US3790928A

US3790928A - Transducer pressure release system

Info

Publication number: US3790928A
Application number: US00872433A
Authority: US
Inventors: O Schoen
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1969-10-29
Filing date: 1969-10-29
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05

Abstract

A transducer pressure release system wherein the transducer element is supported between a radiating and a load mass, both of which are resiliently supported in a watertight housing. A pair of magnetic coacting coils, one of which is affixed to said housing and the other to one of the masses, are supplied current through a control means from a constant voltage source. The control means receives an input signal from a displacement sensor which detects the movement of one of the masses and fixes a current through the coils to restore the masses to a constant separation therebetween, thus providing isolation and proper pressure release.

Description

ijnited States Patent [191 Schoen, Jr.

[ TRANSDUCER PRESSURE RELEASE SYSTEM [75] Inventor: Oscar W. Schoen, Jr., Ontario,

Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

22 Filed: Oct. 29, 1969 21 Appl. No.: 872,433

3,349,367 10/1967 Wisotsky ..340/8X V0. 73466 LDNTROLLED VHF/051.6 UR/ZENT 5o u/zcE Primary Examiner-Richard A. Farley Attorney, Agent, or Firm-Richard S. Sciascia; Arthur A. McGill [57] ABSTRACT A transducer pressure release system wherein the transducer element is supported between a radiating and a load mass, both of which are resiliently supported in a watertight housing. A pair of magnetic coacting coils, one of which is affixed to said housing and the other to one of the masses, are supplied current through a control means from a constant voltage source. The control means receives an input signal from a displacement sensor which detects the movement of one of the masses and fixes a current through the coils to restore the masses to a constant separation therebetween, thus providing isolation and proper pressure release.

6 Claims, 2 Drawing Figures TRANSDUCER PRESSURE RELEASE SYSTEM 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.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to deep underwater transducer mounting and compensation and more particularly pertains to a system of isolation and pressure release wherein a set of coacting electric coils are energized and controlled by the movement of the face element of a transducer structure to maintain a constant spacing of the masses abutting the transducer and to pressure release a ceramic transducer without loss of mechanoacoustic efficiency.

2. Description of the Prior Art In the field of electroacoustic transducers which are subjected to extreme static pressures, it has been the general practice to employ standard pressure release techniques to maintain the efficiency of the transducer at great sea depths. In order to overcome changes in ambient (static) pressure encountered, it has been the practice to minimize the deflection of the radiating mass relative to the transducer element by providing pressure release or an element which will compensate for the environmental hydrostatic pressure. Compressible pressure-relief elements inside the housing have been employed for this purpose. These have generally been of two types. One type is a gas medium such as air within the housing and in contact with the radiating mass. The air or gas pressure is changed in accordance with the ambient hydrostatic pressure to provide the necessary stiffness. The other technique involves the use of solid materials, some of which contain air pockets or cells, such as foam rubber and plastics. Such techniques have been found unsatisfactory at great depths in that these conventional materials collapse under extreme hydrostatic pressure and their pressure release capabilities are substantially reduced or eliminated entirely. Further, since these materials act as non-linear springs, a loss in compliance and an increase in internal loss of the material occurs, as the vibrating mass or element is increasingly coupled to the housing and results in a marked decrease in efficiency with an increase in the resonant frequency.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a pressure release system for a deep submergence transducer that has all the advantages of similarly employed prior art devices and has none of the above described disadvantages. To attain this, the present invention provides a unique transducer mass arrangement wherein the stress applied to the transducer by the environmental pressure on the radiating mass is compensated and serves as a pressure release. The relative movement of the load mass is detected and the current through a set of opposing magnetic coils is controlled thereby to apply a restoring force to one of the transducer masses.

An object of the present invention is to provide a simple, inexpensive, direct and reliable pressure release arrangement for a deeply submerged transducer.

Another object is to provide an automatic hydrostatic environmental pressure compensation structural arrangement for underwater transducers.

A further object is to provide a self compensating efficient transducer without loss of compliance, increase in internal loss and decoupled from the housing.

