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Differential pressure responsive magnetically actuated switch responsive only to sudden pressure changes

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US3786211A
US3786211A US3786211DA US3786211A US 3786211 A US3786211 A US 3786211A US 3786211D A US3786211D A US 3786211DA US 3786211 A US3786211 A US 3786211A
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Prior art keywords
pressure
means
field
chamber
valve
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R Popp
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Colt Industries Operating Corp
Coltec Industries Inc
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Chandler Evans Inc
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H35/00Switches operated by change of a physical condition
    • H01H35/24Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow
    • H01H35/242Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow operated by one particular pressure-time function
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H35/00Switches operated by change of a physical condition
    • H01H35/24Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow
    • H01H35/247Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow the switch being of the reed switch type

Abstract

Apparatus for generating a signal commensurate with a rate of change of a monitored pressure in excess of a preselected value. The apparatus includes means coupled to a spring biased diaphragm for modifying a magnetic field in response to movements of the diaphragm and a field responsive signal generator mounted exteriorly of the housing in which the diaphragm and magnetic field generating means are located.

Description

United States Patent 1 Jan. 15, 1974 DIFFERENTIAL PRESSURE RESPONSIVE MAGNETICALLY ACTUATED SWITCH RESPONSIVE ONLY TO SUDDEN PRESSURE CHANGES [75] Inventor: Roger C. Popp, Chesaning, Mich.

[73] Assignee: Chandler Evans Inc., West Hartford, Conn.

221 Filed: .Iulyl9,1972

211 App]. No.2 273,288

u.s. c1.....'..... 200/83 T, 200/83 L, 200/819 M [51 Int. Cl. HOlh 35/34 [58] Field of Search 200/83 L, 83 T, 81.9 R, ZOO/81.9 M, 83 B, 83 R, 83 A; 335/205 56] References Cited UNITED STATES PATENTS 3,240,894 3/1966 Mansfield, Jr. et al..... 200/83 A 2,869,475 1/1959 BObO 200/83 1. 3,325,6l2 6/1967 Petersen et al. ZOO/81.9 R 3,305,805 2/1967 Tann 335/205 x 3,327,079 6/1967 Widl ZOO/81.9 M ux 2,980,090 4/l96l Sutton et al 200/83 R ux Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-David S. Fishman et al.

[57] ABSTRACT Apparatus for generating a signal commensurate with a rate of change of a monitored pressure in excess of a preselected value. The apparatus includes means coupled to a spring biased diaphragm for modifying a magnetic field in response to movements of the diaphragm and a field responsive signal generator mounted exteriorly of the housing in which the diaphragm and magnetic field generating means are located.

8 Claims, 1 Drawing Figure DIFFERENTIAL PRESSURE RESPONSIVE MAGNETICALLY ACTUATED SWITCH RESPONSIVE ONLY TO SUDDEN PRESSURE CHANGES BACKGROUND OF THE INVENTION I 1. Field ofthe Invention The present invention relates to sensing the rate of change of a monitored pressure. More specifically, this invention is directed to apparatus for producing a pressure differential commensurate with a rate of change of pressureand generating a control signal in response to the thus producedpressure differential. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.

2. Description of the Prior Art While not limited thereto in its utility, the present invention is particularly well suited for use in gas turbine engine instrumentation; expecially or the detection of engine v flameout or stalling conditions. As is well known, a rapid decrease in gas turbine engine compressor discharge or burner pressure is indicative of flameout or stall conditions. Should an engine flameout occur in flight it is essential that the engine ignition system be immediately energized to effect reignition.

Devices responsive to rate of change of pressure for commanding an engine ignition cycle have been available in the prior'art. A particularly successiful prior art device is disclosed in U.S. Pat. No. 3,240,894 issued to G. A. Mansfield, Jr. et alon March 15,1966. While apparatus such as that disclosed in U.S. Pat. No. 3,240,894 have functioned satisfactorily, such prior art devices have been characterized by relative complex- .ity. In addition, there is-a continuing desire in the aero- SUMMARYOF THE INVENTION 'llhe present invention constitutes a novel and improved method and apparatus for detectingand providing a signal commensurate with the rate of change of a monitored pressure suchas, by way ofexample, gas turbine engine compressor discharge or burner pressure. ln accordance with the invention during operation the monitored pressure is applied directly to a first side of a spring biased diaphragm. The monitored pressure is also applied to the second side ofthe diaphragm viaa normally open isolation valve whichincludes a first timing orifice. Thus, under steady state conditions the same pressure will be-applied to both sides of the diaphragm.

