Thermal flow sensors are particularly well-suited for measuring very small differential pressures (<3mbar), as alongside their great zero-point stability, they also have very high sensitivity to low flow speeds.
Differential pressures are measured with membrane pressure sensors as standard. These have a quadratic characteristic curve with low sensor sensitivity around the zero point, and require complex mounting technology in order to stabilize against the transverse effects in the low-pressure range. The use of a thermal flow sensor offers the potential to reduce the costs to a tenth of that required for pressure sensor solution, as long as sufficient gas leakage flows can be tolerated. The challenge is to find a reliable technology that creates capillary flow channels easily and robustly, which can be adjusted to the desired pressure drop. The differential pressure measuring range for the sensor is predominantly determined by the cross-section of the flow channel.
Together the company 2E and Gruner AG, a design has been created for our thermal membrane flow sensor that makes it possible to adapt it on a modular basis easily and cost-efficiently for different applications for measuring very small differential pressures (<300Pa) or flows (<5ml/min air). The key to this successful solution was to bind the sensory elements of the MEMS chip fluidly, mechanically and electrically to the environment using appropriate housing. The differential pressure required for the differential pressure range of the sensor is created by the monolithically integrated flow channel in the MEMS chip. This mean that fluid channels can be created with very small microtechnical tolerances, which guarantee a very high level of reproducibility with very low wall roughness. This monolithic integration of the flow channel within the silicon chip in combination with the innovative molded interconnected device housing results in a high level of sensor miniaturization.