JPH0425499B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a current detection device.

Referring to FIG. 1, in the prior art, a magnetic multivibrator 5 is configured such that a vibrator circuit 1, a saturable reactor 2, capacitors 6, 7, and resistors 106, 107 are connected in parallel. A magnetic multivibrator 5 is constituted by two impedances 3 and 4 for extracting an output. Saturable reactor 2
When the measured current flowing through the primary coil 8 of the saturable reactor 2 is zero, the currents flowing through the secondary coil 9 and the tertiary coil 10 of the saturable reactor 2 are equal, and the voltage difference between the impedances 3 and 4 becomes zero. When the current to be measured flows through the primary coil 8, a difference occurs between the currents flowing through the secondary coil 9 and the tertiary coil 10, and a differential voltage is generated between the impedances 3 and 4. The current flowing through the primary coil 8 is detected by detecting this voltage and operating a response device 11 such as a meter. However, impedances 3 and 4 include capacitors 6 and 7, respectively, and the capacitance values of the capacitors have relatively large variations, resulting in variations in detection current sensitivity and poor productivity. Another prior art is shown in FIG. 2, in which a single capacitor 12 is used to take the output from the magnetic multivibrator circuit.
However, since the capacitor 11 has a large variation in capacitance value, the detection current sensitivity also has a large variation, resulting in poor productivity.

The purpose of the present invention is to solve the above-mentioned technical problems,
It is an object of the present invention to provide a current detection device that prevents variations in detection sensitivity due to impedance elements used and has improved productivity.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is an electrical circuit diagram of one embodiment of the present invention. The current detection device includes a magnetic multivibrator circuit 21 and a sampling pulse generation circuit 22.
, sample and hold circuit 23, and differential amplifier 2
5, delay circuit 26, and window comparator 2
7 and a response device 28.

The magnetic multivibrator circuit 21 includes a resistor 29
, a saturable reactor 30 , and a multivibrator 31 .

The saturable reactor 30 includes a primary coil 32 for flowing a current to be detected, and a pair of secondary coils 33 and tertiary coils 34 for oscillating. The primary coil 32 is connected to a source to be measured (not shown) that derives a current to be detected. Secondary and tertiary coil 3
3 and 34 each have approximately the same number of turns n. One end of each of the secondary and tertiary coils 33, 34 is connected to a resistor 2, which is an impedance, with one end grounded.
9 to a common connection point 35 with each other.
The other end of the secondary coil 33 is connected to a connection point 36 of the multivibrator 31. Tertiary coil 34
The other end is the connection point 3 of the multivibrator 31
Connected to 7.

In the multivibrator 31, the DC power supply 3
Line 39 to which positive voltage +Vcc is applied by 8
A transistor 40 is connected between the connection point 36 and the connection point 36 . Between the line 39 and the connection point 37,
Transistor 41 is connected. transistor 4
The base of 0 is connected to line 39 via resistor 42 and to connection point 37 via resistor 43. The base of transistor 41 is connected to line 39 via resistor 44 and to connection point 36 via resistor 45 .

The magnetic multivibrator circuit 21 configured in this way has a coil applied voltage E and a saturation magnetic flux of φ.
m, number of turns n of the secondary or tertiary coils 33, 34
Then, the period T = 4nφ of the secondary or tertiary coil of the magnetic oscillation circuit known as the Royer circuit
Always oscillates at m/E. The principle that when the current flowing through the primary coil changes, the duty ratio of the current flowing through the secondary or tertiary coil changes as follows.
An example is shown in "Basic Magnetic Engineering" published by Gakukensha on March 19, 1980, pages 158 to 162, and an outline of its operation will be explained below.

When the current in the primary coil 32 is zero, the duty ratio of the period T1 is 50%. The secondary coil 33 and the tertiary coil 34 have a half period T1/2.
Currents having the same value flow in different periods and in mutually different periods. Therefore, the current from the secondary coil 33 for every half cycle and the current from the tertiary coil 34 for every different half cycle continuously flow through the resistor 29, and a voltage V is generated.

The polarity of the primary current flowing through the primary coil 32 is 1.
2 flowing to the secondary coil 33 by the secondary coil 32
If the direction is equal to the secondary current, the secondary current will decrease;
Conversely, the tertiary current flowing through the tertiary coil 34 increases. In this case, due to the decrease in the secondary current, the voltage applied to the secondary coil 33 increases and the period for reaching saturation becomes shorter, and conversely, the voltage applied to the tertiary coil 34 decreases and saturates. It takes a longer time to reach . Therefore, the duty ratio of the oscillation period T1 is
Varies from 50%. That is, the primary current changes the secondary and tertiary currents in proportion to the primary current, and the duty ratio also changes.

