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Publication numberUS3821897 A
Publication typeGrant
Publication dateJul 2, 1974
Filing dateOct 17, 1972
Priority dateOct 17, 1972
Also published asCA982848A1, DE2351940A1, DE2351940B2, DE2351940C3
Publication numberUS 3821897 A, US 3821897A, US-A-3821897, US3821897 A, US3821897A
InventorsFrazel W
Original AssigneeGen Signal Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Pressure sensing probe
US 3821897 A
Abstract
A pressure sensing probe having an elongated housing with an elastic diaphragm located at one end of the housing. The outer face of the diaphragm is substantially flush with the outer wall surface of the housing. An interior cavity is formed in the housing with at least a portion of the inner face of the diaphragm being in communication with the interior cavity. Also in communication with the interior cavity are a fluid supply port containing a flow-restricting supply orifice, a fluid output pressure port, and a fluid exhaust port containing a flow-restricting exhaust nozzle, each of which are formed in the walls of said housing. The diaphragm is normally biased inwardly by a biasing spring having its one end attached to an armature secured to the inner face of the diaphragm. The other end of the biasing spring is attached to an armature stem guide fixedly secured within the cavity of the housing which maintains the spring in constant tension. The armature also has a stem that passes downwardly within the biasing spring and through the armature stem guide. The lower end of the armature stem acts as a flapper which when the armature stem is raised and lowered varies the flow of fluid through the exhaust nozzle positioned beneath the flapper to control the amount of fluid passing outwardly through the fluid exhaust port. A fluid supply regulator is connected to the fluid supply port and a fluid exhaust regulator is connected to the fluid exhaust port in order to control the pressure of the fluid supplied through the orifice to the fluid cavity of the probe and to control the pressure of the fluid exhausted through the nozzle from the fluid cavity of the probe. The fluid output pressure port is also connected directly to each of the pressure regulators, thereby providing a pilot pressure for each of the regulators. The function of the probe is to reproduce exactly in fluid pressure the changes in the fluid pressure to which the sensing diaphragm is exposed. The probe output pressure reading will always be greater than the actual fluid pressure if the diaphragm is preset with an inward bias by the biasing spring. This probe biasing allows negative fluid pressures to be read out on the instrument as positive fluid pressures, thus enabling it to deal with negative heads of pressure.
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Description  (OCR text may contain errors)

United States Patent [1 1 F razel [111 3,821,897 [451 July 2,1974

[ PRESSURE SENSING PROBE Wilbur H. Frazel, Riverside, R1.

[73] Assignee: General Signal Corporation, New

York, NY.

22 Filed: Oct. 17, 1972 21 Appl. No.: 298,408

[75] Inventor:

[52] US. Cl. 73/213, 73/388 BN, 137/85 Primary Examiner-Richard C. Queisser Assistant ExaminerJohn P. Beauchamp Attorney, Agent, or Firm-Barlow & Barlow 5 7 ABSTRACT A pressure sensing probe having an elongated housing with an elastic diaphragm located at one end of the housing. The outer face of the diaphragm is substantially flush with the outer wall surface of the housing. An interior cavity is formed in the housing with at least a portion of the inner face of the diaphragm being in communication with the interior cavity. Also in communication with the interior cavity are a fluid supply port containing a flow-restricting supply ori- OUTPUT gRESSURE FLUID SUPPLY 6O PRESSURE FLUID EXHAUST fice, a fluid output pressure port, and a fluid exhaust port containing a flow-restricting exhaust nozzle, each of which are formed in the walls of said housing. The diaphragm ,is normally biased inwardly by a biasing spring having its one end attached to an armature secured to the inner face of the diaphragm. The other end of the biasing spring is attached to an armature stem guide fixedly secured within the cavity of the housing which maintains the spring in constant tension, The armature also has a stem that passes downwardly within the biasing spring and through the armature stem guide. The lower end of the armature stem acts as a flapper which when the armature stem is raised and lowered varies the 'flow of fluid through the exhaust nozzle positioned beneath the flapper to control the amount of fluid passing outwardly through the fluid exhaust'port. A fluid supply regulator is connected to the fluid supply port and a fluid exhaust regulator is connected to the fluid exhaust port in order to control the pressure of the fluid supplied through the orifice to the fluid cavity of the probe and to control the pressure of the fluid exhausted through the nozzle from the fluid cavity'of the probe. The fluid output pressure port is also connected directly to each,

