Pressure transducer with media isolation and negative pressure measuring

Abstract

A pressure sensor die is provided with a flexible membrane and a plunger which combine to amplify a low pressure signal while also providing media isolation between a fluid being measured and the internal components of a pressure sensor. One embodiment of the pressure sensor disposes an end of the plunger in direct contact with a pressure sensor die while another embodiment disposes an elastomeric diaphragm between the plunger and the pressure sensor die. This second embodiment creates a chamber between the plunger and the pressure sensor die in which a fluid is captured by movement of the plunger. The captured fluid is decreased in volume by movement of the plunger and the resulting increase in pressure in transmitted to a pressure sensitive portion of a pressure sensor die. The device is particularly useful in conjunction with applications where media isolation is required between the fluid being measured and the components of the pressure sensor, such as kidney dialysis machines. It is also particularly useful where electrical isolation is required to prevent any possible shock hazard that could otherwise result from fluid communication between the fluid being measured and the electrically conductive portions of the pressure sensor. One embodiment of the pressure sensor comprises a means for preloading a pressure sensor die at atmospheric pressure in order to permit the device to measure both positive and negative pressures within the first chamber.