Excitation circuit for electromagnetic flowmeter

摘要

An electromagnetic flowmeter provided with a field coil to create a magnetic field across the flow tube through which the fluid to be metered is conducted, the flowmeter having an excitation circuit adapted to supply periodic current to the coil in alternating polarity and to maintain the intensity of the current at a constant level. The circuit includes a polarity-reversing commutator whose input is connected to a current supply source through an actuatable switch, and whose output is connected through a cable to the coil. The switch is actuated by a switching regulator generating actuating pulses whose duty cycle is modulated in accordance with an applied control signal. A reference signal is derived from the field coil that is proportional to varying current flow therethrough and is compared with a set point to produce a control signal that depends on the difference therebetween. This control signal is applied to the switching regulator to modulate its pulse duty cycle and thereby so actuate the switch as to maintain the intensity of current supplied to the coil at a substantially constant level.