Flowmeter system with improved loop gain

Claim 2

A flowmeter system of the phase lock loop type comprising, in combination: transducer means for transmitting acoustic compression waves upstream and downstream in a fluid flowing in a path; circuit means for measuring the phase difference between the transducer means in the fluid flow path of acoustic compression waves transmitted upstream and circuit means for measuring the phase difference between said transducer means in the fluid flow path of the acoustic compression waves transmitted downstream; circuit means for producing a difference signal dependent on the difference between the two phase differences, the magnitude and sign of which being directly related to the instantaneous fluid flow rate and its direction; circuit means for producing a sum signal representing the sum of the two phase differences; circuit means for automatically adjusting the frequency of the acoustic compression waves to a frequency where a fixed wavelength distance, in the fluid flow medium, occurs across the path between the transducer means; and active filter means connected between said summing means and automatic frequency adjusting means for filtering and increasing the amplitude of the sum signal so that relatively small difference signals produce large signals at said automatic frequency adjusting means to increase the loop gain of the system.

Claim 3

The flowmeter system as claimed in claim 1 wherein said active filter means includes an operational amplifier connected as an integrator.

Claim 4

The flowmeter system as claimed in claim 1 where said system includes summing means for producing a sum signal representing the sum of the two phase differences and wherein said active filter is connected between summing means and said automatic frequency adjusting means.

Claim 5

A flowmeter system for measuring a fluid along a path comprising in combination: means defining a path for confining a fluid flow; a first and second transducer disposed along said path; a transducer control circuit coupled to said first and said second transducer to cause said first transducer to produce first acoustic compressions in the fluid and said second transducer to produce a first received signal when said first acoustic compressions are sensed thereby during a first transmit-receive cycle and to cause said second transducer to produce second acoustic compressions in the fluid and said first transducer to produce a second received signal when said second acoustic compressions are sensed thereby during a second transmit/receive cycle; said control circuit including: means to switch from said first to said second transmit-receive cycle; first measurement means to measure a first phase difference comprising the phase difference between the first acoustic compression produced by said first transducer and said received signal produced by said second transducer during each said first transmit-received cycle; second measurement means to measure a second phase difference comprising the phase difference between the second acoustic compression produced at said second transducer and said second received signal produced by said first transducer during each said second transmit/receive cycle; difference means responsive to said first and said second measurement means to produce a difference signal whose magnitude equals the difference between one said first phase difference and one said second phase difference wherein the magnitude of said difference signal is directly related to the instantaneous fluid flow rate and the algebraic sign of said difference signal represents the direction of fluid flow along the path; means to automatically adjust the frequency of the acoustic compressions produced by each said transducer to a frequency where a fixed wavelength distance, in the fluid flow medium, occurs across the distance of either said transducer, thereby maintaining operation at the acoustic resonance to maximize the magnitude of the received signal produced at the other transducer so that said difference signal output is insensitive to the velocity of sound in the fluid; summing means responsive to said first and second measurement means to produce a sum signal; said automatic frequency adjusting means being responsive to said sum signal, and an active filter means between said summing means and said automatic frequency adjusting means to magnify the sum signal so that a minute sum signal will cause said automatic adjustment means to respond thereby increasing the gain of the system.

Claim 6

A flowmeter system for measuring a fluid along a path comprising in combination: means defining a path for confining a fluid flow; a first and second transducer disposed along said path; a transducer control circuit coupled to said first and said second transducer to cause said first transducer to produce first acoustic compressions in the fluid and said second transducer to produce a first received signal when said first acoustic compressions are sensed thereby during a first transmit-receive cycle and to cause said second transducer to produce second acoustic compressions in the fluid and said first transducer to produce a second received signal when said second acoustic compressions are sensed thereby during a second transmit/receive cycle; said control circuit including: means to switch from said first to said second transmit-receive cycle; first measurement means to measure a first phase difference comprising the phase difference between the first acoustic compression produced by said first transducer and said received signal produced by said second transducer during each said first transmit-received cycle; second measurement means to measure a second phase difference comprising the phase difference between the second acoustic compression produced at said second transducer and said second received signal produced by said first transducer during each said second transmit/receive cycle; difference means responsive to said first and said second measurement means to produce a difference signal whose magnitude equals the difference between one said first phase difference and one said second phase difference wherein the magnitude of said difference signal is directly related to the instantaneous fluid flow rate and the algebraic sign of said difference signal represents the direction of fluid flow along the path; means to automatically adjust the frequency of the acoustic compressions produced by each said transducer to a frequency where a fixed wavelength distance, in the fluid flow medium, occurs across the distance of either said transducer, thereby maintaining operation at the acoustic resonance to maximize the magnitude of the received signal produced at the other transducer so that said difference signal output is insensitive to the velocity of sound in the fluid; summing means responsive to said first and second measurement means to produce a sum signal; said automatic frequency adjusting means being responsive to said sum signal, and an active filter means between said summing means and said automatic frequency adjusting means to magnify the sum signal so that a minute sum signal will cause said automatic adjustment means to respond thereby increasing the gain of the system.

