US 2713788 A
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July 26, 1 955 J. c. GQFF APPARATUS FOR Mx-:AsuRING THE DENSITY oF GAsEs Filed Feb. 4. 1953 United States Patent() APPARATUS FR MEASURING THE DENSITY F GASES John C. Goff, 'Silver Spring, Md., assigner to the United States of America as represented by the Secretary of the Navy Application February 4, 1953, Serial No. 335,178
4 Claims. (Cl. 73-3li) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates to device for measuring the density of fluids. More particularly, the invention relates to a device for measuring the density of fluids by passing the fluid through a whistle or nozzle which is capable Vof producing an audible signal of variable pitch in accordance with the density of the fluid, the signal being picked up by a microphone, amplified, filtered to remove undesirable frequencies such, for example, as the higher harmonics, and entered into a heterodyne circuti. The heterodyne circuit has an oscillator connected thereto which provides oscillations of a predetermined frequency and which is heterodyned against the amplified audio signal to provide a beat which changes in accordance with the density of the fluid passing through the nozzle, thermostatic means being provided in the oscillator to com-l pensate for changes in temperature of the fluid, which changes have the effect of changing the density of the fluid.
The output of the heterodyne circuit may be employed to actuate a tape recorder, thus providing a record of the changes inthe density of the fluid. It is also within the province of this invention to cause the output of the heterodyne circuit to actuate apparatus for operating a mixing valve wherein the density of the fluid fed into the nozzle is varied in accordance with the output of the yheterodyne circuit to provide a fluid of substantially constant density.
An object of the present invention is to provide a -new and improved apparatus for determining the density of fluids by comparing the audible frequency caused by the passing of the fluid through a nozzle with the output of an oscillator of predetermined frequency.
Another object is to provide an improved apparatus for determining the density of iiuids in which a microphone is employed to pick up the sound of the fluid passing through a nozzle, the amplified signal of such sound being heterodyned against a signal of known frequency.
Still another object is to provide apparatus for audibly determining variations in the density of fluids and having apparatus for controlling the density of the fluids in accordance with such determination.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same; becomes better understood by reference to the following? detailed description when considered in connection with the accompanying drawing wherein:
The single ligure is a diagram of the apparatus and circuit of the present invention.
Referring more particularly to the drawing wherein like numerals indicate like parts, 10 indicates a Whistle or nozzle having a calibrated orifice for producing an audible signal which varies in frequency in accordance with the density of the lluid as the fluid passes through `fluid passing `through nozzle 10.
2,713,788 Patented July 26, 1955 the orice at a constant rate. Nozzle 10 is mounted on one end of a conduit 11, there being a pump 12 mounted in conduit 11 to supply fluid to nozzle 10 under constant pressure.
lf desired mixing valve 13 has the outlet fitting thereof connected to conduit 11 and has inlet connection 14 having fluid of higher density and inlet connection 15 having fluid of lower density than the desired density for AIt is obvious that by proper manipulation of mixing valve 13 a substantially constant density may be maintained for the fluid passing through nozzle 10. Driving gears 1'6 of valve 13 are operatively connected to a servomotor 17 which moves valve 13 in either direction to control the density of the uid in a manner to be hereinafter more fully described.
Positioned adjacent nozzle 10 is a transducer such for example as microphone 21 which picks up the sound of the iluid passing through whistle 10. The signal output of microphone 21 is amplified by audio amplifier 22 which .may be of a conventional variety. The output of amplifier 22 is passed through filter 23 to a heterodyne circuit 24. Filter 23 is of a type wherein the higher harmonic frequencies present in the amplified signal are suppressed.
An oscillator circuit 25 is provided for supplying to the heterodyne circuit an oscillating signal of predetermined .frequency which is heterodyned .against the amplified audio signal to produce a heat signal which changes as the frequency of 'the audio signal changes in accordance with the variations of density of the fluid.
Vin order to compensate for variations in temperature of Athe iluid, a thermostat 26 is placed adjacent the nozzle 10 or, 4if desire-d, in the path of the fluid. As the temperature of the fluid changes in response to changes in the ambient temperature or other causes, thereby changing the density of the fluid, the thermostat 26 moves a temperature compensating device here shown as an arm 27 of variable resistor .28 to vary the frequencyof the output of oscillator 25, thus to provide an oscillatory signal to the heterodyne circuit the frequency of which is varied in accordance withl the temperature of the fluid thereby to compensate for density changes due to temperature.
It is, also, desirable to provide a pressure compensating device, here shown as device 18 which moves contact arm 19 `of variable resistor 20. Arm 19 and resistor 20 are connected Vin parallel with Varm 27 and .resistor 28 of oscillator 25 to vary the oscillator frequency in the same manner as arm 27 and resistor 2S, when pressure in conduit 11 varies thus to compensate for variations in pitch of the audible signal caused by such variations in pressure of the fluid.