The diaphragm is mechanically connected to the movable armature of a magnet assembly. The armature normally shunts the field generated by a fixed position magnet. A magnetic field responsive switch is positioned exteriorly of the apparatus housing in such a manner as to be energized by the field if the shunting effect of the armature is disrupted by the armature being pulled away from the magnet.

Should the monitored pressure decrease rapidly a pressure differential will be developed across the diaphragm since the pressure at the second side thereof will be prevented from rapidly decaying by the first tim ingorifice. The diaphragm may thus be deflected and will move against the bias spring and the force provided by the attraction of the magnet assembly for the armature thereby causing the armature to be separated from the magnet and the field responsive switch energized. Movement of the diaphragm will also cause closing of the isolation valve thereby trapping a charge of gas inside the device at the second side of the diahragm. The trapped charge is bled off through a second timing orifice and, by variation in size of the second timing orifice, various hold-in times for the apparatus may be selected. When the pressure differencial across the diaphragm is reduced sufficiently by leakage through the second timing orifice, or by recovery of the sensed pressure, the bias spring will reset thediaphragm. Return of the diaphragm to its initial state will cause reopening of the isolation valve and simultaneous return of the armature to the field shunting position whereby BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing which is a cross-sectional side elevation view ofa preferred embodiment of the mechanicalportions of the invention coupled with a schematic showing of the electron portions of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The disclosed embodiment of the invention comprises a housing indicated generally at 10. A cap 12 engages housing 10 and cooperates therewith to define a pressure vessel. A connector portion of cap 12 is provided with an internally threaded aperature 14 for coupling to a pressure probe, not shown, of conventional design. An angularly oriented passage 16 provides communication between aperture 14 and the interior of' the pressure vessel. Aperture l4 terminates, at its lower end, in a threaded section of reduced diameter which supports a first isolation valve defining member indicated generally at 18. While the operation of the isolation valve will be described in detail below, it is to be noted that member 18 defines an adjustable stop which may be vertically positioned by means of insertion of a suitable tool into a socket 20 formed in member 18 and accessible via aperture 14.

The interior of the pressure vessel defined by housing 10 and cap 12 is divided into a pair of opposed cham-' bers by a flexible diaphragm 22 mounted in the manner shown. Diaphragm 22 thus divides the pressure vessel into an accumulator chamber 24 and a sensing chamber 26. Diaphragm 22 is biased toward accumulator chamber 24 by spring 28.

A second isolation valve defining member, which cooperates with adjustable member 18, is indicated at 30. Valve member 30 is mounted on diaphragm 22 and includes a mechanical stop portion 32 which cooperates with the base of portion 18 to define the upward limit of motion of the valve and thus of the diaphragm. Valve member 30 also includes an extension 33 which extends upwardly from stop portion 32. Extension 33 is provided with a through-hole which defines an entrance orifice. The orifice in extension 33 opens into a channel 34 in member 30; the channel and orifice defining a conduit which provides communication between chambers 24 and 26. The sensed pressure, under normal steady state conditions, is applied to sensing chamber 26 via passage 16 and thence to accumulator chamber 24 via passage 34 to thereby balance the diaphragm 22 in the position shown.

A decay or first timing orifice defining member 35 is positioned in passage 34 in member 30 in the interest of controlling the rate of flow between chamber 24 and chamber 26. While decay orifice defining member 35 can be eliminated by resort to precise machining of the entrance orifice in extension 33, manufacturing economies generally dictate the use of the entrance orifice in combination with the precisely machined smaller decay orifice. As will be obvious to those skilled in the art, should the sensed pressure rapidly decrease, in view of the differences in size between passage 16 and the decay orifice defined by member 35, the pressure in ensuring chamber 26 will fall at a much greater rate than the pressure within accumulator chamber 24. Should the pressure differential thus produced become sufficiently large, the diaphragm 22 will be deflected thus shutting, in the manner to be described below, the normally open isolation valve and entrapping fluid in chamber 24 at a pressure higher than that in chamber 26.

