Hitachi, Ltd.

Tsutomu Okayama

Yoshitaka Matsuoka

Hideo Sato

Satoshi Shimada

Akira Ikegami

Kazuji Yamada

Yasumasa Matsuda

Motohisa Nishihara

Yoshimi Yamamoto

Takeo Nagata

Mitsuo Ai

Takashi Kugaya

Katsuya Katohgi

An alternatable constant current circuit is provided which supplies positive and negative polarities of rectangular wave current to an inductive load such as in an exciting circuit of an electromagnetic flowmeter and in a slanted magnetic field system of a nuclear magnetic resonance imaging device at a high current inversion speed and a low power loss, wherein the capacitance of an output capacitor in a switching power source circuit is lowered, the regenerative output voltage of the output capacitor is applied to the inductive load during the current inversion period therein via a polarity inversion circuit, further the load current is controlled by a current control circuit at a predetermined value and the output voltage of the switching power source circuit is also controlled so as to maintain the collector-emitter voltage Vce of a current control transistor in the current control circuit constant, whereby an oscillation is generated in the circuit including the inductive load and the output capacitor during the current inversion to charge the output capacitor to an excessively high voltage and further the output voltage of the output capacitor in the switching power source circuit rises due to a decrease of the collector-emitter voltage Vce thereof to thereby cause an output voltage jump-up of the output capacitor and to hasten the current inversion in the inductive load.

Alternatable constant current circuit

A differential pressure measuring transducer assembly of semiconductor material including a pressure receiving section producing a displacement when pressure is applied, and a stationary section of large thickness located at an outer periphery of the pressure receiving section. The pressure receiving section is composed of a large thickness portion extending to the stationary section at the outer periphery, and a small thickness portion occupying the rest of the pressure receiving section, and a gauge resistance is provided to the large thickness portion.

Differential pressure measuring transducer assembly

A two-terminal current regulator has a sensing resistor, a reference voltage generator, a current controller, an error amplifier for controlling the current controller such that a voltage drop across the sensing resistor is equalized to a reference voltage generated by the reference voltage generator, and a current distributor for distributing currents to the reference voltage generator, current controller and the error amplifier such that the currents are proportional to a current flowing through the sensing resistor. Thus, a high precision constant current characteristic is attained.

Two-terminal current regulator

A displacement transducer for measuring displacement brought about by pressure, strain or the like comprises a sensor for producing an electric signal representative of displacement, an output amplifier for amplifying the signal output from the sensor, an exciting circuit for exciting the sensor with a current or voltage and adapted for controlling excitation in dependence on deviation thereof from a reference value, and a correcting circuit for correcting the excitation of the sensor thereby to correct non-linearity of the output signal from the sensor. The correcting circuit includes a first voltage divider circuitry of a fixed dividing factor and a second voltage divider circuitry of a variable dividing factor connected in parallel with the first divider circuitry. The reference value is corrected by the voltage dividing factor of the second divider circuitry thereby to correct the excitation of the sensor. Correction of the non-linearity of the output signals of negative and positive polarities can be made with only a single correcting circuit.

Displacement transducer

A pressure transducer has at least one pressure transmitting space filled with liquid, a space for a pressure to be sensed connected to the pressure transmitting space through a diaphragm, and a pressure sensitive element in the pressure transmitting space for transducing a pressure transmitted from the space for the pressure to be sensed to the pressure transmitting space through the diaphragm to an electrical signal. A printed circuit board wired to electrically connect terminals of the pressure sensitive element is arranged closely to the element and thin temperature sensitive elements for temperature-compensating the pressure sensitive element are arranged on the printed circuit board.

Pressure transducer

A bridge circuit with four arms including semiconductor strain gauge elements has input terminals for coupling a DC power supply with a pair of diagonally opposite junctions of the bridge circuit per se and output terminals coupled with a pair of remaining diagonally opposite junctions. Initial zero-point temperature compensators each are connected in series and in parallel to each of semiconductor strain gauge elements on adjacent two arms of the bridge circuit. Temperature compensators for zero-point shift adjustment are each provided between the adjacent arms closer to each output terminal. A temperature compensator for span adjustment is provided between one of the input terminals and the DC power source. A constant current control unit for feeding a constant current to the bridge circuit is provided between the other input terminal and the DC power supply.

Semiconductor strain gauge with temperature compensator

Two differential amplifiers are provided each having two input terminals. One of the input terminals of each differential amplifier receives an output signal derived from a measuring circuit, while the other terminals of the differential amplifiers are coupled to each other. Output signals of the respective differential amplifiers control correspondingly two series-connected current control circuits, respectively. With such a circuit arrangement, a current flowing through a receiving unit connected in series to the two current control circuit is controlled in response to the output signal from the measuring circuit.

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Katsuta, Japan

Tsutomu Okayama