Acoustic flowmeter

Claim 2

In a system for measuring the flow of fluid in a pipe wherein a pair of transducers is mounted on the pipe opposite each other and wherein one of the transducers is downstream from the other and wherein there is a pair of oscillators for exciting the transducers, there being one such oscillator associated with each transducer, the improvement comprising: means for selecting one of the oscillators to thereby excite one of the transducers such that only one of them is excited at any given time in the transmit mode such that an acoustic wave is transmitted across the pipe and is received by the other transducer in the receive mode and such that each of the transducers is alternatively in the transmit mode and the receive mode; amplitude servo means connected to the transducers such that its input is connected to the receIve mode transducer and its output is connected to the transmit mode transducer such that the amplitude of the signal received by the receive mode transducer is maintained constant; frequency servo means having its input connected to the receive mode transducer and its output connected to the oscillator associated with the transmit mode transducer such that the frequency of the said oscillator is maintained within predetermined limits; and means for obtaining the difference between the frequencies of the two oscillators, which difference frequency is a function of the flow velocity of the fluid in the pipe.

Claim 3

In a system for measuring the flow of fluid in a pipe wherein a pair of transducers is mounted on the pipe opposite each other and wherein one of the transducers is downstream from the other and wherein there is a pair of oscillators for exciting the transducers, there being one such oscillator associated with each transducer, the improvement comprising: means for selecting one of the oscillators to thereby excite one of the transducers such that only one of them is excited at any given time in the transmit mode such that an acoustic wave is transmitted across the pipe and is received by the other transducer in the receive mode and such that each of the transducers is alternatively in the transmit mode and the receive mode; amplitude servo means connected to the transducers such that its input is connected to the receIve mode transducer and its output is connected to the transmit mode transducer such that the amplitude of the signal received by the receive mode transducer is maintained constant; frequency servo means having its input connected to the receive mode transducer and its output connected to the oscillator associated with the transmit mode transducer such that the frequency of the said oscillator is maintained within predetermined limits; and means for obtaining the difference between the frequencies of the two oscillators, which difference frequency is a function of the flow velocity of the fluid in the pipe.

Claim 4

In a system for measuring the flow of fluid in a pipe wherein a pair of transducers is mounted on the pipe opposite each other and wherein one of the transducers is downstream from the other and wherein there is a pair of oscillators for exciting the transducers, there being one such oscillator associated with each transducer, the improvement comprising: means for selecting one of the oscillators to thereby excite one of the transducers such that only one of them is excited at any given time in the transmit mode such that an acoustic wave is transmitted across the pipe and is received by the other transducer in the receive mode and such that each of the transducers is alternatively in the transmit mode and the receive mode; amplitude servo means connected to the transducers such that its input is connected to the receIve mode transducer and its output is connected to the transmit mode transducer such that the amplitude of the signal received by the receive mode transducer is maintained constant; frequency servo means having its input connected to the receive mode transducer and its output connected to the oscillator associated with the transmit mode transducer such that the frequency of the said oscillator is maintained within predetermined limits; and means for obtaining the difference between the frequencies of the two oscillators, which difference frequency is a function of the flow velocity of the fluid in the pipe.

Claim 5

The invention of claim 1 wherein the amplitude servo means comprises: a single radio frequency amplifier, having an input and an output, whose input is connected to either of the transducers whichever is in the receive mode; a pair of difference amplifiers, each having at least two inputs and an output there being one such difference amplifier associated with each transducer in the transmit mode; a pair of driver amplifiers, there being one such driver amplifier associated with each transducer in the transmit mode, each such driver amplifier having at least two inputs and an output; the output of the radio frequency amplifier being selectively connected to one of the inputs of the difference amplifier associated with the transducer in the transmit mode; a reference voltage directly connected to the other input of both difference amplifiers; the output of each difference amplifier being connected to one of the inputs of its associated driver amplifier; the other input of each driver amplifier receiving excitation from its associated oscillator when its associated transducer is in the transmit mode.

Claim 6

The invention of claim 2 including a peak detector diode connected between the output of the radio frequency amplifier and the inputs to the difference amplifiers.

Claim 7

The invention of claim 3 wherein the frequency servo means comprises: a control logic counter having an input and a plurality of outputs; the input of the control logic counter being selectively connected to the output of the oscillator in the transmit mode; a threshold detector having an input and an output, its input being connected to the output of the radio frequency amplifier; a comparator having at least two inputs and an output; an output of the control logic counter being connected to an input of one of the driver amplifiers such that signal is transmitted to the driver amplifier when its associated elements are in the transmit mode; an output of the control logic counter being connected to an input of the comparator and the output of the threshold detector being connected to a second input of the comparator such that the signals therefrom are compared to produce a difference therebetween at the output of the comparator; a second pair of difference amplifiers, there being one such amplifier associated with each transducer, each of said amplifiers having two inputs and an output; the output of the comparator being selectively connected to one of the inputs of one of the pair of the second pair of difference amplifiers whose associated transducer is in the transmit mode; a reference voltage connected to the other input of each of the second pair of difference amplifiers so that the difference amplifier develops a difference signal between the signal from the comparator and the reference voltage; the output of the said difference amplifier being connected to its associated oscillator so that the frequency is adjusted in a predetermined direction depending upon the sign and amplitude of the difference signal.

Claim 8

The invention of claim 2 wherein the frequency servo means comprises: a control logic counter having an input and a plurality of outputs; the input of the control logic counter being selectively connected to the output of the oscillator in the transmit mode; a threshold detector havinG an input and an output, its input being connected to the output of the radio frequency amplifier; a comparator having at least two inputs and an output; an output of the control logic counter being connected to an input of one of the driver amplifiers such that signal is transmitted to the driver amplifier when its associated elements are in the transmit mode; an output of the control logic counter being connected to an input of the comparator and the output of the threshold detector being connected to a second input of the comparator such that the signals therefrom are compared to produce a difference therebetween at the output of the comparator; a second pair of difference amplifiers, there being one such amplifier associated with each transducer, each of said amplifiers having two inputs and an output; the output of the comparator being selectively connected to one of the inputs of one of the pair of the second pair of difference amplifier whose associated transducer is in the transmit mode; a reference voltage connected to the other input of each of the second pair of difference amplifiers so that the difference amplifier develops a difference signal between the signal from the comparator and the reference voltage; the output of the said difference amplifier being connected to its associated oscillator so that the frequency is adjusted in a predetermined direction depending upon the sign and amplitude of the difference signal.