall IC 13 and the Hall element 21 of the Hall IC 14, and the Hall voltage obtained by the differential amplifier 24 is sampled and held in the Hall ICs 13 and 14. Output to.
Next, the control signal Ct is inverted by the control circuit 30 so that the Hall element 21 of the Hall IC 13 and the Hall element 21 of the Hall IC 14 are inverted and normally operated (for example, the second operation mode).

Similar to the first operation mode, a predetermined constant voltage is applied from the power supply circuit 2 to the Hall element 21 of the Hall IC 13 and the Hall element 21 of the Hall IC 14, and is obtained by the differential amplifier 24 in each Hall IC 13, 14. The Hall voltage is output to the sample hold circuit 26.
In each Hall IC 13, 14, the Hall voltage held in each of the sample hold circuits 25, 26 is input to the calculator 27, and the average value of the two hold voltages is obtained. Thereby, in Hall IC13, 14, the Hall voltage from which the unbalanced voltage was isolate | separated is obtained, respectively.

The Hall voltages output from the Hall ICs 13 and 14 are added by the adder 4. Here, since the Hall element 21 of the Hall IC 13 and the Hall element 21 of the Hall IC 14 are arranged so as to perform normal operation and reversal operation (or vice versa), unbalance included in the outputs of the Hall ICs 13 and 14, respectively. The sign of the voltage is inverted, and this addition process cancels the unbalanced voltage regardless of temperature changes. Further, the output level of the added Hall voltage is doubled, and a highly accurate measurement result is obtained.
Further, in the filter unit 5, a feedback current proportional to the number of turns of the closed loop winding 28 is applied to the output of the adder 4, and a wide frequency band is secured while reducing switching noise by the filter effect.

As described above, according to the embodiment of the present invention, the switching operation of alternately switching the current terminal and the output terminal of the Hall element is performed, and the average value of the Hall voltage obtained in each case is not obtained. The balanced voltage is separated from the Hall voltage.
In addition, since the two Hall elements 21 are reversed in the magnetic field (Hall ICs 13 and 14 operate normally and reversely with each other), the unbalanced voltage can be canceled regardless of the temperature change by adding both outputs. And a Hall voltage with double output can be obtained.
Furthermore, unlike conventional filtering that narrows the frequency band, closed-loop filtering reduces the switching noise while extending the frequency band range of the sensor and significantly improving the full-scale sensitivity error. it can.

In the above embodiment, the multiplexer 23 is included in the Hall ICs 13 and 14. In this case, since the switching circuit is included in the IC package, the sensor can be constructed at a relatively low cost.
However, the current sensor according to the present invention is not limited to this configuration, and any packaging configuration can be adopted. For example, the Hall ICs 13 and 14 may be configured not to include the multiplexer 23 and subsequent circuits. Alternatively, the multiplexer 23 may be included, but the subsequent circuit may not be included. Alternatively, all the circuits may be made into one package.

  The current sensor according to the present invention will be further described based on examples. In this example, the current sensor described in the above embodiment was manufactured, and in particular, the effect of the closed loop filter was verified.

FIG. 3 shows waveforms measured using the current sensor of the present invention (with a closed loop filter). FIG. 3A shows the measurement result when the measured current is 0A, and FIG. 3B shows the measurement result when the measured current is 1A (500 Hz).
FIG. 4 shows a waveform measured by removing the closed loop type filter from the current sensor of the present invention. FIG. 4A shows the measurement result when the measured current is 0A, and FIG. 4B shows the measurement result when the measured current is 1A (500 Hz).
As shown in the waveforms of FIGS. 3 and 4, it was confirmed that the use of a closed-loop filter lowered the cut-off frequency and greatly reduced noise.

DESCRIPTION OF SYMBOLS 1 Current sensor 2 Power supply part 3 Hall element part 4 Adder (addition means)
5 Filter unit 11 Battery power supply 12 Zener diode 13 Hall IC
14 Hall IC
21 Hall element 23 Multiplexer (switching means)
24 differential amplifier 25 sample hold circuit 26 sample hold circuit 27 calculator (calculation means)
28 closed loop winding 30 control circuit (control signal output means)

Claims (2)

A magnetic core that generates a magnetic flux corresponding to the measurement current;
A pair of Hall elements arranged in a gap formed in the magnetic core and outputting a voltage corresponding to the magnetic flux density in the gap;
In each of the pair of Hall elements, switching means for alternately switching the current terminal and the output terminal based on a control signal;
Control signal output means for outputting the control signal so that the control signals input to the switching means are mutually inverted in the pair of Hall elements;
For each Hall element, computing means for calculating the average value of the Hall voltage sequentially output from the output terminal replaced by the switching means,
Adding means for adding and outputting the Hall voltage calculated for each Hall element by the calculating means;
A closed-loop winding provided in a subsequent stage of the adding means,
A feedback current proportional to the number of turns of the closed loop winding is applied to the measurement current based on the Hall voltage output from the adding means, and the switching noise due to the switching means is reduced. . A current sensor filtering method for outputting a voltage corresponding to a magnetic flux density in the gap by a pair of Hall elements arranged in the gap formed in the magnetic core,
In each of the pair of Hall elements, performing switching for alternately switching the current terminal and the output terminal based on a control signal;
Outputting the control signals so that the control signals used for the switching are mutually inverted in the pair of Hall elements;
For each Hall element, calculating an average value of the Hall voltage sequentially output from the output terminal replaced by the switching;
Adding and outputting the average value of the Hall voltage calculated for each Hall element;
Applying a feedback current proportional to the number of turns of the closed loop winding through which the measurement current flows to the measurement current based on the Hall voltage obtained by the addition, and reducing noise due to the switching. The current sensor filtering method.

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