JPS60161564A - Automatic exciting bridge type electric current sensor - Google Patents

Abstract

PURPOSE:To enable current measurement in low power consumption and with high sensitivity, by automatic switching of the output polarity of an operating amplifier for each maximum magnetic flux density of a perforated magnetic core. CONSTITUTION:A single-hole magnetic core 4 penetrates with its outside surface an exciting winding 2 and an input winding 3. A bridge circuit of current sensing part 100 is composed of variable resistances 6, 10 and 11, winding 2 and condenser 5. Further when a backing current from an indicating circuit is applied to a terminal 300a, magnetic field is generated in the direction backing the magnetic field caused by a current lex subject to measurement applied to the magnetic core by the backing coil 300. To a non-inversion input P of the operating amplifier OP1, an output of the winding 2 and to a inversion input N, a voltage of a point B is applied respectively and, after segregation of positivity and negativity of each input voltage difference, a corresponding saturation DC current is delivered. And, at each maximum magnetic flux density, alternative automatic switching at the saturation DC current of OP1 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a self-excited bridge-type current generator that uses the nonlinear characteristics of a magnetic material with a single hole and the high gain characteristics of an operational amplifier to generate an AC voltage in order to measure DC voltage. Regarding sensors.

In conventional bridge circuits, among the four elements that make up the AC bridge, at least one element 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 the 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 measuring magnetic field using an unbalanced voltage amplitude, but it is impossible to measure the polarity (direction of application) of the measuring magnetic field. .

However, the present invention relates to a self-excited bridge type current sensor that solves these drawbacks by using a duty ratio of the output duration of the positive and negative saturation voltages of an operational amplifier, and is configured as a current sensor for current measurement using a perforated magnetic core. be.

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

The first feature of the present invention is to configure a self-excited bridge circuit using a magnetic semiconductor coupling circuit system, and to directly apply the positive and negative saturated DC voltages of the operational amplifier in the bridge to the bridge circuit to determine the strength and polarity of the current. The point is that it is possible to do this.

This enables highly sensitive current measurement with low power consumption.

The third feature is that the power and signal transmission and reception methods of AC excitation voltage and double frequency signals found in magnetic modulators and bridge circuits are
The AC-AC transmission method was previously used, but in the present invention, by improving it to a DC-DC method (direct current transmission method) with less attenuation, high-sensitivity current measurement is possible even with a cord length of several hundred meters. be.

The fourth feature is that the main basic circuits such as the AC excitation power supply, multiplier, tuned amplifier, and synchronous rectifier in the circuit configuration of the bridge circuit and magnetic modulator are not required at all, and the magnetic semiconductor coupling is simplified. This enabled the circuit to measure the strength and polarity of the current.

The fifth 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.

FIGS. 1A to 1E show examples of the material composition of a single-hole magnetic core 1 made of a single-hole matrix material used in the present invention.

(a) shows an example of a punched, fired, or processed magnetic core, (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.

Since the object of the present invention can be achieved with any shape or configuration, there is no particular limitation thereon. The magnetic core l has a single hole, but 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 sputtering 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. FIG. 2(a) shows the basic configuration of the present invention, in which the magnetic core 4 with the excitation winding fixed with a mold or the like is a single-hole magnetic core, and the excitation winding 2 of terminals 2a and 2b and the terminals 3a and 3b are arranged on the outside. The input winding 3 of the input circuit is passed through.

Although the number of turns of the input winding 30 is one turn in the figure, it may generally be one turn. The capacitor 5 is added for the purpose of absorbing noise components generated from the magnetic core, and is connected to the winding terminals of the terminals 2a and 2b. Figure 2 (b
), (c), part of the measured current Iin is sent to the input winding 3 inside the single hole, and the rest is sent to the single or multiple conductor 3 outside the single hole.
An example of an input circuit that allows the signal to flow to 0 is shown below. The feature of this circuit is that by bypassing the current and measuring only Iex that is shunted to a predetermined current magnitude, it is possible to measure a large current Iin with a small magnetic core. That's true. That is, it is possible to measure Iin by converting the magnetic field generated by the current Iex passing through the magnetic core. Such an input circuit configuration has the great advantage that the alternating current induced from the magnetic core to the input winding is short-circuited by the conductor 30, thereby blocking electromagnetic induction.