Should the diaphragm 22 be deflected so as to cause mechanical stop portion 32 to contact the base of adjustable member 18, the entrance orifice defining extension 33 on member 30 will contact a valve element 36. Valve element 36 will be loaded against the entrance orifice by spring 38 thus closing the isolation valve and interrupting communication between sensing chamber 26 and passage 34. As noted, this action will trap fluid in accumulator chamber 24. To insure that the pressure differential across the diaphragm will not become excessive, the isolation valve will be closed with portion 32 seated against the adjustable stop defined by member 18 before element 36 contacts the internal stop shoulder provided in the bore in member 18 in which the valve element 36 moves. Accordingly, pressure in chamber 24 in excess of a level determined by spring 38 will act on valve element 36 to further compress spring 38 thereby opening the valve. The isolation valve thus performs the dual function of pressure relief valve.

A pivotal lever 42 is mounted in chamber 24 for rotation about pivot 44. A first end of lever 42 is mechanically connected, as indicated at 46, to the bottom of isolation valve member 30 and moves therewith. The opposite end of lever 42 is pinned to an armature member 48 comprised of magnetic material. Armature member 48 is movable vertically in a bore provided therefor in housing 10. Upward deflection of diaphragm 22 will produce clockwise rotation of lever 42 about pivot 44 with the resultant downward translation of armature 48. Downward motion of the armature will not, of course, occur until the attraction between the armature and associated magnets 50-52 is overcome. This provides a desirable negative rate breakaway mechanism operating characteristic and permits the use of lower forces to operate the device than have been employed in similar prior art apparatus. The ability to employ lower operating forces, in turn, permits a smaller accumulator volume for the same dynamic response with the resultant reduction of mechanical loads within the mechanism.

A magnet assembly, comprising the oppositely disposed magnets 50 and 52, is mounted above armature 48 in an enlarged portion of the bore in which the armature moves. The pole pieces at the lower ends of magnets 50 and 52 are normally shunted by armature 48 and thus the magnetic field produced by the magnets is confined to the region intermediate the facing poles. Although not essential for operation, it is usually considered desirable to provide a shock absorbing member 54 positioned between the upper ends of magnets 50 and 52 and a cap 56; member 54 absorbing the forces generated by impact of armature 48 against the magnets when the right hand end of lever 42 moves in the counterclockwise direction.

Continuing further with a discussion of the machanical features of the disclosed embodiment, housing 10 is provided with an additional bore 60 which provides communication between chambers 24 and 26 via a second timing orifice. The size of the timing orifice will be determined by the diameter of a bore formed in insert 62; the insert being threadably engaged in bore 60 and being replaceable via a removable cap 64 to acheive the desired operating characteristics. This second timing orifice will permit chamber 24 to bleed down to the pressure of chamber 26 in a preselected time whereupon the pressure balance across diaphragm 22 will be reestablished and the isolation valve reopened thereby resetting the control. Thus, the size of the timing orifice in insert 62 dictates the period during which the present invention will provide an electrical output signal after the pressure being monitored stabilizes at a new level lower then the original steady state value. If deemed desirable, the second timing orifice can be employed to bleed down chamber 24 to the ambient atmosphere rather than to chamber 26.

The housing 10 of the present invention will be formed from non-magnetic material and will be provided with a blind hole which terminates adjacent the line of contact between armature 48 and magnets 50 and 52. A reed type magnetic field responsive switch 72 is positioned, in any suitable manner, in the bottom of hole 70 so as to be influenced by the field produced by the magnets when the shunting effect of armature 48 is removed. As noted above, the field between the facing lower pole pieces of magnets 50 and 52 is normally confined by armature 58. However, should the armature be pulled away from the magnets by the upward deflection of diaphragm 22, the field between the magnet pole pieces will expand to encompass switch 72 thereby causing closing of the normally open contacts of the switch. The closing of switch 72 will result in the application of a gating signal to a power switching device, such as a silicon controlled rectifier 74, whereby the power switching device will be rendered conductive and current will be-supplied from a source 76 to a load 78. The load 78 may be the ignition system of a gas turbine engine. The silicon controlled rectifier 74 or equivalent switching device will be selfcommutating whereby the opening of the contacts of reed switch 72 will result in extinguishing of the device and opening of the current path between source 76 and load 78.

