Apparatus for measuring the density of a fluid by resonance

Claim 2

A sensor unit for measuring the density of a fluid, comprising a first resonant structure disposed in a closed chamber to vibrate at a characteristic frequency, a second resonant structure supported to vibrate at a characteristic frequency and having a passageway therethrough for fluid whose density is to be measured, and means fixedly securing said first and second resonant structures together in unitary assembly and in close thermal coupling thereby to adapt said unit For use at a relatively high temperature of about 300*C.

Claim 3

A sensor unit as claimed in claim 1, each of said resonant structures comprising a hollow cylinder.

Claim 4

A sensor unit as claimed in claim 2, said cylinders being coaxial.

Claim 5

A sensor unit as claimed in claim 2, each said cylinder being fixedly supported at one end and having its other end free.

Claim 6

A sensor unit as claimed in claim 4, said cylinders being coaxial and the free ends of said cylinders being disposed adjacent each other.

Claim 7

A sensor unit as claimed in claim 1, said resonant structures being hollow coaxial cylinders each supported at only one end, and a conduit extending coaxially through said first resonant structure and communicating with said passageway of said second resonant structure.

Claim 8

A sensor unit as claimed in claim 1, and means to adjust the pressure in said closed chamber.

Claim 9

A sensor unit as claimed in claim 1, and means to excite vibrations to said resonant structures and means for sensing vibrations in said resonant structures.

Claim 10

Apparatus for measuring the density of a fluid, comprising a sensor unit comprising a first resonant structure disposed in a closed chamber to vibrate at a characteristic frequency, a second resonant structure supported to vibrate at a characteristic frequency and having a passageway therethrough for fluid whose density is to be measured, means fixedly securing said first and second resonant structures together in unitary assembly and in close thermal coupling thereby to adapt said unit for use at a relatively high temperature of about 300*C., means to excite vibrations in said resonant structures, means for sensing vibrations in said resonant structures, and first and second amplifiers, said first amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said first resonant structure in a feedback loop for maintaining vibration of said first resonant structure, and said second amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said second resonant structure in a feedback loop for maintaining vibration of said second resonant structure.

Claim 11

Apparatus for measuring the density of a fluid, comprising a sensor unit comprising a first resonant structure disposed in a closed chamber to vibrate at a characteristic frequency, a second resonant structure supported to vibrate at a characteristic frequency and having a passageway therethrough for fluid whose density is to be measured, means fixedly securing said first and second resonant structures together in unitary assembly and in close thermal coupling thereby to adapt said unit for use at a relatively high temperature of about 300*C., means to excite vibrations in said resonant structures, means for sensing vibrations in said resonant structures, and first and second amplifiers, said first amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said first resonant structure in a feedback loop for maintaining vibration of said first resonant structure, and said second amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said second resonant structure in a feedback loop for maintaining vibration of said second resonant structure.

Claim 12

Apparatus as claimed in claim 9, and means coupled to the outputs of said amplifiers to compare the characteristic frequencies of vibration of said first and second resonant structures and to derive therefrom a signal indicative of the density of a fluid in said passageway.

Claim 13

Apparatus as claimed in claim 10, said comparison means comprising a mixer circuit for deriving a difference frequency signal from said characteristic frequencies.

Claim 14

Apparatus as claimed in claim 11, and a frequency-to-current converter coupled to said mixer circuit and responsive to said difference frequency signal to derive a current which varies with said difference frequency.

Claim 15

Apparatus as claimed in claim 12, said frequency-to-current converter being coupled to said mixer circuit through a signal-shaping circuit.

Claim 16

Apparatus as claimed in claim 12, and a Deprez instrument responsive to the current output of said converter and calibrated in density values.

Claim 17

Apparatus as claimed in claim 11, and a digital frequency meter coupled to said mixer circuit to display said difference frequency.

Claim 18

Apparatus as claimed in claim 10, said comparison means comprising a digital frequency meter to display the characteristic frequency of the output of said second amplifier using the characteristic frequency of the output of said first amplifier as a reference.

Claim 19

Apparatus for measuring the density of a fluid, comprising a sensor unit comprising a first resonant structure disposed in a closed chamber to vibrate at a characteristic frequency, a second resonant structure supported to vibrate at a characteristic frequency and having a passageway therethrough for fluid whose density is to be measured, means fixedly securing said first and second resoNant structures together in unitary assembly and in close thermal coupling thereby to adapt said unit for use at a relatively high temperature of about 300*C., means to excite vibrations in said resonant structures, means for sensing vibrations in said resonant structures, first and second amplifiers, said first amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said first resonant structure in a feedback loop for maintaining vibration of said first resonant structure, and said second amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said second resonant structure in a feedback loop for maintaining vibration of said second resonant structure, means coupled to the outputs of said amplifiers to compare the characteristic frequencies of vibration of said first and second resonant structures and to derive therefrom a signal indicative of the density of the fluid in said passageway, said comparison means comprising a mixer circuit for deriving a difference frequency signal from said characteristic frequencies, means responsive to the rate of flow of said fluid to derive a signal representing the rate of flow, and a multiplier responsive to said difference frequency signal and said rate of flow signal to derive a signal indicative of the mass flow of said fluid.

Claim 20

Apparatus for measuring the density of a fluid, comprising a sensor unit comprising a first resonant structure disposed in a closed chamber to vibrate at a characteristic frequency, a second resonant structure supported to vibrate at a characteristic frequency and having a passageway therethrough for fluid whose density is to be measured, means fixedly securing said first and second resoNant structures together in unitary assembly and in close thermal coupling thereby to adapt said unit for use at a relatively high temperature of about 300*C., means to excite vibrations in said resonant structures, means for sensing vibrations in said resonant structures, first and second amplifiers, said first amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said first resonant structure in a feedback loop for maintaining vibration of said first resonant structure, and said second amplifier having its input and output respectively coupled to the vibration sensing means and exciting means associated with said second resonant structure in a feedback loop for maintaining vibration of said second resonant structure, means coupled to the outputs of said amplifiers to compare the characteristic frequencies of vibration of said first and second resonant structures and to derive therefrom a signal indicative of the density of the fluid in said passageway, said comparison means comprising a mixer circuit for deriving a difference frequency signal from said characteristic frequencies, means responsive to the rate of flow of said fluid to derive a signal representing the rate of flow, and a multiplier responsive to said difference frequency signal and said rate of flow signal to derive a signal indicative of the mass flow of said fluid.

Claim 21

Apparatus as claimed in claim 17, and a linearizer electrically connected between said mixer circuit and said multiplier.

Claim 22

Apparatus as claimed in claim 17, said rate of flow signal-deriving means comprising a turbine flow meter.

Claim 23

Apparatus as claimed in claim 9, the characteristic frequencies of vibration of said first and second resonant structures being equal when said second resonant structure is in vacuum.