Claim 7

The flowmeter system as claimed in claim 4 wherein said active filter includes an operational amplifier connected to operate as an integrator.

Claim 8

The flowmeter as claimed in claim 4 wherein said active filter includes a capacitor and resistance in series with an operational amplifier in parallel with said capacitor.

Claim 9

A phase lock loop flowmeter system for measuring a fluid along a path comprising, in combination: a tubular body defining a path for confining fluid flow; an adjustable oscillator for producing a signal at an adjustable frequency; a switching circuit to alternately switch said signal into an upstream signal and a downstream signal; a first transducer means and a second transducer means being disposed in spaced relation to each other along said tubular body, said first transducer means responsive to said upstream signal and said second transducer means responsive to said downstream signal, said first transducer means producing upstream acoustic compressions in the fluid responsive to said upstream signal and said second transducer means responds to said upstream acoustic compressions by producing an upstream received signal, said second transducer means producing downstream acoustic compressions in the fluid responsive to said downstream signal and said first transducer means responds to said downstream acoustic compressions by producing a downstream received signal; a phase detector responsive to each said upstream signal and to each said upstream received signal to produce an upstream phase difference which comprises the phase difference between said upstream signal and said upstream received signal, said phase detector also being responsive to each said downstream signal and to each said downstream received signal to produce a downstream phase difference which comprises the phase difference between said downstream signal and said downstream received signal; means to produce the sum of one said upstream phase difference and one said downstream phase difference; means responsive to the sum of one said upstream phase difference and one said downstream phase difference to adjust the fequency of said adjustable oscillator to a frequency where a fixed wavelength distance occurs across the distance between said transducer when responding to said sum; and active filter means connected between the means to produce the sum and the means responsive to the sum to amplify the output of the means to produce the sum so that small sums will be amplified causing the means responsive to the sum to respond to said amplified small sums to thereby increase the loop gain of the system.

Claim 10

A phase lock loop flowmeter system for measuring a fluid along a path comprising, in combination: a tubular body defining a path for confining fluid flow; an adjustable oscillator for producing a signal at an adjustable frequency; a switching circuit to alternately switch said signal into an upstream signal and a downstream signal; a first transducer means and a second transducer means being disposed in spaced relation to each other along said tubular body, said first transducer means responsive to said upstream signal and said second transducer means responsive to said downstream signal, said first transducer means producing upstream acoustic compressions in the fluid responsive to said upstream signal and said second transducer means responds to said upstream acoustic compressions by producing an upstream received signal, said second transducer means producing downstream acoustic compressions in the fluid responsive to said downstream signal and said first transducer means responds to said downstream acoustic compressions by producing a downstream received signal; a phase detector responsive to each said upstream signal and to each said upstream received signal to produce an upstream phase difference which comprises the phase difference between said upstream signal and said upstream received signal, said phase detector also being responsive to each said downstream signal and to each said downstream received signal to produce a downstream phase difference which comprises the phase difference between said downstream signal and said downstream received signal; means to produce the sum of one said upstream phase difference and one said downstream phase difference; means responsive to the sum of one said upstream phase difference and one said downstream phase difference to adjust the fequency of said adjustable oscillator to a frequency where a fixed wavelength distance occurs across the distance between said transducer when responding to said sum; and active filter means connected between the means to produce the sum and the means responsive to the sum to amplify the output of the means to produce the sum so that small sums will be amplified causing the means responsive to the sum to respond to said amplified small sums to thereby increase the loop gain of the system.

Claim 11

A flowmeter system of the phase lock loop type comprising, in combination: transducer means for transmitting acoustic compression waves upstream and downstream in a fluid flowing in a path; circuit means for measuring the phase difference between the transducer means in the fluid flow path of acoustic compression waves transmitted upstream and circuit means for measuring the phase difference between said transducer means in the fluid flow path of the acoustic compression waves transmitted downstream; circuit means for producing a difference signal dependent on the difference between the two phase differences, the magnitude and sign of which being directly related to the instantaneous fluid flow rate and its direction; circuit means for producing a sum signal representing the sum of the two phase differences; circuit means for automatically adjusting the frequency of the acoustic compression waves to a frequency where a fixed wavelength distance, in the fluid flow medium, occurs across the path between the transducer means; and active filter means connected between said summing means and automatic frequency adjusting means and responsive to the sum signal to maintain the dynamic range of the system substantially unaffected by a change in fluid flow or fluid density.

Claim 12

A flowmeter system of the phase lock loop type comprising, in combination: transducer means for transmitting acoustic compression waves upstream and downstream in a fluid flowing in a path; circuit means for measuring the phase difference between the transducer means in the fluid flow path of acoustic compression waves transmitted upstream and circuit means for measuring the phase difference between said transducer means in the fluid flow path of the acoustic compression waves transmitted downstream; circuit means for producing a difference signal dependent on the difference between the two phase differences, the magnitude and sign of which being directly related to the instantaneous fluid flow rate and its direction; circuit means for producing a sum signal representing the sum of the two phase differences; circuit means for automatically adjusting the frequency of the acoustic compression waves to a frequency where a fixed wavelength distance, in the fluid flow medium, occurs across the path between the transducer means; and active filter means connected between said summing means and automatic frequency adjusting means and responsive to the sum signal to maintain the dynamic range of the system substantially unaffected by a change in fluid flow or fluid density.

