JPH0211109B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current sensor that constitutes a self-exciting circuit using a magnetic core with high magnetic flux and an operational amplifier, and detects current through the self-exciting operation of this circuit.

A magnetic modulator using a circular magnetic core, which is representative of the conventional current measurement method, is called a "magnetic amplifier for measurement".
(edited by the Magnetic Amplifier Specialist Committee of the Institute of Electrical Engineers of Japan, December 1962)
As described in ``Modulator excitation method'' on page 76 (published by Denkishoin on January 1st), it was a separately excited type in which the AC excitation power source was a separate circuit. Therefore, in the basic configuration, as shown in "Specific examples of attached circuits for each system" on page 94 of the above-mentioned book, the magnetic sensing section (modulator MM in the above-mentioned book) using a ring-shaped magnetic core, and the magnetic core of several K
A drive circuit section with a built-in AC excitation power supply that excites at excitation frequencies from Hz to several tens of KHz, a synchronous rectifier section that amplifies the frequency double (2) component of the magnetic core and performs phase detection,
Create a two-component reference signal from the excitation frequency,
A multiplier circuit for input to the synchronous rectifier is always required, and it also includes a display circuit to display the strength of the current, so the circuit configuration is complex and has a large number of parts, making it necessary to reduce the size of the overall device. Deleting part of each circuit section was fundamentally a difficult problem. Therefore, it has been particularly difficult to install the current sensor in a limited local space.

The present invention provides a self-oscillation type current sensor that eliminates the drawbacks of the prior art, greatly reduces the number of parts using a very simple circuit system, and can be used even in a limited local space.

That is, the present invention includes a single-hole magnetic core that generates a magnetic path in an annular direction, an operational amplifier for exciting the magnetic core, a first winding for excitation wound around the magnetic core, and a second winding for inputting the operational amplifier. and a third winding arranged so that the current to be measured passes through the hole in the magnetic core, the first winding being connected to the output terminal side circuit of the operational amplifier, and the second winding being connected to the input circuit of the operational amplifier. Connected to the inverting terminal and non-inverting terminal side of the terminal side circuit, respectively, the positive excitation time and negative excitation time starting from the value determined by the current value to be measured in the operational amplifier are used to saturate the operational amplifier, which has both positive and negative polarities. By converting the DC voltage into a positive half-cycle excitation time and a negative half-cycle excitation time, and feeding back this saturated DC voltage to the first winding to bring the single-hole magnetic core into a self-excited state, the periods of positive and negative excitation times can be changed. This is a self-oscillation type current sensor configured to measure the current value to be measured from the length ratio, and in which a capacitor is connected in parallel between the terminals of the second winding. First, the first feature is that the current sent from the drive circuit section to the magnetic sensing section is a direct current transmission, the magnetic core and the operational amplifier itself constitute a self-exciting circuit, and the output signal from the current sensing section depends on the input current. A square wave alternating current signal whose ratio of positive and negative half-cycle periods is variable depending on the applied magnetic field generated by the electric field, and a direct current signal obtained by integrating this signal is used as the target signal for current detection. number of parts
The point is that we have realized a DC-DC transmission method that allows current detection signals to be extracted even from a distance of 10 m to several 100 m.

The second feature is that a highly stable current-sensitive self-exciting circuit is constructed by using a high-permeability material such as ferrite, amorphous material, or permalloy as the magnetic core used in the current-sensing section. As a result, a high-frequency AC excitation power source and an AC amplitude stabilizing circuit are no longer necessary, and measures to prevent AC excitation current from attenuating and signal voltage from attenuating in the transmission path are completely unnecessary.

The third feature is that the input current flow direction and strength are directly converted into the output voltage polarity and voltage value without using phase detection or amplitude detection circuits, and signal processing is performed by the current sensing section itself. This is because it has a function that allows you to do so.

The fourth feature is that the current sensing section is driven by two positive and negative DC stabilized power supplies, which allows the power supply for the operational amplifier used in the signal processing circuit to be shared, and also enables common grounding. .

