US3885592A

US3885592A - Pure fluid passive square function generator

Info

Publication number: US3885592A
Authority: US
Inventors: Tadeusz M Drzewiecki
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1973-10-11
Filing date: 1973-10-11
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27

Abstract

A fluidic circuit, the output signal of which is proportional to the square of the input signal supplied thereto. The circuit comprises means for supplying an input signal and means for taking an output pressure signal proportional to the pressure of the input signal. Generation of a pressure output proportional to the square of the input pressure signal is accomplished by impacting a jet of fluid emanating from a linear resistor onto another linear resistor or a stagnation plenum. The stagnated pressure is a function of the square of the input pressure.

Description

' United States Patent [191 Drzewiecki [4 1 May 27, 1975 PURE FLUID PASSIVE SQUARE FUNCTION GENERATOR 3,595,258 7/1971 Kinnel 137/842 Primary Examiner-William R. Cline Attorney, Agent, or FirmNathan Edelberg; Robert P.

Gibson; Saul Elbaum [57] ABSTRACT A fluidic circuit, the output signal of which is proportional to the square of the input signal supplied thereto. The circuit comprises means for supplying an input signal and means for taking an output pressure signal proportional to the pressure of the input signal. Generation of a pressure output proportional to the square of the input pressure signal is accomplished by impacting a jet of fluid emanating from a linear resistor onto another linear resistor or a stagnation plenum. The stagnated pressure is a function of the square of the input pressure.

6 Claims, 5 Drawing Figures 'lOOL PURE FLUID PASSIVE SQUARE FUNCTION GENERATOR RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, used, and licensed by or for the United States Government for governmental purposes without the payment to the inventor of any royality thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to pure fluid systems in general and, more specifically, to a pure fluid system capable of producing a fluid pressure output signal that is directly proportional to the square of the pressure of the fluid input signal supplied to the system.

2. Description of the Prior Art Any computational circuit, of an analog nature, generally requires a squaring capability. This is especially true in the case of analog flueric computational circuits.

In the past, analog flueric computations of squares of a particular input function have been done by complicated networks of amplifier and feedback loops. This is amply illustrated in US. Pat. No. 3,459,206 entitled Statistical Device, issued to Dexter.

The use of amplifier feedback loops is costly and complicated. By taking advantage of the natural fluidic non-linearity of a stagnating flow of simple passive circuit can be constructed that can approximate, to a fairly good degree, the square function. The closest prior art to the invention of the applicant is Colston, Pure Fluid Function Generating System, US. Pat. No. 3,250,469. Colston obtains his square function in two fundamentally different ways. These are:

l. Feeding an input pressure source through a capillary or linear resistor connected in series to an orifice which is connected to ambient; the output pressure which is proportional to the square of the input pres sure is taken from the junction between the linear resistor and the orifice; and

2. By passing the input pressure source through a linear resistor or capillary and utilizing the output pressure of the capillary as a square function of the input pressure.

An important aspect of this invention is the discovery that if a linear resistor is subjected to a pressure and grounded or connected to ambient, and the resulting flow is then stagnated, the stagnation pressure will be proportional to the square of the pressure driving the resistor.

It is therefore an object of this invention to provide a pure fluid square function generator which utilizes the stagnated flow from a linear resistor to produce a stagnation pressure proportional to the square of the pressure driving the resistor.

In addition, it is an object of this invention to provide a pure fluid active square function generator which enables power to be drawn off from the circuit producing the square function, that power being proportional to the square in pressure of the input function or source.

These and other objects of the present invention will become more fully apparent with reference to the following specifications and drawings which relate to two preferred embodiments of the present invention.

SUMMARY OF THE INVENTION In accordance with the disclosure herein presented this invention provides a pure fluid square function generator which comprises a series combination of a linear resistor having a fluid source and means for catching and stagnating the emitted jet from said resistor, and wherein said means comprises a stagnation plenum connected to the catcher and having an output port for measurement of the pressure at said plenum. A modification of the generator is provided so that power may be withdrawn with a pressure proportional to the square of the input source pressure. This means comprises two linear resistors connected in series one end of which is grounded to ambient and the other end of which acts as a catcher and stagnation plenum.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following decription and from the accompanying drawings in which:

FIG. 1a is a diagrammatic sketch of the pure fluid passive square function generator.

FIG. 1b is a cross sectional view of a specific model of the pure fluid passive square function generator.

FIG. 10 is end view of the illustration of FIG. 1b.

FIG. 1d is a graph of the output function versus the input pressure for the pure fluid passive square function generator.

