JPS60196678A - Differential self-exciting bridge type current sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect an input current with high sensitivity, by negating uniform parallel magnetic field components applied to two magnetic cores by diffential connection and using the operation amplifier in a bridge as a voltage control switching element. CONSTITUTION:Magnetic cores 4a, 4b are inserted into the central space part of a glass tube around which exciting winding 2 is wound in reversed polarity. Now, when the output of an operation amplifier OP1 is changed over to positive saturation DC voltage, the magnetic flux density level in a united magnetic core is rapidly returned to the magnetic flux density level prescribed by input current to be measure inputted to terminals 50a, 50b. As said magnetic flux density level approaches positive max. magnetic flux density, the impedance Z2 of the exciting winding 2 is lowered and, when Z2<R10 is formed, negative saturation DC voltage is generated in the output of the operation amplifier OP1. By this mechanism, the saturation DC voltage of the operation amplifier OP1 is automatically changed over every time when the united magnetic core reaches positive and negative max. magnetic flux density and this output is integrated by an operation amplifier OP2 and the direction and intensity of the input current are displayed by an indicator 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current sensor that can detect an input current with high sensitivity by canceling field components using differential connections and effectively applying a magnetic field generated by an input current to be measured to a magnetic core.

In conventional bridge circuits, at least one of the four elements that make up the AC bridge is an inductance element with a magnetic core placed in the center of the coil, and the impedance of the inductance element is changed by the magnetic field applied to this magnetic core. The magnetic information is extracted as a change in the unbalanced voltage amplitude value of the bridge.

From this type of bridge circuit, it is possible to measure the strength of the applied magnetic field by measuring the unbalanced voltage amplitude, but until now it has been impossible to measure the current magnetic field separately from the external magnetic field. be.

A closed magnetic circuit annular magnetic core, which has been twisted, has poor productivity.
Difficulties in winding the annular magnetic core, variations in magnetic properties due to the winding of the annular magnetic core, cumbersome setting work before and after winding, high manufacturing cost of the wound magnetic core, etc. The above contained major problems.

However, the present invention solves these drawbacks by changing the duty ratio of the output duration of the positive and negative saturation voltages of the operational amplifier, and also uses a differential magnetic core to construct a differential self-excited bridge type current sensor for current measurement. This relates to current sensors.

In other words, a self-excited bridge circuit whose operating region is the nonlinear magnetic custom-made region of the magnetic core that makes the most of high magnetic permeability, low coercive force, and characteristics is constructed using a magnetic semiconductor coupling method, and the square wave output voltage of the output terminal of the operational amplifier is The duration of the positive and negative half cycles can be controlled by the magnetic field generated by the current to be measured.

The first feature of the present invention is that the windings of the first magnetic core and the second magnetic core are
The wires are connected so that the outer peripheral disturbance magnetic field becomes a differential input to the magnetic core and is canceled out, and the magnetic field generated by the input current is effectively applied to the magnetic core.1. This is the point I made to make it clearer. The second feature (constitutes a self-excited bridge circuit using a magnetic semiconductor coupling circuit system, uses an operational amplifier in the bridge as a voltage-controlled switching element that operates with voltage input, and directly applies the positive and negative saturated DC voltages to the bridge circuit. The point is that it is possible to know the strength and polarity of the current by applying it to the current.

The third feature is that high-sensitivity current measurement is possible with low power consumption by using small amounts of magnetic materials such as amorphous, permalloy, ferrite, and pure iron, which have high magnetic permeability and low coercive force, as the magnetic core. That's true.

The fourth feature is that the method of transmitting and receiving AC excitation voltage and double frequency signals seen in magnetic modulators and bridge circuits is the AO-AC transmission method, but in the present invention, By improving the I) C-D C method (direct current transmission method) with less attenuation, it has become possible to perform highly sensitive current measurements even when the cord length is several hundred meters.

The fifth feature is the AC excitation power supply, multiplier, and tuning increase +l required in the circuit configuration of the bridge circuit and magnetic modulator.
It is possible to measure the strength and polarity of current using a simplified magnetic semiconductor coupling circuit without requiring any major basic circuits such as a J-equipment or synchronous rectifier.

The sixth feature is that the circuit configuration is simplified by using a common ground for the bipolar DC stabilized power supply of the operational amplifier and the display circuit section.