The fifth feature is that the current sensor has very low power consumption, so it can be said to be a highly practical and versatile current sensor system that can coexist on a linear IC level printed circuit board. In other words, the current value for exciting the magnetic core is 10 mA or less, which is sufficient for the output of the operational amplifier, and operation is possible without the addition of an excitation current amplification circuit using an external power transistor.

A detailed explanation will be given below with reference to the drawings.

FIGS. 1a to 1c show examples of the material composition of a single-hole magnetic core 1 made of a magnetic material for the single-hole magnetic core used in the present invention.
A shows an example of a magnetic core that has been punched, fired, or etched, b shows an example of a magnetic core wound with a tape-shaped magnetic material, and c shows an example of a magnetic core wound with a thin ribbon wire or wire rod. Since the object of the present invention can be achieved with any shape or configuration, there is no particular limitation thereon.
Although the magnetic core 1 has a single hole, its shape is not limited either. The materials used are also not limited to pure iron, silicon steel, permalloy, amorphous, ferrite, etc. Of course, it is also possible to use a thin film obtained by manufacturing a sputter or the like.

FIG. 2 shows the basic configuration of the winding wire wound around the magnetic core of the current sensor according to the present invention. Figure 2a shows the basic configuration of the present invention, in which the magnetic core 5 with the excitation winding and the operational amplifier input winding fixed in a mold or the like is a single-hole magnetic core, and the first winding for excitation of the terminals 2a and 2b is outside the single-hole magnetic core. line 2 and the second winding 3 for the op amp input.
The third winding 4 for inputting the current to be measured, which is the terminals 4a and 4b, is passed through. The number of turns of the third winding 4 is one turn in the figure, but generally any number of turns may be used as long as the condition of electromagnetically loose coupling is satisfied.
Capacitor 6 is added for the purpose of adjusting the switching timing of the operational amplifier and absorbing noise components generated from the magnetic core, as well as stabilizing self-excited oscillation. It is connected to the winding terminals of terminals 3a and 3b, and creates a resonant circuit. It consists of Figures 2b and 2c show an example of an input circuit in which a part of the measured current Iin flows through the input winding 4 inside the single hole, and the rest flows through one or more shunt conductors 40 outside the single hole. . The feature of this circuit is that it bypasses the current and measures only Iex shunted to a predetermined current magnitude.
The purpose of this invention is to enable measurement of a large current Iin with a small magnetic core. That is, it is possible to measure Iin by converting it from the magnetic field created by the input current Iex passing through this magnetic core. In such an input circuit configuration, since the AC component induced from the magnetic core to the second winding 3 is short-circuited by the conductor 40, there is a great advantage that the electromagnetic induction component is blocked from flowing into the input circuit.

FIG. 3 shows the operating principle of the present invention at B-
FIG. 3 is a diagram for explaining using Iex characteristics. Third
Figure a shows the B-Iex characteristic of the magnetic core 5 when the input current Iex is zero (Iex=0). Since hysteresis exists in the magnetic core 5, 1 of the excitation
In the cycle →→
You will follow the route →→. here,
When Iex = 0, when a positive DC voltage is applied to the excitation winding 2 connected to a high resistance and the magnetic core 5 is excited to the maximum magnetic flux density Bm by the positive excitation field, as shown in the figure, The range of magnetic flux density change is △B ₁₂ . If the DC voltage is made zero at the same time that the magnetic flux density of the magnetic core 5 reaches Bm, the magnetic field applied to the magnetic core 5 disappears, and the magnetic flux density level quickly returns from the point to the level of the point. Next, when a negative DC voltage is applied and the magnetic core 5 is excited by a negative excitation field to the negative maximum magnetic flux density -Bm, the range of change in magnetic flux density becomes △B ₃₄ , and |△B ₁₂ | =｜△
B ₃₄ | holds true. However, as shown in Fig. 3b, when the magnetic field generated by the positive input current I'ex (>0) is applied to the magnetic core 5, the excitation cycle is repeated starting from this state. Thinking about it, first, the range of change in magnetic flux density when a positive excitation field is applied is △B′ ₁₂ , and when a negative excitation field is applied, it becomes △B′ ₃₄ , so between △B′ ₁₂ and △B′ ₃₄ , Clearly, |△B′ ₁₂ |<|△B′ ₃₄ | holds true. In other words, t' The relational expression +<t'- holds true.

