Abstract: An electromagnetic flowmeter using an exciting current of a rectangular wave form supplied to an exciting coil for excitation, wherein a DC voltage produced by rectifying a frequency power source, is applied by way of a voltage regulating circuit to an exciting circuit, and a switching device is connected in series between the exciting circuit and the voltage regulating circuit and is controlled by a DC reference voltage determining the level of the exciting voltage and a timing signal determining the switching timing for the exciting current. The invention enables accurate and rapid control of the waveform of the exciting current, reduces costs, and can be used for different voltages without any substantial change of circuitry.

Abstract: An electromagnetic flowmeter for measuring the flow rate of a ferromagnetic slurry which is conducted through a flow tube having electrodes mounted thereon, the slurry intercepting a magnetic field to induce a signal in the electrodes which depends on flow rate. The field is established by an electromagnetic circuit whose core has a gap defined by the tube, an excitation coil being wound about the core. The magnetic resistance of the circuit changes as a function of the ferromagnetic concentration of the slurry, this change affecting the inductance of the coil. To provide an output signal which accurately reflects flow rate regardless of ferromagnetic concentration, the output signal is corrected in accordance with the changing inductance of the excitation coil.

Abstract: A magnetic flowmeter whose electromagnet is excited by a low-frequency excitation current that is derived from an on-off alternating current whose frequency is higher than that of a commercial power line source, the on-off current being modulated by a low-frequency wave. A reference voltage-detecting transformer is interposed between the excitation coil of the electromagnet and an excitation current source. The primary of the transformer is constituted by a pair of windings wherein the excitation current is caused to flow in one direction in the first primary winding and a current produced by the counter-electromotive force generated in the excitation coil in every on-off transient of the excitation current is caused to flow in the opposite direction in the second primary winding.

Abstract: A technique for exciting the electromagnet of a magnetic flowmeter in which a fluid to be metered is conducted through a flow tube having detecting electrodes, the fluid intercepting a magnetic field established by the electromagnet to induce a signal in the electrodes indicative of flow in a high flow-rate range as well as in a low flow-rate range. In this technique, derived from the electrode signal is a control signal whose frequency is a function of the velocity of the fluid passing through the tube, the excitation current supplied to the electromagnet being governed by the control signal so that it has a frequency which is higher in the high flow-rate range and lower in the low flow-rate range.

Abstract: An electromagnetic flowmeter in which a low-frequency rectangular wave is supplied to the electromagnet coil of the flowmeter to produce an excitation current establishing a magnetic field which is intercepted by the fluid passing through the flow tube to induce a signal voltage in the electrodes disposed in the tube. This signal voltage is proportional to flow rate and is accompanied by an objectionable D-C noise component. To eliminate this noise component, the signal voltage is passed through a first high-pass filter, and to compensate for errors introduced by this filter, the signal voltage derived from the first filter is divided by a comparison voltage derived from the excitation current, but only after this comparison voltage passes through a second high-pass filter having essentially the same characteristics as the first filter.

Abstract: A magnetic flowmeter whose electromagnet is excited by a low-frequency excitation current, the flowmeter including flow tube electrodes yielding a flow rate signal. A reference voltage-detecting transformer is provided in the excitation circuit to produce a reference voltage that reflects fluctuations in the excitation current. Fluctuations in the flow rate signal as a result of fluctuations in the excitation current are eliminated by dividing the flow rate signal by the reference-voltage signal.

Abstract: An excitation system for a magnetic flowmeter provided with a flow tube through which the fluid to be metered is conducted, the tube having a pair of electrodes mounted at diametrically-opposed positions thereon and including an excitation coil to establish a magnetic field in the tube which is normal to the tube's axis and to a transverse axis passing through the electrodes, the fluid intersecting the magnetic field to induce a flow rate signal in said electrodes, the system including a full-wave rectifier coupled to a commercial power line source which produces sinusoidal a-c power whose wave periodically crosses a zero line. A switch is interposed between the rectifier and said excitation coil.

Abstract: A magnetic flowmeter whose electromagnet is excited by a low-frequency excitation current having an a-c component and a d-c component, the flowmeter including flow tube electrodes yielding a flow rate signal. A reference-voltage detecting transformer is provided to produce a reference-voltage proportional to the a-c component of the excitation current. Fluctuations in the flow rate signal as a result of fluctuations in the a-c component of the excitation current are eliminated by dividing the flow rate signal by the reference-voltage signal. In order to eliminate from the reference-voltage detecting transformer the unwanted magnetic flux generated by the d-c component of the excitation current, compensating means are provided to generate a counter magnetic flux, whereby saturation of the transformer core and the resultant distortion of the reference voltage signal are avoided.

Abstract: A circuit arrangement for a bi-directional output electromagnetic flowmeter including a polarity-detecting circuit arranged to detect the polarity of an input derived from the flowmeter. Means are provided to invert the input polarity and switching means are provided to select the inverted or non-inverted signal in accordance with the output of the polarity-detecting circuit. Thus a constant polarity output signal is obtainable at all times, even though the flow direction in a flow tube changes from time to time.

Abstract: A magnetic flowmeter wherein liquid to be metered is conducted through a flow tube to intersect a transverse magnetic field established by an electromagnet. The voltage induced in the fluid is transferred to a pair of electrodes mounted at diametrically-opposed positions on the flow tube. The electromagnet is energized by a low-frequency wave which is produced by applying the output of a full-wave rectifier to the excitation coils of the electromagnet through a switching element. The switching element acts to chop the full-wave rectified output in accordance with high-frequency pulses whose frequency is higher than that of a commercial electric power line, the duty cycle thereof being modulated by a low-frequency, sinusoidal wave whose frequency is less than that of the commercial line.