of the pressure regulators, thereby providing a pilot pressure for each of the regulators. The function of theprobe is to reproduce exactly in fluid pressure the changes in the fluid pressure to which the sensing diaphragm is exposed. The probe output pressure reading will always be greater than the actual fluid pressure if the diaphragm is preset with an inward bias by the biasing spring. This probe biasing allows negative fluid pressures to be read out on the instrument as positive fluid pressures, thus enabling it to deal with negative heads of pressure.

8 Claims, 5 Drawing Figures mnmnm 2:914 1821.897

' SHEET 1 0F 3 PILOT PRESSURE OUTPUT gRESSURE FLUID SUPPLY 60 FLUID PRESSURE EXHAUST FlG.l

BACKGROUND OF THE INVENTION In the measurement of fluid flow in a pipeline it is I common practice to install a differential producer such as a Venturi tube which allows inferential determination of flow rate by measurement of pressure differential. The general configuration of the Venturi tube and other similar devices, and their theory of operation are well known in the art. Presently to measure pressures developed in the differential producer, piezometer holes are usually drilled in the wall of the device communicating with the interior at two prescribed points, namely the inlet and thethroat. Pipes commonly lead from these pressure .taps to an external secondary device which may display the differential pressure and/or convert it to an analogous signal which may be pneumatic, electric, etc., in nature.

When the pipeline fluid contains settleable solid material, as in the cases of sewage, sludge, slurries, etc., trouble is often experienced because the open pressure taps and pipes connecting to them eventually become fouled with accumulations of solid material to the extent that accuracy of measurement of the pressure is affected. Many means of dealing with this difficulty are available, but most only slow but do not entirely eliminate accumulation. Others, which are capable of preventing accumulation in taps and piping, require constant surveillance and maintenance to assure proper operation and may in themselves variably bias the detected pressure and hence affect accuracy.

SUMMARY OF THE INVENTION The pressure sensing probe is a force balance device which operates to maintain exact balance between the force created by the fluid pressure acting on the outside of the sensing diaphragm plus the inward force of the biasing spring, and the force of the fluid pressure within the housing acting on the inside of the sensing diaphragm. Adjustment is made so that with the sensing diaphragm exactly in its neutral position, the flapper is in its operating position close to the nozzle such that the fluid flow through the nozzle is controlled. Fluid pressure within the housing will be a function of pressure of fluid supplied to the orifice and pressure loss across the orifice determined by orifice size andrate of flow of fluid through it. With the flapper close to the nozzle, highly restricting flow, rate of flow through the orifice will be low, loss across the orificewill therefore be small, and housing pressure will be high, approaching fluid supply pressure. With the flapper farther away from the nozzle, restricting flow less, rate of v flow through the orifice will be higher, loss across the orifice will therefore be greater, and housing pressure will be lower, retreating from fluid supply pressure. Supply and exhaust pressures also have a major effect on housing pressure for any given flapper-nozzle separation.

In a condition of balance the amount of fluid allowed to flow through the orifice by the flapper-nozzle couple is just sufficient to create a housing pressure to exactly balance the sensed pressure plus the biasing spring equivalent pressure. If sensed pressure increases, the system unbalances and the flapper-nozzle separation decreases slightly to restrict the flow of the fluid,

thereby raising housing pressure enough to again achieve balance. The required new housing fluid pressure is produced by a slight decrease in flapper-nozzle separation. In other words, the flapper assumes a new slightly-changed position relative to the nozzle.