FIG. 3 is a diagram for explaining the operating principle of the present invention using the B-Iex characteristic of the magnetic core 4. Figure 3(a) is
This shows the B-Iex characteristics of the magnetic core 4 when the current to be measured Iex is zero (Iex = 03).Since the magnetic core 4 has hysteresis, in one cycle of excitation,
As shown in the figure, the route will be followed as follows: ■→■→■→■→■. Here, when Iex = 00 state,
When a positive DC voltage is applied to the excitation winding 2 and the magnetic core 4 is excited to the maximum magnetic flux density Bm by a positive excitation field, the magnetic flux density becomes ΔB+2 during the change as shown in the figure. If the DC voltage is made zero at the same time that the magnetic flux density of the magnetic core 4 reaches Bm, the magnetic field applied to the magnetic core 4 disappears, and the magnetic flux density level quickly returns from point (2) to the level of point (2). Next, when a negative DC voltage is applied and the magnetic core 4 is excited by a negative excitation field with a negative maximum magnetic flux density -Bmt, ΔB31 is obtained during the magnetic flux density change, and 1ΔB1□1=1ΔB
541 is established.

However, as shown in FIG. 3(b), the magnetic field generated by the positive current to be measured I'ex ()0)
If we consider the case without changing the above-mentioned excitation cycle from the state in which the excitation field is applied to '34 and Nasi, ΔB']2 and 687340 clearly hold 1ΔB'+21(1ΔB'34+. In other words, when the DC voltage for excitation is zero, the magnetic core 4 is changed to positive or negative. The relational expression t' + <t'- is established between the positive excitation period t' and the negative excitation period t'- required for excitation to the maximum magnetic flux density level.

Next, as shown in Fig. 3(C), the negative current to be measured I''
When the above-mentioned excitation cycle is repeated from the state where the magnetic field generated by ex ((0) is applied to the magnetic core 4, a magnetic flux density change of ΔB"12 during positive excitation and ΔB"34 during negative excitation is observed. Between the excitation period t"+ and the negative excitation period t"-, t"1>t"- is established.

There, t''c, 'Jl In order to prevent the excitation DC voltage value applied to the core-4 during the excitation cycle described above from decreasing or fluctuating even at the maximum magnetic flux density level of the magnetic core 4, as shown in the current detection circuit in Fig. 4. Variable resistor 6 in series with excitation winding 2
and adjust the impedance using this variable resistor. Also, as soon as the magnetic flux level of the magnetic core 4 reaches the maximum magnetic flux density level ■ or ■, the DC voltage Vc,
Considering the case where the polarity of -Vc is switched, terminal 7
The voltage waveform e at the terminal 8 (or terminal 8) is observed as a square wave voltage waveform having both positive and negative polarities.

Figure 5 shows that, based on these assumptions, EX=0, I'
The figure shows the voltage waveform e at the terminal 7 in each case of ex〉0,
'ten, t# ten and negative half-cycle duration t-11/-
1t"- is the current to be measured 1ex, I'ex.

It can be seen that it is controlled by Pex. Therefore, Ce
It is possible to measure current by integrating the voltage integral value Eoz E'o, E''o and converting and displaying the sign and voltage value in correspondence with the polarity and strength of the current being measured eX. I know what I can do.

FIG. 6 is an overall circuit diagram for automatically implementing the operating principle of the present invention. Functionally, the current sensing section 100, the display circuit section 200. It is established from the DC stabilized power supply section 250.

First, as four elements constituting the bridge circuit of the current sensing section 100, a variable resistor 6 and an excitation winding 2 are connected to the - side.
and a capacitor 5 are present, and a variable resistor 11 and a variable resistor 10 are present on the other side. Countermeasure volume, 933
00 generates a magnetic field in the direction of canceling the magnetic field generated by the current to be measured Iex applied to the magnetic core 4. This is because the canceling current output from the display circuit section 200 is input to the terminal 300a. It is executed well. This feedback system is aimed at stabilizing the circuit system of the current sensing part and improving the linearity of the input/output characteristics, which represents the relationship between the output voltage and the current being measured, and is extremely difficult to use in practice. Useful. However, this canceling winding 30
Even if 0 is omitted, the object of the present invention does not change. The input to each input terminal of the operational amplifier OPI is the non-inverting terminal P.
Terminal 2a of excitation winding 2 is input through node A,
The voltage at node B is input to the inverting terminal N via node B of variable resistors 10 and 11. operational amplifier OP
The operation of 1 is based on the input voltage difference eA between the P, , and N terminals,
It does not operate as an amplifier that amplifies -ej, but identifies whether the input voltage difference eA, -eB is positive or negative, and adjusts the positive or negative saturation DC voltage accordingly. It functions as a code discriminator that outputs . The capacitor 5 absorbs the noise components generated in the magnetic core 4 and stabilizes the self-excitation operation by suppressing the effects of rapid magnetic flux changes, such as the magnetic flux flyback phenomenon caused by switching between positive and negative voltages applied to the bridge. It is desirable to insert it because it has the function of