A pen recorder 29 receives the output of the heterodyne circuit 4and records variations therein on a moving tape 39, thus providing an accurate indication of the variaice tions of density of the fluid.
It is, also, within the province of the kpresent invention to maintain a substantially constant density of uid at nozzle 10 by providing apparatus for operating valve 13 in laccordance with variations of density of the Huid, to supply more high density fluid vand less low density fluid to nozzle 10 when the density at the orifice thereof falls below a predetermined density and to supply less high density liuid and more low density fluid to nozzle 10 when the density at the orifice thereof rises above a predetermined density. l'n order to provide such result automatically, a servo control circuit 31 is connected to the output of heterodyne circuit 24 and is iniiuenced by a rise in the density of the fluid to energize servomotor 17 to move valve 13 in a direction to admit more low density fluid in conduit 11. When there is a reduction in the density of the fluid, servomotor 17 is energized by servo control circuit 31 to move valve 13 in a direction to admit more high density uid to conduit 11. This is accom- -plished by frequency discrimination provided in the circuit whereby the variations of frequency of the beat signal of the heterodyne circuit above or below a predetermined frequency, which is indicative of the desired fluid density, causes the servomotor to move the valve in either direction, respectively in accordance with frequencies above and below the predetermined frequency. It is clear that,
by an inspection of the recording of the beat frequency,
the -amount of density variation above or below a predetermined density will be readily apparent.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed as new and desired to be secured by Letters Patent of the United States is:
l. Apparatus for measuring the density of fluids comprising, a nozzle having fluid flowing therethrough at a constant rate, said nozzle producing an audible signal variable in pitch in accordance with the density of said fluid, a transducer for providing an electrical signal variable in frequency in accordance with the variations in pitch of said audible signal, means for providing a signal of substantially constant frequency, means for controlling said constant frequency signal including a thermostat positioned adjacent said nozzle and responsive to changes in temperature of said fluid impinging thereagainst as the fluid flows from said nozzle, means for heterodyning the variable electrical signal against said substantially constant signal, and means for recording the output of said heterodyning means.
2. Apparatus for measuring the density of fluids comprising, in combination, a nozzle for producing an audible signal variable in accordance with the density of a fluid passing therethrough, means for pumping said fluid through said nozzle at a constant rate, -a microphone mounted adjacent said nozzle for picking up the audible signal, means connected to said microphone for amplifying said signal, means for filtering undesirable frequencies from the amplified signal and connected to the amplifying means, oscillator means for providing a constant signal, means for heterodyning the amplified signal against said constant signal, means for recording the output of said heterodyning means, a source of high density fluid, a source of low density fluid, a mixing valve for connecting said sources with said pump means and for varying the proportions of fluids, means including a reversible motor for controlling said valve, and a servo control circuit connected to the output of the heterodyning means for operating said motor in a direction to energize the valve control means selectively in accordance with changes in density at the nozzle.
3. Apparatus for maintaining a substantially constant density for a fluid comprising, in combination, a whistle for producing an audible signal variable in accordance with the density of the fluid passing therethrough, means for pumping said fluid through said whistle at a constant rate, a microphone mounted adjacent said whistle for picking up the audible signal, means connected to said microphone for amplifying said signal, means for filtering undesirable frequencies from the amplified signal and connected to said amplifying means, oscillator means for prov1ding a constant signal, means for heterodyning the amplified signal against said constant signal, a source of high density fluid, a source of low density fluid, a mixing valve for connecting said sources with said pumping means and for varying the proportions of high and low density fluids in order to maintain a predetermined density at the nozzle, servomotor means for controlling said valve, and a servo control circuit connected to the output of the heterodyne means and to said servomotor for energizing the servo means selectively in accordance with changes in density at the nozzle.
4. Apparatus for measuring the density of fluids, cornprising in combination, a whistle, means for pumping the fluid through said whistle, said whistle producing an audible signal variable in accordance with the density of said fluid, pressure sensitive means between said pumping means and said whistle, thermoresponsive means controlled by fluid impinging thereagainst from said whistle, a pair of variable resistance elements in parallel and controlled by said pressure sensitive means and by said thermoresponsive means respectively, a transducer for providing an electrical signal in accordance with variations of said audible signal, oscillator means providing a second signal of a frequency jointly controlled by said resistance elements and variable by said pressure sensitive means in accordance with the pressure of said fluid and by said thermoresponsive means, means for heterodyning said electrical signal against said second signal, and means for recording the output of said heterodyning means.
References Cited in the file of this patent UNITED STATES PATENTS 1,528,586 Tate Mar. 3, 1925 2,283,750 Mikelson May 19, 1942 2,458,164 Hill et al Jan. 9, 1949 2,519,015 Bensen Aug. 15, 1950