Wink of Knowledge: smart mass flow controller 

Why this test? 

With conventional thermal mass flow meters and controllers (MFM/MFC), associated parameters must be set manually for each specific gas or binary gas mixture. 

In cooperation with Innovative Sensor Technology (IST AG), we are currently working on the development of a thermal flow meter called FGF. This module simultaneously measures density, temperature, pressure, and mass flow and calculates the derived measured variables in a single device. The density measurement enables the differentiation of pure gases and the determination of the concentration of binary gas mixtures. This allows the measured flow rate to be corrected and the mass flow to be converted into a volume flow in real time. This means that a sensor with a single, generic gas calibration can be used for (almost) any number of gases. 

A prototype mass flow controller has now been developed based on the FGF. Thanks to the versatile and precise sensor technology, the volume flow can be controlled precisely and independently of the gas. The controller parameters of the valve are automatically optimized for the current gas or binary gas mixture. 

What is a Wink of Knowledge? 

Do you need to quickly measure, draw or do/build something? The speed with which the result may be achieved counts more than the perfect (scientific) approach. For this reason, we have introduced the Wink of Knowledge. Science in the wink of an eye, so to speak. We don’t want to prove anything scientifically. We simply want to quickly demonstrate something pragmatically. If you are interested, we would be happy to discuss these results in more detail with you and your project. 

Results 

After a series of measurements with the mass flow controller, it was found that there is a clear correlation between the ideal controller parameters and the density, as shown in Figure 1. 

The correlation between the optimal controller parameters and the density is because gas becomes heavier with increasing density, which in turn leads to a slower reaction of the valve. 

The current required to open the valve is significantly lower as the density of the gas increases. We also refer to this valve parameter as the zero offset. This is due to the fact that a heavier gas exerts more pressure on the valve when closed compared to a lighter gas. 

With the help of the trend line function, the respective parameters for the controller and the zero-point offset can now be calculated. This means that all valve parameters for any gases or binary gas mixtures within a known density range can be optimally set without manual correction. 

Figure 1: Density dependence of the parameters 

Figure 2 shows the difference between the measured flow rate of our MFC prototype, without specific parameters for the gas mixture, compared to a conventional mass flow controller for a binary mixture of 50% nitrogen and 50% carbon dioxide. 

The orange measurement curve clearly shows that the controller of the conventional MFC does not settle into a stable state, especially at higher flow rates. Thanks to the integrated density measurement and concentration determination of the FGF, the optimal valve parameters are set automatically. This results in short settling times and a stable flow control, which can be seen in the red measurement curve, independent of the mixing ratio over the entire flow range – a patented world first! 

Figure 2: Measured flow of our MFC prototype and a conventional MFC 

Which sensors were used? 

Density sensor DGF-i1

  • Click here to learn more about our sensor

Flow sensor SFS01

  • Click here to learn more about the mass flow sensor of the IST AG.

The density measurement, on which the clean gas detection and concentration determination is based, was carried out with the DGF density sensor for gases from TrueDyne Sensors AG.

The gas flow and its direction were determined using the SFS01 thermal flow sensor from IST AG. 

Conclusion 

Our prototype of a mass flow controller based on the FGF shows clear advantages in the gas-dependent control of flow rates compared to conventional MFCs. By automatically adjusting the valve parameters depending on the density, the mass flow can be controlled precisely and independently of the gas. This enables stable, flexible, and precise flowmeasurement and control in a wide range of applications without having to adjust any parameters manually. 

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