Next, as shown in Figure 3c, the negative input current
If the above excitation cycle is repeated starting from the state where the magnetic field generated by I″ex (<0) is applied to the magnetic core 5, the magnetic flux will be △B″ ₁₂ during positive excitation and △B″ ₃₄ during negative excitation. Density changes are observed, and the positive excitation period t″+
During the negative excitation period t″-, t″+>t″- holds true.Therefore, the excitation DC voltage value applied to the magnetic core 5 during the above-mentioned excitation cycle is at the maximum magnetic flux density level of the magnetic core 5. As shown in the current detection circuit in Figure 4, the first
A variable resistor 7 is connected in series with the winding 2, and impedance is adjusted by this variable resistor. Also, as soon as the magnetic flux level of the magnetic core 5 reaches the maximum magnetic flux density level or the DC voltage Vc, -
Considering the case where the polarity of Vc is switched, the voltage waveform e at the terminal 8 will be observed as a square wave voltage waveform having both positive and negative polarities. Figure 5 shows that under these assumptions, Iex=0,
The voltage waveform e at terminal 8 is illustrated for each case I′ex>0, I″ex<0. As can be seen, the positive half-cycle durations t+, t′+ of the bipolar square wave , t″+ and the negative half-cycle durations t−, t′−, t″− are the input currents Iex, I′ex, I″ex
It can be seen that it is controlled by Therefore, current measurement is possible by integrating e and converting and displaying the signs and voltage values of the voltage integral values Eo, E′o, and E″o in correspondence with the polarity and strength of the current to be measured Iin. It turns out that it can be done.

Next, the operating principle of the present invention will be explained using a specific circuit.

FIG. 6 shows an example of a circuit that automatically implements the operating principle of the present invention, and shows a current sensing section 10 that automatically switches the DC voltage that excites the magnetic core 5.
0. Drive circuit section 2 with built-in positive/negative drive DC power supply S
00, it consists of a display circuit section 300 that integrally amplifies the output of the current sensing section 100.

First, the current sensing section 100 will be explained.
The inverting terminal 10a of the operational amplifier 9 is grounded G,
The non-inverting terminal 10b has a second input terminal for operational amplifier input.
Terminal 3a of winding 3 is connected, and terminal 3b is grounded. The capacitor 6 is connected to both ends of the winding 3, absorbs the noise component generated by the magnetic core 5, and forms a resonant circuit for the winding 3 in terms of circuit configuration, thereby stabilizing the timing operation when switching the DC voltage. It contributes to the A variable resistor 7 is connected to the output terminal 8 of the operational amplifier 9, and this resistor adjusts the voltage waveform of the output terminal 8, in other words, adjusts the load impedance including the variable resistor 7 and the first winding 2. and make the output terminal voltage waveform as square wave as possible.

