A low hydraulic capacitance pressure sensor for integration with a micro viscosity detector

A design is presented for a micromachined differential viscometer, that is suitable for integration into a planar hydrodynamic chromatography system (HDC) for polymer analysis. The viscometer consists of four equal flow restrictions and two pressure sensors, connected in a Wheatstone bridge configuration. Since this viscometer requires an ultra-low hydraulic capacitance differential pressure sensor, a pressure sensor is presented of which the internal volume displacement was reduced considerably compared to commercially available sensors. An optical method was used to detect membrane deflections with a magnitude of approximately 0.01 nm. This method lead to a linearity of 1% over the measured pressure range and a resolution of 2 Pa. With this pressure sensor integrated into the viscosity detector, viscosity measurements were performed on the viscosity difference of ethanol and water.