The inlet probe senses line pressure and the throat probe senses line pressure less differential. The quantity of real interest is the difference between the two sensed pressures. The accuracy obtained with these novel pressure sensing probes is of a magnitude better than have previously been demanded of a pressure sensing device. Only because the design of the probe stays within a single physical domain, pressure, with a single interfacing diaphragm, is the device able to perform the conversion so successfully. One-to-one tracking is automatic in this case, since a single diaphragm presents the same effective area to the fluid on the outside and the fluid on the inside. Thus no calibration is required. Sensitivity and accuracy of pressure balance are not dependent on magnitude of the sensed pressure.

In order for the probe, as so far described, to follow an increased pressure applied to the outside of the diaphragm it is necessary that the flapper assume a new position slightly closer to the nozzle. This increment of position change, no matter how small, associated with the rate of the biasing spring, spring rate of the diaphragm due to its elasticity, effective area change of the diaphragm, and changes in reaction force due to fluid flow around the-repositioned flapper, results in pressure changes within the probe substantially, but not exactly, equal to pressure changes outside. For highly precise reproduction of pressure changes, this error is not tolerable, especially in cases where the measured pressure varies widely. With given supply and exhaust pressures, given orifice and nozzle sizes, and a given position of the'flapper with respect to the nozzle within its throttling range, the pressure within the probe will be at some intermediate value between supply and exhaust pressures. Then if both supply and exhaust pres-.

sures are changed by exactly the same given amount, the intermediate pressure will also change by exactly the given amount without requiring any change whatsoever in flapper position relative to the nozzle, since pressure drop across the system and therefore fluid flow through the system and loss across the orifice, will all remain constant. By changing supply and exhaust pressure in one-to-one relationship to probe output pressure changes, the latter can be made to follow pressure changes acting on the outside surface of the diaphragm without any sustained position changes of the flapper and the associated errors.

The output pressure of the probe is used as a pilot pressure for the pair of fluid control regulators, one

spring-biased to maintain its downstream pressure (up stream pressure of the orifice) at a value always a selected increment above its pilot pressure. Similarly the exhaust regulator is biased to maintain its upstream pressure (downstream pressure of the nozzle) at a ,value always a selected increment below its pilot pressure. Both regulators control fluid flow to accomplish this regulation. I

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view illustrating a pair of,pressure sensing probes having their diaphragms inserted into holes provided respectively at the inlet and throat areas of a Venturi tube; i

FIG. 2 is a partial cross section view illustrating how the pressure sensing probe is secured to the hole in the wall of the Venturi tube;

FIG. 3 is a cross sectional view illustrating the pressure sensing probe;

FIG. 3A is a magnified view of the end-of the pressure sensing probe having the diaphragm located therein;

FIG. 4 is a cross section view of an alternative embodiment of a pressure sensing probe.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawings, a pair of pressure sensing probes generally designated are schematically illustrated as being secured to the outer wall of a Venturi tube 20. One probe could be attached to the inlet area of the Venturi tube and the other probe attached to the throat area. One manner in which the individual probes can be attached to the Venturi tube is best illustrated in FIG. 2. In that figure it is shown that a boss 21 would be formed in the outer face of wall 22 of the Venturi tube in the area where the pressure sensing probe is to be attached. The boss would have'a hole drilled down from its top all the way through to the interior surface 23 of the Venturi tube and this hole would have an outer bore 24 of a greater diameter than the inner bore 26. The diameter of the inner bore would be substantially the same as the outer diameter of the neck 12 of the pressure sensing probe. A portion of outer bore 24 would be threaded as at 25 to receive the threading on gland bushing 28. Bushing 28 would have a bore 29 whose diameter would be substantially the same as a portion of the pressure sensing probe that would be inserted through bore 29. An annular channel 30 would be formed in this bore to receive an O-ring 32 in order to provide a pressure tight seal to prevent Another probe would be similarly installed at the sec-.