Next, the self-excitation operation will be explained.

Here, for ease of understanding, the capacitor 5 is omitted and the resistance value of 1 variable resistor 6.10.11 is R6,&o,
Rn, the impedance of the excitation winding 2 is 22, the impedance just before the magnetic core 4 reaches the maximum magnetic flux density Bm is 22m-, and the impedance when it reaches 10Bm is 22m, and between these, R6> 22 and R
h>Rlo, and R6=Rn and Z2m
>Rio) Let us consider only one case where 22m is established. If, at this moment, the output voltage of the output terminal 7 of the operational amplifier OP+ is switched to the positive saturated DC voltage +Vs, the magnetic flux density level in the magnetic core 4 is the magnetic flux density level specified by the current to be measured. 4 (state ■)]. Then, the positive voltage ea (>0) divided by the resistor 11 and IO is input to the inverting terminal N, and the non-inverting terminal P A positive voltage eA (〉0) determined by the voltage division between the resistor 6 and the impedance of the excitation winding 2 is input to .

Here, the impedance z2 of the excitation winding is very large because the magnetic core 4 is in a magnetic flux unsaturated state, and the resistance l
Since Z2>RIO is established between the operational amplifier OPr and the operational amplifier OPr, the sign of the operational amplifier input voltage difference becomes positive (eA-eB'>o), and the output voltage of the operational amplifier OPr maintains the positive saturated DC voltage +Vs. However, the magnetic flux density level in the magnetic core 4 gradually increases, and the maximum positive magnetic flux density Bm gradually increases.
As the magnetic permeability decreases, the excitation winding 2
The impedance Z2 of decreases, and just before the magnetic core 4 reaches the maximum positive magnetic flux density Bm, Zz = Zzm-, and at this point Z2 m -> Rio holds, but in the next instant 1, the magnetic core 4 Since the maximum magnetic flux density Bm is reached (■
state), this time Z2 = 22m (Rio).As a result, the relationship eA-< eB is established and the operational amplifier OP
The sign of the input voltage difference between + input terminals is positive (eA-e,,
>01 state to negative (eA-eB (o)) state, a negative saturated DC voltage -Vs is generated at the output terminal 7 of the operational amplifier OP+.This voltage is then connected between the terminal 7 of the bridge and the ground. At the same time that the current is applied during the G period, the magnetic flux density level of the magnetic core 4 quickly returns to the level defined by the current to be measured (state ■).

Entering this negative excitation cycle ° and Z2>RIOle
The relationship A〈0, e,〈0, eA-eB〈0 is established,
The magnetic flux change in the magnetic core 4 proceeds in the opposite direction. As time passes, the magnetic flux density level of the magnetic core 4 increases.
When the negative maximum magnetic flux density -Bm is reached (state of ■), Z
2 = Z2 m <Rio, eA> eB holds true, and the sign of the input voltage difference of the operational amplifier OP+ is positive (eA
, -eB > O], and a positive saturated DC voltage element Vs appears at the output terminal 7 of the OPI.

From the above circuit operation explanation, it can be seen that the magnetic core 4 has a maximum magnetic flux density Bm
It has become clear that the saturated DC voltage ±Vs of the operational amplifier OP+ is automatically switched alternately each time the voltage reaches -Bm.

In addition, the current to be measured Ie is applied to the input winding 3 wound around the magnetic core 4.
x N I'ex (> 0), ■"ex ((If the above operation is performed with 01 input, the operational amplifier OP
It is easy to understand that a square wave voltage waveform as shown in FIG. 5 is observed at the + output terminal. However, if you want to be accurate, the value Vc in Figure 5 should be ±V
It is sufficient to read it by replacing it with s.