Next, to explain the principle of self-excitation operation, suppose that the operational amplifier 9 is positively saturated and the voltage at the terminal 8 is the saturation voltage V _S (>0).
The excitation current flows through the winding 2 through the resistor 7 and into the ground G. At this time, an induced voltage is generated in the winding 3 via the magnetic core 5. Since the polarity of this induced voltage is positive on the terminal 3a side, a positive voltage is input to the non-inverting terminal 10b of the operational amplifier 9, and as a result, the operational amplifier 9 continues to output a positive saturated voltage output V _S. During this time, the magnetic core 5 is still being excited, and while it is being excited until it reaches the maximum magnetic flux density level Bm, the magnetic permeability of the magnetic core 5 gradually decreases, and as the induced voltage decreases, the coil impedance of the winding 3 also decreases. extremely low. At this time, the charge that has been charged in the capacitor 6 by the induced voltage will be discharged. However, since the capacitor 6 and the winding 3 constitute a resonant circuit, the voltage at the terminal 3a of the winding 3, which was positive until now, changes to a negative voltage, and the voltage at the non-inverting terminal 10b of the operational amplifier 9 changes from positive to negative. A negative voltage signal is input to the output terminal 8, and the output voltage e _p of the output terminal 8 automatically becomes the negative DC saturation voltage -
Switch to _VS. And in the next moment, the magnetic core 5
The magnetic flux density level in the magnetic core 5 quickly returns to the level specified by the input current Iex, and then due to the negative saturation voltage -V _S , the magnetic flux density change in the magnetic core 5 changes toward the negative maximum magnetic flux density level -Bm. I will do it. At this time, the voltage at the terminal 3a of the winding 3 is, of course, negative, so the operational amplifier 9
The output voltage e ₀ continues to be held at -V _S , and the capacitor 6 is charged with an electric charge due to the induced voltage. By the time the magnetic flux density level of the magnetic core 5 reaches the negative maximum magnetic flux density level -Bm, the capacitor 6 starts discharging, and then due to the resonance phenomenon, the non-inverting terminal 10b of the operational amplifier 9 has a reversed polarity. An input voltage signal (>0) is input, and the output terminal voltage e _p is switched to the positive DC saturation voltage V _S .

In this way, the drive DC voltage ±Vc applied to the operational amplifier 9 alternately changes the saturation voltage ±V S to the output terminal 8 of the operational amplifier 9 in response to the voltage signal induced in the operational amplifier input winding of the magnetic core ₅ . At the same time, the period length ratio (duty ratio) between the positive period and the negative period of this bipolar saturated voltage waveform (output voltage waveform) is controlled by the current to be measured Iin. .

Note that the function of the capacitor 6 is replaced by the magnetic core 5 so that the stray capacitance existing between the windings is used to perform the function of the capacitor 6.
This is possible by appropriately selecting the winding wire diameter and the number of windings to be wound. In this case, it is obvious that the capacitor 6 does not need to be attached. In FIG. 6, 300 is a display circuit section, and the square wave output voltage e _p is at the non-inverting terminal 1 of the buffer 12.
1, or via an integrating circuit consisting of a resistor 13 and a capacitor 14 or a low-pass filter (not shown), and is input to a non-inverting terminal 15 of an operational amplifier 16 for gain adjustment, where it is amplified. The amplification degree of the operational amplifier 16 is the measured current Iex
Resistance 17 to 2 can be selected depending on the strength of
0 is connected between the output terminal of the operational amplifier 16, the inverting terminal, and the ground terminal. In addition, an operational amplifier 1 is installed immediately after the circuit consisting of the resistor 13 and the capacitor 14.
It is also possible to configure the circuit so that 6 operates as a comparator, and to extract the presence or absence of the current to be measured as an output voltage Eo of H or L level. 21 is a capacitor inserted for the purpose of removing unnecessary AC noise components. 22 is a changeover switch for arbitrarily selecting the degree of amplification A, B, C; 23 is an indicator which has a function of displaying the polarity and strength of the current. 24 is
The value of the current flowing into the indicator 23 is adjusted using a variable resistor. Reference numeral 200 denotes a drive circuit section, which is a supply source of positive and negative DC voltages ±Vc for the operational amplifier. Figure 7 shows
The self-excitation operation of the current sensing section 100 shown in FIG.
This is an example of a modified circuit for stable execution even after application of a strong magnetic field.

The impedance 25 in FIG. 7a is a resistance,
Or a capacitor, or a parallel circuit consisting of a resistor and a capacitor. The inverting terminal 10a of the operational amplifier 9 is connected to the terminal 2b of the first winding 2, and the self-excitation stop phenomenon caused by the application of a strong magnetic field is restored by the negative feedback action of the terminal voltage of 25. ing.

