Integrated pressure-flow-temperature sensor for hydraulic systems

The design of a miniature low-cost MEMS (Micro-Electronic Mechanical Systems) based sensor for sensing pressure, flow and temperature in fluid power systems is presented. The sensor is small enough to be incorporated into hydraulic components such as pumps, motor and cylinders. Considerable literature exists on the development of MEMS-based pressure and temperature sensors; therefore the primary challenge addressed in this paper is a low cost flow sensing method that does not impose extra energy dissipation into the system. The flow sensing principle adopted for use with the sensor utilizes the small pressure differences that develop as fluid flows through any geometry. As an example to prove the validity of this principle, pressure-flow relationships are determined for an elbow geometry. Specifically, the pressure differences arising from the momentum change of the fluid as it passes through the elbow are correlated to the flow rate of the fluid through the bend. The pressure-flow correlations derived from theoretical modeling, computational fluid dynamic (CFD) simulation, and experimental measurement using the flow bend geometry are compared and a calibration scheme determined. The first generation MEMS sensor incorporates pressure, flow and temperature measurement capability on a single sensor die. Pressure sensing is accomplished with piezoresistive strain elements, and temperature sensing is done with a thermister.