Fluid-independent flow sensor using a combination of thermal flow sensor and vibronic density sensor

Thermal flow sensors are integrated in many applications. The reasons for this are the simple measurement principles underlying the sensors, the flexibility for the application and the cost efficiency. However, thermal flow sensors have the disadvantage that the signal is dependent on the fluid, as the thermal parameters can differ between fluids, thus requiring fluid-specific calibration. In this paper, a new approach is presented to compensate for this fluid dependence. The approach uses a combination of a thermal flow sensor and a vibronic density sensor. The information from the density sensor is used to determine the fluid and thus compensate for the fluid dependence of the thermal flow sensor. This results in a fluid-independent flow meter. The developed procedure has been tested with air, nitrogen, carbon dioxide, argon, and helium. The tests have shown that a measurement accuracy can be achieved which is typically less than 2.5 % of the full-scale value.