FIG. 2 is a diagramatic sketch of the pure fluid active square function generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention disclosed herein may be understood with respect to its broad aspects by reference first to FIG. 1a where there is shown a diagrammatic view of an embodiment of the invention encompassing the pure fluid passive square function generator. For this particular circuit the input pressure P may be related to the output pressure P by the following equation:

where p is the density of the fluid.

A is the area of the capillary (linear resistor).

R is the resistance to the flow of the capillary.

This equation may be derived as follows: Let Q represent the flow of fluid through the linear resistor of resistance R. Then, since the linear resistor is vented to ambient 13, the pressure in the resistor is However, P may be assumed equal to zero since it is the ambient pressure.

If we consider the pressure of the jet 10 exiting from the linear resistor R to be P and the pressure entering the catcher 9 to be P and write Bernoullis equation between the exit from the linear resistor and the catcher 11, we obtain where v is the velocity of the fluid as it exits the linear resistor, and v is the velocity of the fluid at the end of the catcher 9 in the stagnation plenum 11. However, since v is the velocity of the fluid in the stagnation plenum 11, it characteristically must be zero. Hence solving Bernoullis equation v V 2P /p. Having previously asserted that the flow Q P /R, we now assert VA Q and for a parabolic profile if /2 v where \7 is the average velocity of the fluid within the jet 10 issuing from the resistor R. Returning to our solution of Bernoullis equation and substituting for v in terms of R, A, and P we obtain the above declared equation relating to P to P.,.

The second embodiment of the invention comprising a pure fluid active square function generator may best be understood by reference to FIG. 2 wherein there is shown a diagramatic circuit of the invention. In this particular embodiment of the invention, the output pressure P is proportonal to the square of the input pressure P., by a different constant. The equation may also be derived from application of Bernoullis equation. Specifically, in the embodiment:

In order to draw power, the jet 16 vented to the ambient 14 is received by linear resistor R Resistor R is series connected to linear resistor R Resistor R is vented to ambient 15. Power is drawn from between resistor R as output pressure P Reference is now made to FIG. 1b and FIG. whereion there is illustrated a specific working model of the invention. In this embodiment, fluid enters through the input port 20 and travels along the linear resistor with the flow therefrom impinging upon the catcher opening 31. Fluid entering the catcher opening 31 travels along the catcher tube 32 and enters or stagnates at the stagnation plenum 22. The pressure of the fluid in this stagnation plenum 22 may be measured by suitable means currently known in the art.

Vents

21 and 41 are on the side of the catcher tube 32 and connected directly to ambient pressure. A portion of the fluid travelling through linear resistor 30 vents itself to ambient through these

vents

21 and 41. The pressure at the output port 22 is directly proportional to the square of the pressure at the input port 20.

As can be seen in FIG. 1c the length of the capillary is approximately 200 times its thickness L. Moreover, its width is approximately 24 times its thickness, 24L. Continuing, the output vents are approximately 12L. The catcher tube 32 has a width of approximately 2L.

The central principal axis of the vents are located approximately 16L from the central principal axis of the catcher tube 32 and approximately 12L behind the plane of the mouth or opening 31 of the catcher tube 32.

- In FIG. 1d, curve A is an actual plot of P (the output pressure), versus P (the input pressure), of the pure fluid passive square function generator as shown in FIG. lb and FIG. 1c.

It is to be understood that the inventor does not desire to be limited to the exact detail of construction shown and described for obvious modifications will occur to a person skilled in the art pertaining hereto.

What is claimed is:

1. A passive fluidic function generator for generating an output pressure signal which is proportionally related to the square of an input pressure signal, said generator comprising in combination; input port means for connection to an input fluid pressure signal source; linear fluidic resistor means connected to said input port means for transmitting a pressure signal therethrough; a fluidic catcher means for catching and receiving the pressure signal as it exits said linear fluidic resistor means, said linear fluidic resistor means being connected directly to said fluidic catcher means to form a passage of uniform cross-section between said input port means and said fluidic catcher means; at least one vent to the ambient disposed between said fluidic resistor means and said catcher means; means defining a fluidic stagnation plenum connected to said catcher means for stagnating the pressure signal exiting said linear fluidic resistor means; and an output port means coupled to said stagnation plenum means for providing an output pressure signal, said output pressure signal being functionally related to the square of the input pressure signal.

2. The function generator of claim 1 wherein said resistor means is a capillary tube.

3. The function generator of claim 2 wherein said tube has a thickness L, a width 24L, and a length ZOOL.

4. The function generator of claim 3 wherein the input port means to said capillary and said vents each have a radius 12L.

5. The function generator of claim 4 wherein said catcher means has a width 2L and a thickness L.

6. The function generator of claim 2, wherein two vents to ambient are provided at the end of said capillary one located on each side of said catcher.

Claims

3. The function generator of claim 2 wherein said tube has a thickness L, a width 24L, and a length 200L.