Pressure transmitter with simplified pressure sensing head

Claim 2

A pressure sensing head comprising head structure having a substantially flat back-up surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said surface so that said first face faces said surface, means for applying a fluid pressure force to said second face which is representative of a fluid pressure to be sensed, said surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said surface, a first fluid chamber of expansible volume having fluid communication with said first face, and a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and exerting a deforming force on said first face which deforms and bows-out said diaphragm away from said surface into a dome shape to form a second fluid chamber between said first face and said surface which is completely filled with said fluid, said diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said diaphram about its said normal bowed-out position to only that extent which causes said diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, whereby the pressure of said fill fluid is consistently representative of said fluid pressure to be sensed throughout said normal operating range.

Claim 3

Apparatus as specified in claim 1, wherein said first chamber includes a deflectable control diaphragm as one of the walls of said first chamber.

Claim 4

Apparatus as specified in claim 2, wherein the stiffness of said control diaphragm is of the order of one hundred times the stiffness of said barrier diaphragm.

Claim 5

A pressure sensing head comprising head structure having a substantially flat back-up surface and a second surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said back-up surface so that said first face faces said back-up surface, means for applying a fluid pressure force to said second face which is representative of a fluid pressure to be sensed, said back-up surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said second surface to form a first fluid chamber of expansible volume between one side of said control diaphragm and said second surface, passage means providing fluid communication between said first chamber and said first face, and a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said passage means and exerting a deforming force on said first face which deforms and bows-out said barrier diaphragm away from said back-up surface into a dome shape to form a second fluid chamber between said first face and said back-up surface which is completely filled with said fluid, said barrier diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said barrier diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said barrier diaphragm about its said normal bowed-out position to only that extent which causes said barrier diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, whereby the pressure of said fill fluid is consistently representative of said fluid pressure to be sensed throughout said normal operating range.

Claim 6

A pressure sensing head comprising head structure having a substantially flat back-up surface and a second surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said back-up surface so that said first face faces said back-up surface, means for applying a fluid pressure force to said second face which is representative of a fluid pressure to be sensed, said back-up surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said second surface to form a first fluid chamber of expansible volume between one side of said control diaphragm and said second surface, passage means providing fluid communication between said first chamber and said first face, and a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said passage means and exerting a deforming force on said first face which deforms and bows-out said barrier diaphragm away from said back-up surface into a dome shape to form a second fluid chamber between said first face and said back-up surface which is completely filled with said fluid, said barrier diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said barrier diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said barrier diaphragm about its said normal bowed-out position to only that extent which causes said barrier diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, whereby the pressure of said fill fluid is consistently representative of said fluid pressure to be sensed throughout said normal operating range.

Claim 7

A pressure sensing head comprising head structure having first and second substantially flat back-up surfaces, a third surface, and a fourth surface, a first substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said first back-up surface so that said first face faces said first back-up surface, a second substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said second back-up surface so that said first face of said second barrier diaphragm faces said second back-up surface, means for applying a first fluid pressure force to said second face of said first barrier diaphragm which is representative of a first fluid pressure to be sensed, said first back-up surface physically matching said first face of said first barrier diaphragm sufficiently to fully back up and support said first barrier diaphragm and prevent its deleterious deformation in the presence of values of said first fluid pressure force which force said first barrier diaphragm to bottom-out against said first back-up surface, means for applying a second fluid pressure force to said second face of said second barrier diaphragm which is representative of a second fluid pressure to be sensed, said second back-up surface physically matching said first face of said second barrier diaphragm sufficiently to fully back up and support said second barrier diaphragm and prevent its deleterious deformation in the presence of values of said second fluid pressure force which force said second barrier diaphragm to bottom-out against said second back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said third and fourth surfaces to form a first fluid chamber of expansible volume between one side of said control diaphragm and said third surface, and to form a second fluid chamber of expansible volume between the other side of said control diaphragm and said fourth surface, first passage means providing fluid communication between said first chamber and said first face of said first barrier diaphragm, second passage means providing fluid communication between said second chamber and said first face of said second barrier diaphragm, a first preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said first passage means and exerting a deforming force on said first face of said first barrier diaphragm which deforms and bows-out said first barrier diaphragm away from said first back-up surface into a dome shape to form a third fluid chamber between said first face of said first barrier diaphragm and said first back-up surface which is completely filled with said fluid, and a second preselected quantity of a substantially incompressible fill fluid completely filling said second chamber and said second passage means and exerting a deforming force on said first face of said second barrier diaphragm which deforms and bows-out said second barrier diaphragm away from said second back-up surface into a dome shape to form a fourth fluid chamber between said first face of said second barrier diaphragm and said second back-up surface which is completely filled with said fluid, said stiffnesses of said barrier diaphragms and said quantities of said fill fluids, and hence said deforming forces, being preselected, in the absence of said fluid pressure forces on said second faces, to cause said deforming forces normally to bow-out the respective barrier diaphragms by preselected amounts to normal bowed-out positions for which the traversal of the difference between said first and second fluid pressure forces throughout its normal operating range deflects said barrier diaphragms about their normal bowed-out positions to only those extents which cause said barrier diaphragms to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform unvarying, and consistent deflection vs. pressure characteristic, whereby the difference between the pressures of said first and second fill fluids is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 8

