Constant-current duty-cycle driver for electromagnetic flowmeter
First Claim
1. In an electromagnetic flowmeter provided with a flow tube having a pair of electrodes mounted at diametrically-opposed positions thereon, and an electromagnet having an excitation coil to produce a transverse magnetic field within said tube, the voltage induced in the liquid passing through said tube and intersecting said field being transferred to the electrodes to provide a flow-induced signal;
- an energy-efficient driver to excite said electromagnet, said driver comprising;
A. a full-wave rectifier connectable to an a-c line supplying power having a predetermined frequency and producing a rectified voltage;
B. a first transducer so connected between the rectifier and the coil as to apply the rectified voltage thereto in one polarity when this transistor is rendered conductive;
C. a second transistor so connected between the rectifier and the coil as to apply the rectified voltage thereto in the reverse polarity when this transistor is rendered conductive;
D. pulse generating means to generate a train of pulses having a constant repetition rate and a variable duty cycle;
E. Gating means to alternately actuate the transistors at a predetermined gating rate with said train of pulses whereby the rectified voltage is intermittently applied to the coil during successive positive and negative gating intervals whereby current is caused to flow in the coil, first in one direction and then in the reverse direction; and
F. Means responsive to current flow in said coil to produce a control signal which is applied to the pulse generating means to vary the duty cycle of the pulses in the train to correct for fluctuations in said current to produce current flow in the coil at a substantially constant level.
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Accused Products
Abstract
A driver for the excitation coil in the electromagnet of an electromagnetic flowmeter, wherein the fluid to be metered is conducted through a flow tube to intersect the transverse magnetic flux field created by the electromagnet. The driver includes an a-c line rectifier whose output is coupled to the coil by a pair of switching transistors, the control electrodes of which are connected to the output of a comparator having first and second input terminals. Applied to the first terminal of the comparator is an alternating square wave voltage, each cycle of which has a positive and a negative gating pulse such that the transistors are alternately actuated, the arrangement being such that the rectified output is applied by the transistors to the coil with a polarity which is alternately reversed. The comparator includes a positive feedback loop connected between its output and the first terminal to produce a pulsatory output so that during each negative and positive gating interval, the coil is excited by a train of pulses whose duty cycle is varied in a manner regulating current flow through the coil to maintain a substantially constant current level.
17 Citations
9 Claims
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1. In an electromagnetic flowmeter provided with a flow tube having a pair of electrodes mounted at diametrically-opposed positions thereon, and an electromagnet having an excitation coil to produce a transverse magnetic field within said tube, the voltage induced in the liquid passing through said tube and intersecting said field being transferred to the electrodes to provide a flow-induced signal;
- an energy-efficient driver to excite said electromagnet, said driver comprising;
A. a full-wave rectifier connectable to an a-c line supplying power having a predetermined frequency and producing a rectified voltage; B. a first transducer so connected between the rectifier and the coil as to apply the rectified voltage thereto in one polarity when this transistor is rendered conductive; C. a second transistor so connected between the rectifier and the coil as to apply the rectified voltage thereto in the reverse polarity when this transistor is rendered conductive; D. pulse generating means to generate a train of pulses having a constant repetition rate and a variable duty cycle; E. Gating means to alternately actuate the transistors at a predetermined gating rate with said train of pulses whereby the rectified voltage is intermittently applied to the coil during successive positive and negative gating intervals whereby current is caused to flow in the coil, first in one direction and then in the reverse direction; and F. Means responsive to current flow in said coil to produce a control signal which is applied to the pulse generating means to vary the duty cycle of the pulses in the train to correct for fluctuations in said current to produce current flow in the coil at a substantially constant level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- an energy-efficient driver to excite said electromagnet, said driver comprising;
Specification