To briefly summarize operation of the disclosed embodiment of the invention, the device is shown in its normal deenergized state with the pressure across diaphragm 22 being balanced. The pressure in chamber 26 will closely track the pressure being monitored and should this pressure decrease rapidly a pressure differential will be created across diaphragm 22 since the first timing orifice, as defined by member 35, limits the rate at which the pressure in chamber 24 can decay. When the forces on diaphragm 22 resulting from the pressure differential become sufficient to overcome the attraction of magnets 50-52 for armature 48, the diaphragm 22 will be deflected upwardly thereby closing the isolation valve 18-30 and trapping fluid at a relatively high pressure in chamber 24.

When diaphragm 22 deflects upwardly lever 42 will pivot thereby pulling armature 48 away from the magnet assembly. The field between the poles of magnets 50 and 52 will thereupon no longer be shunted and will expand and cause the closing of the contacts of field responsive switch 72. The closing of switch 72 will, through the action of power switching device 74, apply current from source 76 to a load 78.

The fluid trapped in chamber 24 will, with the isola-' tion valve closed, bleed off either to chamber 26 or the ambient atmosphere via the timing orifice in member 62 and the pressure across diaphragm 22 will, after a preselected time delay, become balanced whereupon biasing spring 28 will force the diaphragm back to its initial position thereby reopening the isolation valve. As the diaphragm moves downwardly the lever 42 will be rotated counterclockwise and amrature 48 will be again attracted to magnets 50-52 thus shunting the magnetic fields and permitting the reopening of the contacts of switch 72. The reopening of the contacts of switch 72 will deenergize the power switching device 74 and isolate the load 78 from the current source 76.

To summarize the unique features of the present invention when compared to the prior art, the invention combines the isolation valve, relief valve and adjustable stop to thereby greatly reduce the weight and complexity of apparatus for providing a signal commensurate with a rate of change of a monitored pressure. The foregoing is accomplished by incorporating a novel penumatic isolation valve into an adjustable stop assembly and additionally providing for the pressure relief function to be integral with the isolation valve function. By using magnetism to provide the primary break-away force the present invention eliminates the need for the shafts and seals to transfer motion through the pressure vessel wall which have characterized the prior art.

While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spiritand scope of the invention. Accoringly, it is to be understood that the present invention has been described by way of illustration and not limitation.

What is claimed is:

1. In a differential pressure responsive device, said device being characterized by a housing having a flexible wall therein for dividing the housing into a pair of chambers, the device further being characterized by means for applying a pressure being monitored continuously to a first of said chambers, the improvement comprising:

means mounted on the flexible wall and defining a restricted path for the flow of fluid therethrough whereby the monitored pressure may be applied to the second chamber via said restricted path;

valve means mounted in the first chamber and cooperating with said restricted flow path defining means to close said restricted flow path when said flexible wall moves in a first direction, the closing of said flow path entrapping fluid in the second chamber;

linkage means connected to the flexible wall for generating a mechanical force commensurate with movements of the wall in said first direction in response to rates of decrease in the monitored pressure greater than a preselected rate;

means positioned within said housing for generating a magnetic field;

armature means connected to said linkage means for movement in response to the generation of a mechanical force thereby, said armature means cooperating with said magnetic field generating means to establish first and second operative conditions; and

magnetic field responsive signal generating means located exteriorly of the housing, said signal generating means providing output signals commensurate with the operative condition established by said armature means and magnetic field generating means.

2. The apparatus of claim 1 wherein said valve means comprises:

adjustable stop means mounted from the housing.

3. The apparatus of claim 2 wherein said adjustable stop means comprises:

a stop member extending into the first chamber, said stop member having a recess therein;

a valve member extending in said stop member recess, said valve member cooperating with said flow path defining means to perform a valving function when said flexible wall moves; and

means resiliently biasing said valve element toward said flow path defining means.

