JPH06109770A - High-precision current sensor - Google Patents

Abstract

PURPOSE:To maintain the excellent characteristics of a magnetic balance type current sensor by preventing a magnetic substance core from being excited due to the abnormal rise of power voltage, and avoiding the occurrence of an offset error in the sensor. CONSTITUTION:This sensor is so constituted that an ordinary magnetic balance type current sensor is additionally provided with a voltage detecting section 1, a delaying section 2A for causing a delay in output from the section 1, an amplifying section 2B for amplifying output from the section 2A, and a power supply control section 3 for driving the sensor in response to output from the section 2B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high precision current sensor.

[0002]

2. Description of the Related Art FIG. 2 shows a basic structure of a conventional magnetic balance type current sensor using a magnetoelectric conversion element. The principle of this current sensor will be described. A magnetic flux is generated in the core CR by the primary current I1 flowing through the primary coil L1. The magnetic flux in the air gap GP of the core CR is detected by the magnetoelectric conversion element MS, for example, a Hall element, and the secondary coil L2 wound around the core CR receives the converted output of the magnetoelectric conversion element MS as a power supply amplifier A.
A secondary current I2 is supplied from MP to form a magnetic equilibrium state in which the magnetic flux of the core CR eliminates, and in this magnetic equilibrium state, the equal ampere-turn law, that is, I1 × N1 = I2
× N2 (N1 and N2 are the number of turns of the primary and secondary coils)
Is applied to measure the secondary current I2 to measure the primary current I1.

Both positive and negative voltages (+ V, -V) are supplied to the current sensor for measuring the alternating primary current I1 having the structure shown in FIG. When one of the voltages becomes a low voltage state, the power amplifier AMP malfunctions.

Among the malfunctions of the power amplifier AMP, a particular problem is that the primary current I1 is zero and the secondary current I2 is zero.
Is to excite the core CR, and for this reason,
This is because the offset error of the current sensor persists due to the residual magnetic flux even after the power supply is in the normal state.

In order to solve this, in the conventional current sensor shown in FIG. 2, the voltage detection unit 1 and the power supply control unit 2 are arranged so that the current sensor is driven only when the power supply is normal. An example of the conventional voltage detection unit 1 and power supply control unit 2 is the circuit shown in FIG. That is, the zener diode ZD is turned off by a single power source or a low voltage, and the forward bias voltage due to the resistors R10 and R20 is not generated, so that the transistors TR1 and TR2 are also turned off and the current sensor is not driven.

[0006]

The prior art shown in FIG. 3 has the following problems.

First, when a power source is supplied to such a voltage detecting section 1 through a general contact type switch,
At the initial stage of power-on, fine switching frequently occurs, so-called chattering phenomenon, and the secondary current I2 transiently flows due to the follow-up delay to excite the core CR.

Second, when a bipolar power supply is controlled by the two transistors TR1 and TR2, it is difficult to synchronize due to variations in their characteristics, and a time difference easily occurs in the activation of the drive voltages Vs ⁺ and Vs ^−. , Exciting the core as above.

That is, in the conventional example, the generation of the offset error of the current sensor cannot be avoided due to the residual magnetic flux accompanying the excitation of the core CR. Once an offset error occurs, it is essential to remove the current sensor and demagnetize (demagnetize) by applying a damped oscillatory alternating current or an alternating magnetic field. Is. Conventionally, with respect to the second problem, attempts have been made to match the characteristics by selecting (pairing) the transistors and to utilize the FET transistor, but a certain effect is obtained as compared with an increase in labor and cost burden. Hard to achieve.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a magnetic balance type current sensor, a means for detecting a power supply voltage supplied to the current sensor, and It is characterized by comprising delay means for delaying the detection output of the detection means, and power supply control means for supplying power to the current sensor in response to the output of the delay means.

[0011]

According to the present invention, by adding the delay function, the drive of the current sensor is started after a lapse of a predetermined time after it is determined that the power supply is normal. In addition, it is possible to make a sharp decision by adding a function to amplify the output signal by judging whether the voltage of the power supply is normal, that is, whether or not a voltage equal to or higher than a predetermined value is supplied without being lost. To do.

