Abstract: A magnetic excitation circuit is used as a circuit for providing a magnetic excitation electric current based on a magnetic excitation power supply voltage to a magnetic excitation coil of an electromagnetic flow meter. The magnetic excitation circuit includes four voltage storing circuits that store and output a driving voltage that is charged by a common driving voltage. The voltage storing circuits are connected respectively between the control terminals and the output terminals of four switching elements. When the four switching elements are turned ON in relation to a positive interval or a negative interval, the four switching elements operate by the driving voltages that are outputted from the respective voltage storing circuits.

Abstract: In a signal amplifying circuit, a flow rate signal, inputted between flow rate signal input terminals of a connector, is inputted into one input terminal and the other input terminal of an instrumentation amplifier through resistive elements and subjected to differential amplification. The amplified output signal thereof is outputted to a sample hold circuit through a coupling capacitor. The flow rate signals, inputted between the flow rate signal input terminals, are buffered by buffer amplifiers, and output signals thereof are outputted to a fault detecting circuit. An interconnection, which connects one of the flow rate signal input terminals and a non-inverting input terminal of one of the buffer amplifiers, is guarded by a guard ring pattern. An interconnection, which connects the other one of the flow rate signal input terminals and a non-inverting input terminal of the other one of the buffer amplifiers, is guarded by another guard ring pattern.

Abstract: In a signal amplifying circuit, a flow rate signal, inputted between flow rate signal input terminals of a connector, is inputted into one input terminal and the other input terminal of an instrumentation amplifier through resistive elements and subjected to differential amplification. The amplified output signal thereof is outputted to a sample hold circuit through a coupling capacitor. The flow rate signals, inputted between the flow rate signal input terminals, are buffered by buffer amplifiers, and output signals thereof are outputted to a fault detecting circuit. An interconnection, which connects one of the flow rate signal input terminals and a non-inverting input terminal of one of the buffer amplifiers, is guarded by a guard ring pattern. An interconnection, which connects the other one of the flow rate signal input terminals and a non-inverting input terminal of the other one of the buffer amplifiers, is guarded by another guard ring pattern.

Abstract: A magnetic excitation circuit is used as a circuit for providing a magnetic excitation electric current based on a magnetic excitation power supply voltage to a magnetic excitation coil of an electromagnetic flow meter. The magnetic excitation circuit includes four voltage storing circuits that store and output a driving voltage that is charged by a common driving voltage. The voltage storing circuits are connected respectively between the control terminals and the output terminals of four switching elements. When the four switching elements are turned ON in relation to a positive interval or a negative interval, the four switching elements operate by the driving voltages that are outputted from the respective voltage storing circuits.

Abstract: Gain switching is performed by a DC amplifying circuit. The DC amplifying circuit is provided with individual gain generating circuits and a gain selecting circuit, and saturation preventing circuits are provided in earlier stages than the individual gain generating circuits. The individual gain generating circuit generates a gain G1, the individual gain generating circuit generates a gain G2 (where G2>G1), and the individual gain generating circuit generates a gain G3 (where G3>G2). The gain selecting circuit selects, as a used gain generating circuit, one of the individual gain generating circuits, and sends the output thereof to an A/D converting circuit in a later stage.

Abstract: Gain switching is performed by a DC amplifying circuit. The DC amplifying circuit is provided with individual gain generating circuits and a gain selecting circuit, and saturation preventing circuits are provided in earlier stages than the individual gain generating circuits. The individual gain generating circuit generates a gain G1, the individual gain generating circuit generates a gain G2 (where G2>G1), and the individual gain generating circuit generates a gain G3 (where G3>G2). The gain selecting circuit selects, as a used gain generating circuit, one of the individual gain generating circuits, and sends the output thereof to an A/D converting circuit in a later stage.

Abstract: In a constant current circuit, a constant current is caused to flow through a resistor, thereby causing a constant voltage to occur across the resistor. This constant voltage is then superimposed on an output signal of an operational amplifier that is to be fed back to the drain of a field effect transistor, thereby maintaining the same potential in an AC manner between the output terminal of the operational amplifier and the drain of the field effect transistor. In this way, the gate and drain of the field effect transistor is caused to exhibit the same potential in an AC manner, so that no current will occur through the stray capacitance between the gate and drain of the field effect transistor. As a result, similarly to a case of using a feedback capacitor, the input impedance of the field effect transistor can be raised.

Abstract: In a constant current circuit, a constant current is caused to flow through a resistor, thereby causing a constant voltage to occur across the resistor. This constant voltage is then superimposed on an output signal of an operational amplifier that is to be fed back to the drain of a field effect transistor, thereby maintaining the same potential in an AC manner between the output terminal of the operational amplifier and the drain of the field effect transistor. In this way, the gate and drain of the field effect transistor is caused to exhibit the same potential in an AC manner, so that no current will occur through the stray capacitance between the gate and drain of the field effect transistor. As a result, similarly to a case of using a feedback capacitor, the input impedance of the field effect transistor can be raised.