Capacitive differential pressure sensor with coupled diaphragms

Details Capacitive differential pressure sensor with coupled diaphragms Capacitive differential pressure sensor with coupled diaphragms

2000-09-06

2002-08-13

Oen, William (Department: 2855)

Measuring and testing

Fluid pressure gauge

Diaphragm

Reexamination Certificate

active

06431003

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to pressure sensors, and more particularly, to micromachined differential pressure sensors.
Differential pressure sensors are used in a wide variety of settings to compare the relative pressures of two fluids. Most existing differential pressure sensors include a pair of diaphragms mounted in a housing, and each diaphragm is exposed to the pressure of one of the fluids. The pressure of each fluid independently deflects the associated diaphragm such that the pressure of each fluid can be calculated, for example, using a look-up chart referencing the deflection of each diaphragm. The difference in pressure of the two fluids may then be calculated. However, the use of two conventional capacitive sensor to measure differential pressure may not consistently provide accurate results.
Micromachining techniques are often used to form transducers used in conjunction with small components or in confined spaces. However, most existing differential pressure sensors cannot be used to measure high common pressure, are relatively large and expensive, and typically include a metallic or ceramic diaphragm. Metallic or ceramic diaphragms are relatively inflexible and difficult to machine. Furthermore, the gap of the capacitor in existing capacitive pressure sensors may be exposed to a media, which can compromise the accuracy of the sensor. Accordingly, there is a need for a improved differential pressure sensor, and a quick and inexpensive method for manufacturing a micromachined differential pressure sensor. There is also a need for a micromachined differential pressure sensor that can accurately measure differential pressure.
SUMMARY OF THE INVENTION
The present invention is a micromachined capacitive differential pressure sensor which includes a pair of diaphragms, each diaphragm being exposed to a fluid. The diaphragms are coupled together for movement, thereby increasing the accuracy of the sensor and reducing the sensitivity of the sensor to common pressure. The sensor is also relatively easy and inexpensive to manufacture. The gap between the capacitors is not exposed to the external media, thereby providing a stable capacitance value.
In a preferred embodiment, the invention is a pressure sensor for measuring the differential pressure of a first and a second fluid. The sensor includes a housing having an internal opening, a first diaphragm disposed in the opening and exposed to the first fluid, and a second diaphragm disposed in the opening and exposed to the second fluid. The first diaphragm and the second diaphragm are each made of a conductive material and coupled together such that the differential pressure of the first and second fluids deflects the first and second diaphragms in the same direction. The deflection of the first and second diaphragms can be sensed to determine the differential pressure.
Other objects and advantages of the present invention will be apparent from the following description and the accompanying drawings.


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PCT International Search Report; PCT Application No. PCT/US 00/07646; filed on Mar. 23, 2000.

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