A pressure sensing head comprising head structure having first and second substantially flat back-up surfaces, a third surface, and a fourth surface, a first substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said first back-up surface so that said first face faces said first back-up surface, a second substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said second back-up surface so that said first face of said second barrier diaphragm faces said second back-up surface, means for applying a first fluid pressure force to said second face of said first barrier diaphragm which is representative of a first fluid pressure to be sensed, said first back-up surface physically matching said first face of said first barrier diaphragm sufficiently to fully back up and support said first barrier diaphragm and prevent its deleterious deformation in the presence of values of said first fluid pressure force which force said first barrier diaphragm to bottom-out against said first back-up surface, means for applying a second fluid pressure force to said second face of said second barrier diaphragm which is representative of a second fluid pressure to be sensed, said second back-up surface physically matching said first face of said second barrier diaphragm sufficiently to fully back up and support said second barrier diaphragm and prevent its deleterious deformation in the presence of values of said second fluid pressure force which force said second barrier diaphragm to bottom-out against said second back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said third and fourth surfaces to form a first fluid chamber of expansible volume between one side of said control diaphragm and said third surface, and to form a second fluid chamber of expansible volume between the other side of said control diaphragm and said fourth surface, first passage means providing fluid communication between said first chamber and said first face of said first barrier diaphragm, second passage means providing fluid communication between said second chamber and said first face of said second barrier diaphragm, a first preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said first passage means and exerting a deforming force on said first face of said first barrier diaphragm which deforms and bows-out said first barrier diaphragm away from said first back-up surface into a dome shape to form a third fluid chamber between said first face of said first barrier diaphragm and said first back-up surface which is completely filled with said fluid, and a second preselected quantity of a substantially incompressible fill fluid completely filling said second chamber and said second passage means and exerting a deforming force on said first face of said second barrier diaphragm which deforms and bows-out said second barrier diaphragm away from said second back-up surface into a dome shape to form a fourth fluid chamber between said first face of said second barrier diaphragm and said second back-up surface which is completely filled with said fluid, said stiffnesses of said barrier diaphragms and said quantities of said fill fluids, and hence said deforming forces, being preselected, in the absence of said fluid pressure forces on said second faces, to cause said deforming forces normally to bow-out the respective barrier diaphragms by preselected amounts to normal bowed-out positions for which the traversal of the difference between said first and second fluid pressure forces throughout its normal operating range deflects said barrier diaphragms about their normal bowed-out positions to only those extents which cause said barrier diaphragms to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform unvarying, and consistent deflection vs. pressure characteristic, whereby the difference between the pressures of said first and second fill fluids is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 9

