Signal recovery system for vortex type flowmeter

Claim 2

A signal recovery system for a vortex-type flowmeter wherein the fluid is directed past a vortex-producing element to cause vortex shedding at a fundamental frequency proportional to flow rate, said shedding being detected by a sensor yielding an electrical signal subject to intermittent fading for relatively brief periods due to flow disturbances which inhibit vortex shedding, said system comprising: A. an electronic flywheel constituted by a voltage-controlledoscillator; B. means coupled to said sensor to produce a control voltage whose amplitude is a function of said fundamental frequency, said means having a relatively slow decay characteristic whereby the control voltage is sustained during fading periods; C. means applying said control voltage to said oscillator to generate an output frequency which depends on the amplitude of said voltage and which continues during said fading periods, and; D. means to drive a continuous flow rate indication from said oscillator output frequency.

Claim 3

A system as set forth in claim 1, wherein said vortex-producing element is an obstacle mounted in a flow conduit.

Claim 4

A system as set forth in claim 1, wherein said means coupled to said sensor includes a frequency-to-voltage converter to produce a control voltage whose amplitude is proportional to the frequency of the applied input.

Claim 5

A system as set forth in claim 3, wherein the output of said converter is applied as one input to a mixer whose output is applied to said oscillator to effect coarse control thereof, the other input of the mixer being derived from a phase detector which compares the fundamental frequency with a frequency derived from said oscillator to produce a voltage which is added in the mixer to the first input voltage to effect fine settiNg of the oscillator.

Claim 6

A system as set forth in claim 4, wherein said oscillator operates at a frequency which is a predetermined multiple of the fundamental frequency, and the frequency derived from said oscillator and applied to the phase detector is derived by a counter which divides down the oscillator frequency to correspond to the fundamental frequency.

Claim 7

A signal recovery system for a vortex-type flowmeter wherein the fluid is directed past a vortex-producing element to cause vortex shedding at a fundamental frequency proportional to flow rate, said shedding being detected by a sensor yielding an electrical signal subject to intermittent fading for relatively brief periods due to flow disturbances which inhibit vortex shedding, said system comprising: A. an electronic flywheel constituted by a voltage-controlled-oscillator operating at a multiple of the fundamental frequency; B. means to generate a coarse setting voltage for said oscillator including a trigger coupled to the sensor to produce square wave pulses at a corresponding rate, and a frequency-to-voltage converter coupled to the trigger to produce a first voltage whose amplitude is a function of said rate, said converter having a predetermined decay characteristic sustaining said first voltage during said fading, C. means to generate a fine setting voltage for said oscillator including a counter coupled to said oscillator to divide down the frequency thereof so that it corresponds to said fundamental frequency, and a phase detector coupled to said counter to compare the counter frequency with the fundamental frequency to produce a second voltage, D. a mixer to combine said first and second voltages to produce an output voltage which is applied to said oscillator to control same; and E. means to convert the output of said oscillator to a current for operating a flow rate indicator.

Claim 8

A signal recovery system for a vortex-type flowmeter wherein the fluid is directed past a vortex-producing element to cause vortex shedding at a fundamental frequency proportional to flow rate, said shedding being detected by a sensor yielding an electrical signal subject to intermittent fading for relatively brief periods due to flow disturbances which inhibit vortex shedding, said system comprising: A. an electronic flywheel constituted by a voltage-controlled-oscillator operating at a multiple of the fundamental frequency; B. means to generate a coarse setting voltage for said oscillator including a trigger coupled to the sensor to produce square wave pulses at a corresponding rate, and a frequency-to-voltage converter coupled to the trigger to produce a first voltage whose amplitude is a function of said rate, said converter having a predetermined decay characteristic sustaining said first voltage during said fading, C. means to generate a fine setting voltage for said oscillator including a counter coupled to said oscillator to divide down the frequency thereof so that it corresponds to said fundamental frequency, and a phase detector coupled to said counter to compare the counter frequency with the fundamental frequency to produce a second voltage, D. a mixer to combine said first and second voltages to produce an output voltage which is applied to said oscillator to control same; and E. means to convert the output of said oscillator to a current for operating a flow rate indicator.

Claim 9

A system as set forth in claim 6, wherein said sensor output is applied to said trigger through an automatic-gain-control amplifier whose output amplitude is proportional to the frequency of the applied sensor signal, said phase detector comparing the output of said amplifier with the output of said counter.

Claim 10

A system as set forth in claim 6, wherein said trigger is a Schmitt trigger.

Claim 11

A system as set forth in claim 1, further including a frequency doubler to double the frequency of the trigger pulses applied to said converter.