The standard for measuring mass flow rates for years has been the use of coils around a steel capillary. The new CMOSens® technology combines the measuring principle in a miniature thermal sensor with all the high-precision signal-conditioning circuitry on a single CMOS microchip. This significantly enhances speed and accuracy.
CMOSens® makes use of gas-flow sensors, which are a pressure-stabilized membrane, with a glass-passivation layer and which is closed from the front, is etched into the silicon chip from below. Settling of contaminants is prevented by the flat glass surface. Simultaneously, the rear air cushion allows the pressure-tight membrane to be used even if there are strong vibrations.
The key features of CMOSens® are:
- The sensor reacts to changes of the gas flow within only 1.7 ms (1/e).
- Programmable, highly accurate amplification and evaluation of the generated analog sensor signal is possible with the patented CMOS evaluation circuitry integrated on the same chip.
- Typically, a CMOSens® gas-flow sensor measures a sensor voltage of only 500nV with long-term stability and without noise.
- Two similarly integrated 16-bit A/D converters digitize the signals of the flow sensor and the additional temperature sensor into packets of 0.7 ms.
- The CMOSens® chip can be operated with a digital or analog output according to need.
- Since a CMOSens® mass-flow sensor thermally reacts around 1000 times faster and the the generated signal is linearized and temperature compensated on the CMOSens® chip every 0.5ms, direct and much faster control can be realized. Settling time of less than 150ns are achieved by the CMOSens® MFC
- Through the symmetry of the sensor element and the offset-compensated evaluation circuit integrated on the sensor chip, CMOSens® gas-flow sensors typically achieve an offset stability of <0.01% FS/y.
- Based on demand a CMOSens® MFCs can achieve an accuracy of 0.8% of reading (setpoint) or even more in the range of 10%-100% fullscale.
- In parallel with the CMOSens® flow sensors, a stainless steel housing with integrated flow channel and vacuum-tight glass feeding troughs was developed for electrical contacts.
- All of the analog signal processing is performed on the same chip for CMOSens® sensors. This has the advantage of eliminating noise-susceptible solder points for small analog signals.