| 摘要 |
<p>CONSTANT-CURRENT DUTY-CYCLE DRIVER FOR ELECTROMAGNETIC FLOWMETER Inventor: Roy F. Schmoock, a citizen of the United States of America and resident of Yardley, Pa. 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 whereby 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 whereby during each negative and positive gating interval, the coil is excited by a train of pulses. The duty cycle of these pulses is varied as a function of a reference voltage derived from the current flowing through the coil and applied to the second input terminal, thereby regulating current flow through the coil to maintain a substantially constant current level.</p> |