In FIG. 7b, the negative feedback effect due to the impedance 25 is separated from the first winding 2, and the variable resistor 26
This is implemented using a series circuit with

FIG. 8 shows an example of application of the present invention. The circuit configuration of the current sensor 1000 includes a current sensing section 100
An example is shown in which an integrating circuit is connected after , a comparator is connected after that, and the display is displayed using an LED.
That is, a comparator which receives the output voltage of the integrating circuit as an input signal is connected, the input signal level is checked against a preset reference voltage value, and this is converted into a high level or low level signal voltage and output. As the comparator used here, it is sufficient to use a known comparator (including a window comparator), and it is sufficient to use the comparator by taking advantage of its characteristics according to each purpose. Then, depending on the output of the comparator, for example, a relay that generates an alarm is operated, or an LED is displayed.

FIG. 8a shows an example in which an electromagnetic relay is in the make state (ON) and is used to ensure that current is flowing. By incorporating the entire current sensor into an electromagnetic relay and checking the presence or absence of current flowing through each contact, it becomes possible to construct a self-diagnostic electromagnetic relay that detects abnormalities in operation. In this case, it is also possible to use a single power supply (for example, 24V), so that the ground G in Figures 6 and 7 is raised to a voltage level that is half that of a single power supply.
It is obvious that this can be easily achieved by creating an intermediate potential point using a voltage divider circuit using an IC or resistor. FIG. 8b shows an example of application for determining the disconnection status of a lamp or the like. In some automobiles, the lighting status of various lamps L cannot be checked directly from the driver's seat. Therefore, if a current sensor 1000 with a warning lamp is placed in the driver's seat, the lighting state of the lamp can be confirmed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the material composition of a single-hole magnetic core 1 made of a single-hole magnetic material used in the present invention, and FIG.
The figure is a diagram showing the basic configuration of the winding wound around the magnetic core of the current sensor in the present invention, and FIG. 3 is a diagram for explaining the operating principle of the present invention using the B-Iex characteristic of the magnetic core 4. , FIG. 4 is a circuit diagram of the current detection section,
Figure 5 shows Iex = 0, I'ex > 0, I''ex in Figure 3.
A diagram of the voltage waveform e _p at the terminal in each case of <0, Figure 6 shows a current sensing section that automatically switches the DC voltage that excites the magnetic core, a drive section with a built-in positive/negative drive DC power supply, and a current sensing section. Figure 7 shows an example of a modified circuit that can stably perform the self-excitation operation of the current sensing section in Figure 6 even after a strong magnetic field is applied. The figure shown in FIG. 8 is a diagram showing an example of application. 1...Single hole magnetic core, 2...First winding for excitation, 3
...Second winding for operational amplifier input, 2a, 2b,
3a, 3b... terminal, 4... third winding for inputting the current to be measured, 5... magnetic core to which the winding is fixed, 6... capacitor, 7... variable resistor, 8... output terminal, 9
...Operation amplifier, 10a...Inverting terminal, 10b...
...Non-inverting terminal, 40... Shunt conductor, 100... Current sensing section, 200... Drive section, 300... Display circuit section, G... Earth.

Claims (1)

[Claims] 1. A single-hole magnetic core that generates a magnetic path in an annular direction, an operational amplifier for exciting the magnetic core, a first winding for excitation wound around the magnetic core, and a first winding for inputting the operational amplifier. It consists of two windings and a third winding arranged so that the current to be measured passes through the hole in the magnetic core.The first winding is connected to the output terminal side circuit of the operational amplifier, and the second winding is connected to the operational amplifier. is connected to the inverting terminal and non-inverting terminal side of the input terminal side circuit of the operational amplifier, and the positive excitation time and negative excitation time are connected to the positive and negative polarities of the operational amplifier starting from the value determined by the current value to be measured in the operational amplifier. The saturated DC voltage is converted into a positive half-cycle excitation time and a negative half-cycle excitation time, respectively, and the saturated DC voltage is fed back to the first winding to bring the single-hole magnetic core into a self-excited state, thereby changing the positive and negative excitation times. A self-oscillating current sensor configured to measure a current value to be measured from a period length ratio. 2. A self-oscillating current sensor according to claim 1, wherein a capacitor is connected in parallel between the terminals of the second winding.