CMOSens® in Liquid Flow Measurement
For more than 30 years, thermal mass flow measurements using coils around a steel capillary have been the standard in the precise measurement and dosing of mass flow rates.
The new CMOSens® Technology integrates this basic physical measuring principle in an extremely fast, miniaturized thermal sensor with all of the high-precision signal-conditioning circuitry on a single CMOS microchip. A heating element on the microchip adds a minimal amount of heat to the medium for the thermal flow measurement. Two temperature sensors, symmetrically positioned above and below the source of the heat, detect even the slightest temperature differences, thus providing the basic information about the spread of the heat, which itself is directly related to the flow rate. Integration on a single chip ensures that the sensitive analog sensor signals can be amplified with high precision, digitalized and further processed. Semiconductor technology also allows small, battery-operated sensor modules to run very well.
Digital signal processing and the stored calibration data together provide repeatability of < 0.6% of the measurement value and allow for the output of a linear, completely calibrated, temperature-compensated flow measurement signal with speeds up to 1000 values per second. As this type of sensor has a completely digital internal function, output signals may be provided as either analog or digital outputs.
In addition to interesting solutions for gas applications, CMOSens® Technology allows mass flow measurements for ultra low liquid flow rates. Sensors based on this new principle are extremely fast, small, lightweight, and can be produced in large quantities. The accurate measurement of volume flow within the range of several milliliters per minute, and even down to the sub-nanoliter range, poses no problem.
Just a straight flow channel
In the most diverse application areas, a liquid medium must be completely separated from its environment, and pressure resistance must be ensured. To this end, Sensirion has come up with a surprising solution, which has been patented in the meantime: Special packaging means the highly sensitive microsensor chip is media-isolated by the flow channels wall which can be made of glass, ceramic or plastic. The chip can measure mass flows inside the channel in nanoliters, microliters, or milliliters per minute with the greatest accuracy. The sensor for the fluid system is a simple, straight tubing without seals, dead volumes or restrictions. According to the flow range, the internal diameter can be several millimeters or micrometers. A digital sensor for liquid flow based on this new technology is already up to 100 times faster, 10 times smaller and 25 times lighter than previous conventionally designed flow meters, which means optimization potential is not exhausted and battery-operated variants are possible.