Claim 13

A flowmeter system comprising: means defining a path for confining the flow of a fluid medium therethrough, first and second transducers disposed along said flow path and connected to circuitry including a voltage controlled oscillator and a switching means for alternately generating and receiving upstream and downstream acoustic compression waves in the fluid medium between the transducers and for generating a signal in response to the received acoustic compression waves, said circuitry being of the phase lock loop type and further including, phase detector means for measuring the phase difference, if any, between the transmitted acoustic compression waves and the received acoustic compression waves, means connected to said phase detector means for producing a sum signal and a difference signal dependent upon the measured phase difference and transmitting said sum signal to said voltage controlled oscillator for adjusting the frequency of the acoustic compression waves to maintain the length of said waves constant in the fluid medium, said circuitry then operating at the adjusted frequency for flow measurement, means responsive to said difference signal for generating signals representing the direction and magnitude of the flow of the fluid medium, and an active filter means including a high gain operational amplifier whose input is connected to said means for producing said sum signal and whose output is connected to the voltage controlled oscillator to reduce the amount of sum signal required to adjust the oscillator output frequency thereby maintaining a constant full scale range of flow measurement capability which would otherwise be diminished by the larger amount of sum signal present in the system.

Claim 14

A flowmeter system comprising: means defining a path for confining the flow of a fluid medium therethrough, first and second transducers disposed along said flow path and connected to circuitry including a voltage controlled oscillator and a switching means for alternately generating and receiving upstream and downstream acoustic compression waves in the fluid medium between the transducers and for generating a signal in response to the received acoustic compression waves, said circuitry being of the phase lock loop type and further including, phase detector means for measuring the phase difference, if any, between the transmitted acoustic compression waves and the received acoustic compression waves, means connected to said phase detector means for producing a sum signal and a difference signal dependent upon the measured phase difference and transmitting said sum signal to said voltage controlled oscillator for adjusting the frequency of the acoustic compression waves to maintain the length of said waves constant in the fluid medium, said circuitry then operating at the adjusted frequency for flow measurement, means responsive to said difference signal for generating signals representing the direction and magnitude of the flow of the fluid medium, and an active filter means including a high gain operational amplifier whose input is connected to said means for producing said sum signal and whose output is connected to the voltage controlled oscillator to reduce the amount of sum signal required to adjust the oscillator output frequency thereby maintaining a constant full scale range of flow measurement capability which would otherwise be diminished by the larger amount of sum signal present in the system.

Claim 15

A flowmeter system comprising: means defining a path for confining the flow of a fluid medium therethrough, first and second transducers disposed along said flow path and connected to circuitry which includes a voltage controlled oscillator and a switching means for alternately generating and receiving upstream and downstream acoustic compression waves in the fluid medium by and between the transducers and means for generating a signal in response to the received acoustic compression waves, said circuitry being of the phase lock loop type and further including, phase detector means for measuring the phase difference between the transmitted acoustic compression waves and the received acoustic compression waves, means connected to said phase detector means for producing a sum signal and a difference signal dependent upon the measured phase difference, said sum signal being transmitted to said voltage controlled oscillator for adjusting the frequency of the acoustic compression waves to maintain the length of said waves constant in the fluid medium as a measure of fluid density, said circuitry then operating at the adjusted frequency for flow measurement, means responsive to said difference signal for generating signals representing the direction and magnitude of the flow of the fluid medium, and an active filter means connected between said means for producing said sum signal and the voltage controlled oscillator to reduce the amount of sum signal required to adjust the oscillator output frequency thereby maintaining a constant full scale range of flow measurement capability at the measured fluid density.

Claim 16

A flowmeter system comprising: means defining a path for confining the flow of a fluid medium therethrough, first and second transducers disposed along said flow path and connected to circuitry which includes a voltage controlled oscillator and a switching means for alternately generating and receiving upstream and downstream acoustic compression waves in the fluid medium by and between the transducers and means for generating a signal in response to the received acoustic compression waves, said circuitry being of the phase lock loop type and further including, phase detector means for measuring the phase difference between the transmitted acoustic compression waves and the received acoustic compression waves, means connected to said phase detector means for producing a sum signal and a difference signal dependent upon the measured phase difference, said sum signal being transmitted to said voltage controlled oscillator for adjusting the frequency of the acoustic compression waves to maintain the length of said waves constant in the fluid medium as a measure of fluid density, said circuitry then operating at the adjusted frequency for flow measurement, means responsive to said difference signal for generating signals representing the direction and magnitude of the flow of the fluid medium, and an active filter means connected between said means for producing said sum signal and the voltage controlled oscillator to reduce the amount of sum signal required to adjust the oscillator output frequency thereby maintaining a constant full scale range of flow measurement capability at the measured fluid density.