4. The apparatus of claim 3 wherein said armature means is movable relative to said magnetic field generating means and shunts the magnetic field in a field operative condition whereby said field responsive signal generating meansis deenergized.

5. The apparatus of claim 1 further comprising:

means in said housing for defining a timing orifice,

said timing orifice providing communication between the second chamber and a region at a pressure corresponding to that in the first chamber, said timing orifice determining the rate at which fluid trapped in the second chamber will escape to equalize the pressure across the flexible wall whereby said isolation valve will be opened.

6. The apparatus of claim 3 further comprising:

means in said housing for defining a timing orifice, said timing orifice providing communication be tween the second chamber and a region at a pressure corresponding to that in the first chamber, said timing orifice determining the rate at which fluid trapped in the second chamber will escape to equalize the pressure across the flexible wall whereby said isolation valve will be opened.

7. The apparatus of claim 6 wherein said armature means is movable relative to said magnetic field gener- 7 8 ating means and shunts the magnetic field in a first opity of the point of operative cooperation between erative' condition whereby said field responsive signal said armature and fi ld generating means; and

generating means is deenergized.

8. The apparatus of claim 7 wherein said field responh f l t give Signal generating means comprises: 831 SW] c or genera mg slgnas commensura e a magnetic field responsive switch, said switch being with the Position of the flexible Wallmounted to the exterior of the housing in the vicinelectronic circuit means responsive to the state of

Claims (8)

1. In a differential pressure responsive device, said device being characterized by a housing having a flexible wall therein for dividing the housing into a pair of chambers, the device further being characterized by means for applying a pressure being monitored continuously to a first of said chambers, the improvement comprising: means mounted on the flexible wall and defining a restricted path for the flow of fluid therethrough whereby the monitored pressure may be applied to the second chamber via said restricted path; valve means mounted in the first chamber and cooperating with said restricted flow path defining means to close said restricted flow path when said flexible wall moves in a first direction, the closing of said flow path entrapping fluid in the second chamber; linkage means connected to the flexible wall for generating a mechanical force commensurate with movements of the wall in said first direction in response to rates of decrease in the monitored pressure greater than a preselected rate; means positioned within said housing for generating a magnetic field; armature means connected to said linkage means for movement in response to the generation of a mechanical force thereby, said armature means cooperating with said magnetic field generating means to establish first and second operative conditions; and magnetic field responsive signal generating means located exteriorly of the housing, said signal generating means providing output signals commensurate with the operative condition established by said armature means and magnetic field generating means.
2. The apparatus of claim 1 wherein said valve means comprises: adjustable stop means mounted from the housing.
3. The apparatus of claim 2 wherein said adjustable stop means comprises: a stop member extending into the first chamber, said stop member having a recess therein; a valve member located in said stop member recess, said valve member cooperating with said flow path defining means to perform a valving function when said flexible wall moves; and means resiliently biasing said valve element toward said flow path defining means.
4. The apparatus of claim 3 wherein said armature means is movable relative to said magnetic field generating means and shunts the magnetic field in a field operative condition whereby said field responsive signal generating means is deenergized.
5. The apparatus of claim 1 further comprising: means iN said housing for defining a timing orifice, said timing orifice providing communication between the second chamber and a region at a pressure corresponding to that in the first chamber, said timing orifice determining the rate at which fluid trapped in the second chamber will escape to equalize the pressure across the flexible wall whereby said isolation valve will be opened.
6. The apparatus of claim 3 further comprising: means in said housing for defining a timing orifice, said timing orifice providing communication between the second chamber and a region at a pressure corresponding to that in the first chamber, said timing orifice determining the rate at which fluid trapped in the second chamber will escape to equalize the pressure across the flexible wall whereby said isolation valve will be opened.
7. The apparatus of claim 6 wherein said armature means is movable relative to said magnetic field generating means and shunts the magnetic field in a first operative condition whereby said field responsive signal generating means is deenergized.
8. The apparatus of claim 7 wherein said field responsive signal generating means comprises: a magnetic field responsive switch, said switch being mounted to the exterior of the housing in the vicinity of the point of operative cooperation between said armature and field generating means; and electronic circuit means responsive to the state of said switch for generating signals commensurate with the position of the flexible wall.
US3786211A 1972-07-19 1972-07-19 Differential pressure responsive magnetically actuated switch responsive only to sudden pressure changes Expired - Lifetime US3786211A (en)