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

FIG. 1 shows the basic configuration of a current detection element in the present invention. la and lb are glass tubes, and on the outside there are terminals 2a,
The excitation winding 2 at terminal 2b and the cancellation winding 3 at terminals 3a and 3b have nine turns. This canceling winding may be added as necessary. The capacitor 5 absorbs noise components generated from the magnetic core, and is connected to the winding terminals 2a and 2b, and the terminals 2b and 3b are connected to ground G. The winding polarity of the excitation winding 2 is the same as that of the first magnetic core 4 as shown in the figure.
a and the second magnetic core 4b have opposite polarities. glass tube 1
a.

A magnetic core 4 a + 4 b, such as an amorphous magnetic wire, is inserted into the central space of 1 b as a magnetic material. Amorphous magnetic materials with high magnetic permeability and low coercive force are most suitable as magnetic core materials, but other materials such as ferrite,
It is not limited to permalloy wire, pure iron, etc. Further, the shape is not limited to other shapes such as a ribbon shape. The first magnetic core 4a is provided with a terminal 50a for passing the current to be measured.

An input circuit 50 having 50b is added near or in close contact with the magnetic core.

FIG. 2 is a diagram for explaining the operating principle of the present invention using B-i characteristics as an integrated magnetic core that integrates the magnetic characteristics of the first magnetic core and the second magnetic core, for ease of understanding. Second
Figure (a) shows that if the input current ■ is zero (1=0), that is, if the magnetic heart is guided by a parallel magnetic field,
This figure shows the 13-1 characteristics of an integrated magnetic core when two magnetic cores are arranged in parallel. Since hysteresis exists in magnetic materials, one cycle of excitation follows a path of ■→■→■→■→■ as shown in the figure. Here, when a positive DC voltage is applied to the excitation winding 2 in the state of I-0 and the excitation winding 2 is excited to the maximum magnetic flux density B m by a positive excitation field, as shown in the figure, during the change in magnetic flux density, ΔB+2 Become. Then, if the DC voltage is made zero at the same time that the magnetic flux density as an integrated magnetic core reaches Brn,
Since the magnetic field exciting the magnetic core disappears, the magnetic flux density level quickly returns from point ■ to the level at point ■. Next, when a negative DC voltage is applied and the integrated magnetic core is excited by a negative excitation field to the negative maximum magnetic flux density -Bm, the magnetic flux density becomes △1334 during the change, and 1△B+21=lΔB54
1 will hold true.

However, as shown in FIG. 2(b), for the sake of simplicity, the above-mentioned excitation cycle is Considering the case of repeating , first, the magnetic flux density change d] when applying a positive excitation field is ΔB'1□, and when applying a negative excitation field it becomes ΔI3'34, and Δr3'12 and Δ
Between B'34, there is clearly iΔ137. □１〈１△I
3'341 holds true. In other words, between the positive excitation period tJ- and the negative excitation period t'- required for the excitation DC voltage to excite the integrated magnetic core from zero to the positive or negative maximum magnetic flux density level, t'+ The relational expression <t'- holds true.

Next, as shown in Fig. 2(c), the negative input current 1'' (
< 0) is flowing into the input circuit 50 of the first magnetic core, and when the above-mentioned excitation cycle is repeated, a magnetic flux density change of ΔB"12 during positive excitation and ΔB"34 during negative excitation is observed. During the positive excitation period 1... During the positive excitation period t''-, t
""->t"- holds true.

Therefore, in order to prevent the excitation DC voltage value applied to the magnetic core during the above-mentioned excitation cycle from decreasing or fluctuating even at the maximum magnetic flux density level of the integrated magnetic core, it is variable in series with the excitation winding 2 as shown in the current detection circuit in Figure 3. A resistor 6 is connected, and this variable resistor is used to adjust the Q and impedance of the resonant circuit. Therefore, considering the case where the polarity of the DC voltage Vc, -V is automatically switched as soon as the magnetic flux level of the integrated magnetic core reaches the maximum magnetic flux density level ■ or ■, terminal 7 (or terminal 8) If the voltage waveform e at The voltage waveform e at the terminal 7 in each case of <O is illustrated. As can be seen from the figure, the positive half-cycle durations i +, t', t'' and the negative half-cycle durations 1, t/, (//-) of the bipolar square wave are the inputs under test. Current 1., I
It can be seen that it is controlled by ', I''. Therefore, e
Integrate and convert its voltage product directly to E. E'o I E"o
It can be seen that by converting and displaying the sign and voltage value in correspondence with the polarity and strength of the input current 1, it is possible to measure the current to be measured. Therefore, when implementing this principle in an actual circuit, when a magnetic core is excited with alternating current in a state where it is polarized by direct and current magnetic field components applied to the magnetic core, a second harmonic component is induced in the winding. The voltage is input to a voltage controlled switching element and used as a duty ratio change/change output.

