Signal conditioner for recovering dominant signals from swirl-type meters

Claim 1

A signal conditioner adapted to extract the dominant frequency from the compositE output signal of a swirl or vortex type flowmeter and to exclude low and high frequency noise components therefrom so that by measuring the dominant frequency, an accurate reading is obtained of flow rate, said conditioner comprising: A. a square-wave-generating trigger having a differential characteristic wherein a change in output state takes place when the amplitude of the signal applied thereto exceeds a predetermined high level, the trigger reverting to its original state when the amplitude of said signal falls below a predetermined lower level, no change in state occurring with respect to amplitude fluctuations lying within the fixed window defined by the two levels, B. a voltage-responsive variable attenuator adapted to produce attenuation to a degree determined by an applied control voltage, C. means including an amplifier to apply the composite signal from the flowmeter through the variable attenuator and said amplifier to the input of the trigger, and D. wave-shaping means coupled to the output of said amplifier to produce a control voltage whose amplitude is a function of frequency and to apply said control voltage to said attenuator to cause the amplitude of said composite signal applied to said trigger to increase as the frequency thereof increases in order to vary the apparent width of the fixed window, thereby effectively broadening the window for low frequencies and narrowing the window for high frequencies to effect lowfrequency noise rejection at high operating frequencies and high-frequency noise rejection at low operating frequencies.