Flow and pressure sensor for harsh fluids

#The present invention relates generally to sensors utilized to detect the quality of fluids, including gas and liquid. The invention also relates to thermal sensors of such fluids, such as fluid flow or property sensors implemented on silicon in microstructure form. The present invention additionally relates to differential pressure sensors utilized in association with flow sensors. The present invention specifically relates to techniques and systems thereof for preventing contamination of such sensors which may come into contact with harsh gases or liquids that can corrode, contaminate with radioactive or live pathogens, freeze-up, overheat, deposit particles or condensate on sensing elements of such sensors.

#Flow sensors are utilized in a variety of fluid-sensing applications for detecting the quality of fluids, including gas and liquid. Thermal sensors of such fluids, which detect the fluid flow or property of fluid, can be implemented, for example, as sensors on silicon in microstructure form. For convenience sake, and without limitation, the term “flow sensor” will be utilized generically hereinafter for such thermal sensors. The reader will appreciate that such sensors may be also utilized to measure primary properties such as temperature, thermal conductivity, specific heat and other properties; and that the flows may be generated through forced or natural convection.

#Generally, a thermal-type flow sensor typically comprises a substrate that includes a heating element and a proximate heat-receiving element or two. If two such sensing elements are used, they are preferably positioned at upstream and downstream sides of the heating element relative to the direction of the fluid (liquid or gas) flow to be measured. When fluid flows along the substrate, it is heated by the heating element at the upstream side and the heat is then transferred non-symmetrically to the heat-receiving elements on either side of the heating element. Since the level of non-symmetry depends on the rate of gas flow, and that non-symmetry can be sensed electronically, such a flow sensor can be used to determine the rate and the cumulative amount of the fluid flow.

#The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.

#FIG. 1 illustrates a schematic diagram of a flow sensor involving harsh fluids, in accordance with a preferred embodiment of the present invention;

#FIG. 2 depicts an alternative schematic diagram of a flow sensor involving harsh fluids in which bi-directional flow is represented, in accordance with an alternative embodiment of the present invention;

#The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate an embodiment of the present invention and are not intended to limit the scope of the invention.

#The present invention discloses a number of novel features for preventing contamination of sensors exposed to harsh fluids. The use of an auxiliary purge stream to prevent contamination of sensitive flow sensors through corrosion, radioactive or bacterial contamination, overheating, freeze-up, condensation, and particulate matter deposition is a primary feature of the present invention. The use of a symmetric purge stream on the legs of a bypass flow sensor so that that the sensor is able to respond to bi-directional flow is also a feature of the present invention. The present invention also discloses the ability to convert an unidirectional sensor to a bi-directional sensor by adding a non-symmetrical flow bias to its ports. Additionally, the use of an auxiliary purge stream to prevent contamination of sensitive flow-based differential sensors is also disclosed herein. The present invention also features the use of an auxiliary purge stream to enable the sensitive measurement of small changes in absolute pressure, in addition to preventing contamination of the sensitive flow sensor.

#By implementing the present invention in the context of flow sensor applications, a number of advantages are realized. The flow-based sensor configuration illustrated herein, specifically with reference to FIG. 1, presents several advantages of differential pressure membrane sensor approaches, including lower cost, a wider flow range, longer and more reliable service life, increased sensitivity of the sensor itself, lack of the force exerted by present-day steel membranes utilized to contain a buffer liquid, such as, for example, silicone oil and a lower flow restriction. Additionally, a heater or heater line is no longer required to avoid condensation at the sensor element.