Hereinafter, details of the present invention will be explained from a magnetic core.

FIG. 5 is a diagram for explaining the arrangement relationship between the first magnetic core and the second magnetic core. In the present invention, the windings, shapes, and arrangements of the two magnetic cores operating differentially with respect to parallel magnetic fields include all cases that accomplish the purpose. Note that the cancellation winding is omitted in the figure.

Figure 5(a) shows an example of a configuration with one linear magnetic core or two linear magnetic cores. In the case of one magnetic core, two Consider it divided into two magnetic cores. Even in the simple configuration, the influence of parallel external magnetic fields becomes almost unaffected by the differential connection.

Since the first magnetic core 4a is unbalanced by the input current flowing through the input circuit 5° located around it, a second harmonic component appears between the terminals 2a and 2b of the resonant circuit. For this reason, the output of an operational amplifier operating at high-level mode becomes a square wave with a varying duty ratio. In reality, an operational amplifier with a poor slew rate naturally transforms into a katana wave or a triangular wave.

The shunt conductor 500 is used to measure the strong input current ■.
It is inserted for the purpose of suppressing the input current value applied to the magnetic core and for the purpose of suppressing the AC induced component from the magnetic core to the input circuit, and may be inserted as necessary. Note that it is possible to change the shunt ratio of the input terminal and the reduction rate of the AC induced component by inserting a resistor or the like in the middle part of the input circuit 50 and the middle part of the shunt conductor 500.

FIG. 5(b) is a diagram in which an input circuit 50° 500 mm turn is formed on a printed circuit board P such as a glass epoxy board or a ceramic board, and a magnetic core 4a is adhesively fixed thereon. This configuration is characterized by a great advantage in cost reduction during the time of battle.

Figures 5(c) and r): (A) Remove the influence of external magnetic fields and effectively apply the input current magnetic field generated by the current flowing through the input circuit 50 to the two magnetic cores 4a and 4b. An example of a configuration that makes it possible is shown below.

Naturally, it is also possible to eliminate the influence of disturbance magnetic noise by housing the magnetic cores 4a, 4b or the operational amplifiers in a magnetic Sorbi case made of S-Malloy or the like. Regarding the size and shape of the magnetic core, please refer to Part 5.
As a modified type of the one shown by the dotted line in Figure (C),
4; I of a semicircle with one magnetic core.

It is also possible to construct an annular magnetic core with an open magnetic path having an extremely small gap by configuring 4b and bringing the end faces together.

FIG. 6 is an overall circuit diagram for automatically implementing the operating principle of the present invention. Functionally, it consists of a current sensing section 100, a display circuit section 200, and a DC stabilized power supply section 300.

First, as elements constituting the bridge circuit of the current sensing section 100, the variable resistor 6, the excitation winding 2, and the capacitor 5 are present on the negative side, and the variable resistor 11 and the variable resistor 10 are present on the other side. Further, one end of each side of the bridge is connected to the output terminal 7 of the operational amplifier OP, and the other end is connected to the ground GK. The cancellation winding 3 generates a magnetic field in a direction that cancels the magnetic field of the current to be measured applied to the first magnetic core 4a, and the cancellation current output from the display circuit section 200 is input to the terminal 3a. It is executed by nine. This feedback system is aimed at stabilizing the circuit system of the current sensing section and improving the linearity of the input/output characteristics, which represents the relationship between the output voltage and the magnetic field gradient being measured, and is extremely difficult to implement in practice. It is useful for

However, even if the cancellation winding 3 is omitted, the object of the present invention does not change. Also, terminal 0. Replace the element between terminals A and 7 with the element between terminals A and 7, insert a capacitor between terminals O and 1, and connect non-inverting terminal P of operational amplifier 01)1 to node B. Modified circuit configurations in which the inverting terminal N is connected to the node A also belong to the scope of the present invention.

The inputs to each input terminal of the operational amplifier 01)1 are as follows: Non-inverting terminal PK is input to terminal 2a of primary winding 2 via node A, and inverting terminal N is input to node B of variable resistor 10.11. It is input via 几. Operation of operational amplifier OP is P, N
An increase d that amplifies the input voltage difference CA-CB between the terminals.
It is not operating as a controller, but the input voltage difference ez
The capacitor functions as a voltage-controlled switching element that identifies whether eB is positive or negative and outputs a positive or negative saturated DC voltage accordingly. 5 has the function of stabilizing self-excitation operation by absorbing noise components generated in the magnetic core and completely suppressing the effects of rapid changes in magnetic flux, so it is inserted because the interwinding capacitance alone is insufficient. It is desirable to do so.