As a result, first, the chattering phenomenon that frequently occurs at the initial stage of power-on is avoided by delaying the start of driving the current sensor due to the above delay function.

Next, for example, the difficulty of synchronization caused by variations in the characteristics of the transistors forming the power supply control unit is as follows.
The amplification function eliminates the influence of the characteristic difference of the transistors by applying a strong forward bias voltage to these transistors at once.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 4 is a circuit diagram of the voltage detection unit 1, the delay unit 2A, the amplification unit 2B and the power supply control unit 3. The configuration is the same as that of FIG. 2 except for the configuration shown in FIG. A Hall element is used as the magnetoelectric conversion element MS of this embodiment.

[0016] First, the voltage supplied from the Zener voltage V _ZD and the power supply of the zener diode ZD and the voltage detecting unit 1, the Zener diode ZD a series circuit of resistors R1 shown in FIG. 4 [V ⁺ - (V ^-)] Are almost the same,
The Zener diode ZD is switched on. As a result, a current due to this switch-on flows through the delay unit 2A, but the time constant [C ×
R2], the output voltage VD of the delay unit 2A rises with a delay characteristic.

In the amplifier section 2B, a voltage V from the delay section 2A is reached after a predetermined time has passed since the Zener diode ZD was switched on.
The transistor TR3 is switched on by D, and the amplified strong current is output. That is, the resistance R4
A current flows between R3, the collector and emitter of the transistor TR3, and the resistor R5.

Therefore, the transistor T of the power supply controller 3
R1 and TR2 are switched on at a dash with a sufficient forward bias voltage generated by the currents flowing in the bias resistors R4 and R5, and generate output voltages Vs ⁺ and Vs ⁻ with almost no time difference. To drive.

FIG. 5 is a diagram showing an example of characteristics of this embodiment.
In this example, the positive voltage V ⁺ and the negative voltage V ⁻ supplied from the power supply with a voltage of ± 15 V are applied to the voltage detection unit 1 at time T1 and T2 with a time difference and with a chattering phenomenon. Due to the delay function of the section 2A, the drive voltages Vs ⁺ and Vs ⁻ rise at the same time at the time T3, and also rise sharply due to the amplifying action of the amplifying section 2B. Here, the Zener voltage V
_ZD is set to 20V.

As described above, the above problems are avoided without being affected by the time difference at the time of turning on the power source, the intermittent single power source state due to chattering, the voltage drop state, and the like.

[0021]

According to the present invention, the occurrence of an offset error due to an abnormal supply of the power supply voltage is avoided, and a remarkable effect is produced especially in a high precision current sensor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic configuration example of the present invention.

FIG. 2 is an explanatory diagram of a conventional basic configuration example.

FIG. 3 is a circuit diagram of a conventional example.

FIG. 4 is a circuit diagram of an embodiment of the present invention.

FIG. 5 is a diagram showing a characteristic example of an embodiment of the present invention.

[Explanation of symbols]

ZD Zener diode TR1 to TR3 Transistor 1 Voltage detection unit 2A Delay unit 2B Amplification unit 3 Power supply control unit V ⁺ , V ^- Positive supply voltage, Negative supply voltage GND Ground Vs ⁺ , Vs ^- Positive drive voltage, Negative drive voltage CR Ferromagnetism Body core GP Air gap MS Magnetoelectric conversion element AMP Power amplifier I1, I2 Primary current, Secondary current L1, L2 Primary coil, Secondary coil R1 to R5, R10, R20 Resistance C capacitor VD Delay unit output voltage

Claims (2)

[Claims] 1. A magnetic balance type current sensor, a means for detecting a power supply voltage supplied to the current sensor, a delay means for delaying a detection output of the detection means, and the current in response to the output of the delay means. A high-precision current sensor, comprising a power supply control means for supplying power to the sensor. 2. The high precision current sensor according to claim 1, further comprising an amplifying means for amplifying an output of the delay means between the delay means and the power supply control means.