200 is a display circuit section, which includes an operational amplifier OP 2 for integrating and amplifying the output voltage of the current sensing section 100, an integrating capacitor 12 connected to this, and 11 resistors 13, 14, 16, .
18, a choke coil 17, and an indicator needle 19.

At the output of the operational amplifier OP2, the blade terminal 15, a positive or negative DC voltage value corresponding to the polarity of the current to be measured, - and its magnitude, is observed.

The choke coil 17 prevents the alternating current component from the current sensing section 100 from affecting the display circuit section when current flows in the direction of canceling the magnetic field generated by the 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. 25
0 is a DC stabilized power supply section, operational amplifier OP+,
This is only for driving OF2. Current sensing section 100
Transmission between the display circuit and the display circuit section achieves the purpose with only the DC component.
The transmission and reception of signals is completely done using the C-DC system. Therefore, for example, in the measurement room there is a DC stabilized power supply section 25.
By installing the display circuit section 200 and the display circuit section 200, it becomes possible to monitor, in the measurement room, changes in the current that the current sensing section 100, which is attached several hundred meters away, is sensitive to.

FIG. 7 shows another circuit example of the current sensor shown in FIG.

The current sensing section 100' has an output voltage E.

In order to adjust the DC voltage level (shown in block 200'), a circuit is added to the excitation winding 2 to flow a current for level adjustment.The variable resistor 40 is connected to the Vc power supply for driving the operational amplifier. The current is caused to flow through the winding 2 through the resistor 41 through its intermediate junction.

Depending on the position of the contact S in the variable resistor 40, the duty ratio of Vs on the output voltage of the operational amplifier OPr changes, and ±V
This also makes it possible to increase or decrease the level of the integrated voltage value Eo of s. 400 is a comparator which takes the voltage Eo as an input signal, and checks the input signal level against a preset reference voltage value, converts it into a high level or low level signal voltage, and outputs it. be. The comparator used here is a well-known comparator (including a window comparator), and it is sufficient to take advantage of its characteristics depending on the application. 500 is the display circuit section that outputs the comparator. Depending on Ec, for example, a relay that generates an alarm is activated and an LED is displayed.

Figure 8 shows an example of its application. Figure 8(a) is an electrical diagram. By using the entire current sensor 1000 for each contact of an electromagnetic relay, it is 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), and a voltage divider circuit using a resistor is used to raise the ground G 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. FIG. 8(b) is an example of an 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 the drawing]

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. 3 is a diagram showing the basic configuration of the present invention, FIG. 3 is a diagram for explaining the operating principle of the present invention using the magnetic core 40B-Iex characteristics, FIG. FIG. 6 is an overall circuit diagram for automatically carrying out the operating principle of the present invention; FIG. 7 is another circuit example of the current sensor shown in FIG. 6. FIG. 8 is a diagram showing an application example. In the figure, 1 is the magnetic core, 2 is the excitation winding, 3 is the input winding, 2a,
2b, 3a, 3b are terminals, 4 is a magnetic core to which the winding is fixed, 5
is a capacitor, 17 is a choke coil, 19 is an indicator needle,
30 is a single-hole conductor, 40 is a variable resistor, 100 is a magnetic sensing section, 200 is a display circuit section, 250 is a DC stabilized power supply section, 300 is a cancellation winding, 400 is a comparator, 500 is a display circuit section, A , B is the node, G is the ground, OP+,
OF2 is an operational amplifier, P is a non-inverting terminal, and N is an inverting terminal. Agent Patent Attorney Masamitsu Akizawa and 2 others Figure 63 Q Figure n Figure 5

Claims (1)

[Scope of Claims] A single-hole magnetic core that collects a magnetic field generated by a current to be measured along the direction of a magnetic path around a hole in a perforated magnetic material; an input circuit in which the current flows through an input winding passing through a hole in the single-hole magnetic core; a first element is an excitation winding wound around the single-hole magnetic core;
a bridge circuit in which an element, a third element, and a fourth element are configured by resistors, and a positive or negative saturated DC voltage corresponding to the sign of a bridge unbalanced voltage at an intermediate point of the bridge circuit is applied between the terminals of the bridge circuit. Operation type current °C.