Fuji Electric Co., Ltd.

Yujiro Kitaide

Takahiro Kudo

Kimitada Ishikawa

Takeshi Matsubara

An overload current protection device for cutting off power applied from a power supply to a load () such as a motor by means of a contactor (switch) () at overloading. With the configuration, an element () having a magnetic impedance effect as current detection units () is used to thereby expand a current detection range by eliminating magnetic saturation due to a core, a problem with a conventional current transformer, thereby providing at low costs an overload current protection device having a wide current detection range.

Overload current protection device using magnetic impedance element

In an overload current protection device for cutting off power from a power supply to a load () such as a motor by means of a contactor (switch) () at overloading, an MI element having a magnetic impedance (MI) effect as current detectors (, and) is installed at a position capable of detecting a current flowing through the secondary winding of power supply transformers (, and) that generate a control power supply to thereby reduce costs without using a constant voltage power supply and expand a current detection range by eliminating magnetic saturation due to a core, a problem with a conventional current transformer, thereby providing at low costs a high-precision overload current protection device having a wide current detection range.

A small, low-cost, wide-range current sensor excellent in environmental resistance and noise resistance and high in accuracy, and an application device, a DC magnetic field is applied to two magnetic elements () having a magnetic impedance effect by means of a magnet (), while a negative feedback magnetic field is applied to both elements by means of a coil (). The variation of the magnetic field depending on the external magnetic field applied to the magnetic elements () is detected by detection units (). The difference between the output is amplified by a differential amplifier unit (). Thus, detection is achieved in a wide range while eliminating the influence of the noise.

Current sensor and overload current protective device therewith

To provide a magnetism detection apparatus that is small and low in cost and power consumption, a biasing coiland a negative-feedback coil are integrated with a magnetic impedance element having a magnetic impedance effect in a resinous structure. The magnetism detection apparatus has a reduced magnetic resistance between the magnetic impedance element and the coil, thereby making it possible to apply a bias magnetic field and a negative-feedback magnetic field to the magnetic impedance element with a reduced power consumption.

Magnetic sensor

A pressure in a pressurizing chamber of a micromachine apparatus for transferring a fluid is measured inexpensively under an actual-use or a similar condition. A piezoelectric element used as an actuator for applying a pressure to the fluid in the pressurizing chamber is also used as a pressure sensor. A charge amplifier is used to measure the amount of charge Q.sub.1 applied to an electrode of the piezoelectric element when the piezoelectric element is driven while the pressurizing chamber filled with the fluid, and the amount of charges Q.sub.2 when the piezoelectric element is driven while the chamber contains no fluid. The obtained signals are inputted to a storage and operation processing device to determine (Q.sub.1 -Q.sub.2) to determine the pressure of the fluid in the pressurizing chamber. The piezoelectric element or capacitor for the purposes of comparison can be used to simultaneously measure Q.sub.1 and Q.sub.2.

Growing community of inventors

Kanagawa, Japan

Yujiro Kitaide