ond prescribed pressure sensing point in the Venturi tube. With these highly accurate pressure transfer devices at the two appropriate points in the Venturi tube, a secondary device connected to these probes will receive exact pressures and there will be no possibility of fouling of secondary devices and/or the connecting pipesby pipeline fluidj One possible construction of the pressure sensing probe is illustrated in FIGS. 3 and 3A and they will serve as basis for an explanation of the operation of the probe. The probe 10 has a sealed housing 13 formed with an interior cavity 14 within which the movable components of the probe are located. A source of suitable fluid under appropriate pressure isconnected to a fluid supply port in the housing. Fluid pressure enters the probe through orifice 15a and passes into the interiorcavity 14 of the probe. This cavity is also bounded by the output pressure port 16, the interior walls 17 of the probe, diaphragm l8 and fluid exhaust port 19. Diaphragm 18 is suitably attached to an armature 40 into which is screwed an armature stem 41. The

diaphragm, its armature and the armature stem move as a unit in response to differential pressures on the two sides of the diaphragm. The armature stem is of such length that with the diaphragm initsneutral position (so that its outer surface is exactly flat) the face 48 of the free end of the stem centered by the armature stem guide 44 is positioned approximate to the face of the exhaust nozzle 46.

I If the face of the armature stem touches the nozzle, it seals off passage of fluid from' the probe cavity to the fluid exhaust port 19. If the armature stem is lifted off the nozzle, a passage for fluid is provided. The effective size of the passage and hence its resistance to fluid flow depend upon the extent of separation between the-armature stem end and the nozzle. The face of the armature stem then constitutes a flapper 48 working against the nozzle 46. The operation of an orifice and a nozzleflapper couple is well known in the art.

Operation of the probe will now be discussed. First of all, assume the following condition: 1) Thefluid supply pressure is substantially greater than the pressure to be measured which acts upon the outside surface of the diaphragm; 2) the fluid exhaust pressure is substantially less than the pressure to be measured; 3) the biasing spring 49 extending between the diaphragm armature 40 and the armature stem guide 44 is adjusted to exert no force on the diaphragm with the latter in its neutral position.

In situation I, with the probe in a condition of equilibrium, pressure inside the probe substantially equals that outside, so that forces acting on the diaphragm, which is in its neutral position, exactly balance. At this neutral position of the diaphragm the position of the flapper 48 1 relative to the nozzle 46 is such as to produce the pressure existing inside the probe.

In situation II suppose the pressure acting on the outside surface of the diaphragm increases; since the j forces no longer exactly balance, the flapper tends to move closer to the nozzle. As this happens, its restrictive effect on fluid flow through the system and out through the nozzle increases and pressure inside the probe correspondingly increases. A new condition of equilibrium will be reached when the pressure inside the probe again substantially equals that outside. It will be noted that the flapper must be slightly closer to the nozzle to produce a new higher pressure inside the probe. However, due to the extreme sensitivity of pressure within the probe to flapper position, this sustained position change may be only a small fraction of a thousandth of an inch.

In situation III the pressure outside the diaphragm 18 drops and the flapper 48 moves away from nozzle 46 very slightly to a new position with respect to the nozzle. This produces a new lower pressure inside the probe substantially equal to the new lower pressure outside.

In this manner pressure changes within the probe and in any dead ended system connected to it, follow pressure changes acting on the outside surface of the diaphragm. v

The above description describes the action when the biasing spring exerts no force on the diaphragm. The situation will now be described when the biasing spring is adjusted to pull inwardly on the diaphragm, 18. At a condition of equality of pressures acting on the inside and outside of the diaphragm, the system then would no longer be an exact balance since the spring force is unopposed. An additional increment of flapper position movement towards the nozzle takes place until an additional increment of pressure inside the probe is produced which acting upon the effective area of the diaphragm creates an additional increment of force to balance the spring force. Now a new balance exists and the pressure inside the probe equals that outside plus an increment due to spring pull. Since the spring pull is substantially constant, it follows that the pressure inside the probe is always higher than that outside by a constant amount. However, changes in pressure inside are always substantially equal to changes in outside pressure.