A differential pressure to electrical signal transmitter comprising head structure having a substantially flat back-up surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said surface so that said first face faces said surface, means for applying a fluid pressure force to said second face which is representative of a first fluid pressure to be sensed, said surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said surface, a first fluid chamber of expansible volume having fluid communication with said first face, a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and exerting a deforming force on said first face which deforms and bows-out said diaphragm away from said surface into a dome shape to form a second fluid chamber between said first face and said surface which is completely filled with said fluid, said diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said diaphragm about its said normal bowed-out position to only that extent which causes said diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, differential pressure sensor means including a sensing element having first and second element portions and an electrical output connection and operative to produce in said output connection a signal representative of the difference between the pressures of two fluids acting, respectively, on said first and second element portions, first means for applying the pressure of said fill fluid to said first element portion, and second means for applying to said second element portion a second fluid pressure to be sensed, whereby the difference between the pressures acting on said first and second element portions is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 10

A differential pressure to electrical signal transmitter comprising head structure having a substantially flat back-up surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said surface so that said first face faces said surface, means for applying a fluid pressure force to said second face which is representative of a first fluid pressure to be sensed, said surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said surface, a first fluid chamber of expansible volume having fluid communication with said first face, a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and exerting a deforming force on said first face which deforms and bows-out said diaphragm away from said surface into a dome shape to form a second fluid chamber between said first face and said surface which is completely filled with said fluid, said diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said diaphragm about its said normal bowed-out position to only that extent which causes said diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, differential pressure sensor means including a sensing element having first and second element portions and an electrical output connection and operative to produce in said output connection a signal representative of the difference between the pressures of two fluids acting, respectively, on said first and second element portions, first means for applying the pressure of said fill fluid to said first element portion, and second means for applying to said second element portion a second fluid pressure to be sensed, whereby the difference between the pressures acting on said first and second element portions is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 11

Apparatus as specified in claim 6, wherein said first chamber includes a deflectable control diaphragm as one of the walls of said first chamber.

Claim 12

Apparatus as specified in claim 7, wherein the stiffness of said control diaphragm is of the order of one hundred times the stiffness of said barrier diaphragm.

Claim 13

Apparatus as specified in claim 6, wherein said sensor means is located at a position which is remote from said head structure, said first means includes a capillary tube which is connected between said first chamber and said sensor means and which is filled with said fill fluid, and said fill fluid pressure is transmitted to said first element portion by said fill fluid in said tube.

Claim 14

A differential pressure to electrical signal transmitter comprising head structure having a substantially flat back-up surface and a second surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said back-up surface so that said first face faces said back-up surface, means for applying a fluid pressure force to said second face which is representative of a first fluid pressure to be sensed, said back-up surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said second surface to form a first fluid chamber of expansible volume between one side of said control diaphragm and said second surface, differential pressure sensor means including a sensing element having first and second element portions and an electrical output connection and operative to produce in said output connection a signal representatiive of the difference between the pressures of two fluids acting, respectively, on said first and second element portions, passage means providing fluid communication between said first chamber, said first face, and said first element portion, a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said passage means and exerting a deforming force on said first face which deforms and bows-out said barrier diaphragm away from said back-up surface into a dome shape to form a second fluid chamber between said first face and said back-up surface which is completely filled with said fluid, said barrier diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said barrier diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said barrier diaphragm about its said normal bowed-out position to only that extent which causes said barrier diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, and means for applying to said second element portion a second fluid pressure to be sensed, whereby the difference between the pressures acting on said first and second element portions is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 15