Next, the self-excitation operation will be explained.

Here, for ease of understanding, variable resistor 6.10.
The resistance value of 11 is R6, RIO1I'11, the impedance of the negative winding 2 is Z2, the impedance just before the maximum magnetic flux density of the integrated core reaches 10 Bm is Z2m-, and the impedance when it reaches ±Bm is As Z2 m, aa>Z2 and R11>RIO,
and R6= it, 1 and Z2 m >RIO>
Let us consider only one case where Z2 m holds true. Suppose, at this moment, the operational amplifier O
The output voltage of output terminal 7 of P1 is positive saturated DC voltage +■5
Once switched to , the magnetic flux density level at the integrated magnetic flux rapidly returns to the magnetic flux density level n defined by the input current to be measured (state ■). And the inverting terminal N is divided by resistors 11 and 10 to a positive voltage e
When B (>O) is input, it becomes K, and the non-inverting terminal PK
A positive voltage eA (>0) determined by the voltage division between the resistor 6 and the impedance of the excitation winding 2 including the capacitor 5 is input. Here, the impedance Z2 of the excitation winding is very large because the integrated magnetic core is in a magnetic flux unsaturated state, and Z2:) a is established between it and the resistor 10, so the operational amplifier input voltage difference The sign is positive (eA-cn
,')0), and the output voltage of the operational amplifier OP1 maintains the positive saturated DC voltage +V≦. However, as the magnetic flux density level in the integrated magnetic core gradually increases,
As the maximum positive magnetic flux density Bm gradually approaches 11, the impedance z2 of the excitation winding 2 decreases as the magnetic permeability decreases.
decreases, and just before the magnetic core reaches the maximum positive magnetic flux density Bm, Z2 = Z2 m-, and at this point Z2 m
＞几1° has been established, but in the next moment the integrated magnetic core reaches the maximum magnetic flux density Bm (state of ■), and now Z2
-Z2 rn < Rho. The result eA<
Since the relationship e13 is established and the sign of the input voltage difference between the input terminals of the operational amplifier 0P10 changes from a positive (cAeB) 0 ) state to a negative (eA −eB<O) state, the output terminal 7 of the operational amplifier OP Negative saturated DC voltage -V5
occurs. This voltage is applied between terminal 7 of the bridge and ground G, and at the same time, the magnetic flux density level of the integrated magnetic core quickly returns to the level specified by the input current to be measured (state ■). . When entering this negative excitation cycle, Z2>IL+o: eA<o: cB(
0; The relationship cA, -eB(O holds true, and the magnetic flux change in the integrated magnetic core proceeds in the opposite direction.As time passes, the magnetic flux density level of the integrated magnetic core increases to the negative maximum magnetic flux density. -B When reaching m (state of ■) 'Z2
= Z2rn<RroseA>eB is established, and the sign of the input voltage difference of the operational amplifier OP is positive (eAeB)
0 ), and a positive saturated DC voltage +Vs appears at the output terminal 7 of OP.

From the explanation of the circuit operation in ``2'' below, operational amplifier OP1 is activated every time the integrated magnetic core reaches a maximum magnetic flux density of 10Bm or 13m.
It has become clear that the saturated DC voltmeter VS is automatically switched alternately.

In addition, the magnetic core 4aK input current I, I', ()O), I
If the above operation is performed with ``(ku0) applied,
It is easy to understand that a square wave voltage waveform as shown in FIG. 4 is observed at the output terminal of the operational amplifier OPl. However, for accuracy, it is sufficient to read the value by replacing Vc in FIG. 4 with ±Vs.

In the 200fl-i display circuit section, there is an operational amplifier OP2 that integrates and amplifies the output voltage of the current sensing section 100, a capacitor 12 for integration connected to this, and resistors 13, 14, and 16.
．． 18, a choke coil 17, and an indicator needle 19.

At the output terminal 15 of the operational amplifier OP2, a positive or negative DC voltage value is observed, which corresponds to the direction and strength of the input current.