In the preceding description of operation it was pointed out that in order for the probe to follow an increased pressure applied to the outside of the diaphragm it was necessary that the flapper assume a new position slightly closer to the nozzle. This increment of position change, no matter how small, associated with the rate of the biasing spring, spring rate of the dia-' phragm due to its elasticity, the effective area change of the diaphragm, and the changes in reaction force due to fluid flow around the repositioned flapper, result in pressure changes within the probe substantially but not exactly equal to pressure changes outside. For highly precise reproduction of pressure changes this error is not tolerable especially in cases where the measured pressure varies widely.

For given supply and exhaust pressures, given orifice and nozzle sizes, and a given position of the flapper with respect to the nozzle within its throttling range, the pressure within the probe will be at some intermediate value between supply and exhaust pressures. If both supply and exhaust pressures are changed by exactly the same given amount, the intermediate pressure will also change by exactly the given amount without requiring any change whatsoever in flapper position relative to the nozzle since pressure drop across the system' and therefore fluid flow through the system and pressure drop across the orifice, will all remain constant. By changing supply and exhaust pressures in one-to-one relationship to probe output pressure changes, the latter can be made to follow pressure changes acting on the outside surface of the diaphragm without any sustained position changes of the flapper and the asso-.

ciated errors.

As shown in FIG. 1 the output pressure P of the probe is used as a pilot pressure for a pair of fluid control regulators 60 and 62. Regulator 60 maintains fluid pressure at the supply port of the probe and regulator 62 maintains fluid pressure at the exhaust port 19. The supply regulator 60 is spring biased by a value C to maintain its downstream pressure at a value always a selected increment above its pilot pressure. Similarly the exhaust regulator 62 is biased by a value C to maintain its upstream pressure at a value always a selected increment below its pilot pressure. Both regulators control fluid flow to accomplish this regulation. Construction and operation of regulators, the function of which are described above, are well known in the art and are commercially available. Therefore description of their operation will not be detailed here.

The pressure sensing probe system shown in duplicate in FIG. 1 produces an output pressure, changes in which follow in a one-to-one relationship to changes in pressure applied to the outside surface of diaphragm 18. In equilibrium it is an essentially perfect null balance device, hence it has no error proportional to magnitude of the pressure measured. Resolution is infinite. It may be biased to produce an output pressure higher or lower than the measuredpressure by any selected constant amount. .The probes speed of response is a function of orifice and nozzle size which determine maximum rates of rise and fall respectively of pressure within the probe and any connected dead-end system.

An alternative pressure sensing probe construction is illustrated in FIG. 4. In this embodiment the supply fluid enters the probe through nozzle 146 and exhausts through orifice a. Analysis similar to the foregoing shows that the operation of this type probe is equivalent to that of the probe shown in FIG. 3 where the supply fluid enters through the orifice 15a and exhausts through the nozzle 46. It will be noted in FIG. 4 that nozzle flapper operation is the reverse of that of FIG. 3, in that an inwardly moving diaphragm moves the flapper 148 away from the nozzle, not toward it. This embodiment additionally has a centering diaphragm for mounting the stem 141 and a bias adjusting stem 154 attached to one end of biasing spring 149. A protective cap 156 covers the endof the bias adjusting stem. The remaining elements of the alternative pressure sensingprobe are essentially the same as that of the probe described in FIG. 3 with the numbers of the elements in FIG. 4 all being preceded by a one hundred numeral.

While the foregoing descriptions have stressed the use of the pressure sensing probe as applied to a Venturi tube carrying contaminated fluid, it is evident that the probe may be used in any application where pressure must be sensed, particularly where highly precise 'results are required. It may, for instance, be used to gage levels in Parshall flumes, weirs, Kennison nozzles, etc., or in tanks, reservoirs, standpipes, wells, etc. It may be used for pressure, level, flow, etc. measurement of dangerous as well as solids-bearing fluids. Many other applications are possible and practical.

