Differential pressure transmitter with pressure sensor protection

A differential pressure to electrical signal transmitter comprising

• a head structure having a plurality of surfaces,
• a first barrier diaphragm mounted in spaced and sealed relationship to a first one of said surfaces to form a first fluid chamber between one face of said first diaphragm and said first surface,
• a second barrier diaphragm mounted in spaced and sealed relationship to a second one of said surfaces to form a second fluid chamber between one face of said second diaphragm and said second surface,
• means for applying a first force to the other face of said first diaphragm which is representative of a first fluid pressure and which urges said first diaphragm toward said first surface,
• means for applying a second force to the other face of said second diaphragm which is representative of a second fluid pressure and which urges said second diaphragm toward said second surface,
• control diaphragm means mounted in spaced and sealed relationship to third and fourth ones of said surfaces to form a third fluid chamber between one face of said diaphragm means and said third surface, and to form a fourth fluid chamber between another face of said diaphragm means and said fourth surface,
• differential pressure sensor means located at a position remote from said head structure and 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, said element experiencing only a minute displacement as said pressure difference traverses its normal operating range,
• first passage means interconnecting said first chamber and said third chamber,
• second passage means interconnecting said second chamber and said fourth chamber,
• a first length of capillary tubing extending between said head structure and said sensor means and constituting a fluid connection between said first element portion and said first and third chambers,
• a first substantially incompressible fill fluid completely filling said first and third chambers, said first passage means, and said first length of capillary tubing and acting on said first element portion by way of said first length of capillary tubing,
• a second length of capillary tubing extending between said head structure and said sensor means and constituting a fluid connection between said second element portion and said second and fourth chambers, and
• a second substantially incompressible fill fluid completely filling said second and fourth chambers, said second passage means, and said second length of capillary tubing and acting on said second element portion by way of said second length of capillary tubing, the dimensions of said first and second lengths of capillary tubing being such as to minimize the transfer of sensor-damaging heat and pulses through said fill fluids from said head structure to said element,
• the relative stiffness of said diaphragm means and said barrier diaphragms being made such that an excessive value of either of said first and second fluid pressures causes the corresponding one of said barrier diaphragms to bottom-out on the corresponding one of said first and second surfaces, and causes said diaphragm means to deflect away from the corresponding one of said third and fourth surfaces, thereby preventing said pressure difference on said element from exceeding said normal operating range and adversely displacing said element, wherein
• said control diaphragm means consists of first and second control diaphragms,
• said one face of said diaphragm means is one face of said first control diaphragm,
• said another face of said diaphragm means is one face of said second control diaphragm,
• said head structure has fifth and sixth surfaces,
• said first control diaphragm is mounted in spaced and sealed relationship to said fifth surface to form a fifth fluid chamber between the other face of said first control diaphragm and said fifth surface,
• said second control diaphragm is mounted in spaced and sealed relationship to said sixth surface to form a sixth fluid chamber between the other face of said second control diaphragm and said sixth surface,
• said first passage means includes an interconnection to said sixth chamber,
• said second passage means includes an interconnection to said fifth chamber,
• said first fill fluid completely fills said sixth chamber, and
• said second fill fluid completely fills said fifth chamber.