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 drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a structural cross-sectional view of a complete transducer embodiment made in accordance with the principle of this invention and employing a LVDT displacement element; and,

FIG. 2 is another embodiment made in accordance with this invention showing in cross-section the structural arrangement and in schematic the wiring arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the illustrated embodiment of FIG. 1, a watertight enclosure or housing 10 having an openend 11 is closed thereacross by a radiating end mass 12. The end mass 12 is supported by a ring flange 13 to which it is circumferentially joined by a waterproof elastomeric adhesive 14 such as vulcanized rubber or epoxy. The opposite end of the ring flange 13 is bolted as at 15 to the housing 10 with a waterproof ring gasket 16 therebetween. This form of mounting permits limited movement of the radiating mass into and out of the housing while it is in direct face contact with the surrounding external liquid environment and resiliently supported by the housing. Supported centrally by the radiating mass is a cylindrical ceramic transducer 17 (which may be of other forms). One such support, as illustrated, is by threading one end 18 of the transducer in a mating threaded opening 19 in the inner face of mass 12. Thus the transducer and the radiating mass act relatively as a unitary vibrating structural element. As is standard practice, the transducer has been polarized and provided with electroded faces across which the electrical signal may be applied, causing the transducer to contract and elongate, which in turn vibrates the mass 12 therewith. The above described details have been deleted from the drawing, as well as the electrical connections thereto, for the sake of simplicity and clarity. Since the transducer will elongate it must be provided with some means (backing) to hold one end thereof fixed to permit its motion to be applied to the mass 12. For this purpose an extremely large non-radiating backing end mass 20 is provided. Even though this nonradiating mass is made as large as practically possible, some motion will exist and must be isolated from the generated acoustic output signal. The mass is cemented or affixed along its peripheral face 21 to the housing by a pressure release material such as is the case of the radiating mass 12. Imperfections of these isolating techniques arise from the use of these materials placed between the transducer housing and the vibratingelement. As the external pressure is increased, the transducer is forced to translate and bear against this isolation material. Since this material acts as a non-linear spring, this results in a loss of compliance and an increase in internal loss of the material and the vibrating element becomes increasingly mechanically coupled to the housing.

The loading end mass is provided with a central cylindrical extension 22 which extends into the hollow core of the transducer but is not in contact therewith. The end face 23 of the ceramic transducer tightly abuts the end load mass 22. Carried by the opposite face 24 of the load mass 20 for movement therewith is the core 25 and arm 26 of the linear variable differential transformer (LVDT) 27. The transformer itself is an electro-mechanical transducer which produces a voltage output directly proportional to the displacement of a movable armature or magnetic core 25. The core is axially positioned inside three transformer coils consisting of a primary 28 and two secondaries 29 connected in series opposition which are encased and fixedly supported by the rear housing wall 29 by structural support 30. When the primary is energized with alternating current from an excitation source 32, a voltage output appears across the secondary circuit when the magnetic core is displaced from its central or null position. Suitable linear variable differential transformers are presently available on the commercial market. Such transformers are fully described in the data sheets of Columbia Research Laboratories, Inc. of Woodlyn, Pa. and available therefrom.

An annular recess 33 in the forward face 34 of load mass 20 carries a solenoidally wound coil 35 so as to provide an axially directed magnetic field when excited. Disposed forward of and in face to face relation with said load mass is a coil support member 36 which is in a form so that its outer edge surface 37 is rigidly fastened to the housing 10 and its central portion 38 deleted to permit the passage therethrough of the transducer 17. This support member is also provided with an annular recess 39 which is opposite and in registration with load mass recess 33 and has therein a solenoid coil 40. The

coils

35 and 40 are coupled and connected to a variable current source 41 in a manner so that their respective generated magnetic fields coact to produce a force on the load mass 20 directed toward the radiating mass 12. This in effect forces the transducer in that direction (P,,,,,,,) so as to compensate for the external hydrostatic pressure (P To this end, the displacement voltage derived from the LVDT is applied to the control input of the source 41 to control the current supplied to the two coacting coils and thereby hold the transducer in a fixed position irrespective of the hydrostatic pressure applied to the transducer without coupling to the housing.