The purpose of the choke coil 17 is to prevent the alternating current component from the current sensing section 100 from affecting the display circuit when a current flows in a direction that cancels the magnetic field of the input current to be measured that is applied to the magnetic core 4. It is inserted to stabilize the self-excited operation by blocking the induced current flowing due to the induced voltage induced in the canceling winding. It is also possible to substitute this choke coil 17 with a resistor. Reference numeral 300 is a DC stabilized power supply unit for driving the operational amplifiers op, , 0I)2. In the present invention, the purpose of the transmission between the current sensing section 100 and the display circuit section is achieved with only a DC component.Since the transmission between the current sensing section 100 and the DC stabilized power supply section 300 is also a DC component, The power transmission and reception, signal transmission and reception 1l-1: All data are in the C-DC system. Therefore, for example, a DC stabilized power supply section 300 and a display circuit section 200 are installed in the measurement room, and the current change sensitive to the current sensing section 100, which is not installed in several LO'Ons, can be detected in the measurement room. This makes it possible to monitor the

FIG. 7 shows a modified circuit of the current sensing section 100, in which a cancellation winding 3 is inserted in place of the resistor 110 shown in FIG. 6, and the cancellation current circuit is omitted.

Finally, referring to the application of the present invention, in Fig. 6, a comparator having the voltage Eo as an input signal is connected after the operational amplifier OP2, and the input signal level is checked against a preset reference voltage value. ko f'Li
It can also be converted to a high level or low level signal voltage and output. The comparators used and used here are known comparators (including window comparators)
It is enough to use it according to its purpose and take advantage of its characteristics. Depending on the output of the comparator, for example, a relay that generates an alarm can be operated, or an LED display can be displayed.

Figure 8 shows an example of its application. First, FIG. 8(a) shows an example in which an electromagnetic relay is in a make state (ON) and is used to detect that a current is definitely flowing. By using the entire current sensor 1000 at each contact point of an electromagnetic relay, it becomes possible to construct a self-diagnostic electromagnetic relay that detects abnormalities in operation.

In this case, it can also be used with a single power supply (for example, 24V), and a voltage divider circuit using a resistor can be used to raise the ground O in Figures 6 and 7 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 . FIG. 8 (1)) is 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 sensor is placed in the driver's seat, it is possible to check the lighting state of the lamp.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the basic configuration of the current detection element according to the present invention, Fig. 2 is an explanatory diagram illustrating the operating principle of the present invention using the B-i% property of the integrated magnetic core, and Fig. 3 is an explanatory diagram showing the basic configuration of the current detection element according to the present invention. Figure 4 is a diagram of the voltage waveform e at the terminal in each case of I=0.1'>0, l'' (0 in Figure 3), Figure 5 is a diagram of the specific arrangement of the magnetic core Figure 6 shows one part of the overall circuit consisting of a current sensing section that automatically switches the DC voltage that fully excites the magnetic core, a DC stabilized power supply section, and a display circuit that integrally amplifies the output of the current sensing section.
FIG. 17 is a diagram showing an example of a modified circuit of the current sensing section of FIG. 6, and FIG. 8 is a diagram showing an applied example. In the figure, la, 1bij glass tube, 2 is excitation winding, 3 is cancellation winding, 2a, 21), 3a, 3
b is a terminal, 4a and 4b are magnetic cores, 5 is a capacitor, 17 is a choke coil, 19 is an indicator, 100 is a current sensing part,
200 is a display circuit section, 300 is a DC stabilized power supply section, 10
00 is the current sensor, A,, I3 is the node *OPI,
Oll, , is an operational amplifier, P is a non-inverting terminal, N is an inverting terminal, and G is a ground. Agent Patent attorney Masamitsu Akizawa and 2 others No. 51 ゞ------ (6) 500 (C) (d) Soup 6 figure + Vc piece 7 figure

Claims (4)

[Claims] (1) Two magnetic cores function as a differential input for parallel outer magnetic fields, and the magnetic field generated by the current to be measured is concentrated along the magnetic path direction of the magnetic material in the form of a deep magnetic path. an input circuit that allows the current to be measured to flow through the input winding so that the current to be measured flows through the input winding; a first element is a differentially connected excitation winding wound around both of the magnets; a bridge circuit in which the element and the fourth element are constituted by a resistor and a capacitor, and a positive or negative saturated DC voltage corresponding to the sign of the bridge unbalanced voltage at the midpoint of the bridge circuit is applied between the terminals of the bridge circuit. A differential self-excited bridge type current sensor comprising an operational amplifier as a voltage controlled switching element. (2) The differential self-excited bridge type current sensor according to claim 1, wherein a capacitor is connected in parallel between the excitation windings to stabilize the self-excited oscillation operation. (3) A differential self-excited bridge type current sensor according to claim 1 or 2, wherein the entire current to be measured flows through the input circuit. (4) The differential automatic excitation bridge type current sensor according to claim 1' or 2, wherein a shunt conductor is added so that a part of the current to be measured flows through the input circuit.