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4084072A (en) * 1975-05-20 1978-04-11 Aisin Seiki Kabushiki Kaisha Pressure differential switch device
US4396301A (en) * 1981-07-15 1983-08-02 Thiokol Corporation Sensing device for detecting changes in variable quantities
EP0279390A1 (en) * 1987-02-17 1988-08-24 Huba Control Ag Pressure-operated membrane switch
EP0431217A2 (en) * 1989-12-08 1991-06-12 Jan Ballyns Delta P/delta t pressure sensor system
US5068503A (en) * 1989-04-11 1991-11-26 Hans Sladky High-pressure sensor for fluid conditions and method and apparatus using same
US5122628A (en) * 1990-05-25 1992-06-16 Fike Corporation Sudden pressure rise detector
EP0580810A1 (en) * 1991-04-19 1994-02-02 Robertshaw Controls Company Temperature operated switch construction
US6414254B1 (en) * 1999-10-15 2002-07-02 Chiaphua Industries Limited Electrical pressure sensing switch
US6452122B1 (en) * 1999-03-31 2002-09-17 Leroy Peter C. Pressure sensing device

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2869475A (en) * 1951-12-21 1959-01-20 Phillips Petroleum Co Control system
US2980090A (en) * 1956-02-24 1961-04-18 Bendix Corp Fuel injection system
US3240894A (en) * 1962-12-31 1966-03-15 Holley Carburetor Co Differential pressure responsive device
US3305805A (en) * 1963-11-14 1967-02-21 Tann David Proximity switch
US3325612A (en) * 1964-06-26 1967-06-13 Sanders Associates Inc Fluid flow sensing device
US3327079A (en) * 1964-03-12 1967-06-20 Bosch Gmbh Robert Magnetically operated electric switch

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2869475A (en) * 1951-12-21 1959-01-20 Phillips Petroleum Co Control system
US2980090A (en) * 1956-02-24 1961-04-18 Bendix Corp Fuel injection system
US3240894A (en) * 1962-12-31 1966-03-15 Holley Carburetor Co Differential pressure responsive device
US3305805A (en) * 1963-11-14 1967-02-21 Tann David Proximity switch
US3327079A (en) * 1964-03-12 1967-06-20 Bosch Gmbh Robert Magnetically operated electric switch
US3325612A (en) * 1964-06-26 1967-06-13 Sanders Associates Inc Fluid flow sensing device

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4084072A (en) * 1975-05-20 1978-04-11 Aisin Seiki Kabushiki Kaisha Pressure differential switch device
US4396301A (en) * 1981-07-15 1983-08-02 Thiokol Corporation Sensing device for detecting changes in variable quantities
EP0279390A1 (en) * 1987-02-17 1988-08-24 Huba Control Ag Pressure-operated membrane switch
US5068503A (en) * 1989-04-11 1991-11-26 Hans Sladky High-pressure sensor for fluid conditions and method and apparatus using same
EP0431217A2 (en) * 1989-12-08 1991-06-12 Jan Ballyns Delta P/delta t pressure sensor system
EP0431217A3 (en) * 1989-12-08 1991-12-27 Jan Ballyns Pressure sensor system
US5122628A (en) * 1990-05-25 1992-06-16 Fike Corporation Sudden pressure rise detector
EP0580810A1 (en) * 1991-04-19 1994-02-02 Robertshaw Controls Company Temperature operated switch construction
EP0580810A4 (en) * 1991-04-19 1994-04-06 Robertshaw Controls Company
US6452122B1 (en) * 1999-03-31 2002-09-17 Leroy Peter C. Pressure sensing device
US6414254B1 (en) * 1999-10-15 2002-07-02 Chiaphua Industries Limited Electrical pressure sensing switch

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Owner name: COLT INDUSTRIES INC., A PA CORP.

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Effective date: 19870706