Consider now the embodiment shown in FIG. 2 wherein a portion of the entire structure is similar or identical to that disclosed in FIG. 1. The housing 100, the radiating mass 112 and its associated parts, the ceramic transducer 117, as well as the load mass 120 are such similar components. Here the displacement sensing means employed includes a piezoresistive transducer or pressure sensitive resistance element, some of which are fully described in the data sheets of Clark Electronic Laboratories of Palm Springs Calif, and in the February 1963 issue of Instruments and Control Systems on pages 93 and 94. Such materials respond to changes in applied pressure with large changes in electrical resistance and hence are referred to as pressure transducers. Affixed rigidly to the rear wall 124 of mass 120 is push rod 142 whose opposite end terminates at one electrode 143, which with electrode 144 forms a sandwich for the piezoresistive material 145. Electrode 144 is insulated from the housing by a backing plate 146 which is supported'by the housing rear wall 130. Annular support 136 fastened to the housing along its peripheral edge is provided with an annular recess 139 and carries therein solenoid coil 140. The coil support is disposed proximate the forward portion of the housing with the coil face directed rearwardly. A second coil support member 146 is carried by the radiating mass 112 on an annular arm 147 which is affixed thereto and the supported coil 148 is in face to face relation with opposing coil 140. The electrical resistance of the piezoresistive material decreases when it is compressed. One electrode 144 is connected to base 149 'of transistor 150 while the other electrode 143 is connected via variable limiting resistor 151 to the emitter 152 of the transistor. The coils are tied in parallel with one end thereof connected to the collector 153 and with the other end tied to one output terminal 154 of constant voltage supply 155. This output terminal 154 is also connected to the base 149 through fixed resistor 156. The other output terminal 157 is connected to one terminal of the limiting resistor 151.

When the piezoresistive material is compressed by hydrostatic pressure on the radiating mass the resultant reduction in resistance causes a more positive voltage to appear at the base terminal 149 terminating in an increased current through the coils. This increase in coil current increases the magnetic force so as to increase the force P and offset the hydrostatic force P and thereby provide the necessary pressure release compensation therefor.

I claim:

1. An automatic pressure release system for an underwater transducer arrangement which comprises:

a waterproof housing having an opening at one end thereof,

a radiating mass resiliently mounted across said one end,

a load mass resiliently supported in said housing for movement toward and away from said radiating mass,

a transducer element supported between and in contact with said masses,

a pair of coacting magnetic field coils, one of said coils rigidlyaffixed to said housing and the other of said coil coupled to one of said masses,

a source of electrical energy for activating said coils,

a displacement sensing means coupled to said load mass for sensing the displacement thereof and providing an output dependent on said displacement,

a control means connected to receive said sensing means output and coupling therethrough said source and said coils for automatically controlling the activation of said coils to maintain a constant separation between said coils, independent of the hydrostatic pressure externally applied to said radiating mass.

2. The pressure release system according to claim 1 wherein said source of electrical energy is a constant voltage source.

3. The pressure release system according to claim 1 wherein said control means includes wherein 531d dlsplacemem Sensmg means 15 3 1111631 a transistor having a base, emitter and collector elevariable displacement transformer.

4. The pressure release system according to claim 2 wherein said displacement sensing means is a piezoresistive element.

ment, circuit means connecting the output of said piezoresistive element between said base and said emitter,

5. The pressure release system according to claim 3 and wherein said control means is a voltage controlled varisecond cn'cult means Connectmg 531d Source between able current source. said emitter and sald base.

6. The pressure release system according to claim 4

Claims

1. An automatic pressure release system for an underwater transducer arrangement which comprises: a waterproof housing having an opening at one end thereof, a radiating mass resiliently mounted across said one end, a load mass resiliently supported in said housing for movement toward and away from said radiating mass, a transducer element supported between and in contact with said masses, a pair of coacting magnetic field coils, one of said coils rigidly affixed to said housing and the other of said coil coupled to one of said masses, a source of electrical energy for activating said coils, a displacement sensing means coupled to said load mass for sensing the displacement thereof and providing an output dependent on said displacement, a control means connected to receive said sensing means output and coupling therethrough said source and said coils for automatically controlling the activation of said coils to maintain a constant separation between said coils, independent of the hydrostatic pressure externally applied to said radiating mass.

3. The pressure release system according to claim 1 wherein said displacement sensing means is a linear variable displacement transformer.

5. The pressure release system according to claim 3 wherein said control means is a voltage controlled variable current source.

6. The pressure release system according to claim 4 wherein said control means includes a transistor having a base, emitter and collector element, circuit means connecting the output of said piezoresistive element between said base and said emitter, and second circuit means connecting said source between said emitter and said base.