Connection points 36 and 37 are connected to inputs of sampling pulse generation circuit 22, respectively. The sampling pulse generation circuit 22 generates a sampling pulse with a pulse width T2 in response to a signal from the connection point 36, that is, at a predetermined time within a half period T1/2 in which the current flowing through the secondary coil 33 flows to the resistor 29. is output on line 46. In addition, the sampling pulse generation circuit 22 performs sampling of a pulse width T2 in response to a signal from a connection point 37, that is, at a predetermined time within a half cycle T1/2 in which the current flowing through the tertiary coil 34 flows to the resistor 29. A pulse is output on line 47. Note that T1/2>T2 is selected.

The sample hold circuit 23 includes a switch 48,
49, resistors 50, 51 and capacitors 52, 5
It has 3. Connection point 35 is grounded via switch 48, resistor 50 and capacitor 52.
Connection point 35 is grounded via switch 49, resistor 51 and capacitor 53. A connection point 54 between the resistor 50 and the capacitor 52 is connected to the differential amplifier 25.
connected to one input of the A connection point 55 between the resistor 51 and the capacitor 53 is connected to the other input of the differential amplifier 25. The switches 48 and 49 are, for example, analog switches, and the switches 48 and 49 are analog switches.
47, respectively. Switches 48 and 49 each become conductive only when a sampling pulse is applied. The time constant due to capacitors 52 and 53 is the pulse width
It is chosen to be sufficiently smaller than T2. The capacitor 52 is rapidly charged to the voltage of the resistor 29 when the switch 48 is turned on, and the capacitor 52 is charged rapidly to the voltage of the resistor 29 when the switch 48 is turned on.
The charging voltage is maintained until the next conduction. Capacitor 53 connects resistor 29 when switch 49 is conductive.
The charging voltage is rapidly charged to a voltage of , and the charging voltage is maintained until the next time the switch 49 is turned on.
The time constant due to capacitors 52 and 53 is the pulse width
Since it is selected to be sufficiently small compared to T2, even if the capacitance values of capacitors 52 and 53 have an error from the predetermined capacitance value, the effect of that error can be almost ignored, and moreover, the voltage of resistor 29 Can be held accurately.

The differential amplifier 25 amplifies the difference between the charging voltages of the connection points 54 and 55, that is, the capacitors 52 and 53, and provides the amplified difference to the delay circuit 26.

The delay circuit 26 includes a resistor 56 and a capacitor 5.
It has 7. The output of the differential amplifier 25 is connected to a resistor 56.
and grounded via a capacitor 57. A connection point 58 between the resistor 56 and the capacitor 57 is connected to the input of the window comparator 27. This delay circuit 26 prevents the reaction device 28 from erroneously operating due to the instantaneous current flowing through the primary coil 32. Furthermore, the detection sensitivity of the alternating current flowing through the primary coil 32 is adjusted.

The window comparator 27 has two discrimination levels VL and VH sandwiching the ground, and also has a latch function. When the absolute value of the charging voltage at the connection point 58, that is, the capacitor 57, exceeds the absolute value of the positive discrimination level VH or the negative discrimination level VL, the window comparator 27 holds the base of the transistor 59 at a high level and latches it. Transistor 59 therefore remains conductive and responsive device 28, such as an indicator or relay, is energized and operated. When the charging voltage of the connection point 58, that is, the capacitor 57, is between the negative discrimination level VL and the positive discrimination level VH, the window comparator 27
holds the base of transistor 59 at a low level and latches it. Therefore, transistor 59
continues to shut off, and the response device 28 is deenergized. When the window comparator 27 is a comparator having only one discrimination level, the primary coil 3
When an alternating current flows through the window comparator 2, the output from the comparator becomes a pulse according to the cycle of the alternating current, causing an inconvenience.However, in the present invention, since the window comparator 27 has a latch function, such inconvenience is eliminated. will not occur. Furthermore, since the window comparator 27 has two discrimination levels VL and VH with the ground in between, it is possible to prevent detection from becoming impossible due to the polarity of the DC current flowing through the primary coil 32 or the polarity of the half cycle of the AC current. I can escape.

