Electromagnetic fluid flow meter with tolerance to spurious signals

Abstract

An electromagnetic fluid flow meter includes a probe or spool type transducer whose output is coupled through a preamplifier to a sampling switch. The output of the sampling switch is processed by a signal processing amplifier and then coupled through a phase sensitive demodulator to utilization circuits. To reduce the effect of spurious signals, a storage device is connected at the output of the phase sensor demodulator, such as a capacitor. The effect of the spurious voltages is eliminated by first detecting the presence of a spurious voltage or occurrence of an event capable of producing a spurious voltage and then disabling the phase sensitive demodulator so that the signal previously applied to the utilization circuits, which is also stored on the storage device, is maintained during the presence of the spurious voltages. In one form of the invention in which the electromagnetic flow meter is of the spool type, spurious voltages may be induced by triboelectric effects. Such voltages are sensed by comparing the absolute value of the signal against a reference. In another embodiment in which the flow meter may be of a probe type suspended in an open channel, spurious signals may be induced by vertical motion of the probe. Vertical velocity, when sensed, produces a signal to disable the phase sensitive demodulator. The disablement may be for either a predetermined period of time or only so long as the spurious voltage exists.