A differential pressure to electrical signal transmitter comprising head structure having a substantially flat back-up surface and a second surface, a substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said back-up surface so that said first face faces said back-up surface, means for applying a fluid pressure force to said second face which is representative of a first fluid pressure to be sensed, said back-up surface physically matching said first face sufficiently to fully back up and support said diaphragm and prevent its deleterious deformation in the presence of values of said fluid pressure force which force said diaphragm to bottom-out against said back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said second surface to form a first fluid chamber of expansible volume between one side of said control diaphragm and said second surface, differential pressure sensor means including a sensing element having first and second element portions and an electrical output connection and operative to produce in said output connection a signal representatiive of the difference between the pressures of two fluids acting, respectively, on said first and second element portions, passage means providing fluid communication between said first chamber, said first face, and said first element portion, a preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said passage means and exerting a deforming force on said first face which deforms and bows-out said barrier diaphragm away from said back-up surface into a dome shape to form a second fluid chamber between said first face and said back-up surface which is completely filled with said fluid, said barrier diaphragm stiffness and said fill fluid quantity, and hence said deforming force, being preselected, in the absence of said fluid pressure force on said second face, to cause said deforming force normally to bow-out said barrier diaphragm by a preselected amount to a normal bowed-out position for which the traversal of said fluid pressure force throughout its normal operating range deflects said barrier diaphragm about its said normal bowed-out position to only that extent which causes said barrier diaphragm to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, and means for applying to said second element portion a second fluid pressure to be sensed, whereby the difference between the pressures acting on said first and second element portions is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 16

Apparatus as specified in claim 10, wherein stiffness of said control diaphragm is of the order of one hundred times the stiffness of said barrier diaphragm.

Claim 17

Apparatus as specified in claim 10, wherein said sensor means is located at a position which is remote from said head structure, said passage means includes a capillary tube which is connected between said first chamber and said sensor means and which is filled with said fill fluid, and said fill fluid pressure is transmitted to said first element portion by said fill fluid in said tube.

Claim 18

A differential pressure to electrical signal transmitter comprising head structure having first and second substantialy flat back-up surfaces, a third surface, and a fourth surface, a first substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said first back-up surface so that said first face faces said first back-up surface, a second substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said second back-up surface so that said first face of said second barrier diaphragm faces said second back-up surface, means for applying a first fluid pressure force to said second face of said first barrier diaphragm which is representative of a first fluid pressure to be sensed, said first back-up surface physically matching said first face of said first barrier diaphragm sufficiently to fully back up and support said first barrier diaphragm and prevent its deleterious deformation in the presence of values of said first fluid pressure force which force said first barrier diaphragm to bottom-out against said first back-up surface, means for applying a second fluid pressure force to said second face of said second barrier diaphragm which is representative of a second fluid pressure to be sensed, said second back-up surface physically matching said first face of said second barrier diaphragm sufficiently to fully back up and support said second barrier diaphragm and prevent its deleterious deformation in the presence of values of said second fluid pressure force which force said second barrier diaphragm to bottom-out against said second back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said third and fourth surfaces to form a first fluid chamber of expansible volume between one side of said control diaphragm and said third surface, and to form a second fluid chamber of expansible volume between the other side of said control diaphragm and said fourth surface, differential pressure sensor means including first and second sensor chambers, an electrical output connection, and a sensing element which is subjected to and responsive to the pressure difference between fluids within said first and second sensor chambers to produce in said output connection a signal representative of said pressure difference, first passage means providing fluid communication between said first fluid chamber, said first face of said first barrier diaphragm, and said first sensor chamber, second passage means providing fluid communication between said second fluid chamber, said first face of said second barrier diaphragm, and said second sensor chamber, a first preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said first passage means and exerting a deforming force on said first face of said first barrier diaphragm which deforms and bows-out said first barrier diaphragm away from said first back-up surface into a dome shape to form a third fluid chamber between said first face of said first barrier diaphragm and said first back-up surface which is completely filled with said fluid, and a second preselected quantity of a substantially incompressible fill fluid completely filling said second chamber and said second passage means and exerting a deforming force on said first face of said second barrier diaphragm which deforms and bows-out said second barrier diaphragm away from said second back-up surface into a dome shape to form a fourth fluid chamber between said first face of said second barrier diaphragm and said second back-up surface which is completely filled with said fluid, said stiffnessess of said barrier diaphragms and said quantities of said fill fluids, and hence said deforming forces, being preselected, in the absence of said fluid pressure forces on said second faces, to cause said deforming forces normally to bow-out the respective barrier diaphragms by preselected amounts to normal bowed-out positions for which the traversal of the difference between said first and second fluid pressure forces throughout its normal operating range deflects said barrier diaphragms about their normal bowed-out positions to only those extents which cause said barrier diaphragms to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, whereby the difference between the pressures of said fluids within said first and second sensor chambers is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 19