Referring to FIG. 4, assume that the primary current of the primary coil 32 is zero as shown in FIG. 41 before time t1. The secondary current of the secondary coil 33 and the tertiary current of the tertiary coil 34 are shown in FIG.
and half period T/ as shown in FIG.
Currents having the same value flow every two and at mutually different periods. Therefore, the voltage across resistor 29 becomes as shown in FIG. 4. Sampling pulses applied from sampling pulse generating circuit 22 to switches 48 and 49 via lines 46 and 47, respectively, are shown in FIGS. 4-5 and 4-6, respectively. Therefore, the connection points 54, 55
That is, the charging voltages of capacitors 52 and 53 are equal as shown in FIG. 47 and FIG. 48, respectively. Since the charging voltages of the capacitors 52 and 53 are equal, the output of the differential amplifier 25 is zero as shown in FIG. 4, and the output of the connection point 58, that is, the delay circuit 26, is zero as shown in FIG. 4. Yes, the output of the window comparator 27 is maintained at a low level as shown in FIG. 4, 11. The reaction device 28 is therefore not energized.

Next, after time t1, the polarity of the primary current in the primary coil 32 is in the direction of arrow 60, and the DC current is in the fourth direction.
Assume that the flow is as shown in FIG. The secondary current and the tertiary current are currents having different values in proportion to the primary current, which flow every half period T1/2 and at mutually different periods, as shown in Fig. 4 2 and Fig. 4 3, respectively. . Therefore, the voltage across the resistor 29 becomes as shown in FIG. capacitor 52
The charging voltage of is decreased as shown in FIG. 4 in response to a sampling pulse via line 46. The charging voltage of capacitor 53 is determined in response to a sampling pulse via line 47 as shown in FIG.
rise as shown in . Therefore, differential amplifier 2
The output of No. 5 increases from zero in a stepwise manner as shown in FIG. 4. The delay circuit 26 outputs the signal with a delay of a certain time W determined by the capacitor 52, as shown in FIG. 4. When the output of the delay circuit 26 exceeds the discrimination level VH, the window comparator 2
The output of No. 7 becomes high level as shown in FIG. 4, 11. The reaction device 28 is therefore energized into operation.

As described above, according to the present invention, one terminal of each of the secondary and tertiary coils of the saturable reactor is commonly connected to the resistor, and the voltage generated in the resistor is sampled in synchronization with the period of the magnetic multivibrator circuit. Depending on the pulse, the current flowing through the secondary or tertiary coil is temporally differentiated and held in a sample and hold circuit. Since the resistance values have small variations, the detected voltages also have small variations.
The sample and hold circuit has two capacitors to hold voltages corresponding to the currents flowing through the secondary and tertiary coils, respectively. Even if the capacitance values of these capacitors have relatively large variations, there is no variation in the held voltage. Therefore, variations in detection sensitivity are prevented and productivity is improved. In addition, since a sampling pulse generation circuit and a sample hold circuit are used, even if there are variations in the magnetic properties of the saturable reactor, the absolute value of the current flowing through the secondary and tertiary coils will not change. The current flowing through the primary coil can be detected.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the prior art;
The figure is a block circuit diagram of one embodiment of the present invention, and FIG. 4 is a diagram for explaining its operation. 21... Magnetic multivibrator, 22... Sampling pulse generation circuit, 23... Sample hold circuit, 25... Differential amplifier, 27... Wind comparator, 28... Response device, 29...
Resistor, 30...Saturable reactor, 31...Multivibrator, 32...Primary coil, 33...
Secondary coil, 34...Third coil.

Claims (1)

[Claims] 1 a saturable reactor having a primary coil for the current to be detected, a secondary coil for oscillation and a tertiary coil magnetically coupled to the primary coil;
An impedance connected to one end of the secondary coil and the tertiary coil, and an impedance connected to one end of the secondary coil and the tertiary coil.
A magnetic multivibrator circuit with each output connected to the other end of the next coil forms a magnetic multivibrator circuit that oscillates at a predetermined period, and the impedance voltage applied every half period of the period is transmitted through a differential amplifier. In a current detection device that discriminates between levels and operates a response device when the discrimination level is exceeded, the impedance is a resistance, and this resistance is connected to one end of the secondary coil of the saturable reactor and one end of the tertiary coil of the saturable reactor. The coils are connected in series with one end thereof connected in common, and further include a sampling generation circuit that outputs a pair of sampling pulses synchronized with the cycle of the magnetic multivibrator circuit, and a resistor that responds to the sampling pulses of the sampling generation circuit. A current detection device comprising: a sample-and-hold circuit that divides and holds the voltage of each half period, and provides a pair of held outputs of the sample-and-hold circuit to the differential amplifier.