What is claimed is: 1. A pressure sensing probe comprising a housing, an elastic diaphragm located in one wall of said housing, an interior cavity formed in said housing, at least a portion of the inner face of said diaphragm being in communication with said interior cavity, a fluid supply port formed in a wall of said housing with saidfluid supply port being in communication with said interior cavity, a fluid output pressure port formed in a wall of; said housing with said fluid output pressure port being in communication with said interior cavity, v a fluid exhaust port formed in a wall of said housing with said fluid exhaust port being in communication with said interior cavity, means including ,a nozzle between the supply and exhaust ports and a flapper to vary the fluid flow through said cavity, said flapper coupled to said diaphragm, f a fluid supply regulator connected to said fluid supply port and a fluid exhaust pressure regulator connected to said fluid exhaust port and means connecting said fluid output pressure port to each of said regulators, said fluid supply regulator maintaining fluid supply pressure to said fluid supply port a fixed increment above the pressure at said output pressure port and said fluid exhaust regulator maintaining pressure from said fluid exhaust port a fixed increment below pressure at said output pressure port, a flow restricting orifice between said fluid supply regulator and said interior cavity.

2. A pressure sensing probe as recited in claim 1 wherein the outer face of said diaphragm is substantially flush with the outer wall surface of said housing.

3. A pressure sensing probe as recited in claim 1 further comprising means for biasing said diaphragm comprising an armature attached to the inner face of said diaphragm and a biasing spring having its one end attached to said armature and its other end attached to spring anchoring means on said housing.

4. A pressure sensing probe as recited in claim 3 wherein said armature has a stern that passes downwardly within said biasing spring and through a guide aperture formed in said spring anchoring means.

5. A pressure sensing probe as recited in claim 3 wherein the lower end of said armature stem forms a flapper which when it rises and falls varies the flow of fluid through said nozzle.

6. A pressure sensing probe as recited in claim 3 including a centering diaphragm in said cavity wherein the lower end of the armature passes through said centering diaphragm to which it is secured.

7. A pressure sensing probe as recited in claim 9 wherein a biasing spring is attached to the lower end of the armature and to the housing together with means for adjusting the bias of said spring.

8. A pair of the pressure sensing probes such as the probe recited in claim 1 in combination with a Venturi tube, said first pressure sensing probe having the outer face of its flexible diaphragm inserted in a tap in the inlet area of the Venturi tube and said second pressure sensing probe having the outer face of its flexible diaphragm inserted in a tap in the throat area of the Venturi tube, both of the outer faces of said flexible diaphragms, being substantially flush with the inner wall surface of said Venturi tube.

. UNITED STATES PATEN'Ij OFFICE .CERTIFICATE OF CORRECTION Patent NO. Dated I 2,

Inventor( 1!) Wilbur H. F razel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 8, line 8, cancel the numeral "9" and insert in lieu thereof the numeral" 6 Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting'officer Commissioner of atents USCOMM-DC 50376-P59 i U.S. GOVERNMENT PRINTING OFFICE I", 0-358-35,

FORM PO-1050 (10-69)

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3934471 *Jan 29, 1974Jan 27, 1976Percy William WhiteFlow monitoring system
US4671109 *Dec 16, 1985Jun 9, 1987D. Halmi And Associates, Inc.Flow measuring device for liquids bearing entrained solids
US6021677 *Aug 12, 1998Feb 8, 2000Asea Brown Boveri AgPipeline system for the controlled distribution of a flowing medium and method for operating such a pipeline system
Classifications
U.S. Classification73/861.47, 73/700, 137/85
International ClassificationG01F1/38, G01L7/02, G01F1/34, G01L7/08, G01L7/00
Cooperative ClassificationG01F1/386, G01L7/08
European ClassificationG01L7/08, G01F1/38B