A differential pressure to electrical signal transmitter comprising head structure having first and second substantialy flat back-up surfaces, a third surface, and a fourth surface, a first substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said first back-up surface so that said first face faces said first back-up surface, a second substantially flat, deformable barrier diaphragm of a preselected stiffness having first and second faces and a peripheral edge which is sealed to said second back-up surface so that said first face of said second barrier diaphragm faces said second back-up surface, means for applying a first fluid pressure force to said second face of said first barrier diaphragm which is representative of a first fluid pressure to be sensed, said first back-up surface physically matching said first face of said first barrier diaphragm sufficiently to fully back up and support said first barrier diaphragm and prevent its deleterious deformation in the presence of values of said first fluid pressure force which force said first barrier diaphragm to bottom-out against said first back-up surface, means for applying a second fluid pressure force to said second face of said second barrier diaphragm which is representative of a second fluid pressure to be sensed, said second back-up surface physically matching said first face of said second barrier diaphragm sufficiently to fully back up and support said second barrier diaphragm and prevent its deleterious deformation in the presence of values of said second fluid pressure force which force said second barrier diaphragm to bottom-out against said second back-up surface, a control diaphragm mounted in spaced and peripherally sealed relationship to said third and fourth surfaces to form a first fluid chamber of expansible volume between one side of said control diaphragm and said third surface, and to form a second fluid chamber of expansible volume between the other side of said control diaphragm and said fourth surface, differential pressure sensor means including first and second sensor chambers, an electrical output connection, and a sensing element which is subjected to and responsive to the pressure difference between fluids within said first and second sensor chambers to produce in said output connection a signal representative of said pressure difference, first passage means providing fluid communication between said first fluid chamber, said first face of said first barrier diaphragm, and said first sensor chamber, second passage means providing fluid communication between said second fluid chamber, said first face of said second barrier diaphragm, and said second sensor chamber, a first preselected quantity of a substantially incompressible fill fluid completely filling said first chamber and said first passage means and exerting a deforming force on said first face of said first barrier diaphragm which deforms and bows-out said first barrier diaphragm away from said first back-up surface into a dome shape to form a third fluid chamber between said first face of said first barrier diaphragm and said first back-up surface which is completely filled with said fluid, and a second preselected quantity of a substantially incompressible fill fluid completely filling said second chamber and said second passage means and exerting a deforming force on said first face of said second barrier diaphragm which deforms and bows-out said second barrier diaphragm away from said second back-up surface into a dome shape to form a fourth fluid chamber between said first face of said second barrier diaphragm and said second back-up surface which is completely filled with said fluid, said stiffnessess of said barrier diaphragms and said quantities of said fill fluids, and hence said deforming forces, being preselected, in the absence of said fluid pressure forces on said second faces, to cause said deforming forces normally to bow-out the respective barrier diaphragms by preselected amounts to normal bowed-out positions for which the traversal of the difference between said first and second fluid pressure forces throughout its normal operating range deflects said barrier diaphragms about their normal bowed-out positions to only those extents which cause said barrier diaphragms to deflect without oil canning, and thus to deflect with only an essentially continuous, uniform, unvarying, and consistent deflection vs. pressure characteristic, whereby the difference between the pressures of said fluids within said first and second sensor chambers is consistently representative of the difference between said first and second fluid pressures to be sensed throughout said normal operating range.

Claim 20

Apparatus as specified in claim 13, wherein the stiffness of said control diaphragm is of the order of one hundred times the stiffnes of said barrier diaphragms.

Claim 21

Apparatus as specified in claim 13, wherein said sensor means is located at a position which is remote from said head structure, said first passage means includes a first capillary tube which is connected between said first fluid chamber and said first sensor chamber, which is filled with said first fill fluid, and which provides said fluid communication with said first sensor chamber, and said second passage means includes a second capillary tube which is connected between said second fluid chamber and said second sensor chamber, which is filled with said second fill fluid, and which provides said fluid communication with said second sensor chamber.